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Nov 2010

Volume 28, Issue 6, pp. L15-1422

Issue Cover Spotlight Figure

J. Vac. Sci. Technol. A 28, 1285 (2010); http://dx.doi.org/10.1116/1.3490017 (14 pages)

Patricia A. Thiel, Mingmin Shen, Da-Jiang Liu, and James W. Evans
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Asymmetric diffusion as a key mechanism in Ni/Al energetic multilayer processing: A first principles study

M. Petrantoni, A. Hemeryck, J. M. Ducéré, A. Estève, C. Rossi, M. Djafari Rouhani, D. Estève, and G. Landa

J. Vac. Sci. Technol. A 28, L15 (2010); http://dx.doi.org/10.1116/1.3491182 (3 pages)

Online Publication Date: 12 October 2010

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Adsorption and penetration of Al and Ni atoms into Ni(111) and Al(111), respectively, are investigated through first principles calculations, shedding light into the driving forces impacting Al/Ni interfaces produced during multilayer deposition. The authors show that Ni deposition follows an exothermic path toward penetration associated with small activation barriers while Al on Ni(111) path is endothermic accompanied with high activations. Moreover, Ni and Al penetrations proceed through interstitial and substitutional sites, respectively. These differentiated behaviors at early deposition stages illustrate that dual processing conditions are required to achieve the growth of specific Ni/Al interfaces during multilayer deposition processes and that a local melting process at the interface is mandatory to arrive at the formation of a proper barrier layer.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.43.Bc Ab initio calculations of adsorbate structure and reactions
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.43.Fg Adsorbate structure (binding sites, geometry)
68.35.Fx Diffusion; interface formation

Application of contactless electroreflectance to study the epi readiness of m-plane GaN substrates obtained by ammonothermal method

R. Kudrawiec, R. Kucharski, M. Rudziński, M. Zając, J. Misiewicz, W. Strupiński, R. Doradziński, and R. Dwiliński

J. Vac. Sci. Technol. A 28, L18 (2010); http://dx.doi.org/10.1116/1.3504359 (4 pages) | Cited 1 time

Online Publication Date: 28 October 2010

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The authors have applied contactless electroreflectance (CER) spectroscopy to study the epi readiness of m-plane GaN substrates obtained by the ammonothermal method. It has been clearly observed that the CER resonance, which is related to the energy gap transition, appears for samples with a well-polished surface. The sharpness of this resonance is directly related to the surface quality. The broadening of energy gap transition can be used as a parameter to quantify the surface quality. For samples polished with optimal conditions, this broadening (γpol) is close to the broadening observed for the cleaved GaN surface (γclev) with m-plane orientation (150–190 vs 135 meV). The quality of the polishing process can be evaluated by analyzing the γclev/γpol ratio, where γclev/γpol = 1 corresponds to an excellent polishing process. In the authors’ case, this ratio has been determined to be close to 1 for well-polished samples.
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78.20.Jq Electro-optical effects
81.65.Ps Polishing, grinding, surface finishing
71.20.Nr Semiconductor compounds
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EDITORIAL

Gerry Lucovsky, Editor “Emeritus”

J. Vac. Sci. Technol. A 28, P1 (2010); http://dx.doi.org/10.1116/1.3511690 (1 page)

Online Publication Date: 1 November 2010

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99.10.Np Editorial note
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.35.-p Nanoelectronic devices
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Adsorbate-enhanced transport of metals on metal surfaces: Oxygen and sulfur on coinage metals

