Papers by Cristiano Albonetti
Materials, Jan 25, 2024
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Journal of Solid State Chemistry, Nov 1, 2004
The synthesis method for obtaining sub-micrometric structures of rare earth manganese-based mixed... more The synthesis method for obtaining sub-micrometric structures of rare earth manganese-based mixed oxide compounds is described. Pore wetting of porous polycarbonate templates with the liquid precursor was followed by a two-stage thermal treatment to obtain single phase La 0.325 Pr 0.300 Ca 0.375 MnO 3 hollow and solid structures, with external diameter determined by the sacrificial template pore size. The first thermal stage, a microwave assisted denitration process, determines the shape of the structures. The second treatment, performed at 1073 K, allows to obtain the crystallographic structure of the compound. A variety of techniques (scanning and transmission electron microscopy, scanning probe microscopy) allowed to fully characterize the microstructure and morphology of these self-standing manganite nanostructures. For 1 mm pore size templates we obtained tubes, with external diameter around 800 nm and wall thickness around 150 nm; densely packed nanoparticles sized 20-50 nm are the building blocks of the walls. For pore size below 0.1 mm, solid nanowires were obtained, the size of constituent crystallites being around 10 nm. Overall obtained material exhibits ferromagnetic ordering below 200 K.
Microscopie a scansione di forza di nanostrutture molecolari: morfologia, proprietà, nanofabbricazione
Electrochemical fabrication of cobalt and nickel tips for scanning tunneling microscopy
Journal of vacuum science & technology, Nov 1, 2005
Scanning tunneling microscopy (STM) is a powerful technique to map the distribution of the densit... more Scanning tunneling microscopy (STM) is a powerful technique to map the distribution of the density of electronics states of conductive surfaces with angstrom (Å) resolution. STM requires sharp conductive tips in order to operate in ambient conditions, which are stable with respect to oxidation. We describe a procedure to obtain high quality tips from wires of different materials such as Co and Ni. We discuss in detail the electrochemical process employed in the fabrication of the tips and assess the shape of the tips by optical microscopy and scanning electron microscopy (SEM). These tips yield high-resolution STM images even after a few weeks of exposure to air.
Al<sup>+</sup> Ion Implanted On-Axis <0001> Semi-Insulating 4H-SiC
Materials Science Forum, Jun 1, 2015
P-type 4H-SiC layers have been obtained by different 400°C Al+ ion implantation processes of semi... more P-type 4H-SiC layers have been obtained by different 400°C Al+ ion implantation processes of semi insulating 4H-SiC wafers and identical 1950°C/5 min post implantation annealing. Implanted Al+ concentration have been 4.7×1018, 9.3×1018, and 4.7×1019 cm-3, thickness of the implanted layer about 630 nm. Electrical characterizations have been performed in the temperature range 100 – 580 K. With decreasing temperature, the onset of a hole conduction through an impurity band has been seen for all the specimens.
Journal of materials chemistry. A, Materials for energy and sustainability, 2023
A four-step methodology for the valorization of polysaccharide-based materials into bifunctional ... more A four-step methodology for the valorization of polysaccharide-based materials into bifunctional heterogeneous catalysts, active in the conversion of CO 2 and epoxides into cyclic carbonates, is presented. The synthesis protocol consists of (i) pyrolysis of the starting material to produce biochar; (ii) oxidation to increase the number of-OH and-COOH functionalities; (iii) anchoring of (3-aminopropyl) triethoxysilane (APTES) on the surface of the oxidized biochar; (iv) quaternarization of the amine groups into alkylammonium iodide salts. The versatility of the method was demonstrated by applying the same protocol to six different polysaccharidic materials and wastes: six catalysts with no appreciable differences in terms of chemical composition and catalytic activity were obtained. The bifunctionality given by-OH and ammonium iodide groups was confirmed by several analyses performed on the catalysts. An extensive characterization (elemental analysis composition, FTIR, Raman, SEM, XPS and porosimetry) was done on all the functionalized biochars for every synthetic step. The catalysts were widely investigated in their activity for the conversion of CO 2 and epoxides into cyclic carbonates, demonstrating to be effective under mild conditions (3 bar of CO 2 ; 70°C; 7 h). TONs and TOFs were calculated for each catalyst and condition. Yields up to 96%, with >99% selectivity, were obtained for terminal epoxides. The recyclability of the bifunctional heterogeneous catalysts was also confirmed over five cycles.
Native Silicon Oxide Properties Determined by Doping
The chemical-physical properties of native oxide layers, spontaneously forming on crystalline Si ... more The chemical-physical properties of native oxide layers, spontaneously forming on crystalline Si wafers, can be strictly correlated to the dopant type and the doping level. In particular, our investigations have focused on oxide layers forming upon air exposure in a clean room after Si wafer production, for doping concentration levels from ≈ 10 13 to ≈ 10 19 cm-3. In order to determine these correlations, we have studied the surface, the bulk, and its interface with Si. The surface is investigated with contact angle, thermal desorption and atomic force microscopy obtaining information on the surface energy, cleanliness, and morphology, respectively. The thickness is measured with Ellipsometry and the chemical composition with X-ray Photoemission Spectroscopy. The electrostatic charges within the oxide layer and at the interface with Si are studied with Kelvin Probe Microscopy. We find that some properties show an abrupt change, i.e. thickness, while others present a maximum, i.e. silanol concentration and Si intermediate-oxidation states, at a critical doping concentration of ≈ 2.1•10 15 cm-3. Additionally, two electrostatic contributions originate from the silanols present on the surface and the net charge distributed within the layer. Lastly, the surface roughness also depends on the doping concentration, showing a minimum at the same critical doping concentration. These findings can be fully reproduced for oxide layers re-grown in a clean room after a chemical etching of the native ones.
