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Growth of graphene on SiO2 with hexagonal boron nitride buffer layer
摘要： One-through process of graphene growth on insulator substrates with inserting a hexagonal boron nitride (h-BN) buffer layer is expected to yield significant improvements in performance of electron transport properties of graphene devices due to the alleviation of the interface interaction between graphene and insulators and the enhancement of the flatness of the substrate. In this study, we successfully fabricated a graphene/h-BN/SiO2 heterostructure by direct chemical vapor deposition (CVD) without mechanical transfer processes. It was found that h-BN promotes the growth of graphene on SiO2 whereas the graphene growth without the h-BN layer is extremely difficult. The electronic structures of graphene and h-BN were investigated by using micro-Raman spectroscopy and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The B and N K-edge NEXAFS revealed that substitutional oxygen impurities with the chemical form of BN3?xOx (x = 1, 2, 3) are present in both h-BN/SiO2 and graphene/h-BN/SiO2. The number of O substitutional impurities is two times larger in graphene/h-BN/SiO2 than in h-BN/SiO2, which is presumed to be due to the reaction with oxygen from SiO2 and methanol during the graphene growth. The interfacial interaction between graphene and h-BN was found to be weak in graphene/h-BN/SiO2. The present study shows that the h-BN layer grown with CVD can be a superior buffer layer for graphene devices which enables direct graphene growth on it and to decrease the interactions with insulator substrates.
关键词： NEXAFS,h-BN,Chemical vapor deposition,Buffer layer,Graphene
更新于2025-09-23 15:23:52
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Investigation of local geometrical structure, electronic state and magnetic properties of PLD grown Ni doped SnO2 thin films
摘要： We have investigated the ferromagnetic behavior, electronic states and local geometrical structure of Ni (2 and 10 at %) doped SnO2 thin films. The films were successfully fabricated with the help of pulsed laser deposition (PLD) technique on Si (100) substrate under ultrahigh vacuum (UHV) condition. X-ray diffraction (XRD) results revealed the single phase character of SnO2 rutile lattice structure with P42/mnm space group. The inclusion of Ni ions into SnO2 matrix induced oxygen vacancy (Vo), enhanced the distortion in octahedral local symmetry and reduced the oxidation state of the host Sn4+ (SnO2) to Sn3+ (Sn2O3) these details have been estimated by Raman scattering, Near edge X-ray absorption fine structure (NEXAFS) spectra at Ni L3,2 and O K edges. Further quantitative details on the local geometrical structure around Ni ions were obtained via fitting the experimental Fourier transforms EXAFS spectra |X(R)| with FEFF6 code. The magnetization measurements performed at room temperature (RT) infers that the observed magnetic behavior of the films seems to be relevant to the same crystal growth condition (UHV) and might not be limited directly to the Ni dopant concentrations. The FM signal and the role of surface defects have been discussed based spin-split impurity band difference in the saturation moments even with increase the Ni content. Hence, the similarity in Ni doped SnO2 films displayed ferromagnetic (FM) signal, and there was no significant Ferromagnetism etc. percolation mechanism.
关键词： surface defects,XANES spectra,SnO2 nanostructured thin film,PLD,local symmetry,XRD,NEXAFS
更新于2025-09-23 15:22:29
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Polarization Dependence in the Carbon K-edge Photofragmentation of MAPDST Photoresist: an Experimental and Theoretical Study
摘要： The use of tunable soft X-rays from synchrotron radiation (SR) opens the possibility of inducing selective chemical bond scission due to its high localization in a chemical bond. The selective fragmentation of a potential extreme ultraviolet (EUV) resist, poly(4-(methacryloyloxy) phenyldimethylsulfoniumtriflate (MAPDST), was examined using inner shell polarized SR excitation. Selective bond dissociation processes were studied using a combination of carbon K-edge excitation, angle-resolved irradiation, and NEXAFS spectroscopy. Detailed theoretical calculations carried out with the FEFF9 modeling program allowed the interpretation of all the observed experimental features. NEXAFS results indicated that the aromatic group of the polymer lies parallel to the substrate surface. FEFF9 theoretical calculations confirmed the origin of the splitting of the main C 1s →π*C=C resonances observed. The transition C1s → πα*C=C (285.3 eV) can be associated with the four internal carbons of the aromatic ring. The transition C1s → πβ*C=C (286.9 eV) was assigned to the carbon atoms attached to the oxygen and sulfur atoms. According to the theoretical calculations, the origin of the splitting is due to the different absolute energy of C1s. The results showed a strong selective dissociation effect when the excitation energy was tuned to C1s → πα*C=C transition and the electric field vector of the photon was perpendicular to the substrate plane (grazing angle). On the contrary, other transitions were in general less affected. When the SR irradiation angle changed from grazing to normal incidence, the intensity of the C1s → π*C=C transitions was almost unaffected by 285.3 eV photons. The experimental results suggest that site-specific core excitation combined with the direction of the electric field vector of the incidence SR, can efficiently control the localization of the photon energy to produce selective bond dissociation in MAPDST thin films. The results presented here can also be useful to guide new processing lithographic methods for EUVL using the polarization properties of light in ordered polymeric thin films.
