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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 3 • Date May 2009

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Displaying Results 1 - 25 of 32
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Nonsinusoidal buckling of thin gold films on elastomeric substrates

    Page(s): L9 - L12
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    Buckling of stiff thin films on compliant substrates represents a variety of applications, ranging from stretchable electronics to micro-nanometrology. Different but complementary to previously reported sinusoidal buckling waves, this letter presents a nonsinusoidal surface profile of buckled thin Au films on compliant substrates, specifically, a secondary dip on top of buckling wave or rather broadened wave top with very sharp trough. This nonsinusoidal profile is likely due to tension/compression asymmetry, i.e., different strengths in tension and compression resulted from the polycrystalline, grained microstructure of metal film. Finite element analysis with asymmetric tension/compression material model has reproduced the experiments well qualitatively. View full abstract»

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  • Innovative technique for tailoring intrinsic stress in reactively sputtered piezoelectric aluminum nitride films

    Page(s): 417 - 422
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    Novel technical and technological solutions enabling effective stress control in highly textured polycrystalline aluminum nitride (AlN) thin films deposited with ac (40 kHz) reactive sputtering processes are discussed. Residual stress in the AlN films deposited by a dual cathode S-Gun magnetron is well controlled by varying Ar gas pressure, however, since deposition rate and film thickness uniformity depend on gas pressure too, an independent stress control technique has been developed. The technique is based on regulation of the flux of the charged particles from ac plasma discharge to the substrate. In the ac powered S-Gun, a special stress adjustment unit (SAU) is employed for reducing compressive stress in the film by means of redistribution of discharge current between electrodes of the S-Gun leading to controllable suppression of bombardment of the growing film. This technique is complementary to AlN deposition with rf substrate bias which increases ion bombardment and shifts stress in the compressive direction, if required. Using SAU and rf bias functions ensures tailoring intrinsic stress in piezoelectric AlN films for a particular application from high compressive -700 MPa to high tensile +300 MPa and allows the gas pressure to be adjusted independently to fine control the film uniformity. The AlN films deposited on Si substrates and Mo electrodes have strong (002) texture with full width at half maximum ranging from 2° for 200 nm to 1° for 2000 nm thick films. View full abstract»

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  • Precise and high-speed control of partial pressures of multiple gas species in plasma process chamber using pulse-controlled gas injection

    Page(s): 423 - 429
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    Multiprocesses in a single plasma process chamber with high throughput require precise, sequential, high-speed alteration of partial pressures of multiple gas species. A conventional gas-distribution system cannot realize this because the system seriously overshoots gas pressure immediately following valve operation. Furthermore, chamber volume and conductance of gas piping between the system and chamber should both be considered because they delay the stabilizing time of gas pressure. Therefore, the authors proposed a new gas-distribution system without overshoot by controlling gas flow rate based on pressure measurement, as well as a method of pulse-controlled gas injection immediately following valve operation. Time variation of measured partial pressure agrees well with a calculation based on an equivalent-circuit model that represents the chamber and gas piping between the system and chamber. Using pulse-controlled gas injection, the stabilizing time can be reduced drastically to 0.6 s for HBr added to pure Ar plasma, and 0.7 s for O2 added to Ar/HBr plasma; without the pulse control, the stabilizing times are 3 and 7 s, respectively. In the O2 addition case, rapid stabilization can be achieved during the period of line/space pattern etching of poly-Si on a thin SiO2 film. This occurs without anomalous etching of the underlying SiO2 film or the Si substrate near the sidewall, thus obtaining a wide process margin with high throughput. View full abstract»

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  • Deep Modification of materials by thermal stress wave generated by irradiation of high-current pulsed electron beams

    Page(s): 430 - 435
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    High-current pulsed electron beams generate modifications in materials over a depth range of a few hundred micrometers, far beyond the heat-affected zone. In this article, the authors presented relevant experimental results in a stainless steel substrate and described the associated transient thermal and stress processes. They attributed the deep modification to an intense stress wave arising from drastic heating of the materials about 2∼3 μm below the surface as a result of the deep penetration of electrons. Thanks to the large amplitude at several gigapscals the stress wave exerted intense impacts over a long distance. They also revealed that the interactions were dependent on the grain orientation. View full abstract»

