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23 Aug 2010

Volume 97, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 081901 (2010); http://dx.doi.org/10.1063/1.3457448 (3 pages)

Zhaofeng Li, Rongkuo Zhao, Thomas Koschny, Maria Kafesaki, Kamil Boratay Alici, Evrim Colak, Humeyra Caglayan, Ekmel Ozbay, and C. M. Soukoulis
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Effects of release holes on microscale solid–solid phononic crystals

Y. M. Soliman, M. F. Su, Z. C. Leseman, C. M. Reinke, I. El-Kady, and R. H. Olsson, III

Appl. Phys. Lett. 97, 081907 (2010); http://dx.doi.org/10.1063/1.3476354 (3 pages) | Cited 2 times

Online Publication Date: 25 August 2010

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Solid–solid phononic crystals exhibit wider band gaps than those observed with air–solid phononic crystals. For micromachined phononic crystal devices it is advantageous to release the phononic crystal to avoid propagation losses. In a solid–solid phononic crystal operating in the low megahertz range, due to the large lattice constant, it is necessary to place release holes in the center of the inclusions to release devices from the substrate while minimizing the effect the release hole has on the band gap. In this report, we investigate the effect of release holes on phononic band gaps and highlight the need for careful design. It was determined that release holes of radius rair holes/rinclusion = 0.26 can reliably release a phononic crystal membrane composed of W inclusions in SiO2 without significantly compromising the phononic band gap.
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62.65.+k Acoustical properties of solids
07.10.Cm Micromechanical devices and systems
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.66.Fn Inorganic compounds

Optical properties of surface modified polypropylene by plasma immersion ion implantation technique

Sk. Faruque Ahmed, Myoung-Woon Moon, Chansoo Kim, Yong-Jun Jang, Seonghee Han, Jin-Young Choi, Won-Woong Park, and Kwang-Ryeol Lee

Appl. Phys. Lett. 97, 081908 (2010); http://dx.doi.org/10.1063/1.3481417 (3 pages) | Cited 3 times

Online Publication Date: 25 August 2010

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The optical band gap and activation energy of polypropylene (PP) induced by an Ar plasma immersion ion implantation technique were studied in detail. It was revealed that the structural alternation with an increase in polymer chain cross-linking in the ion beam affected layer enhanced the optical properties of PP. The optical band gap, calculated from the transmittance spectra, decreased from 3.44 to 2.85 eV with the Ar plasma ion energy from 10 to 50 keV. The activation energy, determined from the band tail of the transmittance spectra, decreased while the electrical conductivity increased with the Ar plasma ion energy.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.41.+e Polymers, elastomers, and plastics
72.80.Le Polymers; organic compounds (including organic semiconductors)
78.40.Me Organic compounds and polymers
78.30.Jw Organic compounds, polymers
52.77.Dq Plasma-based ion implantation and deposition

Carbon nanotube initiated formation of carbon nanoscrolls

Zhao Zhang and Teng Li

Appl. Phys. Lett. 97, 081909 (2010); http://dx.doi.org/10.1063/1.3479050 (3 pages) | Cited 5 times

Online Publication Date: 26 August 2010

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The unique topology and exceptional properties of carbon nanoscrolls (CNSs) have inspired unconventional nanodevice concepts, yet the fabrication of CNSs remains rather challenging. Using molecular dynamics simulations, we demonstrate the spontaneous formation of a CNS from graphene on a substrate, initiated by a carbon nanotube (CNT). The rolling of graphene into a CNS is modulated by the CNT size, the carbon–carbon interlayer adhesion, and the graphene–substrate interaction. A phase diagram emerging from the simulations can offer quantitative guideline toward a feasible and robust physical approach to fabricating CNSs.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.U- Carbon/carbon-based materials
81.30.Dz Phase diagrams of other materials
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Optical spectroscopy of cubic GaN in nanowires

J. Renard, G. Tourbot, D. Sam-Giao, C. Bougerol, B. Daudin, and B. Gayral

Appl. Phys. Lett. 97, 081910 (2010); http://dx.doi.org/10.1063/1.3478004 (3 pages) | Cited 4 times

Online Publication Date: 26 August 2010

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We show that highly homogeneous cubic GaN can be grown by plasma-assisted molecular beam epitaxy on wurtzite GaN nanowires. The line width of the donor bound exciton is below 3 meV and can reach 1.6 meV in the best parts of the studied sample. This allows to perform a detailed spectroscopy of cubic GaN, and, in particular, to determine the precise spectral positions of the donor bound exciton, the fundamental free exciton and the split-off exciton in a photoluminescence experiment.
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78.67.Uh Nanowires
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
52.77.Dq Plasma-based ion implantation and deposition

