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Mar 2013

Volume 31, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

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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On the significance of thermoelectric and thermionic emission currents induced by chemical reactions catalyzed on nanofilm metal–semiconductor heterostructures

Ievgen I. Nedrygailov, Eduard G. Karpov, Eckart Hasselbrink, and Detlef Diesing

J. Vac. Sci. Technol. A 31, 021101 (2013); http://dx.doi.org/10.1116/1.4774217 (5 pages)

Online Publication Date: 16 January 2013

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The possible origins and the magnitude of an electric current arising in nanofilm metal–semiconductor heterostructures when the metal surface is used to catalyze an exothermic chemical reaction are discussed. Two key mechanisms are considered that are responsible for the current generation: electron motion due to a temperature drop across the metal–semiconductor interface (thermionic emission mechanism) and the Seebeck effect in the two layers (thermoelectric mechanism). It is predicted that (i) current up to 10−3 A·cm−2 can arise, (ii) thermoelectric mechanism due to the Seebeck effect in the semiconductor layer plays a dominant role for the current generated under stationary chemical reaction conditions, and (iii) thermoelectric current strongly depends on the temperature. The carrier transport through the metal–semiconductor interface is described by the thermionic emission theory. The obtained results are discussed in view of the experimental data reported earlier for the chemical reaction-induced currents in metal/n-Si structures.
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73.40.Ns Metal-nonmetal contacts
79.40.+z Thermionic emission
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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Effects of rapid thermal annealing on electrical, optical, and structural properties of Ni-doped In2O3 anodes for bulk heterojunction organic solar cells

Jun Ho Kim, Tae-Yeon Seong, and Han-Ki Kim

J. Vac. Sci. Technol. A 31, 021201 (2013); http://dx.doi.org/10.1116/1.4774212 (5 pages)

Online Publication Date: 7 January 2013

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The authors investigated the effects of rapid thermal annealing (RTA) on the electrical, optical, and structural properties, and work functions of Ni-doped In2O3 (INO) anodes prepared by a DC/RF co-sputtering process for use in bulk heterojunction organic solar cells (OSCs). By RTA processing at 600 °C, the authors obtained the optimized INO anodes with a sheet resistance of 28 Ω/sq, an optical transmittance of 82.93%, and a work function of 5.02 eV, which are acceptable in OSC fabrication. In particular, the 600 °C annealed INO anode showed much higher optical transmittance in the near infrared wavelength region than the conventional ITO film, even though it had a low resistivity of 5.66 × 10−4 Ω cm. The OSC fabricated on the annealed INO anode showed a higher power convention efficiency of 2.65% than the OSC with as-deposited INO anodes (2.19%) because the fill factors of the OSC are critically dependent on the sheet resistance of the anode.
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68.55.aj Insulators
88.40.hj Efficiency and performance of solar cells
88.40.jr Organic photovoltaics
73.30.+y Surface double layers, Schottky barriers, and work functions
78.30.Hv Other nonmetallic inorganics
81.15.Cd Deposition by sputtering

Chemical reactions at CdS heterojunctions with CuInSe2

Angel Aquino and Angus Rockett

J. Vac. Sci. Technol. A 31, 021202 (2013); http://dx.doi.org/10.1116/1.4775341 (6 pages)

Online Publication Date: 9 January 2013

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The stability of the CdS/CuInSe2 (CIS) heterojunction is critical to understanding the projected lifetime of CIS devices and the effect of processing conditions on the nanoscale chemistry of the heterojunction. This article reports the results of annealing heterojunctions between CdS deposited by chemical bath deposition and single crystal and polycrystalline CIS films between 200 and 500 °C for 10 to 150 min. No atomic movement was observed by secondary ion mass spectrometry at temperatures of 300 °C and below. At 400 °C even for the shortest time studied, Cu and In were found throughout the region initially consisting of CdS only and Cd was found to have moved into the CIS. In the polycrystal, annealing at 500 °C resulted in movement of Cd throughout the CIS layer. No time dependence was observed in the 400 and 500 °C anneals indicating that a reaction had occurred forming a compound that was in thermodynamic equilibrium with the remaining CIS. Diffusion turns on rapidly between 300 and 400 °C, indicating a high activation energy for atomic movement (∼2.4 eV). The onset of diffusion is consistent with the onset of Cu diffusion in CIS.
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68.55.ag Semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
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Study on the etching characteristics of amorphous carbon layer in oxygen plasma with carbonyl sulfide