Patricia A. Thiel, Mingmin Shen, Da-Jiang Liu, and James W. Evans

J. Vac. Sci. Technol. A 28, 1285 (2010); http://dx.doi.org/10.1116/1.3490017 (14 pages) | Cited 2 times

Online Publication Date: 23 September 2010

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Coarsening (i.e., ripening) of single-atom-high, metal homoepitaxial islands provides a useful window on the mechanism and kinetics of mass transport at metal surfaces. This article focuses on this type of coarsening on the surfaces of coinage metals (Cu, Ag, Au), both clean and with an adsorbed chalcogen (O, S) present. For the clean surfaces, three aspects are summarized: (1) the balance between the two major mechanisms—Ostwald ripening (the most commonly anticipated mechanism) and Smoluchowski ripening—and how that balance depends on island size; (2) the nature of the mass transport agents, which are metal adatoms in almost all known cases; and (3) the dependence of the ripening kinetics on surface crystallography. Ripening rates are in the order (110)>(111)>(100), a feature that can be rationalized in terms of the energetics of key processes. This discussion of behavior on the clean surfaces establishes a background for understanding why coarsening can be accelerated by adsorbates. Evidence that O and S accelerate mass transport on Ag, Cu, and Au surfaces is then reviewed. The most detailed information is available for two specific systems, S/Ag (111) and S/Cu(111). Here, metal-chalcogen clusters are clearly responsible for accelerated coarsening. This conclusion rests partly on deductive reasoning, partly on calculations of key energetic quantities for the clusters (compared with quantities for the clean surfaces), and partly on direct experimental observations. In these two systems, it appears that the adsorbate, S, must first decorate—and, in fact, saturate—the edges of metal islands and steps, and then build up at least slightly in coverage on the terraces before acceleration begins. Acceleration can occur at coverages as low as a few thousandths to a few hundredths of a monolayer. Despite the significant recent advances in our understanding of these systems, many open questions remain. Among them is the identification of the agents of mass transport on crystallographically different surfaces e.g., 111, 110, and 100.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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Influence of deposition parameters on the microstructure and properties of nitrogen-doped diamondlike carbon films

L. Sun, H. K. Li, G. Q. Lin, and C. Dong

J. Vac. Sci. Technol. A 28, 1299 (2010); http://dx.doi.org/10.1116/1.3482010 (8 pages)

Online Publication Date: 23 September 2010

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CNx films were prepared on cemented carbide substrates by a pulsed bias arc ion-plating method with two graphite targets and using N2/Ar mixture gases. The effects of the deposition parameters, such as substrate negative-bias voltage, duty cycle, and nitrogen flow rate, on the structures and properties of CNx films were investigated using Raman spectra and nanoindentation. The properties of CNx films are closely related to the film structures. For CNx films deposited at a different bias voltage, the CNx film deposited at a bias voltage of −300 V had the highest hardness. The ID/IG ratio and G peak position decreased and then increased with increasing bias voltage, and the minimum values, which correspond to the highest sp3 content, were obtained at a bias voltage of −300 V. For the CNx films deposited at different duty cycles, the hardness and elastic modulus decreased with increasing duty cycle. For the CNx films deposited at different nitrogen flow rates, the results show that first the ID/IG ratio decreases and sp3 content increases with increasing nitrogen flow rate, and then the ID/IG ratio increases and sp3 bond content decreases after the nitrogen flow rate exceeds 10 SCCM (SCCM denotes cubic centimeter per minute at STP). The hardness and elastic modulus of the CNx film prepared at a nitrogen flow rate of 10 SCCM reached the maximum values of 32.1 and 411.8 GPa, respectively.
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68.55.ag Semiconductors
61.72.-y Defects and impurities in crystals; microstructure
81.05.Mh Cermets, ceramic and refractory composites
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.uf Graphite
78.30.Jw Organic compounds, polymers

Intrinsic p-type ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition

Yen-Chin Huang, Zhen-Yu Li, Li-Wei Weng, Wu-Yih Uen, Shan-Ming Lan, Sen-Mao Liao, Tai-Yuan Lin, Yu-Hsiang Huang, Jian-Wen Chen, and Tsun-Neng Yang

