Pitak Eiamchai

Highly-Sensitive Surface-Enhanced Raman Spectroscopy (SERS)-based Chemical Sensor using 3D Graphene Foam Decorated with Silver Nanoparticles as SERS substrate.

In this work, a novel platform for surface-enhanced Raman spectroscopy (SERS)-based chemical sensors utilizing three-dimensional microporous graphene foam (GF) decorated with silver nanoparticles (AgNPs) is developed and applied for methylene blue (MB) detection. The results demonstrate that silver nanoparticles significantly enhance cascaded amplification of SERS effect on multilayer graphene foam (GF). The enhancement factor of AgNPs/GF sensor is found to be four orders of magnitude larger than that of AgNPs/Si substrate. In addition, the sensitivity of the sensor could be tuned by controlling the size of silver nanoparticles. The highest SERS enhancement factor of ∼5 × 104 is achieved at the optimal nanoparticle size of 50 nm. Moreover, the sensor is capable of detecting MB over broad concentration ranges from 1 nM to 100 μM. Therefore, AgNPs/GF is a highly promising SERS substrate for detection of chemical substances with ultra-low concentrations.

Fabrication and Characterization of Antibacterial Ag-TiO2 Thin Films Prepared by DC Magnetron Co-Sputtering Technique

In this study, silver-doped titanium dioxide (Ag-TiO2) thin films were prepared co-sputtering technique in order to promote photo-induced antibacterial applications. The high-purity Ag (99.995%) and Ti (99.995%) were simultaneously co-sputtering on BK7 glass and silicon (100) wafers substrate. The structure, morphology, surface roughness and optical properties were characterized by grazing-incidence X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM) and UV-Vis spectrophotometer, respectively. The results showed that the as-deposited Ag-TiO2 thin films had high transparency in the visible range. The antibacterial activity was studied in the presence and in the absence of UV irradiation against Escherichia coli as a model for Gram-negative bacteria. The results indicated that, in comparison to conventional TiO2 films, the Ag-TiO2 thin films exhibited excellent antibacterial properties under the UV illumination.

Functionalization of Au Nanoparticles on ZnO Nanorods through Low-Temperature Synthesis

Hybrid nanomaterials exhibit multi-functionalities, which is synergy or enhanced physical and optical properties over their single components with promising potentials for various applications in dye-sensitized solar cell and photocatalytic materials. In this present research, the Au nanoparticles were prepared at HAuCl4 concentration of 0.5 mM on ZnO nanorod templates and silicon wafer substrate by hydrothermal reaction process. The prepared samples were investigated the crystal structure, chemical composition and morphologies by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and field-emission scanning electron microscopy (FESEM), respectively. The XRD results shown that ZnO was preferred orientation along the c-axis (002). The FE-SEM images indicated to the difference of size-Au NPs decorated on ZnO nanorods and silicon wafer. The relationship between the surface area and the size of Au NPs of the prepared samples was investigated and possible growing mechanism of Au NPs on ZnO nanorods templates will be discussed.

Portable surface-enhanced Raman spectroscopy for insecticide detection using silver nanorod film fabricated by magnetron sputtering

In order to increase agricultural productivity, several countries heavily rely on deadly insecticides, known to be toxic to most living organisms and thus significantly affect the food chain. The most obvious impact is to human beings who come into contact, or even consume, pesticide-exposed crops. This work hence focused on an alternative method for insecticide detection at trace concentration under field tests. We proposed a compact Raman spectroscopy system, which consisted of a portable Raman spectroscope, and a surface-enhanced Raman scattering (SERS) substrate, developed for the purpose of such application, on a chip. For the selected portable Raman spectroscope, a laser diode of 785 nm for excitation and a thermoelectric-cooled CCD spectrometer for detection were used. The affordable SERS substrates, with a structure of distributed silver nanorods, were however fabricated by a low-energy magnetron sputtering system. Based on an oblique-angle deposition technique, several deposition parameters, which include a deposition angle, an operating pressure and a substrate rotation, were investigated for their immediate effects on the formation of the nanorods. Trace concentration of organophosphorous chemical agents, including methyl parathion, chlorpyrifos, and malathion, adsorbed on the fabricated SERS substrates were analyzed. The obtained results indicated a sensitive detection for the trace organic analyses of the toxic chemical agents from the purposed portable SERS system.

Surface-enhanced Raman scattering using silver nanocluster on anodic aluminum oxide template sensor toward protein detection.

Abstract The affordable surface-enhanced Raman scattering (SERS) substrates, with a structure consisting of densely distributed round-shape silver nanoclusters on anodic aluminum oxide (AAO) template, is fabricated by magnetron sputtering and anodization processes. The physical investigations show that the silver nanoclusters with size distribution ranging from 10 to 30 nm uniformly distributed on the top and in the bottom of the AAO nanochannels. The SERS activities from adsorbed probe molecules, i.e., methylene blue, on the SERS substrate surface indicate a high Raman enhancement factor for trace organic analysis. The SERS substrate is successfully utilized in the detection of a trace amount of three different proteins, bovin serum albumin, immunoglobulin G, and cardiac troponin T, also adsorbed on the substrate surface. Several spectral bands containing important molecular structures of these proteins are clearly observed and identified. The obtained results indicated a step forward to label-free biomolecular detections in chip-based biosensors.

