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Figure IX.26. Diagram of the model represented for a moiré superstructure. Pt atoms are represented by blue spheres, whereas the hexagonal lattice of graphene is represented by black spheres. The angle between the black dotted line and the Pt[1 1 0]surface direction (x axis) represents the crystallographic angle, ® = 25.1° for this case. The orange spheres are C atoms with the lowest mismatch for a given ®, which define the moiré unit cell indicated by the black rhombus. The angle between the orange dashed line and the Pt{l 1 0] direction is the moiré apparent angle (2). The white arrow in the inset represents the mismatch. Adapted from [902], copyright American Chemical Society. — Figure 202 IX.26. Diagram of the model represented for a moiré superstructure. Pt atoms are represented by blue spheres, whereas the hexagonal lattice of graphene is represented by black spheres. The angle between the black dotted line and the Pt[1 1 0]surface direction (x axis) represents the crystallographic angle, ® = 25.1° for this case. The orange spheres are C atoms with the lowest mismatch for a given ®, which define the moiré unit cell indicated by the black rhombus. The angle between the orange dashed line and the Pt{l 1 0] direction is the moiré apparent angle (2). The white arrow in the inset represents the mismatch. Adapted from [902], copyright American Chemical Society.

Related Figures (261)

Figure I.2. GNR bottom-up synthesis concept. GNR synthesis is achieved by deposition of halogen-substituted precursor monomers at a substrate temperature To, followed by their activation (halogen cleavage) at T), polymerization at T,, and cyclodehydrogenation at T3.

Figure 1.3. Overview of bottom-up synthesized GNRs. X marks the leaving group, which is typically a halogen atom (X = Br, I, Cl). References are: 5-AGNR [44-47], 7-AGNR: [21], 9-AGNR: [48], 13-AGNR: [49], S-13-AGNR: [50], Bo-7-AGNR: [51, 52], Chevron: [21], No-Chevron: [53, 54], Ng-Chevron: [55], NH-Chevron: [56], 6-ZGNR: [57], 6-ZGNR + : [57], (3,1)-ChGNR: [58], (4,1)-ChGNR.

Figure 1.4. Characterization of 7-AGNRs on their growth substrate and after substrate transfer. (a) Large-scale STM topography image (bias: —0.5 V; current: 5 pA; T: 4.5 K; scale bar: 30 nm) showing high coverage 7-AGNRs on Au(1 1 1). Inset: small-scale STM image (bias: 0.1 V; current: 30 pA; scale bar: 3 nm). The apparent height of individual 7-AGNRs is 0.19 nm. (b) Constant-height nc-AFM frequency shift image (bias: 2 mV; oscillation amplitude: 0.3 A; T: 4.5 K; scale bar: 1 nm) taken with a CO-functionalized tip. (c) Raman spectra of 7-AGNR on Au(1 1 1) recorded under ambient conditions after synthesis (green curve) with indicated peak positions of the main modes, and after transfer to Si/SiO. (black curve; laser 532 nm, power of 2 mW, three scans of 20s). (d) RBLM peak position for 5-AGNRs, 7-AGNRs and 9-AGNRs (red markers), together with predicted width-dependent RBLM wavenumbers for AGNRs [65].

Figure I.5. Formation of CNMs and GRM from aromatic self-assembled monolayers. (a) Schematic illustration of the fabrication route for CNMs and graphene: Self-assembled monolayers are (i) prepared on a substrate then (ii) crosslinked by electron irradiation to form CNMs of monomolecular thickness. The CNMs are (iii) released from the underlying substrate, and further annealing at 900 °C transforms them into graphene. (b) Chemical structures of the different precursor molecules used for synthesis of CNMs and graphene. Figure adapted from Ref. [73], copyright American Chemical Society.

Figure I.6. Helium ion microscope (HIM) images of free-standing CNMs. After crosslinking the nanomembranes aretransferred onto TEM grids and images were taken at different magnifications (see scale bar). CNMs are prepared from: (a) Naphtalene-2- thiol (NPTH, (2a)); (b) 3-(biphenyl-4-yl)propane-1-thiol (BP3, (2b)). (c) 2-Cyano-11-(1’-[4/-(S-Acetylthiomethyl)pheny]] acetyl)-5,8,14,17-tetra(3’,7’-dimethyloctyl)-hexa-peri-hexabenzocoronene (HBC-CN, (3c)); (d) [1”,4/,1/,1]-Terphenyl-4-thiol (TPT, (1c)); (e) 2-Bromo-11-(1/-[4’-(S-Acetylthiomethyl) phenyl ]acetyl)-5,8,14,17-tetra(3’,7’-dimethyloctyl)-hexa-peri- hexabenzocoronene (HBC-Br, (3b)); (f) $,S’-(3/,4/,5’,6’-Tetraphenyl-[1,1/:2’,1’-terphenyl]-4,4”-diyl) diethanethioate (HPB, (3a)). The upper left insets show the precursor molecules. The CNMs in (a)—(c) are suspended over Cu grids, CNMs in (d)—(f) over Cu grids with thin holey carbon film. The numbers in the lower left corners in (a)—(d) indicate the CNM thicknesses, as determined from XPS before the transfer. HIM images e and f show CNMs with nanopores, the lower insets show the respective distributions (in%) of pore diameters (in nm). Figure adapted from [73], copyright American Chemical Society.

Figure I.7. Conversion of 1,1’-biphenyl-4-thiols (BPT) CNMs into nanocrystalline GRM upon annealing. (a) HIM image of BPT CNM annealed to 1000 K ona AuTEM grid. (b) Atomic structure of a similar sample obtained by aberration-corrected high- resolution TEM (AC-HRTEM, 80kV). The inset shows a magnified grain boundary where arrangements of carbon atoms into pentagons and heptagons are highlighted. (c) RT sheet resistivity of the samples as a function of annealing T. (d) T dependencies of the normalized sheet conductivity demonstrate the change in electrical transport mechanism, i.e. insulator to metal transition. Figure (b) adapted from [73], figures (c) and (d) adapted from [79], copyright American Chemical Society.

Figure I.8. Conversion of BPT CNMs into graphene on Cu foils. (a) Raman spectra (Aexc = 532 nm) of the conversion of BPT CNMsasa function of T. The sheets after annealing were transferred from Cu onto Si wafers with 300 nm SiO . (b) HRTEM micrograph of the sheet resolves the honeycomb lattice of graphene. The single layer nature can be determined from the HRTEM image contrast. It is further verified by the SAEDin (c). (d) RT resistivity in vacuum as a function of back-gate voltage using Hall bar devices schematically depicted in (e). (f) Quantum Hall effect at 0.3 K and 15 T. The upper plot shows Shubnikov—de Haas oscillations with the corresponding filling factors and the lower plot shows the Hall resistance as a function of back gate voltage, i.e. varied charge carrier density. Figure adapted from [74], © Wiley-VCH Verlag GmbH & Co. KGaA.

Figure 1.9. Direct growth of patterned graphene. (a) Schematic of direct growth of patterned graphene. (b) SEM image of graphene microstructures directly written on top of Cu by irradiating a BPT SAM with a focused electron beam (3 keV, 75 mC cm™ (left) —125 mC cm~? (right)) and subsequent annealing (800 °C). (c) Same structure after transfer to a SiO./Si wafer. Figure adaptec from [80], © Wiley-VCH Verlag GmbH & Co. KGaA. 2

Figure 1.10. Hybrid LMH of 0d and 2d carbons. (a)—(e) Schematic representation of the LMH assembly. (a) Formation of a NBPT SAM on Au. (b) Electron irradiation induced crosslinking and reduction of the terminal nitro groups into amino groups. (c) Formation of a free-standing JNM with the terminal N- and S-faces. (d) Functionalization of the N- and S-faces with Ceo and AuNPs. (e) Assembly of a (Cgo-JNM),, (here n = 3) hybrid heterostructure by mechanical stacking. Color code for atoms: black—C, grey—H, blue—N, green—S, and red—O. (f) HIM images in the scanning transmission ion mode shows the immobilization of 16nm Au NPs ona JNM which are uniformly distributed with an coverage ~50%. (g) HIM image of an JNM- (Ceo-JNM); heterostructure spanning a Si window. (h) Young’s moduli of JNM, Cgo-JNM and JNM-(Cgo-JNM),, (m = 1,2, and 3). Figure adapted from [113], with permission of The Royal Society of Chemistry.

Figure II.2. (a) Optical micrograph acquired with an oil-immersion objective (20 x ) and an one-wave retarder to generate interference colours and (b) SEM picture of the same graphite.

Figure II.4. SEM images graphite 0-200 jum (>0.2 mm; 10% max) and a graphite 0-600 jum. Adapted from [146].

Figure II.5. Schematic of microfluidization process. Graphite flakes in SDC/water are added in the inlet reservoir. An intensifier pump applies high pressure (207 MPa) and forces the suspension to pass through the microchannel of the interaction chamber where intense -y ~ 9.2 x 107s! is generated. The processed material is cooled down and collected from the outlet reservoir. The process can be cycled several times [178]. Adapted from [178].

Figure II.6. SEM images taken from coatings comprising (a) starting graphite, (b) after 5 cycles and (c) after 100 cycles. Reproduced from [178].

