超声搅拌化学浴沉积法制备大颗粒和致密的CdS薄膜

采用超声搅拌化学浴法(UCBD)在SnO2:F透明导电玻璃衬底上制备了CdS薄膜.研究了退火和CdCl2处理对UCBD-CdS薄膜的表面形貌、晶体结构和直接带隙的影响,比较了沉积时间对UCBD-CdS薄膜中CdS聚集体颗粒大小和堆积致密性的影响.结果表明,CdCl2处理可使CdS聚集体中的小颗粒重新熔合在一起,但CdS聚集体的大小并没有改变.在UCBD-CdS薄膜的沉积过程中,CdS薄膜的横向和纵向生长速率之比会随着沉积时间的不同而改变,且沉积时间是获得大颗粒的CdS聚集体和致密的UCBD-CdS薄膜的重要影响因素.当沉积时间为40min时,获得的UCBD-CdS薄膜较致密,CdS聚集体的大小为180nm,膜厚为80.8nm,适合作为薄膜太阳电池的窗口层.     

Preparation of combinatorial arrays of polymer thin films for transmission electron microscopy analysis

We present a new method for harvesting multiple thin film specimens from polymer combinatorial libraries for transmission electron microscopy (TEM) analysis. Such methods are of interest to researchers who wish to integrate TEM measurements into a combinatorial or high-throughput experimental workflow. Our technique employs poly(acrylic acid) plugs, sequestered in an elastomer gasket, to extract a series of film patches from gradient combinatorial libraries. A strategy for simultaneous deposition of the array of film specimens onto TEM grids also is described. We demonstrate our technique using nanostructured polymer thin film libraries as test cases in which the nanoscale details can be successfully imaged. Microscopy of test case specimens demonstrates that these samples are of sufficient quality for morphology screening via TEM, and in some cases are sufficient for more detailed morphological studies.     

Automated grain mapping using wide angle convergent beam electron diffraction in transmission electron microscope for nanomaterials

The grain size statistics, commonly derived from the grain map of a material sample, are important microstructure characteristics that greatly influence its properties. The grain map for nanomaterials is usually obtained manually by visual inspection of the transmission electron microscope (TEM) micrographs because automated methods do not perform satisfactorily. While the visual inspection method provides reliable results, it is a labor intensive process and is often prone to human errors. In this article, an automated grain mapping method is developed using TEM diffraction patterns. The presented method uses wide angle convergent beam diffraction in the TEM. The automated technique was applied on a platinum thin film sample to obtain the grain map and subsequently derive grain size statistics from it. The grain size statistics obtained with the automated method were found in good agreement with the visual inspection method.     

Thickness dependence of the structural,mechanical and electrical properties of Ni films deposited on polyimide by ion beam‐assisted deposition (IBAD)

Ni thin films with different thicknesses were deposited on pre‐treated polyimide substrates by ion beam‐assisted deposition. Dependence of structural, mechanical and electrical properties of the Ni films on their thickness was investigated. The results showed a clear correlation between film properties and film thickness. The inter‐diffusion at the interface regions of the films with different deposition time were demonstrated by transmission electron microscopy and X‐ray photoelectron spectroscopy. With increasing film thickness, surface roughness of the Ni films firstly decreased and then increased, while the grain size gradually increased. Residual stress of the Ni thin films decreased with increasing Ni film thickness up to 202 nm and then slightly increased as the film thickness further increased. Resistivity decreased, and temperature coefficient of resistivity (TCR) increased with increasing film thickness due to the enhancement of crystallization degree and the increase in grain size. The decrease in surface roughness and residual stress also contributed to the decrease of resistivity and the increase of TCR of the films. An optimal film thickness is suggested, which yielded a relatively high TCR value and low levels of both surface roughness and residual stress. Copyright © 2012 John Wiley & Sons, Ltd.     

Microstructures in High-Tc Bi-based Superconductors

Microstructures of high-Tc Bi-based superconductors in a disk form and a tape form sheathed by Ag are examined by SEM and TEM. The disk specimens were prepared by the sol-gel method and are compact with few cavities. Bi-2212 or Bi-2223 grains grow with short heating times leading to rapid increases in magnetization. However, magnetization drops with further heating due to the formation of 2201 areas in the 2212 matrix or 2212 areas in the 2223 matrix together with the amorphization within the matrix. In the tape specimens prepared by conventional powder processing methods, thin plate-like grains grow large with some cavities among them. The Jc increases together with the grain growth and then drops slowly as the amorphization of the grains occurs.     

Site-specific specimen preparation by focused ion beam milling for transmission electron microscopy of metal matrix composites.