J. Vac. Sci. Technol. A 28, 1307 (2010); http://dx.doi.org/10.1116/1.3484138 (5 pages) | Cited 1 time

Online Publication Date: 23 September 2010

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The structural, electrical, and optical properties of ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) under various gas flow ratios of [H2O]/[DEZn] (VI/II ratio) ranging from 0.55 to 2.74 were systematically examined. Hall effect measurements exhibited an evident effect of the VI/II ratio on the conduction type of the intrinsic films. An n-type film was fabricated at the VI/II ratio = 0.55; however, p-type ZnO films with the hole concentration of the order of 1017 cm−3 could be achieved at VI/II ratios higher than 1.0. In particular, the highest mobility of 91.6 cm2/V s and the lowest resistivity of 0.369 Ω cm have been achieved for the specimen fabricated at the VI/II ratio = 1.10. Moreover, room-temperature photoluminescence (PL) measurements demonstrated an interstitial Zn (Zni) donor defect related emission at 2.9 eV for the n-type film, while a Zn vacancy (VZn) acceptor defect related one at 3.09 eV for the p-type films. The existence of material intrinsic defects was further confirmed by low temperature PL measurements conducted at 10 K. Conclusively, the conduction type of undoped ZnO films deposited by AP-MOCVD is resolved by the VI/II ratio used, which causes the formation of various kinds of intrinsic defects, Zni otherwise VZn. p-type ZnO films with the hole concentration in the range of (1.5–3.3)×1017 cm−3 can be achieved with good reproducibility by modulating a VI/II ratio the range 1.0–2.2 for the AP-MOCVD process.
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68.55.ag Semiconductors
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors

Numerical simulation of turbomolecular pump over a wide range of gas rarefaction

Felix Sharipov

J. Vac. Sci. Technol. A 28, 1312 (2010); http://dx.doi.org/10.1116/1.3484139 (4 pages) | Cited 1 time

Online Publication Date: 23 September 2010

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A gas flow through a turbomolecular pump is modeled by the direct-simulation Monte Carlo method over a wide range of gas rarefaction covering the free-molecular, transitional, and hydrodynamic regimes. Several values of the rotor speed are considered. The main characteristics of the pump, such as maximum pumping speed and compression ratio, are reported. It is pointed out that in the range between the free-molecular and transitional regimes, the pump characteristics change slightly, but they vary significantly in the hydrodynamic regime. It is shown that the pumping speed increases in the hydrodynamic regime when the rotor speed is high, but it decreases for a small value of the speed. The compression ratio always decreases when approaching the hydrodynamic regime.
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47.85.Dh Hydrodynamics, hydraulics, hydrostatics
47.45.Dt Free molecular flows
47.11.-j Computational methods in fluid dynamics

Reflectance and substrate currents of dielectric layers under vacuum ultraviolet irradiation

H. Sinha, D. B. Straight, J. L. Lauer, N. C. Fuller, S. U. Engelmann, Y. Zhang, G. A. Antonelli, M. Severson, Y. Nishi, and J. L. Shohet

J. Vac. Sci. Technol. A 28, 1316 (2010); http://dx.doi.org/10.1116/1.3488594 (3 pages) | Cited 3 times

Online Publication Date: 23 September 2010

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The reflectance of low-k porous organosilicate glass (SiCOH) as a function of photon energy under synchrotron vacuum ultraviolet (VUV) radiation was measured using a nickel mesh reflectometer. The authors found that during VUV irradiation, the reflectance of SiCOH and the substrate current were inversely correlated. Thus, reflectance can be inferred from substrate current measurements and vice versa. The authors conclude that reflectance or substrate current measurements can determine the photon energies that are absorbed and, therefore, cause dielectric damage during processing. Thus, reducing the flux of deleterious photon energies in processing systems can minimize dielectric damage.
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78.66.Jg Amorphous semiconductors; glasses
78.66.Qn Polymers; organic compounds
77.55.Bh Low-permittivity dielectric films
68.55.-a Thin film structure and morphology
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds

Comparative study on passivation of GaAs0.86P0.14/Al0.6Ga0.4As near-surface quantum well

Suparna Pal, S. D. Singh, S. Porwal, S. W. D’Souza, S. R. Barman, and S. M. Oak

J. Vac. Sci. Technol. A 28, 1319 (2010); http://dx.doi.org/10.1116/1.3490021 (7 pages) | Cited 1 time

Online Publication Date: 23 September 2010

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The authors report a comparative study on ex situ passivation of a near-surface GaAs0.86P0.14/Al0.6Ga0.4As quantum well using various sulfide solutions and nitrogen plasma treatments. The built-in surface electric field is changed via band bending by applying various surface passivation conditions. The band bending is measured using x-ray photoelectron spectroscopy. Reduction in surface electric field in the range of 10–35 kV/cm is observed depending on different passivation conditions. The photoreflectance spectra show enhancement in intensity and blueshift of ∼ 3 meV accompanied by significant reduction in the broadening parameter of the observed e1-lh1 transitions. Among all the methods studied here, passivation by Na2S⋅xH2O is found to be most effective as it removes the native oxide layer completely leading to almost flat band condition.
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81.65.Rv Passivation
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.47.Fg Semiconductor surfaces
78.67.De Quantum wells