关键词： NEXAFS spectroscopy,FEFF9 modeling,selective bond dissociation,synchrotron radiation,polarization dependence,MAPDST photoresist
更新于2025-09-23 15:21:21
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Temperature Dependence in the NEXAFS Spectra of <i>n</i> -Alkanes
摘要： The Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of orthorhombic single crystals of n-octacosane (n-C28H58), recorded at room temperature (298 K) and at cryogenic temperatures (93 K), show distinct differences. The characteristic carbon 1s → σ*C-H band in the NEXAFS spectrum of n-C28H58 is broader and has a lower energy onset in its room temperature spectrum than in its NEXAFS spectrum recorded at cryogenic temperatures. Density functional theory simulations show that nuclear motion and molecular disorder contribute to the observed spectral broadness and are the origin of the low-energy onset of the C-H band in the room temperature spectrum.
关键词： Temperature Dependence,Quantum Chemistry,n-Alkanes,NEXAFS,Molecular Structure,Spectroscopy
更新于2025-09-11 14:15:04
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Silicon Oxide-Rich Diamond-Like Carbon: A Conformal, Ultrasmooth Thin Film Material with High Thermo-Oxidative Stability
摘要： Silicon oxide-containing diamond-like carbon (a-C:H:Si:O) films are a promising class of protective coatings for environmentally-demanding applications owing to their lower residual stresses and superior thermal stability and oxidation resistance relative to undoped diamond-like carbon. However, existing versions of a-C:H:Si:O deposited by traditional methods such as plasma-enhanced chemical vapor deposition (PECVD) undergo substantial degradation and oxidation at temperatures above 250 °C. This, together with the difficulty of PECVD in depositing conformal coatings on complex geometries such as high-aspect-ratio features, has limited the applicability of a-C:H:Si:O. Here, the unique capabilities of plasma immersion ion implantation and deposition (PIIID) to grow silicon oxide-rich diamond-like carbon materials that are ultrasmooth, continuous, and conformal on high-aspect-ratio topographies are explored. The high concentration of silicon and oxygen in PIIID-grown films (23 ± 5 at.% and 11 ± 4 at.%, respectively) is unrivalled for this class of materials, and drastically increases the resistance to oxidation at high temperatures, compared with PECVD-grown films. The results open the path for using a-C:H:Si:O in applications involving exposure of materials to extreme environments.
关键词： ultrasmooth films,X-ray photoelectron spectroscopy (XPS),diamond-like carbon,NEXAFS,thermal stability
更新于2025-09-10 09:29:36
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Evidence for Primal sp <sup>2</sup> Defects at the Diamond Surface: Candidates for Electron Trapping and Noise Sources
摘要： Many advanced applications of diamond materials are now being limited by unknown surface defects, including in the fields of high power/frequency electronics and quantum computing and quantum sensing. Of acute interest to diamond researchers worldwide is the loss of quantum coherence in near-surface nitrogen-vacancy (NV) centers and the generation of associated magnetic noise at the diamond surface. Here for the first time is presented the observation of a family of primal diamond surface defects, which is suggested as the leading cause of band-bending and Fermi-pinning phenomena in diamond devices. A combination of density functional theory and synchrotron-based X-ray absorption spectroscopy is used to show that these defects introduce low-lying electronic trap states. The effect of these states is modeled on band-bending into the diamond bulk and it is shown that the properties of the important NV defect centers are affected by these defects. Due to the paramount importance of near-surface NV center properties in a growing number of fields, the density of these defects is further quantified at the surface of a variety of differently-treated device surfaces, consistent with best-practice processing techniques in the literature. The identification and characterization of these defects has wide-ranging implications for diamond devices across many fields.
