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2 Aug 2010

Volume 97, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 051101 (2010); http://dx.doi.org/10.1063/1.3470591 (3 pages)

Pascal Böhi, Max F. Riedel, Theodor W. Hänsch, and Philipp Treutlein
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Electrochemical hydrogen termination of boron-doped diamond

René Hoffmann, Armin Kriele, Harald Obloh, Jakob Hees, Marco Wolfer, Waldemar Smirnov, Nianjun Yang, and Christoph E. Nebel

Appl. Phys. Lett. 97, 052103 (2010); http://dx.doi.org/10.1063/1.3476346 (3 pages) | Cited 11 times

Online Publication Date: 4 August 2010

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Boron-doped diamond is a promising transducer material for numerous devices which are designed for contact with electrolytes. For optimized electron transfer the surface of diamond needs to be hydrogen terminated. Up to now H-termination of diamond is done by plasma chemical vapor deposition techniques. In this paper, we show that boron-doped diamond can be H-terminated electrochemically by applying negative voltages in acidic solutions. Electrochemical H-termination generates a clean surface with virtually no carbon–oxygen bonds (x-ray photoelectron spectroscopy), a reduced electron affinity (scanning electron microscopy), a highly hydrophobic surface (water contact angle), and a fast electron exchange with Fe(CN)6−3/−4 (cyclic voltammetry).
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81.65.Cf Surface cleaning, etching, patterning
82.80.Fk Electrochemical methods
81.05.ug Diamond
07.07.Mp Transducers
82.45.Gj Electrolytes
68.03.Cd Surface tension and related phenomena
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Vertical low-voltage oxide transistors gated by microporous SiO2/LiCl composite solid electrolyte with enhanced electric-double-layer capacitance

Jie Jiang, Jia Sun, Bin Zhou, Aixia Lu, and Qing Wan

Appl. Phys. Lett. 97, 052104 (2010); http://dx.doi.org/10.1063/1.3477949 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2010

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Vertical low-voltage indium-tin oxide field-effect transistors (FETs) gated by microporous SiO2-based solid electrolyte are fabricated at room temperature. Our results indicate that Li ions can enhance the electric-double-layer capacitance of the microporous SiO2 solid electrolyte and reduce the operation voltage of the vertical FETs from 1.5 to 0.8 V. Such vertical low-voltage FETs exhibited a good performance with a high current output ( ∼ 1.0 A/cm2), a low subthreshold swing (<80 mV/decade), and a large on-off ratio (>106), respectively. An operation mechanism which provides a better insight into the oxide-based vertical FETs is discussed.
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85.30.Tv Field effect devices

Transparent p-type SnOx thin film transistors produced by reactive rf magnetron sputtering followed by low temperature annealing

Elvira Fortunato, Raquel Barros, Pedro Barquinha, Vitor Figueiredo, Sang-Hee Ko Park, Chi-Sun Hwang, and Rodrigo Martins

Appl. Phys. Lett. 97, 052105 (2010); http://dx.doi.org/10.1063/1.3469939 (3 pages) | Cited 20 times

Online Publication Date: 4 August 2010

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P-type thin-film transistors (TFTs) using room temperature sputtered SnOx (x<2) as a transparent oxide semiconductor have been produced. The SnOx films show p-type conduction presenting a polycrystalline structure composed with a mixture of tetragonal β-Sn and α-SnOx phases, after annealing at 200 °C. These films exhibit a hole carrier concentration in the range of ≈ 1016–1018 cm−3; electrical resistivity between 101–102 Ω cm; Hall mobility around 4.8 cm2/V s; optical band gap of 2.8 eV; and average transmittance ≈85% (400 to 2000 nm). The bottom gate p-type SnOx TFTs present a field-effect mobility above 1 cm2/V s and an ON/OFF modulation ratio of 103.
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85.30.Tv Field effect devices

Resistive switching transition induced by a voltage pulse in a Pt/NiO/Pt structure

