Laser induced forward transfer of metal oxides using femtosecond double pulses

Laser induced forward transfer (LIFT) of ZnO and TiO₂ thin films onto Si has been realized with femtosecond double pulses of equal intensity, as a basic form of pulse shaping. In an effort to investigate the possibility to control the spatial distribution of the transfer via pulse separation, we used separation times varying from 0 to 10 ps. We have found that the size of the transferred spots increases by as much as 50% for pulse separation up to 500 fs, while for longer pulse separations the transferred spots acquire a constant area.     

Laser induced forward transfer of conducting polymers

We report on laser printing of conducting polymers directly from the solid phase. Laser induced forward transfer is employed to deposit P3HT:PCBM films on glass/ITO/PEDOT:PSS substrates. P3HT:PCBM is widely used as the active material in organic solar cells. Polyaniline films, which are also printed by laser induced forward transfer, find many applications in the field of biotechnology. Laser printing parameters are optimized and results are presented. To apply solid-phase laser printing, P3HT:PCBM films are spun cast on quartz substrates, while aniline is in-situ polymerized on quartz substrates.     

Laser forward transfer of silver electrodes for organic thin-film transistors

Organic thin-film transistors (OTFTs) with top- and bottom-contact configurations were fabricated using silver nano-inks printed by laser forward transfer for the gate and source/drain electrodes with pentacene and poly-4-vinylphenol as the organic semiconductor and dielectric layers, respectively. The volume of the laser-printed Ag pixels was typically in the subpicoliter (0.2–0.4 pl) range. The top-contact OTFTs resulted in lower contact resistance compared to those obtained from the bottom-contact OTFTs, and showed improved overall device performance. The top-contact OTFTs exhibited field-effect mobilities of ∼0.16 cm² V⁻¹ s⁻¹ and on/off current ratios of ∼10⁵.     

Influence of CuO catalyst in the nanoscale range on SnO2 surface for H2S gas sensing applications

The dispersal of CuO catalyst on the surface of the semiconducting SnO₂ film is found to be of vital importance for improving the sensitivity and the response speed of a SnO₂ gas sensor for H₂S gas detection. Ultra-thin CuO islands (8 nm thin and 0.6 mm diameter) prepared by evaporating Cu through a mesh and subsequent oxidation yield a fast response speed and recovery. Ultimately nanoparticles of Cu (average size = 15 nm) prepared by a chemical technique using a reverse micelle method involving the reduction of Cu(NO₃)₂ by NaBH₄ exhibited significant improvement in the gas sensing characteristics of SnO₂ films. A fast response speed of ∼14 s and a recovery time of ∼60 s for trace level ∼20 ppm H₂S gas detection have been recorded. The sensor operating temperature (130° C) is low and the sensitivity (S = 2.06 × 10³) is high. It is found that the spreading over of CuO catalyst in the nanoscale range on the surface of SnO₂ allows effective removal of excess adsorbed oxygen from the uncovered SnO₂ surface due to spill over of hydrogen dissociated from the H₂S-CuO interaction.     

Laser induced reverse transfer of gold thin film using femtosecond laser

Laser induced reverse transfer (LIRT) has been executed first time using a Mega Hertz pulse frequency femtosecond laser radiation under ambient conditions. Research has been conducted to understand the evolution of deposited structures with regard to pulse energy. Solid deposition of gold could be deposited on quartz substrate only if pulse energy falls within a certain range. For the experiment conducted in this work, it is 36-40 nJ. For energies above this range, crests appear in the middle of the deposition. There is a threshold in maximum applicable pulse energy, 82 nJ in this exepriment, beyond which further increase in pulse energy results in only traces of deposited material. Results also show that the width of deposited line increases with the increase in pulse energy and decreases with the increase in scan speed. These observations have been explained using the dynamics of ablated plume.     

Ethanol sensing properties of SnO2 thin films

Tin dioxide thin films have been deposited on alumina substrates by different methods in order to test their reliability as a breath analyser. Despite the obvious simplicity of spray pyrolysis, both the structural and electrical properties of the films thus prepared were strongly dependent to the deposition conditions. The samples exhibited poor crystallinity and porous microstructure. They were sensitive to ethanol vapour but since the resistance of the samples reached several MΩ, antimony doping was performed to fit a more convenient detection range. An alternative method was then used to prepare tin dioxyde thin films by evaporation of metallic tin followed by thermal oxidation. In this case, grain size was enhanced up to 100 nm but films remained highly porous. The ethanol sensitivity of evaporated samples was determined. In order to study more accurately the influence of microstructure on sensing ability, dense thin films were prepared using a CVD method with tetrabutyl tin as precursor. Preliminary results indicated that films with different crystallite sizes could be grown by varying the deposition temperature. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Synthesis of Au-functionalized SnO2 nanotubes using TeO2 nanowires as templates and their enhanced gas sensing properties

