Major Growth Direction Research Articles

SIMULATION AND FABRICATION OF Ag/ZnO-NANORODS/Ag ULTRAVIOLET DETECTORS ON p-TYPE SILICON

Hydrothermal method was successfully utilized to grow ZnO-nanorods on p-type silicon substrate. The highly dense grown ZnO-nanorods are well-aligned, and perpendicularly to substrate confirmed by scanning electron microscopy. The X-ray diffraction analysis confirmed that the [002] orientation was the major growth direction of the ZnO nanorods. A shadow masks have used to fabricate Metal–semiconductor–metal (MSM) structure. Three arrays of Ag interdigitated electrodes were then deposited onto the ZnO-nanorod/Si substrates. The current characteristics of [Ag/ZnO-nanorod/Ag]/Si devices were investigated range of -2 to +2 V. The as-fabricated devices showed a contrast ratio (i.e., the photocurrent/dark current) of 1.17 along with room temperature 0.115 mA/W responsivity at 365 nm and -2 V. A simulation analysis for the theoretical MSM structure has also been done in this work. A Visual TCAD was also used to simulate this device. A comparative study of experimentally and theoretically obtained results was also carried out and both results were found in good agreement of each other.

Morphologies of Primary Cu6Sn5and Ag3Sn Intermetallics in Sn–Ag–Cu Solder Balls

This article focuses on the morphologies of primary Cu6Sn5 and Ag3Sn intermetallics in small Sn–Ag–Cu (O $270~\mu \text{m}$ ) solder balls. The Cu6Sn5 phase showed a large variety of different shapes and sizes, ranging from facetted hexagonal rods, to partly facetted splitting crystals and parallel growing branches, to dendritic crystals without facets. The results of electron backscatter diffraction (EBSD) measurements confirm [0001] as the major growth direction and the { $10\bar {1}0$ } planes as facets of the hexagonal rods. The formation of crystals splitting parallel to the { $10\bar {1}0$ } planes may be caused by a slight deviation of the major growth direction toward $\langle 2\bar {1}\bar {1} 0\rangle $ . Primary Ag3Sn intermetallics showed less morphology variations and solidified as typical plate structures with a planar and an irregular side. Sixfold star-shaped formations of multiple plates arranged around a common center have been investigated by EBSD. All plates appear to have the same hexagonal orientation and possible growth directions are parallel to the { $10\bar {1}0$ } planes. However, these pseudohexagonal structures showed color differences between plates of different growth directions, if investigated with polarized light microscopy. Those orientation differences were not detectable by EBSD. Possible interpretations are discussed on the basis of the orthorhombic distorted lattice and by possible twinning mechanisms.

Contributions of the mechanical properties of major structural polysaccharides to the stiffness of a cell wall network model

The molecular mechanisms regulating the expansive growth of the plant cell wall have yet to be fully understood. The recent development of a computational cell wall model allows quantitative examinations of hypothesized cell wall loosening mechanisms. Computational cell wall network (CWN) models were generated using cellulose microfibrils (CMFs), hemicelluloses (HCs), and their interactions (CMF-HC). For each component, a range of stiffness values, representing various situations hypothesized as potential cell-wall-loosening mechanisms, were used in the calculation of the overall stiffness of the computational CWN model. Thus, a critical mechanism of the loosening of the primary cell wall was investigated using a computational approach by modeling the molecular structure. The increase in the stiffness equivalent of the CMF-HC interaction results in an increase in the Young's modulus of the CWN. In the major growth direction, the CWN stiffness is most sensitive to the CMF-HC interaction (75%). HC stiffness contributes moderately (24%) to the change in the CWN stiffness, whereas the CMF contribution is marginal (1%). Minor growth direction exhibited a similar trend except that the contributions of CMFs and HCs are higher than for the major growth direction. The stiffness of the CMF-HC interaction is the most critical mechanical component in altering stiffness of the CWN model, which supports the hypothesized mechanism of expansin's role in efficient loosening of the plant cell wall by disrupting HC binding to CMFs. The comparison to experiments suggests additional load-bearing mechanisms in CMF-HC interactions.

