Surface studies on bimetallic thiocyanate ligand based single crystals of MnHg(SCN)4, CdHg(SCN)4 and ZnCd(SCN)4

Bimetallic SCN ligand based single crystals of manganese mercury thiocyanate (MMTC), cadmium mercury thiocyanate (CMTC) and zinc cadmium thiocyanate (ZCTC) are grown by slow solvent evaporation technique. The growth mechanism and surface features are investigated by optical microscopic techniques such as scanning electron microscopy (SEM) and atomic force microscopy (AFM). The laser induced surface damage measurements were carried out using a Q-switched Nd:YAG laser at 1064 nm with laser beam of 1.0 Hz and pulse duration 25 ps. The laser damage threshold values of MMTC, CMTC and ZCTC are found to be 15.9, 22.9 and 19.7 GW/cm², respectively. The SEM analysis of MMTC reveals the formation of elongated dendrite growth pattern caused by the fluctuations of Mn and Hg metal ligands when thiocyanate (SCN) bridges them. The etching study indicates the occurrence of different types of etch pit patterns like terraced triangles, pillars, pyramids and rods. The AFM images confirm the formation of three major hillocks with cavities in MMTC. The measured roughness values for CMTC crystal are very much lower than that of MMTC.     

Atom force microscopy study on HTHP as-grown diamond single crystals

For understanding the mechanism of diamond growth at high temperature–high pressure (HTHP) from a metallic catalyst–graphite system, it is of great interest to perform atomic force microscopy (AFM) experiments, which provide a unique technique different from that of normal optical and electronic microscopy studies, to study the topography of HTHP as-grown diamond single crystals. In the present paper, we report first AFM results on diamond single crystals grown from a Fe-Ni-C system at HTHP to reveal the growth mechanism of diamond single crystals at HTHP. AFM images for as-grown diamond samples show dark etch pits on the (111) surface, indicating dislocations. Some fine particles about 100–300 nm in dimension were directly observed on the (100) diamond surface. These particles are believed to have been formed through transition of graphite to diamond under the effect of the catalyst and to have been transported to the growing diamond surface through a metallic thin film by diffusion. The roughness of the (100) diamond surface is found to be about several tens of nanometers through profile analysis. The diamond growth at HTHP, in a sense, could be considered as a process of unification of these fine diamond particles or of carbon-atom-cluster recombination on the growing diamond crystal surface. Successive growth interlayer steps on the (111) diamond surface were systemically examined. The heights of the growth interlayer steps were measured by sectional analysis. It was shown that the heights of the growth interlayer steps are quite different and range from about 10 to 25 nm. The source of the interlayer steps might be dislocations. The diamond-growth mechanism at HTHP could be indicated by the AFM topography of the fine diamond particles and the train-growth interlayer steps on the as-grown diamond surfaces. Received: 29 March 2001 / Accepted: 20 August 2001 / Published online: 2 October 2001     

On the physical transformations of processed pharmaceutical solids

Atomic force microscopy Phase Imaging, an adaptation of Tapping Mode AFM was used to visualise physico-mechanical variations on the surface of crystalline materials after being subjected to mechanically induced lattice damage. Large crystals (100-500 microm) of lactose were nucleated on AFM sample stubs, imaged and subjected to a milling process. The milled samples were then imaged at specific humidity using Phase Imaging. Phase and Amplitude images of the re-crystallised lactose suggested an ordered crystalline state with multiple platelets present across the surface. In comparison, the morphology and surface properties after a 1-min mill time suggested milling had a dramatic effect on the surface characteristics of the re-crystallised lactose. Phase and Topographical imaging during exposure to elevated humidities (70% RH) indicated both morphological and physico-mechanical changes that may be linked to surface amorphous re-crystallisation.     

Investigation of heteroepitaxial diamond films by atomic force and scanning tunneling microscopy

We report on Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) investigations on chemical vapour deposited heteroepitaxial diamond films. Besides the good macroscopic crystal morphology a statistical tilt up to ±5.2° of the oriented crystallites has been found relative to the silicon substrates. By optimizing the process conditions, however, the crystal tilt of the films can be reduced, resulting in an improved film perfection. On crystallite (001)-surfaces a substructure of growth facets or islands has been found and high resolution STM images have established a 2×1 surface reconstruction on these growth facets. AFM and SEM were applied to study the morphology of diamond nuclei initially grown on the silicon substrate. Strong island like (Volmer-Weber) growth has been found, with a nucleus height to diameter ratio of 1:1. While the islands are growing in size with respect to time of nucleation, its aspect ratio does not change, due to the high surface free energy of the diamond relative to silicon.     

