ICMCTF2011 Session GP: Symposium G Poster Session

Austempered ductile iron (ADI) is an attractive engineering material due to its excellent strength, toughness and the low cost. This study utilized electroless nickel (EN) and cathodic arc evaporation (CAE) technologies, with the known advantage of low processing temperature, to treat the ADI substrates. The eligibility of applying the EN and CAE-TiN duplex coatings on ADI, along with the coating properties, such as structure, roughness, and adhesion were evaluated and analyzed. Moreover, polarization tests were performed to further understand the effect of both the coatings on the corrosion behavior of ADI. The results showed that the unique microstructure of ADI did not deteriorate after EN and CAE treatments. Corrosion resistance of ADI in 3.5% NaCl solution could have a noticeable improvement via the use of EN/TiN duplex coatings.

In this study, we synthesized a-C:H films on polyethylene terephthalate (PET) substrates, which have the highest gas barrier properties of the common polymer materials, with a line type atmospheric-pressure plasma CVD apparatus. The gas permeability of the films on PET was measured by a gas permeation tester, the surface of the films was observed by scanning electron microscope (SEM). In addition, we conducted an ultraviolet ray transmission measurement, an accelerated weathering test and cyclic fatigue test.

According to observation by SEM, the a-C:H films consisted of tiny particles which sizes were around 200 nm.

Ultraviolet permeability of the a-C:H films was 0-28 % in the ultraviolet range 320-400 nm, while ultraviolet permeability of uncoated films was 50-80 %.

Work supported by FAPESP.

Low-k insulating materials with the relative dielectric constants lower than 2 have been required for modern ultra large-scale integration (ULSI) technology. So far, many efforts have been made to develop new low-k interlayers for multilevel interconnection in ULSI. Carbon nitride (CN_x) has a great potential for low-k material because of its excellent properties such as extreme hardness, high resistivity, and low dielectric constant. While the CN_x films have been studied by using various deposition techniques, the liquid-phase deposition has been attempted as an alternative deposition technique by using organic liquid containing nitrogen. In this work, we have studied composition, bonding structure, and electrical properties of CN_x films deposited using liquid acrylonitrile.

The CN_x films were deposited by application of DC bias voltage to n-Si substrates immersed in acrylonitrile. Continuous, uniform films are obtained by applying both positive and negative bias voltage. Measurements of X-ray photoelectron spectra (XPS) show the presence of C, N, and O as major components of the deposited films. The atomic ratios of nitrogen to carbon (N/C) are determined as 0.2 – 0.3 for the as-grown samples. While the films deposited under positive bias mainly consist of C and N, considerable amounts of oxygen and sodium are also contained in the films deposited under negative bias. From analysis of C 1s and N 1s spectra, the major bonding state of the CN_x film deposited under negative bias can be attributed to a mixed phase of C≡N and hydrogenated C=N bonds. On the other hand, the CN_x film deposited under positive bias consists of the partially hydrogenated C=N bond.

Metal-insulator-semiconductor (MIS) structures were fabricated using the CN_x insulating layers to evaluate the electrical properties of the deposited films. For the films deposited under positive bias, three distinct regions of accumulation, depletion, and inversion are shown in the C-V characteristics. On the other hand, MIS capacitor fabricated using the films deposited under the negative bias show anomalous behaviors such as a hysteresis shift in their C-V curves, suggesting that the CN_x films deposited under negative bias application are unsuitable for the dielectric material. The lowest relative dielectric constant of 2.6 was determined using the accumulation capacitance and the thickness of the CN_x film. Since the dielectric constant comparable to the existing low-k materials can be obtained, the liquid deposited CN_x film is a promising ultralow-k material that is required for the multilevel interconnection for ULSI circuits.

Thin films of In_2-xFe_xO₃ were deposited on glass substrates using ultrafast microwave annealing technique. It is well known that SiC is an excellent absorber of microwaves. Hence, microwave heating provides ultra-fast ramp rates (> 1000ºC/s) and very-high annealing temperature (up to 2100°C) conditions required for depositing In_2-xFe_xO₃ films. In this method, microwaves (~ 1 GHz) from a source are amplified and directly coupled to the SiC through a microwave heating head. The indium iron oxide powder is placed on SiC sample. Since the sample is placed in microwave transparent surroundings, the microwaves are absorbed by the SiC sample only, leading to extremely high heating rates. This feature contrasts microwave annealing with resistive and inductive heating furnaces, where the heating source not only heats the sample but also the surrounding ambient. Similarly, as soon as the microwave source is turned off, the sample cools down rapidly because of cool ambient surrounding the sample. The glass substrate was placed directly on top of the hearth thus we were able to obtain deposited films. The structural, and transport properties of the films showed similar properties to that of the bulk samples.

