Control over Alignment and Growth Kinetics of Si Nanowires through Surface Fluctuation of Liquid Precursor

Control over alignment and growth kinetics of vertically aligned Si nanowire (<i>v</i>-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 (<i>D</i>_d) and tilting angle (<i>T</i>_a) of the bubbler, the SiCl₄ precursor concentration would fluctuate to different degrees. The different SiCl₄ concentrations afforded the fine-tuning of <i>v</i>-SiNW array properties like alignment and growth kinetics. The degree of alignment of <i>v</i>-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 <i>v</i>-SiNW arrays could be employed in advanced nanoelectronic devices

Annealed Au-Assisted Epitaxial Growth of Si Nanowires: Control of Alignment and Density

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

Effects of Hydrogen Partial Pressure in the Annealing Process on Graphene Growth

Graphene domains with different sizes and densities were successfully grown on Cu foils with use of a chemical vapor deposition method. We investigated the effects of volume ratios of argon to hydrogen during the annealing process on graphene growth, especially as a function of hydrogen partial pressure. The mean size and density of graphene domains increased with an increase in hydrogen partial pressure during the annealing time. In addition, we found that annealing with use of only hydrogen gas resulted in snowflake-shaped carbon aggregates. Energy-dispersive X-ray spectroscopy (EDX) and high-resolution photoemission spectroscopy (HRPES) revealed that the snowflake-shaped carbon aggregates have stacked sp² carbon configuration. With these observations, we demonstrate the key reaction details for each growth process and a proposed growth mechanism as a function of the partial pressure of H₂ during the annealing process

Axon-First Neuritogenesis on Vertical Nanowires

In this work, we report that high-density, vertically grown silicon nanowires (<i>vg</i>-SiNWs) direct a new <i>in vitro</i> developmental pathway of primary hippocampal neurons. Neurons on <i>vg</i>-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 <i>vg</i>-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 <i>in vivo</i>