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14 Jul 2008

Volume 93, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 023303 (2008); http://dx.doi.org/10.1063/1.2953179 (3 pages)

Takafumi Kawanishi, Takaaki Fujiwara, Megumi Akai-Kasaya, Akira Saito, Masakazu Aono, Junichi Takeya, and Yuji Kuwahara
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Emission color tunable light-emitting diodes composed of InGaN multifacet quantum wells

M. Funato, K. Hayashi, M. Ueda, Y. Kawakami, Y. Narukawa, and T. Mukai

Appl. Phys. Lett. 93, 021126 (2008); http://dx.doi.org/10.1063/1.2956404 (3 pages) | Cited 16 times

Online Publication Date: 18 July 2008

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We demonstrate that the apparent emission colors of InGaN-based light-emitting diodes using microstructured multifacet quantum wells as active layers can externally be controlled over a wide spectral range that encompasses green to blue or white at a color temperature of 4000 K to blue along the Planckian locus. The controllability relies on facet-dependent polychromatic emissions. The pulsed current operation with the appropriate duties varied their relative intensities and the consequent apparent colors without seriously affecting the total number of emitted photons, particularly for the blue to green variation.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
78.60.Fi Electroluminescence
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Absolute density and temperature of O(1D2) in highly Ar or Kr diluted O2 plasma

Keigo Takeda, Seigo Takashima, Masafumi Ito, and Masaru Hori

Appl. Phys. Lett. 93, 021501 (2008); http://dx.doi.org/10.1063/1.2957679 (3 pages) | Cited 4 times

Online Publication Date: 14 July 2008

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The absolute density and translational temperature of excited O atoms [O(1D2)] in O2 surface-wave-excited plasmas (SWPs) with high Kr or Ar dilution were measured by using vacuum ultraviolet laser absorption spectroscopy. It was observed that the absolute density of O(1D2) in Kr/O2 SWP was lower than that in Ar/O2 SWP above a pressure of 90 Pa, and the O(1D2) had an elevated temperature of around 2000 K in the SWPs. Furthermore, the O(1D2) flux was identified as a key parameter in the oxidation process. These results are very important knowledge relevant to plasma oxidation.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)

Ablation of liver cancer cells in vitro by a plasma needle

Xianhui Zhang, Maojin Li, Rouli Zhou, Kecheng Feng, and Size Yang

Appl. Phys. Lett. 93, 021502 (2008); http://dx.doi.org/10.1063/1.2959735 (3 pages) | Cited 34 times

Online Publication Date: 16 July 2008

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A plasma needle using a dielectric barrier discharge reactor at atmospheric pressure with a funnel-shaped nozzle was developed. The preliminary characteristics of the plume and applications to the ablation of cultured human hepatocellular carcinoma (HCC) BEL-7402 cell line were presented. The effect of oxygen, which was injected into argon plasma afterglow region through a steel tube, was studied. The efficiency of argon-oxygen plasma depends sensitively on the oxygen concentration in argon plasma. Large differences between spectra in atmosphere and those in Dulbecco’s modified eagle medium are found. It is found that ultraviolet rays, O, OH, and Ar radicals can reach the bottom of solution and act on HCC cells and there is an optimum input power to get the most radicals.
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87.53.Jw Therapeutic applications, including brachytherapy
87.19.xj Cancer
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Ag nanocrystal-incorporated germano-silicate optical fiber with high resonant nonlinearity

Aoxiang Lin, Xueming Liu, Pramod R. Watekar, Youngjoo Chung, and Won-Taek Han

Appl. Phys. Lett. 93, 021901 (2008); http://dx.doi.org/10.1063/1.2957029 (3 pages) | Cited 6 times

Online Publication Date: 14 July 2008

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Silver nanocrystal-incorporated germano-silicate optical fiber was fabricated by modified chemical vapor deposition and solution doping techniques. By measuring the wavelength shift of the fringes obtained from the long-period fiber grating pair, upon pumping with an argon-ion laser at 499 nm, the resonant nonlinear refractive index around 1550 nm was estimated to be 5.4×10−16 m2/W. The observed high resonant optical nonlinearity of the silver nanocrystal-incorporated fiber is attributed to the contribution from the surface plasmon resonance of silver nanocrystals embedded in the fiber core.
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42.81.Bm Fabrication, cladding, and splicing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Dj Gratings
73.22.Lp Collective excitations
42.65.-k Nonlinear optics