Figure II.7. (a) Rs and film thickness as a function of processing cycles for a formulation with 73 wt% flakes, (b) bulk and critical thickness as a function of loading (70 cycles). All samples are dried for 10 min at 100 °C. Reproduced from [178].

Figure II.8. (a) Effect of SDC concentration at fixed processing cycles (~60 cycles, 20 min, red) compared to sonication processing (9h, black). (b) Effect of surfactant concentration 0.5 g1~! (red) and 9 g1~! (black) and process cycles. (c) Effect of process pressure 20 k psi (black) 30 k psi (red). (d) Effect of centrifugation parameters; (e) effect of using NaCMC asa stabilizer. Dashed red line represents sonication processing using the same NaCMC loading. (f) Effect of increased graphite loading.

Figure II.9. (a) AFM height scans of flakes microfluidized for 20, 60 and 100 cycles. (b) Histogram showing the lateral size distribution of flakes with increasing process cycles. (c) Histogram showing the AFM height distribution for increasing process cycles.

Figure II.10. Supramolecular assembly of melamine between SLG.

Figure II.11. FLG powder (left) and its dispersion in cell culture medium (right).

Figure II.13. (a)—(c) SEM image of GO solutions sonicated for different times, then spin coated on 300 nm SiO,/Si(1 00): 0 h-GC (a), 2 h-GO (b), and 26 h-GO (c). (d) Flake size distribution of the 0 h-GO, 2 h-GO and 26 h-GO samples from SEM statistics. (e) Optical map of mIPM cells incubated with GO. Red dots indicate where Raman spectra was taken to detect internalization of GO into the cell. Adapted from [238], with permission of The Royal Society of Chemistry.

internalization and the effects on cellular functional- ity [235]. Flakes with the smallest lateral dimensions (<300nm) were better internalized by primary mac- rophages. A ‘mask effect’ was observed due to the 2d shape of GO, with a preferential parallel orientation of the GO sheets onto to the cellular surface. GO. The electrochemical GO production can be achieved in two sequential steps starting using flex- ible graphite paper as anode and Pt asa cathode. In the first step (typically 20 min), a stage-I GIC is formed in concentrated H2SO,. In the second step, diluted (50 wt%) H2SO, is used as electrolyte and the GIC as anode. Within seconds, the intercalation compound is oxidized and exfoliated. The dispersion produced is then filtered and washed to remove sulfuric acid and then redispersed by bath sonication if desired. Due to the lower acid concentration in the exfoliation step compared to the traditional Hummer’s method, the dispersion is less viscous facilitating the filtration and washing step. Importantly, the process can be designed An efficient an green electrochemical oxidation of graphite to GO was reported [306]. Compared to tra- ditional GO synthesis, the process bears the advantage that it is scalable, fast (<30 min opposed to hundreds of hours) and the risk of explosions is minimized. While electrochemical exfoliation has been developed to synthesize GRM with minimal oxidation (see sec- tion II.5), it has previously not been used to prepare

Figure II.15. Schematic representation of the route followed for the preparation of RGO composite aerogels. waters, but also for immiscible substances in biphasic systems [1730]. In energy storage applications, ARGO was proposed as electrodes for supercapacitors, Li-ion, Na-ion or metal-air batteries [341]. freezing of a GO suspension, then subsequently freeze- dried to sublime the ice crystals formed within the structure. This process is useful for the preparation of a variety of a homogeneous nanostructured compos- ites, with application in energy storage, catalysis, sens- ing or separation [350], it offers a better control on the porosity of the resultant materials. The modification of parameters such as T or immersion rate, impacts the textural properties of the resultant material. Ice-templating also allows gives structures with hier- archical porosity, which can favor the transport and diffusion of molecules to the whole surface of the material, highly desired in adsorption processes for separation and purification purposes and catalytic applications, not only of soluble pollutants in waste Ice-templated ARGO have been investigated as self-standing electrodes for energy storage devices [351]. These structures can be assembled into the elec- trochemical cells without the need of binders, which do not contribute to the capacity of the electrode, but can decrease its conductivity and block the access of the electrolyte ions to the surface of the active materi- als. As anodes for Li ion batteries (LIBs), sp? graphene not only improves the electrodes electronic conductiv- ity, thus enhancing the power of the device, but it can also buffer the volume changes undergone by some

Figure II.16. Photographs of GO aerogels prepared form different suspensions: (a) GO (2mg ml '), (b) GO (6mg ml), (c) Sn-GO and (b) RGO composite aerogel, obtained after thermal reduction of GO aerogels at 800 C.

Figure II.18. (a) Reaction scheme for the quantitative electron transfer from various GICs to PhCN leading to dissolved K* ions and the red coloured radical anion PhCN.-. (b) Photograph of a sealed vial containing KC in a concentration of 5.0 x 10-'Min PhCN.-, adapted from [375]. Figure II.17. Representative SEM images of (a) A-RGO, (b) A-Sn-RGO, (c) A-SnO2-RGO and (d) A-Si-RGO.

Figure II.19. Characterization of chemically exfoliated MoS; with different intercalation conditions. (A) TGA weight loss of MoS, and MoS, chemically intercalated with excess of BuLi and MoS). Bottom: mass profiles for m/z = 15-18 which constitute the main weight loss in chemically exfoliated MoS, using excess BuLi. (B) AFM thickness histograms of MoS) intercalated using excess MoS (top) and BuLi (bottom). Inset: representative images. Adapted from [379], copyright American Chemical Society.

Figure II.20. Illustrations of graphite after intercalation, expansion, electrochemical exfoliation and reduction steps (from left to right).Adapted from [348], © Wiley-VCH Verlag GmbH & Co. KGaA.

Figure II.21. AFM images of HOPG basal surface after treatment by (a) sonication-assisted, (b) chemical exfoliation, (c) electrochemical exfoliation. Z-range: (a) 400 nm, (b) 600 nm, (c) 1 jum. (d)—(f) gradient-filtered version of each image. (g)—(j) Schematic representation of the structure of the HOPG substrate after exfoliation procedures. (j)—(1) Height profiles taken along th lines shown in (a)—(c). From [137], © Wiley-VCH Verlag GmbH & Co. KGaA.

Figure II.22. (a) Binding energy versus relative difference in interlayer distance predicted by vdW (DF2-C09) or non-vdW (revPBE) functionals. Materials classified as easily exfoliable, potentially exfoliable, or with high binding energy are colored differently. Well- known LMsare highlighted in the plot. Adapted from [407], © Springer Nature. (b) Calculated heat of formation for 216 1L-TMDs in the 2H and IT phases. Oxides have the highest stability, followed by sulfides, selenides, and tellurides, in that order. The stability decreases as the metal ion goes through the transition-metal series. Adapted from [412], copyright American Chemical Society. (c) Examples of patterns predicted for free-standing 1L B polymorphs, from close-packed triangular, honeycomb. The numbers at the bottom right of each model mark the hole density, S1 and S2 are the observed phases. Adapted from [423], © Springer Nature.

Figure III.1. Sorting of GRM flakes by ultracentrifugation. The SBS approach allows separating thin and small lateral sized flakes (supernatant) from thicker and larger ones, which precipitate at the bottom of the ultracentrifuge tube as pellet. The final flake Dimensions (lateral size, final flake N) depend on the centrifugal acceleration, material and medium.

Table III.1. Overview of mean lateral sizes using LCC. For each material, the ‘large/thick’ and ‘small/thin’ fractions are defined by the midpoint of the centrifugation boundaries (given as central g). Data includes centrifugation in solvents (NMP, IPA) and aqueous SC solution. cific sizes are targeted, some centrifugation steps can be skipped. E.g. if medium-sized flakes are desired, the sample can be centrifuged at only two different cen- trifugal accelerations and the sediment redispersed. In first approximation, flake size selection occurs by mass in such a standard cascade, still making it difficult to select large (41m), thin (1-3 L) flakes like in homoge- neous SBS. However, a design of secondary cascades [186] involving a combination of long (14h), low- speed centrifugations (~1/5 of the lower g-boundary of the initial trapping) to remove thicker material and short (60 min), high-speed centrifugations (above the higher g-boundary of the initial trapping) to remove very small (10—20nm) flakes has shown potential to overcome this limitation yielding a ~75% 1L (mean N ~1.3) with an average lateral size ~40 nm in the case of WS, [186]. dispersion compared to homogeneous SBS, where the sediments are discarded. The procedure was thus found to be ideal to study size effects in applications [452]. It was applied to WS) and MoS, [186, 245, 452, 453] as Ni(OH), [240], GaS [188], BP [190] and FLG [176, 236] in solvents [176, 188, 190] as well as aque- ous surfactant [177, 186, 236, 240, 452] or polymer systems [453]. Due to its versatility and the large acces- sible quantities, other reports adopted the procedure [454, 455]. Typical mean lateral sizes and N are given in table III.1 for a range of materials.

Figure III.2. Schematic representation of liquid cascade centrifugation. Adapted from [186], copyright American Chemical Society.

Table III.2. Specifications to consider for different printing methods.

Figure III.3. Newtonian and non-Newtonian flow behavior of functional inks. Adapted from [166], © Wiley-VCH Verlag GmbH & Co. KGaA.

Figure III.4. Rheology modifiers in 50:50 water/ethanol solution at 1 wt% loading.

Figure III.5. (a) Viscosity as a function of shear rate for an ink with 73 wt% flakes, (b) viscosity at 100 s1 for different wt% of FLC flakes. Reproduced from [178].

