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26 Sep 2011

Volume 99, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 131101 (2011); http://dx.doi.org/10.1063/1.3641907 (3 pages)

Linas Minkevičius, Vincas Tamošiūnas, Irmantas Kašalynas, Dalius Seliuta, Gintaras Valušis, Alvydas Lisauskas, Sebastian Boppel, Hartmut G. Roskos, and Klaus Köhler
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Factorial toughening at microcorrugated metal-ceramic interfaces

Saurabh Garg, Ranganath Teki, Michael W. Lane, and Ganpati Ramanath

Appl. Phys. Lett. 99, 133101 (2011); http://dx.doi.org/10.1063/1.3618670 (3 pages) | Cited 1 time

Online Publication Date: 26 September 2011

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We report 10-fold higher toughness at microcorrugated copper-silica interfaces than their planar counterpart and separate the contributions of adhesion, metal layer plasticity, and debond shielding. While corrugations parallel to the crack path toughen the interface due to debond area increase, orthogonal corrugations result in additional toughening due to debond shielding and shielding-induced plasticity that can be more than twice higher than the shielding effect itself. These insights into the toughening mechanisms at corrugated interfaces should enable the design of high integrity heterointerfaces in a wide variety of micro-/nano-structured thin films and composites.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.fq Plasticity and superplasticity
62.20.mt Cracks
68.35.Ct Interface structure and roughness
81.40.Lm Deformation, plasticity, and creep

Thermoelectric effect in high mobility single layer epitaxial graphene

Xiaosong Wu, Yike Hu, Ming Ruan, Nerasoa K. Madiomanana, Claire Berger, and Walter A. de Heer

Appl. Phys. Lett. 99, 133102 (2011); http://dx.doi.org/10.1063/1.3641424 (3 pages) | Cited 1 time

Online Publication Date: 26 September 2011

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The thermoelectric response of high mobility (∼20 000 cm2/V s at 4 K) single layer epitaxial graphene on silicon carbide substrates has been experimentally investigated. The temperature dependence of the thermopower displays a strong deviation from the Mott relation at a carrier density of 1 × 1012 cm−2, reflecting the importance of the screening effect. In the quantum Hall regime, the amplitude of the thermopower peaks is lower than a quantum value, despite the high mobility of the sample. In addition, a temperature dependence for the amplitude is observed, unexpected by theories. The Nernst signal changes it sign as the magnetic field increases.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.43.-f Quantum Hall effects
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Wp Fullerenes and related materials

Atomistic mechanisms of moisture-induced fracture at copper-silica interfaces

Dandapani Vijayashankar, Hong Zhu, Saurabh Garg, Ranganath Teki, R. Ramprasad, Michael W. Lane, and Ganpati Ramanath

Appl. Phys. Lett. 99, 133103 (2011); http://dx.doi.org/10.1063/1.3622304 (3 pages) | Cited 3 times

Online Publication Date: 26 September 2011

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Tailoring the chemo-mechanical properties of metal-dielectric interfaces is crucial for many applications including nanodevice wiring, packaging, composites, and catalysis. Here, we combine moisture-induced fracture tests, electron spectroscopy, and density functional theory calculations to reveal fracture toughness partitioning and atomistic delamination mechanisms at copper-silica interfaces. Copper plasticity is supported above a threshold work of adhesion and delamination occurs by moisture-induced Cu-O bond scission in Cu-O-Si bridges. These results provide insights into the effects of the nature of metal-oxygen bonding on moisture-induced delamination of metal-dielectric interfaces.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
62.20.mm Fracture
68.35.Gy Mechanical properties; surface strains

Electronic structure of the nitride-like structures formed on platinum and titanium nanoclusters

M. Grishin, A. Gatin, V. Kharitonov, and B. Shub

Appl. Phys. Lett. 99, 133104 (2011); http://dx.doi.org/10.1063/1.3644499 (3 pages)

Online Publication Date: 27 September 2011

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The molecular nitrogen adsorption on single titanium and platinum nanoclusters was investigated by scanning tunneling microscopy and spectroscopy with the “inverted” mode of spectroscopic measurements. Certain physical characteristics of electron structure of surface covered with adsorbed nitrogen were discovered.
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73.22.-f Electronic structure of nanoscale materials and related systems
68.43.Mn Adsorption kinetics
71.20.Gj Other metals and alloys

