Query: 6H-SiC

title: Microstructural evolution of helium irradiated 6H SiC subjected to different irradiation conditions and annealing temperatures: A multiple characterization study
abstract: The microstructural phenomena occurring in 6H SiC subjected to different irradiation conditions and annealing temperatures were investigated to assess the suitability of 6H SiC as a structural material for nuclear applications. To this aim, a single crystal of 6H SiC was subjected to He+ irradiation at 300 keV with different fluences and at temperatures ranging from 25 to 750 degC. Rutherford backscattering/channeling (RBS/C) X ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were combined to shed light on the microstructural changes induced by irradiation and subsequent annealing (750 to 1500 degC) At room temperature, amorphization starts to occur at a fluence of 2.5 x 1016 cm 2 (0.66 dpa) On the contrary, amorphization was prevented at high irradiation temperatures and fluences. Furthermore, a thin and highly strained region located around the maximum He concentration (Rp) formed. This region results from the accumulation of interstitial atoms which are driven toward the highly damaged region under the actions of a strain gradient and high temperature. Regardless of the fluence and irradiation temperature, the material stores elastic energy, which leads to the trapping of He in dissimilar defect geometries. For irradiation temperatures below 750 degC, helium was accumulated in bubbles which coarsened after annealing. On the other hand, for an irradiation temperature of 750 degC, helium was trapped in platelets (even for medium fluence) which evolved into a homogeneous dense array of cavities during annealing. DFT calculations show that the bubbles are under high pressure and contribute to developing the overall tensile strain in the single crystal 6H SiC.

title: Study on nanomechanical properties of 4H SiC and 6H SiC by molecular dynamics simulations
abstract: This article aimed to study the nanomechanical properties of silicon carbide under nanoindentation and nanoscratching by the molecular dynamics (MD) First, the MD models were established and experimentally verified. Then, the MD results were used to analyze the subsurface morphology and crystal defects occurring during the processes, which are comparatively difficult to study through experiments. For comparison, the C face and the Si face of 4H SiC and 6H SiC were selected for research. The results indicate that 4H SiC shows greater normal resistance than 6H SiC for both faces, and the C face may be easier to machine than the Si face for both 4H and 6H SiC. In addition, the hexagon amorphous patterns were found in the horizontal cross sections views after the indentation, which were deemed to make up of two mutually central symmetric triangles. The results show that these amorphous patterns may be caused by the slip systems of 4H SiC and 6H SiC, which are mainly take place on the (0001) basal plane and along the directions, depending on their special lattice structures. Through MD simulations, the formation mechanism of sub surface damage of SiC substrates is much clearer.

title: Growth of atomically thick transition metal sulfide filmson graphene/6H SiC(0001) by molecular beam epitaxy
abstract: We report the growth and characterization of atomically thick NbS2, TaS2, and FeS films on a 6H SiC(0001) substrate terminated with monolayer or bilayer epitaxial graphene. The crystal and electronic structures are studied by scanning tunneling microscopy and reflection high energy electron diffraction. The NbS2 monolayer is solely in the 2H structure, while the TaS2 monolayer contains both 1T and 2H structures. Charge density waves are observed in all phases. For the FeS films, the tetragonal structure coexists with the hexagonal one and no superconductivity is observed.

title: Study of the crystal and electronic structure of graphene films grown on 6H SiC (0001)
abstract: The structural, chemical, and electronic properties of epitaxial graphene films grown by thermal decomposition of the Si face of a semi insulating 6H SiC substrate in an argon environment are studied by Raman spectroscopy, atomic force microscopy, the low energy electron diffraction method, X ray photoelectron spectroscopy, angle resolved photoemission spectroscopy and X ray absorption spectroscopy at the carbon K edge. It is shown that the results of a systematic integrated study make it possible to optimize the growth parameters and develop a reliable technology for the growth of high quality single layer graphene films with a small fraction of bilayer graphene inclusions.

title: Hexagonal phase pure wide band gap e Ga2O3 films grown on 6H SiC substrates by metal organic chemical vapor deposition
abstract: In this paper, hexagonal structure phase pure wide band gap e Ga2O3 films were grown by metal organic chemical vapor deposition on 6H SiC substrates. The e Ga2O3 films with good crystal quality were verified by high resolution X ray diffraction. The out of plane epitaxial relationship between e Ga2O3 films and 6H SiC substrates is confirmed to be e Ga2O3 (0001)/6H SiC (0001) and the in plane epitaxial relationship is also confirmed to be e Ga2O3 112 0> /6H SiC 112 0> The SEM and AFM images show that the e Ga2O3 films are uniform and flat. The e Ga2O3 films are thermally stable up to approximately 800 degC and begin to transform into b phase Ga2O3 at 850 degC. Then, they are completely converted to b Ga2O3 films under 900 degC. The high quality e Ga2O3 films with hexagonal structure have potential application in the optoelectronic field.

