Development and utility of a new 3-D magnetron source for high rate deposition of highly conductive ITO thin films near room temperature.

As transparent conductive films, indium tin oxide (ITO) materials are being extensively used as electrodes in various technological and optoelectronic applications. The demand for ITO films is firmly increasing because of the widespread market growth in these industries, but the available solutions only partly fulfill the prerequisites of high transmittance, low resistivity, large area process, cost-effective manufacturing, high growth rate and low-temperature process. The present work demonstrates a possible framework for the detailed study of ITO coatings in addition to the development of a novel highly confined 3-D magnetron source (3DMS) that can be simply used for tailored products. In this work, the deposition conditions are optimized through plasma chemistry by utilizing various in situ plasma diagnostics. The emphasis is given to studying the effects of different deposition conditions such as power density and oxygen (O2) flow. Measurements show that the 3DMS can efficiently produce very high-density plasmas at a low-discharge voltage. The combined effect of high electron density and energy flux favors high growth rate deposition up to ∼1.75 nm s-1. By controlling the plasma parameters, energy flux on the substrate, In3+, Sn4+, oxygen vacancies, and mobility, highly transparent ITO film with a very low resistivity of ∼4.2 × 10-4 Ω cm is fabricated at low-temperature using a 3DMS process with the incorporation of O2 flow.

Multi c-BN Coatings by r.f Diode Sputtering and Investigation of Wear Behavior.

Cubic boron nitride (c-BN) films on tool substrates are tendency to delaminate. Therefore, many research groups have studied improvement of c-BN synthesis method and deposition processes due to many potential applications. In this paper, we show that the adhesion property of c-BN layer system can be improved by deposing multi c-BN layers. The multi c-BN layers were deposited by r.f (13.56 MHz) diode sputtering apparatus on cemented carbide tool substrates with a TiAlN adhesion layer. For industrial applications, we performed turning and milling experiments under dry and high speed cutting conditions. In this multi c-BN layer system, the lifetime of the tool is affected by the physical properties of the substrate and coated layers such as substrate grain size, thickness of the TiAlN and first c-BN layer and the total number of c-BN layers in this system. Mostly, fine grain size substrates showed longer lifetimes of over 4 times than raw one. In the turning performance, mono TiAlN layer systems were about two times lower lifetime than mono and multi c-BN layer system, moreover, we could be improved adhesion property for milling performance on tool substrates with binary multi c-BN layer systems under dry and high speed cutting conditions. The new application results of the multi c-BN layer system confirm that the high potential of c-BN coatings on cutting tools.

Surface Energy in Nanocrystalline Carbon Thin Films: Effect of Size Dependence and Atmospheric Exposure.

Surface energy (SE) is the most sensitive and fundamental parameter for governing the interfacial interactions in nanoscale carbon materials. However, on account of the complexities involved of hybridization states and surface bonds, achieved SE values are often less in comparison with their theoretical counterparts and strongly influenced by stability aspects. Here, an advanced facing-target pulsed dc unbalanced magnetron-sputtering process is presented for the synthesis of undoped and H/N-doped nanocrystalline carbon thin films. The time-dependent surface properties of the undoped and H/N-doped nanocrystalline carbon thin films are systematically studied. The advanced plasma process induced the dominant deposition of high-energy neutral carbon species, consequently controlling the intercolumnar spacing of nanodomain morphology and surface anisotropy of electron density. As a result, significantly higher SE values (maximum = 79.24 mJ/m2) are achieved, with a possible window of 79.24-66.5 mJ/m2 by controlling the experimental conditions. The intrinsic (size effects and functionality) and extrinsic factors (atmospheric exposure) are resolved and explained on the basis of size-dependent cohesive energy model and long-range van der Waals interactions between hydrocarbon molecules and the carbon surface. The findings anticipate the enhanced functionality of nanocrystalline carbon thin films in terms of selectivity, sensitivity, and stability.

Shaping thin film growth and microstructure pathways via plasma and deposition energy: a detailed theoretical, computational and experimental analysis.