Journal of Materials Chemistry A
A four-step method was applied to biomass and waste polysaccharides, obtaining char-based bifunct... more A four-step method was applied to biomass and waste polysaccharides, obtaining char-based bifunctional catalysts active in CO2 conversion into cyclic carbonates.
Substrate roughness influence on the order of nanografted Self-Assembled Monolayers
Chemical Physics Letters
Adjacent patches of alkanethiol molecules whose chain lengths range from 11 to 15 carbon atoms ar... more Adjacent patches of alkanethiol molecules whose chain lengths range from 11 to 15 carbon atoms are fabricated by nanografting within a Self-Assembled Monolayer matrix. Atomic Force Microscopy and Electrostatic Force Microscopy are employed to investigate their structural and electronic properties, highlighting the key role of the substrate roughness. In particular, the topographic phase signal allows to establish an odd–even dependence of the local stiffness versus the alkyl chain length, while the electrostatic force signal provides evidence that the conformational order versus the alkyl chain length follows an asymmetric parabolic trend induced by the substrate roughness.
Materials Science Forum
Encapsulating SiC with a carbon layer (C-cap) is a widely used technique to avoid step bunching d... more Encapsulating SiC with a carbon layer (C-cap) is a widely used technique to avoid step bunching during post implantation annealing. In this work we propose a mechanism that explains the roughening that the surface unavoidably undergoes during annealing under the C-cap. We investigated the reactions occurring at the interface between 4H-SiC and the C-cap by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy carried out at different stages of the sample processing: just after annealing, after C-cap removal in dry Oxygen, and after cleaning in buffered oxide etch solution. Our observations show that, even though the C-cap roughens for increasing annealing temperature and time, it is not visibly damaged even after 1950 °C 30 min annealing. After the C-cap removal the 4H-SiC surface was covered by a network of clusters that are eventually removed by buffered oxide etch solution. This occurrence suggests that, during the post-implantation annea...
CCDC 833431: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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Hydrophilic self-assembly monolayers for pentacene-based thin-film transistors
The analysis of the formation of ultra-thin organic films is a very important issue. In fact, it ... more The analysis of the formation of ultra-thin organic films is a very important issue. In fact, it is known that the properties of organic field effect transistors are strongly affected by the early growth stages. For instance, in the case of sexithiophene deposited on thermal SiOx, the presence of domains made of molecules with the backbone parallel to the substrate surface has been indirectly evidenced by photoluminescence spectroscopy and directly imaged by Ultrasonic Force Microscopy. On the contrary, photoluminescence spectroscopy have failed to observe sexithiophene deposited on native SiOx. In this paper, we show how Scanning Probe Microscopy techniques combined with post-annealing process are able to identify a flat-lying molecular layer on the native SiOx. By using Lateral Force Microscopy and Atomic Force Microscopy in Intermittent Contact we investigate its mechanical properties and, by using Ultrasonic Force Microscopy, we directly identify the structure of flat-lying mole...
Probing antimicrobial activity of star-like polymers by AFM based experiments
In recent decades, Organic Thin Film Transistors (OTFTs) have attracted lots of interest due to t... more In recent decades, Organic Thin Film Transistors (OTFTs) have attracted lots of interest due to their low cost, large area and flexible properties which have brought them to be considered the building blocks of the future organic electronics. Experimentally, devices based on the same organic material deposited in different ways, i.e. by varying the deposition rate of the molecules, show different electrical performance. As predicted theoretically, this is due to the speed and rate by which charge carriers can be transported by hopping in organic thin films, transport that depends on the molecular arrangement of the molecules. This strongly suggests a correlation between the morphology of the organic semiconductor and the performance of the OTFT and hence motivated us to carry out an in-situ real time SPM study of organic semiconductor growth as an almost unprecedent experiment with the aim to fully describe the morphological evolution of the ultra-thin film and find the relevant mor...
