Synthesis of radial-aligned GaN nanorods by ammoniating Ga2O3 films on Mg layer deposited on Si(111) substrates

Radial-aligned GaN nanorods were synthesized by ammoniating Ga₂O₃ films on Mg layer deposited on Si(111) substrates. The products were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectra (FTIR) and high-resolution transmission electron microscopy (HRTEM). The SEM images indicated that the products consisted of radial-aligned GaN nanorods. The XRD and the selective area electron diffraction (SAED) patterns showed that nanorods were hexagonal GaN single crystals.     

Synthesis of single-crystal GaN nanowires on Si(111) substrate by ammonification technology

GaN nanowires have been synthesized on Si(111) substrate through ammoniating Ga₂O₃/BN films under flowing ammonia atmosphere at the temperature of 900 °C. The as-synthesized GaN nanowires were characterized by X-ray diffraction (XRD), selected-area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results demonstrated that the nanowires are hexagonal wurtzite GaN and possess a smooth surface with diameters ranging from 40 to 100 nm and lengths up to several tens of micrometers. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

Preparation of Li2B4O7 thin films by chemical solution decomposition method

Li₂B₄O₇ polycrystalline films on silica glass and Si(111) substrates were prepared by chemical solution decomposition(CSD) method. After spin coating, the wet film was dried at 200 °C, and then annealed at different temperatures to form polycrystalline Li₂B₄O₇ film. These annealed films were characterized by using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), transmission electron microscope (TEM) and selective area electron diffraction (SAED). All these results show that the main component of the film is Li₂B₄O₇ crystalline phase and the average crystalline size of these films is in the range of 20-50 nm.     

氮化ZnO/Ga2O3薄膜合成GaN纳米管

利用射频磁控溅射法在Si(111)衬底上先溅射ZnO中间层,接着溅射Ga2O3 薄膜,然后ZnO/Ga2O3薄膜在管式炉中常压下通氨气进行氮化,高温下ZnO层在氨气的气氛中挥发,而Ga2O3薄膜和氨气反应合成出GaN纳米管.X射线衍射(XRD)测量结果表明利用该方法制备的GaN具有沿c轴方向择优生长的六角纤锌矿结构.利用傅里叶红外光谱(FTIR)研究了所制备样品的光学性质.利用透射电子显微镜(TEM)和选区电子衍射(SAED)观测了样品的形貌和晶格结构.     

Crystal orientation changes of Ag thin films on the Si(111) substrate due to tribo-assisted recrystallization

Crystal orientation changes of Ag thin films due to the tribo-assisted recrystallization have been studied using grazing incidence X-ray diffraction with synchrotron radiation. After preparation of an Si(111) √3 × √3-Ag surface, a 5-nm-thick Ag film was deposited on the surface at the substrate temperature of 303 K in an ultra-high vacuum chamber. The friction experiments were carried out using a diamond pin-on-plate type tribometer just after the Ag deposition in the same UHV chamber. We found that the coefficient of friction of the Ag films on the Si(111) √3 × √3-Ag surface decreases from 0.07 to 0.03, with increasing reciprocal sliding cycles. In synchronization with the coefficient change, Ag{100} grains are gradually disappearing. As a result, the Ag{111} grains cover the entire surface after 50 sliding cycles. Moreover, we found that the domain size of the Ag{111} grains increases with increasing reciprocal sliding cycles by measuring the rocking curve width. These results directly show that the Ag(111) plane is the sliding plane of friction and the coefficient of friction of Ag films is determined by the fraction of the Ag(111) grains in the Ag films. Moreover, to clarify the reaction between the Ag film and the Si substrate due to the tribo-assisted recrystallization, the substrate strain has been studied by an extremely asymmetric X-ray diffraction technique using synchrotron radiation.     

