Graphene by CVD

This paper focuses on the development of patterned graphene/substrate by means of green nanosecond pulse laser irradiation. Monolayer graphene samples supported on a Si/SiO 2 substrate were patterned using 532 nm laser irradiation under fluence conditions ranging from 31 mJ/cm 2 and to 4240 mJ/cm 2 . Raman spectroscopy was used to investigate the effect of laser irradiation on the graphene. It was found that at 356 mJ/cm 2 selective ablation of the graphene occurs. However, at fluence values above 1030 mJ/cm 2 (when damage to the substrate is observed) no ablation of the graphene takes place. In contrast, its graphenic structure was found to have been modified. Only at fluence values where the ablation of the substrate occurs, is graphene eliminated in an area almost equivalent to that of the ablated substrate. In this case, additional damage to the graphene sheet edges is produced. The increment in the number of oxygenated functional groups in these regions, as measured by XPS spectroscopy, suggests that this damage is probably caused by thermal phenomena during the ablation of the substrate.

We report a simple, green and cost effective synthesis of graphene via chemical reduction of graphene oxide in alkaline aqueous solution. Extensive characterizations have been studied to confirm the formation of graphene in sodium carbonate solution. Cyclic voltammetry was used to study the electrochemical properties of the prepared graphene-modified glassy carbon electrode using potassium ferricyanide as a redox probe. Based on the result, with the addition of graphene to the glassy carbon electrode the current flow increases and the peak also broadens as compared to graphite and graphene oxide. This method is fast, cost effectively, and green as nontoxic solvents are used which will not result in contamination of the products. Thus, this method can serve for the preparation of graphene which can be effectively used in sensors, electronic devices and supercapacitors.

This study explores the use of graphene coatings to enhance the electrical conductivity and corrosion resistance of aluminum busbars. Graphene was synthesized via Chemical Vapor Deposition and transferred onto aluminum, with comparisons made against bare and tin-coated samples. A single graphene layer significantly increased surface conductivity, achieving 11 times better performance than tin-coated and 33 times better than uncoated aluminum before corrosion. Characterization using Raman spectroscopy, resistivity measurements, and wettability tests confirmed successful graphene synthesis and transfer. Long-term performance was tested in NaCl solution, where graphene-coated samples exhibited only a 10.71% resistance increase, compared to 21.80% for tin-coated and 197.90% for uncoated aluminum. Initially, graphene improved water repellency, but after corrosion, the samples became hydrophilic. Despite its limitations in maintaining durability under harsh conditions, graphene proves highly effective in improving aluminum's electrical and anticorrosive properties, with potential for further optimization.

In the course of the PhD thesis large area homogeneous strictly monolayer graphene films were successfully synthesized with chemical vapor deposition over both Cu and Si (with surface oxide) substrates. These synthetic graphene films were characterized with thorough microscopic and spectrometric tools and also in terms of electrical device performance. Graphene growth with a simple chemo thermal route was also explored for understanding the growth mechanisms. The formation of homogeneous graphene film over Cu requires a clean substrate. For this reason, a study has been conducted to determine the extent to which various pre-treatments may be used to clean the substrate. Four type of pre-treatments on Cu substrates are investigated, including wiping with organic solvents, etching with ferric chloride solution, annealing in air for oxidation, and air annealing with post hydrogen reduction. Of all the pretreatments, air oxidation with post hydrogen annealing is found to be most efficie...

Monolayer Tungsten Diselenide (WSe2) exhibits tremendous advantages as a channel material for next-generation field-effect-transistors (FETs). This paper reviews the relevant physics and properties of WSe2 and highlights the excellent scalability of monolayer WSe2 for ultra-short channel (sub-5 nm) FETs. The crucial role of metal-WSe2 contacts in determining the performance of monolayer WSe2 FETs is also emphasized using experiments guided by ab-initio density functional theory (DFT). With a suitably chosen contact, a back-gated monolayer WSe2 FET on Al2O3 substrate is shown to exhibit both high mobility and high ON-current.

A single graphene layer is superior many ways preferably in electronic devices application. However, mild modification of the graphene network could open a new potential to the ultrathin graphene membrane. Moreover, recent studies demonstrated that a few simple techniques could generate and control the nanopores size on single layer graphene sheet simultaneously. This review paper will discuss all potential techniques that are capable to generate nanopores structure on the pristine single layer graphene network.

