物理气相输运法生长AlN六方微晶柱

采用物理气相输运法(Physical Vapor Transport, PVT), 在1700 ~ 1850℃生长温度下制备出AlN六方微晶柱; 晶柱长度在1 cm左右, 宽度在200 ~ 400 μm, 光学显微镜下观察为六棱柱形状并呈透明浅黄色光泽; 扫描电子显微镜和原子力显微镜测试表明: AlN晶柱表面为整齐台阶状形貌, 台阶宽度为2 ~ 4 μm, 高度在几个纳米; 拉曼光谱测试AlN晶柱具有良好结晶质量。PVT 法生长AlN六方微晶柱主要是在偏低温度下AlN晶体生长速率较慢, Al原子和N原子有足够时间迁移到能量较低位置结晶生长, 进而沿着<0001>方向形成柱状结构。AlN六方微晶柱是对一维半导体材料领域的补充, 通过对晶柱尺寸及杂质控制的进一步研究, 有望在微型光电器件领域表现出应用价值。     

TiB2超硬薄膜的合成及性能

采用离子束溅射方法制备了ＴｉＢ２硬质薄膜，ＡＦＭ观察表明薄膜表面非常光谱，ＡＥＳ、ＸＲＤ和ＸＰＳ分析证明薄膜中主要是Ｂ、Ｔｉ比为１．８，六方结构的ＴｉＢ２多晶体、且呈现强烈的（１０１）择优取向，由超显微压痕测量系统测得的加载、卸载曲线计算得到的薄膜的显微硬度比高达４８ＧＰａ     

Effects of substrate parameters on structure and optical properties of ZnO thin films fabricated by pulsed laser deposition

Highly oriented zinc oxide thin films have been grown on quartz, Si (1 1 1) and sapphire substrates by pulsed laser deposition (PLD). The effect of temperature and substrate parameter on structural and optical properties of ZnO thin films has been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectra and PL spectra. The experimental results show that the best crystalline thin films grown on different substrate with hexagonal wurtzite structure were achieved at growth temperature 400–500 °C. The growth temperature of ZnO thin film deposited on Si (1 1 1) substrate is lower than that of sapphire and quartz. The band gaps are increasing from 3.2 to 3.31 eV for ZnO thin film fabricated on quartz substrate at growth temperature from 100 to 600 °C. The crystalline quality and UV emission of ZnO thin film grown on sapphire substrate are significantly higher than those of other ZnO thin films grown on different substrates.     

Novel concept for the aggregation structure of fatty acid monolayers on the water surface and direct observation of molecular arrangements in their monolayers

The aggregation structure of fatty acid monolayers on water subphases of different pH’s was investigated by means of transmission electron microscopy. Fatty acid monolayers exhibited the phase transition from an amorphous state to a crystalline one by surface compression in the case of a highly dissociated state of hydrophilic groups, whereas they did not show the phase transition in the case of a slightly dissociated state. The aggregation structure of monolayers on the water surface was systematically classified into “the crystalline monolayer”, “the amorphous monolayer” and “the compressing crystallized monolayer” with respect to thermal and chemical (intermolecular repulsive) factors. Molecular-resolution images of fatty acid molecules in the monolayers on mica substrate were successfully observed with an atomic force microscope (AFM) for the first time. The AFM image of a lignoceric acid monolayer prepared at a surface pressure of 5mNm⁻¹ showed a two-dimensional periodic structure with locally disordered molecular arrangements. Also, the nondestructive AFM image observation was successful for a stearic acid monolayer which was prepared by a multistep creep method, indicating that a high mechanical stability of the monolayer is inevitably required for the nondestructive AFM observation.     

Structure and microstructure of combustion synthesized MgO nanoparticles and nanocrystalline MgO thin films synthesized by solution growth route

In this work we describe the synthesis, micro structure (XRD, SEM, AFM) of magnesium oxide nanoparticles and magnesium oxide thin films synthesized by urea-based combustion method and solution growth route using magnesium nitrate as the source of Mg. We used fuel-to-oxidizer ratio (Ψ) as a control parameter to investigate how lattice parameter, particle size, and micro strain vary with Ψ = 0.25–2 in the steps of 0.25. Earlier we have studied NiO as a substitutional solute in MgO (Rao KV, Sunandana (2005) Solid State Phys 50:235). The average crystalline size of MgO was estimated from the full width half maximum (Gaussian and lorentzian fits) of the X-ray diffraction peaks using Sherrer’s formula and Williamson–Hall plot. The particle size varies from 15(±0.3) nm to 60(±1.2) nm as Ψ is varied systematically. Surface areas of the MgO powders measured using BET method were used to calculate the particle size, which is comparable with the crystalline size calculated from XRD. We also calculated porosity and microstrain in the MgO nanoparticles with varying Ψ. Thin films of MgO are well characterized from XRD and AFM. The size of the particles and RMS roughness of the thin films were calculated using AFM.     