Jong Kyu Kim, Sung Il Cho, Nam Gun Kim, Myung S. Jhon, Kyung Suk Min, Chan Kyu Kim, and Geun Young Yeom

J. Vac. Sci. Technol. A 31, 021301 (2013); http://dx.doi.org/10.1116/1.4780122 (7 pages)

Online Publication Date: 28 January 2013

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Carbonyl sulfide (COS) was added to oxygen as the additive etch gas for etching of amorphous carbon layers (ACL), and its effect on the etching characteristics of ACLs as the etch mask for high aspect ratio contact SiO2 etching was investigated. When a 50 nm amorphous carbon hole was etched in a gas mixture of O2 + 5% COS, not only did the etch profile of the ACL change more anisotropically but also the top/bottom opening ratio of the etch profile was improved by about 37% compared to those etched without COS. The improved ACL etch characteristics were related to the sidewall passivation of the amorphous carbon hole by the carbon sulfide related layer during the etching of the ACL. The distortion of the amorphous carbon hole was also reduced by about 6% due to the uniform deposition of the carbon sulfide related layer on the sidewall of the amorphous carbon hole. This uniform deposition improved the etch profile and opening ratio of the amorphous carbon hole, ultimately resulting in the enhanced contact oxide etching characteristics as evidenced by 5% improvement in the contact oxide opening and 20% improvement in the mask etch selectivity during the etching of an oxide having 20:1 high aspect ratio.
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81.65.Cf Surface cleaning, etching, patterning
81.65.Rv Passivation
81.05.U- Carbon/carbon-based materials
52.77.Bn Etching and cleaning
61.43.Er Other amorphous solids

Low ion energy RF reactor using an array of plasmas through a grounded grid

Michaël Chesaux, Alan A. Howling, Christoph Hollenstein, Didier Dominé, and Ulrich Kroll

J. Vac. Sci. Technol. A 31, 021302 (2013); http://dx.doi.org/10.1116/1.4790423 (8 pages)

Online Publication Date: 6 February 2013

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A reactor using localized remote plasma in a grid electrode is presented in this study. The aim is to reduce the ion bombardment energy inherent in RF capacitively coupled parallel plate reactors used to deposit large area thin film silicon solar cells. High ion bombardment energy could cause defects in silicon layers and deteriorate electrical interfaces, therefore, by reducing the ion bombardment energy, lower defect density might be obtained. In this study, the low ion bombardment energy results from the reactor design. By inserting a grounded grid close to the RF electrode of a parallel plate reactor, the electrode area asymmetry is increased while retaining the lateral uniformity required for large area deposition. This asymmetry causes a strong negative self-bias voltage, which reduces the time-averaged plasma potential and thus lowers the ion bombardment energy. In addition to the self-bias, the time evolution of plasma light emission and plasma potential RF waveform are also affected by the grid, thereby further reducing the time-averaged plasma potential and ion bombardment energy. Finally, a good correlation between the measured time-averaged plasma potential and measured low ion bombardment energy is found in a broad range of RF voltages.
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52.50.Dg Plasma sources
52.77.Dq Plasma-based ion implantation and deposition
52.80.Pi High-frequency and RF discharges

Noninvasive, real-time measurements of plasma parameters via optical emission spectroscopy

Shicong Wang, Amy E. Wendt, John B. Boffard, Chun C. Lin, Svetlana Radovanov, and Harold Persing

J. Vac. Sci. Technol. A 31, 021303 (2013); http://dx.doi.org/10.1116/1.4792671 (13 pages)

Online Publication Date: 22 February 2013

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Plasma process control applications require acquisition of diagnostic data at a rate faster than the characteristic timescale of perturbations to the plasma. Diagnostics based on optical emission spectroscopy of intense emission lines permit rapid noninvasive measurements with low-resolution (∼1 nm), fiber-coupled spectrographs, which are included on many plasma process tools for semiconductor processing. Here the authors report on rapid analysis of Ar emissions with such a system to obtain electron temperatures, electron densities, and metastable densities in argon and argon/mixed-gas (Ar/N2, Ar/O2, Ar/H2) inductively coupled plasmas. Accuracy of the results (compared to measurements made by Langmuir probe and white-light absorption spectroscopy) are typically better than ±15% with a time resolution of 0.1 s, which is more than sufficient to capture the transient behavior of many processes, limited only by the time response of the spectrograph used.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Competing reactions during metalorganic deposition: Ligand-exchange versus direct reaction with the substrate surface