Understanding the science and engineering of thin films using plasma assisted deposition methods with controlled growth and microstructure is a key issue in modern nanotechnology, impacting both fundamental research and technological applications. Different plasma parameters like electrons, ions, radical species and neutrals play a critical role in nucleation and growth and the corresponding film microstructure as well as plasma-induced surface chemistry. The film microstructure is also closely associated with deposition energy which is controlled by electrons, ions, radical species and activated neutrals. The integrated studies on the fundamental physical properties that govern the plasmas seek to determine their structure and modification capabilities under specific experimental conditions. There is a requirement for identification, determination, and quantification of the surface activity of the species in the plasma. Here, we report a detailed study of hydrogenated amorphous and crystalline silicon (c-Si:H) processes to investigate the evolution of plasma parameters using a theoretical model. The deposition processes undertaken using a plasma enhanced chemical vapor deposition method are characterized by a reactive mixture of hydrogen and silane. Later, various contributions of energy fluxes on the substrate are considered and modeled to investigate their role in the growth of the microstructure of the deposited film. Numerous plasma diagnostic tools are used to compare the experimental data with the theoretical results. The film growth and microstructure are evaluated in light of deposition energy flux under different operating conditions.

Low temperature plasma processing for cell growth inspired carbon thin films fabrication.

The recent bio-applications (i.e. bio-sensing, tissue engineering and cell proliferation etc.) are driving the fundamental research in carbon based materials with functional perspectives. High stability in carbon based coatings usually demands the high density deposition. However, the standard techniques, used for the large area and high throughput deposition of crystalline carbon films, often require very high temperature processing (typically >800 °C in inert atmosphere). Here, we present a low temperature (<150 °C) pulsed-DC plasma sputtering process, which enables sufficient ion flux to deposit dense unhydrogenated carbon thin films without any need of substrate-bias or post-deposition thermal treatments. It is found that the control over plasma power density and pulsed frequency governs the density and kinetic energy of carbon ions participating during the film growth. Subsequently, it controls the contents of sp(3) and sp(2) hybridizations via conversion of sp(2) to sp(3) hybridization by ion's energy relaxation. The role of plasma parameters on the chemical and surface properties are presented and correlated to the bio-activity. Bioactivity tests, carried out in mouse fibroblast L-929 and Sarcoma osteogenic (Saos-2) bone cell lines, demonstrate promising cell-proliferation in these films.

La/Sm/Er Cation Doping Induced Thermal Properties of SrTiO3 Perovskite.

The La/Sm/Er cations with different radii doping SrTiO3 (STO) as model Sr0.9R0.1TiO3 (R = La, Sm, Er) were designed to investigate structural characteristics and thermal properties by the molecular dynamics simulation with the Green-Kubo relation at 300-2000 K. The structural characteristics were composed of lattice constant, atoms excursion, and pair correlation function (PCF). The thermal properties consisted of heat capacity and thermal conductivity. The lattice constant of R-doped exhibited less than the STO at 300-1100 K and more than STO at 1500-2000 K, which was encouraged by atom excursion and PCF. The thermal properties was compared with literature data at 300-1100 K. In addition, the thermal properties at 1100-2000 K were predicted. It highlights that thermal conductivity tends to decrease at high temperature, due to perturbation of La, Sm, and Er, respectively.

Simple realization of efficient barrier performance of a single layer silicon nitride film via plasma chemistry.

