Ti/n型6H-SiC(0001)接触界面的研究

用同步辐射光电子能谱(SRPES)和X射线光电子能谱(XPS)的方法研究了Ti/n型6H-SiC(0001)的接触界面。Ti/n型6H-SiC(0001)样品采用磁控溅射的方法获得,然后将表面的Ti用氩离子刻蚀的方法慢慢刻蚀掉,Ti2p3/2用XPS测得,结合能从刻蚀时间为245 min的457.86 eV逐渐移动到刻蚀时间为255 min时的457.57 eV,移动约为0.3 eV。Si2p用同步辐射光测得,结合能从刻蚀245 min时的101.12 eV移动到干净的100.67 eV,峰形状未发生变化,表明Ti与衬底之间没有发生化学反应,SiC的价带发生弯曲,形成的势垒高度为0.89 eV。向SiC上蒸Si 2.5 min,退火30 min,观察LEED花样,发现当发射电流为30mA,能量37 eV时,SiC表面有√3*√3重构,发射电流为40 mA时,有6√3*6√3的重构。     

In-situ synchrotron radiation photoemission spectroscopy study of the initial atomic layer deposition of Al2O3 film on Si(001) substrate

In-situ synchrotron radiation photoemission spectroscopy and X-ray photoemission spectroscopy have been used to investigate the initial stages of Al2O3 growth on a Si(001) substrate by atomic layer deposition (ALD). The core level spectra of Si 2p, O 1s, and Al 2p as well as the valence band spectra were measured at every half reaction in the trimethylaluminum (TMA)-H2O ALD process. The line shape changes and binding energy shifts of the core level spectra reveal that Al2O3 is predominantly formed with a small amount of Si oxide in the initial stages without the formation of Al silicate. All core level spectra were alternately shifted toward higher and lower binding energies sides at every half ALD reaction. This can be explained by the band bending effect induced by different chemical species on the surface during the TMA-H2O ALD reaction. The valence band spectra showed that four cycles of ALD reactions were necessary to complete the electronic structure of the Al2O3 film with a valence band offset of 3.73 eV.     

Structural and electrical properties of swift heavy ion beam irradiated Co/Si interface

Synthesis of swift heavy ion induced metal silicide is a new advancement in materials science research. We have investigated the mixing at Co/Si interface by swift heavy ion beam induced irradiation in the electronic stopping power regime. Irradiations were undertaken at room temperature using 120 MeV Au ions at the Co/Si interface for investigation of ion beam mixing at various doses: 8 × 10¹², 5 × 10¹³ and 1 × 10¹⁴ cm⁻². Formation of different phases of cobalt silicide is identified by the grazing incidence X-ray diffraction (GIXRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation.I–V characteristics at Co/Si interface were undertaken to understand the irradiation effect on conduction mechanism at the interface.     

Photoelectron spectroscopy of ion-irradiated B-doped CVD diamond surfaces

Chemical vapour deposition (CVD) diamond films were irradiated by 1 keV argon ions at room temperature with doses ranging from 3.6 × 10¹² to 1.1 × 10¹⁶ Ar⁺ cm². The influence of sputtering on the valence band density of states of a boron-doped CVD diamond film was investigated by ultraviolet photoelectron spectroscopy and the changes in the plasmon features were observed by X-ray photoelectron spectroscopy of the carbon Is core level and its loss region. A gradual change from typical diamond features to amorphous carbon was observed after prolonged bombardment times. Above a critical dose D_crit of 5.8 × 10¹⁴ Ar⁺ cm² the damaged surface layer is characterized by a splitting of the C Is bulk peak into two components: a bulk-like diamond peak at 285.3 eV binding energy and a defect peak with 1 eV lower binding energy, which is attributed to the production of an amorphous sp²-rich carbon matrix. Moreover additional occupied states in the range of 0–4 eV binding energy, completely different to those observed on reconstructed diamond surfaces, were observed in the valence band spectra of the ion-irradiated diamond surface. These filled states can also be attributed to the amorphous carbon matrix which is formed at high doses. At very low doses (< 3 × 10¹⁴ ions cm²) only a band bending of the C Is diamond core level peak, along with the formation of some occupied states in the band structure at around 3.8 eV binding energy was observed. A comparison with annealed hydrogen-free CVD diamond surfaces shows some similarities concerning these filled states. The obtained spectra are compared with other crystalline and amorphous forms of carbon and the results are discussed in terms of an irradiation-induced change in the atomic structure of the surface. A comparison of ion bombarded and annealed diamond samples clearly shows that no graphitization takes place in the latter case.     

