Depth Dependence of Tetragonal Distortion of a ZnO/Mg0.1Zn0.90/ZnO Heterostructure Studied by Rutherford Backscattering/Channeling

Rutherford backscattering and channeling are used to characterize the structure of a ZnO/Mg0.1Zn0.90/ZnO heterostructare grown on a sapphire （0001） substrate by rf plasma-assisted molecular beam epitaxy. The results show that the Mg0.1Zn0.90 layer has the same hexagonal wurtzite structure as the underlying ZnO layer, and the heterostructure has a good crystalline quality with xmin = 5%, which is the ratio of the backscattering yields of aligned and random spectra in the near-surface region. Using the channeling angular scan around an off-normal （1213） axis in the {1010} plane of both ZnO and MgZnO layer, the tetragonal distortion εT, which is caused by the elastic strain in the epilayer, is determined. The depth dependence of εT is obtained by using this technique. It can clearly be seen that the elastic strain rapidly decreases with the increase in thickness of the ZnO film in the early growth stage and becomes slightly larger in the region of the Mg0.1Zn0.9O layer.     

Tetragonal Distortion of GaN Epilayer with Multiple Buffer Layers on Si （111） Studied by RBS/Channelling and HRXRD

Rutherford backscattering （RBS）/channelling and high resolution x-ray diffraction （HRXRD） have been used to characterize the tetragonal distortion of a GaN epilayer with four Alx Ga1-xN and single AIN buffer layers grown on a Si （111） substrate by metal-organic vapour phase epitaxy （MOVPE）. The results show that a 1000nm GaN epilayer with a perfect crystal quality （Xmin = 1.54%） can be grown on the Si （111） substrate in virtue of multiple buffer layers. Using the RBS/channelling angular scan around an off-normal （1213） axis in the （1010） plane and the conventional HRXRD θ - 20 scans normal to GaN （0002） and （1122） planes at the 0° and 180° azimuth angles, the tetragonal distortion eT, which is caused by the elastic strain in the epilayer and different buffer layers, can be obtained respectively. The two experiments are testified at one result, the tetragonal distortion of GaN epilayer is nearly to a fully relaxed （eT = 0）.     

A Comparison of GaN Epilayers with Multiple Buffer Layers and with a Single Buffer Layer Grown on Si（111） Studied by HRXRD and RBS/Channeling

Two hexagonal GaN epilayers （samples A and B） with multiple buffer layers and single buffer layer are grown on Si （111） by metal-organic vapour phase epitaxy （MOVPE）. From the results of Rutherford backscattering （RBS）/channeling and high resolution x-ray diffraction （HRXRD）, we obtain the lattice constant （a and c） of two GaN epilayers （aA = 0.3190 nm, cA = 0.5184 nm and aB = 0.3192 nm, CB = 0.5179 nm）, the crystal quality of two GaN epilayers （ ХminA=4.87%, ХminB =7.35% along 〈1-↑213〉 axis） and the tetragonal distortion eT of the two samples along depth （sample A is nearly fully relaxed, sample B is not relaxed enough）. Comparing the results with the two samples, it is indicated that sample A with multiple buffer layers have better crystal quality than sample B with a single buffer layer, and it is a good way to grow GaN epilayer on Si （111） substrates using multiple buffer layers to improve crystal quality and to reduce lattice mismatch.     

Photovoltaic Characteristic of La0.7Sr0.3MnO3/ZnO p-n Heterojunction

We report on the photovoltaic properties of Lao.7Sro.3MnO3//ZnO heterojunction fabricated by pulsed laser deposition methods. Nanosecond photovoltaic pulses are observed in this junction in the wavelength range from ultraviolet-visible to infrared. A qualitative explanation is presented, based on an analysis of the photovoltaic signals of p-n heterojunction.     