Figure III.6. Inkjet printing of microfluidized ink after 20 process cycles. (a) Typical jetting behaviour showing good droplet formation and the absence of satellite droplets. (b) Printed serpentine-type resistors after 20, 40 and 80 passes. (c) Resistance change whilst 3-point bending of three devices under tensile and compressive strain.

Figure III.7. Schematic of the screen printing process. FLG ink is applied to the screen and the squeegee is lightly passed over the screen to fill the mesh. This is then passed over the screen at a higher pressure, such that the ink is pushed through the mesh onto the substrate. The wet film is then left to dry to produce the final design. Reproduced from [553], with permission from Elsevier.

Figure III.8. (a) Demonstration of screen printing, (b) capacitive touchpad design (29cm x 29cm) printed on paper, (c) the line resolution is 100 xm. Reproduced from [178].

Figure IV.1. (a) Orientation of graphane on the Si-face relative to 4H-SiC. (b) LEED diffraction of MLG on 4H-SiC, showing the diffraction spots of SiC, SLG and the buffer layer (6 V 3 x 6 V 3)R30. (c) Schematics of graphene growth on the top 6H/4H-SiC(0001) and bottom(0 00 T) surfaces. Adapted from [585], © Springer Nature.

Figure IV.2. (a) Partial pressure of different vapour spices versus temperature in equilibrium with a crystal on SiC. (b) Schematics of graphene formation by Si sublimation [608] (reprinted with permission from Elsevier). For simplicity, the growth of graphene in (b) refers to the growth on the carbon face and, consequently, there is not buffer layer.

Figure IV.3. Sublimation reactor (a) Picture. (b) Sketch of the vertical RF-heated furnace in cross-section [607]. (c) distributior in the crucible. The diameter of the crucible in (c) is 50 mm and the height of the growth cavity (marked by black lines) is 5mm. Adapted from [607].

Figure IV.4. Graphene layers grown on the Si-face (a) in vacuum, (b) under Ar [588]. Field of view is 20 jum. The lines are identified as BLG by counting the number of minima in the LEEM reflectivity as a function of the electron beam intensity. Adapted from [588,589].

Figure IV.5. Confinement controlled sublimation. (a) In UHV Si that is sublimated from the SiC surface at high T escapes. (b) In the CCS method, SiC is in quasi-equilibrium with its own vapour (c) picture of the CCS furnace. Adapted from [597].

Figure IV.6. MLG on C-face topography images. (a) 4 x 4nm STM image (reproduced with permission from [626]). (b) 400 x 400nm STM image. The blue square represents the size of the STM scan in (a) [626].(c) 40 um x 40 jum AFM scan. The white lines are graphene pleats. (d) 400 nm long STEM image across areas of different moiré pattern, showing that the top layer is flat (rms < 50 pm) and continuous (from [627], with permission from AAAS). (e) SEM image of a graphene pleat (from [621], witl permission from Elsevier).

Figure IV.7. Raman spectroscopy for graphene layers on 4H-SiC C-face (a)SLG, inset AFM image. The black trace is the raw data (SiC + Graphene), blue is the bare SiC spectrum; the red trace is the graphene spectrum once the SiC Raman peaks are substractec [631] (b) MLG with the Raman contribution for SiC removed. The inset shows a Lorenzian 2D peak for this 10LG. Figure adapted from [630], © IOP Publishing.

Figure IV.8. Stacking sequences and possible terraces on (a) 4H-SiC, (b) 6H-SiC, and (c) 3C-SiC surfaces. Large (blue) and small (red) circles represent Si and C atoms, respectively. Length of arrows indicates different step decomposition velocities. (d) Schematic depiction of the formation process of EG via sublimation of Si from the SiC surface. Adapted from [640], with permission from Elsevier.

Figure IV.9. SiC Step pinning under an evaporated amorphous carbon grid. (a) Schematics of step pinning (before annealing, upper frame). After annealingat 1350 °C (lower frame), the steps accumulate at one side of the grid in each enclosure providing large terraces at a locations defined by the grid. The arrow point the direction of the flow. (b) AFM image after annealing and (c) topographic profile within the grid (top) before and (bottom) after step bunching annealing, showing that a large terrace has developed. Adapted from [642], with the permission of AIP Publishing.

Figure IV.10. (a) AFM phase images of initial stage of the buffer layer formation, and (b) LEED pattern of the buffer layer (electron energy 60 eV) grown under Ar (in the reactor of figure IV.3) [643].

Figure IV.11. Size increase of LG from7 x 7mm’ to 20 x 20mm?. The size of reflectance maps (red scale) are 30 um x 30 pun [643].

A general recipe is provided in Ref. [652]. Figure IV.13 shows a side view of the off-axis SiC substrate used for graphene growth, where the off-axis surface is tilted at a specified angle (off-axis angle) from the basal plane surface toward the [1 120] SiC direction. Controlling the tilt angle allows to change step heights, terrace widths and a growth rates. 3LG, respectively, over the substrate or stacked over other graphene layers [601]. In fact, like for the (000 1) on-axis face, the graphitization starts from the step edges and propagates gradually to the centre of the ter- race [601—603, 655]. In this case, the C atoms at ter- race kinks and step edges have a lower coordination number, thereby leading to an easier breaking of the bonds at these sites. For this reason, the probability of SiC decomposition and further surface diffusion of C atoms is increased and graphitization of the SiC surface occurs [655]. Regarding the growth kinetics, anisotropy of the Si desorption rate is always present and, thus, different SiC steps have different evapora- tion rates [601]. In addition, increase in the miscut angle increases the step density, thereby leading to an increase in graphene thickness at this region [601].

Figure IV.13. (Top panel) Diagram illustrating off-axis surfaces of 4H-SiC and (bottom panel) schematic drawing of the off-axis 4H-SiC surface after graphitization [643].

Figure IV.14. (Left panel) AFM images. Effect of graphitization temperature on the surface morphology of the sample 8°-off axis (0001) 4H-SiC: 1600 °C (a), 1700 °C (b) and 2000 °C (c). The phase contrast maps on the same samples are also demonstrated ((d)-(f), respectively). (right panel) STM image of a sample annealed at 2000 °C. Adapted from [654], with permission of The Royal Society of Chemistry.

Figure IV.15. Graphitization thickness versus T at 60 min for 8° off cut Si- and C-face 4H SiC and for Si-face on axis 4H substrate (adapted with permission from [614]).

Figure IV.16. Principal crystallographic planes of (a,b)hexagonal and (c,d) cubic SiC. Figure IV.17. LEEM images of graphene grown on (00 1) cubic SiC before (left panel) and after optimization (right panel). In the first case, we have 4—5LG, while optimized growth allows to obtain 1-3 LG with increased domain size up to 10 jzm.Field of view is 25 jum. Adapted from [661].

Figure IV.18. (left) LEEM image of graphene grown by thermal decomposition at 1900 °C on (1 10 0) oriented 6H-SiC substrates, scale bar 5 micron, adapted from [643]. (right) SEM image of graphene grown on 6H-SiC, scale bar 3 micron (1120).

Figure IV.19. Graphene growth mechanism on (a) the polar (Si) face SiC with offcut toward [1 12 0] and (b) the nonpolar a/m face with slight offcut along [0001]. The growth on the polar face proceeds laterally while the growth on the nonpolar face is limited by the vertical growth rate. The zigzag structure shown on the polar face step edge is a consequence of two possible lateral growth directions. Adapted from [667], copyright American Chemical Society.

Figure IV.20. Schematic view of graphene on SiC(000 1). The graphene layer resides on top of the buffer layer. The buffer layer is structurally equivalent to graphene but strongly bound to the SiC substrate. Dangling bonds (db) are present due to the lattice mismatch between graphene and SiC. Drawing not to scale (after [645,670]).

Figure IV.21. Schematic view of the conversion of the buffer layer into quasi-freestanding SLG on H-saturated SiC(000 1) (also referred to as SiC(000 1)-H) and of SLG on the buffer layer into quasi-freestanding BLG on SiC(000 1)-H. After [645,670].

Figure IV.22. (a) Cls core level spectra of the buffer layer, SLG, BLG, =TLG and TLG, on substrated and quasi freestanding (QF). The H-intercalation leads to a disappearance of the buffer layer components (S1,S2) and an increase of the graphene-related component. The signal due to SiC shifts to lower binding energy due to a change of band bending. (b) ARPES intensity maps versus electron energy and momentum of SLG and BLG on the buffer layer as well as QFSLG and QFBLG on H-terminated 6H-SiC(000 1). (c) Si-H stretch mode of the H-saturated SiC(0 00 1) surface below QFSLG and QFBLG. (d) Representative Raman spectra of QDSLG and QFBLG. (a) adapted from [708] and (b) adapted from [707], both © IOP Publishing Ltd; (c) and (d) adapted with permission from [704].