Au-functionalized SnO₂ nanotubes were prepared for use as gas sensors using TeO₂ nanowires as templates. Transmission electron microscopy revealed tube diameters, tube lengths and tube wall thicknesses ranging from 50 to 200 nm, 5 to 50 μm, and 13 to 18 nm, respectively. The Au-functionalized SnO₂ nanotube sensors showed responses of 179–473 % to 1–5 ppm NO₂ at 300 ^°C. These values are much higher than those obtained using bare SnO₂ nanotubes synthesized in this study and most other SnO₂ one-dimensional nanostructure-based sensors reported in the literature. The NO₂ gas sensing mechanism of the Au-functionalized SnO₂ nanotube sensors is also discussed.     

Studies on pyrolytically sprayed SnO2 and Sb-SnO2 thin films for LPG sensor applications

Undoped and antimony doped tin oxide thin films of different thicknesses were prepared on mineral glass substrate by spray pyrolysis method via sol-gel route. Both the films show good transmittance in the visible region. Band gap energy of both films lies between 3 to 3.5 eV. X-ray diffraction studies of undoped and antimony doped tin oxide thin films for various annealing temperature show polycrystalline tetragonal structure of SnO₂ with preferred orientation of (110) and (101), respectively and from the XRD data, grain size were also evaluated. AFM images of Undoped and antimony doped tin oxide thin films annealed at 375 °C depict the film thickness and indicate uniform surface pattern without dark pits and with strains of some ups exceeding the specified limit. The prepared films were tested in a specially developed test rig for Liquefied Petroleum Gas detection at different operating temperatures. The response characteristics of the films for LPG detection show maximum sensitivity and minimum response time at the operating temperature 400 °C. Studies indicate that antimony doped tin oxide thin film are one among the suitable candidates for LPG detection with a detection sensitivity and response time (t90) of 11 and 140 seconds, respectively. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Synthesis of coryphantha elephantidens-like SnO2 nanospheres and their gas sensing properties

In this work, coryphantha elephantidens-like SnO₂ with porous structures were prepared successfully by a simple hydrothermal route, through adjusting the temperature of hydrotherm. Its morphology was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET). Compared to the regular nanospheres, the coryphantha elephantidens-like SnO₂ nanospheres had obviously higher gas-sensing response, owing to the special structure with large specific surface area (161.16 m² g^?1). It surprised us that the coryphantha elephantidens-like SnO₂ sensor could easily distinguish between ethanol and acetone, whose chemical property were similar. Moreover, it also exhibited wide measurement range, fast response speed (less than 10 s) and good repeatability at a low temperature (180 °C) to ethanol. The desirable specific surface area and pore volume were conducive to molecules adsorption and diffusion, which were believed to be the major cause of the improvement of gas sensing performance.     

不同浓度C掺杂SnO_2的第一性原理计算

采用基于密度泛函理论的第一性原理对不同浓度C掺杂SnO_2体系的晶体结构、能带结构、态密度以及光学性质进行了计算.结果表明:掺杂C原子后,晶胞体积和晶格常数都略微增大,且随着掺杂浓度的增大而增大,能带的禁带宽度则随着浓度的增大而减小.在光学性质中,掺杂C原子后体系的光吸收边都向低能方向移动,随着掺杂浓度的增大,体系红移的幅度也增大.     

Influence of pH in La-doped SnO2 nanoparticles towards sensor applications

The present investigation has been carried out to optimize the pH level of lanthanum (La)-doped tin dioxide (SnO₂) nanoparticles towards the potential application in gas sensor. The La-doped SnO₂ nanoparticles were synthesized by sol-gel method in different pH values varying from acidic to base nature. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), ultraviolet (UV), photoluminescence (PL), and scanning electron microscopy (SEM) techniques. The XRD, UV, and PL analyses show the pH influences on the crystallite size of La-doped SnO₂ nanoparticles. The SEM images show the formation of porous structure at pH 11. Also, the electrical conductivity of 1 mol% La-doped SnO₂ at pH 3 and pH 11 were measured by impedance analyzer. In addition, we have fabricated and demonstrated device performance of synthesized La-doped SnO₂ nanoparticles for gas-sensing application. Real-time current response and long-time response to the gas sensing were also studied for the fabricated device.