A Simple Route of Morphology Control and Structural and Optical Properties of ZnO Grown by Metal-Organic Chemical Vapour Deposition

Employing the metal-organic chemical vapour deposition （MOCVD） technique, we prepare ZnO samples with different morphologies from the film to nanorods through conveniently changing the bubbled diethylzinc flux （BDF） and the carrier gas flux of oxygen （OCGF）. The scanning electron microscope images indicate that small BDF and OCGF induce two-dimensional growth while the large ones avail quasi-one-dimensional growth. X-ray diffraction （XRD） and Raman scattering analyses show that all of the morphology-dependent ZnO samples are of high crystal quality with a c-axis orientation. From the precise shifts of the 20 locations of ZnQ （002） face in the XRD patterns and the E2 （high） locations in the Raman spectra, we deduce that the compressive stress forms in the ZnO samples and is strengthened with the increasing BDF and OCGF. Photoluminescence spectroscopy results show all the samples have a sharp ultraviolet luminescent band without any defects-related emission. Upon the experiments a possible growth mechanism is proposed.     

Investigation of Oxygen Vacancy and Interstitial Oxygen Defects in ZnO Films by Photoluminescence and X-Ray Photoelectron Spectroscopy

ZnO films prepared at different temperatures and annealed at 900^o C in oxygen are studied by photoluminescence （PL） and x-ray photoelectron spectroscopy （XPS）. It is observed that in the PL of the as-grown films the green luminescence （GL） and the yellow luminescence （YL） are related, and after annealing the GL is restrained and the YL is enhanced. The 0 ls XPS results also show the coexistence of oxygen vacancy （Vo） and interstitial oxygen （Oi） before annealing and the quenching of the Vo after annealing. By combining the two results it is deduced that the GL and YL are related to the Vo and Oi defects, respectively.     

用卢瑟福背散射/沟道技术研究ZnO/Zn0.9Mg0.1O/ZnO异质结的弹性应变

利用卢瑟福背散射/沟道技术对射频等离子体辅助分子束外延法生长在蓝宝石衬底上的ZnO/Zn_0.9Mg_0.1O/ZnO异质结进行了组分分析，并得到了异质结弹性应变随深度的变化，应变由界面向表面逐渐释放，并由负变正，且在ZnO与Zn_0.9Mg_0.1O界面处轻微增大.负的应变是由于ZnO与衬底的晶格失配和热失配，而逐渐变为正值是Zn_0.9Mg_0.1O与ZnO的晶格常数差异及弹性应变的 关键词： 异质结 卢瑟福背散射/沟道 弹性应变 ZnMgO     

Fabrication of NiCo2O4 nanofibers by electrospinning

The spinel NiCo₂O₄ nanofibers with diameters of 50-100 nm were prepared by high temperature calcinations of a simple inorganic-polymer composite fibers, which were obtained by electrospinning of the PVA/cobalt acetate/nickel acetate composite precursor. The crystallinity, purity, and surface morphology of the as-prepared NiCo₂O₄ nanofibers were investigated by XRD, FT-IR, SEM, respectively.     

Effect of Post-Annealing on Microstructural and Electrical Properties of N^＋Ion-Implanted into ZnO：In Films

We fabricate p-type conductive ZnO thin films on quartz glass substrates by codoping of In-N using radio frequency magnetron sputtering technique together with the direct implantation of acceptor dopants （nitrogen）. The effects of thermal annealing on the structure and electrical properties of the ZnO films are investigated by an x-ray diffractometer （XRD） and a Hall measurement system. It is found that the best p-type ZnO film subjected to annealed exhibits excellent electrical properties with a hole concentration of 1.22 × 10^18 cm^-3, a Hall mobility of 2.19 cm^2 V^-1 s^- 1, and a low resistivity of about 2.33 Ωcm, indicating that the presence of In may facilitates the incorporation of N into ZnO thin films.     

Morphological and structural characterizations of CrSi2 nanometric films deposited by laser ablation

The structure and morphology of chromium disilicide (CrSi₂) nanometric films grown on 〈1 0 0〉 silicon substrates both at room temperature (RT) and at 740 K by pulsed laser ablation are reported. A pure CrSi₂ crystal target was ablated with a KrF excimer laser in vacuum (∼3 × 10⁻⁵ Pa). Morphological and structural properties of the deposited films were investigated using Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GID), X-ray reflectivity (XRR), scanning (SEM) and transmission electron microscopy (TEM). From RBS analysis, the films’ thickness resulted of ∼40 nm. This value is in agreement with the value obtained from XRR and TEM analysis (∼42 and ∼38 nm, respectively). The films’ composition, as inferred from Rutherford Universal Manipulation Program simulation of experimental spectra, is close to stoichiometric CrSi₂. GID analysis showed that the film deposited at 740 K is composed only by the CrSi₂ phase. The RT deposited sample is amorphous, while GID and TEM analyses evidenced that the film deposited at 740 K is poorly crystallised. The RT deposited film exhibited a metallic behaviour, while that one deposited at 740 K showed a semiconductor behaviour down to 227 K.     