TableIV.1. Typical parameters for intercalating hydrogen under the buffer layer [658, 704, 708]. Li-compounds. Na partial and inhomogeneous inter- calation occurs already at RT directly after deposition, although most of the Na remained on the surface and formed Na droplets. Na intercalation is promoted both by electron/photon beam exposure and by moderate annealing at ~100 °C. Annealing at higher T results in de-intercalation and Na desorption from the surface 700]. Other elements intercalation would be appeal- ing, such as nitrogen, that is predicted to provide charge neutral QFSLG [726] ond procedure in Ref. [685] was carried out ex-situ by annealing in O2 with best results at 270 °C at 200 mbar. The Raman spectra, however, demonstrated that both processes lead to the formation on numerous defects. In Ref. [683] the oxygen intercalation to transform SLG into a BLG was carried out by annealing in air at 600 °C for 40 min. A heat up ramp of 50° per minute was used. They confirmed the decoupling of the buffer layer and the formation of a high quality BLG.

Figure IV.23. Sketch of the apparatus used for intercalating hydrogen between the buffer layer and the SiC(000 1) substrate [658, 704, 708]. After [719].

TableIV.2. Characterization techniques for QFSLG and QFSLGon H-terminated SiC(000 1).

Figure IV.24. Examples of sidewall ribbons (a)—(d) on natural steps, 20 nm high. (a) Topographic AFM image, (b) lateral force AFM image, revealing graphene (dark) on the sidewall, (c) profile of the steps along the red line in (a) [615]. (d) Example of isolatec ribbon more that 80 zm long, 38 nm high (top) lateral force AFM—the ribbon is bright; (bottom) 3d rendition by combining topography and lateral force. (e) Cross-sectional TEM high resolution image of a sidewall trench etched in SiC, recrystallized at a stable facet angle of ~30°, over which MLG is draped. Adapted from Ref. [734], copyright American Chemical Society.

Figure IV.25. (a) Principle of Si-wafer to graphitized SiC-wafer bonding with the SOI technology, and (b) SEM image of the cross- sectional bonding showing graphene at the interface (after [737]). (c) Growth of graphene on an epilayer of SiC grown on Si(100), schematics and LEED diffraction, showing rotational order on 3C-SiC(1 00) compatible with C-termination, and Bernal stacking on 3C-SiC(1 11) compatible with Si-termination. Adapted from Ref. [738], © IOP Publishing Ltd.

Figure IV.26. Raman measurements of SLG grown by CVD on SiC (SiC Raman peak subtracted) (a) spectrum, (b) map 20mm x 20mm (BLG on the step edges is depicted in red), (c) histogram of FWHM(2D) [751].

Cu cools, and forms FLG under the already grown graphene [783]. These layers grow under the graphene on Cu as a result of precipitation upon cooling [783]. Even though it was reported that C might diffuse under the growing graphene to form FLG [784], it is more difficult to accept this mechanism since it does not take into account the C dissolved into Cu. If only the intentional C from the dissociation of methane were present, then a small percentage of the surface area would be covered with adlayers. However, in some cases many FLG have been observed across the surface of Cu/graphene and this can only be explained by the presence of other sources of C, and isothermal growth asa result of supersaturation [785]. It was also reported [791] that the surface of Cu can be covered with a high concentration of unwanted C from ambient, poor cleaning and cleaning using hydrocarbons.This can give rise to a high concentration of nuclei as well as FLG beyond the solubility limit of C in Cu [785]. The presence of the uncontrolled and unwanted C is also supported by anecdotal reports indicating that graphene can be grown on metal surfaces in the absence of a C precursor. Ref. [786], pointed out the importance of a high H,/CH, ratio in the growth of SLG. The benefit of a high hydrogen concentration may arise from the details of the reactions at the metal surface, but also from the presence of excess oxygen in the growth chamber. This is highlighted by the fact, that graphene is etched during cooling in the absence of Hz or CH, [787]. The effect of growth parameters such as T, and CH, flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene led to the definition of a 2-step CVD strategy for the growth of large single crystal graphene [788]. High-throughput growth of graphene on Cu foil was achieved at ambient pressure, interesting to reduce costs [789].

Figure V.2. (Upper) Schematic diagram of the thermal profile during graphene growth, type of gasses used and steps duration in case of growth SLG at 1000 °C, (Lower Left) Optical image of a graphene domain grown on molten Cu ona Mo substrate. Scale bar is 100 jm. (Lower Right) Raman spectrum of a graphene grown on molten Cu.

Figure V.3. Optical images of (a) continuous and (b) discontinuous graphene films on Cu.

Figure V.4. SEM images of graphene layers on (a) Cu_mono, (b) Cu_6N, (c) Cu_5N and (d) Cu_3N substrates. Scale bars are 1 jum.

Figure V.5. Atomic resolution STM of graphene ona Cu mono-crystalline substrate with the Fourier transform (upper right inset). Adapted from [812] with the permission of AIP Publishing.

Figure V.6. Higher T near the edges of the substrate causes local Cu melting while the inner part is unaffected.

Figure V.7. (a) Cu ‘pocket’ enclosure. (b) Enclosing flat Cu foil with a quartz cover. (c) growth of graphene on Cu assisted by a continuous oxygen supply. Adapted from [766] (© IOP Publishing Ltd) and [825] (© Springer Nature).

Figure V.8. Electropolishing set-up. (a) Three-quarter view. (b) Side view, showing the parallel orientation of the copper foil and the counter-electrode. Adapted from [766], © IOP Publishing Ltd.

Figure V.9. Nucleation density of graphene when using (a) hydrogen annealing, (b) argon annealing (c) argon annealing and sample enclosure. Adapted from [766], © IOP Publishing Ltd.

Figure V.10. (a) Typical growth scheme for a low pressure CVD process for SLG on Cu. (b) Optical dark field microscopy image of SLG on Cu foil using the process depicted in (a). Panel (B) is adapted from [832], with permission from AAAS.

Figure V.11. Seeded arrays of large-crystal graphene. (a) Array with 200 jum periodicity and 100 jum crystal size. (b) Array with 500 jum periodicity and 350 jum crystal size Adapted from [841].

Figure V.12. Raman spectrum at the centre of aSLG domain (black) and averaged across a 20 x 20 um region of the film (red). (t 1(D)/I(G)map. (c) FWHM(2D)map. Adapted from [850], with permission from Elsevier.

Figure V.13. (a) Optical micrograph of GNRs on SiO) used for GFET devices. (b) SEM image of an individual GNR ribbon with second layer islands visible as darker spots. (c) Ips versus Vas curves for GFETs (red) as-fabricated and (black) after vacuum annealing. Adapted from [850], with permission from Elsevier.

Figure V.14. Characterization of GF from Ni foam precursor. SEM images of (a) Ni foam as received, (b) and (c) GF. (d) Photographs of foam at different stages of the synthesis process. (e) TEM image of GE (f) Electron diffraction pattern from the foar area in (e). (g) XRD patterns of (i) Ni foam, GF etched with (ii) HNO3, (iii) FeCl; followed by hot HCl and (iv) hot FeCl; followed by hot HCL. (h) Raman spectrum of GE, adapted from [873], with permission of Springer.

Figure V.15. Fabrication principle of graphene foams illustrated by SEM images. (a) Metal particles, in this case Ni, are assembled in a vessel to get (b) a 3d structure. (c) At high T (~600 °C) interconnected metal foams are created; this process is implemented in the CVD annealing step. The scale bars are 20 jum. Adapted from [875], © IOP Publishing Ltd.

Figure V.16. (a) Raman spectra of GF grown on Cu (red curve) at 900 °C and Ni (black curve) at 600 °C. (b) SEM micrograph of GF grown at 800 °C after metal etch. (c) Optical image of Ni foams fabricated at 800 °C and 1100 °C using a Ni powder. Scale bar in (b) is 20 pm and in (c) 5mm. Adapted with permission from [873,875].

Figure V.17. (a) SEM image of GF from pellet of Ni/NiO NPs pressed under ~440kg cm 7. The resulting pellets are too compact, with only small areas of porosity where NPs resist tight packing. (b) and (c) SEM images of the GF from pellet of Ni/NiO NPs pressed under ~50kg cm~?. (d) Raman spectrum from HD-GF sample. (e) and (f) TEM images of the HD-GF foam. (g) Electron diffraction pattern from the area in (f). Adapted from [873], with permission of Springer.

Figure V.18. (a) Sketch of graphene formation by both direct chemisorption/deposition on Cu (and precipitation/segregation on Ni) [882] (with permission of the PCCP Owner Societies). (b) Computed optimized structures of representative carbon clusters along the graphene growth-by-aggregation on Cu(1 1 1) and (100) surfaces [883] (copyright American Chemical Society). (c) Evolution of graphene grown via thermal decomposition of methane on Cu(1 1 1). Top: Schematic illustration of the surface intermediates at different reaction conditions. Bottom: overview of STM images showing (C.a) carbon clusters, (C.b) the boundary between carbon cluster (left) and defective graphene (right), (C.c) defective graphene, and (C.d) vacancy-free graphene, at differen reaction stages [884] (copyright American Chemical Society).

Figure V.19. Effect of O on graphene growth kinetics. SEM images of graphene domains grown on (A) OF-Cu and (B) OF-Cu (O). Isotope-labeled Raman maps of I(2D) on Si for growth at (C) and (D) 1035 °C and (E) and (F) 885 °C. The isotope switching intervals are indicated below each image. (G) Logarithmic plots of graphene domain growth rate dr/dt versus 1/T. The error bars ar from calculations of different domains for each case, and the activation energy Ea is extracted from the slope of the linear fit. (J) and (H) Atomic-scale schematics of graphene edge growth on Cu with and without the assistance of O, respectively. (I) DFT calculated energies of different configurations of H attachment, in reference to H in H. The energy spread of H at the graphene edge is due to the computational uncertainty resulting from the lattice mismatch between graphene and Cu. Adapted from [791] with permission from AAAS.