This work describes the application and usefulness of the focused ion beam (FIB) technique for the preparation of transmission electron microscopy (TEM) samples from metal matrix composite materials. Results on an Aldiamond composite, manufactured by the squeeze casting infiltration process, were chosen for demonstration. It is almost impossible to prepare TEM specimens of this material by any other conventional method owing to the presence of highly inhomogeneous phases and reinforcement diamond particles. The present article gives a detailed account of the salient features of the FIB technique and its operation. One of the big advantages is the possibility to prepare site-specific TEM specimens with high spatial resolution. The artifacts occurring during the specimen preparation, for example, Ga-ion implantation, curtain effects, amorphous layers, bending of the lamella, or different milling behaviors of the materials have been discussed. Furthermore, TEM examination of the specimens prepared revealed an ultrafine amorphous layer of graphite formed at the interface between the Al and diamond particles that may affect the interfacial properties of the composite materials. This may not have been feasible without the successful application of the FIB technique for production of good quality site-specific TEM specimens.     

Improved sputter depth resolution in Auger composition‐depth profiling of polycrystalline thin film systems using single grain depth profiling

Today in‐depth profiling of microelectronics thin film systems is one of the important applications of Auger electron spectroscopy. It is used to monitor the elemental in‐depth composition after different manufacturing processes to control the quality of these processes. For instance, the layer interdiffusion and reactions with various process gases are analyzed. In addition, interface contaminations have to be controlled, because they strongly influence the properties of the whole thin film system. For polycrystalline layers, the depth resolution of sputter depth profiling is limited by the sputter yield differences attributed to grains having different crystalline orientations relative to the incoming ion beam. If depth profiling can be performed on single grains only, the poor depth resolution caused by these sputter yield differences can be avoided. Unfortunately, the approach works only on a few samples because single grains must be identified and have to have grain sizes that are in the dimensions of the layer thickness. Using methods of in situ sample preparation, however, allows application of single grain depth profiling to an extended range of thin film systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Imaging thin films of nanoporous low-k dielectrics: comparison between ultramicrotomy and focused ion beam preparations for transmission electron microscopy.

Ultramicrotomy, the technique of cutting nanometers-thin slices of material using a diamond knife, was applied to prepare transmission electron microscope (TEM) specimens of nanoporous poly(methylsilsesquioxane) (PMSSQ) thin films. This technique was compared to focused ion beam (FIB) cross-section preparation to address possible artifacts resulting from deformation of nanoporous microstructure during the sample preparation. It was found that ultramicrotomy is a successful TEM specimen preparation method for nanoporous PMSSQ thin films when combined with low-energy ion milling as a final step. A thick, sacrificial carbon coating was identified as a method of reducing defects from the FIB process which included film shrinkage and pore deformation.     

Characterization and electrochemical deposition of natural melanin thin films

Melanin is an important class of biological pigments because of its distinct chemical and physical properties. The electrochemical deposition of natural melanin thin films was studied using two different techniques; constant potential and cyclic voltammetry along with a deposition time of five hours. The thin films deposited electrochemically on a fluorine-doped tin oxide conductive glass substrate using the constant potential method, exhibited faster growth rate and better adhesion to the fluorine-doped tin oxide working electrodes than those deposited using the cyclic voltammetry method. The thin films deposited on the fluorine-doped tin oxide conductor glass using the constant potential method were also more homogeneous than those deposited via the cyclic voltammetry technique. The increase of film thickness is related to the increase of electrochemical deposition time. Interestingly, the electrochemical deposition using the constant potential method had the advantage of consuming less electric charge. The physical and chemical structures of the melanin thin films were characterized using ultraviolet–visible absorption spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. The ultraviolet–visible absorption spectra showed the correlation between the variation of deposition rates of melanin and the type of electrochemical technique employed as well as the thickness of the film. The average thickness of the film is 500 nm which absorb 40% of light in both type of films. The atomic force microscopy images illustrated the homogeneous deposition of the melanin molecules on the fluorine-doped tin oxide conductive glass substrate, indicating that the thickness of the thin films can be controlled. We estimated an average grain size of 14.093 Å. The ease of preparing such thin films of organic materials can open new avenues towards the use of soft conductors, in contrast to the complex preparation of industrial semiconductors.     