Thermodynamic model for heterogeneous bubble nucleation in a temperature gradient

Di Wu, Yuan-Yuan Duan, and Zhen Yang

Appl. Phys. Lett. 97, 081911 (2010); http://dx.doi.org/10.1063/1.3483191 (2 pages) | Cited 3 times

Online Publication Date: 26 August 2010

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A thermodynamic model for heterogeneous bubble nucleation was developed to include the effect of the fluid temperature gradient next to a heated wall. An increase of the wall temperature gradient (heat flux) is shown to suppress bubble nucleation or increase the superheat needed for nucleation. Bubble nucleation is completely suppressed above a critical temperature gradient. The onset of nucleate boiling is shown to be related to the intersection of the qw″−Tw curve of the boiling system and the qw,c″−Tw curve of the fluid. The theoretical predictions agree with experimental results.
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65.20.De General theory of thermodynamic properties of liquids, including computer simulation
47.55.dp Cavitation and boiling
64.60.qe General theory and computer simulations of nucleation
64.70.fh Boiling and bubble dynamics
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Influence of electron-electron scattering on transport characteristics in monolayer graphene

X. Li, E. A. Barry, J. M. Zavada, M. Buongiorno Nardelli, and K. W. Kim

Appl. Phys. Lett. 97, 082101 (2010); http://dx.doi.org/10.1063/1.3483612 (3 pages) | Cited 6 times

Online Publication Date: 23 August 2010

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The influence of electron-electron scattering on the distribution function and transport characteristics of intrinsic monolayer graphene is investigated via an ensemble Monte Carlo simulation. Due to the linear dispersion relation in the vicinity of the Dirac points, it is found that pair-wise collisions in graphene do not conserve the ensemble average velocity in contrast to conventional semiconductors with parabolic energy bands. Numerical results indicate that electron-electron scattering can lead to a decrease in the low field mobility by more than a factor of 2 for moderate electron densities. The corresponding degradation in the saturation velocity is more modest at around 15%. At high densities, the impact gradually diminishes due to increased degeneracy.
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72.80.Vp Electronic transport in graphene
72.20.Fr Low-field transport and mobility; piezoresistance
73.22.Pr Electronic structure of graphene

High temperature electrical conduction in nanoscale hafnia films under varying oxygen partial pressure

Changhyun Ko, Michael Shandalov, Paul C. McIntyre, and Shriram Ramanathan

Appl. Phys. Lett. 97, 082102 (2010); http://dx.doi.org/10.1063/1.3482940 (3 pages) | Cited 3 times

Online Publication Date: 23 August 2010

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Point defect equilibration in nanocrystalline hafnium oxide thin films in the monoclinic (m-HfO2) phase was studied by electrochemical measurements performed under varying temperature and oxygen partial pressure (PO2) on films of 35–63 nm thickness on single crystal MgO and Al2O3 substrates. The conductance varied as (PO2)n, where n is the in the range ∼ +1/11 to ∼ +1/14, at high PO2. The increasing conductance with PO2 suggests that the electronic conduction in the HfO2 films is p-type and oxygen interstitials or hafnium vacancies, rather than oxygen vacancies, could be dominant charged point defects in nanocrystalline, undoped m-HfO2 films.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.D- High-permittivity gate dielectric films
73.63.Bd Nanocrystalline materials
61.72.jd Vacancies

Tuning single GaAs quantum dots in resonance with a rubidium vapor

N. Akopian, U. Perinetti, L. Wang, A. Rastelli, O. G. Schmidt, and V. Zwiller

Appl. Phys. Lett. 97, 082103 (2010); http://dx.doi.org/10.1063/1.3478232 (3 pages) | Cited 4 times

Online Publication Date: 23 August 2010

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We study single GaAs quantum dots with optical transitions that can be brought into resonance with the widely used D2 transitions of rubidium atoms. We achieve resonance by Zeeman or Stark shifting the quantum dot levels. We discuss an energy stabilization scheme based on the absorption of quantum dot photoluminescence in a rubidium vapor. This offers a scalable means to counteract slow spectral diffusion in quantum dots.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects
78.20.Ls Magneto-optical effects

Interface-controlled layer exchange in metal-induced crystallization of germanium thin films

