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14 Jun 2010

Volume 96, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 241101 (2010); http://dx.doi.org/10.1063/1.3449576 (3 pages)

Rui Chen, H. D. Sun, T. Wang, K. N. Hui, and H. W. Choi
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Noise-driven signal transmission using nonlinearity of VO2 thin films

Teruo Kanki, Yasushi Hotta, Naoki Asakawa, Tomoji Kawai, and Hidekazu Tanaka

Appl. Phys. Lett. 96, 242108 (2010); http://dx.doi.org/10.1063/1.3455335 (3 pages) | Cited 5 times

Online Publication Date: 17 June 2010

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We demonstrated signal transmission using the nonlinearity of VO2 in the manner of stochastic resonance (SR). A correlated insulator state of VO2 changes nonlinearly to a metallic state when an applied bias voltage increases beyond a threshold. The transition of the states between insulator and metal is adaptable to the SR theory. In this study, the response to a weak pulse signal was optimized by a particular level of noise via SR. Numerical SR simulations suggests the existence of multiple threshold channels in the insulating state, spontaneously enhancing the reliability of signal transmission.
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73.61.Ng Insulators
73.50.Td Noise processes and phenomena
73.50.Fq High-field and nonlinear effects
72.60.+g Mixed conductivity and conductivity transitions

Resistive switching behaviors of ZnO nanorod layers

Wen-Yuan Chang (張文淵), Chin-An Lin (林晉安), Jr-Hau He (何志浩), and Tai-Bor Wu (吳泰伯)

Appl. Phys. Lett. 96, 242109 (2010); http://dx.doi.org/10.1063/1.3453450 (3 pages) | Cited 22 times

Online Publication Date: 17 June 2010

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We have fabricated vertically aligned ZnO nanorod layers (NRLs) on indium tin oxide (ITO) electrodes using a hydrothermal process. The Pt/ZnO NRL/ITO capacitor exhibits bipolar resistive switching behavior. The resistive switching behavior may be related to the oxygen vacancies and/or zinc interstitials confined on the surface of the ZnO NRs, giving rise to the formation of straight and extensible conducting filaments along each vertically aligned ZnO NR. Superior stability in resistive switching characteristics was also observed, demonstrating that ZnO NRLs have the potential for next-generation nonvolatile memory applications.
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73.63.Bd Nanocrystalline materials
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Study of piezoresistance under unixial stress for technologically relevant III-V semiconductors using wafer bending experiments

Aneesh Nainani, Jung Yum, Joel Barnett, Richard Hill, Niti Goel, Jeff Huang, Prashant Majhi, Raj Jammy, and Krishna C. Saraswat

Appl. Phys. Lett. 96, 242110 (2010); http://dx.doi.org/10.1063/1.3436561 (3 pages) | Cited 4 times

Online Publication Date: 17 June 2010

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In this work, effect of uniaxial stress is studied by wafer bending on p/n-channel candidates for III-V based complimentary logic. p-GaSb has 2× higher piezoresistance (π) coefficient than p-In0.53Ga0.47As, which combined with high hole-mobility in GaSb makes it an attractive candidate for III-V p-metal-oxide-semiconductor-field-effect-transistor. Limitation on maximum stress introduced by wafer bending is improved when the III-V channel is grown epitaxially on silicon. 250 MPa of stress is achieved by wafer bending on III-V channel grown on silicon substrate, which is 5× higher than maximum stress achieved on III-V substrate.
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73.61.Ey III-V semiconductors
68.55.ag Semiconductors

Transport properties of the electron gas in ZnO/MgZnO heterostructures

A. Gold

Appl. Phys. Lett. 96, 242111 (2010); http://dx.doi.org/10.1063/1.3455881 (3 pages) | Cited 6 times