Figure V.20. (A) sketch of graphene CVD growth ona Ni surface [885, 886] through the carbon diffusion and cooling processes. (B) (Top-left) the hexagonal structure of the graphene domain can be identified in the STM image, while the right side shows the quasi-square structure of the carbide Ni,C. The domain boundary between the two phases is in the same atomic plane and without any defect pattern. This indicates that the two phases form a line interface. (Top-right) the carbide and graphene lattices are superimposed in the region indicated by the rectangle in the top-left panel. (Bottom) Top and side views of the optimized atomic structure of the graphene/NipC interface [887] (copyright American Chemical Society).

Figure V.21. A glassy carbon filament (a) is mounted on an UHV electrical feedthough (b) and resistively heated (c). Tis simultaneously measured with an optical pyrometer and a type-C thermocouple located on the back side. The C Source is placed in a deposition UHV sys- tem, base pressure 1 x 10~!° mbar heated using a DC current. The T calibration of the cell is performed in a separate UHV system with a base pressure 1 x 107° mbar. The T in the hottest spot of the filament is meas- ured using a dual-color optical pyrometer through an optical window located in front of the cell. Evapora- tion of carbon starts above 2000 °C. Using a DC cur- rent ~14 A (~100 W) the filament is at 2014 °C. A clear correlation of the increase of the partial pressure of atomic mass unit number 12 (a.m.u.) is observed in a residual gas analyzer (quadrupole) with source temperature. The presence of amu 12 can be associated to the evaporation of monoatomic carbon. The depo- sition rateis3 x 10°-*SLGs"1. of the surface with a surface morphology similar to growth from decomposition of hydrocarbons or aro- matic molecules.

Figure V.22. (a) LEED pattern on SLG/Pt(1 11). (b) STM image showing a moiré and the atomic corrugation of graphene. Adapte from [910], with permission from Elsevier.

The simplest and more efficient way of improving the thermal contact is the use of thicker Cu substrates. above the growth T, until the initial pressure is restored (~10~!° mbar) after elimination of impu- rities (water, CO, CO). Usually the crucible is spot welded to two pieces of steel that are clamped to Cu rods. It is important to have a good electrical contact between Ta crucible and rods, otherwise the whole evaporator will be heated and the result will be a rise in the base pressure of the chamber and, therefore, a dirty evaporation. In situ surface techniques such as LEED, AES or STM can provide valuable information with no need to expose the sample to the air, thus avoiding surface contamination. Figure V.26 is a LEED pattern of a Cu foil after cleaning, where multiple spots, corre- sponding to different grain orientations, are observed. Once the substrate is clean and the molecules purified, the growth consists in exposing the sub- strate to the molecules at the chosen growth T. Typi- cal parameters are: evaporation T ~ 450 °C, substrate size ~15 x 20mm”, 10cm evaporator/sample distance and growth time ~90 min. Coverage can be tuned by changing the exposure time. An important step is to have initially the substrate at the growth T before the Ceo molecules start to sublimate, avoiding any Cg arriving to the sample surface when this is still cold. Different growth trials have been made by first depos- iting the molecules on the cold surface and making a post-annealing, but this procedure shows less satis- factory results. Once the evaporation is finished, it is important to keep the sample hot until the evaporator gets cold.

Figure V.23. Sketch of the coexisting processes leading to the growth of graphene ona Pt(1 11) surface by MBE.

Figure V.25. (a) Mounting of a Cu foil in a Ta sample holder. (b) Bending of the 25 zm Cu foil produced by Cu thermal expansion.

Figure V.26. LEED pattern at 107 eV of a Cu foil after cleaning and prior to the C¢o evaporation.

Figure V.27. LEED patterns with a beam energy of (a) 50 eV and (b) 56 eV, where the ring of polycrystalline graphene is observed. (c) and (d) AFM topography images where Cu flat terraces are observed. Wrinkles crossing the terraces (pointed by black arrows). (e) Raman spectrum at 532 nm. The inset shows an optical image with Cu grains visible.

Figure V.28. STM images of SLG grown from Co on: (a) Pt(111),(6 x 6)nm, 0.11 V,2.3 nA. (b) Ir(111), (15 x 15)nm, 1.2 V, 2.6 pA and (c) Cu(111),(27 x 27nm), —0.4 V, 2.7 pA. In every image different moiré superstructures are shown.

TableV.1. Tand typical evaporation times needed to grow SLG from thermal decomposition of Ceo for different substrates (at a sample-evaporator distance ~10cm). the large area grapnene flim to the desired substrate for applications that normally induces contamination, wrinkles or even breakage of graphene. In this scenario, the game changing breakthrough would be the development of processes to deposit directly high quality graphene films and single crystals on arbitrary substrates avoiding the transference step and, if possible, at lower T than catalytic approaches. The first route involves the direct CVD synthesis on insulators or dielectrics at T > 1000 °C with examples of synthesis surpassing 1500 °C [943]. Along the high T, atmospheric pressure and CH, as precursor diluted typically in Ar and/or H; are the most common parameters. Synthesis of SLG and FLG films was on reported on Si3N4 [938, 939], sapphire (Al,O3) 940-943] and silicon oxides in different structures 944-946] with final R, between 5 kQ) [944] and 800 Q [945]. FLG grains were also deposited on h-BN flakes at 1000 °C in atmospheric pressure CVD [947] and on MgO nanocrystal powder by LP CVD at lower T between 325 and 875 °C [948]. Other substrates include SiC [611] and SrTiO; [949] with pw ~1800 and 1050cm?-V-!-s~!. Even though, the typical grain size is smaller (between 0.5 and 10 jum) and the amount of defects higher in comparison with the graphene synthesized with the catalytic approach, the final properties of the deposited graphene resemble transferred material grown on catalytic metals [945].

Figure V.29. Pictorial sketch corresponding to the thermal PVD decomposition of Ceo on the mentioned Cu foils, and Cu, Pt and Ir single-crystal surfaces, as well as the coexisting subsequent processes leading to the growth of graphene.

Figure V.30. Schematic illustration (left) and picture (right) of a r-(ECR-CVD) Plasma system. This consists of a gas delivery system with flow controllers, an ASTEX AX 2000 microwave power source with optic fiber coupling the power to the discharge plasma chamber with an ECR magnet surrounding it. The activated gases are transported by forced convection, with two electrode attracting electrons and ions. The substrate is independently heated. A two stage pumping system generates the vacuum. Adapted from [816], © IOP Publishing Ltd.

Figure V.32. Graphene on quartz at H)/C)H) = 55/0.25:0.20 (sccm), PT = 5.4 x 10~? mbar, P = 100 W for 5 min nucleation time, 9h growth. AEM lateral force image of the sample grown at (a) T = 650 °C and, (b) high magnification lateral force image of a single flake from sample and below the corresponding atomic lattice periodicity of the flake along with the Fast-Fourier transform in the inset of the periodicity image in (a)—(c) AFM lateral force image of the sample grown at T = 700°. (d) and (f) Individual Raman spectra acquired at grain positions, for samples in (a) and (c), respectively. (e) High resolution XPS Cls core level spectrum (black dots) of the sample grown at 650 °C. The C-sp” graphitic component (blue, 284.6 eV), C-H (green, 285.6 eV) likely from H-terminated edges, and C—O (cyan, 286.5 eV) species. The component at (magenta, 283 eV) can be ascribed to remainders of the growth process (e.g. CpH4Si at 282.5 eV) or to the interaction with substrate (e.g. SiC C(1s) is 282.5—283.5 eV). Adapted from [774], © IOP Publishing Ltd.

Figure V.33. Characterization of continuous film T’ = 650 °C, H2/C)H = 55/0.25:0.20 (sccm), PT = 5.4 x 10-? mbar: P = 100 W. (a) and (b) AFM topographic images of graphene deposition on quartz for 5 min nucleation time and 10h growth. (c) Transmittance spectra before (95%) and after (92%) post-growth annealing. (d) Height profiles taken along the corresponding lines in (b) (film thickness, cyan).

Figure V.34. Graphene on quartz T = 650°C, PT = 5.4 x 10 ? mbar: P = 100 W. f; = 5min. f = 690 min. Topographic (top row) and corresponding lateral force (bottom row) AFM images of samples grown at increasing pressure from (a) and (c) H2/C,H2 = 55 0.25:0.20 (sccm) to (b) and (d) H2/C,H»2 = 55/0.30:0.25 (sccm). The increase in the number of FLG with increasing pressure is seen.

Figure V.35. (a) Side view of the different DFT-computed steps along the reduction process of the [1 1 — 20] quartz surface (adapted from [774], © IOP Publishing Ltd): starting from the clean hydroxylated surface [976] across subsequent protonation barrierless steps and detachment of H,O molecules (see inset), which lead to slight surface reconstructions, and H-passivation of the surface. (b) sketch corresponding to the coexisting processes leading to the growth of graphene on a quartz single-crystal surfac from the different plasma products by PECVD: adsorption, decomposition and dehydrogenation of the reaction precursors, towar graphene nucleation and formation.

