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May 2013

Volume 31, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

J. Vac. Sci. Technol. A 31, 030801 (2013); http://dx.doi.org/10.1116/1.4794357 (24 pages)

Yalin Dong, Qunyang Li, and Ashlie Martini
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ToF-SIMS depth profiling of organic solar cell layers using an Ar cluster ion source

Vincent S. Smentkowski, Gilad Zorn, Amanda Misner, Gautam Parthasarathy, Aaron Couture, Elke Tallarek, and Birgit Hagenhoff

J. Vac. Sci. Technol. A 31, 030601 (2013); http://dx.doi.org/10.1116/1.4793730 (6 pages)

Online Publication Date: 27 February 2013

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Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) is a very powerful technique for analyzing the outermost layers of organic and biological materials. The ion fluence in static SIMS is usually kept low enough to prevent decomposition of the organic/molecular species and as a result ToF-SIMS is able to detect and image high mass molecular species, such as polymer additives. Depth profiling, in contrast, uses a high ion fluence in order to remove material between each analysis cycle. Unfortunately, the high ion fluence results in not only erosion but also decomposition of the organic species. Recently, high mass Ar cluster ion sources have become available and are enabling depth profiling through organic layers. In this paper, the authors demonstrate that they can obtain and maintain molecular information throughout an organic solar cell test layer when erosion is performed using an Ar1500+ cluster ion source for material removal. Contrary they show that they cannot maintain molecular information when low energy monoatomic ion beams are used for material removal.
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88.40.H- Solar cells (photovoltaics)
88.40.jr Organic photovoltaics

Theoretical investigation of cubic B1-like and corundum (Cr1−xAlx)2O3 solid solutions

Björn Alling, Ali Khatibi, Sergei I. Simak, Per Eklund, and Lars Hultman

J. Vac. Sci. Technol. A 31, 030602 (2013); http://dx.doi.org/10.1116/1.4795392 (5 pages)

Online Publication Date: 14 March 2013

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First-principles calculations are employed to investigate the stability and properties of cubic rock-salt-like (Cr1−xAlx)2O3 solid solutions, stabilized by metal site vacancies as recently reported experimentally. It is demonstrated that the metal site vacancies can indeed be ordered in a way that gives rise to a suitable fourfold coordination of all O atoms in the lattice. B1-like structures with ordered and disordered metal site vacancies are studied for (Cr0.5Al0.5)2O3 and found to have a cubic lattice spacing close to the values reported experimentally, in contrast to fluorite-like and perovskite structures. The obtained B1-like structures are higher in energy than corundum solid solutions for all compositions, but with an energy offset per atom similar to other metastable systems possible to synthesize with physical vapor deposition techniques. The obtained electronic structures show that the B1-like systems are semiconducting although with smaller band gaps than the corundum structure.
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61.66.Fn Inorganic compounds
71.15.-m Methods of electronic structure calculations
71.20.Nr Semiconductor compounds
61.72.jd Vacancies

Enhancement of solution-processed zinc tin oxide thin film transistors by silicon incorporation

Sung Ryul Mang, Dae Ho Yoon, In Young Jeon, Ho Kyoon Chung, and Lyong Sun Pu

J. Vac. Sci. Technol. A 31, 030603 (2013); http://dx.doi.org/10.1116/1.4795760 (4 pages)

Online Publication Date: 20 March 2013

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Thin film transistors (TFTs) with Si incorporation in zinc tin oxide (ZTO) channel layer were fabricated using a sol–gel process, and the effect of Si incorporation in ZTO systems was investigated with respect to optical, structural, and electrical properties. The Si effectively controlled the generation of the oxygen vacancies examined by x-ray photoelectron spectroscopy, which affected the electrical properties of the silicon zinc tin oxide (SZTO) TFTs. As the Si concentration increased in the ZTO systems, the threshold voltage shifted in the positive direction, the on–off current ratio increased due to the effective reduction of the off current, and the subthreshold swing decreased. At a Si mole ratio 0.02, the SZTO TFTs exhibit favorable electrical properties of Vth = 3.0 V, μFE = 1.90 cm2 V−1 s−1, S.S = 0.38 V/decade, and Ion/off = 1.66 × 107. Thus, the SZTO is a promising material for backplanes of displays.
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85.30.Tv Field effect devices
61.72.jd Vacancies
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Low-temperature CVD of η-Mn3N2−x from bis[di(tert-butyl)amido]manganese(II) and ammonia

Teresa S. Spicer, Charles W. Spicer, Andrew N. Cloud, Luke M. Davis, Gregory S. Girolami, and John R. Abelson

J. Vac. Sci. Technol. A 31, 030604 (2013); http://dx.doi.org/10.1116/1.4799036 (6 pages)

Online Publication Date: 8 April 2013

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Manganese nitride films are grown by low-pressure chemical vapor deposition from the novel precursor bis[di(tert-butyl)amido]manganese(II) and ammonia. Mixed-phase films containing crystalline manganese nitride can be grown on substrates at temperatures as low as 80 °C. Above 200 °C, the films consist entirely of crystalline manganese nitride. The crystalline material has the same tetragonal unit cell as η-Mn3N2, but composition analysis of the Mn:N suggests that the material is best denoted as η-Mn3N2−x with x ∼ 0.7. Both oxygen and carbon contamination in the bulk of the films are <1 at. %. Deposition rates of up to 10 nm/min are observed. The growth of crystalline films of a ceramic material at such low temperatures and high rates is highly unusual. The authors attribute this outcome to the presence of high-moment manganese atoms in mixed valence states and to vacancies in the nitrogen sublattice; both features lower the energies needed to break and reform metal-nitrogen bonds and thus allow the deposited atoms to settle more easily into a low-energy ordered arrangement.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
71.28.+d Narrow-band systems; intermediate-valence solids
61.72.jd Vacancies
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Molecular dynamics simulation of atomic friction: A review and guide

