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| 2. |
- Kakanakova-Gueorguieva, Anelia, et al.
(författare)
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Material proposal for 2D indium oxide
- 2021
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 548
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Tidskriftsartikel (refereegranskat)abstract
- Realization of semiconductor materials at the two-dimensional (2D) limit can elicit exceptional and diversified performance exercising transformative influence on modern technology. We report experimental evidence for the formation of conceptually new 2D indium oxide (InO) and its material characteristics. The formation of 2D InO was harvested through targeted intercalation of indium (In) atoms and deposition kinetics at graphene/SiC interface using a robust metal organic chemical vapor deposition (MOCVD) process. A distinct structural configuration of two sub-layers of In atoms in "atop" positions was imaged by scanning transmission electron microscopy (STEM). The bonding of oxygen atoms to indium atoms was indicated using electron energy loss spectroscopy (EELS). A wide bandgap energy measuring a value of 4.1 eV was estimated by conductive atomic force microscopy measurements (C-AFM) for the 2D InO.
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| 3. |
- Kakanakova-Gueorguieva, Anelia, et al.
(författare)
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MOCVD of AlN on epitaxial graphene at extreme temperatures
- 2021
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Ingår i: CrystEngComm. - : ROYAL SOC CHEMISTRY. - 1466-8033. ; 23:2, s. 385-390
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Tidskriftsartikel (refereegranskat)abstract
- The initial stages of metal organic chemical vapor deposition (MOCVD) of AlN on epitaxial graphene at temperatures in excess of 1200 degrees C have been rationalized. The use of epitaxial graphene, in conjunction with high deposition temperatures, can deliver on the realization of nanometer thin AlN whose material quality is characterized by the appearance of luminescent centers with narrow spectral emission at room temperature. It has been elaborated, based on our previous comprehensive ab initio molecular dynamics simulations, that the impact of graphene on AlN growth consists in the way it promotes dissociation of the trimethylaluminum, (CH3)(3)Al, precursor with subsequent formation of Al adatoms during the initial stages of the deposition process. The high deposition temperatures ensure adequate surface diffusion of the Al adatoms which is an essential factor in material quality enhancement. The role of graphene in intervening with the dissociation of another precursor, trimethylgallium, (CH3)(3)Ga, has accordingly been speculated by presenting a case of propagation of ultrathin GaN of semiconductor quality. A lower deposition temperature of 1100 degrees C in this case has better preserved the structural integrity of epitaxial graphene. Breakage and decomposition of the graphene layers has been deduced in the case of AlN deposition at temperatures in excess of 1200 degrees C.
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| 4. |
- Kakanakova-Gueorguieva, Anelia, et al.
(författare)
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Nanoscale phenomena ruling deposition and intercalation of AlN at the graphene/SiC interface
- 2020
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Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372. ; 12:37, s. 19470-19476
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Tidskriftsartikel (refereegranskat)abstract
- The possibility for kinetic stabilization of prospective 2D AlN was explored by rationalizing metal organic chemical vapor deposition (MOCVD) processes of AlN on epitaxial graphene. From the wide range of temperatures which can be covered in the same MOCVD reactor, the deposition was performed at the selected temperatures of 700, 900, and 1240 degrees C. The characterization of the structures by atomic force microscopy, electron microscopy and Raman spectroscopy revealed a broad range of surface nucleation and intercalation phenomena. These phenomena included the abundant formation of nucleation sites on graphene, the fragmentation of the graphene layers which accelerated with the deposition temperature, the delivery of excess precursor-derived carbon adatoms to the surface, as well as intercalation of sub-layers of aluminum atoms at the graphene/SiC interface. The conceptual understanding of these nanoscale phenomena was supported by our previous comprehensiveab initiomolecular dynamics (AIMD) simulations of the surface reaction of trimethylaluminum, (CH3)(3)Al, precursor with graphene. A case of applying trimethylindium, (CH3)(3)In, precursor to epitaxial graphene was considered in a comparative way.
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| 5. |
- Kovacs, Andras, et al.
(författare)
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Graphoepitaxy of High-Quality GaN Layers on Graphene/6H-SiC
- 2015
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Ingår i: ADVANCED MATERIALS INTERFACES. - : Wiley: 12 months. - 2196-7350. ; 2:2
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Tidskriftsartikel (refereegranskat)abstract
- The implementation of graphene layers in gallium nitride (GaN) heterostructure growth can solve self-heating problems in nitride-based high-power electronic and light-emitting optoelectronic devices. In the present study, high-quality GaN layers are grown on patterned graphene layers and 6H-SiC by metalorganic chemical vapor deposition. A periodic pattern of graphene layers is fabricated on 6H-SiC by using polymethyl methacrylate deposition and electron beam lithography, followed by etching using an Ar/O-2 gas atmosphere. Prior to GaN growth, an AlN buffer layer and an Al0.2Ga0.8N transition layer are deposited. The atomic structures of the interfaces between the 6H-SiC and graphene, as well as between the graphene and AlN, are studied using scanning transmission electron microscopy. Phase separation of the Al0.2Ga0.8N transition layer into an AlN and GaN superlattice is observed. Above the continuous graphene layers, polycrystalline defective GaN is rapidly overgrown by better quality single-crystalline GaN from the etched regions. The lateral overgrowth of GaN results in the presence of a low density of dislocations (approximate to 10(9) cm(-2)) and inversion domains and the formation of a smooth GaN surface.
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| 6. |
- Lo Nigro, Raffaella, et al.
