Grain boundary chemical structure of high purity α silicon carbide was investigated by an atomic resolution high voltage transmission electron microscope (ARHVTEM). Each of a ‘darker’ spots and each of the ‘brighter’ spots in the image have been identified to be silicon (Si) and carbon (C). Two (0001)/(1107) Σ 9 CSL grain boundaries were observed. One boundary showed a rigid body translation of 1/3 <1100> to the component crystals and the other did not. The unit period of the boundary was determined to 2.26 nm along >1120<. Two 6-membered, four 5-membered and 7-membered rings build up the boundary. Each ring consists of three C-C pairs, one Si-Si pair and non-paired Si atoms. In the case without the rigid body translation the number of lone Si atoms are four and only two Si atoms were determined in the other case. The observed structures suggest that the chemical structure of a grain boundary dominantly influences the grain boundary energy.

We have developed a nanostructure manipulation device (NSMD) to apply tension to a single nanoparticle chain aggregate (NCA) mounted in a transmission electron microscope. The system was used for studying stretching and contraction of carbon chain aggregates. Carbon NCAs generated by laser ablation of a graphite target were stretched and bent using the NSMD. The NCA was stretched up to 310% of its initial length before becoming taut and then breaking. The broken NCA contracted rapidly showing its elastic behavior. The NCA was plastically deformed during stretching through unraveling of kinks along the NCA. However, the unraveling was irreversible so that the chain formed a loop with a big curvature as its two ends were brought closer together.

The I-V characteristics of small Sin clusters and short C20 chains between atomistic Al leads were calculated using a new ab initio transport code based on a nonequilibrium Greens function formalism. All of the Si diaplay metallic I-V characteristics with typical conductances ranging between tow and three (units Go = 2e2/h). The transport properties of these molecular devices may be understood in terms of both the bandstructure ofelectrodes, and the molecular levels of the clusters as modified by the lead environment. Turning to the short C20 chains, these behave as short C20 chains, these behave as short nanowires whose tranmission depends sensitively on the orientation and distance between the individual C20 molecules. Transport through the molecular chains is accompained by a significant amount of charge transfer, which however remains localized at the electrode/molecular interface.

The morphology and the atomic structure of a hexagonal gallium nitride (h-GaN) grain boundary was investigated employing a conventional TEM and an atomic resolution high voltage transmission electron microscope (ARHVTEM).

GaN was grown on a patterned GaAs (001) substrate by the metalorganic vaporphase epitaxy (MOVPE) method using selective area growth (SAG) and epitaxial lateral overgrowth (ELO) process. The pattern mask was aligned along [110] direction of the GaAs (001) substrate. Cubic GaN (c-GaN) grew in the window of the patterned substrate. h-GaN was nucleated on the {111} plane of the c-GaN and grew in the lateral direction to fabricate a grain boundary in the halfway between two masks. The resulting symmetric tilt grain boundary was a Σ 9 CSL boundary. The boundary plane was in most cases parallel to the {3308} plane. Structural analysis revealed that the boundaries consist of ordinary 6-memebered rings and some 5-membered and 7-membered rings. Additionally, the expected atomic bonding angle deviates from the experimental findings. The different bonding angle was attributed to contributions of ionic bonding in GaN.

We investigated the interplay between different mechanisms of the lateral and vertical segregation in the synthesized via “grafting from” approach symmetric A/B (where A and B are poly(styrene-co-2,3,4,5,6-pentafluorostyrene) and poly(methylmethacrylate), respectively) polymer brushes upon exposure to different solvents. We used X-ray photoemission electron spectroscopy and microscopy (X-PEEM), AFM, water contact angle measurements, and oxygen plasma etching to study morphology of the brushes. The ripple morphology after toluene (nonselective solvent) revealed elongated lamellar-like domains of A and B polymers alternating across the surface. The dimple-A morphology consisting of round clusters of the polymer A was observed after acetone (selective solvent for B). The top layer was enriched with the polymer B showing that the brush underwent both the lateral and vertical phase segregation. A qualitative agreement with predictions of SCF theory was found.