Minority carrier lifetime in polycrystalline silicon solar cells studied by photoassisted Kelvin probe force microscopy

Masaki Takihara, Takuji Takahashi, and Toru Ujihara

Appl. Phys. Lett. 93, 021902 (2008); http://dx.doi.org/10.1063/1.2957468 (3 pages) | Cited 7 times

Online Publication Date: 14 July 2008

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We have proposed a method to evaluate minority carrier lifetime through photovoltage measurements by photoassisted Kelvin probe force microscopy and have applied it to characterize a polycrystalline silicon solar cell. The results indicate that the lifetime significantly decreases in the vicinity of a grain boundary of the polycrystalline material. The photovoltage distribution around the grain boundary is also discussed by considering a contribution of both the intrinsic surface potential and the lifetime.
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84.60.Jt Photoelectric conversion
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Mm Grain and twin boundaries
72.80.Cw Elemental semiconductors

Influence of oxygen concentration in sputtering gas on piezoelectric response of aluminum nitride thin films

Morito Akiyama, Toshihiro Kamohara, Kazuhiko Kano, Akihiko Teshigahara, and Nobuaki Kawahara

Appl. Phys. Lett. 93, 021903 (2008); http://dx.doi.org/10.1063/1.2957654 (3 pages) | Cited 12 times

Online Publication Date: 14 July 2008

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The authors have investigated the influence of oxygen concentration in sputtering gas on the piezoelectric response of aluminum nitride (AlN) thin films prepared on silicon substrates. The piezoelectric response strongly depends on the oxygen concentration, and changes from +6.8 to −7.0 pC/N with increasing oxygen concentration from 0% to 1.2%. The polar direction drastically inverts from the Al polarity to N polarity. When the oxygen concentration in sputtering gas was 1.2%, the oxygen concentration in the AlN films was 7 at. %. Furthermore, the growth rate of the AlN films gradually decreases with increasing oxygen concentration in sputtering gas.
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77.55.-g Dielectric thin films
77.65.Bn Piezoelectric and electrostrictive constants
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Cd Deposition by sputtering

Evolution mechanisms of the surface morphology of grains in ZnO thin films grown on p-InP substrates due to thermal annealing

J. M. Yuk, J. Y. Lee, Y. S. No, T. W. Kim, and W. K. Choi

Appl. Phys. Lett. 93, 021904 (2008); http://dx.doi.org/10.1063/1.2957467 (3 pages) | Cited 1 time

Online Publication Date: 15 July 2008

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Transmission electron microscopy (TEM), high-resolution TEM, and atomic force microscopy images showed that the columnar structure and the surface morphology of grains in ZnO thin films grown on p-InP substrates were changed due to thermal treatment. The surface morphology variation of the ZnO thin films was attributed to the curvature modification of the subpopulations consisting of ZnO grains. While the top surface of the ZnO grains became parallel with the {0001} planes due to thermal treatment, the curvature of the subpopulations in the ZnO grains became rough. Evolution mechanisms of the surface morphology of ZnO thin films are described.
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68.55.ag Semiconductors
68.47.Fg Semiconductor surfaces
81.40.Gh Other heat and thermomechanical treatments
68.37.Og High-resolution transmission electron microscopy (HRTEM)
68.37.Ps Atomic force microscopy (AFM)

Effect of indium on phase-change characteristics and local chemical states of In–Ge–Sb–Te alloys

H. J. Shin, Youn-Seon Kang, Anass Benayad, Ki-Hong Kim, Y. M. Lee, M.-C. Jung, Tae-Yon Lee, Dong-Seok Suh, Kijoon H. P. Kim, CheolKyu Kim, and Yoonho Khang