Enhanced reflection from arrays of silicon based inverted nanocones

Haider Butt, Qing Dai, Ranjith Rajasekharan, Timothy D. Wilkinson, and Gehan A. J. Amaratunga

Appl. Phys. Lett. 99, 133105 (2011); http://dx.doi.org/10.1063/1.3633119 (3 pages) | Cited 1 time

Online Publication Date: 27 September 2011

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We report enhanced reflection displayed by arrays of silicon based inverted nanocones. Theoretical studies suggest that such arrays display enhanced reflection and photonic band gaps within the optical and near infrared regions. Measured results show three to four fold enhancement in reflection and agree well with calculations. Such arrays can be used to enhance infrared reflection in photovoltaic devices which mostly contribute towards heating.
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81.16.-c Methods of micro- and nanofabrication and processing
81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Am Elemental semiconductors and insulators
61.46.-w Structure of nanoscale materials

Ultra-low thermal conductivity of ellipsoidal TiO2 nanoparticle films

Patrick E. Hopkins, Manish Mittal, Leslie M. Phinney, Anne M. Grillet, and Eric M. Furst

Appl. Phys. Lett. 99, 133106 (2011); http://dx.doi.org/10.1063/1.3644987 (3 pages) | Cited 4 times

Online Publication Date: 27 September 2011

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We report on the thermal conductivity of a series of convectively assembled, anisotropic titania (TiO2) nanoparticle films. The TiO2 films are fabricated by flow coating a suspension of ellipsoidal colloidal nanoparticles, resulting in structured films with tailored orientational order. The thermal conductivities depend on nanoparticle orientation and can be less than amorphous TiO2 films due to inter-nanoparticle boundary scattering. This nanoparticle ordering presents a unique method for manipulating the thermal conductivity of nanocomposites.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.60.Wm Other nonelectronic physical properties
81.16.Rf Micro- and nanoscale pattern formation
82.70.Kj Emulsions and suspensions
68.55.aj Insulators

Characterization of channel strain evolution upon the silicidation of recessed source/drain Si1−xGex structures

S.-W. Kim, J.-H. Yoo, S.-M. Koo, D.-H. Ko, and H.-J. Lee

Appl. Phys. Lett. 99, 133107 (2011); http://dx.doi.org/10.1063/1.3633346 (3 pages) | Cited 1 time

Online Publication Date: 27 September 2011

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This letter reports on Ni germanosilicide formation on recessed Si0.82Ge0.18 source/drain structures and its effects on channel strain. A combination of transmission electron microscopy techniques, including nanobeam diffraction, shed some light on a previously unrecognized factor in the channel strain evolution during silicidation: a Ge accumulation layer produced at the bottom of the germanosilicide layer. The formation of such a Ge rich layer added an additional compressive strain to the channel strain upon moderate silicidation, while the contribution of thermal strain arising from the cooling cycle became dominant in an excessively silicided sample, which turned the channel strain into a tensile value.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Frequency response of graphene phonons to heating and compression

X. X. Yang, J. W. Li, Z. F. Zhou, Y. Wang, W. T. Zheng, and Chang Q. Sun

Appl. Phys. Lett. 99, 133108 (2011); http://dx.doi.org/10.1063/1.3645015 (3 pages) | Cited 4 times

Online Publication Date: 27 September 2011

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The thermally softened and the mechanically stiffened graphene phonons have been formulated from the perspective of bond order-length-strength correlation with confirmation of the C–C bond length in the single-layer graphene contracting from 0.154 to 0.125 nm and the binding energy increasing from 0.65 to 1.04 eV. Matching theory to the measured temperature- and pressure-dependent Raman shift has derived that the Debye temperature drops from 2230 to 540 K, the atomic cohesive energy drops from 7.37 to 3.11 eV/atom, and the binding energy density increases from 250 to 320 eV/nm3 compared with the respective quantities of bulk diamond.
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63.22.Rc Phonons in graphene
78.67.Wj Optical properties of graphene
81.05.ue Graphene
78.30.Na Fullerenes and related materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Gh Other heat and thermomechanical treatments

