Molecular Dynamics Simulation of Copper Nanofilm Self-Assembly on Silicon Substrate under Gas-Discharge Plasma Conditions

High Energy Chemistry - Using the molecular dynamics method, the sputtering of a copper target and the subsequent formation of a copper nanofilm on a silicon substrate has been modeled. The process...     

磁控溅射制备择优取向氮化铝薄膜

AlN薄膜;磁控反应溅射;磁控溅射制备择优取向氮化铝薄膜;晶面取向;X射线衍射     

RFA as control method of the reactive sputtering process of TiN films

In-situ X-ray fluorescence (XRF) analysis has been used to control the deposition process of Ti-N films on steel substrates during reactive sputtering. The analysis system consisted of a tungsten X-ray tube, secondary targets of Cu, Fe and Cr and a Si (Li) detector. The sputtering off the Ti target has been determined indirectly by plasma monitoring using optical emissions spetroscopy (OES) of the Ti atoms, and the film growth has been measured directly by XRF analysis of the surface mass of Ti atoms deposited on the substrate. For zero bias voltage and varying N₂ flow the increment of surface mass per deposition time has been found to incrase linearly with the intensity of the OES signal of Ti. A negative bias voltage U_B100 V changes strongly the growth rate by resputtering effects, especially in the range where stoichiometric TiN is formed.     

Influence of Substrate-Target Distance on Structural and Optical Properties of Ga and (Al + Ga)-doped ZnO Thin Films Deposited by Radio Frequency Sputtering

Ga-doped ZnO and (Ga?+?Al) co-doped ZnO thin films were deposited on glass substrates by radio frequency magnetron sputtering for three distances d between a substrate–target. The influence of the distance between substrate–target upon structure, microstructure, vibrational properties, and optical band gap of the thin films was analyzed by X-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy, and optical transmission measurements. The diffraction patterns revealed that the ZnO film crystallites are preferentially oriented with the (002) planes parallel to the substrate surface. AFM images show a smooth and uniform surface as well as a high compact structure. The Raman results reveal that the co-doping with Al?+?Ga introduces 2B₁(low) band and leads to the increase of intensity for longitudinal-optic’s band. In the visible region, the average value of the transmittance was above 80%.     

Preparation of tantalum oxynitride thin film photocatalysts by reactive magnetron sputtering deposition under high substrate temperature

This work spotlights the formation behavior of visible light-responsive tantalum oxynitride (TaON) thin film photocatalysts under high substrate temperature in radiofrequency reactive magnetron sputtering deposition. The results emanating from the optimization of the sputtering conditions demonstrated that sputtered N atoms with high kinetic energy generated by controlling target–substrate distances and total pressures in the sputtering chamber were necessary to grow TaON phase even under N₂-rich atmosphere. Based on these findings, TaON thin film photocatalysts were successfully synthesized by single-step sputtering under a high substrate temperature of 1073 K before heat treatment. The optimal thickness of TaON thin film photocatalysts was extrapolated to be 450 nm by photoelectrochemical measurements under visible light irradiation (λ > 450 nm), in which distinct photocurrents corresponding to water oxidation were observed. Moreover, the photoelectrochemical activity was able to be improved by postsynthetic heat treatment in gaseous NH₃ and loading with IrO₂ nanocolloids as cocatalysts. This finding would be because the thin film photocatalyst after heat treatment in NH₃ under appropriate conditions possessed better crystallinity and moderate donor density. The optimized TaON thin film photocatalysts with IrO₂ nanocolloids also exhibited photocatalytic activity for H₂ evolution from aqueous medium containing methanol as a sacrificial electron donor under visible light irradiation (λ > 450 nm).     