Reflection high energy electron diffraction and X-ray studies of AlN films grown on Si(111) and Si(001) by organometallic chemical vapour deposition

The crystallinity of AlN films on silicon substrates grown by organometallic chemical vapour deposition was investigated using X-ray diffraction and reflection high energy electron diffraction (RHEED). Single-crystal films of good quality with atomically smooth surfaces can be epitaxially grown on Si(111) substrates. Epitaxial films can also be grown on Si(001) substrates. These films have previously been reported to have a fibre structure. Different RHEED patterns were observed from the films on Si(111) and Si(001). It is established that the films grown on Si(001) consist of two types of crystallite with the following orientations: [11$\text{2}$0]_AlN//[110]_Si and [11$\text{2}$0]_AlN//[1$\text{1}$0]_Si The thickness dependence of the crystallinity was also investigated. The standard deviation σ of the X-ray rocking curve for the films grown on Si(111) is less than that for the films on Si(001) and is independent of the film thickness. The σ values for the films on Si(001) decrease markedly with increasing film thickness. On the basis of these observations, the growth mechanism of AlN epitaxial films on Si(111) and Si(001) is discussed.     

硅基正六边形氮化镓纳米颗粒薄膜的制备,结构和形貌特性

本文通过在ZnO/Si(111)衬底上,利用JCK-500A型射频磁控溅射系统溅射氧化镓靶得到氧化镓薄膜.然后将硅基Ga2O3置于管武石英炉中,在850℃的氨化温度下氨化15min后,成功制备出GaN薄膜,该薄膜由正六边形的晶粒组成.X射线衍射(XRD)表明GaN具有六方纤锌矿结构,晶格常数为a=0.318nm和c=0.518nm.X射线光电子能谱(XPS)的测试确定了样品中Ga-N键的形成,并且Ga和N的化学计量比为1:1.用扫描电镜(SEM)和原子力显微镜(AFM)观察发现,样品表面非常光滑和平整.透射电镜(TEM)表明薄膜由正六边形晶粒组成.选区电子衍射(SAED)进一步验证了GaN薄膜的六方纤锌矿结构.最后,简单地讨论了其生长机制.     

Growth of diborides thin films on different substrates by pulsed laser ablation

The growth of scandium, titanium and zirconium diborides thin films by pulsed laser ablation technique on different substrates has been studied. In situ reflection high energy electron diffraction and ex situ X-ray diffraction analyses indicate that the films are strongly c-axis oriented on all the substrates and also epitaxial, apart from Si(111), where the in plane orientation is poor. Atomic force microscopy imaging reveals a flat surface in all the epitaxial samples, with roughness lower than 1 nm. The results on silicon carbide and sapphire are very promising for using these materials as buffer layers in magnesium diboride thin films growth, especially to improve epitaxy and to prevent oxygen diffusion from the substrate, and also to study the influence of lattice strain on MgB₂ critical temperature.     

电泳沉积法制备GaN薄膜的结构和组分分析

采用电泳沉积法在Si(111)衬底上制备出了GaN薄膜.用X射线衍射(XRD)、傅立叶红外吸收(FTIR)谱、X射线光电子能谱(XPS)和扫描电镜(SEM)对样品的结构、组分和形貌进行了分析.结果显示所得样品为六方纤锌矿结构的GaN多晶薄膜.     

Influence of growth parameters on the microstructures of erbium films deposited on Si(111) substrates

Erbium films were grown on single crystal Si(111) substrates by electron beam vapor deposition. The microstructures of the erbium films were systematically investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Results indicate that the surface morphologies and microstructures of the erbium films with Si as substrates are susceptible to the substrate temperatures when the deposition rates are fixed. The pure erbium films with columnar grains were obtained at temperatures below 200 °C, but in the films grown at temperatures higher than 350 °C, some pinholes that are composed of erbium silicides were found. The pinholes have triangular shapes which is in accordance with the geometry of the underlying Si(111) substrate. The films grown at a substrate temperature equal or greater than 450 °C have cracks which would be formed due to the different shrinkage degree of erbium and silicon when the substrate temperature was cooled down to room temperature. The films grown at 200 °C show the (002) preferred orientation, which is consistent to the prediction by the theory of surface energy minimization. The deposition rate and deposition time are considered as factors to affect the reaction of the erbium film and the silicon substrate.     