Surface structure and photoluminescence properties of AZO thin films on polymer substrates

Al‐doped zinc oxide (AZO) thin films were deposited on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering method at room temperature. The effects of film thickness on the surface structure and the photoluminescence properties of the films were investigated by atomic force microscopy (AFM), secondary ion mass spectroscopy (SIMS) and room temperature photoluminescence (PL). AFM analysis showed that the surface of all films was extremely flat and uniform at nanoscale. Root mean square (RMS) value of the surface roughness which scanned the surface area of 3 µm by 3 µm and grain size increased with increasing the film thickness. Thus, the surface morphology of the films became rough because of the coarse grains. The depth profile of AZO layers was analyzed by SIMS. It was found that the thickness of the AZO layer is almost same with the desired film thickness. The PL intensity of the dominant peak decreased and shifted slightly towards the shorter wavelengths with increasing the film thickness. According to the relationships between luminescence intensity and crystalline characteristics, it was observed that the intensity of the peak decreased by the increased surface area of the grains. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of B‐doped Si multiple delta‐layer reference materials for SIMS profiling

B‐doped Si multiple delta‐layers (MDL) were developed as certified reference materials (CRM) for secondary ion mass spectrometry (SIMS) depth profiling analysis. Two CRMs with different delta‐layer spacing were grown by ion beam sputter deposition (IBSD). The nominal spacing of the MDL for shallow junction analysis is 10 nm and that for high energy SIMS is 50 nm. The total thickness of the film was certified by high resolution transmission electron microscopy (HR‐TEM). The B‐doped Si MDLs can be used to evaluate SIMS depth resolution and to calibrate the depth scale. A consistency check of the calibration of stylus profilometers for measurement of sputter depth is another possible application. The crater depths measured by a stylus profilometer showed a good linear relationship with the thickness measured from SIMS profiling using the calibrated film thickness for depth scale calibration. The sputtering rate of the amorphous Si thin film grown by sputter deposition was found to be the same as that of the crystalline Si substrate, which means that the sputtering rate measured with these CRMs can be applied to a real analysis of crystalline Si. Copyright © 2005 John Wiley & Sons, Ltd.     

Improved focused ion beam target preparation of (S)TEM specimen--a method for obtaining ultrathin lamellae

Specimen quality is vital to (scanning) transmission electron microscopy (TEM) investigations. In particular, thin specimens are required to obtain excellent high-resolution TEM images. Conventional focused ion beam (FIB) preparation methods cannot be employed to reliably create high quality specimens much thinner than 20 nm. We have developed a method for in situ target preparation of ultrathin TEM lamellae by FIB milling. With this method we are able to routinely obtain large area lamellae with coplanar faces, thinner than 10 nm. The resulting specimens are suitable for low kV TEM as well as scanning TEM. We have demonstrated atomic resolution by Cs-corrected high-resolution TEM at 20 kV on a FIB milled Si specimen only 4 nm thick; its amorphous layer measuring less than 1 nm in total.     

Study of the Interface Microstructures of CVD Diamond Films by TEM

 The characteristics of the interface microstructures between a CVD diamond film and the silicon substrate have been studied by transmission electron microscopy and electron energy loss spectroscopy. The investigations are performed on plan-view TEM specimens which were intentionally thinned only from the film surface side allowing the overall microstructural features of the interface to be studied. A prominent interfacial layer with amorphous-like features has been directly observed for CVD diamond films that shows a highly twinned defective diamond surface morphology. Similar interfacial layers have also been observed on films with a <100> growth texture but having the {100} crystal faces randomly oriented on the silicon substrate. These interfacial layers have been unambiguously identified as diamond phase carbon by both electron diffraction and electron energy loss spectroscopy. For the CVD diamond films that exhibit heteroepitaxial growth features, with the {100} crystal faces aligned crystallographically on the silicon substrate, such an interfacial layer was not observed. This is consistent with the expectation that the epitaxial growth of CVD diamond films requires diamond crystals to directly nucleate and grow on the substrate surface or on an epitaxial interface layer that has a small lattice misfit to both the substrate and the thin film material.     

二氧化钛薄膜的液相沉积法制备研究

常温下,采用锐钛矿型二氧化钛纳米晶为诱导剂,采用液相沉积法制备了二氧化钛薄膜,采用XRD、SEM、AFM对其晶型、平均晶粒尺寸和形貌进行表征。结果表明,室温所制的二氧化钛薄膜为锐钛矿型,平均粒径为5．8nm,二次粒子平均粒径为10nm,薄膜上观察不到明显的孔洞和裂纹,表面均匀平整,以苯酚的光催化氧化作为目标反应,评价了二氧化钛薄膜的光催化活性。     

Structural and Photoluminescence Behaviors of Nano-Structure Thin Film and Bulk Silica Gel Derived Glasses