Figure V.36. AFM topographic images of graphene nuclei and corresponding profiles at 550 °C, PT = 5.4 x 10°? mbar, P = 200 W, H2 = 50sccm, tf) = 5 min, ty = 150 min. (a) C2H) flow: 0.9 sccm in the nucleation and 0.8 sccm in the growth step. (b) C.H) flow: 0.8 sccm in the nucleation and 0.7 sccm in the growth step. Adapted from [981], with permission of The Royal Society of Chemistry.

Figure V.37. (a) AFM topographic image of graphene nuclei at 550 °C, H2/2H = 50/0.9:0.8 (sccm), PT = 5.4 x 10°? mbar: P= 200W,t) = 5min fh = 7h. Vertical scale: 0-5 nm (b) Corresponding profile from a graphene flake in (a). (c) Continuous film. t = 10hand same conditions than (a). Vertical scale: 0-5 nm. (d) Corresponding Raman spectrum of sample (a) (blue) and (c) before (black) and after annealing (red).

Figure V.38. (a) Schematic PECVD system used to grow graphene on Si/SiO). Figure reproduced from [856], with permission from Elsevier. (b) AFM image of the grown graphene film (c) Height profile.

Figure V.39. SEM images of sample with (a) and without (b) and (c) Cu catalyst remains after CVD. Raman spectra with (c) and without (d) Cu catalyst. (e) High resolution SEM image from border area where Cu remains are removed. Adapted from [984], with permission from Elsevier.

Figure V.40. (a)—(c) SEM images of sample before CVD, after CVD and after Cu removal in FeCl. (d) and (e) Raman mapping reveals graphene on the grating. (f) Raman spectrum of the grating area is comparable to that grown outside. Adapted from [987], with permission from Elsevier.

Table V.2. Methods, substrates, precursors and optimal growth conditions. Similarly to Cu, Ni will also melt and recede dur- ing CVD. Since the thickness of the original Ni film was only 10nm the particle size is in sub-jum range. Figures V.41(a) and (b) show the appearance of the Ni particles on PPF pyrolyzed in 800 °C. In Ref. 1001] the T dependence to the PPF graphitization was observed by Raman spectroscopy. Most signifi- cant changes in the structure of the PPF with Ni took place For T = 800 °C or above (see figures V.41(c) and (d)) [1001]. A 2D peak appeared at 2705 cm™!. The D and G peaks became narrower, indicating higher degree of crystallization in to comparison to PPF pyrolyzed in 700 °C and lower T or without Ni catalyst. rier enabled the growth of SLG at 600 °C, with domain size >50 zm and quality that equals the CVD grown films at similar T.

Figure V.41. (a) optical microscope and (b) SEM image of PPF with Ni particles fabricated at 800 °C. SEM reveals non-uniform size and shape of Ni particles (bright particles). Raman spectra shows the evolution of the carbon film as a function of temperature (c) without and (d) with Niin the process. Adapted from [1001].

Figure VI.1. Transfer of SLG from a Cu substrate to a dielectric surface. The top-right and bottom-left insets are the optical micrographs of SLG transferred on SiO,/Si with ‘bad’ and ‘good’ transfer, respectively. The bottom-right is a photograph of a 4.5 x 4.5cm?SLG on quartz substrate. Adapted from [1005], copyright American Chemical Society.

Figure VI.2. Top: Schematic of GRM transfer using polymeric media. Bottom, left: Optical micrograph of CNM transferred onto 5i02/Si showing interference contrast; bottom right: HIM of CNM transferred onto a metal grid without critical point drying. Ruptures and faults, as well as large intact areas of the freestanding nanolayer are visible. Adapted from [75, 1009].

Figure VI.3. HIM image of large freestanding CNMs transferred onto hexagonal TEM grids. (left) The size of each hexagon is 50 jum and the grid is uniformly covered by the CNM. Scale bar is 50 jum. Right) The size of the hexagon is 500 jum and it is completely covered by CNM, no wrinkles or folds seen. Scale bar is 200 jum. Adapted from [1007].

Figure VI.4. Electrochemical exfoliation of graphene from Cu. (a) Schematic diagram of electrochemical cell used for exfoliation, (b)—(d) optical images showing the ‘whole film’ peeling of PMMA-covered graphene form Cu. (e) Graphene film wet transferred onto a 4 inch wafer. (f) Time needed for complete film exfoliation of a5cm x 5cm foil as a function of voltage and electrolyte concentration (at 5 V, red line). Adapted from [779], copyright American Chemical Society.

Figure VI.5. High-speed electrochemical delamination graphene transfer. Adapted from [1021], with the permission of AIP Publishing.

Figure VI.6. (a) Images of stacks of 2, 4, 9, 12, 24, 37, 50 LGs on PMMA. (b) Optical transmittance of MLG stack.

Figure VI.7. High resolution XPS Cls (a) and Ols (b) spectrum of transferred graphene samples before heating (red line), after heating (blue line) and graphene samples without contact with PMMA (black line).

Figure VI.8. AFM and near-field IR images recorded from samples before (a) and after (b) heat treatment. Scan size for eacl measurement was 10 x 10 jum”.

Figure VI.9. Sequential imaging of a PMMA particle at 1130cm~! and 1740.cm7!. Scan size: 200 x 200nm. Figure VI.10. 3-electrode setup used in TOA intercalation and voltammetry experiments. Adapted from [1020], with permission from AAAS.

Figure VI.11. Electrochemical cell used for the electrochemical oxidation of Pt in the Graphene /Pt (1 1 1) stack. RE, is the Ag/AgCl reference electrode, CE the Pt counter electrode and WE the working electrode (ie. stack graphene/ Pt(1 11). The cell is purged with N> and installed inside a Faraday cage.

Table VI.1. Parameters for potential-controlled electrochemical oxidation of Pt(1 11) and Ir(1 11) with SLG on top. Ei stands for the initial potential, Esup for the upper limit of the potential, Ef for the final potential, v for the scan rate and Q for the charge. remains attached to the target substrate. Repeated lamination, at RT or elevated T, can be undertaken to further remove absorbates, bubbles, voids and non- conformalities in the transfer [1719, 1720]. In the case of TRI, the support-coated substrate is finally baked at 120 °C to remove the TRT. following a preliminary casting at 500 rpm for 10—20s. This coated substrate is then placed in contact with the as-grown graphene-on-catalyst. This sandwich is subsequently compressed at 0.2 MPa using a cold-roll laminator, to avoid air pocket formation at the inter- face. The UVA is subsequently cured by exposing the backside of the PET to a UV optical source (365 nm, 20-25 mW m~”) for 10-15 min. The Cu foil is etched in aqueous ammonia persulfate for 12h, rinsed in DI

Figure VI.12. Cyclic voltammetries for graphene on Pt(1 1 1) in0.1M aqueous HCIO, solution. Four different voltammetric treatments have been applied (A, B, C, D), being the scan rate 0.05 V-s 1 in all the cases. The right panels plot the potential program applied to the SLG/Pt electrodes, producing the corresponding cyclic voltammograms of the left panels.

Figure VI.13. Graphene transfer by (a) HPL and (b) UVA, and (b) corresponding optical images and (c) and (d) 550 nm optica transmission maps. Adapted from [1038-1040].

Figure VI.14. (a) Change in normalised resistance (AR/Ro) with bend radius. (b) (AR/RO) for all bending diameters for UVA, HPL, PMMA and ITO. (c) peel strengths for transfer methods. Inset: Typical AFM height maps of fatigued transfers. Adapted from [1038-1040].

Figure VI.16. Free standing 500 nm thick and 10 mm in diameter graphene/PMMA structure. The film is transparent and thus convenient for optical experiments.

$Figure VIL.1. Schematic diagram of vertical CVD growth chamber for hBN growth on metal. Figure VII.2. (a) Optical image of BN film grown on Cu and transfer red onto 90 nm SiO,/Si, scale bar is 50 jm. (b) AFM profile showing the 90 nm thickness and the high roughness. (c) TEM image with scale bar 4 jum and (d) electron diffraction pattern showing the rough/turbostratic nature of the ML-h BN film grown on Cu with scale bar 5 nm.$

Figure VIL.1. Schematic diagram of vertical CVD growth chamber for hBN growth on metal. Figure VII.2. (a) Optical image of BN film grown on Cu and transfer red onto 90 nm SiO,/Si, scale bar is 50 jm. (b) AFM profile showing the 90 nm thickness and the high roughness. (c) TEM image with scale bar 4 jum and (d) electron diffraction pattern showing the rough/turbostratic nature of the ML-h BN film grown on Cu with scale bar 5 nm.

Figure VII.3. (a) SEM image and (b) corresponding EBSD mapping of BN on Ni. (b) TEM image of the BN film transferred polymer-free on holey amorphous carbon TEM grid. HR TEM images and corresponding electron diffractions of (c) and (d) a flat BN area and (e) and (f) a rough BN area with the schematic of the growth process: Van der Merwe for Ni(1 1 1) and Volmer Weber fo1 Ni(110) and Ni(001).

Figure VII.4. (a) 800 °C hot 4 inch wafer in the growth chamber. (b) Low energy electron diffraction (LEED) pattern of h-BN/ Rh(1 11) at 60 eV kinetic energy. (c) STM image of the same surface with U, = —1.2 Vand I, = 0.5 nA.