Tuberculosis determination using SERS and chemometric methods

Nanostructures have been multiplying the advantages of Raman spectroscopy and further amplify the advantages of Raman spectroscopy is a continuous effort focused on the appropriate design of nanostructures. Herein, we designed different shapes of plasmonic nanostructures such as Vertical, Zig Zag, Slant nanorods and Spherical nanoparticles employing the DC magnetron sputtering system as SERS-active substrates for ultrasensitive detection of target molecules. The fabricated plasmonic nanostructures sensitivity and uniformity were exploited by reference dye analyte. These nanostructures were utilized in the label free detection of infectious disease, Tuberculosis (TB). For the first time, TB detection from serum samples using SERS has been demonstrated. Various multivariate statistical methods such as principal component analysis, support vector machine, decision tree and random forest were developed and tested their ability to discriminate the healthy and active TB samples. The results demonstrate the performance of the SERS spectra, chemometric methods and potential of the method in clinical diagnosis.

Crucial role of reactive pulse-gas on a sputtered Zn3N2 thin film formation

Herein, we demonstrate a powerful technique, known as reactive gas-timing (RGT) rf magnetron sputtering, to fabricate high quality Zn3N2 thin films at room temperature without applying any additional energy sources. A single phase of Zn3N2 film formation can only be obtained when a reactive pulse-gas of N2 is utilized. We find that selecting a small atomic mass of sputtered reactive gas coupled with the pulse-gas technique is very crucial to adjust the number of sputtered atoms obtained from the target and enrich the forming energy of the sputtered Zn3N2 films during the deposition process. Our results highlight that the RGT technique is a promising method to fabricate high quality sputtered compound thin films that can be applied in flexible devices. A simplified model of the materials system at the surface region of the de-nitride Zn3N2 during ion bombardment is also presented.

Effect of Oxygen Flow Rate and Post Annealing on Vanadium Oxide Thin Films Prepared by DC Pulse Magnetron Sputtering

In this work, we investigated V2O5 thin films prepared by a DC pulse reactive magnetron sputtering at ambient conditions. The effects of oxygen flow rates during the film deposition and post annealing in air atmosphere were explored. The V2O5 thin films were sputtered from vanadium target onto silicon wafer and glass slide substrates at room temperature. The as-deposited V2O5 thin films were annealed at 200°C under air atmosphere. The films were then examined for their crystallinity, physical microstructures, and optical transmission. The crystallinity and morphology of the films were investigated by grazing incident x-ray diffraction, atomic force microscopy, and field-emission scanning electron microscopy. The optical transmission was determined by UV-Vis Spectrophotometer. The results showed that the as-deposited films were amorphous, whereas the post annealed films indicated V2O5 phase in all samples. The increase in the oxygen flow rates during the deposition led to the decrease in the deposition rate, film thickness, and film surface roughness. In addition, the oxygen flow can increase the average transmission of the V2O5 thin films. The effects of the annealing treatment of the optical transmission spectra will be discussed.

Power Factor of Germanium Antimony Tellurium Thin Film on Al2O3 Ceramic Substrate Deposited by Pulsed–DC Magnetron Sputtering

Germanium–Antimony–Telluride (Ge–Sb–Te) has low electrical resistivity and thermal conductivity for good thermoelectric properties. The Ge–Sb–Te thin films were deposited on Al2O3 ceramic substrate by pulsed–dc magnetron sputtering system using a 99.99 % Ge:Sb:Te of 1:1:1 composite target and annealed at 573, 623, 673, and 723 K for 1 hour in vacuum. The phase identification, atomic composition, morphology and film thickness (d), carrier concentration (n), mobility (µ), Seebeck coefficient (S) and electrical resistivity (ρ) of the as–deposited and the annealed samples were investigated by X–ray diffraction (XRD), energy dispersive X–ray spectroscopy (EDX), field–emission scanning electron microscopy (FE–SEM), Hall–effect measurement, steady state method and calculation of from n and µ, respectively. The results demonstrated that the as–deposited Ge–Sb–Te film showed amorphous phase and annealing changed the phase crystalline. Morphologies of annealed Ge–Sb–Te films showed very large grain size and porosity to obtaining good n and µ. The approximately maximum power factor (P) was 4.22×10−4 W m−1 K−2 at annealing temperature of 723 K.

Applications of surface-enhanced Raman scattering (SERS) substrate

Threats of explosive, toxic and narcotic substances continue growing importance to a number of places around the world. In many recent cases, the treats are coming from unprecedented well-funded, increasing sophisticated and highly mass propaganda of radical or criminal organizations. These are challenging tasks for the defense agencies to implement new technologies and methods to ramp up intelligence gathering and visibility in order to pinpoint and deactivate the threats at multiple levels. Some of the main challenges are to develop faster, more sensitive, less expensive portable systems to facilitate the ultra-low detection of the targeted chemical compounds for anti-terror/criminal purposes. This article is to review the progress of surface-enhanced Raman scattering (SERS) substrate of silver nanorod fabricated by magnetron sputtering technique, developed by our group at NECTEC for defense related applications, which have been published in several previous reports, in order to promote the technique as a major tool for rapid identification of such terror/criminal substances at ultra - sensitive levels. Major highlights are trace detection of several toxic organophosphorous compounds, explosives including TNT and commercial explosives and a narcotic drug based on methamphetamine - at a sensitivity that can compete with, or even better than, conventional methods.