Online Publication Date: 18 June 2010

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We analyze experimental results for the mobility of the two-dimensional electron gas as realized in ZnO/MgZnO heterostructures. For zero temperature we calculate the mobility as function of the electron density for charged-impurity and for interface-roughness scattering. Multiple scattering effects, leading to a metal-insulator transition, are taken into account. The results of our calculation are in good agreement with experimental results. The numbers obtained for the parameters of interface-roughness scattering and charged-impurity scattering are reasonable. We argue that the electron gas in this heterostructure might be spin-polarized.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.10.Ca Electron gas, Fermi gas
68.35.Ct Interface structure and roughness
72.25.-b Spin polarized transport
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.60.+g Mixed conductivity and conductivity transitions

Impact of N- and Ga-face polarity on the incorporation of deep levels in n-type GaN grown by molecular beam epitaxy

A. R. Arehart, T. Homan, M. H. Wong, C. Poblenz, J. S. Speck, and S. A. Ringel

Appl. Phys. Lett. 96, 242112 (2010); http://dx.doi.org/10.1063/1.3453660 (3 pages) | Cited 6 times

Online Publication Date: 18 June 2010

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Deep levels in N-face and Ga-face n-type GaN grown by plasma-assisted molecular beam epitaxy were detected, analyzed and compared using deep level optical spectroscopy (DLOS) and conventional thermal deep level transient spectroscopy (DLTS), which together enable deep level detection throughout the GaN band gap. A redistribution of band gap states was observed between the two GaN crystal growth polarities but with a similar total trap density. Most significant was a tenfold concentration increase in a trap at EC-0.25 eV that is likely related to nitrogen vacancies for the N-face polarity material, with no significant change for the Ga-vacancy-related level at EC-2.60 eV. The DLOS results suggest that carbon impurities, which generate several GaN band gap states, appear to incorporate differently for both crystal polarities with the potential carbon interstitial at EC-1.28 eV being undetected for N-face material. Finally, low concentrations of several new levels in the N-face n-GaN not previously observed in Ga-face n-GaN were observed.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition

Unusual metallic-like transport near the percolation threshold

Ravi Bhatia, C. S. Suchand Sangeeth, V. Prasad, and Reghu Menon

Appl. Phys. Lett. 96, 242113 (2010); http://dx.doi.org/10.1063/1.3455895 (3 pages) | Cited 3 times

Online Publication Date: 18 June 2010

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In multiwall carbon nanotube (MWNT)—polystyrene (PS) composites, a weak temperature dependence of conductivity has been observed at a percolation threshold of 0.4 wt %. The power law [σ(T)∝T0.3] behavior indicates metallic-like behavior, unlike the usual activated transport for systems near the percolation threshold. The low field positive magnetoconductance follows H2 dependence, due to the weak localization in disordered metallic systems. The marginal metallic nature of MWNT-PS at percolation threshold is further verified from the negligible frequency dependence of conductivity, in the temperature range of 300 to 5 K.
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73.63.Bd Nanocrystalline materials
72.20.My Galvanomagnetic and other magnetotransport effects
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Spin wave assisted current induced magnetic domain wall motion

Mahdi Jamali, Hyunsoo Yang, and Kyung-Jin Lee

Appl. Phys. Lett. 96, 242501 (2010); http://dx.doi.org/10.1063/1.3446833 (3 pages) | Cited 5 times

Online Publication Date: 14 June 2010

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The interaction between the propagating spin waves and the current driven motion of a transverse domain wall in magnetic nanowires is studied by micromagnetic simulations. If the speed of domain walls due to current induced spin transfer torque is comparable to the velocity driven by spin waves, the speed of domain wall is improved by applying spin waves. The domain wall velocity can be manipulated by the frequency and amplitude of spin waves. The effect of spin waves is suppressed in the high current density regime in which the domain wall is mostly driven by current induced spin transfer torque.
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75.75.Fk Domain structures in nanoparticles
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Ds Spin waves
75.60.Ch Domain walls and domain structure

Structure, magnetic, and microwave properties of thick Ba-hexaferrite films epitaxially grown on GaN/Al2O3 substrates