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  • Transport and structural properties of silicon films in the amorphous-to-microcrystalline transition region

    Page(s): 436 - 442
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    Undoped hydrogenated microcrystalline silicon c-Si:H) thin films have been deposited by plasma enhanced chemical vapor deposition (PECVD) at low temperature with different hydrogen dilutions and rf powers. Large complexity of microstructure in hydrogenated microcrystalline silicon and the existence of different sizes of crystallites are demonstrated by different characterizations. The authors correlate the transport properties with the structural properties of the rf PECVD grown μc-Si:H in the amorphous-to-crystalline transition region. For chamber pressure of 2.0 Torr and rf power density of 310 mW/cm2, the onset of crystallinity is observed for the film deposited at a hydrogen dilution of 94%. At a hydrogen dilution of 95%, amorphous-to-microcrystalline transition have been observed. This film exhibits a dark conductivity of 2.7×10-7 S cm-1 and a crystalline volume fraction of 21%. The mobility-lifetime product for these films are 3.8×10-6 cm2/V and hole diffusion length is 70 nm. Fourier transform infrared study shows mainly monohydride bonding in this film. This film becomes stable after 30 h of light soaking. View full abstract»

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  • Investigation of interfacial layer development between thin Al2O3 films grown using atomic layer deposition and Si(100), Ge(100), or GaAs(100)

    Page(s): 443 - 448
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    The uncontrolled formation of an interfacial layer between high-κ oxides and semiconductors is a major concern in advanced microelectronics not only for Si-based devices but also for those exploiting the higher mobility of Ge and GaAs. Using transmission electron microscopy, the authors investigate the interfacial layer formed between as-grown thin Al2O3 films, deposited using atomic layer deposition, and oxide free Si(100), Ge(100), and GaAs(100). In particular, they compare the effects of two different oxygen sources (H2O and O3) on interfacial layer formation during the growth process. They show that no interfacial layer can be distinguished unambiguously between the Al2O3 films, grown using TMA and H2O or O3, and all the semiconductor substrates. View full abstract»

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  • Pitting corrosion protection of stainless steel by sputter deposited hafnia, alumina, and hafnia-alumina nanolaminate films

    Page(s): 449 - 455
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    316L stainless steel coated with sputter deposited HfO2, Al2O3, and HfO2Al2O3 nanolaminate films were subjected to direct current cyclic potentiodynamic polarization (DCP) in Hanks’ balanced salt solution electrolyte. Postexposure morphology was characterized by scanning electron microscopy (SEM) with in situ energy dispersive spectroscopy (EDS). SEM/EDS data show that bare steel and steel coated with single-layer HfO2 develop pits with perforated covers. These pits become autocatalytic, consistent with an observed positive DCP hysteresis. On the other hand, SEM/EDS data show that steel coated with Al2O3 and HfO2Al2O3 nanolaminate films does not develop autocatalytic pits, consistent with an observed negative DCP hysteresis. However, Al2O3 splinters upon polarization whereas the HfO2Al2O3 nanolaminate remains intact. The areas of worst damage in the nanolaminate correspond to pit cover rupture before autocatalysis, allowing pit and bulk electrolyte to mix and the newly exposed steel surface to repassivate. The films’ diverse behavior is discussed in terms of a model for perforated pit growth that requires occlusion until an autocatalytic geometry is established. The authors conclude that the key property a film must have to arrest autocatalytic geometry development is- the ability to rupture locally at an early stage of pit growth. View full abstract»

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  • Differential etching behavior between semi-insulating and n-doped 4H-SiC in high-density SF6/O2 inductively coupled plasma