Yalin Dong, Qunyang Li, and Ashlie Martini

J. Vac. Sci. Technol. A 31, 030801 (2013); http://dx.doi.org/10.1116/1.4794357 (24 pages)

Online Publication Date: 11 March 2013

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This paper reviews recent progress in molecular dynamics simulation of atomic-scale friction measured by an atomic force microscopy. Each section of the review focuses on an individual condition or parameter that affects atomic friction including materials, surfaces, compliance, contact area, normal load, temperature, and velocity. The role each parameter plays is described in the context of both experimental measurements and simulation predictions. In addition, the discussion includes an overview of the research community's current understanding of observed effects, guidelines for implementation of those effects in an atomistic simulation, and suggestions for future research to address open questions. Taken together, this review conveys the message that friction at the atomic scale is affected by many interrelated parameters and that the use of molecular dynamics simulation as a predictive tool can be accomplished only through careful model design.
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68.37.Ps Atomic force microscopy (AFM)
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
68.35.Af Atomic scale friction
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Electron-injecting properties of Rb2CO3-doped Alq3 thin films in organic light-emitting diodes

Jin Woo Park, Jong Tae Lim, Jong Sik Oh, Sung Hee Kim, Phuong Pham Viet, Myung S. Jhon, and Geun Young Yeom

J. Vac. Sci. Technol. A 31, 031101 (2013); http://dx.doi.org/10.1116/1.4798302 (7 pages)

Online Publication Date: 3 April 2013

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Rubidium carbonate (Rb2CO3)-doped tris(8-quinolinolato)aluminum (III) (Alq3) thin films have been investigated as electron-injecting materials for organic light-emitting diodes (OLEDs). Electron-only devices consisting of glass/tin-doped indium oxide (ITO)/Rb2CO3-doped Alq3 (10 nm)/aluminum (Al) showed an electron-ohmic contact property between the electrode and the organic layer at the doping concentration of 10% and higher. The electron-injecting ability of these contacts was largely enhanced by the n-doping effect of Rb2CO3 into the Alq3 layer. The ultraviolet photoemission spectra revealed that when the doping concentration was increased, the n-doping effect reduced the carrier-injecting barrier height by lowering the work function at the Rb2CO3-doped Alq3 interfaces. Also, the x-ray photoemission spectra showed that as the doping concentration was increased at the interfaces, Alq3 molecules decomposed in a chemical reaction with Rb2CO3. The OLED device, having the glass/ITO/molybdenum oxide (MoOx, 25%)-doped N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB, 5 nm)/NPB (63 nm)/Alq3 (32 nm)/Rb2CO3-doped Alq3 (10%, 10 nm)/Al (100 nm) structure, showed the best performance at the optimal doping concentration of Rb2CO3-doped Alq3, both the maximum luminance of 114 400 cd/m2 at the bias voltage of 9.8 V and the power efficiency of 2.7 lm/W at the luminance of 1000 cd/m2 were obtained.
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85.60.Jb Light-emitting devices
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Dp Adsorbed layers and thin films

Characterization of thin film adhesion by MEMS shaft-loading blister testing

Maria Berdova, Jussi Lyytinen, Kestutis Grigoras, Anu Baby, Lauri Kilpi, Helena Ronkainen, Sami Franssila, and Jari Koskinen

J. Vac. Sci. Technol. A 31, 031102 (2013); http://dx.doi.org/10.1116/1.4801921 (5 pages)

Online Publication Date: 16 April 2013

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A new microelectromechanical system shaft-loaded blister test was developed and demonstrated to provide stability, repeatability, and simultaneous quantitative measurements of adhesion between thin films deposited on a silicon substrate. The authors assessed adhesion of sputtered platinum, copper, and chromium/copper (300 nm) to underlaying atomic layer deposited (ALD) aluminum oxide. The average adhesion energies for thin films on ALD aluminum oxide were found to be 1.15 ± 0.1 J/m2 for platinum thin films, 1.4 J/m2 for copper thin films, and 1.75 J/m2 for chromium/copper.
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68.35.Np Adhesion
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Beyond hard x-ray photoelectron spectroscopy: Simultaneous combination with x-ray diffraction

Juan Rubio-Zuazo and German R. Castro

J. Vac. Sci. Technol. A 31, 031103 (2013); http://dx.doi.org/10.1116/1.4801915 (8 pages)

Online Publication Date: 29 April 2013

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Hard x-ray photoelectron spectroscopy (HAXPES) is a powerful and novel emerging technique for the nondestructive determination of electronic properties and chemical composition of bulk, buried interfaces and surfaces. It benefits from the exceptionally large escape depth of high kinetic energy photoelectrons, increasing the information depth up to several tens of nanometers. Complementing HAXPES with an atomic structure sensitive technique (such as x-ray diffraction) opens a new research field with major applications for materials science. At SpLine, the Spanish CRG beamline at the European Synchrotron Radiation Facility, we have developed a novel experimental set-up that combines HAXPES and x-ray diffraction (x-ray reflectivity, surface x-ray diffraction, grazing incidence x-ray diffraction, and reciprocal space maps). Both techniques can be operated simultaneously on the same sample and using the same excitation source. The set-up includes a robust 2S + 3D diffractometer hosting a ultrahigh vacuum chamber equipped with a unique photoelectron spectrometer (few eV < electron kinetic energy < 15 keV), x-ray tube (Mg/Ti), 15 keV electron gun, and auxiliary standard surface facilities (molecular beam epitaxy evaporator, ion gun, low energy electron diffraction, sample heating/cooling system, leak valves, load-lock sample transfer, etc.). This end-station offers the unique possibility of performing simultaneous HAXPES + x-ray diffraction studies. In the present work, we describe the experimental set-up together with two experimental examples that emphasize its outstanding capabilities: (i) nondestructive characterization of the Si/Ge and HfO2/SiO2 interfaces on Ge-based CMOS devices, and (ii) strain study on La0.7Ca0.3MnO3 ultrathin films grown on SrTiO3(001) substrate.
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07.85.Jy Diffractometers
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.60.-p Physical properties of thin films, nonelectronic
84.47.+w Vacuum tubes
85.30.Tv Field effect devices
68.55.-a Thin film structure and morphology
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Investigation of shunt path evolution originated from transparent conductive oxides in Si-based thin film solar cells