Nanostructured thin film multilayers, comprising of alternating A/B layers, can exhibit metastable structures in one or both layers. From a classical thermodynamic viewpoint, the reduction interfacial energy is primarily responsible for this stabilizing effect. Based on this idea, a model has been constructed in which phase stability regions are represented as functions of both the bilayer thickness and volume fraction of the one the layers. Applying this classical thermodynamic model to a single, previously reported hcp to bcc transformation in Zr for Zr/Nb multilayers, a phase stability diagram was proposed. Various Zr/Nb multilayers with different bilayer thicknesses and volume fractions have been sputtered deposited. hcp to bcc transformations in the Zr layer were confirmed by x-ray and electron diffraction. Furthermore the Zr/Nb stability diagram predicted a novel hcp Nb phase which was subsequently verified experimentally. Using Zr/Nb as a guide, a similar phase stability diagram was constructed and experimentally determined for Ti/Nb multilayers. For each multilayer system, the reduction in interfacial energy was calculated from the experimentally determined diagram. These values were then compared to estimations of the structural component of the interfacial energy. The structural component was based on the energy per unit area of a misfit dislocation network constructed by an o-lattice. This simple assesment suggests that the reduction of the structural component of the interfacial energy is sufficient to drive the transformation.

The structure and chemistry of interfaces and grain boundaries are known to influence the optical and electrical properties of wide-band gap semiconductors structures. ZnO/AlN/Si(100) heterostructures grown by laser deposition were studied by conventional and high-resolution transmission electron microscopy (HRTEM). The local electronic structure of ZnO grain boundaries was investigated by high resolution Z-contrast imaging using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy in a scanning mode. Zcontrast imaging and EELS were performed simultaneously enabling direct correlations between interface chemistry and local structure to be made. ZnO grain boundaries are composed of a periodic array of a basic structural unit. On the basis of the electron energy-loss near-edge structure (ELNES) of zinc and oxygen edges associated with the ZnO- grain boundaries, the corresponding electronic spectrum was discussed.

Electron-energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) was used to measure nm-scale composition variations in Ge/Si(100) islands grown by molecular beam epitaxy (MBE) at substrate temperatures 400°C ≤T ≤700°C and a growth rate of 1.4 ML/min (1 monolayer, ML=6.78x1014 atoms / cm2). These measurements were correlated with island ensemble morphology determined by atomic force microscopy (AFM). The average Si concentration of the islands and Si/Ge interface width increased monotonically with growth temperature. Integrated island volumes measured by AFM were proportional to the equivalent Ge coverage, øGe, with slopes greater than one for the higher deposition temperatures. This result confirms that the islands grow faster than the Ge deposition rate. Linear behavior of the island volume vs. øGe curves implies that the average Ge composition is independent of island size. The volume at which islands change shape from pyramids to domes correlates well with the average Ge content of the islands in the context of simple strain-scaling arguments. For T=700°C, rapid Si interdiffusion precludes formation of pure Ge pyramids for growth at 1.4 ML/min. Growth at 4.8 ML/min kinetically stabilizes pure Ge pyramid clusters, allowing their formation prior to Si interdiffusion.

Four series of YAG:Ce phosphor powders were synthesized by solid state, co-precipitation, and sol-gel (with two different growth inhibitors, HMDS and PAA respectively) methods, which results in the average particle sizes of 800, 56, 43, and 32 nm respectively. All the nano-scale YAG powders were heat treated below 1000_. Both TEM and XRD results of these nano-scale YAG powders show high degree of crystalline structure. Photoluminescence (PL) characterization shows that the nano-scale YAG phosphor powders emit a higher intensity of luminescence than that of sub-micro sized samples. The effect of different Ce doping level on the PL of (Y3-xCex)Al5O12 shows a maximum at x ∼ 0.01. The Commissiom International de I.Eclairage (CIE) chromaticity coordinates were determined and show different trends of shifts in the resulting PL spectra. Systematic study of the processing parameters characterized by DTA/TGA, XRD, FTIR, and BET will be discussed in detail in the report.

A computationally convenient Green's function method is described for calculation of strain characteristics of quantum dots in an anisotropic semi- infinite solid containing a free surface. Semi-analytic expressions are derived for the strain field due to a quantum dot, strain energy of a quantum dot, and strain- field interaction between 2 quantum dots. Numerical results are presented for the strain field due to a quantum dot in GaAs. It is shown that the effect of the free surface, which has been neglected in earlier calculations using Green's function methods, is quite significant.

The application of exit-plane wave function (EPWF) images for an atomic-scale compositional mapping of interfaces in the GaAs-AlAs system is investigated. Image simulations based on the multislice algorithm were performed to obtain EPWF images over a wide range of compositions and specimen thicknesses. The EPWF-amplitude images were further analyzed by the method of factorial analysis of correspondence. A simultaneous analysis of the effects both thickness and composition on image contrast yielded two eigenvectors representing the individual contributions from the two effects. This separation was however not complete, leaving a residual contribution from thickness on the composition-sensitive eigenvector and vice versa. Extraction of the chemical content from the composition-sensitive eigenvector is still possible by a parameterization of the residual thickness contribution. A simpler procedure for quantifying the composition across an interface is proposed based on the analysis of images of AlxGa(1-x)As with different Al/Ga composition but same specimen thickness.

