Pongpan Chindaudom

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.

Effect of Doping Concentration on the Proton Conductivity of Y-doped BaZrO3 Thin Films

Y-doped BaZrO3 (BYZ) pellets and thin films were fabricated by solid state reaction and co-sputtering technique, respectively. The conductivity of BYZ samples was measured using electrochemical impedance spectroscopy technique in the atmospheres of air, dry H2, and wet H2. As Y content increases from 6 at.% to 20 at.%, the increase of bulk and grain boundary conductivity is observed, while at 30 at.%, the conductivity starts to degrade. The activation energies in bulk and grain boundary are in the range of 0.28-0.40 eV and 0.91-0.96 eV, respectively. BYZ pellets have the highest proton conductivity at the Y doping concentration of 20 at.%. Furthermore, the dense and uniform BYZ thin films of 130-140 nm in thickness were obtained by co-sputtering technique. The conductivities of the BYZ thin films are about 10^3 - 10^4 times those of the pellet samples. The reason of the observed high conductivity is still under further investigation.

Photo-Induced Superhydrophilic TiO2 Films Deposited by DC Reactive Magnetron Sputtering at Room Temperature

Titanium dioxide (TiO2) thin films, 80-170 nm thick were deposited on unheated silicon wafers (100) and glass slides with controlled operating pressure in UHV dc sputtering system with a pressure control gate valve. The dependence of hydrophilic property of the films on the total sputtering pressure of mixed Ar and O2 gases (1-10 mTorr) was investigated. We found that hydrophilic activity as well as the structural and optical properties of the films were strongly related to the pressure maintained during the deposition. The TiO2 film structure and surface morphology were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and spectroscopic ellipsometry (SE). The optical constants of the TiO2 films was determined by SE. XRD showed that the films deposited between 1 – 5 mTorr had both anatase and rutile phase, but the rutile component reduced as the pressure increased. Only anatase peaks were obtained for the films deposited at pressure >5 mTorr. The AFM surface roughness decreased from 4.0 to 1.8 nm as the pressure increased from 1 – 10 mTorr. The contact angle measurement was used to determine the hydrophilicity of the films after exposed to UV light. I

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.

Temperature Dependence of Optical Constants of Silver Film Studied by In Situ Spectroscopic Ellipsometry

A silver film was deposited on silicon wafer by DC unbalance magnetron sputtering system. The temperature dependence of the silver film was investigated. The spectroscopic ellipsometry (SE) with the heating of sample stage (HTC100) was employed for the in situ SE measurement under annealing cycles of the sample from room temperature to 300°C in dry nitrogen gas. The results show that the pseudo dielectric constants (, < ε2>) of the sample varied with an annealing temperature. The real part of pseudo dielectric constant () of annealed Ag film was slightly changed and the imaginary part (< ε2>) was strongly increased at a photon energy below the optical band gap (3.5-4.5 eV). Furthermore, the pseudo dielectric constant of imaginary part at low energy region was changed due to the enhancement of crystallinity of Ag film at 300°C. All measured SE spectra were fitted by Drude-Lorentz optical model, the scattering time and resistivity were obtained.

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.

Spectroscopic Ellipsometry Analyses on Plasma Treatment of Aluminium Oxide Thin Film

Spectroscopic Ellipsometry (SE) was used to analyse the effect of plasma treatment on aluminium oxide thin films. The aluminium oxide thin films were fabricated by reactive DC magnetron sputtering at different operating pressures. The as-deposited thin films were plasma treated at different ambient Ar and O2 conditions. The prepared samples were investigated for physical microstructures with scanning electron microscopy (SEM) and optical characteristics with ellipsometry. The ellipsometric spectra of the prepared samples were measured in the range of 250 to 1650 nm with the incidence angle of 70 degree. Based on the optical model with the Tauc-Lorentz function, the thickness and the refractive index of the films were determined and discussed. The results showed that the thickness and the refractive index of the aluminium oxide thin films were greatly affected after the plasma treatments. In comparison, the results of those prepared at different operating pressures were also discussed. The SE results were confirmed with those from SEM.

Optimizations of Sealing Conditions for Blank Silver Nanorod Used as SERS Substrates

Silver nanorods, prepared on Si substrates by sputtering deposition with the technique glancing-angle deposition (GLAD), were used as surface-enhanced Raman scattering (SERS) substrates. The prepared samples were categorized into two groups based on sealing conditions after the nanorod fabrications. The non-sealed SERS substrates were prepared by purging in the vacuum chamber with argon, oxygen, and ambient air. The sealed SERS substrates were enveloped with several types of packages, i.e., petri dishes, plastic bags, and foils, where they were all handled in a controlled glove box. The samples were characterized by field-emission scanning electron microscopy (FESEM) for the physical morphologies. The samples were further investigated by Raman spectroscopy for Raman spectra of blank substrates of each condition. The results showed that, in case of the non-sealed category, the SERS substrates purged under the argon gas was best optimized to prevent ambient contamination during prolonged period of time. In the case of the sealed category by different packages, the SERS substrates demonstrated the enhancement of the Raman-shift spectra with very small unwanted peaks, and in addition the extended lifetime.

Development of Nanohole Array Patterned by Laser Interference Lithography Technique

Periodic nanohole pattern was created in spin-coated photoresist S1805 on Si substrates by Laser Interference Lithography (LIL). Wavelength of a laser source used in the optical system is 442 nm with the photon energy 2.80 eV. The system was set up to employ two laser beams from a beam splitter to generate interference pattern and expose to the photoresist. There are two parameters (incident angle and exposure time) which are determined due to affecting the ordering and feature of nanohole array. Therefore, the relation of these two parameters and actual dose were investigated and theoretically analyzed to optimize the resolution of LIL technique for nanoholes. The prepared samples after developing in the M26A for 5 sec were analyzed by field-emission scanning electron microscopy (FE-SEM). The results show that the pitch of the pattern is 440 nm and the smallest hole size is 190 nm The best feature is found for a laser fluence of 140 mJ/cm2. This nanohole array patterned by LIL consists of periodic nanostructures for high density storage to fabricate various nanodevices.