Minho Joo, Jungmin Lee, Kyuho Park, Jin-Won Chung, Seh-Won Ahn, and Heon-Min Lee

J. Vac. Sci. Technol. A 31, 031201 (2013); http://dx.doi.org/10.1116/1.4802023 (4 pages)

Online Publication Date: 17 April 2013

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The evolution of the shunt path on the performance of Si-based thin film solar cells with an glass/Al-doped ZnO (AZO)/amorphous (a)-Si:H/a-SiGe:H/Al was investigated by conductive atomic force microscopy, electroluminescence measurement, and transmission electron microscopy. AZO films were highly textured for the light management before the deposition of absorption layers. The cell performance was found to be strongly dependent on the existence of nanocracks formed in a-Si:H/a-SiGe:H layers. The defects by nanocracks are expected to attribute to the leakage current in the cells. The authors introduce two types of shunt path evolution modes: pinhole defects (type A) and highly textured groove of AZO film (type B). Both crack defects by types A and B induced high leakage current, leading to a relatively reduced fill factor on the performance.
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88.40.jj Silicon solar cells
88.40.H- Solar cells (photovoltaics)
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Characteristics of silicon etching by silicon chloride ions

Tomoko Ito, Kazuhiro Karahashi, Song-Yun Kang, and Satoshi Hamaguchi

J. Vac. Sci. Technol. A 31, 031301 (2013); http://dx.doi.org/10.1116/1.4793426 (5 pages)

Online Publication Date: 1 March 2013

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Plasmas generated from halogen-containing gases, such as Cl2 or HBr, have been widely used in gate etching processes for semiconductor chip manufacturing. Such plasmas may contain silicon halide ions formed by the ionization of etching products that enter the plasma. In this study, to illustrate Si etching by such silicon halide ions, the sputtering yield of Si by SiClx+ (with x = 1 or 3) ions has been obtained as a function of the incident ion energy by using a mass-selected ion beam injection system. It has been found that, at sufficiently low energy, the incidence of SiCl+ ions leads to the deposition of Si which may affect profile control in microelectronic device fabrication processes.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Real-time control of electron density in a capacitively coupled plasma

Bernard Keville, Yang Zhang, Cezar Gaman, Anthony M. Holohan, Stephen Daniels, and Miles M. Turner

J. Vac. Sci. Technol. A 31, 031302 (2013); http://dx.doi.org/10.1116/1.4795207 (12 pages)

Online Publication Date: 22 March 2013

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Reactive ion etching (RIE) is sensitive to changes in chamber conditions, such as wall seasoning, which have a deleterious effect on process reproducibility. The application of real time, closed loop control to RIE may reduce this sensitivity and facilitate production with tighter tolerances. The real-time, closed loop control of plasma density with RF power in a capacitively coupled argon plasma using a hairpin resonance probe as a sensor is described. Elementary control analysis shows that an integral controller provides stable and effective set point tracking and disturbance attenuation. The trade off between performance and robustness may be quantified in terms of one parameter, namely the position of the closed loop pole. Experimental results are presented, which are consistent with the theoretical analysis.
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52.77.Bn Etching and cleaning
52.25.-b Plasma properties
52.70.Ds Electric and magnetic measurements

Nitrogen actinometry for measurement of nitrogen radical spatial distribution in large-area plasma-enhanced chemical vapor deposition

Changhoon Oh, Minwook Kang, Seungsuk Nam, and Jae W. Hahn

J. Vac. Sci. Technol. A 31, 031303 (2013); http://dx.doi.org/10.1116/1.4798772 (5 pages)

Online Publication Date: 2 April 2013

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Density distributions of radicals in the large-area silicon nitride (Si3N4) plasma-enhanced chemical vapor deposition (PECVD) process were measured using a spatially resolvable optical emission spectrometer (SROES). To determine the qualitative distribution of a target radical, the authors used optical actinometry with nitrogen (N2) gas as an actinometer. To compare the SROES data and process results, the thickness of the deposited Si3N4 thin films using an ellipsometer was measured. By introducing nitrogen-based optical actinometry, the authors obtained very good agreement between the experimental results of the distributions of atomic nitrogen radical and the deposited thicknesses of Si3N4 thin films. Based on these experimental results, the uniformity of the process plasma in the PECVD process at different applied radio frequency powers was analyzed.
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07.60.Dq Photometers, radiometers, and colorimeters
52.77.Dq Plasma-based ion implantation and deposition
07.60.Fs Polarimeters and ellipsometers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Computational modeling study of the radial line slot antenna microwave plasma source with comparisons to experiments

