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Mar 2013

Volume 31, Issue 2, Articles (02xxxx)

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J. Vac. Sci. Technol. A 31, 020605 (2013); http://dx.doi.org/10.1116/1.4791669 (5 pages)

Peter J. Cumpson, Jose F. Portoles, and Naoko Sano
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X-ray photoelectron spectroscopic study on interface bonding between Pt and Zn- and O-terminated ZnO

Michiko Yoshitake, Petr Blumentrit, and Slavomir Nemsak

J. Vac. Sci. Technol. A 31, 020601 (2013); http://dx.doi.org/10.1116/1.4772464 (5 pages)

Online Publication Date: 19 December 2012

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Interface bonding between Pt and Zn- and O-terminated ZnO surfaces was investigated by precise analysis of x-ray photoelectron spectra. The interfaces were formed by vapor depositing Pt onto the ZnO surfaces in ultrahigh vacuum. The changes in the Zn 2p3/2, O 1s, Zn LMM Auger, and Pt 4f7/2 spectra upon Pt deposition were observed. The changes in the shape of the Zn LMM spectra and the shifts in the binding energy of Zn 2p3/2 and O 1s revealed that there was a metallic Zn component in the Zn LMM and Zn 2p3/2 spectra for Zn-terminated ZnO and a Pt-O component in the O 1s spectra for both Zn- and O-terminated ZnO. Peaks were fitted with multiple components accordingly. The binding energy shifts of Zn 2p3/2 and O 1s for the ZnO component were almost the same, which confirmed that the fitting was reasonable. From the fitting results, the interface bonding was concluded to be O-terminated, i.e., Zn-O-Pt bond formation occurred at the interface for both Zn- and O-terminated ZnO. This clearly demonstrated that the stable interface bonding occurring between Pt and ZnO is Zn-O-Pt bonding whether the ZnO substrate is initially Zn-terminated or O-terminated.
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81.05.Dz II-VI semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.A- Nucleation and growth
61.50.Lt Crystal binding; cohesive energy
79.60.Bm Clean metal, semiconductor, and insulator surfaces

High temperature growth of Ag phases on Ge(111)

Cory H. Mullet and Shirley Chiang

J. Vac. Sci. Technol. A 31, 020602 (2013); http://dx.doi.org/10.1116/1.4772623 (5 pages)

Online Publication Date: 4 January 2013

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The growth of the (3 × 1) and (√3 × √3)R30° phases of Ag on Ge(111) on substrates at temperatures from 540 to 660 °C is characterized with low energy electron microscopy (LEEM) and low energy electron diffraction (LEED). From 540 °C to the Ag desorption temperature of 575 °C, LEEM images show that growth of the (3 × 1) phase begins at step edges. Upon completion of the (3 × 1) phase, the (√3 × √3)R30° phase is observed with a dendritic growth morphology that is not much affected by steps. For sufficiently high deposition rates, Ag accumulates on the sample above the desorption temperature. From 575 to 640 °C, the growth proceeded in a manner similar to that at lower temperatures, with growth of the (3 × 1) phase to completion, followed by growth of the (√3 × √3)R30° phase. Increasing the substrate temperature to 660 °C resulted in only (3 × 1) growth. In addition, for samples with Ag coverage less than 0.375ML, LEEM and LEED images were used to follow a reversible phase transformation near 575 °C, between a mixed high coverage phase of [(4 × 4) + (3 × 1)] and the high temperature, lower coverage (3 × 1) phase.
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81.05.Bx Metals, semimetals, and alloys
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kd Metals and alloys
68.43.Nr Desorption kinetics
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Separation of hot electron current component induced by hydrogen oxidation on resistively heated Pt/n-GaP Schottky nanostructures

Mohammad A. Hashemian, Suhas K. Dasari, and Eduard G. Karpov

J. Vac. Sci. Technol. A 31, 020603 (2013); http://dx.doi.org/10.1116/1.4790122 (5 pages)

Online Publication Date: 4 February 2013

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Studies of chemically induced hot electron flow over Schottky barriers in catalytic planar nanostructures provide a direct insight into underlying charge transfer processes involved in chemical energy dissipation at solid surfaces. A systematic approach is described here to separate the hot electron and thermal current contributions to the total generated current based on in-situ resistive heating of cathode nanolayer of the Schottky structure. The method is applicable at high pressures in the gas phase. Analysis of the current induced by H2 oxidation to H2O on Pt/n-GaP nanostructure is performed for surface temperatures in the range of 453–513 K, and 120 Torr oxyhydrogen environment with 15 Torr H2. All the current components grow monotonously with temperature, while relative fraction of the hot electron current decreases with temperature from 85 to 52%.
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73.40.Ns Metal-nonmetal contacts
81.05.Ea III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
72.20.Ht High-field and nonlinear effects
73.30.+y Surface double layers, Schottky barriers, and work functions