Thermoelectric properties of Bi0.9Sb0.1 prepared by high pressure

The Bi_0.9Sb_0.1 powders were prepared by mechanical alloying and then pressed under 6 GPa at different pressing temperatures. X-ray diffraction spectra showed that the single phase was formed. The nanostructure of grain was observed by bright-field imaging. Electrical conductivity, Seebeck coefficient, and thermal conductivity had been investigated in the temperature range of 80-300 K. The absolute Seebeck coefficient value of 120.3 μV/K was measured at 130 K. The figure-of-merit reached a maximum value of 0.90×10⁻³ K⁻¹ at 140 K.     

High-throughput synthesis and characterization of Mg1−xCaxO films as a lattice and valence-matched gate dielectric for ZnO based field effect transistors

Using composition-spread technique, we have grown metastable Mg_1−xCa_xO solid solution films on ZnO layers by pulsed laser deposition. All the films exhibited (1 1 1) oriented cubic phase. Despite a large miscibility gap, no phase separation took place at growth temperatures up to 700 °C, whereas an optimal growth temperature was found at 400 °C in terms of the crystallinity. The composition-spread films were characterized by X-ray diffraction mapping technique. Both lattice parameters and diffraction intensity increased with increasing the CaO composition. The present isovalent heterointerfaces realized the perfect lattice-matching by properly adjusting the CaO composition, leading to particular interest for ZnO based field effect transistors.     

Growth of a Novel Periodic Structure of SiC/AIN Multilayers by Low Pressure Chemical Vapour Deposition

A novel lO-period SiC/A1N multilayered structure with a SiC cap layer is prepared by low pressure chemical vapour deposition （LPCVD）. The structure with total film thickness of about 1.45~m is deposited on a Si （111） substrate and shows good surface morphology with a smaller rms surface roughness of f.3 nm. According to the secondary ion mass spectroscopy results, good interface of the 10 period SiC/A1N structure and periodic changes of depth profiles of C, Si, A1, N components are obtained by controlling the growth procedure. The structure exhibits the peak reflectivity close to 30% near the wavelength of 322 nm. To the best of our knowledge, this is the first report of growth of the SiC/AIN periodic structure using the home-made LPCVD system.     

Laser Molecular Beam Epitaxy of Multilayer Heterostructure SrNb0.05Ti0.95O3/La0.9Sr0.1MnO3 in 10000 Unit-Cell Layers

Ten thousands of unit-cell multilayer heterosturctures, [SrNb0.05 Ti0.95O3/La0.9 Sr0.1MnO3]3 （SNTO/LSMO）, have been epitaxial grown on SrTiO3 （001） substrates by laser molecular beam epitaxy. The monitor of insitu. reflection high-energy electron diffraction demonstrates that the heterosturctures are layer-by-layer epitaxial growth. Atomic force microscope observation indicates that the surface of the heterosturcture is atomically smooth. The measurements of cross-sectional low magnification and high-resolution transmission electron microscopy as well as the corresponding selected area electron diffraction reveal that the interfaces are of perfect orientation, and the epitaxial crystalline structure shows the orientation relation of SNTO（001）//LSMO（001）, and SNTO[100]//LSMO[100].     

