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

Issue 4 • Date Jul 2013

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Displaying Results 1 - 15 of 15
  • Carbon monoxide-induced reduction and healing of graphene oxide

    Page(s): 040601 - 040601-8
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    Graphene oxide holds promise as a carbon-based nanomaterial that can be produced inexpensively in large quantities. However, its structural and electrical properties remain far from those of the graphene sheets obtained by mechanical exfoliation or by chemical vapor deposition—unless efficient reduction methods that preserve the integrity of the parent carbon-network structure are found. Here, the authors use molecular dynamics and density functional theory calculations to show that the oxygen from the main functional groups present on graphene oxide sheets is removed by the reducing action of carbon monoxide; the energy barriers for reduction by CO are very small and easily overcome at low temperatures. Infrared and Raman spectroscopy experiments confirm the reduction in CO atmosphere and also reveal a strong tendency for CO to heal vacancies in the carbon network. Our results show that reduced graphene oxide with superior properties can be obtained through reduction in CO atmosphere. View full abstract»

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  • Epitaxial V0.6W0.4N/MgO(001): Evidence for ordering on the cation sublattice

    Page(s): 040602 - 040602-4
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    V0.6W0.4N alloys are grown on MgO(001) by ultrahigh vacuum reactive magnetron sputtering from V and W targets in 10 mTorr pure-N2 atmospheres at temperatures Ts ranging from 600 to 900 °C. Based on x-ray diffraction and transmission electron microscopy results, all films have the B1-NaCl crystal structure and grow with a cube-on-cube epitaxial relationship to the substrate, (001)VWN∥(001)MgO and [100]VWN∥[100]MgO. Rutherford backscattering spectrometry analyses show that the N content in V0.6W0.4Nx alloys decreases with increasing Ts from overstoichiometric with x = 1.13 at 600 °C, to approximately stoichiometric with x = 1.08 at 700 °C, to understoichiometric at 800 °C (x = 0.80) and 900 °C (x = 0.75). High-resolution scanning transmission electron microscopy, Z-contrast, and selected-area electron diffraction investigations of V0.6W0.4N(001) alloys grown at 600 and 700 °C reveal the onset of W ordering on adjacent 111 planes of the metal sublattice; no ordering is observed for understoichiometric films grown at higher temperatures. View full abstract»

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  • Fabrication of organic interfacial layers by molecular layer deposition: Present status and future opportunities

    Page(s): 040801 - 040801-18
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    To keep pace with the miniaturization of next generation devices in applications such as electronics, biotechnology, and energy, their constituent polymer thin films must meet challenging requirements such as providing simultaneously ultrathin and conformal coatings. Traditional polymer deposition methods may not be suitable, and as a result, new fabrication methods are needed. Molecular layer deposition (MLD), as an analog to atomic layer deposition, provides precise control over many polymer film properties, such as thickness, composition, morphology, and conformality. Hence, MLD can be a powerful and novel method for fabrication of polymer films. This review article introduces the variety of polymer films that have been developed using MLD together with important film growth characteristics and properties. Examples of MLD polymer applications are provided as well. Finally, challenges and outlooks of the MLD technique are discussed. View full abstract»

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  • Effect of bias application to plasma density in weakly magnetized inductively coupled plasma

    Page(s): 041301 - 041301-5
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    Independent control of the ion flux and energy can be achieved in a dual frequency inductively coupled plasma (ICP) system. Typically, the plasma density is controlled by the high-frequency antenna radio-frequency (RF) power and the ion energy is controlled by the low-frequency bias RF power. Increasing the bias power has been known to cause a decrease in the plasma density in capacitively coupled discharge systems as well as in ICP systems. However, an applied axial magnetic field was found to sustain or increase the plasma density as bias power is increased. Measurements show higher electron temperatures but lower plasma densities are obtained in ordinary ICP systems than in magnetized ICP systems under the same neutral gas pressure and RF power levels. Explanations for the difference in the behavior of plasma density with increasing bias power are given in terms of the difference in the heating mechanism in ordinary unmagnetized and magnetized ICP systems. View full abstract»

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  • Roles of plasma-generated vacuum-ultraviolet photons and oxygen radicals in damaging nanoporous low-k films