Formation of ultrasharp vertically aligned Cu-Si nanocones by a DC plasma process

We report an effective method for the production of ultrasharp vertically oriented silicon nanocones with tip radii as small as 5 nm. These silicon nanostructures were shaped by a high-temperature acetylene and ammonia dc plasma reactive ion etch (RIE) process. Thin-film copper deposited onto Si substrates forms a copper silicide (Cu3Si) during plasma processing, which subsequently acts as a seed material masking the single-crystal cones while the exposed silicon areas are reactive ion etched. In this process, the cone angle is sharpened continually as the structure becomes taller. Furthermore, by lithographically defining the seed material as well as employing an etch barrier material such as titanium, the cone location and substrate topography can be controlled effectively.     

Role of etch products in polysilicon etching in a high-density chlorine discharge

For low-pressure, high-density plasma systems, etch products can play a significant role in affecting plasma parameters such a.s species concentration and electron temperature. The residence time of etch products in the chamber can he long, hence depleting the concentration of the reactants, and leading to a decrease in etch rate. We use a spatially averaged global model including both gas phase and surface chemistry to study Cl₂ etching of polvsilicon. Etch products leaving the wafer surface are assioned to he SiCL₂ and SiCl₄. These species can be fragmented and ionized by collisions with energetic electrons, generating neutral and charged SiCl, products (x=0–4). Two limiting cases of the etch mechanism are found. an ion flux-limited regime and a neutral reactant-limited regime. The high degree of dissociation in high-density plasmas leads to the formation of elemental silicon, which can deposit on the chamber walls and wafer surface. We include surface models for both the wall and the wafer to better understand the role of etch products as a function of flowrate, pressure, and input pwer. A phenomenological model for the surface chemistry is based on available experimental data. We consider the two limiting conditions of nonreactive and reactive walls. These models are perfectly reflective walls, where all silicon-containing species are reflected; and reactive walls, which act as reactive sites for the formation of SiCl₂ and SiCl₄ etch products. The two limiting conditions give significantly different results. A decrease in the absolute atomic silicon density and a weaker dependence of etch rate on flowrate are observed for the reactive wall.     

A simple and highly efficient route to the synthesis of NaLnF(4)-Ag hybrid nanorice with excellent SERS performances

This paper reports the synthesis of a new class of NaLnF(4)-Ag (Ln = Nd, Sm, Eu, Tb, Ho) hybrid nanorice and its application as a surface-enhanced Raman scattering (SERS) substrate in chemical analyses. Rice-shaped NaLnF(4) nanoparticles as templates are prepared by a modified hydrothermal method. Then, the NaLnF(4) nanorice particles are decorated with Ag nanoparticles by magnetron sputtering method to form NaLnF(4)-Ag hybrid nanostructures. The high-density Ag nanogaps on NaLnF(4) can be obtained by the prolonging sputtering times or increasing the sputtering powers. These nanogaps can serve as Raman 'hot spots', leading to dramatic enhancement of the Raman signal. The NaLnF(4)-Ag hybrid nanorice is found to be robust and is an efficient SERS substrate for the vibrational spectroscopic characterization of molecular adsorbates; the Raman enhancement factor of Rhodamine 6G (R6G) absorbed on NaLnF(4)-Ag nanorice is estimated to be about 10(13). Since the produced NaLnF(4)-Ag hybrid nanorice particles are firmly fastened on a silicon wafer, they can serve as universal SERS substrates to detect target analytes. We also evaluate their SERS performances using 4-mercaptopyridine (Mpy), and 4-mercaptobenzoic acid (MBA) molecules, and the detection limit for Mpy and MBA is as low as 10(-12) M and 10(-10) M, respectively, which meets the requirements of the ultratrace detection of analytes. This simple and highly efficient approach to the large-scale synthesis of NaLnF(4)-Ag nanorice with high SERS activity and sensitivity makes it a perfect choice for practical SERS detection applications.     