Revised electrochemical etching system for a reproducible fabrication of ultra-sharp tungsten tips
Journal of Applied Electrochemistry, 2021
This article proposes an improved version of the drop-off electrochemical etching technique, deve... more This article proposes an improved version of the drop-off electrochemical etching technique, developed for a reproducible production of ultra-sharp metal tips. Firstly, a comprehensive survey of other mechanical and physicochemical procedures is made in order to individuate three issues commonly neglected: (i) the influence of external perturbations, (ii) the positions of the electrode (a W wire) and counter-electrode (a Pt ring) and (iii) the counter-electrode shape. These issues need to be carefully fixed, in an enclosed and geometrically well-defined configuration, to better control the opening angle, radius of curvature and aspect ratio. The quality of the tips produced is evaluated comparing their performances, in imaging a reference sample with scanning tunnelling microscopy, to those of commercial tips. Using established procedures and data reported in the literature, an optimal set of the parameters can be identified obtaining high-quality tips with an opening angle < 10° and a radius of curvature ~ 30 nm. Furthermore, achieving a higher reproducibility allows us to investigate the electrochemical process monitoring the time dependence of the current from the etching parameters, such as the wire immersion, electrolyte concentration and applied bias voltage. Thus, the current versus time curves can be analysed in terms of linear scan voltammetry and electrochemical impedance spectroscopy, in order to investigate the phenomena occurring during the wire etching. In particular, at the beginning of the electrochemical process, the replacement of the native W oxide with a thicker layer of WO 3 (H 2 O) x oxide is observed, in agreement with previous observations. Graphic abstract
The Journal of Physical Chemistry C, 2021
The inorganic/molecular spinterface is an ideal platform for generating extraordinary spin effect... more The inorganic/molecular spinterface is an ideal platform for generating extraordinary spin effects. Understanding and controlling these spin-related effects is mandatory for the exploitation of such interfaces in devices. For this purpose, we have investigated the adsorption of α-sexithiophene (α-6T) on La 0.7 Sr 0.3 MnO 3 (LSMO), as one of the prototypical material combinations used in organic spintronic devices. Atomic force microscopy, confocal photoluminescence, Xray photoelectron spectroscopy, and metastable de-excitation spectroscopy unraveled the structure and electronic configuration of 6T for various surface coverages. This data set allowed the determination of characteristic features of occupied states, the band diagram and the work function. Finally, density functional theory enabled us to establish that the spin polarization in 6T molecular orbitals critically depends on the termination layer of LSMO. We believe that this research provides important hints for a comprehensive understanding of spinterface effects in general and provides key suggestions for further engineering of LSMO/6T-based devices. INTRODUCTION: Hybridization at the interface between molecular entities and ferromagnetic metals leads to drastic changes of the properties of both layers [1,2]. Notably, an increase of spin polarization of states around the Fermi level [2], modulation of the magnetic anisotropy [3] and spin reorientation transitions were observed in ferromagnetic layers as well as the appearance of spin polarized states in the molecular material [5]. Such new hybrid interfaces with unexpected spin functionality, named after the seminal paper by Sanvito as "spinterfaces" [6], act as a key element at the molecular level for engineering the properties and the performance of spin-devices. Among the plethora of spinterfaces, those including half-metallic ferromagnetic oxides such as La 0.7 Sr 0.3 MnO 3 (LSMO) are of special interest. LSMO has been coupled to a variety of organic molecules and successfully used in spintronic devices [7,8], even showing the inversion of the sign of the polarization upon the deposition of an organic molecule [9]. Nonetheless, the variability of the composition of the termination layer of LSMO [10-12] hindered a reliable investigation of its interface with organic molecules. In this paper we focus on the coupling between a π-conjugated oligothiophene, 6T (sexithiophene), and LSMO; one of the first hybrid interfaces used in spin injection devices [13]. 6T is a rodlike model organic molecule [14] which contains six thiophene rings linked together; it can be easily sublimated in ultrahigh vacuum (UHV), a prerequisite for the control and reproducibility of interfacial states, and it is also known to form ordered thin layers on solid surfaces. Here, the growth process of 6T on
4H‐SiC surface morphology after Al ion implantation and annealing with C‐cap
Journal of Microscopy, 2020
SummaryThe root mean square (rms) surface roughness extracted from atomic force microscopy is wid... more SummaryThe root mean square (rms) surface roughness extracted from atomic force microscopy is widely employed to complement the characterisation of ion implantation processes in 4H‐SiC. It is known that the protection of a carbon film eliminates or mitigates roughening of the SiC surface during postimplantation annealing. This study, based on a rich original data collection of Al+ ion implanted 4H‐SiC samples, allows for a quantitative description of the surface morphology as a function of the annealing temperature and time and of the Al implanted concentration. With increasing thermal budget, the evolution from flat, to blurred with ripples, granular, and finally jagged surface, results in a monotonous increase in the root mean square roughness. Additional information is given by the trends of the roughness exponent and of the correlation length, extracted from the height‐height correlation function, which account for the surface evolution below 1700°C and for the effect of the Al ...
Factories of the Future, 2019
This chapter reports the progress on the fabrication of thin film CIGSbased solar cells by means ... more This chapter reports the progress on the fabrication of thin film CIGSbased solar cells by means of the low temperature pulsed electron deposition technique. The innovative and multidisciplinary approach aims to solve the main issues preventing a possible industrial scale up of the process, i.e. the need of a fast, reliable and automated process, suitable for both static and dynamic deposition of CIGS solar cells on flexible substrates. The final goal is to open new opportunities, particularly in the emerging field of the building-integrated photovoltaic.
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Papers by Cristiano Albonetti