    Page(s): 041302 - 041302-11
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    One important class of low-k materials used as interconnect dielectrics employs methyl groups added to nanoporous SiO2 matrices. These carbon-doped oxide materials are known to be susceptible to damage from plasma species during various stages of plasma processing. Two key active species generated in O2 plasma are oxygen (O) radicals and vacuum-ultraviolet (VUV) photons. These species are known to cause carbon loss, resulting in damaging increases in dielectric constant throughout the film. However, the mechanisms through which this damage is incurred are poorly understood. By capping the substrate in different ways during plasma exposure, it is possible to expose films to either photons alone or O atoms alone. The authors report measurements of damage induced by VUV photons only, O radicals only, and the combination of O radicals and photons. Through HF stripping, they note that carbon extraction from photons and from radicals yields different outcomes; the profile of carbon concentration within the modified region is different for each case. Damage from photons alone can be modeled and model predictions are in good agreement with measurements. Damage from O atoms alone can only be modeled if it is assumed that the near-surface region has a significantly reduced diffusivity compared to the bulk of the film. Experiment and model agree that both photons alone and O radicals alone damage the material by removing carbon. When radicals and photons are present simultaneously during plasma exposure, however, more C removal appears to be occurring in the model than experimentally observed. Remarkably, if only radicals are exposed to the film after short (10–30 s) plasma exposures, very little additional damage is incurred during this radical-only exposure. The most straightforward interpretation of these results appears to be that photons combine synergistically with radicals in the pores to narrow the pores, thereby reducing film dif- usivity in the C-poor, plasma-damaged regions. View full abstract»

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  • Effects of He and Ar ion kinetic energies in protection of organosilicate glass from O2 plasma damage

    Page(s): 041303 - 041303-7
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    In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Fourier transform infrared studies of He plasma and Ar+ ion bombardment pretreatments of organosilicate glass demonstrate that such pretreatments inhibit subsequent O2 plasma-induced carbon loss by forming a SiO2-like damaged overlayer, and that the degree of protection correlates directly with increased ion kinetic energies, but not with the thickness of the SiO2 overlayer. This thickness is observed by XPS to be roughly constant and <1 nm regardless of ion energies involved. The data indicate that ion kinetic energies are an important parameter in protective noble gas plasma pretreatments to inhibit O2 plasma-induced carbon loss. View full abstract»

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  • Stability and etching of titanium oxynitride films in hydrogen microwave plasma

    Page(s): 041304 - 041304-7
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    Epitaxial titanium oxynitride (TiNO) films deposited on MgO by pulsed laser deposition were treated in hydrogen microwave plasma. Scanning electron microscopy and x-ray photoelectron spectroscopy were used to examine the stability and etching of TiNO which strongly depended on hydrogen gas pressure. TiNO was very chemically stable and remained with good crystallinity under hydrogen pressure below 5300 Pa. With increase of pressure, it may lead to the formation of etch pits in inverse pyramid shape. The etch mechanism as well as the effects of gas pressure and etching time are also presented. View full abstract»

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  • Localized surface plasmon of Ag nanoparticles affected by annealing and its coupling with the excitons of Rhodamine 6G

    Page(s): 041401 - 041401-5
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    Clean and uniformly distributed silver nanoparticles (AgNPs) are deposited on glass substrates using a vacuum evaporation process. The localized surface plasmon resonance (LSPR) of these AgNPs is successfully tuned from 420 to 780 nm by changing the evaporation time from 20 to 180 s. Further, it is found that the LSPR can be shifted to shorter wavelength in the range of 410 to 478 nm by annealing in flowing nitrogen at 200 °C for 10 min. The blueshift is correlated with the changes in microscopic features of the AgNPs, as revealed by SEM and AFM images. Rhodamine 6G (R6G) was chosen as the probe molecule to explore its coupling with AgNPs before and after annealing. Analysis of extinction spectra suggests that strong coupling takes place when the LSPR is close to the absorption of R6G. View full abstract»

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  • Semiconducting p-type MgNiO:Li epitaxial films fabricated by cosputtering method