Laxminarayan L. Raja, Shankar Mahadevan, Peter L. G. Ventzek, and Jun Yoshikawa

J. Vac. Sci. Technol. A 31, 031304 (2013); http://dx.doi.org/10.1116/1.4798362 (11 pages) | Cited 1 time

Online Publication Date: 8 April 2013

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The radial line slot antenna plasma source is a high-density microwave plasma source comprising a high electron temperature source region within the plasma skin depth from a coupling window and low electron temperature diffusion region far from the window. The plasma is typically comprised of inert gases like argon and mixtures of halogen or fluorocarbon gases for etching. Following the experimental study of Tian et al. [J. Vac. Sci. Technol. A 24, 1421 (2006)], a two-dimensional computational model is used to describe the essential features of the source. A high density argon plasma is described using the quasi-neutral approximation and coupled to a frequency-domain electromagnetic wave solver to describe the plasma-microwave interactions in the source. The plasma is described using a multispecies plasma chemistry mechanism developed specifically for microwave excitation conditions. The plasma is nonlocal by nature with locations of peak power deposition and peak plasma density being very different. The spatial distribution of microwave power coupling depends on whether the plasma is under- or over-dense and is described well by the model. The model predicts the experimentally observed low-order diffusion mode radial plasma profiles. The trends of spatial profiles of electron density and electron temperature over a wide range of power and pressure conditions compare well with experimental results.
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52.50.Dg Plasma sources
52.65.-y Plasma simulation
52.75.-d Plasma devices
52.25.-b Plasma properties

Selective etching of TiN over TaN and vice versa in chlorine-containing plasmas

Hyungjoo Shin, Weiye Zhu, Lei Liu, Shyam Sridhar, Vincent M. Donnelly, Demetre J. Economou, Chet Lenox, and Tom Lii

J. Vac. Sci. Technol. A 31, 031305 (2013); http://dx.doi.org/10.1116/1.4801883 (6 pages)

Online Publication Date: 18 April 2013

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Selectivity of etching between physical vapor-deposited TiN and TaN was studied in chlorine-containing plasmas, under isotropic etching conditions. Etching rates for blanket films were measured in-situ using optical emission of the N2 (C3Πu →B3Πg) bandhead at 337 nm to determine the etching time, and transmission electron microscopy to determine the starting film thickness. The etching selectivity in Cl2/He or HCl/He plasmas was poor (<2:1). There was a window of very high selectivity of etching TiN over TaN by adding small amounts (<1%) of O2 in the Cl2/He plasma. Reverse selectivity (10:1 of TaN etching over TiN) was observed when adding small amounts of O2 to the HCl/He plasma. Results are explained on the basis of the volatility of plausible reaction products.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Impact of static magnetic fields on the radial line slot antenna plasma source

Jun Yoshikawa and Peter L. G. Ventzek

J. Vac. Sci. Technol. A 31, 031306 (2013); http://dx.doi.org/10.1116/1.4802737 (10 pages)

Online Publication Date: 26 April 2013

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The radial line slot antenna plasma source is used in semiconductor device fabrication. As is the case for all plasma sources, ever more strict uniformity control requirements are driven by the precision demands of new device technologies. Large volume diffusion plasmas, of which the radial line slot antenna source is one type, must overcome transport effects or diffusion modes that tend to “center peak” the plasma density near the wafer being processed. One way to resolve problematic transport effects is the insertion of magnetic fields into the plasma region. In this paper, the impact of the magnetic field on plasma properties is parameterized as a function of slot configuration. The magnetic field orientation and the magnitude of magnetic field are varied in a computational study in which the source is modeled as a two-dimensional axisymmetric quasineutral plasma. This work employs a finite element model simulation. The magnitude of magnetic fields considered is 50 Gauss maximum with a microwave power of 3000 W at a pressure of 20 mTorr. 20 mTorr is chosen as this is a condition where diffusion effects are challenging to counteract. The study showed that there are specific conditions for slot configuration and magnetic field that improve the plasma controllability and some that do not. Plasma property modulation is most effective when the plasma source region is placed at large radius with axial magnetic fields. There are synergistic effects between the slot location and magnetic field that are important and placing large magnetic fields at the chamber edge alone does not result in improved uniformity. Electron cyclotron resonance (ECR) heating and the impact of pulsing the magnetic fields are presented. ECR heating is not important for the conditions relevant to this paper and pulsing is shown to have benefit.
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52.50.Dg Plasma sources
52.65.Pp Monte Carlo methods
51.20.+d Viscosity, diffusion, and thermal conductivity
52.25.Fi Transport properties
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
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Measurement of the Auger parameter and Wagner plot for uranium compounds

Kiel S. Holliday, Wigbert Siekhaus, and Art J. Nelson

J. Vac. Sci. Technol. A 31, 031401 (2013); http://dx.doi.org/10.1116/1.4793477 (6 pages)

Online Publication Date: 22 February 2013

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In this study, the photoemission from the U 4f7/2 and 4d5/2 states and the U N6O45O45 and N67O45V x-ray excited Auger transitions were measured for a range of uranium compounds. The data are presented in Wagner plots and the Auger parameter is calculated to determine the utility of this technique in the analysis of uranium materials. It was demonstrated that the equal core-level shift assumption holds for uranium. It was therefore possible to quantify the relative relaxation energies, and uranium was found to have localized core-hole shielding. The position of compounds within the Wagner plot made it possible to infer information on bonding character and local electron density. The relative ionicity of the uranium compounds studied follows the trend UF4 > UO3 > U3O8 > U4O9/U3O7 ≈ UO2 > URu2Si2.
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79.20.Fv Electron impact: Auger emission
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

In situ formation and electron-spectroscopic study of bis(arene) V and Cr compounds on a graphite surface