Appl. Phys. Lett. 93, 021905 (2008); http://dx.doi.org/10.1063/1.2959730 (3 pages) | Cited 7 times

Online Publication Date: 15 July 2008

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We introduce single-phase In–Ge–Sb–Te (IGST) quaternary thin film (fcc structure when crystallized) deposited by cosputtering from Ge2Sb2Te5(GST) and In3Sb1Te2 targets. This film, compared with the GST ternary system, provides a significant increase of amorphous-to-crystalline transformation temperature. High-resolution x-ray photoelectron spectroscopy (HRXPS) revealed that, with increasing In amounts, the Sb 4d and Ge 3d core peaks shift toward lower binding energies (BEs), with negligible changes in spectral linewidths, whereas the In 4d and Te 4d core peaks show insignificant changes in BEs. HRXPS interpretation suggests that the Na site in IGST can be occupied by Te, Sb, In, and vacancy, whereas in GST it is occupied only by Te.
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68.55.-a Thin film structure and morphology
61.66.Dk Alloys
64.70.dg Crystallization of specific substances
81.15.Cd Deposition by sputtering
61.72.jd Vacancies
79.60.-i Photoemission and photoelectron spectra

Phase collapse caused by blue-light irradiation in a cyanobridged coordination polymer

Hiroko Tokoro and Shin-ichi Ohkoshi

Appl. Phys. Lett. 93, 021906 (2008); http://dx.doi.org/10.1063/1.2955822 (3 pages) | Cited 6 times

Online Publication Date: 15 July 2008

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In this work, we report a photoinduced phase transition, light-induced phase collapse, using rubidium manganese hexacyanoferrate, RbI0.43MnII[FeIII(CN)6]0.81⋅3H2O, which does not exhibit a phase transition upon changing the temperature. However, when this material is irradiated with blue light at temperature around 100–200 K, the MnII–FeIII phase collapses and the valence isomer MnIII–FeII phase appears. The MnII–FeIII phase is perfectly recovered as the temperature increased. Theoretical analysis suggests that the initial MnII–FeIII phase is a thermodynamically metastable phase, trapped at a local free-energy minimum, while the photogenerated MnIII–FeII phase is the true thermodynamically stable phase below 230 K.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.70.Jk Polymers and organics
64.70.km Polymers
78.30.Jw Organic compounds, polymers
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
42.79.Vb Optical storage systems, optical disks

Influence of Si/Fe ratio in multilayer structures on crystalline growth of β-FeSi2 thin film on Si substrate

Zhengxin Liu, Miyoko Tanaka, Ryo Kuroda, Masato Osamura, and Yunosuke Makita

Appl. Phys. Lett. 93, 021907 (2008); http://dx.doi.org/10.1063/1.2957990 (3 pages) | Cited 5 times

Online Publication Date: 15 July 2008

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The deposited Si/Fe ratio has been found to have a significant influence on crystalline growth of β-FeSi2 film on Si substrate. Stoichiometry is always satisfied by interdiffusion of Si, under both Si-lean and Si-rich conditions. However, Si diffusion from the substrate into the deposited layer, which compensates for deficient Si, induces an undulated interface, as well as Fe and Si vacancies. On the other hand, excess Si is driven to the β-FeSi2/Si interface, which results in a lamellar structure with a large number of small grains. Fe and Si vacancies are significantly reduced by excess Si. These results suggest that precise control of the Si/Fe ratio is essential for good crystallinity and fewer vacancies.
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68.55.ag Semiconductors
81.15.Cd Deposition by sputtering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.66.Bi Elemental solids
61.66.Dk Alloys
68.35.Fx Diffusion; interface formation
61.72.jd Vacancies

Cubic zirconia as a dynamic compression window

D. H. Dolan and T. Ao

Appl. Phys. Lett. 93, 021908 (2008); http://dx.doi.org/10.1063/1.2957996 (3 pages)