Si掺杂锐钛矿相TiO2的电子能带结构

利用基于密度泛函理论的第一性原理方法对Si掺杂前、后锐钛矿相TiO2的电子能带结构、电子态密度以及吸收光谱进行计算。结果表明,Si掺杂导致锐钛矿相TiO2的禁带宽度略增大0.048 eV;掺杂前锐钛矿相TiO2的价带和导带主要由O的2p和Ti的3d轨道构成,Si掺杂后其价带和导带主要由Si的3p、Ti的4s和Ti的3d轨道构成;Si掺杂可导致锐钛矿相TiO2的吸收边蓝移。     

Photoemission studies of the vicinal SiC(100) 4° surface and the Cs/SiC(100) 4° interface

Photoemission studies of the electronic structure of the vicinal SiC(100) 4° surface, which was grown using a new substrate atom substitution method, and the Cs/SiC(100) 4° interface have been performed for the first time. The modification of spectra of the valence band and C 1s and Si 2p core levels in the process of formation of the Cs/SiC(100) 4° interface was analyzed. The suppression of the surface SiC state with a binding energy of 2.8 eV and the formation of a cesium-induced state with a binding energy of 10.5 eV were observed. The modification of the complex component structure in the spectrum of C 1s core level has been detected and examined for the first time. It was found that Cs adsorption on the vicinal SiC(100) 4° surface results in intercalation of graphene islands on SiC(100) 4° with Cs atoms.     

磁性半导体GdxSi1-x的XPS研究

采用离子束技术,在n型硅基片上注入稀土元素钆,制备了磁性/非磁性p-n结.本文中使用的XPS对制备的样品进行测试,利用Origin 7.0提供的PFM工具进行研究,O1s束缚能介于金属氧化物和SiO2中O1s的束缚能之间,Si2p的XPS谱分裂为两个峰,其中一个是单质Si的,另一个介于单质Si和硅化物之间,Gd4d的束缚能介于金属钆和氧化钆中的Gd4d之间,说明GdxSi1-x形成了无定形结构.     

Structural and electrical properties of swift heavy ion beam irradiated Fe/Si interface

The present work deals with the mixing of iron and silicon by swift heavy ions in high-energy range. The thin film was deposited on a n-Si (111) substrate at 10⁻⁶ torr and at room temperature. Irradiations were undertaken at room temperature using 120 MeV Au⁺⁹ ions at the Fe/Si interface to investigate ion beam mixing at various doses: 5 × 10¹² and 5 × 10¹³ ions/cm². Formation of different phases of iron silicide has been investigated by X-ray diffraction (XRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation. I-V measurements for both pristine and irradiated samples have been carried out at room temperature, series resistance and barrier heights for both as deposited and irradiated samples were extracted. The barrier height was found to vary from 0·73–0·54 eV. The series resistance varied from 102·04–38·61 kΩ.     

An XPS study of amorphous MoO3/SiO films deposited by co-evaporation

X-ray photoelectron spectroscopic (XPS) core-level spectra of MoO₃/SiO thin films are presented. The effects of changes in composition, substrate temperature during deposition and annealing on the binding energy of Mo(3d) and Si(2p) core lines in mixed films are compared with those of MoO₃ and SiO. Appreciable changes in Mo(3d) peak positions and slight changes in Si(2p) peak positions are observed. The change in binding energy of the Mo(3d) doublet may be attributed to the effective incorporation of silicon ions in an MoO₃ lattice which may cause the molybdenum orbital to be a little less tightly bound. This helps in the internal electron transfer from the oxygen (2p) to the molybdenum (4d) level as a result of which the molybdenum is readily changed to lower oxidation states during heat treatment. XPS spectra show that the position of the Si(2p) core state shifts monotonically with increasing oxygen concentration from the value of 101.8 to 102.6 eV.     

Synthesis of zirconium silicide in Zr thin film on Si and study of its surface morphology

Zirconium silicide was synthesized on Si (100)/zirconium interface by means of swiftly moving 150 MeV Au ion beam. Thin films of zirconium (~60 nm) were deposited on Si (100) substrates in ultra high vacuum conditions using the electron-beam evaporation technique. The system was exposed to different ion fluencies ranging from 3 × 10¹³ to 1 × 10¹⁴ ions/cm² at room temperature. Synthesized zirconium silicide thin film reasonably affects the resistivity of the irradiated system and for highest fluence of 1 × 10¹⁴ ions/cm² resistivity value reduces from 84.3 to 36 μΩ cm. A low resistivity silicide phase, C-49 ZrSi₂ was confirmed by X-ray analysis. Schottky barrier height was calculated from I–V measurements and the values drops down to 0.58 eV after irradiation at 1 × 10¹⁴ ions/cm². The surface and interface morphologies of zirconium silicide were examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM shows a considerable change in the surface structure and SEM shows the ZrSi₂ agglomeration and formation of Si-rich silicide islands.     