Control of bombardment energy and energetic species toward a superdense titanium nitride film

Zhigang Xie, Adolph Miller Allen, Mei Chang, Phillip Wang, and Tza-jing Gung

J. Vac. Sci. Technol. A 28, 1326 (2010); http://dx.doi.org/10.1116/1.3490018 (4 pages)

Online Publication Date: 24 September 2010

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TiN deposited by dc magnetron sputtering has been widely used as a hard mask material for dielectric patterning in multilevel Cu interconnects. Typically inside a “poison-mode” regime, the film density is 4.5–4.9 g/cm3. The microstructure, varying from columnar structure to nanocrystalline, is controlled by both thermodynamics and surface kinetics through ionization, substrate bias, target voltage, etc. A relatively low density film can be correlated with a porous columnar structure, low mechanical robustness, and weak resistance to plasma etching. However, with controlled growth, an applied substrate bias does not create resputtering and crystal defects. Instead, the authors create film with a maximum density of 5.3 g/cm3. In this high density film, carrier scatterings through grain boundary are greatly suppressed and the film resistivity is as low as 95 μΩ cm, which brings additional benefits as a conductive capping layer. As it is deposited at room temperature, the process minimizes the thermal budget to the underlying low-k dielectric materials to be patterned.
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81.15.Cd Deposition by sputtering
61.43.Gt Powders, porous materials
77.55.Bh Low-permittivity dielectric films
81.65.Cf Surface cleaning, etching, patterning

Surface texture and wetting stability of polydimethylsiloxane coated with aluminum oxide at low temperature by atomic layer deposition

Joseph C. Spagnola, Bo Gong, and Gregory N. Parsons

J. Vac. Sci. Technol. A 28, 1330 (2010); http://dx.doi.org/10.1116/1.3488604 (8 pages) | Cited 3 times

Online Publication Date: 27 September 2010

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The performance of polydimethylsiloxane (PDMS) elastomer in many of its applications, including surface molding and replication, microcontact lithography, and microfluidic device structures, is strongly influenced by its surface properties. While PDMS polymer is simple to use, the surface hydrophobicity and adsorptive properties of PDMS limit its functionality, for example, in aqueous microfluidic applications. Atomic layer deposition (ALD) is a low temperature vapor phase thin film coating technique that has recently been used to modify and encapsulate a wide range of polymer materials. In this work, the authors investigate reactions that proceed when PDMS polymer films are treated with cyclic gas exposure sequences commonly used to perform aluminum oxide ALD. Film growth is characterized by electron and infrared spectroscopy and by contact angle goniometry for a range of surface treatments and postdeposition air exposure times. The authors find that trimethylaluminum/water ALD can produce a smooth and uniform film coating on PDMS at 25–50 °C and that cracks become visible under optical microscopy for films >100 Å thick. At moderate temperatures, unique buckled surface textures appear in the deposited coating, which are ascribed to substrate thermal expansion effects. Aluminum oxide coatings on native PDMS, as well as on PDMS pretreated with UV ozone or oxygen plasma, show a hydrophilic surface condition immediately after deposition, but the surface becomes more hydrophobic after 24–48 h in ambient air or under inert gas storage, likely due to organic species out-diffusion through defects in the ALD coating. Infrared analysis is also used to identify consistent mechanisms associated with subsurface ALD nucleation on cast PDMS layers. These results provide valuable insight into a means to reliably modify the surface of PDMS using vapor phase precursor/surface reactions.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.55.jm Texture
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Dp Adsorbed layers and thin films
68.03.Cd Surface tension and related phenomena

Structural and electrical properties of Cu2O thin films deposited on ZnO by metal organic chemical vapor deposition