    Page(s): 456 - 460
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    The author investigated the etching characteristics of semi-insulating (SI) and n-doped (n-) 4H-SiC substrates at a high etch rate of about 2 μm/min using high-density SF6/O2 inductively coupled plasma. The etch rate of SI-SiC was found to be lower than that of n-SiC, and the etching profile of SI-SiC showed retrograde features with a larger sidewall angle and a rounder etched bottom compared to n-SiC. These characteristics are attributed to the difference in wafer heating and negative charging of the sidewall during plasma etching between both substrates. The temperature of n-SiC increases by radiative heating from the high-density plasma during etching because of the higher free-carrier absorption compared to SI-SiC. Furthermore, the negative charge buildup at the sidewall of SI-SiC becomes stronger because of the lower electrical conductivity compared to n-SiC. View full abstract»

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  • Growth of high-quality SrTiO3 films using a hybrid molecular beam epitaxy approach

    Page(s): 461 - 464
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    A hybrid molecular beam epitaxy approach for atomic-layer controlled growth of high-quality SrTiO3 films with scalable growth rates was developed. The approach uses an effusion cell for Sr, a plasma source for oxygen, and a metal-organic source (titanium tetra isopropoxide) for Ti. SrTiO3 films were investigated as a function of cation flux ratio on (001) SrTiO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates. Growth conditions for stoichiometric insulating films were identified. Persistent (≫180 oscillations) reflection high-energy electron diffraction oscillation characteristic of layer-by-layer growth were observed. The full widths at half maximum of x-ray diffraction rocking curves were similar to those of the substrates, i.e., 34 arcsec on LSAT. The film surfaces were nearly ideal with root mean square surface roughness values of less than 0.1 nm. The relationship between surface reconstructions, growth modes, and stoichiometry is discussed. View full abstract»

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  • Inductively coupled plasma generator for an environmentally benign perfluorocarbon abatement system

    Page(s): 465 - 470
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    Although conventional plasma-resolution-type abatement systems for perfluorocarbons (PFCs) achieve PFC removal efficiencies of more than 98%, they consume a lot of electricity. To diminish global warming by reducing CO2 equivalent emissions, an effective low power-consumption plasma generator is essential. The authors found that the pressure at which the electrical discharge can be maintained at the same rf power supply output increased with the number of turns per unit length of coil. In addition, they revealed that the CF4 removal efficiency rose with increasing pressure. A plasma generator employing a modified cylindrical inductively coupled plasma chamber with 1.1 turns/cm achieved a CF4 removal efficiency of 99.0% under conditions of a CF4 flow rate of 10 cm3/min, a pressure of 0.9 kPa, and a rf power supply output of 1.5 kW. The CO2 equivalent removal efficiency was calculated to be 93.5%, an improvement of 6.7% over that of the previous system. View full abstract»

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  • Gas temperature measurement in CF4, SF6, O2, Cl2, and HBr inductively coupled plasmas

    Page(s): 471 - 478
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    Neutral gas temperature (Tg) is measured in an industrial high-density inductively coupled etch reactor operating in CF4, SF6, O2, Cl2, or HBr plasmas. Two laser diodes are used to deduce Tg from the Doppler widths of 772.38 and 811.5 nm lines absorbed by Ar*(3P2) metastable atoms, when a small amount of argon (5%) is added to the gas flow. With the 811.5 nm beam passing parallel to the wafer, Tg near the wafer surface is obtained by laser absorption technique. With the 772.38 nm beam entering the top of the reactor perpendicular to the wafer surface, the volume averaged temperature is deduced by laser induced fluorescence technique. The volume averaged Tg increases with radio frequency power and with pressure, although the temperature near the walls is only weakly dependent on gas pressure. The main effect of increasing the pressure is an enhancement of the temperature gradient between the discharge center and the wall boundary. Due to the thermal accommodation, the authors always observe a significant temperature jump between the surface and the gas in its vicinity. This gap is typically about 200 K. Gas temperatures for a wide range of pressure and rf powers are reported. These data will be useful to validate and improve numerical models of high-density reactive plasmas. View full abstract»

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  • Rarefied gas flow through a thin slit into vacuum simulated by the Monte Carlo method over the whole range of the Knudsen number

    Page(s): 479 - 484
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    A rarefied gas flow through a thin slit into vacuum is studied on the basis of the direct simulation Monte Carlo method. The mass flow rate and flow field are calculated over the whole range of the gas rarefaction from the free-molecular regime to the viscous one. A comparison to other results on the same problem available in literature is performed. An interpolating formula for the reduced flow rate is obtained. View full abstract»