Inrok Hwang, Myung-Jae Lee, Gyoung-Ho Buh, Jieun Bae, Jinsik Choi, Jin-Soo Kim, Sahwan Hong, Yeon Soo Kim, Ik-Su Byun, Seung-Woong Lee, Seung-Eon Ahn, Bo Soo Kang, Sung-Oong Kang, and Bae Ho Park

Appl. Phys. Lett. 97, 052106 (2010); http://dx.doi.org/10.1063/1.3477953 (3 pages) | Cited 13 times

Online Publication Date: 5 August 2010

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We have observed a switching transition between bistable memory switching and monostable threshold switching in Pt/NiO/Pt structure. Bistable memory switching could be changed to monostable threshold switching by applying a positive electrical pulse with height of 2 V and width between 10−2 and 10−4 s. The change is reversible by applying a negative electrical pulse with the same height and width. By considering polarity- and width-dependence of the switching transition and compositional difference on electrical properties in NiOx, we have proposed a model in which the migration of oxygen ions (O2−) is responsible for the switching transition in Pt/NiO/Pt structures.
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73.40.Rw Metal-insulator-metal structures
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions

Effect of n+GaN cap polarization field on Cs-free GaN photocathode characteristics

N. Tripathi, L. D. Bell, S. Nikzad, and F. Shahedipour-Sandvik

Appl. Phys. Lett. 97, 052107 (2010); http://dx.doi.org/10.1063/1.3476341 (3 pages) | Cited 2 times

Online Publication Date: 6 August 2010

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We report on a Cs-free GaN photocathode structure in which band engineering at the photocathode surface caused by Si delta doping eliminates the need for use of cesium for photocathode activation. The structure is capped with a highly doped n+GaN layer. We have identified that n+GaN cap thickness plays an important role in limiting the effect of polarization induced charges at the GaN surface on the photocathode emission threshold. Physics based device simulations is used for further analysis of the experimental results. Our findings clearly illustrate the impact of polarization induced surface charges on the device properties including its emission threshold.
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85.60.Ha Photomultipliers; phototubes and photocathodes
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uj III-V and II-VI semiconductors

Minority carrier lifetime in type-2 InAs–GaSb strained-layer superlattices and bulk HgCdTe materials

Dmitry Donetsky, Gregory Belenky, Stefan Svensson, and Sergei Suchalkin

Appl. Phys. Lett. 97, 052108 (2010); http://dx.doi.org/10.1063/1.3476352 (3 pages) | Cited 23 times

Online Publication Date: 6 August 2010

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Minority carrier lifetime, τ, in type-2 strained-layer superlattices (SLSs) and in long-wave Hg0.78Cd0.22Te (MCT) was measured by optical modulation response technique. It was shown that at 77 K radiative recombination can contribute to the measured τ values. The Shockley–Read–Hall (SRH) lifetimes were attained as 100 ns, 31 ns, and more than 1 μs for midwave infrared superlattices, long-wave infrared (LWIR) superlattices, and MCT correspondingly. The nature of the difference between the SRH lifetimes in LWIR superlattice and MCT is discussed.
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81.05.Ea III-V semiconductors
81.05.Dz II-VI semiconductors
73.63.-b Electronic transport in nanoscale materials and structures
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors

Enhancement of thermoelectric efficiency in (Ca,Dy)MnO3–(Ca,Yb)MnO3 solid solutions

Yang Wang, Yu Sui, Xianjie Wang, and Wenhui Su

Appl. Phys. Lett. 97, 052109 (2010); http://dx.doi.org/10.1063/1.3477959 (3 pages) | Cited 1 time

Online Publication Date: 6 August 2010

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Transport and thermoelectric (TE) properties have been investigated for the (Ca,Dy)MnO3–(Ca,Yb)MnO3 solid solutions. Resistivity is found to be closely correlated with the structural distortions in this system. The enhanced TE efficiency in the solid solutions can be well attributed to the distortion of electronic density of states along with a strong point defect scattering. Such band structure engineering and phonon engineering have resulted in an effective improvement of the TE performance in these solid solutions and could be applied to more systems.
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72.20.Pa Thermoelectric and thermomagnetic effects
71.20.Ps Other inorganic compounds
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
61.72.J- Point defects and defect clusters
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Subgrain size inhomogeneities in the luminescence spectra of thin film chalcopyrites