Z. Chen, A. Yang, K. Mahalingam, K. L. Averett, J. Gao, G. J. Brown, C. Vittoria, and V. G. Harris

Appl. Phys. Lett. 96, 242502 (2010); http://dx.doi.org/10.1063/1.3446867 (3 pages) | Cited 5 times

Online Publication Date: 14 June 2010

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Thick barium hexaferrite [BaO⋅(Fe2O3)6] films, having the magnetoplumbite structure (i.e., Ba M), were epitaxially grown on c-axis oriented GaN/Al2O3 substrates by pulsed laser deposition followed by liquid phase epitaxy. X-ray diffraction showed (0,0,2n) crystallographic alignment with pole figure analyses confirming epitaxial growth. High resolution transmission electron microscopy images revealed magnetoplumbite unit cells stacked with limited interfacial mixing. Saturation magnetization, 4πMs, was measured for as-grown films to be 4.1±0.3 kG with a perpendicular magnetic anisotropy field of 16±0.3 kOe. Ferromagnetic resonance linewidth, the peak-to-peak power absorption derivative at 53 GHz, was 86 Oe. These properties will prove enabling for the integration of low loss Ba M ferrite microwave passive devices with active semiconductor circuit elements in systems-on-a-wafer architecture.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.70.Gq Microwave and radio-frequency interactions
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
68.55.-a Thin film structure and morphology

Ferromagnetism of double-walled carbon nanotubes

Der-Chung Yan, Shih-Yun Chen, Maw-Kuen Wu, C. C. Chi, J. H. Chao, and Malcolm L. H. Green

Appl. Phys. Lett. 96, 242503 (2010); http://dx.doi.org/10.1063/1.3453867 (3 pages)

Online Publication Date: 14 June 2010

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The pure double-walled carbon nanotubes (DWNTs) and two endohedral DWNTs (DWNTs with materials filled inside) are produced. The filling materials are CoI2 and KI, respectively. The ferromagnetism (FM) is observed in pure DWNTs. The content of residual catalyst Fe is too small to be responsible for the observed FM. On the other hand, after filling KI or CoI2 into the tubes, over 87% of FM is suppressed. This suggests that the origin of FM in nanotubes is mainly from the hydrogen chemisorptions induced in the process of acid purification. With the knowledge of FM origin, it is then possible to enhance FM of carbon nanotubes or graphene for applications relying on magnetism.
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75.50.Dd Nonmetallic ferromagnetic materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
75.30.Cr Saturation moments and magnetic susceptibilities
61.46.Fg Nanotubes
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Phase control of magnetic state of graphite thin films by electric field

Minoru Otani, Yoshiteru Takagi, Mikito Koshino, and Susumu Okada

Appl. Phys. Lett. 96, 242504 (2010); http://dx.doi.org/10.1063/1.3455069 (3 pages) | Cited 5 times

Online Publication Date: 15 June 2010

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Based on first-principle total-energy calculations, we have found that by applying an external electric field it is possible to control the magnetic state of graphite thin film with the rhombohedral stacking arrangement. When exposed to a moderate electric field normal to the film, the surface of a thin film of rhombohedral graphite undergoes a magnetic phase transition from the antiferromagnetic state to the ferromagnetic state. The polarized electron spin is primarily distributed in the bottommost layer of the film, which forms the interface with the negative electrode. The amount of polarized electron spin is calculated to be 0.067 μB/nm2. The ferromagnetic ordering with the characteristic distribution of the polarized electron spin opens the possibility of using graphite thin films in electronic devices with spin degree of freedom.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
72.25.-b Spin polarized transport

Strong crystalline field at the Fe site and spin rotation in olivine LiNi0.99 57Fe0.01 PO4 material by Mössbauer spectroscopy

Woochul Kim, Chan Hyuk Rhee, Hyung Joon Kim, Seung Je Moon, and Chul Sung Kim

Appl. Phys. Lett. 96, 242505 (2010); http://dx.doi.org/10.1063/1.3455312 (3 pages) | Cited 7 times