关键词： surfaces,Fermi-level pinning,defects,diamond,NEXAFS
更新于2025-09-10 09:29:36
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Mn doped BiNbO4 ceramics: Thermal stability, phase transitions, magnetic properties, NEXAFS and ESR spectroscopy
摘要： Thermal stability, magnetic properties, ESR (Electron Spin Resonance) and NEXAFS (Near-Edge X-ray Absorption Fine Structure) spectra of the orthorhombic and triclinic modi?cations of solid solutions BiNb1-xMnxO4-d have been studied. X-ray diffraction determined the reversibility of the phase transition from the high-temperature triclinic modi?cation to the orthorhombic modi?cation at 950 (cid:1)C in the BiNb1-xMnxO4-d solid solutions. The ESR spectra of the triclinic BiNb1-xMnxO4-d revealed the sextet structure of Mn(II) ions with 8.4 mT splitting and some features at g ? 3.80 and 1.47, and a broad diffuse band with g ~ 2.2 having a sextet with 8e9 mT splitting and g ? 2.0 against its background. The measurements of magnetic susceptibility allowed us to calculate the parameters of exchange interactions in dimers and the distribution of manganese atoms (II), (III) and (IV) in dependence on concentrations of the solid solutions in the orthorhombic and triclinic modi?cations. It was established that in the manganese-doped solid solutions of triclinic modi?cation, the degree of aggregation and the nuclearity of the clusters were higher than in the solid solutions of orthorhombic modi?cation. The clusters were presented in the forms of dimers and trimers of Mn(II), Mn(III) and Mn(IV) atoms with different valence atoms with antiferro- and ferromagnetic types of exchange. The solid solutions BiNb1-xMnxO4-d as well as manganese oxides MnO, Mn2O3 and MnO2 were studied by the NEXAFS spectroscopy in order to determine the degrees of oxidation of manganese atoms. The DSC (Differential Scanning Calorimetry) curves of the samples BiNb1-xMnxO4-d revealed the endothermic effects associated with the phase transition from the orthorhombic modi?cation to the triclinic one at 1050 (cid:1)C (x ? 0.03) and 1048 (cid:1)C (x ? 0.06). The melting peaks were observed at 1231 (cid:1)C (x ? 0.03) and 1220 (cid:1)C (x ? 0.06), respectively. The differences in the magnetic characteristics and in the results of ESR and NEXAFs spectroscopy of the BiNb1-xMnxO4-d of orthorhombic and triclinic modi?cations were due to the relative content of Mn(II), Mn(III), Mn(IV) ions and the degree of distortion of their local surroundings, composition and nature of exchange interactions in the clusters of manganese atoms.
关键词： ESR,Phase transitions,NEXAFS,Thermal stability,Magnetic properties
更新于2025-09-09 09:28:46
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Ferromagnetic Behavior and Electronic Characterization of ZnO Nanoparticles
摘要： In this work, Al-doped ZnO nanoparticles encapsulated with amorphous SiO2 were prepared by the wet chemical method. The obtained precursor was annealed and the nanoparticle sizes were controlled by adjusting the annealing temperature. These nanomaterials showed ferromagnetic behavior, even though the ZnO bulk crystal was diamagnetic. The results of electrical conductivity and XANES suggested that ferromagnetism of the Al-doped nanoparticles was results of carrier transport and oxygen vacancies. The Al-doped ZnO nanoparticles are extremely interesting from the perspective of solid state physics. [DOI: 10.1380/ejssnt.2018.406]
关键词： Nano-particles, quantum dots, and supra-molecules,Magnetic, structural, and other properties of nanostructures,Zinc oxide,Luminescence,Near edge extended X-ray absorption fine structure (NEXAFS)
更新于2025-09-04 15:30:14