A variety of oxidation-exfoliation methods have been employed to minimize the restacking effect between the graphene sheets by breaking the van der Waals force, such as chemical treatment, irradiation, thermal annealing and powerful sonication. Each method has its own advantages and disadvantages. Several chemical treatment methods have been developed, but involve harmful reducing agents and are not suitable for mass production. Thermal annealing can produce high quality graphene sheets but it requires a very high temperature of the order of ~1050°C.Irradiation and sonication methods serve as pure exfoliation techniques and always require the help of chemical reduction process. In this work an attempt is made to synthesize and study reduced graphene oxide employing low-cost methods. The uniqueness of the present work is the way the Graphite is partially oxidized using aqua regime and dried at 50°C followed by irradiation with microwaves and subsequent exposure to ultrasonic waves to obtain a few layers of reduced grapheme oxide (rGO). Finally, the product thus obtained is dispersed in ethanol and sonicated for 30 minutes using ultra probe sonicator. A stable colloidal dispersion is formed, which is then dried to collect the solid product. The yield to an extent of 65% obtained in this process appears to be promising for commercialization aspects in applications such as energy storage, photovoltaics and opto-electronics devices etc., Morphology (plane and cross-sectional), structure and phase characteristics of the graphene are studied using experimental techniques that include Electron microscopy, Raman scattering, and X-ray diffraction.

The theoretical discovery of new and stable 2D penta materials has stimulated the technological advancement due to the anticipated exotic properties of such structure, including the recent α phase and β phase of penta-NiPS based on first-principle calculations. Inspired by the similarity between the theoretically proposed penta-NiPS and the experimentally synthesized (α phase) of penta-PdPSe, we proposed herein the β phase penta-PdPSe as a new member of the penta-2D materials. Comprehensive analyses indicated that the β phase penta-PdPSe is thermodynamically, dynamically, mechanically, and thermally stable, similar to the NiPS analog. It was found that β penta-PdPSe is a wide band gap semiconductor with an indirect band gap of 1.58 eV, significantly lower than 2.15 eV for the α phase. Moreover, the two polymorphs of penta-PdPSe are a soft material with 2D Young's modulus of E a = 151 Nm -1

The theoretical discovery of new and stable 2D penta materials has stimulated the technological advancement due to the anticipated exotic properties of such structure, including the recent α phase and β phase of penta-NiPS based on first-principle calculations. Inspired by the similarity between the theoretically proposed penta-NiPS and the experimentally synthesized (α phase) of penta-PdPSe, we proposed herein the β phase penta-PdPSe as a new member of the penta-2D materials. Comprehensive analyses indicated that the β phase penta-PdPSe is thermodynamically, dynamically, mechanically, and thermally stable, similar to the NiPS analog. It was found that β penta-PdPSe is a wide band gap semiconductor with an indirect band gap of 1.58 eV, significantly lower than 2.15 eV for the α phase. Moreover, the two polymorphs of penta-PdPSe are a soft material with 2D Young's modulus of E a = 151 Nm -1

В работе предлагается новый концепт вычислительного субстрата, основанного на нелокальной фазово-коммутативной алгебре Σ. Вместо традиционного разделения «память–процессор» вся информация хранится и обрабатывается одновременно через глобальную фазовую конфигурацию бесконечномерного Σ‑пространства. Показывается, как на его основе можно реализовать алгоритм Гровера, управляя разложением фазы в слоях графен‑сверхпроводящих наночастиц, связанных через делители нуля. Физическое устройство не раскрывается, но утверждается существование топологически связной системы с мгновенной нелокальной связью.

Yüksek lisans tezi başlığı ve tez danışmanı Aydınalp, E. B. (2014). Le concept de l''écriture chez Jacques Derrida-Une analyse thématique et descriptive Université Anadolu, Institut des Sciences de l'Education, Eskişehir/Turquie. [Prof. Dr. Bahadır GÜLMEZ] Doktora tezi başlığı ve danışmanı Aydınalp, E. B. (2018). L'écriture féminine chez Hélène Cixous-une lecture de déconstruction.

Now a day graphene is a promising material for the development of high sensitivity sensing system.current status of the intrinsic mechanical properties of graphene along with properties of bulk graphene based nanocomposite is thoroughly examine. Graphene (G) is a two-dimensional material with exceptional sensing properties. In general gas sensor are produced in field effect transistor configuration on several substrate. The role of substrates on the sensor characteristics has not yet been entirely established.Graphene has gather must interest in research in recent years due to its unique mechanical, electrical, chemical & optical properties that can be developed into various applications with noval functionalities. Graphene-based gas sensor has attracted much attention in recent years due to their variety of structure, unique sensing performance, room temperature working conditions & tremendous application prospectus etc.

A new vertical tunnel FET design based on black phosphorus is presented in this paper adopting asymmetric layer numbers for top and bottom layer with undoped drain. The results show that the SS and Ion/Ioff can be maintained below 10 mV/dec and beyond 10 5 , respectively, when channel length is down to 3 nm.