Jia-Ming Lin, Andrew V. Teplyakov, and Juan Carlos F. Rodríguez-Reyes

J. Vac. Sci. Technol. A 31, 021401 (2013); http://dx.doi.org/10.1116/1.4774031 (17 pages) | Cited 1 time

Online Publication Date: 7 January 2013

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Surface-mediated reactions of metalorganic compounds on solid substrates are key processes in film deposition technology, especially in atomic layer deposition (ALD) or chemical vapor deposition. Since most applications of thin films require high purity, understanding and controlling the mechanisms of desired and undesired surface reactions are of the utmost importance. This work outlines a general approach to understand potential surface reactions during deposition through density functional theory calculations, considering precursors containing the most commonly used types of ligands, namely alkyl (Al(CH3)3), alkoxide (Ti[OC3H7]4), alkylamide (Hf[N(CH3)2]4), diketonate (Cu(acac)2), amidinate (Ni[Pr-amd]2), and cyclopentadienyl (Hf(Cp)2(CH3)2). In all cases, the “desired” ligand-exchange reaction (the basis of most ALD processes) is compared to “undesired” surface reactions, where the ligands of the precursor interact with reactive surface sites and can undergo uncontrolled decomposition pathways, incorporating undesired elements into the growing film. To be able to make an effective comparison across precursor types, all calculations were made considering the same surface model, that of a Si(100) surface, and the same level of theory. Our results show that the undesired ligand-mediated adsorption on reactive sites can often compete (both thermodynamically and kinetically) with the desired ligand-exchange reaction, particularly in the case of alkoxides, alkylamides, and diketonates. The intrinsic reactivity of each precursor (based on their frontier molecular orbitals) is found to determine the manner in which it will react with the surface. This article emphasizes that undesired reactions can often be predicted and evaluated based on the chemical reactivity of each precursor. This approach, applied to specific cases, will be important for probing the chemical performance of a deposition precursor.
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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)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Mn Adsorption kinetics
68.55.-a Thin film structure and morphology

Sample-morphology effects on x-ray photoelectron peak intensities

Cedric J. Powell, Sven Tougaard, Wolfgang S. M. Werner, and Werner Smekal

J. Vac. Sci. Technol. A 31, 021402 (2013); http://dx.doi.org/10.1116/1.4774214 (7 pages)

Online Publication Date: 8 January 2013

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The authors have used the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis to simulate photoelectron spectra from the four sample morphologies considered by Tougaard [J. Vac. Sci. Technol. A 14, 1415 (1996)]. These simulations were performed for two classes of materials, two instrument configurations, and two conditions, one in which elastic scattering is neglected (corresponding to the Tougaard results) and the other in which it is included. The authors considered the Cu/Au morphologies analyzed by Tougaard and similar SiO2/Si morphologies since elastic-scattering effects are expected to be smaller in the latter materials than the former materials. Film thicknesses in the simulations were adjusted in each case to give essentially the same chosen Cu 2p3/2 or O 1s peak intensity. Film thicknesses with elastic scattering switched on were systematically less than those with elastic scattering switched off by up to about 25% for the Cu/Au morphologies and up to about 14% for the SiO2/Si morphologies. For the two morphologies in which the Cu 2p3/2 or O 1s peak intensity was attenuated by an overlayer, the ratios of film thicknesses with elastic scattering switched on to those with elastic scattering switched off varied approximately linearly with the single-scattering albedo, a convenient measure of the strength of elastic scattering. This variation was similar to that of the ratio of the effective attenuation length to the inelastic mean free path for the photoelectrons in the overlayer film. For the two morphologies in which the Cu 2p3/2 or O 1s photoelectrons originated from an overlayer film, the ratios of film thicknesses with elastic scattering switched on to those with elastic scattering switched off varied more weakly with the single-scattering albedo. This weaker variation was attributed to the weaker effects of elastic scattering for photoelectrons originating predominantly from near-surface atoms than for photoelectrons that travel through an overlayer film.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.35.bd Metals and alloys
68.35.bg Semiconductors
68.55.jd Thickness