Antiferromagnetic domain reconfiguration in embedded LaFeO3 thin film nanostructures

Using photoemission electron microscopy in combination with X-ray magnetic linear dichroism, we report reconfiguration upon nanostructuring of the antiferromagnetic domain structure in epitaxial LaFeO3 thin films. Antiferromagnetic (AFM) nanoislands were synthesized using a dedicated process, devised to define nanostructures with magnetic order embedded in a paramagnetic matrix. Significant impact on the AFM domain configuration was observed. Extended domains were found to form along edges parallel to the in-plane <100> crystalline axes of the cubic substrate, with their AFM spin axis parallel to the edge. No such edge-imposed domain configuration was found for nanoislands defined with the edges at 45° with the in-plane crystalline axes. Epitaxial constraints on the film crystalline structure appear to play an important role in the formation of the edge-bound extended AFM domains. The data indicate a magnetostatic origin of this domain reconfiguration.     

Electrodeposited Thin Film ZnTe Semiconductors for Photovoltaic Applications

The electrodeposition of zinc telluride thin films on tin conductive oxide substrates in aqueous solution containing TeO₂ and ZnCl₂ was studied. The electrodeposition mechanism was investigated by cyclic-photovoltammetry. The appropriate potential region where formation of stoichiometric ZnTe semiconductor occurs, was found to be close to _-0.75 V vs. SCE. Annealing of the as-deposited films was carried out at 400^°C to obtain a crystalline phase. The crystallographic structure and film morphology were studied by XRD and SEM analyses, respectively. ZnTe films have the hexagonal structure of wurtzite and they are characterized by good homogeneity. A direct energy gap of 2.25 eV was determined by NIR-VIS-UV spectroscopy, in close agreement with the energy gap of ZnTe single crystals. A fractal dimension of 2.4 was determined by AFM analysis of ZnTe films. The mechanism of the thin film growth has been interpreted in terms of diffusion limited aggregation model.     

射频磁控反应溅射制备ZnO/AlN双层膜的结构和性能

采用射频磁控反应溅射在Si（100）衬底上制备了ZnO/AlN双层膜。使用X射线衍射仪、原子力显微镜（AFM）、LCR测试仪及荧光分光光度计等仪器对样品进行了结构、表面形貌、导电性及荧光光谱的测试,并与相同工艺下制备的ZnO单层薄膜进行了对比研究。结果表明,ZnO/AlN双层膜的c轴择优取向性优于单层ZnO薄膜,薄膜应力更小,且为压应力,晶粒尺寸大于单层膜,表面粗糙度较小,并且其电阻率更低。荧光光谱显示,ZnO/AlN双层膜的结晶质量更好。     

Pressure-induced polymorphous crystallization in bulk Si20Te80 glass

The effect of pressure on the electrical resistivity of bulk Si₂₀Te₈₀ glass has been studied up to a pressure of 8 GPa. A discontinuous transition occurs at a pressure of 7 GPa. The X-ray diffraction studies on the pressure quenched sample show that the high pressure phase is crystalline with hexagonal structure (c/a = 1.5). On heating, the high pressure hexagonal phase has on exothermic decomposition atT = 586 K into two crystalline phases, which are the stable phases tellurium and SiTe₂ obtained by simple heating of the glass.     

Thin films of rare-earth metal silicides in microelectronics

Structure, phase composition and physical properties of thin films of rare-earth metal (REM) silicides (of Y-subgroup) have been studied. The films were formed on (100) and (111) single-crystal Si substrates. X-ray diffraction analysis reveals the formation of a crystalline silicide phase of LnSi_2−x composition with hexagonal structure of the AIB₂-type for all metals except Sc, Gd, Lu. It is established that the crystalline silicide phase formation is determined by the crystallographic orientation of the Si substrate and that there is a relation between crystallographic parameters of REM silicide (REMS) and Si hexagonal lattices: the critical value of lattice parameter mismatch is ± 1.3%, above which REMS has a disordered structure. The kinetics of the silicide phase growth was determined by measuring the conductance of thin-film structures. A model of REMS formation in thin-film structures on an Si substrate is proposed. Based on the model, conditions have been found for the formation of either quasi-amorphous, polycrystalline or monocrystalline REMS layers. The formation of a REMS amorphous film is most probable on a (100) substrate for such metals as Gd and Lu. Epitaxial growth of REMS films is typical of Tm, Er, Ho on (111) substrates. Also, investigation of the current transport in surface barrier diodes of the REM-p-Si and REMS-p-Si types shows that the potential barrier lowers as a result of silicide formation in REM-Si contacts and, accordingly, the silicide work function increases as compared with that of the initial metal. The photoelectric measurements indicate that the silicide-Si contact photosensitivity shifts to a longer optical wavelength as compared to that of the metal-Si contacts.     