Graphene can be synthesized by chemical vapor deposition (CVD) on diverse metal catalysts such as Ir . Among them, Cu has been regarded as the most promising catalytic substrate owing to its lower cost and suitable carbon solubility that suppresses the growth of multilayers . However, the electrical properties of the CVDgrown graphene are not as good as those of exfoliated graphene because of its polycrystallinity and grain boundary originated from the randomly oriented nucleation and growth of graphene islands . It was reported that the Cu (1 1 1) surface showing only 3-4% lattice mismatch with graphene decreases the defect density of graphene, and thus, enhances the electrical property . The Cu (1 1 1) substrates were typically obtained by the deposition and annealing of thin Cu films on sapphire or SiO 2 wafers with limited size and cost . The annealing of polycrystalline

We propose an innovative, easy-to-implement approach to synthesize large-area singlecrystalline graphene sheets by chemical vapor deposition on copper foil. This method doubly takes advantage of residual oxygen present in the gas phase. First, by slightly oxidizing the copper surface, we induce grain boundary pinning in copper and, in consequence, the freezing of the thermal recrystallization process. Subsequent reduction of copper under hydrogen suddenly unlocks the delayed reconstruction, favoring the growth of centimeter-sized copper (111) grains through the mechanism of abnormal grain growth. Second, the oxidation of the copper surface also drastically reduces the nucleation density of graphene. This oxidation/reduction sequence leads to the synthesis of aligned millimeter-sized monolayer graphene domains in epitaxial registry with copper (111). The as-grown graphene flakes are demonstrated to be both single-crystalline and of high quality.

Devitrified silica minerals glass was obtained from stoichiometric tanohataite (LiMn2Si3O8F) mineral prepared by melt quench route. Low-quartz and cristobalite (~19.5 %) were developed in glass during melt cooling and casting the glass melt. However, a scanning electron microscope (SEM) for the devitrified glass showed nanoscale
particles scattered in a few crystallized spots. When it was tested as an anode for lithium-ion batteries, a relatively high initial capacity of ca.785 mAh g􀀀 1 was obtained at 50 mA g􀀀 1 as an initial discharge capacity. Very good stability with excellent capacity retention (sometimes it exceeds 100 %) was observed based on the 2nd discharge capacity until the 500th cycle with about 100 % coulombic efficiency. The sample showed good rate capability as it still delivers a capacity of 26 mAh g􀀀 1 after increasing the current density 40 times of magnitude. Also, it is a flexible material as after this considerable load, it can restore 185 mAh g􀀀 1 after returning to the initial low current (50 mA g􀀀 1). The electrochemical performance was supported by electrochemical impedance (EIS) measurement, which showed a decrease in EIS and an increase in lithium diffusion upon extended cycling. This unique electrochemical performance for this multicomponent non-crystalline glass was formerly supported by XPS characterization, which emphasized the presence of Mn4+ in the synthesized sample.

A novel route for the synthesis of large area graphene by an indigenously built electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD) setup has been reported in this work. A unique 2.45 GHz permanent magnet type ECR PECVD system has been designed and developed for the growth of various nano-structures and films. The apparatus has a unique advantage to synthesize large area graphene at much lower additional substrate heating than heat supplied by an external oven in conventional thermal CVD method. A major amount of heat is supplied here by ECR plasma. Polycrystalline copper foil is used here as a catalytic substrate which is pre annealed inside resonant hydrogen plasma prior to its exposure under precursor gaseous plasma inside the ECR PECVD reactor. Methane is used as carbon precursor along with hydrogen as carrier gas. Argon gas is used for the rapid cooling of the substrate maintaining suitable thermodynamic condition favorable for graphene synthesi...

This work describes the electrochemical performance of a novel composite based on nickel tetrasulfonated phthalocyanine (NiTsPc), deoxyribonucleic acid from calf thymus (CT-DNA) and reduced graphene oxide (rGO) for the electroanalysis of reduced β-nicotinamide adenine dinucleotide (NADH), through electrocatalytic oxidation. The modified electrode was denoted as CT-DNA/NiTsPc/rGO. Fourier transform infrared and ultraviolet-visible spectroscopies were performed to characterize the composite material. The electrochemical performance of the composite for NADH oxidation was investigated by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). The CT-DNA/NiTsPc/rGO modified glassy carbon electrode (GCE) showed an excellent electrocatalytic activity for NADH oxidation with apparent electrocatalytic rate constant (k obs) of 7.35 × 10 5 L mol-1 s-1 and linear response range for NADH from 1 up to 1350 µmol L-1 for n = 12 (r = 0.999). The proposed sensor shows sensitivity, detection limit and quantification limit of 0.014 µA L mol-1 , 0.3 and 1 µmol L-1 , respectively. The prepared sensor was further tested for the determination of NADH in artificial human urine samples, showing promising biomedical applications.

The mechanism of helicity formation of carbon nanotubes still remains elusive that hinders their applications. Current explanations mainly rely on the planar interrelationship between the structure of nanotube and corresponding facet of catalyst in 2D geometry that could amend the structure of grown carbon layer, specifically due to the epitaxial interaction. Yet, the structure of carbon nanotube and circumference of the rims assume involvement of more than one facet i.e. it is 3D problem. By aiming this problem we find that the nanotube nucleation is initiated by cap formation via evolving of graphene embryo across the adjacent facets of catalyst particle. As a result the graphene embryos incorporate in their hexagonic network various polygons to accommodate the curved 3D geometry that initiates cap formation following by elongation of the circumferential rims. Based on these results, also on the census of nanotube caps and the fact that given cap fit only one nanotube wall, we consider carbon cap responsible for the helicity of carbon nanotube. This understanding could provide new avenues towards engineering particles to explicitly accommodate certain helicities via exploitation of the angular distribution of catalyst adjacent facets. Our recent progresses in production of carbon nanotubes, nanotube reinforced composites and their potential applications also will be presented.