Ion flux and ion distribution function measurements in synchronously pulsed inductively coupled plasmas

Melisa Brihoum, Gilles Cunge, Maxime Darnon, David Gahan, Olivier Joubert, and Nicholas St. J. Braithwaite

J. Vac. Sci. Technol. A 31, 020604 (2013); http://dx.doi.org/10.1116/1.4790364 (6 pages)

Online Publication Date: 5 February 2013

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Changes in the ion flux and the time-averaged ion distribution functions are reported for pulsed, inductively coupled RF plasmas (ICPs) operated over a range of duty cycles. For helium and argon plasmas, the ion flux increases rapidly after the start of the RF pulse and after about 50 μs reaches the same steady state value as that in continuous ICPs. Therefore, when the plasma is pulsed at 1 kHz, the ion flux during the pulse has a value that is almost independent of the duty cycle. By contrast, in molecular electronegative chlorine/chlorosilane plasmas, the ion flux during the pulse reaches a steady state value that depends strongly on the duty cycle. This is because both the plasma chemistry and the electronegativity depend on the duty cycle. As a result, the ion flux is 15 times smaller in a pulsed 10% duty cycle plasma than in the continuous wave (CW) plasma. The consequence is that for a given synchronous RF biasing of a wafer-chuck, the ion energy is much higher in the pulsed plasma than it is in the CW plasma of chlorine/chlorosilane. Under these conditions, the wafer is bombarded by a low flux of very energetic ions, very much as it would in a low density, capacitively coupled plasma. Therefore, one can extend the operating range of ICPs through synchronous pulsing of the inductive excitation and capacitive chuck-bias, offering new means by which to control plasma etching.
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52.70.-m Plasma diagnostic techniques and instrumentation
52.80.Pi High-frequency and RF discharges
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Material dependence of argon cluster ion sputter yield in polymers: Method and measurements of relative sputter yields for 19 polymers

Peter J. Cumpson, Jose F. Portoles, and Naoko Sano

J. Vac. Sci. Technol. A 31, 020605 (2013); http://dx.doi.org/10.1116/1.4791669 (5 pages)

Online Publication Date: 11 February 2013

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There is a pressing need for reference data to allow sputter depth-profiling of polymers using cluster and polyatomic ion sources for the quantification of depth in XPS and SIMS. The authors have developed a new method of sputter rate measurement based on a combination of contact masking and white-light interferometry. This allowed us to measure sputter rates for 19 different polymers of technological significance, a much wider set of data than any available previously. The results show a much larger range of sputter yield than might previously have been expected. For example, the sputter yield of PMMA being more than ten times that of poly ether ether ketone when using argon ion clusters of around 4 eV/atom, with other polymers being widely distributed between these extremes. Without reference data for sputter rate this wide range could lead to major errors in depth estimation in sputter depth-profiling of polymer coatings, biomaterials, nanostructures, polymer electronic and polymer photovoltaic devices.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.Fr Polymers; organic compounds

Ytterbium oxide formation at the graphene–SiC interface studied by photoemission

Somsakul Watcharinyanon, Leif I. Johansson, Chao Xia, and Chariya Virojanadara

J. Vac. Sci. Technol. A 31, 020606 (2013); http://dx.doi.org/10.1116/1.4792040 (5 pages)

Online Publication Date: 12 February 2013

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Synchrotron-based core level and angle resolved photoemission spectroscopy was used to study the formation of ytterbium (Yb) oxide at the graphene–SiC substrate interface. Oxide formation at the interface was accomplished in two steps, first intercalation of Yb into the interface region and then oxygen exposure while heating the sample at 260 °C to oxidize the Yb. After these processes, core level results revealed the formation of Yb oxide at the interface. The Yb 4f spectrum showed upon oxidation a clear valence change from Yb2+ to Yb3+. After oxidation the spectrum was dominated by emission from oxide related Yb3+ states and only a small contribution from silicide Yb2+ states remained. In addition, the very similar changes observed in the oxide related components identified in the Si 2p and Yb 4f spectra after oxidation and after subsequent heating suggested formation of a Si-Yb-O silicate at the interface. The electronic band structure of graphene around the math-point was upon Yb intercalation found to transform from a single π band to two π bands. After Yb oxide formation, an additional third π band was found to appear. These π bands showed different locations of the Dirac point (ED), i.e., two upper bands with ED around 0.4 eV and a lower band with ED at about 1.5 eV below the Fermi level. The appearance of three π-bands is attributed to a mixture of areas with Yb oxide and Yb silicide at the interface.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.65.Mq Oxidation
71.20.Tx Fullerenes and related materials; intercalation compounds
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