Atomic force microscopy of photochemistry and the Baeyer–Villiger reaction of 4,4′-dimethylbenzophenone in the solid state

Nanostructures are formed by photodimerization of crystalline 4,4^′-dimethylbenzophenone (1) through intermolecular hydrogen abstraction and Baeyer–Villiger reaction of 1 with m-chloroperoxybenzoic acid (MCPBA) (5) in the solid state. Atomic force microscopy (AFM) reveals that the crystal face (001) of 1 during photodimerization exhibits volcanoes, whereas the same face (001) of 1 yields both craters and volcanoes all over the surface from the contact edge of the crystals during the Baeyer–Villiger reaction. All the experimental results are correlated with the bulk crystal structure. Molecular interpretation of the AFM features of 1 is given. Received: 18 April 2000 / Revised version: 26 July 2000; accepted: 27 July 2000 / Published online: 30 November 2000     

Factors affecting phase and height contrast of diblock copolymer PS-b-PEO thin films in dynamic force mode atomic force microscopy

Asymmetric PS-b-PEO block copolymer exhibits well-ordered cylindrical morphology with nanoscale domain sizes due to microphase separation. Since the PS and PEO blocks have large stiffness difference, this polymer system represents an ideal candidate for studies of the phase contrast behavior in atomic force microscopy (AFM). In this paper, PS-b-PEO films are investigated under different scanning conditions using two different atomic force microscopes. It is found that the phase contrast of the film can be well described in terms of energy dissipation, though the exact phase image may also depend on the scanning parameters (e.g., the repulsive versus attractive regimes) as well as the settings of the microscope. Height variation on sample surface does not have significant effect on phase contrast. However, in order to obtain true topography of the polymer film, care has to be taken to avoid damage to the sample by AFM. Under certain conditions, true topography can be obtained during the first scan in spite of the surface-damaging forces are used.     

Writing of two-dimensional crystal curved lines at the surface of Sm2O3-Bi2O3-B2O3 glass by samarium atom heat processing

Two-dimensional crystal curved lines consisting of the nonlinear optical Sm_xBi_1−xBO₃ phase are fabricated at the surface of 8Sm₂O₃·37Bi₂O₃·55B₂O₃ glass by continuous wave Nd:YAG laser (wavelength: 1064 nm) irradiation (samarium atom heat processing) with a power of ∼0.9 W and a laser scanning speed of 5 μm/s. The curved lines with bending angles of 0-90° or with sine-shapes are written by just changing the laser scanning direction. The polarized micro-Raman scattering spectra for the line after bending are the same as those for the line before bending, indicating that the crystal plane of Sm_xBi_1−xBO₃ crystals to the crystal growth direction might be maintained even after the change in the laser scanning direction. It is found from laser scanning microscope observations that the crystal lines at the surface are swelled out smoothly, giving a height of about 10 μm.     

Synthesis of industrial diamonds using FeNi alloy powder as catalyst

Synthesis of diamond single crystals in Fe80Ni20 C system was carried out in a cubic anvil high-pressure and high-temperature apparatus. This paper reports that the surface morphology and inclusion distribution of the grown diamonds had been observed. It finds that the inclusions in cubic and octahedral diamonds radiated along certain crystal orientation, while the inclusion distribution in cubo-octahedral diamond seemed independent of crystal orientation. By using scanning electron microscope, the surface morphology of the three shapes of diamonds was observed. The results of Mossbauer spectrum indicated that there were iron-inclusions FeaC and Fe-Ni alloy in the diamonds. According to the Fe-C phase diagram, FeaC should have formed during the quenching process. Nickel might have an inhibitory effect on the formation of Fe3C.     

Molecular orientations and photorefractive effects in C60-doped liquid crystals with capillary-flow-induced alignment

Molecular orientations and photorefractive effects of C₆₀-doped nematic liquid crystals were investigated with layer-structured liquid crystal cells where a nematic phase was injected. Regardless of the surface treatments of the layers, liquid crystals injected with nematic phase showed a higher degree of director orientation and photorefractivity than those injected with an isotropic phase. The nematic alignment of liquid crystals in an untreated cell is generated by a capillary flow of liquid crystal during the nematic injection. However, it was observed that the grating formation was delayed a little longer with injection of nematic phase than with injection of isotropic phase. Received: 11 March 2002 / Revised version: 22 April 2002 / Published online: 12 July 2002     

Correlation between growth of high-index faces, relative growth rates and crystallographic structure of crystal