The biggest challenge facing the energy sector today is how to achieve a faster transition from fossil fuel economy to sustainable energy sources. Hydrogen is a clean chemical element that can be associated to high-efficiency fuel cells. However, most industrial H2 production processes are obtained from thermochemical processes that generate large amounts of CO2, such as natural gas (NG) steam reforming and coal gasification. An option to CO2-free H2 production is by water electrolysis based on renewable electricity, however it has technicaleconomic limitations that make its wide use difficult. This article presents a new plasma reformer as an alternative for H2 production that uses NG with CO2 or biogas as feedstock. Conversions of 90% of NG were experimentally obtained, producing H2, CO and reduced graphene oxide in a single pass through the reactor, without catalysts or heat regeneration. The Energy Conversion Efficiency of the prototype presented values close to 50%, without regard the energy of the carbonaceous nanomaterials obtained and depending on the losses between the power supply and the plasma torch. The proposed technology contributes to the transition from fossil fuel to renewable sources, suggesting the production of H2 in a decentralized way for fuel cell electric vehicles.

In this contribution, we report a fundamental study of the factors that set the contact resistivity between metals and highly doped n-type 2D and 3D semiconductors. We investigate the case of n-type doped Si contacted with amorphous TiSi combining firstprinciples calculations with Non-Equilibrium Green functions transport simulations. The evolution of the intrinsic contact resistivity with the doping concentration is found to saturate at ∼2 × 10 −10 .cm 2 for the case of TiSi and imposes an intrinsic limit to the ultimate contact resistance achievable for n-doped Si|amorphous-TiSi (aTiSi). The limit arises from the intrinsic properties of the semiconductors and of the metals such as their electron effective masses and Fermi energies. We illustrate that, in this regime, contacting heavy electron effective mass metals with semiconductor helps reducing the interface intrinsic contact resistivity. This observation seems to hold true regardless of the 3D character of the semiconductor, as illustrated for the case of three 2D semiconducting materials, namely MoS 2 , ZrS 2 and HfS 2 .

Graphene oxide (GO) membranes have been extensively investigated and employed in separating various ions and molecules due to their superior physicochemical properties. However, the inconsistency in their pore structure, difficulty in the precise tuning of their d-spacing, and instability in aqueous solution – especially at extreme pH values – might hinder their separation efficiency. In this research, we systematically investigated the pH-mediated fabrication process of graphene oxide membranes and evaluated the properties of the resulting membranes. Findings from scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses show that a higher fabrication pH results in a thicker GO layer and an enlarged d-spacing due to the deprotonation of the GO's carboxyl groups. Furthermore, pH-assisted crosslinking between polyethyleneimine (PEI) and GO sheets were facilitated and the chemical analysis results suggest that in acidic environments, the dominant reaction involves C–N bond formation at the basal plane, whereas under alkaline conditions, N–Cdouble bondO (amide) bond formation at the edges is more prevalent. This, in return, accordingly shifted the trend in SEM and XRD, where a thinner GP layer and a decreased d-spacing were observed at a higher fabrication pH due to the deprotonation of the incorporated PEI's amine groups. These findings contributed to the nanofiltration (NF) performance of the membranes against different inorganic salts and heavy metal ions. It was discovered that the GPpH11 membrane formed at pH 11 has the highest Pb2+ rejection of >95%, making it a suitable material for heavy metal ions removal.

Multilayer graphene was synthesized by chemical vapor deposition from
mixture of naphthalene/ methanol with ratios (1.5 g: 100 m L) respectively
at ambient pressure and nitrogen as carrier gas with two different flow
at 700 °C. The active sites for growth was Ferrocene with thickness
reach to125 μm. The product was characterized by Raman spectroscopy,
scanning electron microscopy, and Energy Dispersive X-Ray Analysis. The
analysis shows that high flow of carrier gas (250 cm3/min) was succeeded to produce graphene multilayers while the ether (100 cm3/min) witnessed many tubular structure in addition to graphene layers.

The search for ways to synthesize single wall carbon nanotubes (SWCNT) of a given electronic type in a controlled manner persists despite great challenges because the potential rewards are huge, in particular as a material beyond silicon. In this work we take a systematic look at three primary aspects of semiconducting enriched SWCNT grown by chemical vapor deposition. The role of catalyst choice, substrate, and feedstock mixture are investigated. In terms of semiconducting yield enhancement, little influence is found from either the binary catalyst or substrate choice. However, a very clear enrichment is found as one adds nominal amounts of methanol to an ethanol feedstock. Yields of up to 97% semiconducting SWCNT are obtained. These changes are attributed to two known etchant processes. In the first, metal SWCNT are preferentially etched. In the second, we reveal etchants also preferentially etch small diameter tubes because they are more reactive. The etchants are confirmed to have a dual role, to preferentially etch metallic tubes and narrow diameter tubes (both metallic and semiconducting) which results in a narrowing of the SWCNT diameter distribution.