Origin of defects on targets used to make extreme ultraviolet mask blanks

He Yu, Daniel Andruczyk, David N. Ruzic, Vibhu Jindal, and Patrick Kearney

J. Vac. Sci. Technol. A 31, 021403 (2013); http://dx.doi.org/10.1116/1.4788670 (6 pages)

Online Publication Date: 23 January 2013

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Particle formation is a major problem in extreme ultraviolet masks, and one source of these particles has been identified to be the targets used to produce the mask surfaces. In particular, the silicon (Si) and ruthenium (Ru) target appear to produce more particles, especially silicon. The evidence of this is seen as a rough region on the edges of the silicon target. The features in the region were found to be triangular mesas pointing in the direction of the incident beam. The aim of this research is to prevent the mesa formation features on the target and thus reduce particle formation on the target. Both Si and Ru targets were sputtered using different ion beam conditions to understand the mesa formation mechanisms on the target and explore the ion beam conditions that can mitigate mesas. A simple 2D Monte-Carlo computer model (Illinois surface analysis model) was used to understand the formation of mesas with different incident angles of ion beam (0°, 35°, 54°, 75°) that agrees with the shapes of mesas seen in the experiments. Additionally, srim was used to calculate sputtering yields to better understand the different mechanisms between Si and Ru. It is concluded from both experiment and calculation results that an effective way to stop mesas formation is to have a sample oscillating between 0° and the desired angle during sputtering.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Surface reconstruction at the initial Ge adsorption stage on Si(114)-2 × 1

Ganbat Duvjir, Hidong Kim, Otgonbayar Dugerjav, Huiting Li, Moaaed Motlak, Amarmunkh Arvisbaatar, and Jae M. Seo

J. Vac. Sci. Technol. A 31, 021404 (2013); http://dx.doi.org/10.1116/1.4792243 (6 pages)

Online Publication Date: 14 February 2013

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By combined investigation of scanning tunneling microscopy and synchrotron core-level photoemission spectroscopy on the structural and chemical evolution at the initial stage of Ge adsorption on Si(114)-2 × 1, it has been observed that one-dimensional (1D) sawtooth-like nanostructures composed of (113) and (117) facets and 1D trenches adjacent to the (113) facets are readily formed without any wetting layer. Due to the absence of chain structures on the reconstructed Si(114)-2 × 1, enhanced Ge interdiffusion detected from Ge/Si(5 5 12)-2 × 1 has not been found. Instead, Si atoms originating from etched surfaces and arriving Ge atoms form the alloy facets with Ge-rich surfaces. These experimental results prove that, if the direction of the Ge overlayer corresponding to that of the substrate is unstable like the present case, the arriving atoms prefer to form facets covered with the species of lower surface free energies rather than a uniform wetting layer.
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68.35.bg Semiconductors
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.43.Mn Adsorption kinetics
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.08.Bc Wetting

Nanoscale topographic pattern formation on Kr+-bombarded germanium surfaces

Joy C. Perkinson, Charbel S. Madi, and Michael J. Aziz

J. Vac. Sci. Technol. A 31, 021405 (2013); http://dx.doi.org/10.1116/1.4792152 (5 pages) | Cited 1 time

Online Publication Date: 19 February 2013

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The nanoscale pattern formation of Ge surfaces uniformly irradiated by Kr+ ions was studied in a low-contamination environment at ion energies of 250 and 500 eV and at angles of 0° through 80°. The authors present a phase diagram of domains of pattern formation occurring as these two control parameters are varied. The results are insensitive to ion energy over the range covered by the experiments. Flat surfaces are stable from normal incidence up to an incidence angle of θ = 55° from normal. At higher angles, the surface is linearly unstable to the formation of parallel-mode ripples, in which the wave vector is parallel to the projection of the ion beam on the surface. For θ ≥ 75° the authors observe perpendicular-mode ripples, in which the wave vector is perpendicular to the ion beam. This behavior is qualitatively similar to those of Madi et al. for Ar+-irradiated Si but is inconsistent with those of Ziberi et al. for Kr+-irradiated Ge. The existence of a window of stability is qualitatively inconsistent with a theory based on sputter erosion [R. M. Bradley and J. M. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)] and qualitatively consistent with a model of ion impact-induced mass redistribution [G. Carter and V. Vishnyakov, Phys. Rev. B 54, 17647 (1996)] as well as a crater function theory incorporating both effects [S. A. Norris et al., Nat. Commun. 2, 276 (2011)]. The critical transition angle between stable and rippled surfaces occurs 10°–15° above the value of 45° predicted by the mass redistribution model.
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81.16.Rf Micro- and nanoscale pattern formation
81.30.Dz Phase diagrams of other materials
81.65.Cf Surface cleaning, etching, patterning
68.35.bg Semiconductors
61.80.Jh Ion radiation effects
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Modulation of Ni valence in p-type NiO films via substitution of Ni by Cu