According to contemporary crystal growth theories, crystals are bound by low-index faces which are the most slowly growing. However, high-index faces are observed in crystal habits more and more often. In this paper the growth of high-index faces is analysed from a crystallographic perspective. It is shown that the crystallographic structure of a given crystal, expressed by the trigonometric function of appropriate interfacial angles, influences to great degree the crystallisation process and the morphology of crystals, in particular the behaviour of high-index faces. Additionally, it is concluded that at particular crystallographic structure of a crystal, a given high-index face may exist in the habit and develop its size, although it grows much faster than the neighbouring faces. Received 31 July 2001     

Enhanced atomic-scale contrast on Fe3O4 (100) observed with an Fe STM tip

Clean (100) surfaces of a synthetic single crystal of magnetite (Fe₃O₄) have been prepared in situ using current pulses in a scanning tunneling microscope without subsequent annealing. We have observed atomically resolved terraces with rows of Fe²⁺ and Fe³⁺ ions of the B-sublattice (octahedrally coordinated lattice sites). Along these rows a long-distance corrugation (∼12 ?) has been observed at 300 K using in situ prepared Fe tunneling tips. This corrugation is interpreted as a Wigner localization associated with a Verwey transition above 300 K in the top surface layer. Received: 26 September 2000 / Accepted: 27 October 2000 / Published online: 3 May 2001     

KrF excimer laser dry and steam cleaning of silicon surfaces with metallic particulate contaminants

KrF excimer laser-assisted dry and steam cleaning of single-crystal silicon wafers contaminated with three different types of metallic particles was studied. The laser fluence used was 0.3 J/cm². In the dry process, for samples cleaned with 100 laser pulses the cleaning efficiency was 91, 71 and 59% for Au, Cu and W particles, respectively, whilst in steam cleaning the efficiency is about 100% after 5 laser pulses, independently of the type of contaminant. The effects of laser irradiation on the Si surface are investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Laser processing at 0.3 J/cm² does not deteriorate the Si-wafer surface, either in dry or steam cleaning. However, the measured XPS intensity coming from the metallic component is greater on the cleaned surfaces than in the initial condition. Quantification of the XPS results, assuming a stratified overlayer model for the detected species and accounting for the presence of the metallic particles on the surface, showed that the obtained results can be explained by the formation of a fractional metallic monolayer on the cleaned surfaces, due to partial vaporisation of small particles initially present on the sample surface. This contamination of the substrate could be considered excessive for some applications and it shows that the process requires careful optimisation for the required efficiency to be achieved without degradation of the substrate. Received: 14 January 2001 / Accepted: 19 February 2001 / Published online: 20 June 2001     

On the crystal geometry influence on the growth of fast-growing surfaces

The external morphology of a given crystal is determined by the growth conditions, growth time and geometry of the crystal. Up to now, it has been believed that the growth conditions which influence the relative growth rates of surfaces play the key role in the formation of the final crystal morphology. In this paper, it is shown that the geometry of a given crystal, expressed by the trigonometric function of appropriate interfacial angles, may influence to a great degree the crystallisation process and the morphology of crystals. For example, it is shown that at particular geometry of a crystal, a given surface may exist in the habit and develop its size although it grows much faster than the neighbouring surfaces.     

微波合成银包覆金纳米粒子膜的拉曼散射活性研究

采用微波加热加压法和静电吸附自组装法在石英玻璃表面制备了银包覆金纳米粒子薄膜,利用原子力显微镜分析了薄膜的表面形态和结构,测定结晶紫分子在薄膜表面的拉曼光谱。结果表明,银包覆金纳米粒子薄膜具有很强的表面增强拉曼散射效应(SERS)活性和稳定性。     

Structural and physical properties of SrMn2As2

SrMn₂As₂ single crystals were grown by the Sn flux method. Structural features of these crystals were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that the single crystal has a rhombohedral structure and grows along the c-axis direction. The microstructure and layered structural features of this material have been examined by SEM and high-resolution TEM observations. The measurements of in-plane resistivity as a function of temperature demonstrate that SrMn₂As₂ undergoes a phase transition of semiconductor-insulator at a low temperature; the active energies are estimated to be Δ=0.64 and 0.29 eV for two distinct regions. Magnetic measurements show a clear antiferromagnetic (AFM) transition at about T_N=125 K. Therefore, the SrMn₂As₂ material is an AFM insulator at low temperatures and could be a potential parent compound for superconductors.     