This article presents an overview of the research highlights in graphene synthesis by CVD. The growth mechanisms over transition metals and alloys (with emphasis on Cu and Cu alloys) are discussed, including new developments and experiments in transfer‐free graphene growth on dielectric materials. The focus is on the role of the various synthesis parameters, including the thermodynamic aspects of the chemical process, and the physical, chemical, and morphological properties of the substrate catalyst. The relationships between these parameters, and the properties of the as‐grown graphene are discussed. Some important relationships are reviewed and used to influence the fundamental parameters of, and methods for, the synthesis of high quality graphene.

the great benefits of using 2-D materials in the tunnel field-effect transistor (TFET), which is considered a promising candidate for the beyond-CMOS technology. The on-state current of TFET can be enhanced by engineering the band alignment of different 2D-2D or 2D-3D heterostructures. Here we present the internal photoemission spectroscopy (IPE) approach to determine the band alignments of various 2-D materials, in particular SnSe 2 and WSe 2 , which have been proposed for new TFET designs. The metal-oxide-2-D semiconductor test structures are fabricated and characterized by IPE, where the band offsets from the 2-D semiconductor to the oxide conduction band minimum are determined by the threshold of the cube root of IPE yields as a function of photon energy. In particular, we find that SnSe 2 has a larger electron affinity than most semiconductors and can be combined with other semiconductors to form near broken-gap heterojunctions with low barrier heights which can produce a higher on-state current. The details of data analysis of IPE and the results from Raman spectroscopy and spectroscopic ellipsometry measurements will also be presented and discussed.

Tin Diselenide (SnSe 2) is a two-dimensional layered crystal commonly found in octahedral coordination (1T phase). It has been reported to have a high electron affinity of around 5.1 eV and a bandgap of 1 eV [1-2], which can form staggered band alignment with tungsten diselenide (WSe 2) in Thin-TFETs [3]. However, its lack of gate modulation remains a mystery [4]. In this work, we investigate the Fermi level tunability of SnSe 2 by counter doping using a polymer electrolyte, PEO:CsClO 4. This counter doping technique increases the on/off ratio of SnSe 2 field effect transistor (FET) from 2 times to 50 times, a record high value. Meanwhile, a device model of SnSe 2 FET with ion doping and subgap density of states (DOS) has been proposed to fit the experimental data. The extracted effective number of acceptor-like subgap states is as high as 4.16×10 19 cm −3 (in comparison with near 5 × 10 17 cm −3 extracted for amorphous thin-film transistors [5]). This can explain the weak Fermi level tunability of SnSe 2 and direct future material development towards TFETs. Device fabrication: SnSe 2 (from 2D Semiconductors) flakes were exfoliated by scotch tape onto a 285 nm SiO 2 / p-type Si substrate. The presence of SnSe 2 was confirmed by Raman spectroscopy and the flake thickness is 5 nm determined by atomic force microscopy (AFM). Contacts (5 nm Ti/ 100 nm Au) were patterned by e-beam lithography (EBL). Before and after drop-casting PEO:CsClO 4 , DC measurements were performed by a Keithley 4200-SCS parameter analyzer. A customized field probe with a flat metal plate was used to bias the electrolyte. The flat probe was placed above the PEO:CsClO 4 surface, leaving an air gap of several micrometers. Because of the air gap, a large field probe voltage of V F P = −50 V was required to move the negative ions (ClO − 4) closer to SnSe 2 , counter-doping the n + SnSe 2 channel. The device schematic structure and the optical image of the device are shown in Fig.1a and Fig.1b. Results and discussion: SnSe 2 /Ti/Au contact resistance is less than 3 kΩ • µm by four probe measurement (Fig.1c). Figure 1d shows the SnSe 2 FET's transfer characteristics when sweeping the back gate voltage (V BG) before and after applying PEO:CsClO 4. Without the electrolyte, the on/off ratio is around 2 times when V BG is swept from −30 V to 30 V. This low on/off ratio is attributed to a high unintentional n-type doping level in SnSe 2 , which pushes its Fermi level into the conduction band where the DOS is high. To pull the Fermi level near/below the conduction band edge for improving tunability, p-type counter doping is implemented by electrostatically driving negative ions (ClO − 4) to the surface of n + SnSe 2. With electrolyte and V F P = −50 V , Figure 1d shows that the overall current density is lowered, and more importantly, the on/off ratio is increased to 50 times. Even without applying V F P , the electrolyte partially neutralizes charge in the channel due to a finite V DS applied (1 V). Therefore, as shown in Fig.1d, the on/off ratio increases from 2 to 10 times with electrolyte at V F P = 0. However, at a field probe voltage of 0 V, ions tend to be randomly distributed in electrolyte and move under the influence of V DS and V BG. The I D-V DS curves with and without electrolyte are shown in Fig.2a-b. In light of the low on/off ratio, we hypothesized that further turning off the device is impeded by a high subgap DOS. To verify the hypothesis, we introduce an empirical exponential subgap DOS [5] (Fig.2c). Under the long gradual channel approximation, the 1D Poisson equation is used to calculate the free carrier concentration in the channel (electrons in conduction band; and electrons in the subgap states are considered to be localized), which in turn is used to calculate the drain current. The device structures used in simulation are shown in Fig.3a, and the ClO − 4 ions near the SnSe 2 channel are modeled by a sheet of fixed negative charges located at 1 nm above the SnSe 2 surface [6]. Model fitting of the experimental data renders a donor concentration of 2 × 10 19 cm −3 in SnSe 2 , a fixed negative charge density of 2 × 10 13 cm −2 in the electrolyte, and the parameters of the acceptor-like subgap DOS are shown in Fig.2c. The effective number of subgap states is estimated to be as high as 4.2×10 19 cm −3 (N T A × kT). The band diagrams in Fig.3c illustrate how ion counter doping acts like a highly effective back gate, and how band bending in SnSe 2 changes when V BG is changed from −30 V to 30 V. Figure 3d shows that if a sufficiently high back-gate voltage can be applied, the SnSe 2 FET can be turned off according to our model. Since subgap states induce undesired tunneling in the subthreshold region of a TFET, it is necessary to eliminate them to ensure proper operation of TFETs.

