Search

Epitaxial growth of one-dimensional nanowires has received considerable attention for vertically aligned nanoelectronic devices; however, high integration and reproducibility are still significant ...

Controlling the interactions between cells and viruses is critical for treating infected patients, preventing viral infections, and improving virus-based therapeutics. Chemical methods using small molecules and biological methods using proteins and nucleic acids are employed for achieving this control, albeit with limitations. We found, for the first time, that retroviral DNA integration patterns in the human genome, the result of complicated interactions between cells and viruses, can be engineered by adapting cells to the defined nanotopography of silica bead monolayers. Compared with cells on a flat glass surface, cells on beads with the highest curvature harbored retroviral DNAs at genomic sites near transcriptional start sites and CpG islands during infections at more than 50% higher frequencies. Furthermore, cells on the same type of bead layers contained retroviral DNAs in the genomic regions near cis-regulatory elements at frequencies that were 2.6-fold higher than that of cells on flat glass surfaces. Systems-level genetic network analysis showed that for cells on nanobeads with the highest curvature, the genes that would be affected by cis-regulatory elements near the retroviral integration sites perform biological functions related to chromatin structure and antiviral activities. Our unexpected observations suggest that novel engineering approaches based on materials with specific nanotopography can improve control over viral events.

Anisotropic transition metal dichalcogenide (TMDC) domains have stimulated a growing interest mainly due to their electronic properties that depend on the size, shape, and edge structures of the domains. In this work, we investigated the anisotropic morphogenesis and edge terminations of tungsten diselenide (WSe 2 ) domains grown on sapphire substrates by chemical vapor deposition (CVD) using tungsten oxide (WO 3 ) and selenium (Se) powders as precursors. We varied the amount of Se powder and growth temperature during the CVD process, which in turn caused variations in the growth mechanism and kinetic energies of precursors. We succeeded in synthesizing hexagonal, square, circular, and triangular anisotropic WSe 2 domains. They were characterized using scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL) analyses, and atomic force microscopy (AFM). Furthermore, we proposed the growth mechanism of anisotropic WSe 2 domains with different edge terminations based on experimental observations through scanning tunneling microscope (STM).

Here, we investigated the relationship between the surface potentials and molecular interactions in the alucone films grown by molecular layer deposition. Varying the C-C bond order of the organic precursors induced variations in inter-molecular interactions, resulting in variation in the surface potential, associated with the work function of the films.

Exploration of the bioinspired silicification of artificial scaffolds is crucial to understanding and engineering the hierarchically complex and elaborate three-dimensional (3D) frustules of diatoms, which have high porosity and mechanical stability with related gas diffusion and storage properties. Herein, we report on the bioinspired silicification of the nanostructured surfaces of hexagonally close-packed silica bead (hc-SB) arrays using a liquid-phase deposition (LPD) method. This process, governed by the kinetics of silicification, was controlled using the concentration of the reactants and the reaction temperature and monitored in real time using a quartz-crystal microbalance, which allowed the investigation of the silicification on the surface during the LPD reaction. These heterogeneous LPD reactions on hc-SB arrays were optimized to mimic natural 3D hierarchical structures. Anisotropic silicification of the nanostructures occurred owing to differences in the energy and local concentration of silicic acid on the nanostructured surface. A 3D hierarchical pore network was realized via a heterogeneous LPD reaction by controlling the size, location, and arrangement of the SBs. We believe that our silicification process on nanostructured surfaces can lead to great improvements in the bioinspired morphogenesis-based engineering of 3D hierarchical structures.

Control over alignment and growth kinetics of vertically aligned Si nanowire (v-SiNW) arrays, which were grown using chemical vapor deposition (CVD) via a metal catalyst-assisted vapor–liquid–solid (VLS) mechanism, was demonstrated by introducing a homemade bubbler system containing a SiCl4 solution as the Si precursor. Careful control over the bubbler afforded different amounts of SiCl4 supplied to the reactor. By varying the dipping depth (Dd) and tilting angle (Ta) of the bubbler, the SiCl4 precursor concentration would fluctuate to different degrees. The different SiCl4 concentrations afforded the fine-tuning of v-SiNW array properties like alignment and growth kinetics. The degree of alignment of v-SiNWs could be increased with large amounts of SiCl4, which was caused by slight shallow depth or gentle tilting of the SiCl4 solution in the bubbler due to an increasing degree of fluctuation and fluctuation area. The ability to control alignment and growth kinetics of v-SiNW arrays could be employed in a...

Understanding of pore formation in porous anodic alumina is prerequisite for realizing its potential applications in the field of nanofabrication. Here, we explored the impurity-driven pore formation of porous anodic alumina via a two-step anodization process in acid solution with various applied voltages. We varied the purity of Al foil, and found that the branching and bending of pores displayed by low-purity Al foils are originated from an electric-field imbalance that results from the presence of impurities. Also, the pore formation mechanism and characteristic geometry induced by the impurities within the Al foil were investigated using experimental and simulation models.