SeongHo Jeong and Eray S. Aydil

J. Vac. Sci. Technol. A 28, 1338 (2010); http://dx.doi.org/10.1116/1.3491036 (6 pages) | Cited 1 time

Online Publication Date: 27 September 2010

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Cu2O thin films were deposited on ZnO coated glass substrates by metal organic chemical vapor deposition from copper(II) hexafluoroacetylacetonate [Cu(C5HF6O2)2], oxygen gas, and water vapor. The dependence of the structural and electrical properties of Cu2O films on deposition temperature and film thickness was investigated. X-ray diffraction showed that Cu2O thin films grow on ZnO with preferred (220)Cu2O∥(0002)ZnO orientation. The grain size and stress in Cu2O films increase with increasing substrate temperature but decrease with increasing film thickness. The carrier mobility increases with increasing grain size indicating that the carrier transport is limited by scattering from the grain boundaries. Single-phase epitaxial p-type Cu2O films with hole mobilities exceeding 30 cm2/V s are obtained at a deposition temperature of 400 °C.
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73.61.Le Other inorganic semiconductors
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.ag Semiconductors
61.72.Mm Grain and twin boundaries

Influence of the oxidation conditions on the structural characteristics and optical properties of zinc oxide thin films

A. P. Rambu, D. Sirbu, and G. I. Rusu

J. Vac. Sci. Technol. A 28, 1344 (2010); http://dx.doi.org/10.1116/1.3484243 (5 pages) | Cited 1 time

Online Publication Date: 29 September 2010

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ZnO thin films were obtained by two-step oxidation processes of Zn films: heating up to 575 K for 1–2 h followed by heating at higher temperature (775 K) for 1 h. Zinc thin films (d = 450 nm) were deposited by the quasiclosed volume technique under vacuum onto glass substrates maintained at room temperature. The investigation of film structure, performed by x-ray diffraction technique, corroborated with atomic force microscopy, confirmed that as-prepared zinc films are polycrystalline. The as-prepared ZnO films have a polycrystalline wurtzite (hexagonal) structure, with film crystallites preferentially oriented with (002) planes parallel to the substrate. Transmission and absorption spectra were recorded in the spectral domain from 300 to 1400 nm. The energy band gap for respective films determined from absorption spectra ranged between 3.02 and 3.06 eV.
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68.55.ag Semiconductors
78.66.Hf II-VI semiconductors
78.20.-e Optical properties of bulk materials and thin films
68.37.Ps Atomic force microscopy (AFM)
81.05.Dz II-VI semiconductors

Microstructure and property modifications of an AISI H13 (4Cr5MoSiV) steel induced by pulsed electron beam treatment

Kemin Zhang, Jianxin Zou, Thierry Grosdidier, and Chuang Dong

J. Vac. Sci. Technol. A 28, 1349 (2010); http://dx.doi.org/10.1116/1.3490019 (7 pages)

Online Publication Date: 5 October 2010

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In the present work, surface modifications generated by the low energy high current pulsed electron beam (LEHCPEB) treatments have been investigated on an AISI H13 (4Cr5MoSiV) steel. From the observations of scanning electron microscopy, x-ray diffraction, and electron back scattering diffraction determinations, it could be established that the final structure in the melted layer is a mixture of ultrafine δ phase, martensite, and residual austenite. The formation of the heterogeneous microstructures on the surface layer is related to the very rapid heating, melting, solidification, and cooling induced by the LEHCPEB irradiation. After the LEHCPEB treatment, the wear resistance of the steel effectively improved. This can be mainly attributed to the higher hardness of the ultrafine structures formed on the top surface and the hardened subsurface layers after the treatment.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
79.20.Kz Other electron-impact emission phenomena
61.80.Fe Electron and positron radiation effects

