13 research outputs found
Synthesis of silver nanowires towards the development the ultrasensitive AgNWs/SiNPLs hybrid photodetector and flexible transparent conductor
No full textBoron Monolayer Doping: Role of Oxide Capping Layer, Molecular Fragmentation, and Doping Uniformity at the Nanoscale
No full textDoping methodologies using monolayers offer controlled, ex situ doping of nanowires (NWs), and 3D device architectures using molecular monolayers as dopant sources with uniform, self‐limiting characteristics. Comparing doping levels and uniformity for boron‐containing monolayers using different methodologies demonstrates the effects of oxide capping on doping performances following rapid thermal anneal (RTA). Strikingly, for noncovalent monolayers of phenylboronic acid (PBA), highest doping levels are obtained with minimal thermal budget without applying oxide capping. Monolayer damage and entrapment of molecular fragments in the oxide capping layer account for the lower performance caused by thermal damage to the PBA monolayer, which results in transformation of the monolayer source to a thin solid source layer. The impact of the oxide capping procedure is demonstrated by a series of experiments. Details of monolayer fragmentation processes and its impact on doping uniformity at the nanoscale are addressed for two types of surface chemistries by applying Kelvin probe force microscopy (KPFM). These results point at the importance of molecular decomposition processes for monolayer‐based doping methodologies, both during preanneal capping step and during rapid thermal processing step. These are important guidelines to be considered for future developments of appropriate surface chemistry used in monolayer doping applications
Tailored periodic Si nanopillar based architectures as highly sensitive universal SERS biosensing platform
No full textWe report a skeleton key platform for Surface Enhanced Raman Spectroscopy (SERS) based biosensor, utilizing ordered arrays of Si Nanopillars (SiNPLs) with plasmonic silver nanoparticles (AgNPs). The optimized SiNPLs based SERS (SiNPLs-SERS) sensor exhibited high enhancement factor (EF) of 2.4 × 108 for thiophenol with sensitivity down to 10−13 M of R6G molecules. The ordered array of SiNPLs stabilizes the distribution of AgNPs along with the light trapping properties, which resulted in high EF and excellent reproducibility. The uniformity in the arrangement of AgNPs makes a single SiNPLs-SERS substrate to work for all types of biomolecules such as positively and negatively charged proteins, hydrophobic proteins, cells and dyes, etc. The experiments conducted on differently charged proteins, amyloid beta (the protein responsible for alzheimers), E. coli cells, healthy and malaria infected RBCs provide a proof of concept for employing universal SiNPLs-SERS substrate for trace biomolecule detection. The FDTD simulations substantiate the superior performance of the sensor achieved by the tremendous increase in the hotspot distribution compared to the bare Si sensor
Molecular Fingerprint Detection: Molecular Fingerprint Detection Using Portable Water‐Compatible Electronic Tunneling Spectroscopy Device (Adv. Mater. Interfaces 19/2020)
No full textMolecular Fingerprint Detection Using Portable Water‐Compatible Electronic Tunneling Spectroscopy Device
No full textImproved broadband and omnidirectional light absorption in silicon nanopillars achieved through gradient mesoporosity induced leaky waveguide modulation
No full textMetal assisted chemical etching in combination with nanosphere lithography is a low cost fabrication method to produce Si nanopillars (SiNPLs) with controlled size, periodicity and high aspect ratio on a large scale. These SiNPLs show a refractive index gradient condition from top to bottom of the SiNPLs due to the presence of inhomogeneous mesoporous structures. Here, for the first time we report the omnidirectional and polarization insensitive light coupling through mesoporosity induced waveguiding in SiNPLs. The optimized sample shows a minimum reflectance of <4% over a broad range of angles of incidence 8–48°. The inhomogeneous mesoporous structures on the top of SiNPLs act like a three dimensional grating to couple the light into waveguide modes and made headway for the omnidirectional light absorption. By using angle resolved reflectance spectra and angle dependent Raman scattering, we confirmed that the inhomogeneous porosity plays a significant role in the omnidirectional light trapping, especially in the lower wavelength region, where the nanopillar absorption dominates. Finite difference time domain (FDTD) simulations have been performed to examine the omnidirectional light absorption theoretically and to find the leaky waveguide modes associated with the SiNPLs. This work focuses on the porosity induced fundamental light trapping in SiNPLs, which is highly desired in the design of photonic and optoelectronic devices
Charge transport studies on Si nanopillars for photodetectors fabricated using vapor phase metal-assisted chemical etching.