Characterizing microscale biological samples under tensile loading: Stress–strain behavior of cell wall fragment of onion outer epidermis

The results of published studies investigating the tissue-scale mechanical properties of plant cell walls are confounded by the unknown contributions of the middle lamella and the shape and size of each cell. However, due to their microscale size, cell walls have not yet been characterized at the wall fragment level under tensile loading. It is imperative to understand the stress-strain behavior of cell wall fragments to relate the wall's mechanical properties to its architecture. • This study reports a novel method used to characterize wall fragments under tensile loading. Cell wall fragments from onion outer epidermal peels were cut to the desired size (15 × 5 µm) using the focused ion beam milling technique, and these fragments were manipulated onto a microelectromechanical system (MEMS) tensile testing device. The stress-strain behavior of the wall fragments both in the major and minor growth directions were characterized in vacuo. • The measured mean modulus, fracture strength, and fracture strain in the major growth direction were 3.7 ± 0.8 GPa, 95.5 ± 24.1 MPa, and 3.0 ± 0.5%, respectively. The corresponding properties along the minor growth direction were 4.9 ± 1.2 GPa, 159 ± 48.4 MPa, and 3.8 ± 0.5%, respectively. • The fracture strength and fracture strain were significantly different along the major and minor growth directions, the wall fragment level modulus of elasticity anisotropy for a dehydrated cell wall was 1.23, suggesting a limited anisotropy of the cell wall itself compared with tissue-scale results.

Synthesis of Tungsten Oxide Nanoslab Bundles by Microwave Plasma-Enhanced Chemical Vapor Deposition

A large quantity of tungsten oxide nanoslabs was synthesized within 4 min by microwave plasma-enhanced chemical vapor deposition (MPECVD). The structural, geometrical, and chemical compositions of these nanoslabs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. The results of these characterizations confirmed that the nanoslabs with [010] as the major growth direction have a W18O49 structure with thicknesses of 30–50 nm, widths of up to 300–500 nm, and, lengths of up to 800–2000 nm. In XRD spectra, the reflection peaks are representative of monoclinic W18O49. A vapor–solid (VS) mechanism was confirmed for this growth process because no catalyst was used in this growth process.

Rapid formation of tungsten oxide nanobundles with controllable morphology

Tungsten oxide (W18O49) nanobundles with controllable morphology were fabricated on Si substrates within 5min by microwave plasma-enhanced chemical vapor deposition (MPECVD). The crystal structure and chemical composition of these nanobundles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The results of these characterizations confirmed the formation of W18O49 nanobundles with [010] as the major growth direction. SEM images showed that the nanobundles were several micrometers long with diameters of 20–500nm. The morphology of the nanobundles can be controlled by simply adjusting the reaction times to the desired level; nanowires (diameter: 15–30nm), nanorods (diameter: 40–60nm), and nanoslabs (thickness: 30nm) were formed at 1.5, 3, and 4min, respectively. With an increase in reaction times, the nanobundles steadily increased in dimensions to form nanoslabs. Thus, our results indicated that MPECVD is highly effective and suitable for fabrication of various tungsten oxide nanobundles.

Electrochemical Fabrication of InSb Nanowires using Porous Alumina Membrane and their Characterization

ABSTRACTAmong various ways to produce nanowires; anodic alumina membrane (AAM) based synthesis has constantly received much attention because AAM possess a uniform and parallel porous structure which makes them an ideal template material for creating highly ordered nanostructures. In this paper we report fabrication of InSb nanowire arrays with diameter of 200 nm and 30 nm by direct current electrodeposition inside the nanochannels of anodic alumina membranes without subsequent annealing. The nanowires have four major growth direction, [220] being the most dominant with structure defects such as twins. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results demonstrate that these InSb nanowires are uniform with diameters about 200 nm and 30 nm, corresponding to the pore diameter of the AAMs. The nanowires also conduct almost no current in the dark, but when hit with light, they conduct 10,000 times more current. This photoconduction property could lead to a variety of tiny optoelectronic devices potentially useful in future generations of nanoelectronics and chemical sensors. The light-induced conductivity increase and the temperature dependent behavior of the nanowires are also reported.