title: Material removal mechanism of 6H SiC studied by nano scratching with Berkovich indenter
abstract: The aim of this paper was to analyze the deformation characteristics and material removal mechanism of mono crystal silicon carbide. The nano scratching tests were conducted on the surface of 6H SiC (0001) by using Berkovich nano indenter. In the presence of various characterization techniques, a variety of new achievements have been reached. Phase transformation behavior in the nano scratching process of mono crystal silicon carbide (6H SiC) is revealed by using the transmission electron microscope in this work. Amorphous phase and dislocation activities are found near the surface area under the bottom of the scratch which stands as the major cause triggering the plastic removal of this material, with no other forms of crystalline structure found, by which the plastic removal mechanism of mono crystal silicon carbide was well identified. With a crack free surface that had been processed, the chip broke away from the bulk in the form of plastic mode, but the subsurface was covered by cracks with their lengths many times longer than the machined depth. The results of laser Raman indicated that residual amorphous phase exits in the chips under the condition of the plastic removal of this material.

title: The role of interactions between abrasive particles and the substrate surface in chemical mechanical planarization of Si face 6H SiC
abstract: The interactions between abrasive particles and the wafer surface play a significant role in the chemical mechanical planarization (CMP) process. The influence of interactions between silica or ceria nanoparticles and the substrate surface on the CMP of Si face (0001) 6H SiC in different slurries with varied pH values was investigated using zeta potential measurements, SEM observations, friction tests, polishing experiments and XPS analysis. Meanwhile, the interaction forces between the substrate surfaces and the abrasive nanoparticles were also estimated using the Derjaguin Landau Verwey Overbeek (DLVO) theory. Silica particles are prone to adhere to the Si face 6H SiC surface below pH 5 and are repelled above pH 5, while ceria particles tend to adhere to the similarly charged and oppositely charged 6H SiC surfaces. This can be attributed to the fact that the ceria particle possesses a chemical tooth and Si O Ce bonds are formed between ceria particles and the 6H SiC surface. The friction coefficient and material removal rate during the CMP of 6H SiC could be reduced significantly by the adhesion of silica particles on the 6H SiC surface resulting from the electrostatic interaction at pH 2 and 4, while this phenomenon was not observed when ceria particles were adsorbed. The XPS analysis indicated that more oxidized species (e.g. Si C O, Si Ox Cy, Si O2, Si4 C4 x O2, Si4 C4 O4 and C O) were formed during immersion in aq. KMnO4 solution. Finally, an ideal electrostatic interaction between the abrasive particles and the 6H SiC substrate surface during the CMP process was proposed.

title: Recrystallization Phase in He Implanted 6H SiC*
abstract: The evolution of the recrystallization phase in amorphous 6H SiC formed by He implantation followed by thermal annealing is investigated. Microstructures of recrystallized layers in 15 keV He ion implanted 6H SiC (0001) wafers are characterized by means of cross sectional transmission electron microscopy (XTEM) and high resolution TEM. Epitaxial recrystallization of buried amorphous layers is observed at an annealing temperature of 900degC. The recrystallization region contains a 3C SiC structure and a 6H SiC structure with different crystalline orientations. A high density of lattice defects is observed at the interface of different phases and in the periphery of He bubbles. With increasing annealing to 1000degC, 3C SiC and columnar epitaxial growth 6H SiC become unstable, instead of [0001] orientated 6H SiC. In addition, the density of lattice defects increases slightly with increasing annealing. The possible mechanisms for explanation are also discussed.

title: Study on the machined depth when nanoscratching on 6H SiC using Berkovich indenter: Modelling and experimental study
abstract: In order to investigate the deformation characteristics and material removing mechanism of the single crystal silicon carbide at the nanoscale, the nanoscratching tests were conducted on the surface of 6H SiC (0 0 0 1) by using Berkovich indenter. In this paper, a theoretical model for nanoscratching with Berkovich indenter is proposed to reveal the relationship between the applied normal load and the machined depth. The influences of the elastic recovery and the stress distribution of the material are considered in the developed theoretical model. Experimental and theoretical machined depths are compared when scratching in different directions. Results show that the effects of the elastic recovery of the material, the geometry of the tip and the stress distribution of the interface between the tip and sample have large influences on the machined depth which should be considered for this kind of hard brittle material of 6H SiC.

title: Rectifying electrical contacts to n type 6H SiC formed from energetically deposited carbon
abstract: Electrical contacts to n type 6H SiC deposited from carbon fluxes with differing energies (0.12 1.0 keV) have exhibited deposition energy dependent microstructural and electrical properties. Lower deposition energies resulted in resistive amorphous carbon contacts in which transport occurred by tunneling through an interfacial potential barrier consisting of a mixed oxide/carbon layer. With higher average energy and moderately elevated temperature, the interfacial native oxide was removed by implantation/sputtering and Schottky contacts were formed with ideality factors of 1.3 and barrier heights of 0.97 eV. These contacts consisted of graphitic sheets aligned perpendicular to the growth direction. Energetic deposition offers control over microstructural/device properties, compatibility with photolithography and excellent adhesion to the underlying 6H SiC.