Effect of post annealing on structural and optical properties of ZnO thin films deposited by vacuum coating technique

We report the effect of annealing temperature on structural, electrical and optical properties of polycrystalline zinc oxide thin films grown on p-type silicon (100) and glass substrates by vacuum coating technique. The XRD and AFM measurements confirmed that the thin films grown by this technique have good crystalline hexagonal wurtzite structures and homogenous surfaces. The study also reveals that the rms value of thin film roughness increases from 6 to 16 nm, the optical band gap increases from 3.05 to 3.26 eV and resistivity from 0.3 to 5 Ωcm when the post-deposition annealing temperature is changed from 400 to 600 °C. It is observed that ZnO thin film annealed at 600 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Fabrication of an inorganic nano structure for a large area via electrohydrodynamic lithography (EHL)

Electrohydrodynamic lithography (EHL) is one of several unusual lithographic techniques for fabricating sub-micrometer structures over a large area. EHL uses the electrohydrodynamic (EHD) film instability induced by a laterally modulated electric field, which allows it to fabricate not only general organic structures but also structures of various components, such as diblock copolymers and inorganic materials, without contact between the resist and the stamp. Furthermore, EHL is a very special lithographic technique in that diverse structures are fabricated from one stamp via electric field modulation. The electric field is controlled by the replication time, air layer thickness, etc. A replicated inorganic structure was demonstrated from a hexagonal hole and line arrays. The heat treatment of the replicated pattern was carried out to obtain the crystalline phase, after which the samples were characterized via Raman spectroscopy. These values were ascertained using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The results will be useful in providing a facile route for patterning functional metal oxides over a large area. Such a technique can be used to produce photovoltaic cells, memory devices, display devices, etc.     

Solidification of metallic aerosol droplets from floating rafts: a test of the spiral growth mechanism for Cd and Zn

The strain energy developed by surface stresses in a crystalline raft of basal orientation floating on a droplet of melt is calculated and compared to the strain energy of a screw dislocation situated on the raft axis. The suggestion that a dislocation is generated at a characteristic value of the raft/drop radius ratio is tested by making the comparison for arbitrary values of raft aspect ratio and Burgers vector. When b = c, the lattice parameter of the hexagonal crystal, the energies are equal at a combination of aspect ratio and radius ratio that fits experiment. The apparent height of the helical growth step greatly exceeds this value of b and remains to be explained, but the results confirm that a high growth rate anisotropy is required initially to produce the dislocation.     

Synthesis of ZnO nanowires by the hydrothermal method,using sol–gel prepared ZnO seed films

Zinc oxide (ZnO) nanowires with various morphologies are synthesized by the hydrothermal method on silicon substrates coated with ZnO thin films. The ZnO films are used as the seed layer and are prepared using the sol–gel technique. Experimental results demonstrate that the synthesis of ZnO nanowires is dependent on the crystalline properties of the ZnO seed-layer films. Sol concentration is the controlled parameter for the preparation of ZnO seed-layer films in this study. The ZnO films are found to have the hexagonal wurtzite structure with highly preferred growth along the c-axis at suitable sol concentrations. The vertically aligned ZnO nanowire arrays on the substrates are believed to be the result of the epitaxial growth of the ZnO seed layer. Scanning electron microscopy shows that nanowires with uniform distribution in length, diameter, and density are obtained. X-ray diffraction patterns clearly reveal that the ZnO nanowires are primarily grown along the c-axis direction. Transmission electron microscopy and selected-area electron diffraction measurements show that the nanowires have good crystalline properties. The well-aligned and high surface areas of the ZnO nanowires make them a potential candidate for applications in solar cells, field emission devices, and ultra-sensitive gas sensors.     

Synthesis of ultrafine lanthanum hydroxide nanorods by a simple hydrothermal process

Lanthanum hydroxide (La(OH)₃) nanorods with 6–15 nm in width and 200–400 nm in length have been prepared by a simple hydrothermal process. X-ray diffraction (XRD) shows that the nanorods are of hexagonal structure, and furthermore, high-resolution transmission electron microscopy (HRTEM) identifies that the lanthanum hydroxide nanorods are highly crystalline. Moreover, the mechanism for the hydrothermal synthesis of lanthanum hydroxide nanorods has been preliminarily presented.     