Victor M. Bermudez

J. Vac. Sci. Technol. A 31, 031402 (2013); http://dx.doi.org/10.1116/1.4794194 (8 pages)

Online Publication Date: 7 March 2013

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Thin layers of bis(arene) transition metal (TM) compounds have been formed in situ in ultra-high vacuum by depositing Cr or V metal on top of a film of benzene (Bz) or toluene (Tol) ice at 100 K on a graphite substrate. The species thus formed are Cr(C6H6)2, V(C6H6)2, or Cr(C6H5-CH3)2 (termed CrBz2, VBz2, or Cr(Tol)2), and the valence structures have been examined using electron energy loss and ultraviolet photoemission spectroscopies (ELS and UPS). The reaction is “clean” in that there is no indication of side reactions or unwanted by-products, although a small coverage of unreacted TM atoms appears unavoidable. A simple ring substituent (CH3) remains intact during the reaction. Thus, it should be possible to synthesize and study species that are not readily available (or cannot easily be made) in bulk form or that have too low vapor pressure to allow easy in situ deposition. Data have been obtained for VBz2 and Cr(Tol)2, the valence structures of which have not previously been studied in detail using UPS and ELS. Although deeper-lying arene orbitals are essentially unperturbed by formation of the bis(arene)TM sandwich, subtle differences in the TM-related orbitals have been observed and discussed in comparison to CrBz2 with the aid of density functional theory. In the case of VBz2, clear evidence is seen for a molecular reorientation during annealing, based on the ELS polarization dependence. Electron transfer between an adsorbed bis(arene)TM and graphite depends on the occupancy of the highest occupied molecular orbital (HOMO) and on its energy relative to the Fermi level (EF). The small amount of unreacted TM resulting from in situ synthesis causes a large decrease in work function, which shifts the adsorbate HOMO to below EF and thus impedes electron transfer to highly oriented pyrolytic graphite. This is an obstacle to forming doping layers by this method.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.20.At Surface states, band structure, electron density of states
78.40.Ri Fullerenes and related materials
79.20.Uv Electron energy loss spectroscopy
81.05.uf Graphite
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Subnanometer-resolution depth profiling of boron atoms and lattice defects in silicon ultrashallow junctions by ion beam techniques

Lakshmanan H. Vanamurthy, Mengbing Huang, Hassaram Bakhru, Toshiharu Furukawa, Nathaniel Berliner, Joshua Herman, Zhengmao Zhu, Paul Ronsheim, and Bruce Doris

J. Vac. Sci. Technol. A 31, 031403 (2013); http://dx.doi.org/10.1116/1.4795208 (7 pages)

Online Publication Date: 11 March 2013

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The continued research and development effort on silicon ultrashallow junctions has posed a great challenge to materials characterization, due to the need for depth profiling of dopants and silicon lattice defects with a subnanometer resolution. In this work, we report on a method combining ion beam analysis (Rutherford backscattering, ion channeling, and nuclear reaction analysis) with room-temperature UV-assisted oxidation and chemical wet etching for obtaining high-resolution (∼0.5 nm) depth distributions of total boron atoms, electrically activated boron atoms and silicon lattice defects in silicon ultrashallow junctions. The application of this method was demonstrated by profiling silicon junctions as shallow as 8 nm, created by 200-eV boron ion implantation followed annealing by various techniques. The capability to profile boron at such high resolution has resulted in observation of boron segregation. Additionally, the ability for depth profiling Si lattice defects offered by this method has aided in the understanding of thermal and laser annealing effects on defect formation in Si junctions. Our experimental results are compared with those obtained using other techniques such as secondary ion mass spectroscopy and four-point probe, and differences are discussed in detail.
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61.72.U- Doping and impurity implantation
64.75.Qr Phase separation and segregation in semiconductors
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Improvement of the surface quality of semi-insulating InP substrates through a novel etching and cleaning method

Jingming Liu, Youwen Zhao, Zhiyuan Dong, Fengyun Yang, Fenghua Wang, Kewei Cao, Tong Liu, Hui Xie, and Teng Chen

J. Vac. Sci. Technol. A 31, 031404 (2013); http://dx.doi.org/10.1116/1.4798309 (5 pages)

Online Publication Date: 22 March 2013

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Residual impurities and contamination on semi-insulating (SI) InP wafers are detrimental for epitaxial growth and device performance, especially because residual silicon on an SI-InP wafer surface is electrically active and generates an n-type conduction layer at the interface between the epilayer and the InP substrate. In order to reduce the concentration of Si and improve surface quality, the authors investigate a wet-chemical cleaning process for ready-to-use InP substrates. A novel and practical cleaning process was developed by adding an alkaline solution to the conventional acidic cleaning process. Time-of-flight secondary mass spectrometry, a very powerful analysis technique to characterize surfaces and investigate any organic and inorganic contamination present on the InP surface, was used after the samples were etched under different cleaning processes. The results show that the novel etching process effectively reduces the Si contamination.
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81.65.Cf Surface cleaning, etching, patterning
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.55.ag Semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Np Solid phase epitaxy; growth from solid phases

Vibronic fine structure in high-resolution x-ray absorption spectra from ion-bombarded boron nitride nanotubes

Mladen Petravic, Robert Peter, Marijana Varasanec, Lu Hua Li, Ying Chen, and Bruce C. C. Cowie

J. Vac. Sci. Technol. A 31, 031405 (2013); http://dx.doi.org/10.1116/1.4798271 (5 pages)

Online Publication Date: 3 April 2013

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The authors have applied high-resolution near-edge x-ray absorption fine structure measurements around the nitrogen K-edge to study the effects of ion-bombardment on near-surface properties of boron nitride nanotubes. A notable difference has been observed between surface sensitive partial electron yield (PEY) and bulk sensitive total electron yield (TEY) fine-structure measurements. The authors assign the PEY fine structure to the coupling of excited molecular vibrational modes to electronic transitions in NO molecules trapped just below the surface. Oxidation resistance of the boron nitride nanotubes is significantly reduced by low energy ion bombardment, as broken B-N bonds are replaced by N-O bonds involving oxygen present in the surface region. In contrast to the PEY spectra, the bulk sensitive TEY measurements on as-grown samples do not exhibit any fine structure while the ion-bombarded samples show a clear vibronic signature of molecular nitrogen.
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61.82.Rx Nanocrystalline materials
78.70.Dm X-ray absorption spectra
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.80.Jh Ion radiation effects