Online Publication Date: 15 June 2010

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The crystal structure of LiNi0.99 57Fe0.01 PO4 compound has been determined to be orthorhombic by Rietveld refinement method. Temperature dependence of magnetization M shows an anomalous antiferromagnetic behavior. A sudden change in both the magnitude of magnetic hyperfine field and its slope below 11 K suggests that magnetic phase transition related to the spin ordering takes place abruptly. From the result of Mössbauer measurement, it is shown that a strong electric crystalline field of octahedral symmetry including the contribution of spin-orbit coupling and magnetic hyperfine field by space-modulated spin structure is acted to the sites of Fe2+ ions simultaneously at low temperature.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Wx Spin crossover
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Coexistence of inverse and normal magnetocaloric effect in A-site ordered NdBaMn2O6

Q. Zhang, F. Guillou, A. Wahl, Y. Bréard, and V. Hardy

Appl. Phys. Lett. 96, 242506 (2010); http://dx.doi.org/10.1063/1.3453657 (3 pages) | Cited 5 times

Online Publication Date: 15 June 2010

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NdBaMn2O6 exhibits a sequence of two following magnetic transitions: a second-order paramagnetic-ferromagnetic transition at TC = 290 K, followed by a first-order ferromagnetic-antiferromagnetic transition around TN = 210 K, leading to normal and inverse magnetocaloric effects (MCE), respectively. For ΔB = 5 T, the combined |−ΔSMmax| around TC and TN is found to be 2.5 J/kg K and 1.4 J/kgK, respectively. Moreover, the presence of these two −ΔSM peaks spanning over a broad range of temperature leads to a remarkably wide working temperature region, yielding a significant performance in terms of refrigerant efficiency. The present study demonstrates that adjusting the degree of A-site cation ordering in perovskite oxides is an efficient strategy to induce room-temperature MCE.
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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.)

The role of anomalous Hall effect in diluted magnetic semiconductors and oxides

H. S. Hsu, C. P. Lin, S. J. Sun, and H. Chou

Appl. Phys. Lett. 96, 242507 (2010); http://dx.doi.org/10.1063/1.3431294 (3 pages) | Cited 3 times

Online Publication Date: 17 June 2010

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A serious debate has arisen in the development of spintronics regarding contradictory findings on whether or not anomalous Hall effect (AHE) represents the spin polarization nature of carriers in diluted magnetic semiconductors (DMS) and oxides (DMO). Based on our results and on the common AHE characteristics of others reports, here we suggest that only those AHEs for DMSs or DMO which match quantitatively with the magnetic hysteresis loop and which follow the 1.6 scaling relation represent the spin polarization nature of carriers. However, these criteria cannot be used to determine the percentage of magnetic precipitation or of the spin polarized current.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport
81.30.Mh Solid-phase precipitation

Coexistence of sign reversal of both magnetization and exchange bias field in the core-shell type La0.2Ce0.8CrO3 nanoparticles

P. K. Manna, S. M. Yusuf, R. Shukla, and A. K. Tyagi

Appl. Phys. Lett. 96, 242508 (2010); http://dx.doi.org/10.1063/1.3453530 (3 pages) | Cited 11 times

Online Publication Date: 18 June 2010

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We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias field in the La0.2Ce0.8CrO3 nanoparticles. From the high resolution transmission electron microscopy image, and field dependence of thermoremanent and isothermoremanent magnetization measurements, the nanoparticles are found to be of core-shell nature. The core-shell configuration with an antiferromagnetic core of the Cr3+ and Ce3+ spins and a disordered shell with the uncompensated spins, explains the sign reversal of both magnetization and exchange bias field. The present study shows an excellent way of tuning the sign of both magnetization and exchange bias field in a single magnetic system.
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75.60.Jk Magnetization reversal mechanisms
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.75.-c Magnetic properties of nanostructures

Out-of-plane magnetic patterning on austenitic stainless steels using plasma nitriding