Due to the problem of degradation by moisture or oxygen, there is growing interest in efficient gas diffusion barriers for organic optoelectronic devices. Additionally, for the continuous and long-term operation of a device, dedicated flexible thin film encapsulation is required, which is the foremost challenge. Many efforts are being undertaken in the plasma assisted deposition process control for the optimization of film properties. Control of the plasma density along with the energy of the principal plasma species is critical to inducing alteration of the plasma reactivity, chemistry, and film properties. Here, we have used the radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) technique to deposit amorphous silicon nitride (SiNx) barrier films onto a plastic substrate at different pressures. A large part of our efforts is devoted to a detailed study of the process parameters controlling the plasma treatment. Numerous plasma diagnostic techniques combined with various characterization tools are purposefully used to characterize and investigate the plasma environment and the associated film properties. This contribution also reports a study of the correlations between the plasma chemistry and the chemical, mechanical, barrier, and optical properties of the deposited films. The data reveal that the film possesses a very low stress for the condition where the net energy imparted on the substrate is at a minimum. Simultaneously, a relatively high ion flux and high energy of the ions impinging on the film growth surfaces are crucial for controlling the film stress and the resulting barrier properties.

Low temperature synthesis of silicon quantum dots with plasma chemistry control in dual frequency non-thermal plasmas.

The advanced materials process by non-thermal plasmas with a high plasma density allows the synthesis of small-to-big sized Si quantum dots by combining low-temperature deposition with superior crystalline quality in the background of an amorphous hydrogenated silicon nitride matrix. Here, we make quantum dot thin films in a reactive mixture of ammonia/silane/hydrogen utilizing dual-frequency capacitively coupled plasmas with high atomic hydrogen and nitrogen radical densities. Systematic data analysis using different film and plasma characterization tools reveals that the quantum dots with different sizes exhibit size dependent film properties, which are sensitively dependent on plasma characteristics. These films exhibit intense photoluminescence in the visible range with violet to orange colors and with narrow to broad widths (∼0.3-0.9 eV). The observed luminescence behavior can come from the quantum confinement effect, quasi-direct band-to-band recombination, and variation of atomic hydrogen and nitrogen radicals in the film growth network. The high luminescence yields in the visible range of the spectrum and size-tunable low-temperature synthesis with plasma and radical control make these quantum dot films good candidates for light emitting applications.

Size-controlled growth and antibacterial mechanism for Cu:C nanocomposite thin films.

The interdependence of 'size' and 'volume-fraction' hinders the identification of their individual role in the interface properties of metal nanoparticles (NPs) embedded in a matrix. Here, the case of Cu NPs embedded in a C matrix is presented for their profound antibacterial activity. Cu:C nanocomposite thin films with fixed Cu content (≈12 atomic%) are prepared using a plasma process where plasma energy controls the size of Cu NPs (from 9 nm to 16 nm). An inverse relationship between the size-effect on antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria is established through the real time monitoring of an aliquot by inductively coupled plasma mass spectrometry, which confirmed the inverse relationship of Cu ion release from the nanocomposite with varied Cu NP sizes. It was found that enhancing the total power density increases the plasma density as well as effective kinetic energy of the plasma species, which in turn creates a large number of nucleation sites and restricts the island kind of growth of Cu NPs. The mechanism of NP size-control is illustrated on the basis of ion density and nucleation and the growth regime of plasma species. This physical approach to NP size reduction anticipates a contamination-free competitive recipe of size-control to capping based chemical methods.

Plasma engineering of silicon quantum dots and their properties through energy deposition and chemistry.

The characterization of plasma and atomic radical parameters along with the energy influx from plasma to the substrate during plasma enhanced chemical vapor deposition (PECVD) of Si quantum dot (QD) films is presented and discussed. In particular, relating to the Si QD process optimization and control of film growth, the necessity to control the deposition environment by inducing the effect of the energy of the key plasma species is realized. In this contribution, we report dual frequency PECVD processes for the low-temperature and high-rate deposition of Si QDs by chemistry and energy control of the key plasma species. The dual frequency plasmas can effectively produce a very high plasma density and atomic H and N densities, which are found to be crucial for the growth and nucleation of QDs. Apart from the study of plasma chemistry, the crucial role of the energy imparted due to these plasma activated species on the substrate is determined in light of QD formation. Various plasma diagnostics and film analysis methods are integrated to correlate the effect of plasma and energy flux on the properties of the deposited films prepared in the reactive mixtures of SiH4/NH3 at various pressures. The present results are highly relevant to the development of the next-generation plasma process for devices that rely on effective control of the QD size and film properties.