Unique cryogenic pumping array for low sticking coefficient gas flows

Cedrick Ngalande and Andrew D. Ketsdever

J. Vac. Sci. Technol. A 28, 1356 (2010); http://dx.doi.org/10.1116/1.3497029 (7 pages)

Online Publication Date: 7 October 2010

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A radial fin cryogenic pumping array design is described which enhances the pumping efficiency of high enthalpy and high kinetic energy flows in vacuum. In general, these flows have relatively low sticking coefficients due to the large temperature differences between the particles in the flow and the cryogenic pumping surfaces. A Monte Carlo numerical model has been developed to investigate the pumping efficiency of the radial fin array. A comparison of the pumping efficiency of the radial fin array with a flat plate pumping surface has shown that particles with a high sticking coefficient will be pumped better with a simple flat panel, whereas particles with low sticking coefficients will be more efficiently pumped with the radial fin array. A set of experiments has been performed to investigate the pumping efficiency of the radial fin array as manufactured. These experiments compared the radial fin results to a more traditional flat plate pumping surface with a neutral gas flow. The experimental results indicate that there are flow regimes in which the radial fins are more efficient at pumping incident particles than a flat surface.
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07.30.Cy Vacuum pumps

Influence of temperature on the hydrogenated amorphous carbon films prepared by plasma-enhanced chemical vapor deposition

Jiung Wu, Yi-Lung Cheng, and Ming-Kai Shiau

J. Vac. Sci. Technol. A 28, 1363 (2010); http://dx.doi.org/10.1116/1.3497025 (3 pages)

Online Publication Date: 7 October 2010

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Hydrogenated amorphous carbon (a-C:H) films were deposited in a plasma-enhanced chemical vapor deposition (PECVD) system. The substrate temperature at deposition was found to have significant effects on the film stoichiometry, sp2 phase, and optical properties. Raman spectroscopy reveals an increase in sp2-bonded carbon and a continual structure ordering of the sp2 phase with increasing substrate temperature at deposition. Thermal desorption spectroscopy analysis revealed that the onset temperature of CH4 effusion of PECVD a-C:H films increase with increasing substrate temperatures, implicating enhanced structural stability via elevating the substrate temperature at deposition. The extinction coefficient k measured from spectroscopic ellipsometry gradually increases with increasing substrate temperature at deposition, due possibly to the graphitization effect which decreases the optical gap resulting in higher k.
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68.55.-a Thin film structure and morphology
61.43.Er Other amorphous solids
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Influence of strain on the hexagonal motifs of the Ir(100) surface reconstructions: A first-principles study

W. S. Su (蘇萬生), F. C. Chuang (莊豐權), K. M. Lin (林耿民), and T. C. Leung (梁贊全)

J. Vac. Sci. Technol. A 28, 1366 (2010); http://dx.doi.org/10.1116/1.3497027 (5 pages) | Cited 1 time

Online Publication Date: 12 October 2010

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The authors performed first-principles calculations to investigate the effect of the strain on the hexagonal motifs formed on the Ir(100) surface overlayer with (5×1), (8×1), (12×1), and (14×1) periodicities. Their calculations showed that the unstrained (5×1) phase is the most stable phase, which is consistent with previous theoretical calculations and experimental findings. Further analysis on the surface energy versus strain suggests the occurrence of the strain induced phase transition among various hexagonal reconstructions. Such a phenomenon can be further qualitatively elucidated by analyzing the computed average standard deviation of angles between the three adjacent atoms of the hexagonal top layer.
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68.35.bd Metals and alloys
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
68.35.Md Surface thermodynamics, surface energies
65.40.gp Surface energy
68.35.Rh Phase transitions and critical phenomena

Isolation of exchange- and spin-orbit-driven effects via manipulation of the axis of quantization

Takashi Komesu, G. D. Waddill, S.-W. Yu, M. T. Butterfield, and J. G. Tobin

J. Vac. Sci. Technol. A 28, 1371 (2010); http://dx.doi.org/10.1116/1.3498716 (6 pages)

Online Publication Date: 13 October 2010

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Double polarization photoelectron spectroscopy using circularly polarized x-rays and true spin detection has been performed using the 2p core levels of ultrathin films of Fe and Co. This includes both the separation into magnetization- and spin-specific spectra and an analysis of the polarization, asymmetry, and related quantities. It is shown how to selectively manipulate the manifestation of exchange- and spin-orbit effects simply by choosing different axes of quantization. Furthermore, the underlying simplicity of the results can be confirmed by comparison to a simple yet powerful single-electron picture.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
79.60.-i Photoemission and photoelectron spectra
75.70.Ak Magnetic properties of monolayers and thin films