Online Publication Date: 15 July 2008

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Symmetric impact experiments were used to characterize the elastic response of ⟨100⟩ cubic zirconia crystals under shock wave compression. Elastic response was determined from the apparent velocity structure upon free surface release and the preservation of light passing through the compressed sample. The Hugoniot and window correction were determined below 9 GPa, and the estimated elastic limit was found to be near 10 GPa. These results indicate that cubic zirconia may serve as a useful alternate to sapphire in dynamic compression experiments.
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62.50.Ef Shock wave effects in solids and liquids
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.66.Fn Inorganic compounds
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Non-magnetic simplified cylindrical cloak with suppressed zeroth order scattering

Wei Yan, Min Yan, and Min Qiu

Appl. Phys. Lett. 93, 021909 (2008); http://dx.doi.org/10.1063/1.2958344 (3 pages) | Cited 10 times

Online Publication Date: 15 July 2008

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A type of simplified cloaks with matched exterior boundaries is proposed. The cloak uses nonmagnetic material for the TM polarization and can function with a relatively thin thickness. It is shown that the zeroth order scattering of such cloak is dominant among all cylindrical scattering terms. A gap is added at the cloak’s inner surface to eliminate the zeroth order scattering through the mechanism of scattering resonance. The reduction in scattering is relatively smooth, indicating that the proposed scattering reduction method has good tolerance to perturbations. Numerical simulations also confirm that the proposed structure has very low scattering.
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42.25.Fx Diffraction and scattering
42.25.Ja Polarization

Step-induced misorientation of GaN grown on r-plane sapphire

J. Smalc-Koziorowska, G. P. Dimitrakopulos, S.-L. Sahonta, G. Tsiakatouras, A. Georgakilas, and Ph. Komninou

Appl. Phys. Lett. 93, 021910 (2008); http://dx.doi.org/10.1063/1.2953438 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2008

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In the growth of nonpolar (mathmath20) a-plane GaN on r-plane (1math02) sapphire by plasma-assisted molecular beam epitaxy, misoriented crystallites are observed close to the substrate. They have average diameter ∼ 10 nm and are oriented with the (0001)GaN plane approximately parallel to the (2mathmath3)sapph. plane and [01math0]GaN∥[math101]sapph.. This semipolar orientation is promoted by a low misfit (2.4%) between (10mathmath)GaN and (math2math0)sapph. planes. Its introduction, after nitridation treatment, is due to GaN nucleation on {2mathmath3}sapph. step facets inclined at 26° relative to the r-plane. Two variants are observed, leading to twinning when they abut inside the epilayer.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Mm Grain and twin boundaries
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Pseudomorphic SiGe/Si(001) layers synthesized by gas immersion laser doping

Frédéric Fossard, Jacques Boulmer, Dominique Débarre, Jean-Luc Perrossier, Cyril Bachelet, Franck Fortuna, Véronique Mathet, and Daniel Bouchier

Appl. Phys. Lett. 93, 021911 (2008); http://dx.doi.org/10.1063/1.2956674 (3 pages) | Cited 1 time

Online Publication Date: 16 July 2008

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We report on the synthesis of SiGe layers on silicon by gas immersion laser doping. GeCl4 molecules are adsorbed on the surface and further incorporated into the Si top layer by a pulsed laser induced melt/regrowth process. Structural and chemical characterizations of the SiGe layers have been performed by using complementarily Rutherford backscattering spectrometry and x-ray Diffraction which indicate that Ge incorporation in the Si matrix results in a fully strained SiGe layer with gradual Ge concentrations reaching up to 18.5% near the surface.
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81.20.-n Methods of materials synthesis and materials processing
61.72.uf Ge and Si
42.62.-b Laser applications
79.20.Ds Laser-beam impact phenomena

Observation of room temperature ferromagnetism in Ga:ZnO: A transition metal free transparent ferromagnetic conductor

V. Bhosle and J. Narayan

Appl. Phys. Lett. 93, 021912 (2008); http://dx.doi.org/10.1063/1.2953705 (3 pages) | Cited 13 times