This work focuses on understanding the electronic properties of materials to enhance the performance of Tunnel Field Effect Transistor (TFET) through Density Functional Theory (DFT) simulations. Material selection prefers a p-type material with in-plane high density of state (DOS) (and low out-of-plane effective mass, m*, where defined for many layer systems), and high valence band maxima (VBM) energy stacked with an n-type material with low conduction band minimum (CBM) energy (large electron affinity (EA)) that creates a broken or nearly broken band alignment and has low lattice mismatch. SnSe2 is well-suited for an n-type 2D material due to high EA, while WSe2, Black phosphorous (BP) and SnSe are explored for p-type materials. Bilayers consisting of monolayers of WSe2 and SnSe2 show a staggered but nearly broken band alignment (gap of 24 meV) and a high valence band DOS for WSe2. BP-SnSe2 shows a broken band alignment and benefits from a low lattice mismatch. SnSe-SnSe2 shows the...

The mechanical behaviour of a prototype touch panel display which consists of two layers of CVD graphene embedded into PET films is investigated in tension and under contact-stress dynamic loading. In both cases, laser Raman spectroscopy was employed to assess the stress transfer efficiency of the embedded graphene layers. The tensile behaviour was found to be governed by the "island-like" microstructure of the CVD graphene and the stress transfer efficiency was dependent on the size of graphene "islands" but also on the yielding behaviour of PET at relatively high strains. Finally, the fatigue tests, which simulate real operation conditions, showed that the maximum temperature gradient developed at the point of "finger" contact after 80000 cycles does not exceed the glass transition temperature of the PET matrix. The effect of these results on future product development and the design of new graphene-based displays is discussed.

The deformation of monolayer graphene, produced by chemical vapor deposition (CVD), on a polyester film substrate has been investigated through the use of Raman spectroscopy. It has been found that the microstructure of the CVD graphene consists of a hexagonal array of islands of flat monolayer graphene separated by wrinkled material. During deformation, it was found that the rate of shift of the Raman 2D band wavenumber per unit strain was less than 25% of that of flat flakes of mechanically exfoliated graphene, whereas the rate of band broadening per unit strain was about 75% of that of the exfoliated material. This unusual deformation behavior has been modeled in terms of mechanically isolated graphene islands separated by the graphene wrinkles, with the strain distribution in each graphene island determined using shear lag analysis. The effect of the size and position of the Raman laser beam spot has also been incorporated in the model. The predictions fit well with the behavior...

Gold is widely used as the substrate material in many graphene devices, due to its superior optoelectronic properties and chemical stability. However, there has been little experimental investigation on the optical contrast of graphene films on Au substrates. Here we report accurate measurement of the optical contrast spectra of few-layer graphene flakes on bulk Au. We used a high-resolution optical microscopy with a 100x magnification objective, accurately determining the thickness of flakes as small as one micrometer in lateral size, which are highly desired in many applications. The results are in excellent agreement with theoretical calculations and confirmed by Raman and AFM measurements. Furthermore, we demonstrate that the optical contrast spectroscopy is sensitive enough to detect the adsorption of a sub-monolayer airborne hydrocarbon molecules, which can reveal whether graphene is con-taminated and opens the opportunity to develop miniaturized and ultrasensitive molecular s...