Shu Hu (胡澍), Ann F. Marshall, and Paul C. McIntyre

Appl. Phys. Lett. 97, 082104 (2010); http://dx.doi.org/10.1063/1.3480600 (3 pages) | Cited 7 times

Online Publication Date: 24 August 2010

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Low-temperature synthesis of polycrystalline germanium (poly-Ge) thin films is of great interest in thin-film photovoltaic and electronics applications. We demonstrate metal (Al)-induced crystallization to form poly-Ge thin films on both glass and polymer substrates at temperatures as low as 200 °C. An interfacial diffusion control layer, intentionally interposed between the Al and the underlying amorphous Ge (a-Ge) layer, is found to achieve layer exchange while suppressing uncontrolled Ge crystallization within the bilayer samples. Germanium thin films with micron-size grains and (111)-preferred orientation are prepared by controlled Ge nucleation and Ge lateral overgrowth of Al during a-Ge crystallization.
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68.55.ag Semiconductors
64.70.dg Crystallization of specific substances
64.60.Q- Nucleation

A nanoscale Ti/GaAs metal-semiconductor hybrid sensor for room temperature light detection

A. K. M. Newaz, W.-J. Chang, K. D. Wallace, L. C. Edge, S. A. Wickline, R. Bashir, A. M. Gilbertson, L. F. Cohen, and S. A. Solin

Appl. Phys. Lett. 97, 082105 (2010); http://dx.doi.org/10.1063/1.3480611 (3 pages) | Cited 1 time

Online Publication Date: 24 August 2010

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We report an individually addressable Ti/GaAs metal-semiconductor hybrid optical nanosensor with positive photoresistance and a sensitivity that increases as the device dimensions shrink. The underlying physics relates to the crossover from ballistic to diffusive transport of the photoinduced carriers and the geometric enhancement of the effect associated with a Schottky-barrier-coupled parallel metal shunt layer. For a 250 nm device under 633 nm illumination we observe a specific detectivity of D∗ = 5.06×1011 cm √Hz/W with a dynamic response of 40 dB.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.30.+y Surface double layers, Schottky barriers, and work functions

Gate controlled magnetoresistance in a silicon metal-oxide-semiconductor field-effect-transistor

C. Ciccarelli, B. G. Park, S. Ogawa, A. J. Ferguson, and J. Wunderlich

Appl. Phys. Lett. 97, 082106 (2010); http://dx.doi.org/10.1063/1.3475771 (3 pages) | Cited 4 times

Online Publication Date: 25 August 2010

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We present a study of the magnetoresistance (MR) of a Si metal-oxide-semiconductor field-effect-transistor (MOSFET) at the break-down regime when a magnetic field is applied perpendicular to the plane of the device. We have identified two different regimes where we observe a large and gate-voltage dependent MR. We suggest two different mechanisms which can explain the observed high MR. Moreover, we have studied how the MR of the MOSFET scales with the dimensions of the channel for gate voltages below the threshold. We observed a decrease in the MR by two orders of magnitude by reducing the dimensions of the channel from 50×280 μm2 to 5×5 μm2.
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85.30.Tv Field effect devices

Microwave induced zero-conductance state in a Corbino geometry two-dimensional electron gas with capacitive contacts

A. A. Bykov, I. V. Marchishin, A. V. Goran, and D. V. Dmitriev

Appl. Phys. Lett. 97, 082107 (2010); http://dx.doi.org/10.1063/1.3483765 (3 pages) | Cited 1 time

Online Publication Date: 26 August 2010

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Microwave induced photoconductivity of a two-dimensional electron gas in selectively doped GaAs/AlAs heterostructures has been studied using the Corbino geometry with capacitive contacts at a temperature T = 1.6 K and magnetic field B up to 0.5 T. Zero-conductance states have been observed in the samples under study subject to microwave radiation, similarly to the samples with Ohmic contacts. It has been shown that Ohmic contacts do not play a significant role for observation of zero-conductance states induced by microwave radiation.
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81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.40.+w Photoconduction and photovoltaic effects
72.20.My Galvanomagnetic and other magnetotransport effects
61.82.Fk Semiconductors

Extremely low surface recombination velocities on crystalline silicon wafers realized by catalytic chemical vapor deposited SiNx/a-Si stacked passivation layers

Koichi Koyama, Keisuke Ohdaira, and Hideki Matsumura

Appl. Phys. Lett. 97, 082108 (2010); http://dx.doi.org/10.1063/1.3483853 (3 pages) | Cited 7 times