Online Publication Date: 17 July 2008

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This paper reports our results on room temperature ferromagnetism characteristics in Ga-doped ZnO. The Ga-doped ZnO films were grown epitaxially on (0001) sapphire with Ga concentration up to 5 at. %. Detailed x-ray diffraction and high resolution transmission electron microscopy results showed a high-quality epitaxy without the presence of any secondary phases. Magnetic measurements showed characteristic ferromagnetism behavior with room temperature coercivity ∼ 50 Oe, which remained fairly constant with temperature. Upon annealing coercivity disappeared with typical diamagnetic characteristics of ZnO. The x-ray photoelectron spectroscopy and electrical measurements as function of annealing showed a critical role of vacancies and Ga-vacancy complexes to be critical for the observed ferromagnetic behavior.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Nonvolatile electrical bistability and operating mechanism of memory devices based on CdSe/ZnS nanoparticle/polymer hybrid composites

Fushan Li, Dong Ick Son, Bong Jun Kim, and Tae Whan Kim

Appl. Phys. Lett. 93, 021913 (2008); http://dx.doi.org/10.1063/1.2959786 (3 pages) | Cited 3 times

Online Publication Date: 17 July 2008

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Current-voltage (I-V) measurements on Al/(core/shell-type CdSe/ZnS nanoparticles embedded in polymer/indium tin oxide)/glass devices showed a nonvolatile electrical bistability behavior. Capacitance-voltage (C-V) measurements on the devices showed a counterclockwise hysteresis with a flatband voltage shift due to the existence of the CdSe/ZnS nanoparticles. The on/off ratio of the electrical bistability for memory devices with a hybrid [poly-N-vinylcarbazole (PVK) and polystyrene (PS)] matrix layer was larger than those for memory devices with a PVK or a PS layer. Possible operating mechanisms for the devices are described on the basis of the I-V and the C-V results.
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84.30.Sk Pulse and digital circuits

Optical properties of (GeTe, Sb2Te3) pseudobinary thin films studied with spectroscopic ellipsometry

Jun-Woo Park, Seoung Ho Baek, Tae Dong Kang, Hosun Lee, Youn-Seon Kang, Tae-Yon Lee, Dong-Seok Suh, Ki Joon Kim, Cheol Kyu Kim, Yoon Ho Khang, Juarez L. F. Da Silva, and Su-Huai Wei

Appl. Phys. Lett. 93, 021914 (2008); http://dx.doi.org/10.1063/1.2959818 (3 pages) | Cited 12 times

Online Publication Date: 17 July 2008

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The authors measure the dielectric functions of (GeTe, Sb2Te3) pseudobinary thin films by using spectroscopic ellipsometry. By using standard critical point model, they obtained the optical transition (critical point) energies of the amorphous (crystalline) thin films. The optical (indirect band) gap energies of the amorphous (crystalline) phase are estimated from the linear extrapolation of the absorption coefficients. The band structure calculations show that GeTe, Ge2Sb2Te5, and Ge1Sb2Te4 have indirect gap whereas Ge1Sb4Te7 and Sb2Te3 have direct gap. The measured indirect band gap energies match well with electronic band structure calculations.
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78.66.Jg Amorphous semiconductors; glasses
77.22.Ch Permittivity (dielectric function)
64.60.F- Equilibrium properties near critical points, critical exponents
71.20.Nr Semiconductor compounds

Mixed cation phases in sputter deposited HfO2–TiO2 nanolaminates

M. C. Cisneros-Morales and C. R. Aita

Appl. Phys. Lett. 93, 021915 (2008); http://dx.doi.org/10.1063/1.2957670 (3 pages) | Cited 9 times

Online Publication Date: 17 July 2008

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Nanolaminate HfO2–TiO2 films are grown by reactive sputter deposition on unheated fused SiO2, sequentially annealed at 573 to 973 K, and studied by x-ray diffraction. A nanocrystalline structure of orthorhombic (o) HfTiO4 adjacent to an interface followed by monoclinic (m) Hf1−xTixO2 is identified. m-Hf1−xTixO2, a metastable phase, is isomorphous with m-HfO2 and a high pressure phase, m-HfTiO4. A Vegard’s law analysis shows that the Ti atomic fraction in m-Hf1−xTixO2 is much greater than Ti equilibrium solubility in m-HfO2. A space group-subgroup argument proposes that m-Hf1−xTixO2 arises from an o/m-HfTiO4 second order phase transition to accommodate the larger Hf atom.
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81.30.Dz Phase diagrams of other materials
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
64.75.Bc Solubility
77.55.-g Dielectric thin films