Si(111)衬底上6H-SiC薄膜的低压化学气相外延生长与表征

在Si(111)衬底上,采用SiH4-C3H8-H2气体反应体系,通过低压化学气相沉积(LPCVD)工艺外延出结晶质量良好的SiC薄膜.低温光致发光谱表明该薄膜属于6H-SiC多型体.X射线衍射图表明该薄膜具有高度的择优取向性.扫描电子显微镜图表明该薄膜由片状SiC晶粒组成.拉曼光谱和透射电子衍射谱的结果进一步表明该薄膜具有较高的结晶质量.对Si(111)衬底上6H-SiC薄膜的生长机制进行了初步探讨.     

Mechanical properties of amorphous and microcrystalline silicon films

Hydrogen-free amorphous silicon (a-Si) films with thickness of 4.5-6.5 μm were prepared by magnetron sputtering of pure silicon. Mechanical properties (hardness, intrinsic stress, elastic modulus), and film structure (Raman spectra, electron diffraction) were investigated in dependence on the substrate bias and temperature. The increasing negative substrate bias or Ar pressure results in simultaneous reducing compressive stress, the film hardness and elastic modulus. Vacuum annealing or deposition of a-Si films at temperatures up to 600 °C saving amorphous character of the films, results in reducing compressive stress and increasing the hardness and elastic modulus. The latter value was always lower than that for monocrystalline Si(111). The crystalline structure (c-Si) starts to be formed at deposition temperature of ∼ 700 °C. The hardness and elastic modulus of c-Si films were very close to monocrystalline Si(111). Phase transformations observed in the samples at indentation depend not only on the load and loading rate but also on the initial phase of silicon. However, the film hardness is not too sensitive to the presence of phase transformations.     

Synthesis and optical properties of single-crystalline GaN nanorods

Single-crystalline GaN nanorods were successfully synthesized on Si(1 1 1) substrates through ammoniating Ga₂O₃/Mo films deposited on the Si(1 1 1) substrate by radio frequency magnetron sputtering technique. The as-synthesized nanorods are confirmed as single-crystalline GaN with wurtzite structure by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Scanning electron microscopy (SEM) displays that the GaN nanorods are straight and smooth with diameters in the range of 100-200 nm and lengths typically up to several micrometers. X-ray photoelectron spectroscopy (XPS) confirms the formation of bonding between Ga and N. The representative photoluminescence spectrum at room temperature exhibits a strong and broad emission band centered at 371.1 nm, attributed to GaN band-edge emission. The growth process of GaN nanorod may be dominated by vapor-solid (VS) mechanism.     

Growth of PbS nanopyramidal particulate films for potential applications in quantum-dot photovoltaics and nanoantennas

We report a simple interfacial process called the liquid-liquid interface reaction technique (LLIRT) that leads to the formation of nanosized PbS particulate films with hitherto unreported pyramidal morphology. The resultant PbS films were characterized by transmission electron microscopy (TEM) with selected area electron diffraction (SAED), X-ray diffractometery (XRD), atomic force microscopy (AFM), near field scanning optical microscopy (NSOM) and UV-vis spectroscopy. The pyramidal morphology is speculated to originate from the preferred orientation of the 2 2 0 plane of cubic PbS. Our nanopyramidal PbS particulate films display remarkably sharp excitonic peak centered around 656 nm that accounts for a band gap of 1.8 eV suggesting, in turn, their potential application in QD photovoltaics. Interestingly, the feasibility of such nanopyramids to potentially act as nanoantennas (as revealed by the NSOM) is also suggested.     

Growth of SrTiO3 thin epitaxial films by aerosol MOCVD

SrTiO₃ thin films were prepared by aerosol metal-organic chemical vapour deposition on (001) MgO, R-plane Al₂O₃ and (001) Si single-crystal substrates. Strontium tetramethyl heptadionate and titanium n-butoxide dissolved in diethyleneglycol dimethyl ether were used as precursors. The structure of the films was investigated by X-ray diffraction and transmission electron microscopy. Epitaxial films with [001] and [111] orientation perpendicular to the substrate surface were obtained on MgO and Al₂O₃, respectively. The epitaxial films on the MgO substrate were found to be in a relaxed state with lattice parameters corresponding to the bulk values. SrTiO₃ films on the Si substrate were grown as highly textured in the [011]direction and randomly oriented in the plane parrallel to the substrate surface.     