Online Publication Date: 26 August 2010

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Catalytic chemical vapor deposition (Cat-CVD), also called hot-wire CVD, yields silicon-nitride/amorphous-silicon (SiNx/a-Si) stacked layers with remarkably low surface recombination velocities (SRVs) of lower than 1.5 cm/s for n-type crystalline Si (c-Si) wafers, and lower than 9.0 cm/s for p-type wafers. The temperature throughout the formation of stacked layers is lower than 250 °C. The usage of a-Si films significantly enhances the effective carrier lifetime of c-Si wafers, and SiNx films are also essential for reducing SRVs to such low levels.
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73.25.+i Surface conductivity and carrier phenomena
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.Rv Passivation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Cy Elemental semiconductors
68.55.ag Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

The effect of deposition power on the electrical properties of Al-doped zinc oxide thin films

B. S. Chun, H. C. Wu, M. Abid, I. C. Chu, S. Serrano-Guisan, I. V. Shvets, and Daniel. S. Choi

Appl. Phys. Lett. 97, 082109 (2010); http://dx.doi.org/10.1063/1.3483232 (3 pages) | Cited 8 times

Online Publication Date: 27 August 2010

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We investigated the effect on the electronic properties of aluminum (Al)-zinc oxide (ZnO) films by modulating the radio frequency sputtering power. Our experimental results show that increasing the sputtering power increases the Al doping concentration, decreases the resistivity, and also shifts the Zn 2p and O 1s to higher binding energy states. Our local-density approximation (LDA) and LDA+U calculations show that the shift in higher binding energy and resistivity decrease are due to an enhancement of the O 2p–Zn 3d coupling and the modification of the Zn 4s–O 2p interaction in ZnO induced by Al doping.
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73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
81.15.Cd Deposition by sputtering
81.05.Dz II-VI semiconductors
71.20.Nr Semiconductor compounds

Density of trap states measured by photon probe into ZnO based thin-film transistors

Kimoon Lee, Gunwoo Ko, Gun Hwan Lee, Gi bok Han, Myung M. Sung, Tae Woo Ha, Jae Hoon Kim, and Seongil Im

Appl. Phys. Lett. 97, 082110 (2010); http://dx.doi.org/10.1063/1.3483763 (3 pages) | Cited 6 times

Online Publication Date: 27 August 2010

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We report on photo-excited trap-charge-collection spectroscopy, contrived to measure the density of deep-level traps near channel/dielectric interface in a working ZnO based thin-film transistor as a function of photon probe energy. Free charges trapped at a certain energy level are liberated by the correspondingly energetic photons and then electrically collected at the source/drain electrodes. During this photo-electric process, the threshold voltage of TFT shifts and its magnitude provides the density-of-state information of charge traps. In the present work, we directly characterized the density-of-state of ZnO based thin-film transistors with polymer-oxide double dielectrics after evaluating their gate stabilities.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ga II-VI semiconductors
71.55.Gs II-VI semiconductors

Electroluminescence from ZnO nanoflowers/GaN thin film p-n heterojunction

Jaehui Ahn, Michael A. Mastro, Jennifer Hite, Charles R. Eddy, Jr., and Jihyun Kim

Appl. Phys. Lett. 97, 082111 (2010); http://dx.doi.org/10.1063/1.3481415 (3 pages) | Cited 4 times

Online Publication Date: 27 August 2010

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Dielectrophoretic force was employed to position ZnO nanoflowers on a p-type GaN thin film prepatterned with Ti/Al/Ni/Au n-type and Ni/Au p-type contact metallizations. Analytical and finite element calculations were employed to determine the optimal alternating current frequency to attract the randomly dispersed ZnO nanoflowers to the n-type contact located on but isolated from the p-GaN thin film. The n-type ZnO nanoflower/p-type GaN thin film heterojunction displayed rectifying current-voltage behavior characteristic of a pristine p-n junction diode and emitted violet light under forward bias above 4.7–5.5 V.
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85.30.Kk Junction diodes
82.45.-h Electrochemistry and electrophoresis
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Mobility and saturation velocity in graphene on SiO2

Vincent E. Dorgan, Myung-Ho Bae, and Eric Pop

Appl. Phys. Lett. 97, 082112 (2010); http://dx.doi.org/10.1063/1.3483130 (3 pages) | Cited 22 times