Low temperature oxidation of plutonium

Art J. Nelson and Paul Roussel

J. Vac. Sci. Technol. A 31, 031406 (2013); http://dx.doi.org/10.1116/1.4802596 (5 pages)

Online Publication Date: 18 April 2013

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The initial oxidation of gallium stabilized δ-plutonium metal at 193 K has been followed using x-ray photoelectron spectroscopy. On exposure to Langmuir quantities of oxygen, plutonium rapidly forms a trivalent oxide followed by a tetravalent plutonium oxide. The growth modes of both oxides have been determined. Warming the sample in vacuum, the tetravalent oxide reduces to the trivalent oxide. The kinetics of this reduction reaction have followed and the activation energy has been determined to be 38.8 kJ mol−1.
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81.65.Mq Oxidation
82.30.-b Specific chemical reactions; reaction mechanisms
82.40.-g Chemical kinetics and reactions: special regimes and techniques
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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Effect of quantum dot length on the degree of electron localization in polymer wires grown by molecular layer deposition

Tetsuzo Yoshimura and Sho Ishii

J. Vac. Sci. Technol. A 31, 031501 (2013); http://dx.doi.org/10.1116/1.4793478 (5 pages)

Online Publication Date: 25 February 2013

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Polymer multiple quantum dots were fabricated on glass substrates by molecular layer deposition. The quantum dot length was controlled by connecting three source molecules with monomolecular steps in designated sequences and was estimated from theoretical structures to be in the range 0.9–3.1 nm. With decreasing dot length, the absorption peak shifted to higher energy because of the quantum confinement effect; however, the photoluminescence peak shifted to lower energy due to a Stokes shift enhanced by increased π-electron localization. This suggests that π-electrons tend to be tightly confined in quantum dots with reduced lengths.
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81.07.Ta Quantum dots
61.41.+e Polymers, elastomers, and plastics
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
78.55.Kz Solid organic materials
78.67.Hc Quantum dots

Axial resistivity measurement of a nanopillar ensemble using a cross-bridge Kelvin architecture

Abeed Lalany, Ryan Thomas Tucker, Michael Thomas Taschuk, Michael David Fleischauer, and Michael Julian Brett

J. Vac. Sci. Technol. A 31, 031502 (2013); http://dx.doi.org/10.1116/1.4794182 (6 pages)

Online Publication Date: 1 March 2013

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Achieving the full potential of nanopillar electrode based devices, such as next-generation solar cells, catalyst supports, and sensors, requires axial resistivity measurements to optimize electronic performance. Here, the authors demonstrate a technique for direct measurement of the ensemble electrical properties of nanopillar thin films along the structure's longitudinal axis. A cross-bridge Kelvin resistor architecture is adapted to accommodate an indium tin oxide (ITO) nanopillar thin film fabricated by glancing angle deposition (GLAD). As-deposited GLAD ITO nanopillars were found to have a measured resistivity of (1.1 ± 0.3) × 10−2 Ω cm using our technique. Planar ITO films deposited at near normal incidence were found to have a resistivity of (4.5 ± 0.5) × 10−3 Ω cm, determined by the standard four-point-probe technique. These measurements demonstrate the viability of this modified technique for nanopillar characterization, and identify experimental limitations related to device size and edge defects.
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73.61.Ng Insulators
73.63.Bd Nanocrystalline materials

Validity of automated x-ray photoelectron spectroscopy algorithm to determine the amount of substance and the depth distribution of atoms

Sven Tougaard

J. Vac. Sci. Technol. A 31, 031503 (2013); http://dx.doi.org/10.1116/1.4795246 (6 pages)

Online Publication Date: 14 March 2013

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The author reports a systematic study of the range of validity of a previously developed algorithm for automated x-ray photoelectron spectroscopy analysis, which takes into account the variation in both peak intensity and the intensity in the background of inelastically scattered electrons. This test was done by first simulating spectra for the Au4d peak with gold atoms distributed in the form of a wide range of nanostructures, which includes overlayers with varying thickness, a 5 Å layer of atoms buried at varying depths and a substrate covered with an overlayer of varying thickness. Next, the algorithm was applied to analyze these spectra. The algorithm determines the number of atoms within the outermost 3 λ of the surface. This amount of substance is denoted AOS3λ (where λ  is the electron inelastic mean free path). In general the determined AOS3λ is found to be accurate to within ∼10–20% depending on the depth distribution of the atoms. The algorithm also determines a characteristic length L, which was found to give unambiguous information on the depth distribution of the atoms for practically all studied cases. A set of rules for this parameter, which relates the value of L to the depths where the atoms are distributed, was tested, and these rules were found to be generally valid with only a few exceptions. The results were found to be rather independent of the spectral energy range (from 20 to 40 eV below the peak energy) used in the analysis.
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79.60.-i Photoemission and photoelectron spectra
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Polarity control and transport properties of Mg-doped (0001) InN by plasma-assisted molecular beam epitaxy