    Page(s): 041501 - 041501-5
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    Li-doped ternary MgxNi1-xO thin films were deposited on (0001) Al2O3 substrates by a radio frequency (RF) magnetron cosputtering method with MgO and NiO:Li targets. The Mg mole fraction and Li content were relatively controlled by changing RF power for the MgO target over a range of 0–300 W, while the NiO:Li target was kept at 150 W. As a result, all films were epitaxially grown on (0001) Al2O3 substrates with the relationship of [110]NiO||[1110]Al2O3, [112]NiO||[2110]Al2O3 (in-plane), and [111]NiO||[0001]Al2O3 (out-of-plane), and showed p-type semiconducting properties. Furthermore, from x-ray diffraction patterns, the authors found that MgO was effectively mixed with NiO:Li without structural deformation due to low lattice mismatch (0.8%) between NiO and MgO. However, the excess Li contents degraded the crystallinity of the MgNiO films. The band-gap of films was continuously shifted from 3.66 eV (339 nm) to 4.15 eV (299 nm) by the RF power of the MgO target. A visible transmittance of more than 80% was exhibited at RF powers higher than 200 W. Ultimately, the electrical resistivity of p-type MgNiO films was improved from 7.5 to 673.5 Ωcm, indicating that the Li-doped MgNiO films are good candidates for transparent p-type semiconductors. View full abstract»

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  • Mechanical and electrical properties of plasma and thermal atomic layer deposited Al2O3 films on GaAs and Si

    Page(s): 041502 - 041502-7
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    Mechanical and electrical properties of Al2O3 films are compared for plasma-assisted atomic layer deposition (ALD) and thermal ALD on two substrates, GaAs and Si, of different thermal expansion coefficient. Films with stable chemical structure and mechanical residual stress could be produced by both techniques without inducing any damage to sensitive multiquantum-well structures. However, the as-deposited residual stress in the plasma ALD Al2O3 films is lower and decreases, while that in the thermal ALD films increases with the deposition temperature. Moreover, the stress hysteresis observed upon thermal cycles is much lower for the plasma ALD films compared to that for the thermal ALD films. The biaxial elastic modulus (BEM or stiffness parameter) increases with the deposition temperature for both ALD films, being higher for the plasma ALD than that for the thermal ALD at a given temperature. The higher BEM is reflected in better electrical properties of the films. Thus, the leakage current of metal–oxide–semiconductor capacitors with the plasma ALD-Al2O3 film is three orders of magnitude lower and the breakdown voltage 20% higher than that of the capacitors with the thermal ALD film. View full abstract»

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  • Growth window and effect of substrate symmetry in hybrid molecular beam epitaxy of a Mott insulating rare earth titanate

    Page(s): 041503 - 041503-7
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    The conditions for the growth of stoichiometric GdTiO3 thin films by molecular beam epitaxy (MBE) are investigated. It is shown that relatively high growth temperatures (>750 °C) are required to obtain an MBE growth window in which only the stoichiometric film grows for a range of cation flux ratios. This growth window narrows with increasing film thickness. It is also shown that single-domain films are obtained by the growth on a symmetry-matched substrate. The influence of lattice mismatch strain on the electrical and magnetic characteristics of the GdTiO3 thin film is investigated. View full abstract»

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  • Atomic layer deposition of zinc oxide: Understanding the reactions of ozone with diethylzinc

    Page(s): 041504 - 041504-7
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    To understand the reactions involved in the atomic layer deposition (ALD) of zinc oxide films using ozone as the oxygen source, two model systems were examined at the M06-L and M06 levels of density functional theory. The first model involved a two-coordinate zinc complex, HO-Zn-Et, and the second, [(HO)7Zn4(Et)], a cluster having a cubane-like geometry in which each of the zinc ions is four-coordinate. In both cases, the ozone reaction requires two distinct steps to generate a new hydroxyl ligand, which is required for the second phase of the ALD process (reaction with Et2Zn). In step 1, an exothermic insertion of O3 into the Zn-C bond produces an ethyltrioxide (EtOOO) ligand as an intermediate. Subsequently, a mildly exothermic elimination of singlet oxygen produces an ethoxide complex. In step 2, a second equivalent of ozone abstracts a methylene hydrogen from the ethoxide ligand, resulting in the elimination of acetaldehyde and the formation of a hydrotrioxide (HOOO-) ligand that ultimately eliminates O2 and leaves a hydroxide group bound to the zinc. To simulate one complete ALD cycle, Et2Zn was subsequently reacted with the hydroxyl terminated products from step 1, i.e., Zn(OH)2 or Zn4(OH)8. In the cubane-like model, the geometric availability of additional OH groups opens a 1,4 ethane elimination pathway with an activation energy 7.1 kcal/mol lower than that for 1,2-elimination. A series of experimental ZnO depositions using Et2Zn and O3 were run in a reactor that was modified to allow collection of condensable organic products of the reaction. Acetaldehyde was detected, and quantitative nuclear magnetic resonance established a linear correlation between the amount of acetaldehyde and the number of ALD cycles, consistent with the mechanism inferred on the basis of the computational models. View full abstract»