In-plane and tunneling pressure sensors based on graphene/hexagonal boron nitride heterostructures

Yang Xu, Zhendong Guo, Huabin Chen, You Yuan, Jiechao Lou, Xiao Lin, Haiyuan Gao, Hongsheng Chen, and Bin Yu

Appl. Phys. Lett. 99, 133109 (2011); http://dx.doi.org/10.1063/1.3643899 (3 pages) | Cited 10 times

Online Publication Date: 27 September 2011

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An in-plane pressure sensor (IPPS) consisting of graphene sandwiched by hexagonal boron nitride (h-BN) and a tunneling pressure sensor (TPS) consisting of h-BN sandwiched by graphene are demonstrated. The responses as function of external pressure are modeled. The current varies by 3 orders of magnitude as pressure increases from 0 to 5 nN/nm2. The IPPS current is negatively correlated to pressure, whereas TPS current exhibits positive correlation to pressure. The IPPS design is insensitive to the number of wrapping h-BN layers, indicating precise process control is unnecessary. The result paves a viable avenue towards realizing of atomic scale pressure sensors.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Manipulating the spin of single-molecule magnet by thermal spin-transfer torque

Zhengzhong Zhang, Liang Jiang, Ruiqiang Wang, Baigeng Wang, and D. Y. Xing

Appl. Phys. Lett. 99, 133110 (2011); http://dx.doi.org/10.1063/1.3644476 (3 pages) | Cited 5 times

Online Publication Date: 28 September 2011

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We investigate thermally driven electronic transport through a single-molecule magnet (SMM) coupled to a ferromagnetic (FM) lead and a normal-metallic lead. Due to the thermal spin-transfer torque effect, the orientation of the SMM’s spin can be manipulated by temperature bias or gate voltage to be parallel or antiparallel to the FM lead’s magnetization. The present device can be realized by current technologies and has potential application in molecular spintronics or quantum information processing.
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72.15.Jf Thermoelectric and thermomagnetic effects
75.50.Xx Molecular magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Nonlinear electrical properties of carbon nanotube forests

Mikhail E. Kozlov

Appl. Phys. Lett. 99, 133111 (2011); http://dx.doi.org/10.1063/1.3645013 (3 pages) | Cited 1 time

Online Publication Date: 28 September 2011

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Differential conductance of vertically aligned arrays of multi-walled carbon nanotubes (MWNT forests) reveals a zero bias anomaly at room temperature. The anomaly becomes narrower and sharper upon cooling sample down reaching magnitude of 25% of average conductance at 244 K. Further cooling results in decrease of its magnitude that correlates with the slope of temperature dependence of sample’s electrical conductance. The anomaly can be caused by tunneling of charge carriers through nanotube junctions enhanced by temperature gradients induced by measuring currents. Observed phenomenon can be used for the characterization of junction network created by carbon nanotubes in MWNT forests.
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73.63.Fg Nanotubes
73.40.Gk Tunneling

High-responsivity plasmonics-based GaAs metal-semiconductor-metal photodetectors

Ayman Karar, Narottam Das, Chee Leong Tan, Kamal Alameh, Yong Tak Lee, and Fouad Karouta

Appl. Phys. Lett. 99, 133112 (2011); http://dx.doi.org/10.1063/1.3625937 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2011

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We report the experimental characterization of high-responsivity plasmonics-based GaAs metal-semiconductor-metal photodetector (MSM-PD) employing metal nano-gratings. Both the geometry and light absorption near the designed wavelength are theoretically and experimentally investigated. The measured photocurrent enhancement is 4-times in comparison with a conventional single-slit MSM-PD. We observe reduction in the responsivity as the bias voltage increases and the input light polarization varies. Our experimental results demonstrate the feasibility of developing a high-responsivity, low bias-voltage high-speed MSM-PD.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
61.46.-w Structure of nanoscale materials
72.40.+w Photoconduction and photovoltaic effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
73.40.Sx Metal-semiconductor-metal structures