Levent Gütay, Christoph Lienau, and Gottfried Heinrich Bauer

Appl. Phys. Lett. 97, 052110 (2010); http://dx.doi.org/10.1063/1.3475018 (3 pages) | Cited 9 times

Online Publication Date: 6 August 2010

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We report near-field photoluminescence (PL) spectra of Cu(InGa)Se2 thin films recorded with a lateral optical resolution of ≈200 nm and simultaneous detection of the sample topography. Our results reveal significant local variations in the PL spectra, specifically the PL yield, on length scales of 0.2–1.5 μm. Local variations in both the splitting of quasi-Fermi levels μ and the band gap energy are quantitatively extracted from the PL spectra by applying Planck’s generalized law. We show pronounced fluctuations of μ and the band gap on length scales below the grain size. These fluctuations are only weakly correlated with the topographic film structure.
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78.55.Hx Other solid inorganic materials
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
78.66.Li Other semiconductors
68.55.ag Semiconductors
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Reverse-domain superconductivity in superconductor-ferromagnet hybrids: Effect of a vortex-free channel on the symmetry of I-V characteristics

A. Yu. Aladyshkin, D. Yu. Vodolazov, J. Fritzsche, R. B. G. Kramer, and V. V. Moshchalkov

Appl. Phys. Lett. 97, 052501 (2010); http://dx.doi.org/10.1063/1.3474622 (3 pages) | Cited 5 times

Online Publication Date: 2 August 2010

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We demonstrate experimentally that the presence of a single domain wall in an underlying ferromagnetic BaFe12O19 substrate can induce a considerable asymmetry in the current (I)–voltage (V) characteristics of a superconducting Al bridge deposited on top of the substrate. The observed diodelike effect, i.e., polarity-dependent critical current, is associated with the formation of a vortex-free channel inside the superconducting area which increases the total current flowing through the superconducting bridge without dissipation. The vortex-free region appears only for a certain sign of the injected current and for a limited range of the external magnetic field.
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74.25.F- Transport properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Gw Magnetic anisotropy
74.78.-w Superconducting films and low-dimensional structures

Electrically controlled magnetization switching in a multiferroic heterostructure

Yajie Chen, Trifon Fitchorov, Carmine Vittoria, and V. G. Harris

Appl. Phys. Lett. 97, 052502 (2010); http://dx.doi.org/10.1063/1.3475417 (3 pages) | Cited 12 times

Online Publication Date: 2 August 2010

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A demonstration of magnetization reversal via the application of electric field across a multiferroic heterostructure, consisting of a FeCoV ribbon bonded to a lead magnesium niobate-lead titanate crystal, is presented. The magnetization switching occurs by an abrupt change in magnetization near ferromagnetic coercivity, coinciding with an electrical field-induced magnetic anisotropy field. Experiments reveal a converse magnetoelectric coupling of α = μ0(dM/dE) = 1.6×10−7 s m−1 upon magnetization reversal in the strain-mediated heterostructure. The frequency dependence of magnetization switching is presented and explained within the framework of a relaxation model for the multiferroic heterostructure.
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75.85.+t Magnetoelectric effects, multiferroics
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
77.80.-e Ferroelectricity and antiferroelectricity
75.78.Jp Ultrafast magnetization dynamics and switching

Reversibility and irreversibility of magnetocaloric effect in a metamagnetic shape memory alloy under cyclic action of a magnetic field

V. V. Khovaylo, K. P. Skokov, O. Gutfleisch, H. Miki, R. Kainuma, and T. Kanomata

Appl. Phys. Lett. 97, 052503 (2010); http://dx.doi.org/10.1063/1.3476348 (3 pages) | Cited 13 times