Ge-rich Si1-XGeX nanocrystals are formed by the selective oxidation of Si during the dry oxidation of an amorphous Si0.7Ge0.3 layer. The oxidation kinetics of the alloy film shows the activation energies of linear and parabolic rate constants are about 1.35 and 1.02 eV, respectively, based on the model proposed by Deal and Grove. In addition, as a result of the selective oxidation of Si and Ge pile-up during the oxidation process, Ge-rich Si1-XGeX nanocrystals are formed with the size of 5.6 ± 1.7 nm and the spatial density of 3.6×1011/cm2 at 600°C. At higher temperature of 700 and 800°C, the size of nanocrystal is increased to about 20 nm. The nanocrystals formation by oxidation is thought to be due to higher oxidation rate at grain boundary than at bulk grain. Therefore, the dependence of size on temperature is explained with the grain size determined by solid phase crystallization of amorphous film, oxidation rate, and grain growth.

Obtaining electronic and atomic structure of material simultaneously is very important for developing the nano-technology. In this paper, we demonstrate that atomic and electronic structure of an interface can be extracted with combination of Gerchberg-Saxton indirect microscopy and electron spectroscopy imaging (ESI) technique. Basically, Gerchberg-Saxton algorithm includes two projections. Projection in the real space is a maximum entropy (ME) de-convolution process and in reciprocal space is an amplitude substitution process. It has been shown that Gerchberg-Saxton algorithm can extend the structural resolution to near 0.1nm. An application case of Gerchberg-Saxton algorithm to solve the atomic structure for 3C-polytypic SiC boundary is shown.

ESI spectrum processed by FFT interpolation, maximum entropy de-convolution and wavelet transformation allow us to extract 2-dimensional map of the sp2/sp3 with a sub-nanometer resolution. Grain boundary and interface at SiC are good candidates for this study, since the bond distance of Si-C is slightly less than 0.1nm which is not routinely resolvable using a FEG TEM and Si-L (99eV) and C-K-edges (283 eV) locate in a reasonable energy range. The resultant electronic structure can be compared with that calculated using WIEN97. An example of quantitative analysis on 2-dimensional sp3/sp2 map deduced from the C K-edge of ESI spectra acquired from 6H-SiC is given.

Understanding the mechanical behaviour of metallic nanostructures is a key issue for their development. On the one hand, knowledge of the plastic behaviour at various temperatures is essential to control the synthesis, forming, and machining of such materials. Equally, a clear understanding of atomic and mesoscopic mechanisms, involving defects and their interactions, is essential for the control of ageing and functional properties. Regarding plastic deformation at room temperature, there is now evidence for unusual behaviour in nanostructured metals. In addition to high resistance and ductility, tensile testing reveals peculiar elasto-plastic deformation. Such behaviour was initially attributed to grain-boundary sliding. However, intergranular areas (including triple junctions) may possess special properties compared to their microcrystalline counterparts. For example, low activation energies have been measured for grain-boundary diffusion and it has been observed that grain-boundaries may act as dislocation sources and nucleation sites for deformation twinning.

In this paper, we report on analysis on bulk copper nanostructures. Grain-boundaries are studied, by cross-correlating information from mechanical tensile testing and structural analysis, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Macroscopic bulk specimens (with grain size of about 80 nm) are prepared by powder metallurgy techniques, modified to fit to the special properties of nanocrystalline powders. Processing includes coldisostatic pressing, sintering and differential extrusion. The powders used (grain size of 40 nm) are synthesised by evaporation and cryo-condensation of a metallic vapour within liquid nitrogen. Results on mechanical testing and structural analysis will be reported. Emphasis will be placed on the structure of grain-boundaries (type of grain-boundary, grain-boundary thickness) studied by TEM and high resolution TEM image analysed using the geometric phase technique. The nanostructure was revealed to be consist in agglomerate of nano-size grains separated by low angle grain-boundaries. Agglomerates are themselves separerated by general high angle boundaries. These observations will then be related to the unusual mechanical true stress-true strain curves of the metallic nanostructures.