Wei-Yu Chen, Jiann-Shing Jeng, Kuo-Lun Huang, and Jen-Sue Chen

J. Vac. Sci. Technol. A 31, 021501 (2013); http://dx.doi.org/10.1116/1.4774209 (4 pages)

Online Publication Date: 7 January 2013

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10 and 18 at. % copper incorporated NiO films were deposited by reactively sputtering from Ni targets covered with Cu strips of different sizes. A change in the valence of Ni from Ni2+ to Ni3+ is found by x-ray absorption near edge structure analysis after incorporating Cu into the films. All NiO films exhibit p-type conductivity, either without or with Cu additives. However, as compared with the pure NiO films, the carrier concentration of the films incorporating Cu increases, while the resistivity and mobility decrease. This study not only discusses the connections among the physical properties of the NiO films with different Cu contents but also clarifies the role of Cu additives in the NiO films.
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73.61.Le Other inorganic semiconductors
78.70.Dm X-ray absorption spectra
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

Structural, surface, and thermomechanical properties of intrinsic and argon implanted tetrahedral amorphous carbon

Edison F. Motta, Gustavo A. Viana, Douglas S. Silva, Andresa D. S. Côrtes, Fernando L. Freire, Jr., and Francisco C. Marques

J. Vac. Sci. Technol. A 31, 021502 (2013); http://dx.doi.org/10.1116/1.4774326 (8 pages)

Online Publication Date: 11 January 2013

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The structural, surface, and thermomechanical properties of intrinsic and argon incorporated tetrahedral amorphous carbon films deposited using the filtered cathodic vacuum arc process are reported. Argon atoms were simultaneously incorporated during the deposition of the films using an argon ion gun in the energy range of 0–180 eV. Contact angle measurements revealed that all of the deposited films are hydrophobic, regardless of the substrate bias voltage that was applied during the depositions. Thermal desorption spectroscopy measurements revealed that high argon bombarding energy favors films that are structurally more compact and thermally more stable. An investigation unbinding the mechanism of argon effusion and intrinsic stress relief is presented.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.40.Gh Other heat and thermomechanical treatments
68.35.bt Other materials
61.43.Er Other amorphous solids
68.43.Vx Thermal desorption

Atomic layer deposition of TiN for the fabrication of nanomechanical resonators

Nathan Nelson-Fitzpatrick, Csaba Guthy, Somayyeh Poshtiban, Eric Finley, Kenneth D. Harris, Brian J. Worfolk, and Stephane Evoy

J. Vac. Sci. Technol. A 31, 021503 (2013); http://dx.doi.org/10.1116/1.4790132 (7 pages)

Online Publication Date: 5 February 2013

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Films of titanium nitride were grown by atomic layer deposition (ALD) over a range of temperatures from 120 °C to 300 °C, and their deposition rates were characterized by ellipsometry and reflectometry. The stress state of the films was evaluated by interferometry using a wafer bowing technique and varied from compressive (−18 MPa) to tensile (650 MPa). The crystal structure of the films was assessed by x-ray diffraction. The grain size varied with temperature in the range of 2–9 nm. The chemical composition of the films was ascertained by high-resolution x-ray photoelectron spectroscopy and showed the presence of O, Cl, and C contaminants. A mildly tensile (250 MPa) stressed film was employed for the fabrication (by electron beam lithography and reactive ion etching) of doubly clamped nanoresonator beams. The resonance frequency of resonators was assayed using an interferometric resonance testing apparatus. The devices exhibited sharp mechanical resonance peaks in the 17–25 MHz range. The uniformity and controllable deposition rate of ALD films make them ideal candidate materials for the fabrication of ultranarrow (<50 nm) nanobeam structures.
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68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Growth and structure of ZnO thin films on polar (√3 × √3)R30° reconstructed and unreconstructed MgO(111) surfaces by atomic layer deposition