Online Publication Date: 3 August 2010

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We have studied adiabatic temperature change ΔTad in a Ni50Mn36Co1Sn13 metamagnetic shape memory alloy. An irreversible character of ΔTad has been observed in the vicinity of the reverse martensitic transformation. In this region, cyclic application of the magnetic field converts comparatively large inverse magnetocaloric effect (MCE) with ΔTadmax = −0.8 K to a weaker conventional MCE (ΔTadmax = 0.3 K). The crossover of ΔTad has been attributed to the irreversible character of the magnetic field-induced transformation and the closeness of the martensitic transformation and Curie temperature of the austenitic phase TCA.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Lm Deformation, plasticity, and creep
64.70.K- Solid-solid transitions
62.20.fg Shape-memory effect; yield stress; superelasticity

Inverted hysteresis and giant exchange bias in La0.7Sr0.3MnO3/SrRuO3 superlattices

M. Ziese, I. Vrejoiu, and D. Hesse

Appl. Phys. Lett. 97, 052504 (2010); http://dx.doi.org/10.1063/1.3470101 (3 pages) | Cited 13 times

Online Publication Date: 3 August 2010

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The magnetization reversal mechanisms in a La0.7Sr0.3MnO3/SrRuO3 superlattice with ultrathin individual layers were studied. Due to the strong exchange bias between La0.7Sr0.3MnO3 and SrRuO3 layers inverted hysteresis loops were observed at temperatures below 62 K; at higher temperatures the superlattice showed an unconventional reversal mechanism with the magnetically hard SrRuO3 layers switching first on reducing the magnetic field from saturation. These observations were corroborated by micromagnetic simulations and were interpreted as arising from interfacial Bloch walls.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
75.60.Jk Magnetization reversal mechanisms
74.70.-b Superconducting materials other than cuprates
74.78.Fk Multilayers, superlattices, heterostructures
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Bulk sensitive x-ray absorption and magnetic circular dichroism investigation of Mn- and Co-doped ZnO thin films

A. Di Trolio, R. Larciprete, S. Turchini, and N. Zema

Appl. Phys. Lett. 97, 052505 (2010); http://dx.doi.org/10.1063/1.3475925 (3 pages) | Cited 4 times

Online Publication Date: 4 August 2010

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Bulk sensitive L2,3 x-ray magnetic circular dichroism spectra were measured in transmission on Mn- and Co-doped ZnO thin films grown by pulsed laser deposition on soft x-ray transparent silicon nitride membranes. The absorption spectra line shapes support that Mn and Co divalent ions substitute Zn ions ruling out the hint of cluster formation. The lack of dichroic signal at the Mn and Co-edges in such bulk sensitive measurements indicates that the ferromagnetism witnessed by vibrating sample magnetometry measurements could arise from delocalized magnetic moments, due to itinerant electrons associated with defects.
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78.20.Ls Magneto-optical effects
75.30.Cr Saturation moments and magnetic susceptibilities
78.66.Hf II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
61.72.U- Doping and impurity implantation
78.70.Dm X-ray absorption spectra

Investigation of the intermediate phase and magnetocaloric properties in high-pressure annealing Ni–Mn–Co–Sn alloy

S. C. Ma, H. C. Xuan, C. L. Zhang, L. Y. Wang, Q. Q. Cao, D. H. Wang, and Y. W. Du

Appl. Phys. Lett. 97, 052506 (2010); http://dx.doi.org/10.1063/1.3476351 (3 pages) | Cited 3 times

Online Publication Date: 5 August 2010

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The Ni–Mn–Co–Sn alloy is prepared by high-pressure annealing method. Besides the enhanced martensitic transformation temperature and the Curie temperature of austenite, an intermediate phase above the martensitic transformation is observed in this alloy. As a result, two successive magnetic entropy changes with the same sign are obtained around room-temperature, corresponding to the martensitic transformation and intermediate phase transition, respectively. The origin of the intermediate phase for high-pressure annealing Ni–Mn–Co–Sn alloy is discussed.
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75.30.Sg Magnetocaloric effect, magnetic cooling
62.50.-p High-pressure effects in solids and liquids
81.30.Kf Martensitic transformations
81.40.Gh Other heat and thermomechanical treatments
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetic domain compensation effect on the magnetodynamic response of ferromagnetic elements