Adsorption and photocatalytic degradation of methylene blue on Zn1−xCuxS nanoparticles prepared by a simple green method

Nanoparticles of Zn_1−xCu_xS with various dopant contents (0 ≤ x ≤ 0.15) were prepared in water by refluxing for 90 min at about 95 °C. Powder X-ray diffraction (XRD) patterns of the nanoparticles demonstrate that loading of Cu²⁺ ions does not change the crystal structure of ZnS. Scanning electron microscopy (SEM) images demonstrate that size of the nanoparticles decreases with increasing Cu²⁺ ions. UV-Vis diffuse reflectance spectra (DRS) of the nanoparticles show significant absorption in visible light region. Adsorption capacity of the nanoparticles for methylene blue (MB) increases with mole fraction of copper ions. Photocatalytic activity of the nanoparticles toward photodegradation of MB was evaluated under visible light irradiation. The results indicate that Zn_0.85Cu_0.15S nanoparticles exhibit highest photocatalytic activity among the prepared samples. Moreover, effects of refluxing time applied for preparation of the nanoparticles and calcination temperature were investigated.     

Synthesis and characterization of Gd0.1Ce0.9O1.95 thin films by spray pyrolysis technique

The Gd doped ceria (CGO) in thin layers is of great interest for low temperature operation. In the present investigation, we report on the use of spray pyrolysis technique for the synthesis of CGO thin films. The process parameters were optimized for synthesizing Gd_0.1Ce_0.9O_1.95 films. Films were characterized by XRD, EDS, SEM, and AFM and are observed to be phase pure and dense with surface roughness of the order of ∼5 nm. The d.c. conductivity was also measured and is observed to be ∼0.5 S/cm at 623 K.     

Characterization of CdTe films with in situ CdCl2 treatment grown by a simple vapor phase deposition technique

A unique vapor phase deposition (VPD) technique was designed and built to achieve in situ CdCl₂ treatment of CdTe film. The substrate temperature was 400 °C, and the temperature of CdTe mixture with CdCl₂ source was 500 °C. The structural and morphological properties of CdTe have been studied as a function of wt.% CdCl₂ concentration by using X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). XRD measurements show that the presence of CdCl₂ vapor induces (1 1 1)-oriented growth in the CdTe film. SEM measurements have shown enhance growth of grains, in the presence of CdCl₂. From AFM the roughness of the films showed a heavy dependence on CdCl₂ concentration. In the presence of 4% CdCl₂ concentration, the CdTe films roughness has a root mean square (rms) value of about 275 Å. This value is about 831 Å for the non-treated CdTe films.     

La1−xCaxCoO3 perovskite-type oxides: Identification of the surface oxygen species by XPS

A detailed study of the La_1−xCa_xCoO₃ perovskites surface by XPS was carried out since this is a potentially useful tool to identify the oxygen species involved in the catalytic reaction and discriminate them. Mainly, the concentration of surface oxygen vacancies (λ′) can be estimated from the XPS atomic ratio.     

Realization of Ultraviolet Electroluminescence from ZnO Homojunction Fabricated on Silicon Substrate with p-Type ZnO:N Layer Formed by Radical N2O Doping

ZnO homojunction light-emitting diodes are fabricated on Si（100） substrates by plasma assisted metal organic chemical vapour deposition. A p-type layer of nitrogen-doped ZnO film is formed using radical N2O as the acceptor precursor. The n-type ZnO layer is composed of un-doped ZnO film. The device exhibits desirable rectifying behaviour with a turn-on voltage of 3.3 V and a reverse breakdown voltage higher than 6 V. Distinct electrolumineseence emissions centred at 395nm and 490nm are detected from this device at forward current higher than 20mA at room temperature.     

Electro-optic characterization of tetragonal (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals by a modified Sénarmont setup

The refractive indices of tetragonal (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) single crystals were measured with a prism coupler and their linear electro-optic (EO) properties were investigated from 20 to 80 °C by the automated scanning Sénarmont system with an ac field. The composition and temperature effect on the EO coefficients were also discussed. It has been found that their EO coefficients are much larger than that of widely used LiNbO₃ single crystal and the calculated half-wave voltages are also much lower, which enable the operation at lower voltages and the smaller device dimensions. Since the excellent EO properties are very stable and such high quality single crystals with large-size have been obtained, the PMN-xPT single crystals are a very promising candidate for EO modulation applications. By linking to the polarization-related quadratic EO coefficients, we find that the linear EO properties are related with the spontaneous polarization and dielectric constants.