GFET on h-BN/SiO, was improved compared to SiO). Ref. [1076] claims that these h-BN films can be trans- ferred to any substrate making LMhs and LM-based electronic devices possible. VIL.1.3. Growth of h-BN by ion beam assisted deposi- tion on metals and dielectrics

Figure VII.6. XPS from a stoichiometric h-BN produced by IBAD.

Table VII.1. Comparison of the various procedures developed to date for transferring CVD grown BN.

Figure VII.7. Examples of large areas BN film transferred on (a) 90 nm SiO,/Si, (b,c) TEM grid, fromCu and Ni growth substrates.

Figure VII.8. (a) Two zone furnace for TAC of Mo to MoS). (b) Photographs showing different thicknesses MoS) films on fused quartz (top) and SiO, (bottom) substrates. Adapted from [1093], with permission from Elsevier.

Figure VII.9. (a) and (b) Raman spectra and (c) PL of TAC MoS; grown from Mo films of differing thickness. (d) Mo 3d peak for MoS; grown from 1 nm Mo. (e) W 4f peak for WS) grown from a 20 nm W film. Adapted from [1093], with permission from Elsevier. (f) HRTEM image of WS; polycrystalline film. Adapted from [1100], copyright American Chemical Society.

Figure VII.10. (a) MoS, device with Ti/Au contacts. (b) NH3 gas sensing device. (c) Sensor response plot showing percentile resistance change versus time for the MoS; film with a bias voltage of 0.5 V. NH3 exposures range from 300 ppb to 2 ppm. (d) Resistance change (black solid circles) and signal-to-noise ratios (gray open boxes) as a function of NH3 concentration. Inset: full calibration curve ranging from 300 ppb to 200 ppm. Adapted from [1096], © Wiley-VCH Verlag GmbH & Co. KGaA.

Figure VIL.11. Side view of the crystal lattice and unit cell of y-InSe (left), v-In2Se3 (middle) and 3-In2Se; (right). Blue and red spheres correspond to Se- and In-atoms, respectively. The primitive unit cell of y-InSe contains three layers, each consisting of four closely-packed, covalently bonded, atomic sheets in the sequence Se-In—In-Se. For both a- and G-In2Se; phases, the unit cell contains three layers, each consisting of five closely-packed, covalently bonded, atomic sheets in the sequence Se-In—Se—In-Se. In a-In2Se; the outer Se-atoms in each layer are aligned, whereas in 3-In2Se; they are located into the interstitial sites of the Se-atoms ir the neighboring layers, thus leading to a smaller volume in (-In2Se3.

Figure VII.12. (a) Optical image of fine-grained powder of y-InSe. (b) Tube furnace system used for the growth of In)Se3. (c) The source material and the substrate in the quartz tube. (d) Program profile of the furnace heater.

Figure VII.13. Optical micrographs of 3-In2Se;3 layers grown on (a) SiO>/Si, (b) mica, and (c) graphite (T = 600 °C, t = 9hand Ar flow rate ~150 sccm). Different colors correspond to different thicknesses of the layers. This ranges from hundreds of nanometers down to 2.8 nm. Adapted from [1117], © IOP Publishing Ltd.

Figure VII.14. Optical micrographs of 3-InSe3 rods (a) grown on mica at T = 620 °C for t = 9h under an Ar flow rate of 150 sccm, (b) grown on mica at T = 570°C for t = 6h under an Ar flow rate of 150 sccm, and (c) grown on Si/SiO, at T = 600 °C fort = 6h under an Ar flow rate of 170 sccm.

Figure VII.15. (a) Normalized Raman spectra of as-grown (3-In2Se3 layers (top) and exfoliated flakes of a-In,Se3 (bottom) at T = 300K (P = 0.1 mW and \ = 633 nm). (b) Normalized j1PL spectra of bulk y-InSe, G-In.Se3 and a-In2Se3 at T = 300K (A = 633 nm and P = 0.1 mW). (c) Measured and calculated dependence of the peak energy, E, of the PL emission on layer thickness t of as-grown 3-In2Se3 (black dots) and exfoliated Bridgman-grown a-In2Se; (blue dots) and y-InSe (magenta dots) flakes. Inset: Normalized PL spectra of (3-In.Se3 with t~ 50nm and 6 nm at T = 300K. Adapted from [1117], © IOP Publishing Ltd.

Figure VII.16. (a) Schematic set-up for CVD of MoS). (b) mechanism by which MoS, is deposited on the target substrate. Adapted from [1098] CC BY 4.0.

Figure VII.17. (a) SEM image showing continuous MoS, film. Scale bar is 2 zm. (b) Average Raman spectrum measured across a 20 x 20 jum area of the film. (c) Mo 3d core level showing contributions consistent with MoS». (d) PL measured across a 1L region (green) and 2L island (pink). Adapted from [1098].

Figure VII.18. (a) CVD setup for deposition of 1L MoS, using solid precursors, MoO; and S. (b) MoS) deposited on c-plane sapphire. (c) 1L-MoS, covering c-plane sapphire without complete coverage, scale bar is 20 zm. (d) 1L MoS) with complete coverage, bar is 10 jzm. Adapted from [1130], copyright American Chemical Society.

Figure VIL.19. Equilibrium vapor pressure of Mo(CO)g as a function of T based on the measured thermodynamic constants in Ref [1134].

cylinder and near the CVD furnace are installed. They are connected to a sound alarm to alert the appropriate emergency services immediately. In addition, experi- ments thorough He leak test of the assembled CVD system need to the conducted before performing the experiments involving H)S to prevent anyone in the work area from exposure.

Figure VII.21. Dependent growth morphology illustrated by AFM height images of as-grown MoS, on sapphire samples produced at different using Mo(CO)¢ and H)S as model precursors. Scale bar, 250 nm. Adapted from [1142], copyright American Chemical Society.

Figure VII.22. Nucleation density versus 1/T for the samples in figure VII.11. Adapted from [1142], copyright American Chemical Society.

Figure VII.23. (a) Optical absorption and (b) Raman spectra at 532nm from 1L-MoS) grown at 950° C. Adapted from [1142], copyright American Chemical Society.

Figure VII.24. XPS survey spectra of MoS,/sapphire samples from the two growth runs with different chamber pressures (1 atm and 8.5 mbar). XPS measurements were performed with PHI Versaprobe II equipped with x-ray source, Al Ka; hv = 1486.6 eV.

Figure VII.25. Influence of Mo(CO)6:H2S flow rate ratio on MoS2 film composition. (a) and (b) Optical images of two different Mo(CO)6 Ar carrier and H2S mass flow rates of (a) 15 (Mo(CO)6 flow rate of 0.0053 sccm) and 15 sccm, and (b) 5 (Mo(CO)6 flow rate of 0.0018 sccm) and 20 sccm with growth T~ 950 °C, bubbler T~ 30 °C, H2 ~10 sccm, growth pressure ~1 atm, and growth time ~30 min. Scale bar, 25 jum. (c) and (d) Mo 3dand S 2s core-level XPS spectra for the corresponding growth conditions of (a) and (b). (f) S 2p core-level XPS spectra for the corresponding growth conditions of (a) and (b). XPS measurements were performed with PHI Versaprobe II equipped with a Al Ka x-ray source; hv = 1486.6 eV.

Figure VII.26. (a) Optical microscopy of 1L-MoS) with NaCl placed upstream. Scale bar: 25 jum. (b) Raman spectroscopy ona single crystalline 1L-MoS, area (c) optical absorbance. (d) PL spectra from single crystalline 1L-MoS, flake as-grown on sapphire and transferred onto SiO,/Si. Adapted from [1142], copyright American Chemical Society.

Table VII.2. Basic conditions for growth of TMDs.

Figure VII.27.. Growth chamber of the Aixtron HT-BM vertical cold-wall reactor used for growth of graphene on h-BN.

Figure VII.28. Schematic of two fabrication processes of MoS,/h-BN LMHs. The first consists in transferring the CVD grown film from a Cu foil to the center of a Si/SiO> chip, leaving four corners of the substrate to be bare SiO. This substrate is then loaded face up into the CVD system to grow MoS; on it. The MoS, domains will cover both h-BN and SiO areas. The second approach is through a two step PMMA assisted process. The CVD grown h-BN film is first transferred onto the center of a SiO2/Si chip, followed by stacking another layer of CVD grown MoS, on the whole substrate surface, obtaining transferred MoS, domains on h-BN in the central area. Two of the transferred bundaries of h-BN on the SiO; surface in the first fabrication method are labeled A and B. Adapted from [1216], copyright American Chemical Society.

Figure VII.29. (a) Scheme of the furnace used to grow continuous films of WS, on graphene and h-BN; (b) picture of the furnace. Adapted from [1217], with permission of The Royal Society of Chemistry.

Figure VII.30. Different method used to create TMD LMHs, (a) Co- conversion of both metal films together to form TMDs. (b) Sequential conversion of metal films. (c) LMH formation through stacking pre-converted films.

Figure VII.31. (a) Legend for Raman maps. (b) and (c) Raman map of MoS;/WS) Aj peak position for sequentially and co- converted films. (c) and (d) Raman map of MoS,/WS) Be peak position for sequentially and co-converted films. (e) and (f) Raman spectra of MoS,/WS, for sequentially and co-converted films respectively.