Microstructure and ferroelectric properties of r.f. magnetron sputtering derived PZT thin films deposited on interlayer (PbO/TiO2)

Lead zirconate titanate (PZT) thin films were deposited on Pt/Ti/SiO₂/Si and interlayer/Pt/Ti/SiO₂/Si substrate by radio frequency (r.f.) magnetron sputtering with a Pb_1.1Zr_0.53Ti_0.47O₃ target. The crystallization of the PZT thin films was formed only by substrate temperature. When interlayer (PbO/TiO₂) was inserted between the PZT thin film and the Pt electrode, the grain growth and processing temperature of the PZT thin films were considerably improved. Compared to PZT/Pt structure, the dielectric constant and polarization properties of the PZT/interlayer/Pt structure were fairly improved. In particular, PZT/interlayer/Pt at the substrate temperature of 400 °C showed prevalent ferroelectric properties (_r=475.97, tanδ=0.0591, P_r=23 μC/cm²). As a result of an X-ray photoelectron spectroscopy (XPS) depth-profile analysis, it was found that PZT/interlayer/Pt deposited only by substrate temperature without the post-annealing process via r.f. magnetron sputtering method remained independent of each other regardless of substrate temperatures.     

Preparation and characterization of Pd-Ag alloy composite membrane with magnetron sputtering

A Pd-Ag (24 wt%) alloy composite membrane was prepared by the magnetron sputtering. A γ-Al_2O_3 membrane was synthesized by the sol-gel method and used as substrate of the Pd-Ag alloy film. The process parameters of the magnetron sputtering were optimized as a function of the compactness of the Pd-Ag alloy film. The best membrane with a thickness of 1 μm was produced with a sputtering pressure of 2.7 Pa and a substrate temperature of 400℃. The membrane had an H_2/N_2 permselectivity of 51.5--1000 and an H_2 permeation rate of 0.036--1.17×10~(-5)cm~3/cm~2·s· Pa, depending on operating conditions.     

Real-Time Measurement of Thin Film Thickness During Plasma Processing

An in situ single point two-color laser interferometer is used to monitor in real-time the thickness of thin transparent films during processing. The instantaneous change of film thickness is determined by comparing the measured laser reflection interference to that calculated by a model. The etch or deposition rates of the film are determined within 1–2 seconds. The film thickness is also determined in real-time from the phase difference of the reflected laser intensity between the two laser colors. Use of two-color laser interferometry improves the accuracy of the calculated etch or growth rates of the film considerably. Moreover, the two colors provide a clear distinction between film etching and deposition, which may often occur during the same process, and can not be determined by a single color interferometer. The uniformity of the film's etch or deposition rates across the substrate is monitored by an in situ full-wafer image interferometer. The combined use of these two sensors provide instantaneous information of the film thickness, etch or growth rates, as well as time averaged uniformity of the process rates. This diagnostic setup is very useful for process development and monitoring, which is also suitable for manufacturing environment, and can be used for real-time process control.     

Oxidized gold as an ultrathin etch resist applied in microcontact printing

In this report it is described how a gold surface can be treated with an oxygen plasma to become an effective etch mask, with its etch resistive properties based upon electrostatic repulsion. Such a treated gold layer is only temporarily stable and may therefore be employed as a temporary etch barrier that introduces no contaminating species. Deterioration of the barrier properties can be locally expedited in a scheme that is compatible with microcontact printing. This has been achieved by the microcontact printing of a reductant on a fully oxidized gold substrate.     

Synthesis of thick TiO2 nanotube arrays on transparent substrate by anodization technique

A vertically aligned transparent TiO₂ nanotube array (tTNA) of significantly enhanced tube-length 6.3 ± 0.3 µm was successfully synthesized on glass substrates by anodization technique with ammonium fluoride and ethylene glycol-based electrolyte. Prior to anodization, Ti metal was deposited on glass substrate by facing-target sputtering technique with various sputtering pressures at substrate temperature 420 °C to find out the relation between the structural properties of the Ti layer and the corresponding growth mechanism of the TiO₂ nanotube. The study revealed that structural properties of Ti metal layers and its adhesion to the glass substrate, which can be tuned by deposition parameters, play an important role in the process of tTNA formation.     