Fabrication of bioactive, antibacterial TiO2 nanotube surfaces, coated with magnetron sputtered Ag nanostructures for dental applications.

We investigated whether a silver coating on an anodic oxidized titania (TiO2) nanotube surface would be useful for preventing infections in dental implants. We used a magnetron sputtering process to deposit Ag nanoparticles onto a TiO2 surface. We studied different sputtering input power densities and maintained other parameters constant. We used scanning electron microscopy, X-ray diffraction, and contact angle measurements to characterize the coated surfaces. Staphylococcus aureus was used to evaluate antibacterial activity. The X-ray diffraction analysis showed peaks that corresponded to metallic Ag, Ti, O, and biocompatible anatase phase TiO2 on the examined surfaces. The contact angles of the Ag nanoparticle-loaded surfaces were significantly lower at 2.5 W/cm2 input power under pulsed direct current mode compared to commercial, untreated Ti surfaces. In vitro antibacterial analysis indicated that a significantly reduced number of S. aureus were detected on an Ag nanoparticle-loaded TiO2 nanotube surface compared to control untreated surfaces. No cytotoxicity was noted, except in the group treated with 5 W/cm2 input power density, which was the highest input of power density we tested for the magnetron sputtering process. Overall, we concluded that it was feasible to create antibacterial Ag nanoparticle-loaded titanium nanotube surfaces with magnetron sputtering.

Structural and electrical properties of ZnO films deposited with low-temperature facing targets magnetron sputtering (FTS) system with changes in H2 and O2 flow rate.

ZnO has been studied as a strong candidate for high-quality TCO in accordance with increasing demand to replace ITO. The origin of n-doping in ZnO is not clearly understood, but recently, the H2 effect has received attention due to the role it plays in O-rich and O-poor conditions. In spite of recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. To control the electrical conductivity of ZnO, this study was performed using an FTS system with H2 and O2 addition at low processing temperature. The structural and electrical properties of ZnO thin films deposited at various H2 and O2 flow rates were investigated using XRD and a sheet resistance meter. In response to changes in H2 and O2 flow rates, the crystallization and related grain size of the ZnO films were somewhat changed. The sheet resistance increased from approximately 10(-1) to approximately 10(4) M ohm/sq. when the O2 flow rate was increased, and the resistance decreased from approximately 10(-1) to approximately 10(-4) M ohm/sq. when the H2 flow rate was increased. The increase of sheet resistance with O2 flow rates could be explained by decrease of oxygen vacancies. The decrease of sheet resistance with H2 flow rates could be explained by increase of the electrons from interstitial hydrogen atoms. The plasma characteristics were analyzed using optical emission spectroscopy (OES). But, the overall spectrum did not change with the H2 and O2 gas flow rates. So, the dramatic changes in the electrical properties of ZnO thin films could be considered to be a result of changes in chemical composition of the thin films rather than the plasma status.

Plasma-enhanced reactive linear sputtering source for formation of silicon-based thin films.

In this study, an inductively coupled plasma (ICP)-enhanced reactive sputter deposition system with a rectangular target was developed as a linear plasma source for roll-to-roll deposition processes. The longitudinal distribution of the film thickness indicated the feasibility of uniformity control via the control of the power deposition profile of the assisted ICPs. The characteristics of Si films were investigated in terms of the film thickness uniformity and film crystallinity. The results of Raman and X-ray diffraction measurements indicated the crystallization of the Si film with a crystallinity as high as 73%-78% in all the samples of the longitudinal position.

Systematic study of interdependent relationship on gold nanorod synthesis assisted by electron microscopy image analysis.