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  • Optimization of cell geometry for a conventional sputter ion pump by a particle-in-cell simulation

    Page(s): 485 - 491
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    The authors performed simulations of Penning discharge at the low magnetic field using a particle-in-cell computer code to derive the optimum cell geometry of a sputter ion pump (SIP). The energy and angle distributions of incident ions on the cathode of a Penning cell were directly obtained from the simulation. Based on these data, the authors calculated the amount of deposited Ti on the inner surface of the cell, which was found to be proportional to intrinsic pumping speed of a SIP, and then estimated the effective pumping speed for various cell geometries. In this calculation, the incident ions on the outer region of the cathode as well as those at the center were analyzed, and the effect of the ionizationless region on Penning discharge was also taken into account. The calculated values agreed well with the existing experimental data, especially in the region of a small cell radius. The results also show that the cell radius should be at least 5 mm for effective pumping, and the optimum geometrical parameters for a conventional sputter ion pump have the radius of 8.5 mm and the gap of 7 mm at the applied voltage of 5600 V. View full abstract»

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  • Capability of focused Ar ion beam sputtering for combinatorial synthesis of metal films

    Page(s): 492 - 495
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    The authors examined the use of focused Ar ion beam sputtering (FAIS) for combinatorial synthesis. A Langmuir probe revealed that the electron temperature and density for FAIS of metal film deposition was lower than that of other major combinatorial thin film growth techniques such as pulsed laser deposition. Combining FAIS with the combinatorial method allowed the compositional fraction of the Pt–Ru binary alloy to be systematically controlled. Pt–Ru alloy metal film grew epitaxially on ZnO substrates, and crystal structures changed from the Pt phase (cubic structure) to the Ru phase (hexagonal structure) in the Pt–Ru alloy phase diagram. The alloy film has a smooth surface, with the Ru phase, in particular, showing a clear step-and-terrace structure. The combination of FAIS and the combinatorial method has major potential for the fabrication of high quality composition-spread metal film. View full abstract»

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  • Efficiency derivation for the Knudsen pump with and without thermal losses

    Page(s): 496 - 502
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    This article describes the derivation of the efficiency for the Knudsen pump for two cases. First, by neglecting the thermal losses to calculate the maximum efficiency, and second, by including the thermal losses along the length of the channel. The Knudsen pump is a thermally driven pump with no moving parts and which functions on the principle of thermal transpiration. Diffusion is the main mode of mass transport, as opposed to bulk fluid motion. The pump functions when the gases are in a rarefied state. The efficiency without thermal losses is shown to asymptotically approach the value of the ideal gas constant divided by the specific heat capacity, while the efficiency with thermal losses is given for rectangular and circular cross sections and is shown to be independent of length. View full abstract»

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  • Addition of yttrium into HfO2 films: Microstructure and electrical properties

    Page(s): 503 - 514
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    The cubic phase of HfO2 was stabilized by addition of yttrium in thin films grown on Si/SiO2 by metal-organic chemical vapor deposition. The cubic phase was obtained for contents of 6.5 at. % Y or higher at a temperature as low as 470 °C. The complete compositional range (from 1.5 to 99.5 at. % Y) was investigated. The crystalline structure of HfO2 was determined from x-ray diffraction, electron diffraction, and attenuated total-reflection infrared spectroscopy. For cubic films, the continuous increase in the lattice parameter indicates the formation of a solid-solution HfO2Y2O3. As shown by x-ray photoelectron spectroscopy, yttrium silicate is formed at the interface with silicon; the interfacial layer thickness increases with increasing yttrium content and increasing film thickness. The dependence of the intrinsic relative permittivity εr as a function of Y content was determined. It exhibits a maximum of ∼30 for ∼8.8 at. % Y. The cubic phase is stable upon postdeposition high-temperature annealing at 900 °C under NH3. View full abstract»

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  • Auger electron spectroscopy study of reactor walls in transition from an O2 to a Cl2 plasma