铝阳极氧化膜纳米孔阵列的微细结构

用电化学阳极氧化法制备了纳米多孔铝阳极氧化膜(AAO模板).采用原子力显微镜(AFM)测试AAO膜,研究了纳米孔阵列的形成机制.结果表明,在AAO膜的表面,除存在六方形的纳米孔阵列外,在孔端还存在六个微小的隆起,相邻的隆起之间彼此相连,看上去酷似一朵盛开的梅花,花的中心就是六方形纳米孔.二维AFM图像显示,以往用扫描电镜表征的纳米孔阵列,实际上是一幅排列整齐、并呈周期性变化的梅花阵列图案.膜背面阻挡层的AFM二维图像表明,膜胞呈六方形,且排列高度有序.膜胞密度为4.3×109/cm2,与孔密度基本一致.阻挡层的三维照片显示,膜胞的底部存在半球状突起,也呈现出规整的阵列图案.     

The effect of molecular weight on the deformation behaviour of pressure annealed polyethylene

The deformation behaviour of four different grades of polyethylene has been examined as a function of the morphology produced by pressure annealing in the vicinity of the orthorhombic–hexagonal phase boundary. It is concluded that annealing within the hexagonal phase, to produce a “chain-extended” morphology, is appropriate for high molecular weight material as a precursor step in the production of high modulus by solid phase deformation. In low molecular weight material of the same morphology solid phase deformation does not produce improvements in mechanical behaviour. These results are interpreted in terms of the competition between increasing crystal size and the decrease in the coherence of the molecular network brought about by the pressure annealing. The critical parameter is the ratio of lamellar size to number average molecular chain length, rather than lamellar morphology. When this parameter is greater than 0.5 the molecules are incapable of completing two crystalline traverses and the network is affected detrimentally to the extent that it no longer holds the material together. This revised version was published online in November 2006 with corrections to the Cover Date.     

Scanning probe microscopy of intrafibrillar crystallites in calcified collagen

Vertebrate mineralized tissues are composite materials formed by the organized growth of carbonated apatite crystals within a matrix of collagen fibres. Calcified collagen from turkey tendon was investigated using scanning tunnelling microscopy (STM) and atomic force microscopy (AFM). Samples were treated with hydrogen peroxide to enhance the mineralized phase by removing part of the collagen matrix and the results compared with the untreated material. Plate-like crystalline entities with dimensions 35 nm × 5–8 nm by 1.5 nm were seen. These dimensions are consistent with previous reports using transmission electron microscopy (TEM) of calcified tendon and topographic imaging of tendon crystals. The resolution of the images obtained using STM is better than the previously reported pictures obtained using TEM or scanning electron microscopy (SEM). The value of 35 nm is the same as the gap region in the structure of the collagen fibrils. Stacking of plates and plate-aggregates are a dominant feature in the scanning images. These results support the concept of organized intra-fibril mineral crystals within the organic collagen matrix. Electron diffraction and X-ray diffraction were undertaken on the samples and the patterns recorded match those previously reported for carbonated apatite.     

Controlling the phase composition of cadmium sulfide films during pulsed laser deposition

Thin cadmium sulfide films grown by pulsed laser deposition on crystalline and amorphous substrates have been shown to consist of a mixture of a cubic (sphalerite structure) and a hexagonal (wurtzite structure) phase. We have demonstrated the possibility of controlling the percentages of the hexagonal and cubic phases in cadmium sulfide films by varying pulsed laser deposition parameters. Varying the deposition parameters allows one to control the optical and structural parameters and surface morphology of thin cadmium sulfide films.     

Superhydrophobic properties of cotton fabrics functionalized with ZnO by electroless deposition

Cotton fabrics were coated with arrays of ZnO hexagonal prisms using an electroless (catalytic/autocatalytic) deposition process. A typical three step method, similar to those used for electroless deposition of metals on insulating substrates, consisting of pre-activation, activation and deposition steps was employed. The low-dimensional ZnO particles were grown from an aqueous solution containing zinc nitrate as source of zinc ions and dimethylamineborane as reducing agent. The as-obtained ZnO-coated cotton fabrics were characterized from the point of view of structure by X-ray diffraction (XRD) and morphology by scanning electron microscopy (SEM). The XRD studies demonstrate that the ZnO particles have a hexagonal wurtzite crystalline structure. The SEM observations prove that the cotton fibers are homogeneously covered by hexagonal prisms which have uniform base size of approximately 500 nm and height of 1 μm. Optical spectroscopy measurements show that the functionalization with ZnO strongly decreases the transmittance in the UV–vis region of the cotton fabrics. An important characteristic is that the ZnO-functionalized cotton fabrics exhibit superhydrophobicity, with water contact angles exceeding 150°. The technique described is highly reproducible, easy scalable and cheap, allowing a wide range of applications.