0.3 and, (c) SGN18 (Future Carbon AG)—a spherical, defect-rich graphite with I(D)/I(G) ~ 0.4, with a grain size ~20 um. The type of graphite activation used prior to the addition of the trapping electrophile has a significant influence on the outcome of the functionalization sequence and the obtained graphene architectures [1235]. The hydrogenation of graphite the GIC (d) yields polyhydrogenated graphene with the highest hydrogen content when alcohols are used as trapping reagents [1235], whereas for the Birch-type reductive activation (b) the highest hydrogen content is obtained for water [369]. This can be explained by the nature of the solvent. In the latter case, ammonia is used at —75 °C and interacts with the trapping water (formation of ammonium hydroxide in an equilibrium reaction). This underlines that the applied reductive activation conditions of graphite have a fundamental influence on the outcome of the reaction.

Figure VIII.2. (a) Molecular structure of DBT. (b) STM image of DBT assembly on graphite, showing also the unit cell; the possib! molecular packing is also schematized. The position of BF4-counterions is indicative. Lattice parameters: a = 3.9 + 0.1 nm: b= 1.0 + 0.1 nm:a = 89° + 2°:A = 3.9 + 0.1 nm’. (c) and (d) STM height (c) and current (d) images of DBT self-assembled on SLG. The quality of the image is not as good as on graphite, as a result of the few A roughness of the underlying SiOx, causing a blurring effect. (e) Schematic representation of the electrochemical setup used for grafting. WE = graphene; CE = Pt; RE = Ag/AgCl (3 M KCl). Adapted from [1263], copyright American Chemical Society.

Figure VIII.3. Preparation of a vertical casting system for the evaluation of a graphene dispersion.

Figure VIII.5. (a) Comparison of R, of chlorinated and non-chlorinated CVD graphene as function ofN. (b) Transmittance for 1 to 5LG. Adapted from [1316].

Figure VIII.6. (a) 514.5nm Raman spectra of pristine, hydrogenated and chlorinated graphene after hydrogenation. (b) 514.5nn Raman spectra of chlorinated, Cl-SLG, and hydrogenated and chlorinated graphene (Cl-(H-SLG)) directly and after doping and after three months in ambient conditions.

Figure VIII.7. (a) Raman spectra for high and low packing density perylenel SAMs on as-transferred and pre-annealed SLG. Inset Structure of perylene1. Water contact angles on (b) bare SLG, (c) low and (d) high packing density of perylenel on SLG. Adapted from [1323] with permission of The Royal Society of Chemistry.

Figure VIII.8. STM images of (a) as-transferred (top) and subsequently annealed (bottom) CVD-SLG on SiO; and (b) after wet- chemical deposition of perylene1 on the same annealed substrate. (c) line profiles from (b) and (d) zoomed in area with molecular structure overlay. Adapted from [1323] with permission of The Royal Society of Chemistry.

Figure VIII.9. (a) Schematic FLaT, in which perylene fucntionalised graphene is transferred b-d) XPS spectra of perylene on CVD-SLG for each derivitization step. (b) As-transferred perylene1 on SLG. Inset: Partial structure of perylene1 with corresponding nitrogen contributions. (c) Perylenel on SLG after reaction with HATU and EDA. The two new contributions are from HATU residue. Inset: Chemical structure of HATU. (d) After annealing of derivatized sample at 220 °C. The HATU contributions reduce, but the amine signal increases. Inset: Partial structure of perylenel after reaction, depicting corresponding nitrogen contributions. Adapted from [1327] with permission of The Royal Society of Chemistry.

Figure VIII.10. Noncovalent chemical functionalization of SLG. (a) Schematic of the fabrication of NH)-CNM/SLG heterostructures via mechanical stacking of the individual sheets. (b) Microscope image of the fabricated FET with Au contacts in the Hall bar geometry. (c) Mapping of the Raman 2D peak on the active device area. (d) RT homogeneous electrical field effect at different side contacts of the FET asa function of Vc. (e) jz of heterostructure and reference devices. (f) Quantum oscillations ina magnetic field at low T confirming high electronic quality of SLG in the heterostructures. Adapted from [1328] © Wiley-VCH Verle GmbH & Co. KGaA.

Figure VIII.11. Free-radical mechanism for edge-selective functionalization using diazonium species. Adapted from [1336], copyright American Chemical Society.

Figure VIII.13. STM images of the p-aminophenol molecules covalently anchored to the monovacancies created by the soft irradiation of the surface with argon ions in both types of samples: SLG (upper panel) and QFSLG (lower panel). The graphene on SiC was grown as for Ref. [611]. Note that in the images of the SLG sample one can see the (6 V 3 x 6 V 3)R30° reconstruction fron the SiC buffer layer, whereas in the QFSLG sample only the graphene network is seen since intercalated hydrogen has decoupled the buffer layer. The molecules appear as protuberances inserted into the graphene network. Partially adapted from [1340].

Figure VIII.14. (a) N 1s core level spectra after dosing p-AP ona SLG surface without and with atomic vacancies. The N 1s binding energy corresponds to that of a C atom substitutional in the graphene-network. (b) thermal estability of the N 1s peak at RT and after annealing at ~250 °C.

Figure VIII.15. (a) Schematic representation of the approaching of a generic NH>-terminated organic molecule towards a graphene SAV (with a magnetic moment of 1 /.B). (b) For the case of p-AP molecule, most representative geometries for initial state, transition state and final state along the minimum energy path (MEP) for: (top) the first single dehydrogenation of the molecular-NH) group, and (bottom) the second single dehydrogenation of the remaining molecular —NH group and the subsequent incorporation of the molecule via the N atom into the graphene lattice via the graphene SAV.

Figure VIII.16. Representative Cs-corrected STEM-HAADF images of (a) Ih, (c) Dh and (e) fcc NPs and (b-f) their corresponding size distributions for Ih, Dh and fcc, for Au NPs grown by MICS. The FFT and the model of each structure are shown as insets. The mean diameters are also given.

Figure VIII.17. AFM of Au NPs (a) on SiO, and (b) on SLG after a deposition time of 4s and 3s, respectively, to illustrate the importance of the sticking coefficient.

Figure VIII.18. (a) Increment of carriers versus NPs density using UHV and wet chemistry Au salts methods, (b) surface potential versus density of Au, NPs using the UHV method or the wet chemistry Au salts method. After [1378].

Figure VIII.19. TEM images showing wrinkles and crumpling.

Figure VIII.20. Schematic of basal-plane functionalization of MoS). After intercalation with n-butyllithium, the negatively charged MoS) is dispersed in water by mild bath-type sonication leading to an efficient exfoliation into individual sheets. The charges on the MoS, are quenched by the addition of 4-methoxyphenyldiazonium tetrafluoroborate obtaining the functionalized product. Adapted from [379], copyright American Chemical Society. gent is expected to be susceptible to the synthetic sol- vent utilized. Hence the use of different solvents in principle should lead to different MgH> structures and hydrogen performances [1390]. The XPS analysis showed Mg in a completely oxi- dized form, because it difficult to introduce the sample in the XPS instrument avoiding exposure to atmos- phere. The oxygen is ~34%. However, if oxygen is con- sidered as exogenous due to atmosphere exposure, the quantification can be limited to C and Mg core lines. The Mg concentration corresponds to ~27%. Hydrogen was introduced in the reactor at a pres- sure of 10 or 20 bar and the solution heated at 170 °C and stirred at 50rpm overnight [1391]. After 12h, a black/gray precipitate was obtained from the decom- position of n-dibutyl-Mg. The suspension was then transferred in appropriate vessels under inert atmos- phere and the main part of the solvent was removed by using a centrifuge at 5000 rpm (~2000 g). To further dry the material and remove the remaining organic residuals, the material was placed in a dynamic vac- uum ~10~? mbar for ~5h. The exsiccated material was placed in sealed vials, to avoid Mg oxidation, for the characterization [1387, 1392].

Figure VIII.21. Idealized formula scheme depicting the chemical exfoliation of bulk MoS, and subsequent functionalization with 4-iodopheny] substituents under formation of MoS)-I, as well as the preparation of MoS)-templated conjugated microporous polymers (M-CMPs) and the corresponding MoS,/nitrogen-doped porous carbon (M-CMPs-T) hybrids. (i) monomers: 1,3,5-triethynylbenzene and 2,5-dibromopyridine, 2,5-dibromopyrazine, or 2,4,6-trichloro-1,3,5-triazine, argon, Pd(PPh3)4, Cul, Et3N, DME, 100 °C, 3 d; (ii) argon, heating rate: 10 °C min@|, pyrolysis temperature: 700, 800, or 900 °C, 2h.

Figure VIII.22. Fitted XPS Mo 3dand S 2p core level peaks for (a, d) 2H-MoS) (a), (b, e) 2H-MoS)-Cu(OAc)s, and (of defunctionalized 2H-MoS)-Cu(OAc),. Adapted from [1409], © Wiley-VCH Verlag GmbH & Co. KGaA.

Figure VIII.23. (a) Topography of MoS, triangles after 27 cycles of ALD after seeding with a perylene bisimide derivative. The flakes are higher than the surrounding substrate. (b) Line profile along the line marked in (a). The step height is 1.9 nm. (c) Schematic representation of the structure of (a) as indicated by the scan. Adapted from [1414] with permission of The Royal Society of Chemistry.

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