C. Patschureck, R. Kaltofen, I. Mönch, R. Schäfer, L. Schultz, and J. McCord

Appl. Phys. Lett. 97, 052507 (2010); http://dx.doi.org/10.1063/1.3474621 (3 pages)

Online Publication Date: 6 August 2010

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The capacity to tune the ferromagnetic resonance frequency in a soft ferromagnetic film relies on the ability to tailor the uniaxial anisotropy of the film material. We achieved a systematic change in anisotropy field with all other material properties remaining constant by preparing Ni18Fe19/Co60Fe20B20 multilayers. We show that in patterned films deviations from the regular Landau domain pattern occur, which compensate magnetic anisotropy effects and thereby lead to a precessional frequency independent of anisotropy. These results demonstrate that even small changes in the magnetic domain structure counteracts anisotropy adjustments in optimizing the magnetodynamic response in mesoscopic thin film elements.
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75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Gw Magnetic anisotropy
73.21.Ac Multilayers
71.70.Di Landau levels
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Strontium-induced ferroelectriclike relaxor behavior in Bi-based pyrochlores

Huiling Du and Xiang Shi

Appl. Phys. Lett. 97, 052901 (2010); http://dx.doi.org/10.1063/1.3474610 (3 pages)

Online Publication Date: 2 August 2010

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The dielectric properties of stoichiometric dense ceramics (Bi1.5Zn0.5−xSrx)(Ti1.5Nb0.5)O7 (BZSTN, x = 0–0.5) have been investigated as a function of temperature and frequency. A significant relaxation behavior at about 250 °C is induced when moderate Sr2+ is substituted with Zn2+ in Bi1.5Zn0.5Ti1.5Nb0.5O7 (BZTN) ceramics. The observation of hysteretic behavior in the P versus E curves shows the existence of a polar state. The ferroelectriclike relaxor behavior arises mainly from the dynamic response of the micropolar clusters, which exist in the off-center ions doped paraelectric. The ultrahigh permittivity of 245 at ambient temperature could be very promising for integrated capacitors and microwave resonators.
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77.80.Jk Relaxor ferroelectrics
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.55.F- High-permittivity capacitive films

Quantitative determination of anisotropic magnetoelectric coupling in BiFeO3–CoFe2O4 nanostructures

Yoon Seok Oh, S. Crane, H. Zheng, Y. H. Chu, R. Ramesh, and Kee Hoon Kim

Appl. Phys. Lett. 97, 052902 (2010); http://dx.doi.org/10.1063/1.3475420 (3 pages) | Cited 7 times

Online Publication Date: 4 August 2010

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The transverse and longitudinal magnetoelectric susceptibilities (MES) were quantitatively determined for (001) heteroepitaxial BiFeO3–CoFe2O4 nanostructures. Both of these MES values were sharply enhanced at magnetic fields below 6 kOe and revealed asymmetric line shapes with respect to the dc magnetic field, demonstrating the strain-induced magnetoelectric effect. The maximum transverse MES, which reached as high as ∼ 60 mV/cm Oe, was about five times larger than the longitudinal MES. This observation signifies that transverse magnetostriction of the CoFe2O4 nanopillars is enhanced more than the bulk value due to preferred magnetic domain alignment along the [001] direction coming from compressive, heteroepitaxial strain.
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75.85.+t Magnetoelectric effects, multiferroics
75.75.-c Magnetic properties of nanostructures
75.75.Fk Domain structures in nanoparticles
75.30.Gw Magnetic anisotropy

Effect of polarization-memory in SrTiO3/La0.9Sr0.1MnO3 multilayer on Si substrate

Yingtang Zhang, Yiming Zhang, and Shengtao Li

Appl. Phys. Lett. 97, 052903 (2010); http://dx.doi.org/10.1063/1.3476358 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2010