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  • Electrical characteristics of ZrO2/GaAs MOS capacitor fabricated by atomic layer deposition

    Page(s): 041505 - 041505-6
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    GaAs based metal oxide semiconductor capacitors were fabricated with zirconium oxide (ZrO2) using atomic layer deposition. The effect of growth temperature of ZrO2 dielectric films on GaAs was studied. The ZrO2 layers were deposited using tetrakis dimethyl amido zirconium and water in the temperature region of 200–275 °C. The as deposited samples have a significant amount of fixed charge in the bulk of the gate dielectric and at dielectric/semiconductor (ZrO2/GaAs) interface, which causes the flat band shift and frequency dispersion. The postannealing in nitrogen (N2) reduces the flat band shift, frequency dispersion, and capacitance–voltage (C-V) stretch out. In addition, the inversion characteristics of as fabricated capacitor were also improved with respect to the growth temperature and annealing. The gate dielectric stack is qualitatively illustrated through improved C-V characteristics and quantitatively verified by the reduced interface trap density (Dit). The effect of N2 annealing is investigated in detail through electrical characterization and Dit measurements. The authors find that there exists a tradeoff where annealing improves C-V characteristics and reduces the Dit, however, at the cost of higher leakage current. View full abstract»

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  • Influence of laser irradiation and microwave plasma treatment on the thermal properties of graphene platelets

    Page(s): 041506 - 041506-6
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    Graphene platelets synthesized by chemical exfoliation were deposited to form a film on Cu substrate. Samples of the film of graphene platelets were subjected to laser irradiation with wavelength 266 nm, pulse duration 6 ns from Nd-YAG laser at repetition of 10 Hz. Microwave hydrogen plasma treatment was also used for 300 s and 600 s to modify the film of graphene platelets on another set of samples. Raman spectroscopy on the film before and after these different treatments indicated that the crystallite size is reduced and defect density is increased. The samples coated with Au film and pressed with In film on the surface were used to determine the transient thermo reflectance from the surface upon incidence of Nd-YAG laser beam with wavelength 532 nm. Numerical analysis of the variation of thermo reflectance signal with time was used to evaluate the laser or plasma induced changes in the thermal conductivity of graphene film and the interface thermal conductance between Au and graphene. The results showed that the thermal conductivity of graphene platelet film is reduced although the interface thermal conductance is improved. The reduction in thermal conductivity of graphene platelets is explained by the decrease in the crystallite size and increase in defect density. The increase in the interface thermal conductance is also explained to arise from smoothening of the graphene platelet film surface and improvement in the contact between Au and graphene and graphene and Cu induced by laser or microwave plasma irradiation. View full abstract»

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  • Investigation of structure, magnetic, and transport properties of Mn-doped SiC films

    Page(s): 041507 - 041507-4
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    Mn-doped SiC films were fabricated by radio frequency magnetron sputtering technique. The structure, composition, and magnetic and transport properties of the films were investigated. The results show the films have the 3C-SiC crystal structure and the doped Mn atoms in the form of Mn2+ ions substitute for C sites in SiC lattice. All the films are ferromagnetic at 300 K, and the ferromagnetism in films arises from the doped Mn atoms and some extended defects. In addition, the saturation magnetization increases with the Mn-doped concentration increasing. The Mn doping does not change the semiconductor characteristics of the SiC films. View full abstract»

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

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G. Lucovsky
North Carolina State University