(författare)
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Nanotechnology for Electronic Materials and Devices
- 2022
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Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 12:19
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The historical scaling down of electronics devices is no longer the main goal of the International Roadmap for Devices and Systems [...]
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| 7. |
- Pecz, Bela, et al.
(författare)
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Indium Nitride at the 2D Limit
- 2021
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 33:1
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Tidskriftsartikel (refereegranskat)abstract
- The properties of 2D InN are predicted to substantially differ from the bulk crystal. The predicted appealing properties relate to strong in- and out-of-plane excitons, high electron mobility, efficient strain engineering of their electronic and optical properties, and strong application potential in gas sensing. Until now, the realization of 2D InN remained elusive. In this work, the formation of 2D InN and measurements of its bandgap are reported. Bilayer InN is formed between graphene and SiC by an intercalation process in metal-organic chemical vapor deposition (MOCVD). The thickness uniformity of the intercalated structure is investigated by conductive atomic force microscopy (C-AFM) and the structural properties by atomic resolution transmission electron microscopy (TEM). The coverage of the SiC surface is very high, above 90%, and a major part of the intercalated structure is represented by two sub-layers of indium (In) bonded to nitrogen (N). Scanning tunneling spectroscopy (STS) measurements give a bandgap value of 2 +/- 0.1 eV for the 2D InN. The stabilization of 2D InN with a pragmatic wide bandgap and high lateral uniformity of intercalation is demonstrated.
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| 8. |
- Pecz, Bela, et al.
(författare)
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On the Possibility of Realizing a 2D Structure of Si-N Bonds by Metal-Organic Chemical Vapor Deposition
- 2023
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Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 260:10
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Tidskriftsartikel (refereegranskat)abstract
- 2D SiN honeycomb monolayer structures predicted theoretically have been the focus of interest in materials science for a long time, most recently for their semiconducting and ferromagnetic properties. Herein, by investigating metal-organic chemical vapor deposition processes and direct heat treatment of epitaxial graphene in ammonia flow, the possibility of realizing a certain periodic 2D structure via Si-N bonds under epitaxial graphene on SiC (0001) is reported. The result is of interest because it is compatible with semiconductor material deposition technologies and future use in nanoscience and nanotechnology.
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| 9. |
- Schiliro, Emanuela, et al.
(författare)
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Seed-Layer-Free Atomic Layer Deposition of Highly Uniform Al2O3 Thin Films onto Monolayer Epitaxial Graphene on Silicon Carbide
- 2019
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Ingår i: Advanced Materials Interfaces. - : WILEY. - 2196-7350. ; 6:10
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Tidskriftsartikel (refereegranskat)abstract
- Atomic layer deposition (ALD) is the method of choice to obtain uniform insulating films on graphene for device applications. Owing to the lack of out-of-plane bonds in the sp(2) lattice of graphene, nucleation of ALD layers is typically promoted by functionalization treatments or predeposition of a seed layer, which, in turn, can adversely affect graphene electrical properties. Hence, ALD of dielectrics on graphene without prefunctionalization and seed layers would be highly desirable. In this work, uniform Al2O3 films are obtained by seed-layer-free thermal ALD at 250 degrees C on highly homogeneous monolayer (1L) epitaxial graphene (EG) (amp;gt;98% 1L coverage) grown on on-axis 4H-SiC(0001). The enhanced nucleation behavior on 1L graphene is not related to the SiC substrate, but it is peculiar of the EG/SiC interface. Ab initio calculations show an enhanced adsorption energy for water molecules on highly n-type doped 1L graphene, indicating the high doping of EG induced by the underlying buffer layer as the origin of the excellent Al2O3 nucleation. Nanoscale current mapping by conductive atomic force microscopy shows excellent insulating properties of the Al2O3 thin films on 1L EG, with a breakdown field amp;gt; 8 MV cm(-1). These results will have important impact in graphene device technology.
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| 10. |
- Sfuncia, Gianfranco, et al.
(författare)
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2D graphitic-like gallium nitride and other structural selectivity in confinement at the graphene/SiC interface
- 2023
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Ingår i: CrystEngComm. - : ROYAL SOC CHEMISTRY. - 1466-8033. ; 25:41, s. 5810-5817
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Tidskriftsartikel (refereegranskat)abstract
- Beyond the predictions routinely achievable by first-principles calculations and using metal-organic chemical vapor deposition (MOCVD), we report a GaN monolayer in a buckled geometry obtained in confinement at the graphene/SiC interface. Conductive atomic force microscopy (C-AFM) was used to investigate vertical current injection across the graphene/SiC interface and to establish the uniformity of the intercalated regions. Scanning transmission electron microscopy (S/TEM) was used for atomic resolution imaging and spectroscopy along the growth direction. The experimentally obtained value of the buckling parameter, 1.01 & PLUSMN; 0.11 & ANGS;, adds to the existing knowledge of buckled GaN monolayers, which is based solely on predictive first-principles calculations. Our study reveals a discontinuity in the anticipated stacking sequence attributed to a few-layer graphitic-like GaN structure. Instead, we identify an atomic order suggestive of ultrathin gallium oxide Ga2O3, whose formation is apparently mediated by dissociative adsorption of oxygen onto the GaN monolayer. An atomic resolution image of an intercalated structure at a graphene/SiC interface along the growth direction which is determined as a buckled GaN monolayer at the immediate interface with an underlying SiC substrate and ultrathin Ga2O3 on top.
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