Monolayer graphene film/silicon nanowire array Schottky junction solar cells

Chao Xie, Peng Lv, Biao Nie, Jiansheng Jie, Xiwei Zhang, Zhi Wang, Peng Jiang, Zhizhong Hu, Linbao Luo, Zhifeng Zhu, Li Wang, and Chunyan Wu

Appl. Phys. Lett. 99, 133113 (2011); http://dx.doi.org/10.1063/1.3643473 (3 pages) | Cited 13 times

Online Publication Date: 28 September 2011

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Schottky junction solar cells were constructed by combining the monolayer graphene (MLG) films and the Si nanowire (SiNW) arrays. Pronounced photovoltaic characteristics were investigated for devices with both p-MLG/n-SiNWs and n-MLG/p-SiNWs structures. Due to the balance between light absorption and surface carrier recombination, devices made of SiNW arrays with a medium length showed better performance and could be further improved by enhancing the MLG conductivity via appropriate surface treatment or doping. Eventually, a photoconversion efficiency up to 2.15% is obtained by the means of filling the interspace of SiNW array with graphene suspension.
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88.40.H- Solar cells (photovoltaics)

Scanning capacitance microscopy of ErAs nanoparticles embedded in GaAs pn junctions

K. W. Park, H. P. Nair, A. M. Crook, S. R. Bank, and E. T. Yu

Appl. Phys. Lett. 99, 133114 (2011); http://dx.doi.org/10.1063/1.3644144 (3 pages) | Cited 1 time

Online Publication Date: 29 September 2011

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Scanning capacitance microscopy is used to characterize the electronic properties of ErAs nanoparticles embedded in GaAs pn junctions grown by molecular beam epitaxy. Voltage-dependent capacitance images reveal localized variations in subsurface electronic structure near buried ErAs nanoparticles at lateral length scales of 20-30 nm. Numerical modeling indicates that these variations arise from inhomogeneities in charge modulation due to Fermi level pinning behavior associated with the embedded ErAs nanoparticles. Statistical analysis of image data yields an average particle radius of 6-8 nm—well below the direct resolution limit in scanning capacitance microscopy but discernible via analysis of patterns in nanoscale capacitance images.
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73.63.Bd Nanocrystalline materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Nano epitaxial growth of GaAs on Si (001)

Chao-Wei Hsu, Yung-Feng Chen, and Yan-Kuin Su

Appl. Phys. Lett. 99, 133115 (2011); http://dx.doi.org/10.1063/1.3640226 (3 pages) | Cited 1 time

Online Publication Date: 30 September 2011

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Nano epitaxial growth (NEG) is used to develop GaAs monolithic hetero-epitaxy onto Si (001). For the GaAs grown in a nanopatterned trench with an aspect ratio of 5, the dislocations originally generated at the GaAs/Si interface are mostly isolated by the SiO2 sidewall. Compared with the conventional-planar Si substrate, implementing the NEG technique is able to decrease the dislocation density from about 109 cm−2 to almost zero. It is also confirmed that NEG is capable of confining the dislocations within the GaAs initial epitaxial layer (<100 nm), which meets the requirement of relatively less complicated epitaxial processes.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
61.72.Lk Linear defects: dislocations, disclinations

Metallic-nanoparticle assisted enhanced band-to-band tunneling current

Deblina Sarkar and Kaustav Banerjee

Appl. Phys. Lett. 99, 133116 (2011); http://dx.doi.org/10.1063/1.3633343 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2011

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Metallic nanoparticle assisted band-to-band tunneling is proposed, and the impact of such nanoparticle induced states on the tunneling probability and current is modeled and analyzed. An analytical formula for tunneling probability is derived for the case of constant force, and it is shown that the incorporation of these particles in the forbidden gap can lead to a substantial increase in the tunneling current. The effect of the Fermi-level pinning position on the tunneling current is studied, and the pinning value for obtaining maximum improvement in current is discussed depending on the force conditions. It is also shown that an asymmetric pinning is required to leverage maximum benefits from the insertion of metallic nanoparticles.
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73.40.Gk Tunneling
71.20.Be Transition metals and alloys
02.50.-r Probability theory, stochastic processes, and statistics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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