X-ray absorption in GaGdN: A study of local structure

G. Martínez-Criado, O. Sancho-Juan, N. Garro, J. A. Sans, A. Cantarero, J. Susini, M. Roever, D.-D. Mai, A. Bedoya-Pinto, J. Malindretos, and A. Rizzi

Appl. Phys. Lett. 93, 021916 (2008); http://dx.doi.org/10.1063/1.2957984 (3 pages) | Cited 8 times

Online Publication Date: 17 July 2008

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In this study, we report on the incorporation of dilute Gd amounts into GaN films grown by molecular beam epitaxy. A combination of x-ray fluorescence with x-ray absorption spectroscopic techniques enabled us to examine not only the distribution of rare earth atoms in the GaN matrix but also the short-range structural order. Our results show Gd atoms in a trivalent state with tetrahedral coordination, thus substituting Ga in the wurtzite GaN structure.
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68.55.ag Semiconductors
78.70.Dm X-ray absorption spectra
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Reduction of thermal conductivity in wafer-bonded silicon

Z. L. Liau, L. R. Danielson, P. M. Fourspring, L. Hu, G. Chen, and G. W. Turner

Appl. Phys. Lett. 93, 021917 (2008); http://dx.doi.org/10.1063/1.2959063 (3 pages)

Online Publication Date: 18 July 2008

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Blocks of silicon up to 3 mm thick have been formed by directly bonding stacks of thin wafer chips. These stacks showed significant reductions in the thermal conductivity in the bonding direction. In each sample, the wafer chips were obtained by polishing a commercial wafer to as thin as 36 μm, followed by dicing. Stacks whose starting wafers were patterned with shallow dots showed greater reductions in thermal conductivity. Diluted-HF treatment of wafer chips prior to bonding led to the largest reduction of the effective thermal conductivity, by approximately a factor of 50. Theoretical modeling based on restricted conduction through the contacting dots and some conduction across the planar nanometer air gaps yielded good agreement for samples fabricated without the HF treatment.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Structural, mechanical, and electronic properties of ultrathin ZnO nanowires

Baolin Wang, Jijun Zhao, Jianming Jia, Daning Shi, Jianguo Wan, and Guanghou Wang

Appl. Phys. Lett. 93, 021918 (2008); http://dx.doi.org/10.1063/1.2951617 (3 pages) | Cited 21 times

Online Publication Date: 18 July 2008

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We report a structural transformation between the regular wurtzite and the unbuckled wurtzite (hexagonal) structure for ultrathin single-crystalline [0001] ZnO nanowires under uniaxial elongation and compression. Our density functional calculations show that hexagonal structure corresponds to a distinct minimum on the transformation path. Young’s moduli of the ZnO nanowires with the hexagonal structures are larger than those with the wurtzite structures at the same size. Within the nanowire size range considered, Young’s moduli of the ZnO nanowires decrease with increasing wire diameter. The electronic properties of these two types of ZnO nanowires exhibit distinctly different behaviors.
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81.05.Dz II-VI semiconductors
68.65.La Quantum wires (patterned in quantum wells)
73.21.Hb Quantum wires
73.22.-f Electronic structure of nanoscale materials and related systems
62.25.-g Mechanical properties of nanoscale systems
64.70.K- Solid-solid transitions

The influence of stoichiometry on the structural stability and on the optical emission of erbium silicate thin films

R. Lo Savio, M. Miritello, A. M. Piro, F. Priolo, and F. Iacona

Appl. Phys. Lett. 93, 021919 (2008); http://dx.doi.org/10.1063/1.2957034 (3 pages) | Cited 14 times