Kallol Pradhan and Paul F. Lyman

J. Vac. Sci. Technol. A 31, 021504 (2013); http://dx.doi.org/10.1116/1.4791667 (9 pages)

Online Publication Date: 8 February 2013

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Polar heterointerfaces of MgO(111) and the II–VI semiconductor ZnO are of technological interest for transparent conducting electrode applications. Growth and structure of thin films on polar surfaces can be different than on nonpolar surfaces due to the large surface energy of polar surfaces. The authors have grown ZnO on unreconstructed MgO(111)-(1 × 1)-OH terminated and reconstructed MgO(111)-(√3 × √3)R30° polar oxide surfaces using atomic layer deposition (ALD). A homemade ultrahigh vacuum-interfaced viscous-flow ALD reactor with in situ quartz crystal monitor was used to grow ZnO thin films on the MgO(111) substrates. In the ALD process temperature window, the growth rate was found to be ∼2.3 Å/cycle. Atomic force microscopy revealed that the surface roughness increases with ZnO film thickness and that reconstructed MgO(111) is a better substrate for production of smooth ZnO films. X-ray diffraction analysis revealed that ZnO thin films grown at 130 °C are polycrystalline, having the wurtzite structure, with preferential growth along the c-axis. ZnO grown on MgO(111)-(√3 × √3)R30° substrates shows strong preferential growth along the (002) direction. In contrast, growth along the (100) and (101) directions is also observed when grown on MgO(111)-(1 × 1) substrates. These observations indicate that the crystal orientation during ALD ZnO growth depends not only on temperature but also on the surface terminations of the substrates. Optical transmittance spectra were used to find the bandgap of 3.27 eV and sharp ultraviolet cutoff of 380 nm for ALD-grown ZnO thin films. The optical transmission was found to be more then 80% in the visible region.
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68.55.ag Semiconductors
68.35.Md Surface thermodynamics, surface energies
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
78.66.Hf II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Three dimensional reciprocal space measurement by x-ray diffraction using linear and area detectors: Applications to texture and defects determination in oriented thin films and nanoprecipitates

Simon Gaudet, Koen De Keyser, Samuel Lambert-Milot, Jean Jordan-Sweet, Christophe Detavernier, Christian Lavoie, and Patrick Desjardins

J. Vac. Sci. Technol. A 31, 021505 (2013); http://dx.doi.org/10.1116/1.4789984 (13 pages)

Online Publication Date: 13 February 2013

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The authors present a method for the fast and efficient measurement of volumes of reciprocal space by x-ray diffraction using linear and area detectors. The goal of this technique is to obtain a complete overview of the reciprocal space to detect and characterize the nature and orientation of all the phases present. They first explain the detailed procedures and scan strategies required for transforming raw scattering data into three-dimensional maps of reciprocal space and present a complete open-source software package for advanced data processing, analysis, and visualization. Several case studies, chosen to highlight the overall capabilities of the technique, are then introduced. First, thermal diffuse scattering from a monocrystalline Si substrate is characterized by the presence of lines linking diffraction peaks in reciprocal space. Second, a detailed investigation of texture in multiphase thin layers permits us to reveal the unambiguous presence of fiber, axiotaxial, and epitaxial components in oriented films. The visualization of a significant fraction of reciprocal space has allowed us to identify an unexpected metastable phase, which could not be deduced from measurements carried out in the Bragg–Brentano geometry. The technique is then used to study planar defects in nickel silicides formed by solid-state reactions and micro twins in a GaP matrix containing coherent MnP precipitates. Overall, the authors show that the systematic acquisition of significant volumes of reciprocal space permits us to observe behaviors that might otherwise remain undetected when analyses are restricted to typical measurement scans.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
68.55.jm Texture
61.46.-w Structure of nanoscale materials

Characterization of metal oxide layers grown on CVD graphene

Akitomo Matsubayashi, Joseph Abel, Dhiraj Prasad Sinha, Ji Ung Lee, and Vincent P. LaBella

J. Vac. Sci. Technol. A 31, 021506 (2013); http://dx.doi.org/10.1116/1.4792068 (6 pages) | Cited 1 time

Online Publication Date: 14 February 2013

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Growth of a fully oxidized aluminum oxide layer with low surface roughness on graphene grown by chemical vapor deposition is demonstrated. This is accomplished by the deposition of a 0.2 nm thick titanium seed layer on the graphene prior to the deposition of the aluminum under ultra high vacuum conditions, which was subsequently oxidized. The stoichiometry and surface roughness of the oxide layers were measured for a range of titanium and aluminum depositions utilizing ex situ x-ray photoelectron spectrometry and atomic force microscopy. These fully oxidized films are expected to produce good dielectric layers for use in graphene based electronic devices.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.35.bt Other materials
77.55.-g Dielectric thin films
79.60.Dp Adsorbed layers and thin films