The chirality of metal-encapsulated silicene-like nanotubes

The energy stability and electronic structures of (3,3) armchair metal-encapsulated SiNTs (M@SiNTs) are systematically studied by using DFT-GGA calculations. Results show that most the metal-encapsulated SiNTs with the same space group can be stabilized through doping by metal atoms with silicene-like structures. Compared with the different chirality, (4,0) zigzag M@SiNTs are more stable than (3,3) armchair M@SiNTs. The band gaps of (3,3) and (4,0) SiNTs are 1.06 eV and 0.06 eV, they are both semiconductors. But most (3,3) armchair and (4,0) zigzag M@SiNTs are conductors, except (3,3) Sn@SiNT, (4,0) K@SiNT and (4,0) Ba@SiNT are semiconductors with small value of band gaps. The interaction between encapsulated metal and silicon atoms makes out orbital hybridizations, and decreases the gap between valence band and conduction band. Finally, electronic structural analysis shows that metal atoms gain electrons and Si atoms lose electrons as a whole, some electrons transfer from Si to metal atoms.     

EELS and XPS investigations of Ba2Cu3O4Cl2

Electron energy-loss spectroscopy in transmission and x-ray photoelectron spectroscopy have been applied to investigate single crystalline Ba₂Cu₃O₄Cl₂ to obtain the loss-function along the high symmetry directions of the cuprate plane, the Cu2p and O1s excitation edges, and to study the valence band and the core level electronic structure. The lossfunction shows a gap of 1.65eV, practically dispersionless structures between 2 and 8eV, and a volume plasmon located at 25eV. The dielectric function is derived. The excitation edges are a measure for the number of holes located in the Cu like or O like states parallel or perpendicular to the Cu₃O₄ planes. The Cu₂p_3/2 XPS shows three features in the main line and a satellite structure due to two independent copper sites and indicating a strong 3d electron correlation. By interpreting forward scattering features the valence band structure can be assigned to its atomic origin.     

Dynamics of dysprosium silicide nanostructures on Si(001) and (111) surfaces

The growth and coarsening dynamics of dysprosium silicide nanostructures are observed in real-time using photoelectron emission microscopy. The annealing of a thin Dy film to temperatures in the range of 700–1050 °C results in the formation of epitaxial rectangular silicide islands and nanowires on Si(001) and triangular and hexagonal silicide islands on Si(111). During continuous annealing, individual islands are observed to coarsen via Ostwald ripening at different rates as a consequence of local variations in the size and relative location of the surrounding islands on the surface. A subsequent deposition of Dy onto the Si(001) surface at 1050 °C leads to the growth of the preexisting islands and to the formation of silicide nanowires at temperatures above where nanowire growth typically occurs. Immediately after the deposition is terminated, the nanowires begin to decay from the ends, apparently transferring atoms to the more stable rectangular islands. On Si(111), a low continuous flux of Dy at 1050 °C leads to the growth of kinked and jagged island structures, which ultimately form into nearly equilateral triangular shapes.     

Adjustable band position of strontium titanate by doping-free solvents effect and its correlation with photodegradation performance

Strontium titanate (STO) with shape of nanosheet, polyhedron and nanosphere is prepared by one-pot solvothermal method using ethanolamine (EA), diethanolamine (DA) and ethylene glycol (EG), respectively. Upon the different crystalline size and morphology of STO, effect of solvents on nucleation and growth is discussed. In this case, energy band and flat band potential of samples are measured by UV–Vis diffuser reflectance (DRS) and Mott-Schottky (MS). Results show narrow energy band (Eg) 2.68, 2.87 and 3.17 eV of as-synthesized pure STOs (EA-STO, DA-STO and EG-STO) compared with empirical STO. Simultaneously, valence band shows 0.55, 1.80 and 2.21 eV respectively. Rhodamine B (RhB) and methyle orange (MO) are selected as anionic and cationic target contaminants. Correlation of photodegradation performance and valence band is depicted.     

Photoelectrochemically active surfactant free single step hydrothermal mediated titanium dioxide nanorods

Titanium dioxide (TiO₂) nanorods have been successfully synthesized by a simple and cost-effective hydrothermal deposition method onto the conducting glass substrates. Effect of reaction temperature on the growth of TiO₂ nanorods have been investigated by varying the reaction temperature from 140 to 200 °C. The optical, structural, compositional, morphological properties of the synthesized films are studied. X-ray diffraction patterns reveal the formation of polycrystalline TiO₂ with the tetragonal crystal structure possessing rutile phase. The chemical composition and valence states of the constituent elements were analysed by X-ray photoelectron spectroscopy. Field emission scanning electron microscopy images shows the formation of nanorod-like structure with variation in diameter. The optical band gap energy was found to increase from 3.07 to 3.15 eV with the increase in reaction temperature exhibiting a blue shift. The films were photo electrochemically active with the maximum current density of 216 µA/cm² for the sample prepared at 180 °C.     