No full textSi nanopillars (SiNPLs) were fabricated using a novel vapor phase metal-assisted chemical etching (V-Mace) and nanosphere lithography. The temperature dependent current–voltage (I–V) characteristics have been studied over a broad temperature range 170–360 K. The SiNPLs show a Schottky diode-like behavior at a temperature below 300 K and the rectification (about two orders of magnitude) is more prominent at temperature < 210 K. The electrical properties are discussed in detail using Cheung’s and Norde methods, and the Schottky diode parameters, such as barrier height, ideality factor, series resistance, are carefully figured out and compared with different methods. Moreover, the light sensitivity of the SiNPLs has been studied using I–V characteristics in dark and under the illumination of white light and UV light. The SiNPLs show fast response to the white light and UV light (response time of 0.18 and 0.26 s) under reverse bias condition and the mechanism explained using band diagram. The ratio of photo-to-dark current shows a peak value of 9.8 and 6.9 for white light and UV light, respectively. The Si nanopillars exhibit reflectance < 4% over the wavelength region 250–800 nm with a minimum reflectance of 2.13% for the optimized sample. The superior light absorption of the SiNPLs induced fast response in the I–V characteristics under UV light and white light. The work function of the SiNPLs in dark and under illumination has been also studied using Kelvin probe to confirm the light sensitivity
Evolution mechanism of mesoporous silicon nanopillars grown by metal-assisted chemical etching and nanosphere lithography: correlation of Raman spectra and red photoluminescence
No full textWe have fabricated highly ordered, vertically aligned, high aspect ratio silicon nanopillars (SiNPLs) of diameter ~80 nm by combining metal-assisted chemical etching and nanosphere lithography. The evolution of surface morphology of porous silicon nanopillars has been explained, and the presence of mesoporous structures was detected on the top of silicon nanopillars using field emission scanning electron microscopy. The mesoporosity of the SiNPLs is confirmed by Brunauer–Emmett–Teller measurements. The peak shift and the splitting of optical phonon modes into LO and TO modes in the micro-Raman spectra of mesoporous SiNPLs manifest the presence of 2–3 nm porous Si nanocrystallites (P-SiNCs) on the top of SiNPLs and the size of crystallites was calculated using bond polarizability model for spherical phonon confinement. The origin of red luminescence is explained using quantum confinement (QC) and QC luminescent center models for the P-SiNCs, which is correlated with the micro-Raman spectra. Finally, we confirmed the origin of the red luminescence is from the P-SiNCs formed on surface of SiNPLs, highly desired for LED devices by suitably tailoring the substrate
Approaching Angstrom-Scale Resolution in Lithography Using Low-Molecular-Mass Resists (<500 Da)
No full textResists that enable high-throughput and highresolution patterning are essential in driving the semiconductor technology forward. The ultimate patterning performance of a resist in lithography is limited because of the trade-off between resolution, line-width roughness, and sensitivity; improving one or two of these parameters typically leads to a loss in the third. As the patterned feature sizes approach angstrom scale, the trade-off between these three metrics becomes increasingly hard to resolve and calls for a fundamental rethinking of the resist chemistry. Low-molecular-mass monodispersed metalcontaining resists of high atom economy can provide not only very high resolution but also very low line-width roughness without sacrificing sensitivity. Here we describe a modular metal-containing resist platform (molecular mass <500 Da) where a molecular resist consists of just two components: a metal and a radical initiator bonded to it. This simple system not only is amenable to high-resolution electron beam lithography (EBL) and extreme ultraviolet lithography (EUVL) but also unites them mechanistically, giving a consolidated perspective of molecular and chemical processes happening during exposure. Irradiation of the resist leads to the production of secondary electrons that generate radicals in the initiator bonded to metal. This brings about an intramolecular rearrangement and causes solubility switch in the exposed resist. We demonstrate record 1.9−2.0 nm isolated patterns and 7 nm half-pitch dense line-space features over a large area using EBL. With EUVL, 12 nm half-pitch line-space features are shown at a dose of 68 mJ/ cm 2. In both of these patterning techniques, the line-width roughness was found to be ≤2 nm, a record low value for any resist platform, also leading to a low-performance trade-off metric, Z factor, of 0.6 × 10 −8 mJ•nm 3. With the ultimate resolution limited by instrumental factors, potential patterning at the level of a unit cell can be envisaged, making low-molecular-mass resists best poised for angstrom-scale lithography.GR-LUDIMX-G