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SrTiO3/La0.9Sr0.1MnO3 (STO/LSMO) multilayer was fabricated on n-Si (100) substrate by using a computer-controlled laser molecular-beam epitaxy technique. A rectifying behavior was observed in the multilayer. Meanwhile, the capancitance-voltage (C-V) characteristics were investigated, which reveals a hysteresis memory effect in forward and backward bias regions. A detail study suggests that the hysteresis behaviors originate from the cooperation and competition between the interfacial polarization and trapping/detrapping mechanisms. Our results are expected to meet the high desire of the optimization and device design of random access memory.
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85.30.-z Semiconductor devices
68.55.at Other materials

Structural and electrical analysis of the atomic layer deposition of HfO2/n-In0.53Ga0.47As capacitors with and without an Al2O3 interface control layer

A. O’Mahony, S. Monaghan, G. Provenzano, I. M. Povey, M. G. Nolan, É. O’Connor, K. Cherkaoui, S. B. Newcomb, F. Crupi, P. K. Hurley, and M. E. Pemble

Appl. Phys. Lett. 97, 052904 (2010); http://dx.doi.org/10.1063/1.3473773 (3 pages) | Cited 16 times

Online Publication Date: 6 August 2010

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High mobility III-V substrates with high-k oxides are required for device scaling without loss of channel mobility. Interest has focused on the self-cleaning effect on selected III-V substrates during atomic layer deposition of Al2O3. A thin ( ∼ 1 nm) Al2O3 interface control layer is deposited on In0.53Ga0.47As prior to HfO2 growth, providing the benefit of self-cleaning and improving the interface quality by reducing interface state defect densities by ∼ 50% while maintaining scaling trends. Significant reductions in leakage current density and increased breakdown voltage are found, indicative of a band structure improvement due to the reduction/removal of the In0.53Ga0.47As native oxides.
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84.32.Tt Capacitors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
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Self-assembled GaAs islands on Si by droplet epitaxy

C. Somaschini, S. Bietti, N. Koguchi, F. Montalenti, C. Frigeri, and S. Sanguinetti

Appl. Phys. Lett. 97, 053101 (2010); http://dx.doi.org/10.1063/1.3475923 (3 pages) | Cited 5 times

Online Publication Date: 2 August 2010

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We presented an innovative fabrication technique for the self-assembly of GaAs islands on Si substrates by droplet epitaxy. The islands show highly tunable density (from 107 to some 109 islands/cm2) and size (from 75 to 250 nm), and small size dispersion (below 10%). The islands, made by single relaxed crystals with lattice parameters close to the GaAs bulk, show well defined shapes, with a high aspect ratio. The low thermal budget required for the island self-assembly, together with the high scalability of the process, make these islands good candidates for local artificial substrates or local strain sources with the required lattice parameters, band alignment, and crystalline quality as now required for the implementation of high quality devices on Si.
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68.55.A- Nucleation and growth
68.55.ag Semiconductors
61.50.-f Structure of bulk crystals

Amplified nanopatterning by self-organized shadow mask ion lithography

D. Chiappe, A. Toma, Z. Zhang, C. Boragno, and F. Buatier de Mongeot

Appl. Phys. Lett. 97, 053102 (2010); http://dx.doi.org/10.1063/1.3473770 (3 pages) | Cited 4 times

Online Publication Date: 2 August 2010

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The self-organized formation of high aspect ratio dielectric nanostructures can be guided and sped-up recurring to a sacrificial metal film during ion beam sputtering. Following ion irradiation, the metal film evolves into a disconnected array of laterally ordered nanowires, which guide etching of the dielectric substrate. While the amplification rate of large scale features can be described simply in terms of the ratio of the sputtering yields of substrate and film, for small scale features the amplification rate depends on the interplay and lateral range of the smoothing and erosive mechanisms of the two materials.
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85.40.Hp Lithography, masks and pattern transfer

Aqueous-based synthesis of atomic gold clusters: Geometry and optical properties

S. Rath, S. Nozaki, D. Palagin, V. Matulis, O. Ivashkevich, and S. Maki

Appl. Phys. Lett. 97, 053103 (2010); http://dx.doi.org/10.1063/1.3467261 (3 pages) | Cited 1 time