On the change of preferential growth orientation in chemical vapor deposition of titanium carbide by aromatic hydrocarbon precursors

Henrik Pedersen, Ching-Chi Lin, and Lars Ojamäe

J. Vac. Sci. Technol. A 31, 021507 (2013); http://dx.doi.org/10.1116/1.4792723 (5 pages)

Online Publication Date: 15 February 2013

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Thin films of titanium carbide grown by chemical vapor deposition exhibit a strong preferential (111) growth direction if aromatic hydrocarbons, such as benzene, are used as a carbon precursor. If aliphatic hydrocarbons such as methane are used, growth on the (100) surface is preferred. In this study, quantum chemical computations are used to study the adsorption of benzene and methane on the (100) and (111) surfaces to provide an explanation for the changed growth behavior. The adsorption energy of benzene is found to be approximately twice as high on the (111) surface as compared to the (100) surface, and adsorption studies further suggest that benzene chemisorbs on the (111) surface, while it physisorbs on the (100) surface. The studies reveal no significant differences in adsorption energy or behavior for methane on the two surfaces. The authors propose that the higher benzene adsorption energy and different adsorption behavior on the (111) surface are the explanations for the preferential growth orientation.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.43.Mn Adsorption kinetics

Relative lability of gold-oxide thin films in contact with air, solvents, or electrolyte solutions

Kevin M. Cook and Gregory S. Ferguson

J. Vac. Sci. Technol. A 31, 021508 (2013); http://dx.doi.org/10.1116/1.4791687 (5 pages) | Cited 1 time

Online Publication Date: 19 February 2013

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The lability of gold-oxide thin films in contact with air, pure solvents, or electrolyte solutions was investigated by monitoring film thicknesses using spectroscopic ellipsometry. Surface compositions were monitored using low-energy ion scattering. The oxide was inert in air over 24 h, but decomposed partially in tetrahydrofuran (THF) and water, and completely in ethanol, within the same period. The film thicknesses decreased significantly in THF solutions of Bu4NPF6 and Bu4NBF4, but were more inert in solutions of Bu4NClO4 and LiClO4 in the same solvent, making the latter more suitable choices as supporting electrolytes in electrochemical studies.
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68.55.-a Thin film structure and morphology
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.45.Fk Electrodes
82.45.Gj Electrolytes
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Effects of substrate doping on Gd2O3(100)/Si(100) heterostructure

Wattaka Sitaputra and Raphael Tsu

J. Vac. Sci. Technol. A 31, 021509 (2013); http://dx.doi.org/10.1116/1.4793264 (4 pages)

Online Publication Date: 21 February 2013

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Among the three major orientations, i.e., (100), (110), and (111), Gd2O3(100) is known from the energy point of view to be least favorable on Si(100), unless accompanied by an energy reduction mechanism with a subsequent transfer of electrons across the interface into the silicon substrate. Although the growth on p-type Si(100) results in the best structural consideration from XRD, sufficiently satisfactory stability is demonstrated with Gd2O3(100)/n-type Si(100) with a significantly higher mobility enhancement at high carrier concentration with features most desirable for CMOS applications.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.uf Ge and Si
72.20.Fr Low-field transport and mobility; piezoresistance
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Simple Si(111) surface preparation by thin wafer cleavage

William Paul, Yoichi Miyahara, and Peter H. Grütter

J. Vac. Sci. Technol. A 31, 023201 (2013); http://dx.doi.org/10.1116/1.4790475 (4 pages)

Online Publication Date: 6 February 2013

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We describe a simple method to obtain clean Si(111)2 × 1 surfaces with large terrace sizes, up to tens of microns, using commonly available wafers. The sample geometry and cleavage method make it possible to produce semiconductor samples in ultra-high vacuum systems: that are not explicitly designed to cleave samples or prepare semiconductor surfaces by other means. The force required to cleave the samples is sufficiently low such that they can be cleaved using any available transfer arm, manipulator, or wobble stick in the vacuum system. Large atomic terraces on the order of hundreds of nanometers to tens of microns are easily obtained in this way, as characterized by scanning tunneling microscopy.
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81.05.Cy Elemental semiconductors
81.65.-b Surface treatments
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