Perturbations of the two dimensional carbon lattice of graphene, such as grain boundaries, have significant influence on the charge transport and mechanical properties of this material. Scanning tunneling microscopy measurements presented here show that localized states near the Dirac point dominate the local density of states of grain boundaries in graphene grown by chemical vapor deposition. Such low energy states are not reproduced by theoretical models which treat the grain boundaries as periodic dislocation-cores composed of pentagonal-heptagonal carbon rings. Using ab initio calculations, we have extended this model to include disorder, by introducing vacancies into a grain boundary consisting of periodic dislocation-cores. Within the framework of this model we were able to reproduce the measured density of states features. We present evidence that grain boundaries in graphene grown on copper incorporate a significant amount of disorder in the form of two-coordinated carbon atoms. I. Introduction Graphene prepared by chemical vapor deposition (CVD) on metal surfaces, especially copper [1], is

The influence of mixed catalysts for the high yield production of carbon nanotubes (CNTs) has been studied systematically. Based on extensive experimental data a ``Catalyst Volume to Surface Area'' (CVSA) model was developed to understand the influence of the process parameters on the yield and CNT diameter distribution [1]. In our study, we present a refined version of the CVSA model developed by combining experiments and simulations. We discuss our current understanding of the growth mechanism and how the model might be used to increase CNT yields by ...

Na 4 Mn 9 O 18 was recognized as the most interesting material for sodium ion batteries due to its low cost, high specific capacity and good cycle performance. The excellent electrochemical performance of Na 4 Mn 9 O 18 nanostructures was shown in literature. In this work, Na 4 Mn 9 O 18 nanowires were synthesized by hydrothermal reactions of Mn 2 O 3 powder and NaOH solution at the temperatures of 185-205 o C for 48-96 hours. The investigation of composition and structure of the synthesized products via scanning electron microscopy and X-ray diffraction analyses showed that major intermediate products at the low and high temperatures were Mn 3 O 4 and birnessite Na 0.55 Mn 2 O 4 1.5H 2 O, respectively. The synthesized Na 4 Mn 9 O 18 nanowires showed a good electrochemical performance with discharge capacities of over 90 mAhg-1 , and Coulombic efficiencies of more than 91 % at a rate of 0.2C during 30 cycles of charge/discharge.

Direct growth of graphene integrated into electronic devices is highly desirable but difficult due to the nominal ~1000 °C chemical vapor deposition (CVD) temperature, which can seriously deteriorate the substrates. Here we report a great reduction of graphene CVD temperature, down to 50 °C on sapphire and 100 °C on polycarbonate, by using dilute methane as the source and molten gallium (Ga) as catalysts. The very low temperature graphene synthesis is made possible by carbon attachment to the island edges of pre-existing graphene nuclei islands, and causes no damages to the substrates. A key benefit of using molten Ga catalyst is the enhanced methane absorption in Ga at lower temperatures; this leads to a surprisingly low apparent reaction barrier of ~0.16 eV below 300 °C. The faster growth kinetics due to a low reaction barrier and a demonstrated low-temperature graphene nuclei transfer protocol can facilitate practical direct graphene synthesis on many kinds of substrates down to ...

New designs for vertical 2D-materials-based TFETs are proposed in this paper adopting asymmetric layer numbers for the top and bottom layer with undoped source/drain using Black Phosphorus as an example. The results show that abrupt turn-on and Ion/Ioff > 105 can be sustained when the channel length is down to sub-5 nm. The results are benchmarked against other TFETs based on promising 2D materials homo-/hetero-structures, meanwhile, the limitations, as well as guidelines, are presented.

Two dimensional materials such as Transition Metal Dichalcogenides (TMDC) and their bi-layer/trilayer heterostructures have become the focus of intense research and investigation in recent years due to their promising applications in electronics and optoelectronics. In this work, we have explored device level performance of trilayer TMDC heterostructure (MoS2/MX2/MoS2; M=Mo or, W and X=S or, Se) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) in the quantum ballistic regime. Our simulation shows that device 'on' current can be improved by inserting a WS2 monolayer between two MoS2 monolayers. Application of biaxial tensile strain reveals a reduction in drain current which can be attributed to the lowering of carrier effective mass with increased tensile strain. In addition, it is found that gate underlap geometry improves electrostatic device performance by improving sub-threshold swing. However, increase in channel resistance reduces drain current. Besides exploring the prospect of these materials in device performance, novel trilayer TMDC heterostructure double gate Field Effect Transistors (FETs) are proposed for sensing Nano biomolecules as well as for pH sensing. Bottom gate operation ensures these FETs operating beyond Nernst limit of 59 mV/pH. Simulation results found in this work reveal that scaling of bottom gate oxide results in better sensitivity while top oxide scaling exhibits an opposite trend. It is also found that, for identical operating conditions, proposed TMDC FET pH sensors show super-Nernst sensitivity indicating these materials as potential candidates in implementing such sensor. Besides pH sensing, all these materials show high sensitivity in the sub-threshold region as a channel material in nanobiosensor while MoS2/WS2/MoS2 FET shows the least sensitivity among them.