Online Publication Date: 18 July 2008

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We report the effects of thermal annealing performed in N2 or O2 ambient at 1200 °C on the structural and optical properties of Er silicate films having different compositions (Er2SiO5, Er2Si2O7, and their mixture). We demonstrate that the chemical composition of the stoichiometric films is preserved after the thermal treatments. All different crystalline structures formed after the thermal annealing are identified. Thermal treatments in O2 lead to a strong enhancement of the photoluminescence intensity, owing to the efficient reduction of defect density. In particular the highest optical efficiency is associated to Er ions in the α phase of Er2Si2O7.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments
68.55.-a Thin film structure and morphology
61.66.Bi Elemental solids
61.66.Dk Alloys

Electron spin resonance studies of P and B codoped Si nanocrystals

Kazuyoshi Fujio, Minoru Fujii, Kazuaki Sumida, Shinji Hayashi, Masashi Fujisawa, and Hitoshi Ohta

Appl. Phys. Lett. 93, 021920 (2008); http://dx.doi.org/10.1063/1.2957975 (3 pages) | Cited 2 times

Online Publication Date: 18 July 2008

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P- and/or B-doped Si nanocrystals (Si-ncs) embedded in glass matrices were studied by electron spin resonance (ESR) spectroscopy to investigate the origin of strong room-temperature photoluminescence (PL) of n- and p-type impurities codoped Si-ncs below the band-gap energy of bulk Si crystals. It was shown that the intensity and width of the ESR signal depend strongly on impurity concentrations. A clear correlation was observed between the ESR signal width and the PL intensity. The observed correlation suggests that in addition to the geometrical confinement, P and B codoping further localize carriers in Si-ncs, and the strong localization results in the characteristic luminescence properties.
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61.72.uf Ge and Si
61.72.sd Impurity concentration
71.20.Mq Elemental semiconductors
78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
76.30.Lh Other ions and impurities

Size correction in ultrafast laser processing of fused silica by temporal pulse shaping

A. Mermillod-Blondin, C. Mauclair, A. Rosenfeld, J. Bonse, I. V. Hertel, E. Audouard, and R. Stoian

Appl. Phys. Lett. 93, 021921 (2008); http://dx.doi.org/10.1063/1.2958345 (3 pages) | Cited 7 times

Online Publication Date: 18 July 2008

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Laser structuring of bulk dielectric materials involves focusing through air-dielectric interfaces, which is prone to induce spherical aberrations. This elongates the energy deposition volume and restricts the processing accuracy at large focusing depths. Although spatial phase corrections are commonly applied to correct wavefront distortions, we show that temporal forming of ultrafast laser pulses achieves comparable counteracting function, limiting the spatial extent while creating a dominant region of positive index change. We indicate the role of reduced nonlinearity in plasma formation as a control factor which couples the spatial and temporal responses of the material.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.20.-n Methods of materials synthesis and materials processing
78.47.-p Spectroscopy of solid state dynamics
42.62.-b Laser applications
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Impact of oxygen incorporation at the Si3N4/Al2O3 interface on retention characteristics for nonvolatile memory applications

Man Chang, Yongkyu Ju, Joonmyoung Lee, Seungjae Jung, Hyejung Choi, Minseok Jo, Sanghun Jeon, and Hyunsang Hwang

Appl. Phys. Lett. 93, 022101 (2008); http://dx.doi.org/10.1063/1.2957668 (3 pages) | Cited 7 times

Online Publication Date: 14 July 2008

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The correlation between properties of the Si3N4/Al2O3 interface and retention degradation was investigated for metal-alumina-nitride-oxide-silicon-type flash memory devices. The intermixed region near the Si3N4/Al2O3 interface showed an oxygen deficiency, which was confirmed by the binding energy of Al and Si peaks from x-ray photoelectron spectroscopy analysis. This oxygen deficiency led to the enhancement of trap-assisted tunneling current. Additional ambient oxygen annealing can eliminate the oxygen deficiency at the intermixed region, which in turn can significantly reduce charge loss through the blocking oxide. With the aim of better memory characteristics, oxygen incorporation shows promise for future nonvolatile memory applications.
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84.30.Sk Pulse and digital circuits
73.40.Gk Tunneling
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.Cc Kinetics of defect formation and annealing
68.35.Ct Interface structure and roughness
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