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May 2013

Volume 31, Issue 3, Articles (03xxxx)

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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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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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