Nano-structure bulk and thin film silica gel derived glasses were prepared by sol-gel technique. Both samples were derived from the same precursor and subjected to the same heat-treatment regime. Structural information about prepared samples are obtained by analyzing the XRD patterns and TEM micrographs. The bulk samples phase changes from amorphous to -crystoballite at higher temperature (1300°C) than that in the thin film (500°C). The crystallite size depends to a large extent on the heat-treatment temperature. Bulk sample heat treated at 1400°C was as small as 10.4 nm. Thin film samples show higher response to heat-treatment temperature than the bulk samples, where the film is denser, has smaller pores and seems more homogeneous at lower temperature than bulk sample as revealed by SEM. The observed Raman spectra for bulk and thin film samples are in accordance with that of the -crystoballite. The Raman peak intensity is higher for thin film than bulk samples. The photoluminescence PL measurements for bulk samples show a broad intense peak at 532 nm combined with three weak peaks at longer wavelength 587, 635 and 666 nm. The PL peak intensity shows a reasonable decrease with increasing the heat-treatment temperature while the peak position shifted slightly to a lower wavelength. While the thin film samples show a unique peak at wavelength = 523 nm. The appearance of PL bands are interpreted on the light of non-bridged oxygen hole center as well as the structure defects.     

Elaboration and characterization of La2NiO4+δ powders and thin films via a modified sol–gel process

Polycrystalline thin films of La₂NiO_4+δ have been synthesized on yttria stabilized zirconia (YSZ) substrates by dip-coating using a polymeric sol. Crack-free films were obtained after sintering in air at temperatures ranging from 800°C to 1000°C. The microstructure, characterized by SEM, shows the formation of dense polycrystalline films with smooth surface and mean grains size of 140 nm, for films sintered at 1000°C. A correlation between grains size and non-stoichiometry in powders have been made in our processes. The thickness, evaluated for rugosimetry measurements, is thin (80 nm) and is a function of the viscosity of the sol. The higher the thickness, the higher the viscosity. As the non-stoichiometry level is controlled by the oxygen partial pressure, an evolution of non-stoichiometry in thin film has proposed. Then, it is possible by modifying synthesis and processing parameters to prepare thin films with a controlled microstructure (thickness, porosity and non-stoichiometry).     

Ultra thin films of nanocrystalline Ge studied by AFM and interference enhanced Raman scattering

Initial growth stages of the ultra thin films of germanium (Ge) prepared by ion beam sputter deposition have been studied using atomic force microscope (AFM) and interference enhanced Raman scattering. The growth of the films follows Volmer-Weber growth mechanism. Analysis of the AFM images shows that Ostwald ripening of the grains occurs as the thickness of the film increases. Raman spectra of the Ge films reveal phonon confinement along the growth direction and show that the misfit strain is relieved for film thickness greater than 4 nm. Dedicated to Professor C N R Rao on his 70th birthday     

Synthesis of thin dense titania films via an aqueous solution-gel method

Nanostructured titanium dioxide films have been reported to be used in many applications ranging from optics and solar energy devices to gas sensors. This work describes the synthesis of nanocrystalline titania films via an aqueous solution-gel method. The thin films are deposited by spin coating an aqueous citratoperoxo-Ti(IV)-precursor solution onto a silicon substrate. The influence of processing parameters like Ti⁴⁺ concentration and crystallization temperature on the phase formation, crystallite size and surface morphology of the films is studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, the effect of successive layer deposition on the film thickness of the resulting films is studied by means of cross sectional SEM. SEM and TEM micrographs clearly show that, after optimization of the process parameters, thin, smooth, dense nanocrystalline films are synthesized in a reproducible manner. The films are composed of 15–20 nm grains. At higher crystallization temperatures (600, 650°C) also larger particles (40–70 nm) are present. XRD data reveal that a phase pure anatase film is formed at 450°C. Crystallization temperatures equal to or higher than 600 °C however give rise to the formation of both the anatase and rutile crystalline phases. The smoothness of the films is proved by their very low rms surface roughness (≤1.1 nm) measured by AFM.     

Effect of short-chain branching on the morphology of LLDPE-oriented thin films

High-density polyethylene and randomly branched linear low-density polyethylene of varying branch length and content were used to produce oriented thin films. Sample morphology was investigated using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMA). Gelation studies suggested that the film preparation technique may have involved gel-drawing. DSC characterization of samples with approximately equal average branch content revealed very different melting behavior, suggesting differences in crystal size distributions. This was attributed to variations in the distribution of branches within samples. For similar branching distributions, the average melting temperature (and, similarly, crystal size) generally decreased as branch content increased. This was corroborated by TEM, with which crystal thickness was found to decrease as branch content increased. TEM further revealed that the lateral alignment of mosaic blocks and the resultant lamellar character of the thin films was obscured as branch content increased, a result of reduced crystal size, crystallinity, and possibly increased interphase content. DMA of compression-molded material revealed the presence of a beta peak in branched samples only. Moreover, the alpha transition temperature shifted to lower temperatures as branch content increased.