The location-controlled epitaxial growth of vertically aligned Si nanowire (v-SiNW) arrays over large surface area was investigated with Au nanodisks (AuNDs) patterned by KrF stepper lithography. There are two steps for synthesizing v-SiNWs from an AuND pattern: annealing and growth. The annealing process induces the formation of a single Au nanoparticle (AuNP) from an AuND pattern, which consists of several cracked AuNPs. Here, the oxide layer between the AuNDs and Si substrate is necessary for impeding the diffusion of Si atoms into the AuNPs. However, the oxide layer must be removed for properly aligned epitaxial SiNW growth. These SiNW arrays in large area can contribute highly to improve a nanowire-based engineering by controlling the location of SiNWs with consistent pitch.

Uniformly c-oriented AlPO 4 -5 films were prepared on a glass substrate by a simple in-situ growth method. The water content of the synthesis gel played an important role in the synthesis of c -axis-oriented films that were perfectly aligned along the c -axis and exhibited high coverage. We also optimized the growth conditions by varying the reaction time and temperature, and suggested a simple and effective strategy for controlling the thickness of AlPO 4 -5 films. Furthermore, AlPO 4 -5 films with various thicknesses were obtained by adjusting the height and tilt angle of the substrate in the reaction vessel. We believe that this work provides a simple and effective pathway for controlling the thickness and orientation of AlPO 4 -5 films and can therefore expand the possible range of applications of molecular sieve films.

Single-crystalline InSb nanowires were synthesized on a SiO2wafer through the vapor-liquid-solid mechanism by using the chemical vapor deposition method. We also identified the effect of the source container system, closed- or open-boat, which contained SiO2 wafers, on the InSb powder, and the single-crystalline InSb nanowires were found to have different growth mechanisms. The structural characterization of the InSb nanowires was performed using a scanning electron microscope. The crystallinity and the composition of the InSb nanowires were investigated using X-ray diffraction and energy dispersive X-ray spectroscopy. We demonstrated that the InSb nanowires were thick and long, when an open-boat system was used, because the open-boat system can carry a greater amount of the vapor-phase InSb precursor than the closed-boat system. A high yield of the InSb nanowires can be obtained using the open-boat system. Additionally, the diameter of the InSb nanowires was quite thick because of the increased the growth time as a result of the dominant vapor-solid mechanism.

Single-crystalline InSb nanowire was synthesized on wafer via vapor-liquid-solid (VLS) mechanism using chemical vapor deposition method. According to the source container system (open or close) which contain InSb powder and wafer, the single-crystalline InSb nanowires have different growth mechanisms. Structural characterization of the InSb nanowires was examined by scanning electron microscope (SEM). Composition of the nanowires was investigated using x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS). This study demonstrates that length and diameter of the InSb nanowires are long and thick using open-boat system by VLS and additional vapor-solid (VS) mechanisms, because open-boat system can carry a large amount of vapor-phase InSb precursor than close-boat system.

The cross sections of multi-span beams are sometimes suddenly increased at the interior support of continuous beams to resist high negative moment. An earlier study on elastic lateral torsional buckling of stepped beams was conducted to propose new design equations. This research aims to continue the earlier study by considering the effect of inelastic buckling of stepped beams subjected to pure bending and general loading condition. A three-dimensional finite element-program ABAQUS and a statistical program MINITAB were used in the development of new design equations. The inelastic lateral torsional buckling strengths of 36 and 27 models for singly and doubly stepped beams, respectively, were investigated. The general loading condition consists of 15 loading cases based on the number of inflection point within the unbraced length of the stepped beams. The combined effects of residual stresses and geometrical imperfection were also considered to evaluate the inelastic buckling strengths. The proposed equations in this study will definitely improve current design methods for the inelastic lateral-torsional buckling of stepped beams and will increase efficiency in building and bridge design.

This paper extends the study made on determining the inelastic lateral torsional buckling strength of monosymmetric stepped I-beam in consideration of its degree of monosymmetry by making a destructive test while subjecting the beam to a concentrated load. Prior to the test, numerical values of the expected results are estimated by finite element analysis using the program ABAQUS. The numerical results are estimated by creating a model which experiences the same conditions as that of the test specimen. Then, a comparison is made with the experimental results, the results from the proposed equation and the results from the finite element analysis. In succession, the safety and economic feasibility of the proposed equation is evaluated. Finally, the comparisons made showed that the proposed equation yielded results that are acceptable and has values that are similar to the values yielded by the test. More tests are needed to determine if the proposed equation is also suitable for other loading conditions.