Facile fabrication of 2-dimensional arrays of sub-10 nm single crystalline Si nanopillars using nanoparticle masks

A simple procedure for the fabrication of sub-10 nm scale Si nanopillars in a 2-D array using reactive ion etching with 8 nm Co nanoparticles as etch masks is demonstrated. The obtained Si nanopillars are single crystalline tapered pillar structures of 5 nm (top) x 8 nm (bottom) with a density of approximately 4 x 10(10) pillars cm(-2) on the substrate, similar to the density of Co nanoparticles distributed before the ion etching process. The uniform spatial distribution of the Si nanopillars can also be patterned into desired positions. Our fabrication method is straightforward and requires mild process conditions, which can be extended to patterned 2-D arrays of various Si nanostructures.     

Novel fabrication process using nanoporous anodic aluminum oxidation and MEMS technologies for gas detection

A class of nanoporous TiO₂ gas sensors processed by novel anodic aluminum oxidation (AAO) of Al thin films and microelectromechnical systems (MEMS) techniques are presented. To enhance the sensitivity and reduce the sensing dimensions of a gas sensor, a nanoporous surface of the gas-sensitive material on the sensor is required. These sensors can be implemented on silicon or silicon dioxide substrate featuring a thin membrane of micro-hotplate structure featuring micro-heaters, thermometers and electrodes, and thus operate as chemoresistive devices. Combining the AAO method with dry-etch process, a homogeneous and nanoporous SiO₂ surface of the sensor can be effectively configured by modulating various hole diameters and depth, hence replacing conventional photolithography and electrochemical etch. The process integration including AAO, reactive ion etch (RIE) and microfabrication is mainly developed and a feasibility study of PVD TiO₂ thin film deposition upon the porous device is also provided. TiO₂ thin films deposited on the nanoporous surface are investigated and compared with non-porous TiO₂ films. It is encouraging that our fabrication process is able to provide relatively high surface area to enhance sensitivity of the sensor without additional doping steps. Our promising experimental results have revealed these miniature and cost-effective devices are not only compatible, but applicable to smart bio-chemical sensors of next generation.     

Multiscale imaging and tip-scratch studies reveal insight into the plasma oxidation of graphite

The plasma oxidation process of highly oriented pyrolytic graphite (HOPG) has been investigated through a combination of multiscale (micrometric to atomic) imaging by atomic force and scanning tunneling microscopies (AFM/STM) and STM tip-scratching of the HOPG substrate. Complementary information was obtained by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Repetitive imaging of the same HOPG location following a series of consecutive plasma treatments allowed an accurate determination of the plasma etch rates along both the a and c crystallographic directions of the graphite lattice. The etch rates were typically in the range of a few nm per min along the a axis, and the equivalent of 1-6 graphene layers per min along the c axis. The results pointed to the existence of two main plasma etching regimes, related to short (<20-30 min) and long (> or =30 min) treatment times. This was inferred not only from the measured plasma etch rates but also from the observation of fundamental differences in the atomic-scale surface structure of the plasma-treated HOPG samples, and from the general mechanical behavior of the materials under the action of the AFM tip. In particular, atomic-scale STM imaging suggested a change from a defected, but essentially graphitic, surface in the first regime to an amorphous carbon surface in the second regime. Together with AFM and STM, Raman spectroscopy and XPS provided a consistent picture of the surface structure and chemistry of the plasma-modified HOPG in the two regimes. The implications of these results as well as the possible mechanism that drives the plasma etching process in the two regimes are discussed.     