Online Publication Date: 2 August 2010

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Gold clusters synthesized by the solution-based growth technique have exhibited ultraviolet (UV) light emission with nearly zero Stokes shift. Atomic arrangement decided optical properties of the Au microclusters have been studied extensively. In addition to the time-of-flight mass spectra, the comparison of experimental and theoretical emission and absorption spectra confirms the presence of Au8 clusters with the planar hexagon+1-shaped geometry. The observed UV emission is attributed to the transition from the highest occupied to the lowest unoccupied molecular orbitals of the hexagon+1 structured Au8 clusters.
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36.40.Vz Optical properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
32.30.Jc Visible and ultraviolet spectra
32.10.Bi Atomic masses, mass spectra, abundances, and isotopes

Charge carrier separation induced by intrinsic surface strain in pristine ZnO nanowires

Liangzhi Kou, Chun Li, Zi-Yue Zhang, Changfeng Chen, and Wanlin Guo

Appl. Phys. Lett. 97, 053104 (2010); http://dx.doi.org/10.1063/1.3467262 (3 pages) | Cited 2 times

Online Publication Date: 2 August 2010

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We predict by first-principles calculations a spontaneous charge carrier separation mechanism in pristine [0001]-oriented ZnO nanowires. We find that the shrinking strain induced by surface reconstruction causes electrons and holes to separate and move toward the core and surface region, respectively. Such separation can be enhanced by axially applied tensile strain as a result of the enhancement of surface strain induced by the Poisson effect, and be suppressed by compressive axial strain. Similar carrier separations are found in IIB-sulfides. This intrinsic charge separation and tensile strain induced enhancement are expected to shed light on solar cell designs.
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73.21.Hb Quantum wires
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio

Multiwavelength micro-Raman analysis of strain in nanopatterned ultrathin strained silicon-on-insulator

O. Moutanabbir, M. Reiche, A. Hähnel, M. Oehme, and E. Kasper

Appl. Phys. Lett. 97, 053105 (2010); http://dx.doi.org/10.1063/1.3475399 (3 pages) | Cited 6 times

Online Publication Date: 2 August 2010

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We developed a heterostructure to assess accurately the strain evolution upon nanopatterning of 15 nm thick tensile strained silicon-on-insulator (SSOI). Here the long-standing concern of substrate background in micro-Raman analysis was circumvented by the introduction of a Ge layer underneath the buried oxide. Unprecedented insights into the strain behavior in SSOI nanostructures were obtained by combining deep UV and visible micro-Raman probes. We found that the formation of edges results in a strong relaxation near the surface parallel to an increase in the strain at the Si/oxide interface. This disparity in the strain evolution between surface and interface leads to the coexistence of compressive and tensile strained regions within the same structure at a lateral dimension of 50 nm. This heterogeneous distribution of strain should be taken into account in the design and fabrication of SSOI-based nanodevices.
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81.16.Rf Micro- and nanoscale pattern formation
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Selective growth and piezoelectric properties of highly ordered arrays of vertical ZnO nanowires on ultrathin alumina membranes

Liaoyong Wen, Zhengzheng Shao, Yaoguo Fang, Kin Mun Wong, Yong Lei, Lifeng Bian, and Gerhard Wilde

Appl. Phys. Lett. 97, 053106 (2010); http://dx.doi.org/10.1063/1.3474615 (3 pages) | Cited 4 times

Online Publication Date: 3 August 2010

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A well controlled and cost effective method of fabricating highly ordered arrays of vertical zinc oxide (ZnO) nanowires or nanopores is demonstrated where an ultrathin alumina membrane (UTAM) itself is utilized as a substrate for the selective growth of the ordered arrays. A thin film of gold was thermally evaporated on the UTAM followed by the growth of highly regular ZnO nanowires using chemical vapor deposition (CVD). Alternatively, highly ordered ZnO nanopores arrays were also grown by CVD on the bare UTAM. Additionally, piezoelectric currents were generated from the ZnO nanowires during the conductive atomic force microscopy probe tip scan across the array.
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81.07.Gf Nanowires
73.30.+y Surface double layers, Schottky barriers, and work functions
77.65.-j Piezoelectricity and electromechanical effects
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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