    Page(s): 515 - 520
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    In plasma etching processes, the reactor wall conditions can change over time due to a number of intentional and unintentional reasons, leading to a variability in the radical number densities in the plasma, caused by changes in the probabilities for reactions such as recombination at the walls. This leads to loss of reproducibility in the etching process. Here the authors isolated one such effect in which the feed gas was changed in the absence of a substrate. The transient surface composition of an anodized aluminum surface was determined for inductively coupled plasmas as the gas was switched from Cl2 to O2 and vice versa. The study was carried out with the spinning wall method and Auger electron spectroscopy. When the surface was first conditioned in an O2 plasma and then exposed to Cl2 plasmas, a rapid uptake of Cl was found in the first tens of seconds, followed by a slow approach to a steady-state value within ∼5 min of plasma exposure. Conversely, when the surface was exposed to a Cl2 plasma for a long time and then switched to an O2 plasma, the anodized aluminum surface underwent a rapid dechlorination in the first few seconds and then a slow approach to steady state over ∼3 min. Throughout these treatments, the coverages of Si (from erosion of the quartz discharge tube) and O were nearly constant. View full abstract»

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  • Influence of deposition pressure and pulsed dc sputtering on pumping properties of Ti–Zr–V nonevaporable getter films

    Page(s): 521 - 530
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    The performance of a UHV vessel can be improved with a new CERN technology nonevaporable getter (NEG) coating, which is already widely used for accelerator vacuum chambers. Better understanding of the processes involved in NEG film deposition, activation, and poisoning should allow optimization and engineering of the film properties, which are necessary for a particular application. Ti–Zr–V NEG films were created by magnetron sputtering from a single Ti–Zr–V target, and the NEG performance and morphology dependence on deposition pressure, sputtering conditions, and substrate surface roughness have been investigated. It was found that the average grain size of the Ti–Zr–V film was 5–6 nm and was broadly independent of the substrate material and deposition conditions. However, film topography and density were shown to depend very much on the substrate surface roughness and deposition conditions. Rough substrates, high working pressures, and the absence of ion bombardment produced open columnar structures, whereas smooth substrates, ion assistance, and low pressures produced much denser layers. X-ray photoelectron spectroscopy studies have shown that full regeneration occurred at 300 °C but film activation started at temperatures of as low as 160 °C. The CO sticking probability reaches its maximum after activation at 250 °C and is found to be up to 0.3 with a pumping capacity in the range of 0.8–1.2 ML. The samples activated at 160 °C have a reduced pumping speed and capacity by an order of magnitude. View full abstract»

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  • Deep levels and compensation effects in sulfur-doped GaPN layers grown by organometallic vapor phase epitaxy

    Page(s): 531 - 536
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    Two GaPN epilayers, with different N contents of 0.3% and 0.9%, i.e., at the low-doping level and in the dilute-content range, respectively, have been examined by deep level transient spectroscopy (DLTS) and thermal admittance spectroscopy (TAS). DLTS revealed a main peak below 200 K and a low-intensity broad signal above 250 K. For the dominant peak, Arrhenius plots revealed an activation energy of 0.4 eV below the conduction band and a corresponding trap density above 1017 cm-3, in both the samples. The higher N-content sample features for this level a broader line shape and about one-order-of-magnitude larger cross section, as compared with the low N-content epilayer. TAS Arrhenius plots yielded a compressed discrepancy between the signatures of this trap in the two samples, pointing to a common physical origin, likely corresponding to N-split interstitials, and to a possible incidence of Poole–Frenkel effect on this trap behavior. However, the main discrepancy between the results from the two techniques lay in the concentrations as calculated for the signal above 250 K. It was found that DLTS underestimates its intensity by at least one order of magnitude. Based on the extension of TAS data at high temperatures, this controversial signal resulted to correspond to Ga interstitials, which can also form complexes and can thus account for the strong compensation effects observed in these epilayers. View full abstract»

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  • Evolution of metal-compound residues on the walls of plasma etching reactor and their effect on critical dimensions of high-k/metal gate

