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25 Feb 2008

Volume 92, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 92, 081101 (2008); http://dx.doi.org/10.1063/1.2883874 (3 pages)

Marcel W. Pruessner, Todd H. Stievater, and William S. Rabinovich
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Dispersion control and slow light in slotted photonic crystal waveguides

A. Di Falco, L. O’Faolain, and T. F. Krauss

Appl. Phys. Lett. 92, 083501 (2008); http://dx.doi.org/10.1063/1.2885072 (3 pages) | Cited 40 times

Online Publication Date: 25 February 2008

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Slotted photonic crystal waveguides combine the ability to confine light in air with the dispersion control available from photonic crystals. Here, we study the dependence of their dispersion properties on geometry, especially the slot width, and demonstrate slow light operation with group indices in excess of 100.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Magnetoelectric nano-Fe3O4/CoFe2O4∥PbZr0.53Ti0.47O3 composite

Shenqiang Ren and Manfred Wuttig

Appl. Phys. Lett. 92, 083502 (2008); http://dx.doi.org/10.1063/1.2841064 (3 pages) | Cited 7 times

Online Publication Date: 26 February 2008

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A new magnetoelectric hybrid device composed of a nanoparticulate magnetostrictive iron oxide-cobalt ferrite film on a piezoelectric lead zirconic titanate crystal serving as both substrate and straining medium is described. Nano-Fe3O4/CoFe2O4 particles, ranging from 5 to 42 nm, were prepared using a variation of the sol-gel method. A small electric field, 5–10 kV cm−1, applied at the coercive field of the nano-Fe3O4/CoFe2O4 component modulates the film magnetization up to 10% of the saturation magnetization of ferrite. At the smallest particle size of 5 nm, the coercive field is as low as 25 Oe and the inverse MEE voltage coefficient is as high as (10.1 V/cm Oe)−1.
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85.80.Jm Magnetoelectric devices
75.80.+q Magnetomechanical effects, magnetostriction
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Hx Magnetic impurity interactions

Fringing field effects on electrical resistivity of semiconductor nanowire-metal contacts

Jun Hu, Yang Liu, C. Z. Ning, Robert Dutton, and Sung-Mo Kang

Appl. Phys. Lett. 92, 083503 (2008); http://dx.doi.org/10.1063/1.2889534 (3 pages) | Cited 13 times

Online Publication Date: 27 February 2008

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Metal contacts play an important role in nanowire devices and are expected to exhibit qualitatively different properties from those of planar contacts due to small contact cross sections. We numerically investigate certain unique properties of nanowire-metal contacts and demonstrate that contact resistivity increases as nanowire radius shrinks. This increase is more significant for nanowire-three-dimensional metal contacts than for nanowire-one-dimensional metal contacts. The underlying cause for this size effect is identified as the strong fringing field effects, which become more significant as temperature decreases. Our simulation provides a more complete understanding of the size effects on nanowire-metal contacts.
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73.63.Rt Nanoscale contacts
73.63.Nm Quantum wires
73.40.Cg Contact resistance, contact potential

Infrared photocurrent response of charge-transfer exciton in polymer bulk heterojunction

Chia-Ming Yang, Pei-Yu Tsai, Sheng-Fu Horng, Kuan-Chen Lee, Shin-Rong Tzeng, Hsin-Fei Meng, Jow-Tsong Shy, and Ching-Fong Shu

Appl. Phys. Lett. 92, 083504 (2008); http://dx.doi.org/10.1063/1.2839397 (3 pages) | Cited 4 times

Online Publication Date: 27 February 2008

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We study the charge-transfer exciton absorption and photocurrent response in solution-processed bulk heterojunction based on poly(3-hexylthiophene) donor and (6,6)-phenyl-C61-butyric acid methyl ester acceptor in the near-infrared wavelength region. While the exciton absorption exists only for wavelength below 650 nm, direct generation of charge-transfer exciton formed between the donor and acceptor extends the absorption wavelength to 950 nm. For films with micrometer thickness, the photon-to-electron conversion efficiency is about 60% at 750 nm wavelength under reverse voltage bias and the photocurrent to dark current ratio is about 8.6 at 900 nm and remains 3.6 even at 1000 nm. Photodetector with high sensitivity covering exclusively the 650–1000 nm near infrared region can therefore be made without a low bandgap material. The charge-transfer exciton absorption coefficient and photocurrent sensitivity depend on the annealing condition which controls the donor-acceptor morphology.
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72.40.+w Photoconduction and photovoltaic effects
78.30.Jw Organic compounds, polymers
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
71.35.-y Excitons and related phenomena

New analysis of electron energy exchange and cooling in semiconductors

M. S. Chung, S. C. Hong, A. Mayer, P. H. Cutler, B. L. Weiss, and N. M. Miskovsky

Appl. Phys. Lett. 92, 083505 (2008); http://dx.doi.org/10.1063/1.2885086 (3 pages) | Cited 4 times

Online Publication Date: 28 February 2008

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Energy exchange Δε is investigated in field emission from semiconductors. For the first time, a formal theory is developed for the replacement process of the injected charge carriers. It leads to analytic expressions for Δε, which exhibit the dependence on field, temperature, and doping concentration in a parametric form. The analytic and numeric results reveal the important feature that Δε is positive for all temperatures. This implies that field emission from semiconductors always produces cooling of an emitter. When Joule heating is included, there is still a net cooling for a wide range of emitted current densities.
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79.70.+q Field emission, ionization, evaporation, and desorption

High temperature resistance of small diameter, metallic single-walled carbon nanotube devices

Alexander A. Kane, Kevin Loutherback, Brett R. Goldsmith, and Philip G. Collins

Appl. Phys. Lett. 92, 083506 (2008); http://dx.doi.org/10.1063/1.2885092 (3 pages) | Cited 2 times

Online Publication Date: 28 February 2008

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The effects of high temperature cycling on the resistance of metallic single-walled carbon nanotube (SWCNT) devices is measured in situ. Individual, small-diameter SWCNTs contacted by palladium or titanium electrodes were measured from room temperature up to 1000 K in ultrahigh vacuum. Upon the first thermal cycling, the device resistances fluctuate and generally decrease. Pd-contacted devices typically become stable by 450 K, whereas Ti-contacted devices require higher treatments above 600 K. Once these temperatures have been exceeded, subsequent thermal cycling has minimal effects. Heat-treated devices exhibit linear temperature dependences, with Pd and Ti contacts producing average temperature coefficients of −3×10−4/K and 1.1×10−3/K, respectively.
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85.35.Kt Nanotube devices
73.40.Cg Contact resistance, contact potential
81.40.Gh Other heat and thermomechanical treatments

Characterization of electrical and structural properties of strained-Si-on-insulator layers

Chel-Jong Choi, Won-Jin Jung, Myung-Sim Jun, Moon-Gyu Jang, Seong-Jae Lee, June Park, Maeng-Je Seong, Myung-Ho Jung, and Won-Ju Cho

Appl. Phys. Lett. 92, 083507 (2008); http://dx.doi.org/10.1063/1.2885726 (3 pages) | Cited 2 times

Online Publication Date: 28 February 2008

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The electrical and structural properties of strained-Si-on-insulator (sSOI) wafers were investigated. The strain, calculated from two-dimensional reciprocal space mapping, was found to be 0.78%, which is comparable to that of fully relaxed Si1−xGex film with Ge concentration of 20.6 at. %. Based on the Raman peak shift combined with measured value of strain, the strain shift coefficient is extracted to be −736 cm−1. The pseudo-metal-oxide-semiconductor field-effect transistor measurements, employed to characterize the electrical properties of sSOI wafers, showed that both electron and hole mobilities are enhanced by strain. The enhancement factor of electron mobility is larger than that of hole mobility.
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85.30.Tv Field effect devices

Strontium and barium iodide high light yield scintillators

Nerine J. Cherepy, Giulia Hull, Alexander D. Drobshoff, Stephen A. Payne, Edgar van Loef, Cody M. Wilson, Kanai S. Shah, Utpal N. Roy, Arnold Burger, Lynn A. Boatner, Woon-Seng Choong, and William W. Moses

Appl. Phys. Lett. 92, 083508 (2008); http://dx.doi.org/10.1063/1.2885728 (3 pages) | Cited 62 times

Online Publication Date: 28 February 2008

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Europium-doped strontium and barium iodide are found to be readily growable by the Bridgman method and to produce high scintillation light yields. SrI2(Eu) emits into the Eu2+ band, centered at 435 nm, with a decay time of 1.2 μs and a light yield of ∼ 90 000 photons/MeV. It offers energy resolution better than 4% full width at half maximum at 662 keV, and exhibits excellent light yield proportionality. BaI2(Eu) produces >30 000 photons/MeV into the Eu2+ band at 420 nm (<1 μs decay). An additional broad impurity-mediated recombination band is present at 550 nm (>3 μs decay), unless high-purity feedstock is used.
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81.10.Fq Growth from melts; zone melting and refining
29.40.Mc Scintillation detectors

Leakage current mechanisms in top-gate nanocrystalline silicon thin film transistors

Hyun Jung Lee, Andrei Sazonov, and Arokia Nathan

Appl. Phys. Lett. 92, 083509 (2008); http://dx.doi.org/10.1063/1.2887882 (3 pages) | Cited 3 times

Online Publication Date: 28 February 2008

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The leakage current in the top-gate nanocrystalline silicon (nc-Si:H) thin film transistors was examined at various temperatures in an attempt to deduce the underlying off-state conduction mechanisms. Under high gate bias, the leakage current can be attributed to the thermal emission of trapped carriers at the midgap grain boundary states at low drain bias, while the behavior is reminiscent of the Poole–Frenkel emission in the drain depletion region at high drain bias. In contrast, Ohmic conduction through the bulk nc-Si:H channel layer seems to be the dominant mechanism of the leakage current under low gate bias.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

Solitary wave propagation in surface stabilized ferroelectric liquid crystal cells

Jang-Kun Song, M. J. Sufin, and J. K. Vij

Appl. Phys. Lett. 92, 083510 (2008); http://dx.doi.org/10.1063/1.2841670 (3 pages) | Cited 1 time

Online Publication Date: 29 February 2008

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Solitary wave propagation in surface stabilized ferroelectric liquid crystal cells controlled by surface anchoring of the alignment layers is investigated for different conditions of alignment on the two opposite surfaces. We show that the critical field Ec, where the speed of the solitary wave becomes zero, is finite for asymmetric alignment on two surfaces. We also show that the polar anchoring energy difference (Δwp) between the alignment layers can be calculated by measuring Ec, and this depends on the rubbing condition and the material of the alignment layer.
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77.80.-e Ferroelectricity and antiferroelectricity
61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions

Betavoltaics using scandium tritide and contact potential difference

Baojun Liu, Kevin P. Chen, Nazir P. Kherani, Stefan Zukotynski, and Armando B. Antoniazzi

Appl. Phys. Lett. 92, 083511 (2008); http://dx.doi.org/10.1063/1.2887879 (3 pages) | Cited 5 times

Online Publication Date: 29 February 2008

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Tritium-powered betavoltaic micropower sources using contact potential difference (CPD) are demonstrated. Thermally stable scandium tritide thin films with a surface activity of 15 mCi/cm2 were used as the beta particle source. The electrical field created by the work function difference between the ScT film and a platinum or copper electrode was used to separate the beta-generated electrical charge carriers. Open circuit voltages of 0.5 and 0.16 V and short circuit current densities of 2.7 and 5.3 nA/cm2 were achieved for gaseous and solid dielectric media-based CPD cells, respectively.
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84.60.-h Direct energy conversion and storage
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