Soojeong Choi, Feng Wu, Oliver Bierwagen, and James S. Speck

J. Vac. Sci. Technol. A 31, 031504 (2013); http://dx.doi.org/10.1116/1.4795811 (5 pages)

Online Publication Date: 19 March 2013

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The authors report on the plasma-assisted molecular beam epitaxy growth and carrier transport of Mg-doped In-face (0001) InN. The 1.2 μm thick InN films were grown on GaN:Fe templates under metal rich conditions with Mg concentration from 1 × 1017/cm3 to 3 × 1020/cm3. A morphological transition, associated with the formation of V-shape polarity inversion domains, was observed at Mg concentration over 7 × 1019/cm3 by atomic force microscopy and transmission electron microscopy. Seebeck measurements indicated p-type conductivity for Mg-concentrations from 9 × 1017/cm3 to 7 × 1019/cm3, i.e., as it exceeded the compensating (unintentional) donor concentration.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.-j Plasma applications
73.61.Ey III-V semiconductors

Influence of plasma treatment on optical and electrical properties of a-InGaZnO films

Li Xifeng, Xin Enlong, Shi Jifeng, Li Chunya, and Zhang Jianhua

J. Vac. Sci. Technol. A 31, 031505 (2013); http://dx.doi.org/10.1116/1.4798297 (5 pages)

Online Publication Date: 22 March 2013

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Amorphous InGaZnO (a-IGZO) films were prepared by radio frequency magnetron sputtering, and as-deposited a-IGZO films were treated with plasma in plasma-enhanced chemical vapor deposition equipment. The effects of plasma surface treatment on the microstructure and the optical and electrical properties of IGZO films were investigated. X-ray diffraction analysis indicated that the IGZO films were amorphous. Results showed that plasma surface treatment have remarkable influence on the resistivity, carrier concentration, and carrier mobility of IGZO films. The analysis of x-ray photoelectron spectroscopy revealed a correlation between the electrical properties of IGZO films and plasma surface treatment. For all the samples, the average transmission in the visible region is more than 80%.
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68.55.ag Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effects of preparation conditions on the magnetocaloric properties of Gd thin films

Hillary F. Kirby, Dustin D. Belyea, Jonathon T. Willman, and Casey W. Miller

J. Vac. Sci. Technol. A 31, 031506 (2013); http://dx.doi.org/10.1116/1.4795817 (4 pages)

Online Publication Date: 1 April 2013

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The impact of the deposition temperature and chamber gettering on Ta(5 nm)/Gd(30 nm)/Ta(5 nm) thin films magnetocaloric effect properties was investigated. Increasing the deposition temperature generally improves the entropy peak (magnitude, full width at half max, and temperature of the peak) but also leads to significant oxidation. Gettering the chamber prior to deposition not only reduced this oxidation issue but also increased the relative cooling power of films grown at elevated temperatures by as much as 33% over ungettered samples.
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68.55.-a Thin film structure and morphology
75.30.Sg Magnetocaloric effect, magnetic cooling
81.65.Mq Oxidation

Glancing angle deposition on a roll: Towards high-throughput nanostructured thin films

Kathleen M. Krause, Michael T. Taschuk, and Michael J. Brett

J. Vac. Sci. Technol. A 31, 031507 (2013); http://dx.doi.org/10.1116/1.4798947 (9 pages)

Online Publication Date: 4 April 2013

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Increasing the throughput of the powerful single-step glancing angle deposition (GLAD) method using a prototype simplified roll-to-roll (R2R) system has been explored. While the conventional GLAD technique is popular for fabricating nanostructured devices in a single deposition step, it is not a high-output process. To evaluate the feasibility of large area GLAD deposition, the authors examined the geometrical considerations required to eventually achieve GLAD in a roll-to-roll manufacturing system. Nominal deposition and rotation angles were mathematically translated to their effective R2R counterparts, allowing for deposition recipes of the archetype GLAD nanostructures (slanted posts, vertical posts, and square spirals) and the mechanics of the phi-sweep technique to be converted to this space. Representative structures were then deposited, and the phi-sweep technique successfully applied, in a prototype single barrel roller R2R experimental system. This prototype system provides a foundation for moving GLAD from the laboratory to mass production.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Effects of gas environment on electronic and optical properties of amorphous indium zinc tin oxide thin films

Yus Rama Denny, Sunyoung Lee, Kangil Lee, Soonjoo Seo, Suhk Kun Oh, Hee Jae Kang, Sung Heo, Jae Gwan Chung, Jae Cheol Lee, and Sven Tougaard

J. Vac. Sci. Technol. A 31, 031508 (2013); http://dx.doi.org/10.1116/1.4801023 (7 pages)

Online Publication Date: 15 April 2013

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The electronic and optical properties of indium zinc tin oxide (IZTO) thin films grown under different gas environments were investigated by means of x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy (REELS). REELS spectra revealed that IZTO thin films under argon mixed with oxygen had band gaps of 3.07 eV before annealing and 3.46 eV after annealing at 350 °C in air. Meanwhile, the band gap for IZTO thin film grown under oxygen mixed with water and annealed at 350 °C in air was 3.26 eV. Band gaps obtained from REELS spectra are consistent with the optical band gaps obtained using UV-spectrometry. The REELS spectra were quantitatively analyzed based on comparison of the effective cross section for inelastic electron scattering in the REELS experiment to determine the dielectric function and transmittance of the IZTO thin films. It was found that amorphous IZTO films grown under argon mixed with oxygen followed by annealing at 350 °C exhibit higher optical transmittance in the visible-light region, higher carrier mobility, and a high on–off current ratio.
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77.55.-g Dielectric thin films
73.50.Dn Low-field transport and mobility; piezoresistance
77.22.Ch Permittivity (dielectric function)
78.40.Ha Other nonmetallic inorganics
79.20.Uv Electron energy loss spectroscopy
79.60.Dp Adsorbed layers and thin films
81.40.Gh Other heat and thermomechanical treatments

Atomic layer deposition of titanium dioxide using titanium tetrachloride and titanium tetraisopropoxide as precursors