E. Menéndez, J.-C. Stinville, C. Tromas, C. Templier, P. Villechaise, J.-P. Rivière, M. Drouet, A. Martinavičius, G. Abrasonis, J. Fassbender, M. D. Baró, J. Sort, and J. Nogués

Appl. Phys. Lett. 96, 242509 (2010); http://dx.doi.org/10.1063/1.3453567 (3 pages) | Cited 3 times

Online Publication Date: 18 June 2010

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A correlation between the grain orientation and the out-of-plane magnetic properties of nitrogen-enriched polycrystalline austenitic stainless steel surface is performed. Due to the competition between the magnetocrystalline anisotropy, the exchange and dipolar interactions, and the residual stresses induced by nitriding, the resulting effective magnetic easy-axis can lay along unusual directions. It is also demonstrated that, by choosing an appropriate stainless steel texturing, arrays of ferromagnetic structures with out-of-plane magnetization, embedded in a paramagnetic matrix, can be produced by local plasma nitriding through shadow masks.
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75.70.Rf Surface magnetism
75.50.Bb Fe and its alloys
68.35.bd Metals and alloys
68.35.Gy Mechanical properties; surface strains
75.30.Et Exchange and superexchange interactions
52.77.-j Plasma applications
75.30.Gw Magnetic anisotropy
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
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Thermodynamic analysis of moisture absorption phenomena in high-permittivity oxides as gate dielectrics of advanced complementary-metal-oxide-semiconductor devices

Yi Zhao, Koji Kita, and Akira Toriumi

Appl. Phys. Lett. 96, 242901 (2010); http://dx.doi.org/10.1063/1.3455110 (3 pages) | Cited 4 times

Online Publication Date: 15 June 2010

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The moisture absorption phenomena in high-permittivity (k) oxides were analyzed from the view point of the thermodynamic process. The Gibbs free energy change (ΔG) in the moisture absorption reactions were calculated with the thermodynamic data of oxides, water (H2O), and hydroxides. It was found from the calculation results that the moisture absorption is a common phenomenon in high-k oxides, especially in rare earth oxides. The results also show that lanthanum oxide (La2O3) has the largest moisture-absorption-reaction speed among main candidates for high-k gate oxides. Doping a second oxide could be a direct and effective method to enhance the moisture resistance of La2O3 films.
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77.55.D- High-permittivity gate dielectric films
77.22.Ch Permittivity (dielectric function)
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Domain wall contributions in Pb(Zr,Ti)O3 ceramics at morphotropic phase boundary: A study of dielectric dispersion

Li Jin (靳立), Viktor Porokhonskyy, and Dragan Damjanovic

Appl. Phys. Lett. 96, 242902 (2010); http://dx.doi.org/10.1063/1.3455328 (3 pages) | Cited 7 times

Online Publication Date: 16 June 2010

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The dielectric properties of undoped, Nb-, and Fe-doped Pb(Zr,Ti)O3 ceramics with composition near morphotropic phase boundary were investigated in the frequency range from 1 MHz to 20.2 GHz at room temperature. Temperature dependences of dielectric permittivity ε′ and loss ε″ are measured at 100 kHz from 50 to 300 K and around 13.4 GHz from 100 to 300 K. These measurements permit estimation of the upper limit of the intrinsic permittivity and lower limit of the extrinsic contributions to the permittivity as a function of temperature. The extrinsic contributions account for more than 50% of the quasistatic dielectric permittivity in studied samples.
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77.80.Dj Domain structure; hysteresis
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.84.Cg PZT ceramics and other titanates

Electrical properties of monodispersed detonation nanodiamonds

Aysha Chaudhary, Joseph O. Welch, and Richard B. Jackman

Appl. Phys. Lett. 96, 242903 (2010); http://dx.doi.org/10.1063/1.3446966 (3 pages) | Cited 4 times

