Water-assisted growth of nano-floret hybrid nanostructures and their application in sensing platforms

Self-processing (SP) is typically recognized in the context of biological systems. For example, proteins and RNA molecules undergo SP, which includes chemical and structural modifications. Recently, we developed a new strategy for the synthesis of metal-semiconductor hybrid nanostructures relying on self-processing mechanism which yield complex hybrid nanostructures in one step by triggering a programmable cascade of events that is autonomously executed. The semiconductor-metal hybrid nanostructures obtained resemble the morphology of grass flowers, termed here Nano-floret. Interestingly, water are used during the ‘growth’ process of Nano-florets as a mild etchant for synthesis intiation and progression. The synthesis mechanism was directly followed by in situ and ex situ scanning transmission electron microscopy and inductively coupled plasma mass spectrometry analyses. Our results indicate that distinct processing steps including localized oxide etch and metal deposition and process termination can be identified similarly to conventional top-down processing sequences. Please click Additional Files below to see the full abstract

Semiconductor-Metal Nano-Floret Hybrid Structures by Self-Processing Synthesis

We present a synthetic strategy that takes advantage of the inherent asymmetry exhibited by semiconductor nanowires prepared by Au-catalyzed chemical vapor deposition (CVD). The metal–semiconductor junction is used for activating etch, deposition, and modification steps localized to the tip area using a wet-chemistry approach. The hybrid nanostructures obtained for the coinage metals Cu, Ag, and Au resemble the morphology of grass flowers, termed here Nanofloret hybrid nanostructures consisting of a high aspect ratio SiGe nanowire (NW) with a metallic nanoshell cap. The synthetic method is used to prepare hybrid nanostructures in one step by triggering a programmable cascade of events that is autonomously executed, termed self-processing synthesis. The synthesis progression was monitored by ex situ transmission electron microscopy (TEM), in situ scanning transmission electron microscopy (STEM) and inductively coupled plasma mass spectrometry (ICP-MS) analyses to study the mechanistic reaction details of the various processes taking place during the synthesis. Our results indicate that the synthesis involves distinct processing steps including localized oxide etch, metal deposition, and process termination. Control over the deposition and etching processes is demonstrated by several parameters: (i) etchant concentration (water), (ii) SiGe alloy composition, (iii) reducing agent, (iv) metal redox potential, and (v) addition of surfactants for controlling the deposited metal grain size. The NF structures exhibit broad plasmonic absorption that is utilized for demonstrating surface-enhanced Raman scattering (SERS) of thiophenol monolayer. The new type of nanostructures feature a metallic nanoshell directly coupled to the crystalline semiconductor NW showing broad plasmonic absorption

Wafer-Scale Assembly of Semiconductor Nanowire Arrays by Contact Printing

Controlled and uniform assembly of "bottom-up" nanowire (NW) materials with high scalability has been one of the significant bottleneck challenges facing the potential integration of nanowires for both nano and macro electronic circuit applications. Many efforts have focused on tackling this challenge, and while significant progress has been made, still most presented approaches lack either the desired controllability in the positioning of nanowires or the needed uniformity over large scales. Here, we demonstrate wafer-scale assembly of highly ordered, dense, and regular arrays of NWs with high uniformity and reproducibility through a simple contact printing process. We demonstrate contact printing as a versatile strategy for direct transfer and controlled positioning of various NW materials into complex structural configurations on substrates. The assembled NW pitch is shown to be readily modulated through the surface chemical treatment of the receiver substrate, with the highest density approaching ~8 NW/um, ~95% directional alignment and wafer-scale uniformity. Furthermore, we demonstrate that our printing approach enables large-scale integration of NW arrays for various device structures on both Si and plastic substrates, with a controlled semiconductor channel width, and therefore ON current, ranging from a single NW (~10 nm) and up to ~250 um, consisting of a parallel array of over 1,250 NWs.Comment: 14 pages,4 figure

Direct Dopant Patterning by a Remote Monolayer Doping Enabled by a Monolayer Fragmentation Study

The development of new doping methods extending beyond the traditional and well-established techniques is desired to match the rapid advances made in semiconductor (SC)-processing methods and nanostructure synthesis in numerous emerging applications, including the doping of 3D architectures. To address this, monolayer doping (MLD) and monolayer contact doping methods have been introduced recently. The MLD methods enable separation of the doping process of nanostructures from the synthesis step; hence, it is termed ex situ doping. Here, we present a new ex situ MLD method termed remote MLD (R-MLD). The noncontact doping method is based on the thermal fragmentation of dopant-containing monolayers and evaporation processes taking place during annealing of the uncapped monolayer dopant source positioned in proximity, however, without making physical contact with the target SC surface. We present a two-step annealing procedure that allows the study of the dopant monolayer fragmentation and evaporation stages and quantification of the doping levels obtained during each step. We demonstrate the application of R-MLD for achieving a large-scale direct patterning of silicon substrates with sharp doping profiles. The direct dopant patterning is obtained without applying lithographic processing steps to the target substrate. The noncontact doping process, monolayer decomposition, and fragment evaporation were studied using thermogravimetric analysis coupled with mass spectrometry and sheet resistance measurements. The doped patterns were characterized using scanning electron microscopy, scanning capacitance microscopy, and time-of-flight secondary ion mass spectroscopy

Phosphine Oxide Monolayers on SiO2 Surfaces

(Figure Presented) Getting a grip: H-bond formation is shown to be the main mode of interaction for monolayer formation of phosphine oxides on SiO 2 substrates (see images), with covalent reaction involved to a lesser extent. In contrast to the situation with the more widely studied polar phosphonic acids, formation of these monolayers is self-limiting. The results may have important implications for many applications based on phosphine oxide monolayers. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA