Integrated plasma-aided nanofabrication facility: Operation, parameters, and assembly of quantum structures and functional nanomaterials

The development, operation, and applications of two configurations of an integrated plasma-aided nanofabrication facility (IPANF) comprising low-frequency inductively coupled plasma-assisted, low-pressure, multiple-target RF magnetron sputtering plasma source, are reported. The two configurations of the plasma source have different arrangements of the RF inductive coil: a conventional external flat spiral “pancake” coil and an in-house developed internal antenna comprising two orthogonal RF current sheets. The internal antenna configuration generates a “unidirectional” RF current that deeply penetrates into the plasma bulk and results in an excellent uniformity of the plasma over large areas and volumes. The IPANF has been employed for various applications, including low-temperature plasma-enhanced chemical vapor deposition of vertically aligned single-crystalline carbon nanotips, growth of ultra-high aspect ratio semiconductor nanowires, assembly of optoelectronically important Si, SiC, and Al_1-xIn_xN quantum dots, and plasma-based synthesis of bioactive hydroxyapatite for orthopedic implants.     

Surface modification of steel surfaces by electron beam excited plasma processing

The nitriding performance of low power electron beam excited plasma is investigated by characterizing the surface of nitrided low alloy Cr-Mo steels. In this research, a particular attention was given to the effect of the acceleration voltage and processing time on the composition and hardness of the processed samples. In an attempt to maximize the dissociation of N₂, the acceleration voltages applied in our experiments were set within a range that corresponds to the maximum dissociation cross-section of N₂. The results show that the peak intensity of the alpha Fe observed for the unprocessed sample decreases as the acceleration voltage increases. Moreover, the peak intensities depicting the formation of the nitride compound layers, Fe₄N and Fe₃N phases, increases with the acceleration voltage of the electron beam. Consequently, the surface hardness of the treated low alloy steel was increased by more than two times that of the unprocessed specimen.     

Surface modification of CdSe quantum dots for biosensing applications: Role of ligands

For an optimum performance of colloidal nanocrystal devices for a variety of applications such as photonic devices, solar cells and biological labelling, the determining factors are the nanocrystal surface and size. In this work, these two factors have been tuned via wet chemistry to tailor the material properties: The absorption and emission spectra have been tailored by choice of the nanocrystal size; nanocrystal shape by surface modification and photoluminescence (PL) efficiency determined by surface traps, has been tuned via appropriate selection of the nanocrystal capping ligands. Here, we have shown that through ligand-exchange process, the surface of the CdSe quantum dots (QDs) can be modified by replacing the longer-chain ligands of conventional trioctyl phosphine oxide (TOPO) or oleic acid (OA) with shorter-chain ligand of butyl amine. This imparts colloidal stability and water solubility to CdSe QDs for its potential applications in biosensors and biological imaging. It is conjectured that crystallite sizes, oxidation potential of CdSe QDs and stereochemical compatibility of ligands (TOPO, oleic acid and butyl amine) greatly influences the photophysics and photochemistry of CdSe QDs.     

Surface reconstruction and elastic behavior of silicon nanobeams: The impact of applied deformation

Using molecular dynamics calculations with a recently developed modified embedded atom method (MEAM) potential, the overall elastic behavior of silicon (100) nanobeams under externally applied strain at room temperature is investigated. As uniaxial tensile strain increases, the stability range of any relevant reconstructions changes, thus, the surface region undergoes a series of reconstructions. In nanostructures, such as nanoplates, nanobeams, and nanowires, this phenomenon is significant and changes the elastic response. The results indicate that the elastic behavior of nanostructures is not only size-dependent, but also load-dependent.     

A modified Wenzel model for hydrophobic behavior of nanostructured surfaces

A modified Wenzel model was proposed to explore the influence of pore size distributions (PSDs) on water repellency of nanostructured surfaces. Rough surfaces with different porous structures, including surface areas and PSDs, were fabricated by stacking different solid ratios of TiO₂ nanoparticles. These fluorinated surfaces exhibited an excellent hydrophobic performance with the highest value of contact angle ∼ 165°. The PSDs of these surfaces, determined from Dubinin-Stoeckli equation, were found to vary with the solid ratios. The modified Wenzel model incorporated with the PSDs gave a fairly good prediction in describing the variation of contact angle with surface roughness, which is very close to the experimental data. These results demonstrated that the heterogeneity of surfaces caused by different PSDs would induce the hydrophobic behavior.     