Gold nanorods (AuNRs) are excellent photothermal agents to enable a variety of laser stimulated functional polymers. One key issue is to maximize the photothermal conversion efficiency of AuNRs. In this study, the light responsive AuNR/shape memory polymer (SMP) nanocomposites with inclusion of AuNRs of varied aspect ratios were prepared, characterized, and their laser irradiation induced bending behavior was investigated. The critical role of the on-resonance irradiation condition-a close match of the longitudinal plasmon resonance of the AuNR with the wavelength of the incident laser-has been established. It allows for maximizing the photothermal conversion efficiency of AuNRs to result in the rapid and large deformation of the AuNR/SMP nanocomposites. For the AuNR/SMP nanocomposite films prepared under similar processing conditions, the close-to-resonance irradiation at a 1.27 W/cm 2 was able to induce a bending rate of 27°/s and maximum bending angle of 90.4°. In contrast, the off-resonance irradiation at a 1.89 W/cm 2 resulted in negligible response.

Destabilization of LiBH 4 by addition of metal hydrides or borohydrides is a powerful strategy to develop new promising hydrogen storage systems. In this study, we compare the destabilization behavior of the LiBH 4 by addition of MH 2 (M ¼ La, Ce). A notable improvement in the hydrogen desorption temperature, the rate and the weight percentage of hydrogen released is observed for LiBH 4 eMH 2 with respect to LiBH 4. Formation of LaB 6 and CeB 6 after dehydriding of the composites is proved by PXRD. Remarkable hydrogen storage reversibility of LiBH 4 eMH 2 composites is confirmed under moderate conditions: 400 C and 6.0 MPa of hydrogen pressure for 4 h without catalyst. The LiBH 4 eLaH 2 composite exhibits improved hydrogen desorption performance compared with LiBH 4 eCeH 2 composite, but the hydrogen storage reversibility is inferior. Notably, the LiBH 4 eCeH 2 nanocomposite produced by in situ formation of CeH 2 from Ce(BH 4) 3 eLiH displays excellent hydrogen storage properties. The addition of ZrCl 4 as a catalyst improves dehydriding kinetics. The mechanism underlying the enhancement in the LiBH 4 eMH 2 composites is also discussed. Our study is the first work about reversible hydrogen storage in LiBH 4 eLaH 2 .

A novel route for the synthesis of large area graphene by an indigenously built electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD) setup has been reported in this work. A unique 2.45 GHz permanent magnet type ECR PECVD system has been designed and developed for the growth of various nano-structures and films. The apparatus has a unique advantage to synthesize large area graphene at much lower additional substrate heating than heat supplied by an external oven in conventional thermal CVD method. A major amount of heat is supplied here by ECR plasma. Polycrystalline copper foil is used here as a catalytic substrate which is pre annealed inside resonant hydrogen plasma prior to its exposure under precursor gaseous plasma inside the ECR PECVD reactor. Methane is used as carbon precursor along with hydrogen as carrier gas. Argon gas is used for the rapid cooling of the substrate maintaining suitable thermodynamic condition favorable for graphene synthesi...

Research is what I'm doing when I don't know what I'm doing" Wernher von Braun Contents i CONTENTS Agradecimientos v Resumen en castellano vii Preface xxi List of figures and tables xxv I. INTRODUCTION Fabrication and characterization of macroscopic graphene layers on metallic substrates iv 9. Fabrication and characterization of a graphene transistor 9.

Maintaining the rapid development of information technology by scaling down of MOSFET faces two serious challenges. First, the gate field loses control of the channel as it continuously decreases. Second, the fundamental thermionic limit restricts the reduction in supply voltage. Thus, further scaling down necessitates alternative device structures and different switching mechanisms. Here, we report impactionization transistors (IITs) based on nanoscale (~30 nm) vertical graphene/black phosphorus (BP)/indium selenide (InSe) heterostructures. By facilitating the carrier multiplication of the ballistic impact-ionization process as the internal gain mechanism in sub-mean-free-path (sub-MFP) channels, the IITs exhibit a low average subthreshold swing (SS <1 mV/dec) over five current levels. High stability (>10,000 cycles) and small hysteresis (<1%) switching properties are also obtained. The experimental demonstration of such transistor combining steep SS, high ON-state current density,

An efficient modified arc plasma method, where a focusing electric field is superimposed on the arc electric field, is optimized for the bulk generation of highly pure multi-walled carbon nanotubes (MWNTs). Raman spectroscopy and thermogravimetric measurements have been used to optimize the process. It was found that, at the optimized focusing field configuration, this process can utilize about 85% of the consumed anode material as compared to about 35% in the conventional arc plasma method. The sample prepared at the optimized conditions exhibited negligible D band intensity along with a reduced line width (14cm-1) of the G band in the Raman spectrum. The oxidation temperature of this