Effect of sample bias on backscattered ion spectroscopy in the helium ion microscope

G. Behan, J. F. Feng, H. Z. Zhang, P. N. Nirmalraj, and J. J. Boland

J. Vac. Sci. Technol. A 28, 1377 (2010); http://dx.doi.org/10.1116/1.3502667 (4 pages)

Online Publication Date: 20 October 2010

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The authors present experimental results showing the effect of an applied bias voltage on backscattered ion spectra acquired from thin films of ruthenium and hafnia in the helium ion microscope. A characteristic peak associated with the presence of a thin layer of material is observed to shift as a function of sample bias voltage. The magnitude of this shift is measured, and the authors qualitatively estimate the composition of their samples as well as investigate the neutralization of ions by the sample in the helium ion micoscope (HeIM). They discuss the phenomenona in terms of thin films of ruthenium and hafnia and show the implications of these results on HeIM spectroscopy.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.66.Bz Metals and metallic alloys
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Aluminum recycling from reactor walls: A source of contamination in a-Si:H thin films

C. Longeaud, P. P. Ray, A. Bhaduri, D. Daineka, E. V. Johnson, and P. Roca i Cabarrocas

J. Vac. Sci. Technol. A 28, 1381 (2010); http://dx.doi.org/10.1116/1.3503620 (7 pages)

Online Publication Date: 22 October 2010

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In this article, the authors investigate the contamination of hydrogenated amorphous silicon thin films with aluminum recycled from the walls and electrodes of the deposition reactor. Thin films of hydrogenated amorphous silicon were prepared under various conditions by a standard radio frequency plasma enhanced chemical vapor deposition process in two reactors, the chambers of which were constructed of either aluminum or stainless steel. The authors have studied the electronic properties of these thin films and have found that when using an aluminum reactor chamber, the layers are contaminated with aluminum recycled from the chamber walls and electrode. This phenomenon is observed almost independently of the deposition conditions. The authors show that this contamination results in slightly p-doped films and could be detrimental to the deposition of device grade films. The authors also propose a simple way to control and eventually suppress this contamination.
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68.55.ag Semiconductors
81.05.Cy Elemental semiconductors
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Structural and optical properties of yttrium oxide thin films for planar waveguiding applications

Stuart J. Pearce, Greg J. Parker, Martin D. B. Charlton, and James S. Wilkinson

J. Vac. Sci. Technol. A 28, 1388 (2010); http://dx.doi.org/10.1116/1.3503621 (5 pages) | Cited 1 time

Online Publication Date: 22 October 2010

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Thin films of yttrium oxide, Y2O3, were deposited by reactive sputtering and reactive evaporation to determine their suitability as a host for a rare earth doped planar waveguide upconversion laser. The optical properties, structure, and crystalline phase of the films were found to be dependent on the deposition method and process parameters. X-ray diffraction analysis on the “as-deposited” thin films revealed that the films vary from amorphous to highly crystalline with a small broad peak at 29° corresponding to the 〈222〉 reflections of Y2O3. The samples with the polycrystalline structure had a stoichiometry close to bulk cubic Y2O3. Scanning electron microscopy imaging revealed a regular column structure confirming their crystalline nature. The thin film layers which allowed guiding in both visible and infrared regions had lower refractive indices, higher oxygen content, and a more amorphous structure. Higher oxygen pressures during the deposition lead to a more amorphous layer.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.43.Er Other amorphous solids
78.66.Nk Insulators
61.66.Bi Elemental solids
61.66.Dk Alloys

Impact of the gas-surface scattering and gas molecule-molecule interaction on the mass flow rate of the rarefied gas through a short channel into a vacuum

O. Sazhin

J. Vac. Sci. Technol. A 28, 1393 (2010); http://dx.doi.org/10.1116/1.3504596 (6 pages)

Online Publication Date: 27 October 2010

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The rarefied gas flow through a short channel into a vacuum has been investigated computationally using the direct simulation Monte Carlo method. Taking into account the gas-surface scattering and the gas molecule-molecule interaction, the mass flow rate is calculated as a function of gas rarefaction and the length to height ratio. This study demonstrates that the effects of the gas molecule-molecule interaction and the gas-surface scattering can make a noticeable impact on the mass flow rate of the rarefied gas through a short channel into a vacuum. The maximum manifestation of these effects was evaluated.
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47.45.-n Rarefied gas dynamics
47.60.Dx Flows in ducts and channels
47.11.-j Computational methods in fluid dynamics
05.10.Ln Monte Carlo methods