Online Publication Date: 27 August 2010

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We examine mobility and saturation velocity in graphene on SiO2 above room temperature (300–500 K) and at high fields ( ∼ 1 V/μm). Data are analyzed with practical models including gated carriers, thermal generation, “puddle” charge, and Joule heating. Both mobility and saturation velocity decrease with rising temperature above 300 K, and with rising carrier density above 2×1012 cm−2. Saturation velocity is >3×107 cm/s at low carrier density, and remains greater than in Si up to 1.2×1013 cm−2. Transport appears primarily limited by the SiO2 substrate but results suggest intrinsic graphene saturation velocity could be more than twice that observed here.
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61.48.Gh Structure of graphene
81.05.ue Graphene
72.80.Vp Electronic transport in graphene
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Exchange coupled composite bit patterned media

P. Krone, D. Makarov, T. Schrefl, and M. Albrecht

Appl. Phys. Lett. 97, 082501 (2010); http://dx.doi.org/10.1063/1.3481668 (3 pages) | Cited 11 times

Online Publication Date: 24 August 2010

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A micromagnetic study on the magnetization reversal in bit patterned media (BPM) with each bit consisting of an exchange coupled composite (ECC) layer stack is presented. The simulations reveal superior magnetic properties of the combined ECC/BPM scheme, in particular for graded media, using uncorrelated distributions of magnetic anisotropy values in order to lower the switching field while keeping a high thermal stability of the media. In this study, a route for narrowing the switching field distribution of the bit array is provided as well, which is vital for the applicability of the BPM concept in magnetic data storage.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.78.Cd Micromagnetic simulations
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy

Growth of superconducting Sr2RuO4 thin films

Y. Krockenberger, M. Uchida, K. S. Takahashi, M. Nakamura, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 97, 082502 (2010); http://dx.doi.org/10.1063/1.3481363 (3 pages) | Cited 3 times

Online Publication Date: 26 August 2010

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Sr2RuO4 is a superconductor with a low transition temperature (Tc ∼ 1 K), but has a unique character of p-wave symmetry of the order parameter, demanding epitaxial thin films for Josephson junction studies. We have grown c-axis oriented epitaxial films by a pulsed laser deposition technique on (001) surfaces of (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 substrates. Careful tuning of growth conditions yielded in a layer-by-layer growth of high crystallinity films. The films show a residual resistivity ratio (ρ300 K/ρ2 K) as large as 82 and a superconducting transition with a zero resistivity at 0.6 K.
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81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials
74.70.Pq Ruthenates
74.25.fc Electric and thermal conductivity
74.78.-w Superconducting films and low-dimensional structures
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
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The effect of graphite surface condition on the composition of Al2O3 by atomic layer deposition

A. Pirkle, S. McDonnell, B. Lee, J. Kim, L. Colombo, and R. M. Wallace

Appl. Phys. Lett. 97, 082901 (2010); http://dx.doi.org/10.1063/1.3479908 (3 pages) | Cited 8 times

Online Publication Date: 24 August 2010

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We present a study of the nucleation of atomic layer deposition of Al2O3 on highly oriented pyrolytic graphite (HOPG) using trimethlyaluminum (TMA) with ozone as the oxidant (TMA/O3). In situ x-ray photoelectron spectroscopy (XPS) is used to study TMA/O3 depositions on HOPG. We examine the dependence of TMA/O3 nucleation on deposition temperature and characterize the morphology and uniformity of deposited films by ex situ atomic force microscopy. The impact of several predeposition surface treatments of the graphite surface condition is discussed, particularly with regard to the presence of adsorbed atmospheric contamination.
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81.65.-b Surface treatments
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.43.Mn Adsorption kinetics

Oxygen migration at Pt/HfO2/Pt interface under bias operation

T. Nagata, M. Haemori, Y. Yamashita, H. Yoshikawa, Y. Iwashita, K. Kobayashi, and T. Chikyow

Appl. Phys. Lett. 97, 082902 (2010); http://dx.doi.org/10.1063/1.3483756 (3 pages) | Cited 9 times

Online Publication Date: 26 August 2010

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The interfacial electronic states of a Pt/HfO2/Pt diode were investigated by using hard x-ray photoelectron spectroscopy under bias operation. The application of a forward bias to the Pt/HfO2/Pt diode increased the Pt–O bonding peak, providing evidence of Pt electrode oxidization and oxygen vacancy formation around the Pt/HfO2 interface. Under a reverse bias, hafnium was drawn to the Pt electrode, where it took part in Hf–Pt bonding. We achieved the direct observation of oxygen migration at a Pt/HfO2 interface under device operation, which is the key to controlling the electrical properties of metals on oxides.
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85.30.Tv Field effect devices
73.40.Rw Metal-insulator-metal structures