Preferred Orientation of Chemical Vapor Deposited Polycrystalline Silicon Carbide Films

We investigated the mechanism that determines the preferred orientation of polycrystalline silicon carbide (SiC) films prepared by CVD from a mixture of dichlorodimethylsilane (DDS) and He. X-ray diffraction (XRD) measurements indicated that the major growth direction is either the (220) or the (111) plane. We developed a numerical model for predicting the preferred orientation, assuming Langmuir-type adsorption and reaction of the growth species. This model suggests that the (111) plane appears under reaction-limited deposition, while the (220) plane appears under adsorption-limited deposition. Our experimental and numerical results show good qualitative agreement with experimental results for films prepared from methyltrichlorosilane (MTS) and H 2 .

Influence of structural variations on high-resolution electron microscopy images of poly[1,6-di(N-carbazolyl)2,4-hexadiyne] nanocrystals

Abstract High-resolution electron microscopy (HREM) was used to obtain information about structural variations in poly[1,6-di(N-carbazolyl)-2,4-hexadiyne) (polyDCHD) nanocrystals. Several particles in different crystallographic zones were imaged with high spatial resolution of up to 0.19nm, resulting in image information on a subunit-cell level (a = 1.74nm, b = 1.29nm and c = 0.49nm; β = 108.3°, P21/a; Z = 2). The average nanocrystal had a nominally rectangular shape and a size of about 40 nm × 80 nm with the major growth direction along the polymer chains (001). Most of the HREM images correspond to the [100] or [120] zone. In a few cases, it was also possible to image crystals oriented in the [001] zone with the polymer chain axis normal to the carbon substrate. Image interpretation was done by comparison with multislice HREM image simulations based on an approximation for the crystal structure and imaging conditions. These simulations performed for polyDCHD indicate that the HREM image is sensitive to ...

Observations of Microcrystalline Plagioclase Spherulites With the Transmission Electron Microscope

Two thin sections of macroscopic plagioclase spherulites of approximately 1 cm diameter found in a rhyolitic glass have been studied with the transmission electron microscope (TEM). Orientations of the thin sections were chosen to give views down and perpendicular to the major fiber axis. The crystalline fiber phase is high albite microtwinned on the (010) composition plane, elongated in the major growth direction, [001]. Fiber morphology is non‐polygonal with an average fiber diameter of 2000 Å perpendicular to c*. Fibers are separated by a non‐crystalline residuum layer of approximately constant thickness (300–500 Å). Microtwinning relationships, as well as selected area diffraction (SAD) patterns, reveal both crystallographic and non‐crystallographic branching with the former unexpectedly dominant.

Transmission electron microscope study of the bainite transformation in iron-chromium-carbon alloys

Thin foil electron microscope studies of lower bainite formed in two iron-chromium-carbon alloys have been carried out. One of these alloys (Fe-7.9% Cr-1.11% C) has been used previously for the X-ray measurements of the habit plane and the specific variant of the austenite-ferrite orientation relationship. These results have been confirmed in the present thin foil studies. Selected area diffraction and trace analysis studies of carbides in this bainite indicate that there are two types of carbides. One of these carbides precipitates on striations parallel to the major growth direction of the plate. The other carbide appears in the form of short transverse rods between these striations at an angle of 60–70° to the longitudinal direction in a manner characteristic of bainitic carbide in low alloy steels. While the structure of the carbides on the striations has not been uniquely determined, the short rods appearing between the striations were found to exhibit the usual orthorhombic structure of cementite. Trace analysis of the cementite rods shows that they appear to precipitate on a definite (112) ferrite plane. Electron diffraction patterns showing spots from austenite, ferrite, and cementite show that these structures are uniquely related. The ferrite-cementite relationship in this bainite is the standard one exhibited by tempered martensite and lower bainite in other alloys. No evidence of internal twinning was observed in this bainite. The above results have been analysed in terms of a shear model of step-wise lateral growth of the bainite plate. Comparative thin foil studies of lower bainite in a lower chromium alloy (Fe-3.3 Cr-0.66 C) were also made, which show that the mode of carbide formation is different in the two alloys.