Here, we systematically investigated the independent, multiple, and synergic effects of three major components, namely, ascorbic acid (AA), seed, and silver ions (Ag+), on the characteristics of gold nanorods (GNRs), i.e., longitudinal localized surface plasmon resonance (LSPR) peak position, shape, size, and monodispersity. To quantitatively assess the shape and dimensions of GNRs, we used an automated transmission electron microscopy image analysis method using a MATLAB-based code developed in-house and the concept of solidity, which is the ratio between the area of a GNR and the area of its convex hull. The solidity of a straight GNR is close to 1, while it decreases for both dumbbell- and dogbone-shaped GNRs. We found that the LSPR peak position, shape, and monodispersity of the GNRs all altered simultaneously with changes in the amounts of individual components. For example, as the amount of AA increased, both the LSPR peak and solidity decreased, while the polydispersity increased. In contrast, as the amount of seeds increased, both the LSPR and solidity increased, while the monodispersity improved. More importantly, we found that the influence of each component can actually change depending on the composition of the GNR growth solution. For instance, the LSPR peak position red-shifted as the amount of AA increased when the seed content was low, whereas it blue-shifted when the seed content was high.

Growth kinetics of plasma-polymerized films.

The growth kinetics of polymer thin films prepared by plasma-based deposition method were explored using atomic force microscopy. The growth behavior of the first layer of the polythiophene somewhat differs from that of the other layers because the first layer is directly deposited on the substrate, whereas the other layers are deposited on the polymer itself. After the deposition of the first layer, each layer is formed with a cycle of 15 s. The present work represents the growth kinetics of the plasma-polymerized films and could be helpful for further studies on growth kinetics in other material systems as well as for applications of plasma-polymerized thin films.

Controlling conductivity of carbon film for L-929 cell biocompatibility using magnetron sputtering plasmas.

As a material of current interest compatible with many living organisms, carbon has received considerable attention for applications in medicine. To improve and investigate the performance and applications of diamond-like carbon (DLC) films for implantable bio-organs, it is important to optimize the synthesis process from the original deposition conditions to control the characterization of DLC. Simultaneously, it is necessary to develop new techniques and processes that yield DLC films with stronger adhesion to the substrate and better biocompatibility. This work investigates the suitability of sputtering plasmas for application of carbon film biocompatibility in cell growth. This work also reports an approach to the study of the biomedical response of the well-characterized carbon films deposited by a DC unbalanced magnetron sputtering system (UBMS). Conductive carbon films are prepared at a working pressure of 3 mTorr, and their properties are studied under different operating conditions by varying the target power density. In the present work, we have used L-929 cells as the biomaterial. The influence of L-929 cells on the carbon films fabricated using closed field UBMS is studied. The data reveal that the change in L-929 cell growth with 1-5 day's proliferation is caused by the decreasing electrical resistivity with increasing sp2 bonding structure.

Tailoring of antibacterial Ag nanostructures on TiO2 nanotube layers by magnetron sputtering.

To reduce the incidence of postsurgical bacterial infection that may cause implantation failure at the implant-bone interface, surface treatment of titanium implants with antibiotic materials such as silver (Ag) has been proposed. The purpose of this work was to create TiO2 nanotubes using plasma electrolytic oxidation (PEO), followed by formation of an antibacterial Ag nanostructure coating on the TiO2 nanotube layer using a magnetron sputtering system. PEO was performed on commercially pure Ti sheets. The Ag nanostructure was added onto the resulting TiO2 nanotube using magnetron sputtering at varying deposition rates. Field emission scanning electron microscopy and transmission electron microscopy were used to characterize the surface, and Ag content on the TiO2 nanotube layer was analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. Scanning probe microscopy for surface roughness and contact angle measurement were used to indirectly confirm enhanced TiO2 nanotube hydrophilicity. Antibacterial activity of Ag ions in solution was determined by inductively coupled plasma mass spectrometry and antibacterial testing against Staphylococcus aureus (S. aureus). In vitro, TiO2 nanotubes coated with sputtered Ag resulted in significantly reduced S. aureus. Cell viability assays showed no toxicity for the lowest sputtering time group in the osteoblastic cell line MC3T3-E1. These results suggest that a multinanostructured layer with a biocompatible TiO2 nanotube and antimicrobial Ag coating is a promising biomaterial that can be tailored with magnetron sputtering for optimal performance.