Online Publication Date: 17 June 2010

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The electrical properties of monodispersed detonation nanodiamonds (DNDs) have been studied; a resistivity of the order of 1012 Ω/sq has been determined, with only one significant conduction pathway being observed. The dielectric character of the DND particles is also good, with dielectric loss tangent values in the range 0.05–0.5 being recorded. These combined observations suggest DNDs behave in electrical terms similar to thin film diamond, and that electrical applications for DNDs are worthy of pursuit. Since a simple room temperature sonication process has been used for their deposition, coating a wide-range of three-dimensional substrate materials will be possible. A limitation on the electrical use the monodispersed DNDs, at least in the untreated, as-deposited from solution form used here, is the catastrophic loss of diamond-like character at temperatures above 400 °C.
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73.63.Bd Nanocrystalline materials
77.22.Gm Dielectric loss and relaxation

Enhancement of ferroelectricity in Cr-doped Ho2Ti2O7

X. W. Dong, S. Dong, K. F. Wang, J. G. Wan, and J.-M. Liu

Appl. Phys. Lett. 96, 242904 (2010); http://dx.doi.org/10.1063/1.3455100 (3 pages) | Cited 1 time

Online Publication Date: 18 June 2010

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A series of polycrystalline pyrochlore rare-earth titanate Ho2−xCrxTi2O7 are synthesized in order to enhance the ferroelectricity of pyrochlore Ho2Ti2O7. A giant enhancement of polarization P from 0.54 μC/m2 at x = 0 up to ∼ 660 μC/m2 at x = 0.4 is obtained, accompanied with an increment of ferroelectric transition point Tc from Tc ∼ 60 K up to Tc ∼ 140 K. A magnetic anomaly at Tc ∼ 140 K together with the polarization response to magnetic field is identified, implying the multiferroic effect in Ho2−xCrxTi2O7.
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77.80.B- Phase transitions and Curie point
75.85.+t Magnetoelectric effects, multiferroics
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Optical detection of plasmonic and interband excitations in 1-nm-wide indium atomic wires

H. V. Chung, C. J. Kubber, G. Han, S. Rigamonti, D. Sanchez-Portal, D. Enders, A. Pucci, and T. Nagao

Appl. Phys. Lett. 96, 243101 (2010); http://dx.doi.org/10.1063/1.3451461 (3 pages) | Cited 5 times

Online Publication Date: 14 June 2010

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Infrared spectroscopy is demonstrated to sensitively detect electronic excitations in 1-nm-wide wires made of indium. The polarization-dependent spectra measured at room temperature show a strong broadband plasmonic absorption feature in the direction parallel to the wires, while in the perpendicular direction the wires stay nearly transparent in the same spectral range. At 88 K the wires do not show this broadband absorption anymore, but instead, several interband-transition features arise for both polarizations, in agreement to the gap opening of the metal-to-insulator transition as known for this one-dimensional structure.
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78.67.Uh Nanowires
78.30.Er Solid metals and alloys
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.30.+h Metal-insulator transitions and other electronic transitions

Temperature dependence of optical anisotropy of birefringent porous silicon

Kohei Nishida, Minoru Fujii, Shinji Hayashi, and Joachim Diener

Appl. Phys. Lett. 96, 243102 (2010); http://dx.doi.org/10.1063/1.3453449 (3 pages) | Cited 3 times

Online Publication Date: 14 June 2010

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Temperature dependence of the in-plane optical anisotropy of birefringent porous Si produced from a (110) Si wafer is studied. The anisotropy of refractive indices in the [001] and [1math0] directions increased about 0.3% when the temperature rose from 30 to 100 °C. The effective medium approximation could reproduce the experimental result in the low temperature range, while discrepancy appeared at high temperatures. The discrepancy suggests that the structural anisotropy of porous Si starts to relax at relatively low temperatures.
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78.20.Fm Birefringence
61.43.Gt Powders, porous materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Db Elemental semiconductors and insulators

Near-field recording technique for high-resolution fluorescent imaging

C. Moriguchi, W. Inami, C. Egami, Y. Kawata, S. Terakawa, M. Tsuchimori, and O. Watanabe

Appl. Phys. Lett. 96, 243103 (2010); http://dx.doi.org/10.1063/1.3455095 (3 pages) | Cited 1 time