The cross-sections of continuous multi-span beams are sometimes suddenly increased or stepped at the interior supports of continuous beams to resist high negative moments. This paper investigates inelastic lateral-torsional buckling of monosymmetric stepped I-beams subjected to pure bending. A three-dimensional finite-element program ABAQUS and a regression program were used to analytically develop new design equation. The flange thickness ratio, flange width ratio and stepped length ratio were considered as parameters of this study. The combined effects of residual stresses and geometric imperfection on inelastic lateral-torsional buckling of beams are considered. The proposed solution can be easily used to calculation for inelastic lateral torsional buckling strengths of monosymmetric beams with doubly stepped cross sections and to develop new design equations for inelastic lateral-torsional buckling resistances of stepped beams. Key Words : Beam design, Doubly stepped beam, Inelastic buckling, Monosymmetric beam

Understanding metal alloy migration in metal-catalyzed nanowires growth is a prerequisite for improving its potential applications in the field of nanodevices. Here, we explored the surface migration of Au alloys in vertically aligned Si nanowires with different cooling rates. We varied the diameter of Au alloys by controlling the thickness of Au film as a catalyst for SiNW growth, and found that the behavior of Au alloys migration is dependent on size of Au alloys. In addition, the size-dependent migration mechanism of Au alloys was investigated at different cooling rates, which is related to different Au-Si eutectics.

Investigation of molecular interactions in polymeric films is crucial for understanding and engineering multiscale physical phenomena correlated to device function and performance, but this often involves a compromise between theoretical and experimental data, because of poor film uniformity. Here, we report the intramolecular and intermolecular interactions inside the ultrathin and conformal hybrid organic-inorganic alucone films grown by molecular layer deposition, based on sequential and self-limiting surface reactions. Varying the carbon chain length of organic precursors, which affects their molecular flexibility, caused intramolecular interactions such as double reactions by bending of the molecular backbone, resulting in formation of hole vacancies in the films. Furthermore, intermolecular interactions in alucone polymeric films are dependent on the thermal kinetics of molecules, leading to binding failures and cross-linking at low and high growth temperatures, respectively. We illustrate these key interactions and identify molecular geometries and potential energies by density functional theory calculations.

Development of methods enabling the preparation of uniformly aligned polymer thin films at the molecular level is a prerequisite for realizing their optoelectronic characteristics as innovative materials; however, these methods often involve a compromise between scalability and accuracy. In this study, we have grown uniformly aligned polyurea thin films on a SiO2 substrate using molecular layer deposition (MLD) based on sequential and self-limiting surface reactions. By integrating plane-polarized Fourier-transform infrared, Raman spectroscopic tools, and density functional theory calculations, we demonstrated the uniform alignment of polyurea MLD films. Furthermore, the selective-wavelength absorption characteristics of thickness-controlled MLD films were investigated by integrating optical measurements and finite-difference time-domain simulations of reflection spectra, resulting from their thickness-dependent fine resonance with photons, which could be used as color filters in optoelectronics.

This paper investigates inelastic lateral-torsional buckling strengths of I-beams with load height effects. The combined effects of residual stresses and geometrical imperfection on inelastic lateral-torsional buckling of beams are considered. The distribution of the residual stress in the cross-section is same as shown in Pi and Trahair(1995). The initial imperfection of the beam is set by a central displacement equal to 0.1% of the unbraced length of the beam. New moment gradient factors for load height effect of inelastic beams are very similar to the results from finite element analyses. The proposed equations will greatly contribute to calculate the inelastic lateral torsional buckling strengths with load height effect.

In this work, we report that high-density, vertically grown silicon nanowires (vg-SiNWs) direct a new in vitro developmental pathway of primary hippocampal neurons. Neurons on vg-SiNWs formed a single, extremely elongated major neurite earlier than minor neurites, which led to accelerated polarization. Additionally, the development of lamellipodia, which generally occurs on 2D culture coverslips, was absent on vg-SiNWs. The results indicate that surface topography is an important factor that influences neuronal development and also provide implications for the role of topography in neuronal development in vivo.

Nano-scaled metal oxides have been attractive materials for sensors, photocatalysis, and dye-sensitization for solar cells. We report the controlled synthesis and characterization of single crystalline nanowires via a catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) growth mechanism during TiO powder evaporation. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies show that as grown materials are one-dimensional (1D) nano-structures with a single crystalline rutile phase. Also, energy-dispersive X-ray (EDX) spectroscopy indicates the presence of both Ti and O with a Ti/O atomic ratio of 1 to 2. Various morphologies of single crystalline nano-structures are realized by controlling the growth temperature and flow rate of carrier gas. Large amount of reactant evaporated at high temperature and high flow rate is crucial to the morphology change of nanowire.

