Mati Horprathum

Ultrasensitive Hydrogen Sensor Based on Pt-Decorated WO3 Nanorods Prepared by Glancing-Angle dc Magnetron Sputtering

In this work, we report an ultrasensitive hydrogen (H2) sensor based on tungsten trioxide (WO3) nanorods decorated with platinum (Pt) nanoparticles. WO3 nanorods were fabricated by dc magnetron sputtering with a glancing angle deposition (GLAD) technique, and decorations of Pt nanoparticles were performed by normal dc sputtering on WO3 nanorods with varying deposition time from 2.5 to 15 s. Crystal structures, morphologies, and chemical information on Pt-decorated WO3 nanorods were characterized by grazing-incident X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and photoelectron spectroscopy, respectively. The effect of the Pt nanoparticles on the H2-sensing performance of WO3 nanorods was investigated over a low concentration range of 150-3000 ppm of H2 at 150-350 °C working temperatures. The results showed that the H2 response greatly increased with increasing Pt-deposition time up to 10 s but then substantially deteriorated as the deposition time increased further. The optimally decorated Pt-WO3 nanorod sensor exhibited an ultrahigh H2 response from 1530 and 214,000 to 150 and 3000 ppm of H2, respectively, at 200 °C. The outstanding gas-sensing properties may be attributed to the excellent dispersion of fine Pt nanoparticles on WO3 nanorods having a very large effective surface area, leading to highly effective spillover of molecular hydrogen through Pt nanoparticles onto the WO3 nanorod surface.

Texture orientation of silver thin films grown via gas-timing radio frequency magnetron sputtering and their SERS activity

Here we demonstrate a special technique to control a texture orientation of silver (Ag) thin films using gas-timing (GT) rf magnetron sputtering. By utilizing a GT technique, a dense structure and a high ratio of (111)/(200) of Ag films could be obtained without applying additional energy sources. We found that the GT technique not only provides the ability to adjust the number of sputter species from the target, but also generates the self-energy assisted deposition which related to the atomic peening effect. Furthermore, we found that a high (111)/(200) ratio of Ag films strongly affects the SERS activity of the Ag films due to a hot spot effect. Our results highlight that the texture engineering of metal thin films could be accomplished by using a GT technique.

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.

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.

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.

Piezoelectric-Induced Triboelectric Hybrid Nanogenerators Based on the ZnO Nanowire Layer Decorated on the Au/polydimethylsiloxane–Al Structure for Enhanced Triboelectric Performance

Here, we demonstrate a novel device structure design to enhance the electrical conversion output of a triboelectric device through the piezoelectric effect called as the piezo-induced triboelectric (PIT) device. By utilizing the piezopotential of ZnO nanowires embedded into the polydimethylsiloxane (PDMS) layer attached on the top electrode of the conventional triboelectric device (Au/PDMS-Al), the PIT device exhibits an output power density of 50 μW/cm2, which is larger than that of the conventional triboelectric device by up to 100 folds under the external applied force of 8.5 N. We found that the effect of the external piezopotential on the top Au electrode of the triboelectric device not only enhances the electron transfer from the Al electrode to PDMS but also boosts the internal built-in potential of the triboelectric device through an external electric field of the piezoelectric layer. Furthermore, 100 light-emitting diodes (LEDs) could be lighted up via the PIT device, whereas the conventional device could illuminate less than 20 LED bulbs. Thus, our results highlight that the enhancement of the triboelectric output can be achieved by using a PIT device structure, which enables us to develop hybrid nanogenerators for various self-power electronics such as wearable and mobile devices.

Impedance Spectroscopic Inspection Toward Sensitivity Enhancement of Ag-Doped WO3 Nanofiber-Based Carbon Monoxide Gas Sensor

This work reports the impedance analysis and carbon monoxide gas sensing response of tungsten oxide (WO3) nanofibers with silver (Ag) nanoparticle doping. The Ag-doped WO3 nanofibers were prepared by an electrospinning technique. The impedance spectroscopic measurements of undoped and Ag-doped WO3 nanofibers were performed to study the contribution of electrical parameters involved in the electron transport. The impedance modeling obtained from the fitted Nyquist plot shows that the RC components attributed to Ag-WO3 interface are introduced to the system upon Ag addition. Carbon monoxide (CO) gas detection was carried out by resistance measurement using a DC method. The sensitivity of Ag-doped WO3 nanofibers is found to be greater than that of the undoped sample. The improved sensitivity is derived from the high interface resistance between Ag and WO3 grains. The contribution of Ag dopants is conceived to induce electronic structure alteration of the sensor material.

Influence of Growth Conditions on Morphology of ZnO Nanorods by Low-Temperature Hydrothermal Method

Zinc oxide (ZnO) nanorods (NRs) promise high potentials in several applications, such as photovoltaic device, thermoelectric device, sensor and solar cell. In this research, the vertical alignment of ZnO NRs was fabricated by hydrothermal method with various precursor concentrations and growth time on different seed layers (ZnO and Au), which deposited on silicon wafer substrate (100). The crystalline structure and morphology of ZnO NRs have been characterized by x-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) techniques, respectively. The x-ray diffraction pattern shows that the prepared samples have a strong preferred orientation (002) plane. FE-SEM images of the ZnO NRs, it found that the density and aspect ratio were strongly influenced by the seed layer and precursor concentration. In addition, the aspect ratio of ZnO NRs was increased with increasing growth time. This study provides a cost effective method for the fabrication of well aligned ZnO NRs for nano-electronic devices.