Rohan P. Chaukulkar and Sumit Agarwal

J. Vac. Sci. Technol. A 31, 031509 (2013); http://dx.doi.org/10.1116/1.4798385 (5 pages)

Online Publication Date: 18 April 2013

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Most atomic layer deposition (ALD) processes for metal oxides involve the use of a metal precursor and an oxygen source, such as H2O, O3, or an O2 plasma. These ALD processes lead to the formation of an undesirable interfacial oxide during deposition on semiconductor surfaces. As an alternative, some metal oxides other than TiO2 have been deposited using metal alkoxides as the oxygen source. In this article, we report on the ALD of TiO2 using TiCl4 and titanium tetraisopropoxide (TTIP) as precursors. Our surface infrared spectroscopy data shows that over the temperature range of 150–250 °C and the duration of a typical ALD cycle (∼1–10 s), in both half-reaction cycles, the surface reaction mechanism is dominated by alkyl-transfer from the TTIP ligands to Ti-Cl species. At 250 °C, which is the onset for TTIP thermal decomposition, the contribution of the direct decomposition reaction to film growth is negligible. The growth per cycle, ∼0.7 Å at 200 °C, is higher than H2O-based ALD of TiO2 from either TiCl4 or TTIP, but similar to O2-plasma-based processes. X-ray photoelectron spectroscopy data show TiO2 films with only the +4 oxidation state of Ti, and the Cl content is estimated to be 2.5–3.5%. UV–Vis spectroscopy shows a band gap of ∼3.0 eV, which is comparable to the values reported in the literature for amorphous TiO2 thin films.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
71.20.Ps Other inorganic compounds
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
78.66.Nk Insulators
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Electron stimulated desorption from the 316 L stainless steel as a function of impact electron energy

Oleg B. Malyshev, Rebecca M. A. Jones, Benjamin T. Hogan, and Adrian Hannah

J. Vac. Sci. Technol. A 31, 031601 (2013); http://dx.doi.org/10.1116/1.4798256 (5 pages)

Online Publication Date: 1 April 2013

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The electron stimulated desorption (ESD) yields of vacuum chamber wall materials are required as one of the important input parameters in the design of vacuum systems for particle accelerators and many other vacuum systems where energetic electrons hit vacuum chamber walls. In the present study, the ESD yields were measured and analyzed (a) as a function of accumulated electron dose, (b) as a function of the total amount of desorbed gas, and (c) as a function of the energy of electrons bombarding. In this study, three separate 316 L stainless steel samples were bombarded with electrons up to an accumulated electron dose of ∼2 × 1023 e/m2 at three different corresponding electron energies: 50 eV, 500 eV, and 5 keV. Once the required dose was reached, the ESD yield as a function of electron energy was measured between 10 eV and 6.5 keV. The results obtained by both methods were in agreement showing that ESD yield increases with electron energy. Experimental difficulties and problems with interpretation of data relating to such a study are described and discussed in the paper.
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68.43.Rs Electron stimulated desorption
79.20.La Photon- and electron-stimulated desorption

Investigation of the time evolution of STM-tip temperature during electron bombardment

David Hellmann, Ludwig Worbes, Konstantin Kloppstech, Nils Könne, and Achim Kittel

J. Vac. Sci. Technol. A 31, 031602 (2013); http://dx.doi.org/10.1116/1.4802967 (7 pages)

Online Publication Date: 26 April 2013

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In the field of scanning probe microscopy, great attention must be paid to the state of sample and probe with respect to unintentionally adsorbed molecules. There are many techniques for cleaning tips described in literature, among them the use of accelerated electrons as an energy source. So far, all of the setups described yielded either no or only indirect information about the probe's temperature reached during the cleaning procedure. The Near-Field Scanning Thermal Microscopy probe not only serves as scanning tunneling microscope tip, but also includes a thermosensor in the vicinity of the probe's apex. Since the tip's body mainly consists of glass, which has a softening point of 1100 K, it must not be heated excessively in order to prevent its destruction. The authors use electron bombardment for cleaning these unique sensors, while the thermosensor is used as feedback for an automated device which is controlling the procedure. Our findings reveal that probe temperatures of up to 1220 K can be reached for short periods of time without causing any damage. In this article, the authors describe the device as well as experimental data concerning the relation between the energies used for cleaning and the resulting temperature of the probe. The presented data might serve as an indicator for other setups where a direct measurement of the temperature of the apex is impossible.
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07.79.Cz Scanning tunneling microscopes
07.20.Dt Thermometers
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Versatile Rb vapor cells with long lifetimes

John F. Hulbert, Matthieu Giraud-Carrier, Tom Wall, Aaron R. Hawkins, Scott Bergeson, Jennifer Black, and Holger Schmidt

J. Vac. Sci. Technol. A 31, 033001 (2013); http://dx.doi.org/10.1116/1.4795759 (5 pages)

Online Publication Date: 18 March 2013

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The authors report on an approach to the construction of long-lasting rubidium atomic vapor cells. The method uses pinch-off copper cold-welds, low temperature solders, and electroplated copper to create long-lasting hermetic seals between containment chambers of dissimilar geometries and materials. High temperature epoxy, eutectic lead/tin solder, and indium solder were considered as sealing materials. These seals were analyzed using accelerated lifetime testing techniques. Vapor cells with epoxy and bare metal solder seals had a decrease in the rubidium atomic density within days after being heated to elevated temperatures. They also exhibited broadened spectra as a result of rubidium reacting with the seals. However, indium solder seals with a passivation coating of electroplated copper did not exhibit a significant decrease in linewidth or atomic density after being held at 95 °C for 30 days. The authors conclude that this particular seal has no rubidium chemical reaction failure mode and when used in combination with copper cold welding has the potential to create multiplatform vapor cells with extremely long lifetimes.
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88.80.ff Batteries
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