Plasma-surface interactions for advanced plasma etching processes in nanoscale ULSI device fabrication: A numerical and experimental study

Plasma-surface interactions in Cl- and Br-based plasmas have been studied for advanced front-end-of-line (FEOL) etching processes in nanoscale ULSI device fabrication. A Monte Carlo-based atomic-scale cellular model (ASCeM) was developed to simulate the feature profile evolution on nanometer scale during Si etching in Cl₂ and Cl₂/O₂ plasmas, including surface oxidation, inhibitor deposition, and ion reflection and penetration on surfaces. A classical molecular dynamics (MD) simulation for Si/Br and Si/HBr as well as Si/Cl systems was also developed, along with an improved Stillinger-Weber interatomic potential model for Si/halogen interactions, to clarify surface reaction kinetics on atomic scale during Si etching in Cl₂ and HBr plasmas. The numerical results revealed the origin of profile or surface anomalies such as microtrench, roughness, and residue, and also etching fundamentals such as etch yield, product stoichiometry, and atomistic surface structures. Moreover, the etching of high-k dielectric and metal electrode materials, such as HfO₂ and TaN, was investigated in BCl₃- and Cl₂-containing plasmas with and without rf biasing, to gain an understanding of the etch mechanisms and to achieve anisotropic and selective etching of metal/high-k gate stacks.     

Enhanced control over selective-area intermixing of In0.15Ga0.85As/GaAs quantum dots through post-growth exposure to radio-frequency plasma

Post-growth treatment with a low pressure, CF₄-plasma is demonstrated to reliably inhibit the interdiffusion of In and Ga atoms in In_0.15Ga_0.85As/GaAs self-assembled quantum dot wafer structures subjected to rapid thermal annealing temperatures between 700 °C and 800 °C for a duration of 20 s. Comparative studies of the effects of rapid thermal annealing were made on plasma treated samples and samples that were capped with either 200 nm of plasma enhanced chemical vapor deposited SiO₂ or 220 nm of thermally deposited TiO₂ prior to plasma exposure, as well as to uncapped, untreated control samples. Room-temperature photoluminescence spectra were acquired using a Ti-Sapphire laser operating at 742 nm as the excitation source. A bandgap differential of 84 meV (94 nm) was measured across a wafer sample annealed at 775 °C, when contrasting sections that were uncapped and treated with the CF₄-plasma versus sections that were annealed without any treatment to the surface. This was comparable to a sample that was capped with the TiO₂ film, which produced a 73.5 meV (82 nm) variance from the raw, annealed-only sample.     

Fabrication of superhydrophobic surfaces for corrosion protection: a review

ABSTRACT

Steel, aluminium and magnesium are important engineering materials owing to their excellent mechanical properties. However, their applications are limited due to inadequate corrosion resistance. Various coatings and improvement technologies are used to enhance the corrosion resistance in industry and consumer products. Fabrication of hydrophobic surfaces is a very interesting approach to anticorrosion in that it is derived from the superhydrophobicity found in nature. This paper is a general review of the methods to construct a superhydrophobic surface, i.e. a thin coating layer, on various metallic materials surfaces to enhance their anticorrosion property, providing an introduction of the superhydrophobicity, including theory, properties and fabricating methods. Different methods including spray technique, laser ablation, electrochemical deposition, micro-arc oxidation and etching routes were discussed.     

Surface morphology and light scattering properties of plasma etched ZnO:B films grown by LP-MOCVD for silicon thin film solar cells

LP-MOCVD deposited ZnO:B thin films, post-etched by argon plasma processes, were investigated in this study in order to optimise the ZnO:B/p-layer interface when the ZnO:B is used as front electrode of p-i-n a-Si:H solar cells. At varying etching time different surface roughness was obtained and the evolution of the surface morphology was correlated with the texture characteristic and its scattering properties. Atomic force microscopy data were analysed and discussed together with the scattering properties, which are haze parameter and angular resolved scattering (ARS) distribution.The presence of several preferential scattering angles was hypothesized and a deconvolution approach was applied to each angular scattering curve. For each fixed preferential scattering angle θ_i we associated a Gaussian distribution of the scattered light amount related to a well-defined scattering surface. The different preferential scattering angles were correlated to different scattering phenomena, the modifications of the angular scattering curves well agreed with SEM and AFM images.It is well known that a:Si-H solar cells fabricated on MOCVD deposited ZnO:B substrates show poor FF and V_oc values with good J_sc value. We demonstrated that only an effective sharp edge rounding off produced by an appropriately long plasma etching treatment is able to make MOCVD deposited ZnO:B perfectly suitable for high quality a-Si:H based devices.     