Influence of substrate and Ar/N<Subscript>2</Subscript> gas flow ratio on structural,optical and electrical properties of TiN thin films synthetized by DC magnetron sputtering

Titanium nitride (TiN) thin films have been prepared by direct-current reaction magnetron sputtering technique on different substrates (glass and Si) and the influence of substrate and Ar/N₂ gas flow ratio on structural, optical and electrical properties of TiN thin films were discussed. X-ray diffraction suggested that with the ratio of Ar/N₂ decreasing, the diffraction intensity of (111) plane gradually diminished while (200) plane increased and films on Si substrate exhibited better crystalline quality than glass substrate. Improvement of Ar/N₂ ratio is contribute to enhance the deposition rate and the obvious surface roughness were observed when the ratio up to 49. Photoluminescence spectra showed that TiN films on Si substrate showed higher intrinsic emission and lower defect emission. Moreover, the resistivity of TiN films showed obviously decreasing as the flow rate ratio of Ar/N₂ increased, especially films on Si substrate.     

脉冲激光沉积方法生长硅基ZnO薄膜的特性

用脉冲激光沉积法(PLD)在n型硅(111)平面上生长ZnO薄膜.X射线衍射(XRD)在2θ=34°处出现了唯一的衍射峰,半高宽为0.75°;傅里叶红外吸收(FTIR)在414.92cm-1附近出现了对应Zn-O键的红外光谱的特征吸收峰;光致发光(PL)测量发现了位于370和460nm处的室温光致发光峰;扫描电子显微镜(SEM)和选区电子衍射(SAED)显示了薄膜的表面形貌以及晶格结构.利用PLD法制备了具有c轴取向高度一致的六方纤锌矿结构ZnO薄膜.     

Microstructural and textural characterization in MgO thin film using HRTEM

The microstructural and texture evolution of MgO protective films deposited on Si and glass substrates by ebeam evaporation were investigated. MgO films on both types of substrates consisted of a well developed columnar structure showing <111> texture in the cross sectional view and a triangle shape in the plane view. It was found that there is amorphous MgO between each columnar, which occupies 8-25% in the MgO films. The electron energy loss spectroscopy (EELS) spectrum of amorphous MgO showed features of chemical states and electronic structures different from those of crystalline MgO.     

Development of Crystal Al MKIDs by Molecular Beam Epitaxy

We report here the effect of film qualities in superconductors on the properties of Microwave Kinetic Inductance Detectors (MKIDs). The sensitivity of MKIDs between crystal aluminum films and amorphous aluminum films is compared. The good quality and crystallized aluminum films have been prepared by using molecular beam epitaxy. We have confirmed that epitaxial Al(111) films were grown on Si(111) substrates with X-ray diffraction and in-situ reflection high-energy electron diffraction measurements. The amorphous aluminum films on the Si(111) wafers have been deposited by electron beam evaporation. We have measured transmission losses of MKIDs, noise spectrum and relaxation time against optical pulses, changing MKIDs’ bath temperature from 0.11?K to 0.55?K in a dilution refrigerator. Despite of the improvement in normal resistivity, the quasiparticle decay time of both films are equivalent and 450?μs at 0.11?K. The electrical noise equivalent power of the both MKIDs are also comparable and around $10^{-17}~\mbox{W}/\sqrt{\mbox{Hz}}$ . Fabrication details and performance data of both films are presented.     

氨化温度对氨化Si基Ga2O3/Cr膜制备GaN纳米结构的影响

采用磁控溅射的方法在Si(111)衬底上溅射沉积Ga2O3/Cr膜,并通过氨化的方法在Si(111)衬底上成功合成了六方纤锌矿GaN纳米结构材料,研究了不同的氨化温度对合成GaN纳米材料的影响.采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HR-TEM)、傅里叶红外吸收(FTIR)光谱来检测样品的形态,结构和成分,并且讨论了GaN纳米结构的生长机理.研究结果表明,在Cr催化合成GaN纳米结构的过程中,氨化温度对其有重要影响,最佳温度是950℃.