The use of solid lubricant coatings with low friction coefficient began in the 90s with molybdenum disulfide MoS₂ and Diamond-Like Carbon (DLC) films. DLC is currently one of the major solid lubricants and is used in several areas, including spatial area. The main problem addressed here is the degradation of DLC films by atomic oxygen from orbits satellite altitudes between 100 and 300 km. The use of silver nanoparticles dispersed throughout the film provides passivity silver oxide layers which reduces the erosion of the film.

In this paper DLC films with silver nanoparticles were obtained from an adapted magnetron sputtering system. DLC film structures were analyzed by RBS to identify silver presence. AFM analysis was used to identify silver nanoparticle distribution and grain sizes. The grain size was identified in a ranging from 50nm to 150nm. Raman spectra revealed that silver didn’t add any structural change in the film. After these analyses, the corrosion resistance of the films were tested in oxygen discharge using a RIE (Reative Ion Etching) reactor.

The main requirement of the materials used in electrical connectors is to allow low and undisturbed electrical contact resistance. However due engine vibrations and thermal fluctuations fretting wear damages can be activated in the interface decaying the electrical conductance endurance. Since many years, different materials and coating configurations under fretting wear conditions were studied more or less extensively. Between them, the non-noble tin as well as noble gold coatings but very little have been addressed concerning the silver coatings. Keeping in mind the noble properties of silver, compared to tin, and its lower costs, compared to gold, this material can be considered as potentially interesting for electrical contact applications.

The plasma nitrocarburizing is considered a highly promising process for the surface modification of stamping parts because it can lessen distortion of the conformed lattice due to its lower treatment temperature (570–580ºC), and the treatment time for nitrocarburizing is far shorter than for nitriding.

In the present work, samples of austenitic stainless steel AISI 304 were submitted to a plasma nitrocarburizing process under floating potential in a graphite hollow cathode plasma. Experiments were carried out in two plasma working gas: 10% N₂ + 80% H₂ + 10% Ar + vaporized carbon and 20% N₂ + 70% H₂ + 10% Ar + vaporized carbon. The carbon vapor is obtained during the process by sputtering of the graphite hollow cathode surface. The hollow cathode was developed to allow the insertion of samples to be treated, with no contact with the cathode surface, thus characterizing a treatment under floating potential. A special configuration of the experiment allowed a nonuniform plasma heating such that a thermal gradient was produced along the sample. So, the microstructure of the layers formed could be evaluated for a range of temperatures (450 a 550ºC). In order to compare the processes, a condition of nitriding in the plasma working gas 20% N₂ + 70% H₂ + 10% Ar was investigated, also reproducing this temperature gradient. The techniques used for characterization of the samples were: X-ray diffraction, optical microscopy, scanning electron microscopy and microhardness vickers measurements.

The results show the formation of diffusion layers and the presence of phases of nitrides (ε-Fe_2-3(C,N), γ’-Fe₄(C,N), CrN) was detected in nitrocarburized samples of stainless steel AISI 304. They also indicate that plasma nitrocarburizing, in floating potential, is a feasible and effective process for the surface treatment of materials. It is alternative to conventional nitrocarburizing, forming thick and homogeneous composite layers, and can considerably increase the surface hardness of austenitic stainless steel AISI 304.

The purpose of this work is to show the improvement of hybrid p-n junction diode performance by making the hydrophobic n-ZnO film surface. One of the most effective ways to investigate hydrophobic surface properties is a contact angle measurement. A low contact angle between a solid surface and a water-drop indicates that the surface is hydrophilic and has a high surface energy. On the contrary, a high contact angle means that the surface is hydrophobic. In general, most of an inorganic oxide surfaces show hydrophilic state while most of organic semiconductors show hydrophobic states. This mismatch has negative influence on crystalline formation of organic semiconductor deposited on oxide substrates. Therefore, in this work, wet-etching and PDMS treatment were performed to change the hydrophilic characteristics of the ZnO surface into hydrophobicity, and we observed that these changes make some differences in a grain size of an pentacene deposited on surface-treated ZnO and improve electrical characteristics of pentacene/ZnO hybrid p-n junction diode.