掺钨VO_2薄膜的电致相变特性

采用直流磁控溅射与后退火工艺相结合的方法,在掺氟SnO_2(FTO)导电玻璃基底上制备了高质量的掺钨VO_2薄膜,对薄膜的结构、表面形貌和光电特性进行测试,分析了钨掺杂对其相变性能的影响.结果表明,室温下掺钨VO_2薄膜的阈值电压为4.2 V,观察到阈值电压下约有两个数量级的电流突变.随着温度升高,相变的阈值电压降低,且电流突变幅度减小.当施加8 V电压时,分别在不同温度下测试了掺钨VO_2薄膜的透过率.温度为20和50℃时,掺钨VO_2薄膜相变前后的红外透过率差量分别为23%和27%.与未掺杂的VO_2薄膜相比,掺钨VO_2薄膜具有相变温度低、阈值电压低和电阻率小的特点,在高速光电器件中有广阔的应用前景.     

Enhanced performance of a mutually pumped phase-conjugation setup using two photorefractive crystals

A mutually pumped phase-conjugator (MPPC) consisting of two photorefractive crystals is investigated experimentally at a wavelength of about 807 nm. In addition to a Rh:BaTiO₃ crystal, which is used in a modified bridge configuration for phase-conjugation, a Co:BaTiO₃ crystal is used to amplify the phase-conjugate beam by wave-mixing. The phase-conjugate power is at least doubled compared to that using only one crystal, and the beam quality of the phase-conjugate beam is distinctly improved. Moreover, the temporal stability of the phase-conjugate output using two crystals is much higher than that using only one crystal. Received: 7 December 2000 / Revised version: 12 January 2001 / Published online: 27 April 2001     

Surface morphology of MgO (100) crystals implanted with MeV Al+ and Al2+ ions

MgO (100) single crystals are implanted with 1.50-MeV Al⁺ and 3.00-MeV Al₂ ⁺ ions at a fluence of 1×10¹⁵ Al  atoms  cm^-2 under high-vacuum conditions. The surface morphology of the substrate is measured in air using atomic force microscopy and X-ray reflectometry followed by computer-simulated spectrum analysis. The ion-irradiated areas are found to protrude to different heights on the nanometre scale. Small height differences are observed in the areas irradiated by Al⁺ and Al₂ ⁺ ions of comparable energy, dose rate and total fluence. The results indicate that protrusions are most likely caused by implantation-induced point defects (vacancies) generated in the crystal during implantation. Other possibilities for the cause of protrusions are discussed. Thermal treatment stimulates a partial recovery of the implantation damage and alters the topography of MgO surfaces. Received: 22 May 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Enhancement of second harmonic generation efficiency: Cs(I)-doped tris(thiourea)zinc(II) sulphate crystals

The effect of dopant cesium (Cs(I)) over a concentration range from 1 to 10 mol% on the growth process, morphology, thermal and optical properties of tri(thiourea)zinc(II) sulfate (ZTS) single crystals grown by slow evaporation solution growth technique has been investigated. Incorporation of Cs(I) into the crystal lattice was well confirmed by energy dispersive X-ray spectroscopy (EDS). The lattice parameters of the as-grown crystals were obtained by single crystal X-ray diffraction analysis. The reduction in the intensities observed in powder X-ray diffraction patterns of doped specimen and slight shifts in vibrational frequencies in fourier transform infrared spectra (FT-IR) indicate the lattice stress as a result of doping. Thermal studies reveal the purity of the material and no decomposition is observed up to the melting point. High transmittance is observed in the visible region and the cut-off λ is ～280 nm. The surface morphology of the as-grown specimens was studied by scanning electron microscopy (SEM). The second harmonic generation (SHG) efficiency of the host crystal is enhanced greatly in the presence of high concentrations of the dopant.     

Scanning force microscopy of ion-irradiated organic single crystals of benzoyl glycine

Single crystals of the amino acid benzoyl glycine (hippuric acid) are irradiated normal to the as-grown surface by highly charged Bi ions with a kinetic energy of 2.38 GeV and a fluence of 1×10¹⁰ ions/cm². The projectiles create circular craters with a mean diameter of 40 (10) nm on the surface of the crystal as observed by scanning force microscopy (SFM). The mean depth amounts to 4 (1) nm, this value being considered as a lower limit due to the finite radius of curvature of the force cantilever tip. Thus, on the average, each single-ion projectile seems to eject about 10⁴ molecules. On the surface of non-irradiated crystals, SFM reveals terraces of a few monolayers in height. In water, it was possible to visualize the lattice periodicity. Terraces were also observed on the irradiated crystal surface in the presence of the craters, indicating that the crystal is still intact at the given dose. Received: 25 May 2000 / Accepted: 26 May 2000 / Published online: 13 July 2000