    Page(s): 537 - 542
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    It was found that critical dimensions of high-k/metal gates obey the multivariate linear approximation with the precision of 3σ=±0.86 nm, whose explanatory variables are amounts of metal compounds remaining on the plasma reactor walls. To measure their amounts, the authors assumed they are proportional to amounts of atoms sputtered out by Ar plasma and falling onto a Si wafers placed on a wafer stage. In this study, effects of metal compounds of W, Ti, Ta, and Hf, which are used to construct full-metal/high-k gates, were measured. It was found that Ti and Ta compounds dominate the fluctuation of critical dimensions and the dependency of their amount on wafer numbers being etched obeys a simple difference equation. From these results, they can estimate and minimize the fluctuations of critical dimensions in mass fabrications. View full abstract»

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  • Numerical investigation of turbomolecular pumps using the direct simulation Monte Carlo method with moving surfaces

    Page(s): 543 - 547
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    A new approach for performing numerical direct simulation Monte Carlo (DSMC) simulations on turbomolecular pumps in the free molecular and transitional flow regimes is described. The chosen approach is to use surfaces that move relative to the grid to model the effect of rotors and stators on a gas flow. The current article describes the method and compares the results to experimental and theoretical data by Sawada [Bull. JSME 22, 362 (1979)]. The agreement between our results and Sawada’s results are excellent. View full abstract»

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  • Sputter-deposited (Pb,La)(Zr,Ti)O3 thin films: Effect of substrate and optical properties

    Page(s): 548 - 553
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    Optically transparent (Pb,La)(Zr,Ti)O3 (PLZT) thin films were sputter-deposited on SrTiO3(001) and MgO(001) substrates with a SrRuO3(110) bottom electrode. X-ray diffraction analysis showed epitaxial growth of monocrystalline PLZT, with (001) rocking curve full width at half maxima of ∼0.03° and ∼0.3° for films deposited on SrTiO3 and MgO, respectively. In-plane epitaxial alignment of the SrRuO3 and PLZT epilayers was verified from φ-scans. It was established from atomic force microscopy measurements that the PLZT surface roughness meets the requirement for optical waveguide applications. Recorded P-E loops for films grown on both substrates showed a remanent polarization of ∼36 μC/cm2. The refractive index of the PLZT layer was estimated from rutile prism coupling measurements at ∼2.56 for λ=633 nm, consistent with data obtained by spectroscopic ellipsometry. The ferroelectric and optical characteristics of the films, as well as their surface roughness, were not appreciably different for the two substrates. This makes MgO the preferred choice of substrate for optical waveguide devices due to its low refractive index compared to that of SrTiO3. View full abstract»

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  • On the effect of Ta on improved oxidation resistance of Ti–Al–Ta–N coatings

    Page(s): 554 - 560
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    Formation of protective oxide scales is the main reason for the high oxidation resistance of TiAlN based coatings. Here the authors report on further improvement in the oxidation resistance of TiAlN by Ta alloying. An industrial-scale cathodic arc evaporation facility was used to deposit Ti–Al–Ta–N coatings from powder metallurgically produced Ti38Al57Ta5 targets. After oxidation in ambient air, a significantly reduced oxide layer thickness in comparison to unalloyed TiAlN reference material was observed. Energy-dispersive x-ray spectroscopy line scans and secondary ion mass spectroscopy depth profiling showed that the oxide scale consists of an Al-rich top layer without detectable amount of Ta and a Ti–Ta-rich sublayer. Transmission electron microscopy investigations revealed α-Al2O3, rutile-type TiO2, and anatase-type TiO2 as the scale forming oxides. Furthermore, the Ti–Ta-rich sublayer consists of a porous layer at the oxide-nitride interface but appears dense toward the Al-rich top layer. The improved oxidation resistance is explained by doping the TiO2 lattice by replacing Ti4+ with Ta5+ in the rutile lattice, which decreases the oxygen mass transport. This leads to reduced oxidation of Ti under formation of TiO2 at the oxide-nitride interface and is the reason for the excellent oxidation behavior of Ti–Al–Ta–N coatings. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

Full Aims & Scope

Meet Our Editors

Editor
G. Lucovsky
North Carolina State University