The grain size of sputtered-deposited ZnO increased with increasing RF power. After wet-etching in BOE (6:1) and grafting PDMS contact angles of surface-treated ZnO were 103.5, 110.9 and 115.8° at 100, 200 and 300W of RF power, respectively. It is indicated that the more hydrophobic nature, the larger grain size it could have. We confirmed that the grain size of pentacene deposited on the hydrophobic ZnO had lager than as-deposited. When ZnO was deposited at the 100W of RF power, the current density of normal pentacene/ZnO diode was 2.6A /cm² at a forward bias of 12V, while that diode using surface treatment was about twice of 5.2A/cm². Turn-on voltages were approximately 2.5 and 4.8 V for as-deposited and surface-treated pentacene/ZnO , respectively.

We have investigated the characteristics of interface for pentacene/ZnO hybrid p-n junction diode. the grain sizes of pentacene on treated-ZnO were larger than as-deposited ZnO. and the current-density increased with increasing hydrophobicity. This study present improvement of the electrical characteristics of hybrid p-n junction diode using pentacene and ZnO.

The optically-compensated-bend (OCB) mode pi-cell s exhibit fast-response time and wide-viewing angle characteristics. However, OCB-mode requires a transition of the liquid crystal molecule from an initial splay state to the bend state configurations before it can provide quick operation. It may need a high voltage or take a long warm-up time to transform to the bend state. In this study, t he polyimide alignment films have been modified to reduce the splay-to-bend trans i tion time by atmospheric pressure plasma beam treatments . The proposed process method was demonstrated to be highly effective in improving the overall transition time. The number of splay-to-bend nucleation sites in the liquid crystal cell s could be increased dramatically by up to 20 times at the initial stage, and the improvement in the cell warm-up time was achieved at 45-7 1 % reduction at 5.5 V. The various plasma processing parameters were optimized at the plasma power of 700 W, plasma distance of 25 mm, and plasma scan speed of 600 mm/sec . In addition, we maintained the excellent optical properties and response time characteristics for the OCB mode liquid crystal displays.

In this research, the sample tool material used was SKD 61 with a chemical composition of 0.36% C, 5.05% Cr, 1.21% Mo, 0.83% V, 0.92% Si, 0.43% Mn, 0.008% P, >0.001% S, Fe bal. The sample was heat treated, hardened and triple tempered to a hardness of 630 Hv. The sample was then treated in a nitrogen plasma produced by a beam current of 8 A under a working pressure of 0.4 Pa. The temperature was set at 500 degrees centigrade throughout the treatment time. The experimental set up includes bias terminals that reduce the ion density within the vicinity of the tool steel material. This is done to reduce nitriding due to ion and increase the chance of nitriding due to neutral species within the plasma.

The hardness distributions, thickness of the diffusion layer, surface roughness of the nitrided tool steels were examined to determine the mechanical and surface properties. The results of our experiments show that the surface hardness was increased to 1300 Hv, about two times more than the untreated one. The surface hardness is maintained to a depth of 30 micrometers and falls sharply and saturates to the hardness of the untreated samples in about 80 micrometers. The corresponding thickness of the diffusion layer also confirms the same results. The surface conditions were examined by scanning electron microscope and surface roughness measurements. The measured surface roughness was Ra=20 nm slight increase from the pretreatment value of 10 micrometers. However, there is no trace of the compound layer that is usually observed in the ion nitriding processes. This is also confirmed from the X-ray Diffraction peaks, as there is no visible Fe3N and Fe4N peaks observed. These results are attractive as they open new areas of application especially in the coating industry where adhesion remains to be the limiting factor in lots of the hard coatings applied to cutting tools and metal stamping punches.

Small-Scale Batch Nitriding of Tool Steels by Electron Beam Excited Plasma Source

Nitriding of cutting tools uniformly is an important criterion that has to be met for successful processing technique. A major difficulty of using plasma nitriding source for multiple batch-nitriding is the fixed positioning of the samples. The jigs and fixtures or just laying the sample on a solid surface compromises the exposure to the surrounding plasma.