     

Preparation and characterization of Sb-doped SnO2 films with controlled stoichiometry from polymeric precursors

A polymeric precursor method was employed in order to obtain Sb/SnO₂ thin films with well-controlled stoichiometry. The preparative process was studied by TGA–DTA of the precursor solutions. The EDX results show good agreement between the concentration in the precursor solutions and the Sb/Sn ratio in the films. XRD patterns present only the SnO₂ cassiterite-type structure, without the presence of an Sb oxide, even at higher Sb concentrations. The increase in the amount of Sb leads to a decrease in SnO₂ crystallinity. The film surface was analyzed by SEM, showing a cracked-mud type structure with the number of cracks depending on the calcination temperature and the Sb concentration.     

Investigations on Pd:SnO2/porous silicon structures for sensing LPG and NO2 gas

P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions. Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter have been estimated as 25 μm. Pd:SnO₂/PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device. Sensing properties of the device towards liquefied petroleum gas (LPG) and NO₂ gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity and optimum operating temperature of the device towards LPG and NO₂ gas sensing has been estimated as 69% at 180 °C and 52% at 220 °C, respectively. The developed sensor device shows a short response time of 25 and 57 s for sensing LPG and NO₂ gases, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Laser transfer of diamond nanopowder induced by metal film blistering

Blister-based laser induced forward transfer (BB-LIFT) is a promising technique to produce surface microstructures of various advanced materials including inorganic and organic micro/nanopowders, suspensions and biological micro-objects embedded in life sustaining medium. The transferred material is spread over a thin metal film irradiated from the far side by single laser pulses through a transparent support. Interaction of the laser pulse with the metal–support interface under optimized conditions causes formation of a quickly expanding blister. Fast movement of the free metal surface provides efficient material transfer, which has been investigated for the case of diamond nanopowder and diamond-containing suspension. The unique features of the given technique are universality, simplicity and efficient isolation of the transferred material from the ablation products and laser heating.     

Spectral line finding program for atmospheric remote sensing using full radiation transfer

We have developed a line-by-line code to simulate atmospheric spectra in the infrared spectral region assuming a remote light source of selectable temperature. Selecting the source temperature allows simulation of, for example, solar absorption spectra, lunar absorption spectra or emission spectra. The code is applicable for different geometries, from the ground, balloon or from satellite, and allows a simple search for the most suitable lines for the retrieval of atmospheric trace gas concentrations for the different geometries. In addition, a first estimate of the optimized microwindow size and the most important interfering gases that need to be considered is calculated automatically. This approach is of importance in cases where it is necessary to analyze numerous lines simultaneously to get sufficient precision in the trace gas concentration retrievals. Examples for H₂O and CO are given.     

不同晶粒尺寸SnO2纳米粒子的拉曼光谱研究

对晶粒尺寸在4-80 nm范围的纯SnO2纳米颗粒进行了拉曼散射研究.除了SnO2 本征拉曼振动峰外,还有几个新的拉曼振动峰和波长在700 nm左右的一个发光很强而且峰宽很大的荧光峰被观察到.结果所示,当纳米颗粒尺寸减小时,纳米SnO2 颗粒的体相特征拉曼峰变弱,而由缺陷,表面和颗粒尺寸引起的相关效应呈强势.晶粒尺寸在20 nm左右是引起体相拉曼光谱变化的临界尺寸. 晶粒尺寸在20 nm以下,其体相拉曼峰的发生宽化和峰位移动, 以及分别出现在位于571 cm-1 的表面振动峰,位于351 cm-1 处的界面峰和与表面吸附水分子及氢氧基团的N系列拉曼峰是纳米SnO颗粒的主要特征.这些结果反映了纳米颗粒的微结构变化与颗粒尺寸和表面效应以及它们之间相互作用的信息.     

Aryltriazene photopolymer thin films as sacrificial release layers for laser-assisted forward transfer systems: study of photoablative decomposition and transfer behavior

Thin films of a tailor-made photodecomposible aryltriazene polymer were applied in a modified laser-induced forward transfer (LIFT) process as sacrificial release layers. The photopolymer film acts as an intermediate energy-absorbing dynamic release layer (DRL) that decomposes efficiently into small volatile fragments upon UV laser irradiation. A fast-expanding pressure jet is generated which is used to propel an overlying transfer material from the source target onto a receiver. This DRL-assisted laser direct-write process allows the precise deposition of intact material pixels with micrometer resolution and by single laser pulses. Triazene-based photopolymer DRL donor systems were studied to derive optimum conditions for film thickness and laser fluences necessary for a defined transfer process at the emission wavelength of a XeCl excimer laser (308 nm). Photoablation, surface detachment, delamination and transfer behavior of aryltriazene polymer films with a thickness from 25 nm to ∼400 nm were investigated in order to improve the process control parameters for the fabrication of functional thin-film devices of microdeposited heat- and UV-sensitive materials.