Polytetrafluoroethylene Sputtered PES Membranes for Membrane Distillation: Influence of RF Magnetron Sputtering Conditions

Thin films of fluorocarbon were deposited on polyethersulfone membranes via argon plasma sputtering of a poly(tetrafluoroethylene) (PTFE) target in an RF magnetron plasma reactor. The obtained deposited ultrathin coatings had nanoscale roughnesses and high degrees of fluorination. The intensity of fluorine atom in plasma environment during fluorocarbon deposition was investigated. Depending on the deposition conditions comprising working gas pressure, applied RF power, and distance between the target and the substrate, polymeric films with different chemical compositions and/or morphologies were obtained. The morphologies of the films were analyzed by means of SEM, XPS, and AFM. The results suggested that the sputtered film deposited at a higher pressure and longer target–substrate distance and moderate RF power had a surface composition and chemical structure closer to those of the PTFE film. The treated hydrophobic PES membranes with water contact angles as high as 115° were applied for the first time in an air gap membrane distillation setup for removal of benzene as a volatile organic compound from water. The results showed that the plasma-treated membranes have a comparable or superior performance to that of commercial PTFE used in membrane distillation with similar permeate flux and separation factor after 20 h long term performance.     

Structural properties of lithium thio-germanate thin film electrolytes grown by radio frequency sputtering

In this study, lithium thio-germanate thin film electrolytes have been successfully prepared by radio frequency (RF) magnetron sputtering deposition in Ar gas atmospheres. The targets for RF sputtering were prepared by milling and pressing appropriate amounts of the melt-quenched starting materials in the nLi(2)S + GeS(2) (n = 1, 2, and 3) binary system. Approximately 1 μm thin films were grown on Ni coated Si (Ni/Si) substrates and pressed CsI pellets using 50 W power and 25 mtorr (～3.3 Pa) Ar gas pressures to prepare samples for Raman and Infrared (IR) spectroscopy, respectively. To improve the adhesion between the silicon substrate and the thin film electrolyte, a sputtered Ni layer (～120 nm) was used. The surface morphologies and thickness of the thin films were determined by field emission scanning electron microscopy (FE-SEM). The structural properties of the starting materials, target materials, and the grown thin films were examined by X-ray diffraction (XRD), Raman, and IR spectroscopy.     

Monte Carlo simulation study of reflection electron energy loss spectroscopy of an Fe/Si overlayer sample

Reflection electron energy loss spectroscopy (REELS) has been used to study the optical and electronic properties of semi-infinite solid samples, aided by a theoretical model of the interaction between electrons and a solid. However, REELS has not been used to its full capacity in studying nanomaterial samples because of the difficulty in modeling the electron interaction with a layered nanostructure. In this study, we present a numerical calculation result on the spatially varying inelastic mean free path for a sample comprising an Fe layer of varying thickness on an Si substrate. Furthermore, a Monte Carlo model for electron interaction with this Fe-Si layered structure sample is built based on this inelastic scattering cross section and used to reproduce the REELS spectra of Fe-Si layered structures. The simulated spectra of the sample with varying Fe layer thickness on top of a Si substrate were compared with the experimental spectra. This comparison clearly identifies that the Fe layer remaining on top of the experimental Si substrate after Ar⁺ beam sputtering is in the form of a homogeneous mixed layer, where the Fe/Si interface excitation is absent in the experimental spectra owing to pulverization of the Fe/Si interface during the Ar⁺ sputtering process.     

Gold surface plasmon crystal structure based‐on polystyrene template for biosensor application

In this communication, we assembled ordered polystyrene (PS) microsphere array as a template with the drop‐coating method, and the oxygen plasma was used to etch the template to adjust the spacing between the PS microspheres. Nano‐triangular gold array and silver nano‐pyramid array were obtained by ion beam sputtering to deposit precious metal gold and silver. We observed the surface morphology of Au and Au/Ag composite films by scanning electron microscope and characterized the films by X‐ray diffraction and ultraviolet/visible light spectrophotometer. The results show that the etching time of oxygen plasma has an obvious effect in adjusting the spacing between PSs and has a significant effect on the morphology of Au structure.