Study of the effect of plasma-striking atmosphere on Fe-oxidation in thermal dc arc-plasma processing

I. Banerjee, Y. B. Khollam, S. K. Mahapatra, A. K. Das, and S. V. Bhoraskar

J. Vac. Sci. Technol. A 28, 1399 (2010); http://dx.doi.org/10.1116/1.3504597 (5 pages)

Online Publication Date: 1 November 2010

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The effect of plasma-striking atmosphere: air and air+Ar-gas on the crystallization of Fe-oxide phases was studied using dc thermal arc-plasma processing route. The powders were characterized by x-ray diffraction, vibrating sample magnetometry, transmission electron microscopy, and Mössbauer spectroscopy techniques. At room temperature and O2 rich atmosphere, arc-evaporated Fe2+ ions oxidize into either γ-Fe2O3 or Fe3O4 depending upon the combining ratio of Fe with molecular O2. Fe/O ratio could be adjusted using proper flow rate of Ar gas to crystallize the pure γ-Fe2O3.
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52.77.-j Plasma applications
81.65.Mq Oxidation
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Comparison of Ti-Zr-V nonevaporable getter films deposited using alloy or twisted wire sputter-targets

R. Valizadeh, O. B. Malyshev, J. S. Colligon, A. Hannah, and V. M. Vishnyakov

J. Vac. Sci. Technol. A 28, 1404 (2010); http://dx.doi.org/10.1116/1.3504600 (9 pages)

Online Publication Date: 1 November 2010

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A comparison of the performance of nonevaporable getter (NEG) films deposited using two different types of targets has been made to find the one that has the best pumping properties. For the first time, the NEG coating was deposited using a preformed Ti-Zr-V alloy target. The NEG film characterization and pumping properties have been studied in comparison with a film deposited using the commonly used three-wire twisted target. It was demonstrated that the alloy target produces a NEG coating with uniform composition both laterally and in depth. The composition of the film was found to be the same as the target. Film topography and microstructure with 5 nm grain sizes were found to be the same for both targets. The main result is that the activation temperature of the NEG coating deposited using the Ti-Zr-V alloy target is 160 °C, which is 20 °C lower than for NEG coatings deposited using three twisted wires.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
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Novel method for cleaning a vacuum chamber from hydrocarbon contamination

H. D. Wanzenboeck, P. Roediger, G. Hochleitner, E. Bertagnolli, and W. Buehler

J. Vac. Sci. Technol. A 28, 1413 (2010); http://dx.doi.org/10.1116/1.3484242 (8 pages) | Cited 2 times

Online Publication Date: 1 November 2010

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A novel method for cleaning a high vacuum chamber is presented. This method is based on concurrent in situ high-energetic UV light activation of contaminants located in the residual gas and at the vacuum chamber surfaces as well as the in situ generation of highly reactive ozone. Ozone oxidizes the contaminants to volatile species. Investigations by energy-dispersive x-ray analysis of residual gas depositions and mass-spectroscopy measurements of the residual gas in the vacuum chamber identify the contaminant species as hydrocarbons. After a cleaning period of 8 h, a decrease in measured chamber contamination by about 90% could be achieved according to atomic force microscope analysis. Mass spectroscopy measurements using a residual gas analyzer indicate the creation of volatile, carbonaceous species during the cleaning process.
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81.65.Cf Surface cleaning, etching, patterning
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Microstructured optical fiber UHV integration for cold-atom experiments

J.-F. Clément, T. Vitse, and P. Szriftgiser

J. Vac. Sci. Technol. A 28, 1421 (2010); http://dx.doi.org/10.1116/1.3497028 (2 pages)

Online Publication Date: 1 November 2010

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Abstract Unavailable
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42.81.Wg Other fiber-optical devices
37.10.-x Atom, molecule, and ion cooling methods
32.50.+d Fluorescence, phosphorescence (including quenching)
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