Large pyroelectric effect in Fe-doped lithium niobate induced by a high-power short-pulse laser

Kenji Kitamura, Hideki Hatano, Shunji Takekawa, Daniel Schütze, and Masakazu Aono

Appl. Phys. Lett. 97, 082903 (2010); http://dx.doi.org/10.1063/1.3481380 (3 pages) | Cited 4 times

Online Publication Date: 27 August 2010

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We demonstrate the pyroelectric effect induced by a short pulse laser with an intensity up to 6 MW/cm2 which is used to heat the Fe-doped Lithium niobate crystal. 0.2 °C temperature rise induced by a 10 ns laser pulse causes a very large current peak (up to 25 mA) since the rate of temperature rise is extremely large comparing with that induced by using an ordinary heater. On the other hand, the pyroelectric current during the cooling is much smaller because of the slow cooling rate by thermal conduction.
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77.70.+a Pyroelectric and electrocaloric effects
61.72.up Other materials
77.80.-e Ferroelectricity and antiferroelectricity
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Selective electroless coating of palladium nanoparticles on metallic single-walled carbon nanotube

Yiyu Feng, Peng Lv, Xuequan Zhang, Yu Li, and Wei Feng

Appl. Phys. Lett. 97, 083101 (2010); http://dx.doi.org/10.1063/1.3483615 (3 pages) | Cited 2 times

Online Publication Date: 23 August 2010

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The selective electroless coating of palladium (Pd) nanoparticles on metallic single-walled carbon nanotube (SWNT) was studied. The remarkable increase in conductivity of SWNT/Pd films up to fourfold higher than pure SWNT was due to p-type doping and Ohmic contact. Metallic behavior of SWNT/Pd-Field effect transistor (on/off ratio = 1.2) was attributed to more hole carriers and no electrostatic barrier between nanotube and Pd. G-band and radial breathing mode in Raman indicates a definitive increase in the proportion of metallic SWNT. Results indicate Pd are selectively coated on metallic SWNT with more negative potential allowing for the electroless Pd2+ reduction.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.65.-b Surface treatments
68.55.A- Nucleation and growth
73.40.Ns Metal-nonmetal contacts
73.61.-r Electrical properties of specific thin films
85.30.Tv Field effect devices

Effects of surface chemistry on thermal conductance at aluminum–diamond interfaces

Kimberlee C. Collins, Shuo Chen, and Gang Chen

Appl. Phys. Lett. 97, 083102 (2010); http://dx.doi.org/10.1063/1.3480413 (3 pages) | Cited 12 times

Online Publication Date: 23 August 2010

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Synthetic diamond has potential as a heat spreading material in small-scale devices. Here, we report thermal conductance values at interfaces between aluminum and diamond with various surface terminations over a range of temperatures from 88 to 300 K. We find that conductance at oxygenated diamond interfaces is roughly four times higher than at hydrogen-treated diamond interfaces. Furthermore, we find that Al grain structure formation is not strongly dependent on diamond surface chemistry, which suggests that interfacial bonding influences thermal conductance. The results reported here will be useful for device design and for advancing models of interfacial heat flow.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.-y Defects and impurities in crystals; microstructure

Acoustic phonon scattering in Bi2Te3/Sb2Te3 superlattices

Yaguo Wang, Carl Liebig, Xianfan Xu, and Rama Venkatasubramanian

Appl. Phys. Lett. 97, 083103 (2010); http://dx.doi.org/10.1063/1.3483767 (3 pages) | Cited 7 times

Online Publication Date: 24 August 2010

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Ultrafast time-resolved measurements were conducted to investigate long-wavelength acoustic phonon scattering and velocity reduction in Bi2Te3/Sb2Te3 superlattices. We show that both these phenomena suppress heat transfer process, with the phonon scattering contributing more in differentiating the lattice thermal conductivities among films with different periods. Measurements of reduction in the acoustic phonon amplitudes support the decrease in the thermal conductivity for certain superlattice periods, which is not predicted by acoustic mismatch theory. This study is a direct measurement of coherent acoustic phonons in superlattices which is of significant interest to thermoelectrics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.65.Cd Superlattices
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