Valence number transition and silicate formation of cerium oxide films on Si(100)

Interface reactions of a Ce-oxide layer with Si(100) wafers have been characterized by X-ray photoelectron spectroscopy. The ratio of Ce atoms in Ce³⁺ states within the Ce-oxide layer has been found to decrease from 47% at as-deposited sample to 26% after annealing. From detailed reaction analysis of valence number transitions of Ce atoms and the creation of SiO₂ layer at the interface, the reacted Ce³⁺ atoms are converted into silicates and Ce⁴⁺ with a ratio of 2:1. The energy bandgap of Ce-silicate layer has been determined as 7.67 eV and the valence band offset with respect to Si(100) wafer has been extracted as 4.35 eV.     

Effect of simultaneous chemical substitution of A and B sites on the electronic structure of BiFeO3 films grown on BaTiO3/SiO2/Si substrate

Electrical properties and electronic structure of Bi_1?xCa_xFe_1?yMn_yO_3?δ grown by pulsed-laser deposition on BaTiO₃/SiO₂/Si substrate were investigated. Results showed that Ca has drastic effect on symmetry of crystal and electrical poperties of BiFeO₃. On the other hand, Mn revealed to have more radical effect on optical properties and energy gap of the compound. XPS results represented that although Ca tend to decrease Fe valence state, Mn tends to stabilize it at 3+ (at least in this concentrations). UV–visible study yielded bandgap of 2.51–2.81 eV (at 300 K) for different concentrations of Ca and Mn. UV–visible spectra also revealed sub-bandgap defect transitions at 2.2 and 2.4 eV. Slave-particle approach has also been applied to elucidate nature of the metal–insulator transition.     

Valence band offset at GaN/β-Si3N4 and β-Si3N4/Si(111) heterojunctions formed by plasma-assisted molecular beam epitaxy

Ultra thin films of pure β-Si₃N₄ (0001) were grown on Si (111) surface by exposing the surface to radio- frequency nitrogen plasma with a high content of nitrogen atoms. Using β-Si₃N₄ layer as a buffer layer, GaN epilayers were grown on Si (111) substrate by plasma-assisted molecular beam epitaxy. The valence band offset (VBO) of GaN/β-Si₃N₄/Si heterojunctions is determined by X-ray photoemission spectroscopy. The VBO at the β-Si3N4 / Si interface was determined by valence-band photoelectron spectra to be 1.84 eV. The valence band of GaN is found to be 0.41 ± 0.05 eV below that of β-Si₃N₄ and a type-II heterojunction. The conduction band offset was deduced to be ~ 2.36 eV, and a change of the interface dipole of 1.29 eV was observed for GaN/β-Si₃N₄ interface formation.     

Core and valence excitations in Ni2Si

We present an electron energy loss analysis of Ni₂Si around the NiM_2,3 and NiL_2,3 edges and in the range 0–30 eV (valence excitations). An intensity reduction of the Ni L_2,3 edge of the silicide is observed and interpreted in terms of a depletion of d metal electrons at the Fermi level E_F. The reduction in the Ni M_2,3 Fano line shape with respect to that for pure nickel is also described in a similar way. The near-edge region gives information on the partial density of states in the region above E_F and is related to the structures observed in the valence band range. Particular attention was paid to the study of the Ni₂Si local structure obtained from the analysis of the extended energy loss fine structures beyond the Ni M_2,3 level.     

Single crystal growth,structure and properties of TlHgBr3

High-quality inclusion-free single crystals of ternary thallium mercury bromide, TlHgBr₃, were successfully grown by Bridgman–Stockbarger method. For the pristine surface of the TlHgBr₃ single crystal, X-ray photoelectron core-level and valence-band spectra were measured. The comparison on a common energy scale of the X-ray photoelectron valence-band spectrum of TlHgBr₃ and the X-ray emission Br Kβ₂ band, representing peculiarities of the energy distribution of the Br 4p states revealed that the main contribution of the valence Br p states, occurred in the upper portion of the valence band, with also their significant contributions in other valence band regions. It has been determined that TlHgBr₃ is a semiconductor with the bandgap energy value of E_g = 2.51 eV at 100 K. The E_g value decreased up to 2.44 eV when temperature increased to 300 K.