Using a gas mixture of propyne (C3H4) and ammonia (NH3) as a carbon precursor, we have successfully synthesized multiwalled carbon nanotubes (CNTs) by the direct current (dc) plasma enhanced chemical vapor deposition (PECVD) onto Co-sputtered glass at 550°C. As the flow ratio of NH3 to C3H4 in the mixture gas increased, the crystallinity and alignment of CNTs were improved. In addition, the field emission characteristics of CNTs were also improved. the turn-on voltage became lower, and the current density and the field enhancement factor were more increasing. Raman spectroscopy and scanning electron microscopy were utilized to confirm the effect of the gas flow ratio on CNTs. Therefore, the gas flow ratio was found to be one of important factors to govern the crystalline and field emission characteristics of CNTs. The growth mechanism of CNTs using a C3H4 gas is under investigation with the possibility that three carbon atoms in a C3H4 molecule is converted directly to a hexagon of a CNT by combining two molecules.

Full Potential Linearized Augmented Plane Wave calculations have been performed for epitaxial multilayers formed by the noble metals Ag and Cu with a thickness n up to 10 layers. The multilayers have a fcc lattice and are pure or compositionally modulated with a structure of the type Agn Cun or (AgCu)n. For n in the range 2,3 the density of states, evaluated at paramagnetic level, exhibits a sharp reduction of the bandwidth which is consistent with the reduced coordination of these structures. For n ≤ 5 the density of states in the central layers converges to the bulk value while the outer layers retain the narrow bandwidth found at n=2. Due to the absence of charge intermixing and hybridization, these features are shared by multilayers of all composition.

Layered nickel-sulfides (Ni-S) nanocrystals had been successfully prepared by lowtemperature hydrothermal approach. Rietveld X-ray diffraction (XRD) analysis revealed that these layered Ni-S materials have two different hexagonal structure phases, NiS1.03 and NiS, both phases are NiAs-type with space group of P63/mmc. X-ray energy dispersive spectra (XEDS) analysis and TEM observations also confirmed these two nanocrystals of NiS1.03 and NiS. High-resolution transmission electron microscopy (HREM) lattice images indicated moiré fringes with rotational or translational patterns were observed in these layered Ni-S nanophases materials. In particular, it was found that all the simulated HREM images were in good agreement with the observed HREM lattice images. Especially, the simulated SAED patterns obtained from the hexagonal Ni-S crystallographic model showed that the experimental SAED patterns taken along [11.0], [00.1] and [10.0] zone axes presented reflections produced by double diffraction effect.

We used a high current density focused electron beam to modify a GaAs substrate. To avoid any oxidation or carbon contamination problem, an in-situ electron gun, combined with III-V molecular beam epitaxy (MBE) machine, was used. By changing the substrate temperature and the electron beam dwell time on each spot, different sizes of thermal irradiation marks were created. Fabricated spot-diameters in the sub-micrometer range suggest the possible utilization of this process for novel applications with the MBE growth technique.

A series experiments were conducted and reported here on how to employ quartz crystal microbalance (QCM) as a highly mass sensitive sensor to study a-Si film and Si nanocrystals oxidation under ambient oxygen. An experimental calibration procedure has been developed to prevent problems with QCM systems during routine study. With the help of pulsed laser deposition (PLD) technique, one can purposely deposit a thin layer of a heavy element as an insitu calibrant which can be analyzed by RBS quantitatively for QCM. The errors resulted from manufacture's sensor, non-repeatable sensor mounting and handling, temperature cycling history from run to run and so on will be effectively eliminated. Our preliminary results indicate that the oxidation process of a-Si thin films has two stages. A fast oxidation associated with surface and near surface oxidation followed by a slow oxidation. The former is depends on the oxygen vapor pressure in the chamber and the later is oxygen diffusion controlled process.

We investigate quantitatively the non periodic arrangement of atom columns surrounding an obtuse angle dislocation reaction in gold utilizing a CM200 FEG instrument equipped with a spherical aberration corrector. The in-plane component of the Burgers vector of the observed stair-rod dislocation is ⅙ [110]. Column positions are determined from single lattice images and compared with those from a reconstructed electron exit wave. We find that absolute position measurements of 1–3 pm require knowledge of the defocus to better than 1 nm which can be achieved by a reconstruction of the exit-plane wave. In contrast, a defocus value of 8.9 nm already leads to apparent displacements as large as 35 pm if single lattice images are considered. Such discrepancies are either caused by residual lens aberrations or by the superposition of delocalization effects at interfaces caused by defocusing of the objective lens. Commonly, however, only relative displacements are of interest. In this case the CS corrector improves the interpretability of single defocused lattice images with a remarkable signal to noise ratio which is advantageous for in-situ experiments. As an example for analyzing in-situ experiments we determine displacements recorded in a time resolved experiment of radiation induced atom motion on surfaces.