Online Publication Date: 15 June 2010

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We present near-field fluorescent imaging with high resolution using a near-field recording technique. In this technique, optical intensity distribution localized near specimens is recorded as the surface topographic distribution of a photosensitive film. Because the technique does not require the scanning probes for detecting light, it is possible to observe living biological specimens. Fluorescence imaging is one of important tools in investigations of cell structures and functions in biology. We combined near-field recording technique with fluorescence imaging and demonstrated the observations of fluorescent particles beyond the diffraction limit.
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87.64.mt Near-field scanning
07.79.Fc Near-field scanning optical microscopes
87.16.-b Subcellular structure and processes

Self-organized phase segregation between inorganic nanocrystals and PC61BM for hybrid high-efficiency bulk heterojunction photovoltaic cells

Sai-Wing Tsang, Huiying Fu, Jianying Ouyang, Yanguang Zhang, Kui Yu, Jianping Lu, and Ye Tao

Appl. Phys. Lett. 96, 243104 (2010); http://dx.doi.org/10.1063/1.3454923 (3 pages) | Cited 12 times

Online Publication Date: 16 June 2010

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We demonstrate a simple approach to generate phase segregation between colloidal PbS nanocrystals (NCs) and organic [6,6]-phenyl C61 butyric acid methyl ester (PC61BM). Continuous vertical phase segregation is observed in cross-linked composite films of NCs and PC61BM. Hybrid bulk heterojunction photovoltaic cells fabricated with the phase segreated composite layer have achieved the state-of-art power conversion efficiency of 3.7% under one sun of simulated Air Mass 1.5 Global solar irradiation. The presented method can be generally applied in other NC/organic systems for the development of hybrid heterojunction photovoltaic cells.
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88.40.H- Solar cells (photovoltaics)
64.75.Xc Phase separation and segregation in colloidal systems
84.60.Jt Photoelectric conversion

A surface diffusion model for Dip Pen Nanolithography line writing

Sourabh K. Saha and Martin L. Culpepper

Appl. Phys. Lett. 96, 243105 (2010); http://dx.doi.org/10.1063/1.3454777 (3 pages) | Cited 3 times

Online Publication Date: 16 June 2010

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Dip Pen Nanolithography is a direct write process that creates nanoscale dots and lines. Models typically predict dot and line size via assumption of constant ink flow rate from tip to substrate. This is appropriate for dot writing. It is however well-known, though models rarely reflect, that the ink flow rate depends upon writing speed during line writing. Herein, we explain the physical phenomenon that governs line writing and use this to model tip-substrate diffusion in line writing. We accurately predict (i) the increase in flow rate with writing speed and (ii) line width within 12.5%.
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81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
68.35.Fx Diffusion; interface formation

Field assisted sintering of nickel nanoparticles during in situ transmission electron microscopy

Troy B. Holland, Andrew M. Thron, Cecile S. Bonifacio, Amiya K. Mukherjee, and Klaus van Benthem

Appl. Phys. Lett. 96, 243106 (2010); http://dx.doi.org/10.1063/1.3452327 (3 pages)

Online Publication Date: 17 June 2010

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This study reports the in situ transmission electron microscopy (TEM) observation of pressure-less field-assisted sintering of agglomerated nanometric nickel particles. Scanning tunneling microscopy inside the TEM was used to apply an electrical current directly to the powder particles. Electrical testing during the experiment reveals that consolidation occurs in the absence of an external heat source. Neck formation between adjacent particles and attendant increase in local Joule heating causes rapid densification. The results represent a first stepping stone towards achieving a fundamental mechanistic understanding of the atomic-scale processes that enable field-enhanced sintering of conductive nanogranular materials.
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81.07.Bc Nanocrystalline materials
81.07.Wx Nanopowders
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.79.Cz Scanning tunneling microscopes
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