A novel magnetorheological honing process for nano-finishing of variable cylindrical internal surfaces

A novel magnetorheological honing process is designed and developed for nano-finishing of cylindrical internal surfaces with the help of permanent magnets. The radial movement of magnetic tool surface is adjusted as per the internal diameter of different cylindrical components and make it fixed before start of finishing so that it can maintain constant working gap while perform finishing. The present developed magnetic tool surface always constitutes higher magnetic field than the inner surface of ferromagnetic or non-ferromagnetic cylindrical workpiece. This is an important requirement to finish the internal surface of ferromagnetic or non-ferromagnetic cylindrical components because it ensures MR polishing fluid cannot stick on the workpiece surface while performing the finishing. Hence, present developed process is useful for finishing of ferromagnetic cylindrical molds, dies, hydraulic actuators, etc. for its better functional applications after the conventional honing or grinding process. The internal surface roughness of cylindrical ferromagnetic workpiece is dropped to 90?nm from its initial value of 360?nm in 100 minutes of finishing. Further scanning electron microscopy has also been done to understand the surface characteristics of finished workpiece. The results revealed that the developed magnetorheological honing process is capable to perform nano-finishing of internal surface of the ferromagnetic cylindrical components.     

Preparation and characterization of ethylenediamine and cysteamine plasma polymerized films on piezoelectric quartz crystal surfaces for a biosensor

This paper describes a method for the modification of quartz crystal surfaces to be used as a transducer in biosensors that allow recognition and quantification of certain biomolecules (antibodies, enzymes, proteins, etc). Quartz crystal sensors were modified by a plasma based electron beam generator in order to detect the level of the toxin histamine within biological liquids (blood, serum) and food (wine, cheese, fish etc.). Cysteamine and ethylenediamine were used as precursors in the plasma. After each modification step, the layers on the quartz crystal were characterized by frequency measurements. Modified surfaces were also characterized by contact angle, X-ray photoelectron spectroscopy and atomic force microscopy to determine the physical and chemical characteristics of the surfaces after each modification. Finally, the performance of the sensors were tested by the response to histamine via frequency shifts. The frequency shifts of the sensors prepared by plasma polymerization of ethylenediamine and cysteamine were approximately 3230 Hz and 5630 Hz, respectively, whereas the frequency change of the unmodified crystal surface was around 575 Hz.     

Adsorption and diffusion of oxygen on metal surfaces studied by first-principle study:A review

First-principle calculations,especially by the density functio nal theory(DFT),is used to study the structure and properties of oxygen/metal interfaces.Adsorption of oxygen molecules or atoms on metal surfaces plays a key role in surface science and technology.This review is dedicated to the adsorption of oxygen molecules or atoms on metal surfaces and diffusion behavior from first-principle investigation.We hope that this review can provide some useful contributions to understa nd the study of adsorption properties and diffusion behavior on a metal surface at an atomic-scale,especially for those interested in catalytic oxidation and application of corrosion.     

Investigation on the effect of process parameters in atmospheric pressure plasma treatment on carbon fiber reinforced polymer surfaces for bonding

Carbon Fiber Reinforced Polymer (CFRP) is used extensively in aerospace applications. Acceptance of bonded CFRP structures, mainly for aerospace applications, requires a robust surface preparation method with improved process controls to ensure high bond quality. Consistent repeatability is a factor lacking from many surface preparation processes. Atmospheric pressure plasma surface treatment is one of the robust surface preparation processes that have drawn wide attention in recent years. This process is capable of being applied in a production clean room environment that would minimize the risk of contamination and reduce cost. In plasma surface treatment the process parameters are easily controlled, documented providing a repeatable process with a high level of consistency. In this paper, the process parameters for atmospheric pressure plasma surface treatment and their effect on bonding for Out-Of-Autoclave (OOA) CFRP composite panels were fully investigated. A mechanized machine with sensory feedback to plasma treat surfaces was developed to change the process parameters for application on larger panels. By the aid of Design of Experiment (DOE) methodology critical process parameters were identified and a mathematical regression model was developed. The mathematical regression model was used to quantify the effect of process parameters on the bonding strength and the model was optimized to find the optimum settings.     

A combined sensor for the diagnostics of plasma and film properties in magnetron sputtering processes

A combined sensor for the simultaneous measurement of plasma and deposition parameters has been designed and built. It comprises (i) a quartz crystal microbalance, (ii) a planar Langmuir probe and (iii) a calorimetric (Gardon) probe, which allows to measure the deposition rate, typical plasma parameters (plasma density and electron temperature) and the total energy input into a growing film. The combined sensor is electrically insulated against ground, allowing these measurements also for floating or substrate-bias conditions. These parameters are measured (nearly) simultaneously, controlled by a specific measurement and analysis program. The operation of this combined sensor is demonstrated for the deposition of copper and tungsten films with a 2 inch planar magnetron.