Herein, we investigated the wetting behavior of hexagonally close-packed polystyrene bead arrays with different bead diameters and surface flatness. The contact angle was found to be influenced by the surface roughness as well as the contact area of the polystyrene bead array with a water droplet.

Liquid phase deposition (LPD) is a useful method for the production of oxide film with low reaction temperature and production cost. With the report that the LPD of oxide films is conformally processed with uniform thickness and composition, there has been significant attention given to investigating its kinetic controls and growth mechanism on the flat surface. In this work, we explored the LPD of silicon dioxide on the hexagonally close-packed silica beads array as a nanostructured surface. The deposition and etching reactions of SiO2 occurred locally and simultaneously on silica beads, and were distinguished from the amount of fumed silica added in LPD solution. From locally competitive reactions, we obtained the anisotropic morphology of close-packed silica beads, and proposed a mechanism for the local LPD of SiO2 driven by nanostructured surfaces. This work contributes highly to improve metal oxide-based engineering, and also provide greater insight into the topography-driven LPD.

The epitaxial growth of 1D nanostructures is of particular interest for future nanoelectronic devices such as vertical field-effect transistors because it directly influences transistor densities and 3D logic or memory architectures. Silicon nanowires (SiNWs) are a particularly important 1D nanomaterial because they possess excellent electronic and optical properties. What is more, the scalable fabrication of vertically aligned SiNW arrays presents an opportunity for improved device applications if suitable properties can be achieved through controlling the alignment and density of SiNWs, yet this is something that has not been reported in the case of SiNWs synthesized from Au films. This work therefore explores the controllable synthesis of vertically aligned SiNWs through the introduction of an annealing process prior to growth via a Au-catalyzed vapor-liquid-solid mechanism. The epitaxial growth of SiNWs was demonstrated to be achievable using SiCl4 as the Si precursor in chemical vapor deposition, whereas the alignment and density of the SiNWs could be controlled by manipulating the annealing time during the formation of Au nanoparticles (AuNPs) from Au films. During the annealing process, gold silicide was observed to form on the interface of the liquid-phase AuNPs, depending on the size of the AuNPs and the annealing time. This work therefore makes a valuable contribution to improving nanowire-based engineering by controlling its alignment and density as well as providing greater insight into the epitaxial growth of 1D nanostructures.

We report the synthesis and characterization of layer-structure Bi2Se3 nanomaterials. Bi2Se3 nanomaterial has attracted many researchers, because it has a unique three-dimensional topological insulator property characterized by a metallic surface which coexists with an insulating interior. This can be achieved by having large surface-to-volume ratio in the nanomaterial. We synthesized highly single-crystalline topological insulator Bi2Se3 nanomaterials with various morphologies, including straight nanowires, zig-zag nanowires, and nanobelts, by adjusting experimental parameters such as the growth temperature, pressure, and carrier gas flow rate. The results show that the width and length of Bi2Se3 nanowires increase significantly with increasing values of each parameter. Furthermore, we studied the growth mechanism of individual morphologies based on the layered structure of Bi2Se3.

Cellular adhesion and growth on substrates with differing surface topography are known to induce unusual cell behaviors. Here, we investigated the adhesion and growth of human embryonic kidney 293T cells on vertically aligned silicon nanowires. Varying the diameter of nanowires affected their elasticity, which in turn caused variations in cell morphology and adhesion. Calculation of their elastic modulus revealed that long and thin nanowires are easier to deflect and thus provide more focal adhesion sites for adherent cells. And, induced mechanical tension triggered cellular anisotropic growth in the direction of tension, creating a greater rate of filopodium growth than was observed with a bare glass substrate devoid of mechanical tension. This nanotopographical approach provides important insights into the role of artificial substrates in the modulation of cell behavior and a conceptual framework for further analysis of substrate-induced changes in cellular activity. The elasticity of silicon nanowires is found to affect the shape and adhesion of embryonic kidney cells grown on the nanowires. The surface topography and mechanical properties of supports used to grow stem cells are known to affect cell behaviour. Now, Jin Seok Lee and co-workers at Sookmyung Women's University in Seoul, Korea, have shown that long, slender silicon nanowires that are easier to deflect provide more adhesion sites for human embryonic kidney cells than stiffer nanowires. They also found that the application of mechanical tension to the nanowires induced cells to grow along the direction of tension, giving higher growth rates than on tension-free surfaces. These findings provide important insights for guiding future studies of substrate properties used to control cell adhesion and growth. The cell adhesion and growth were studied on vertically aligned silicon nanowires with different diameter. Varying the diameter of nanowires affected their elasticity, resulting in a difference in cell morphology and adhesion. The formation of focal adhesion and anisotropic cell growth was promoted on thin silicon nanowires. Fluorescence analysis demonstrated that the cytoskeletal actin dynamics was affected by the mechanical tension of elastic nanotopography.