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18 Jul 2011

Volume 99, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 032501 (2011); http://dx.doi.org/10.1063/1.3610947 (3 pages)

G. X. Miao, M. D. Mascaro, C. H. Nam, C. A. Ross, and J. S. Moodera
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Correlation of residual impurity concentration and acceptor electron paramagnetic resonance linewidth in isotopically engineered Si

A. R. Stegner, H. Tezuka, H. Riemann, N. V. Abrosimov, P. Becker, H.-J. Pohl, M. L. W. Thewalt, K. M. Itoh, and M. S. Brandt

Appl. Phys. Lett. 99, 032101 (2011); http://dx.doi.org/10.1063/1.3606548 (3 pages)

Online Publication Date: 18 July 2011

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Electron paramagnetic resonance (EPR) experiments on boron acceptors in isotopically engineered 28Si samples with different degrees of chemical and isotopic purity are reported. The strong suppression of isotope-induced broadening effects in this material allows a direct observation of the linear correlation between the width of the inter-subband Δm = 1 EPR line and the concentrations of carbon, oxygen, and boron point defects down to a total concentration of ≈2 × 1015 cm−3. When the impurity level is decreased further, the linewidth does not fall below 2.3 ± 0.2 mT, for which we discuss possible origins.
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71.55.Cn Elemental semiconductors
61.72.uf Ge and Si
76.30.Kg Rare-earth ions and impurities
61.72.J- Point defects and defect clusters

Tuning of anisotropy in two-electron quantum dots by spin-orbit interactions

Y. Liu, F. Cheng, X. J. Li, F. M. Peeters, and Kai Chang

Appl. Phys. Lett. 99, 032102 (2011); http://dx.doi.org/10.1063/1.3610961 (3 pages) | Cited 3 times

Online Publication Date: 18 July 2011

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We investigate the influence of the spin-orbit interactions (SOIs) on the electron distribution and the optical absorption of a two-electron quantum dot. It is shown that the interplay between the SOIs makes the two-electron quantum dot behave like two laterally coupled quantum dots and the anisotropic distribution can be rotated from [110] to [1math0] by reversing the direction of the perpendicular electric field and detect it through the optical absorption spectrum.
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73.21.La Quantum dots
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Hc Quantum dots
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Chip-size formation of high-mobility Ge strips on SiN films by cooling rate controlled rapid-melting growth

Kaoru Toko, Yasuharu Ohta, Takanori Tanaka, Taizoh Sadoh, and Masanobu Miyao

Appl. Phys. Lett. 99, 032103 (2011); http://dx.doi.org/10.1063/1.3611904 (3 pages) | Cited 6 times

Online Publication Date: 21 July 2011

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High-quality Ge-on-insulators (GOIs) are essential structures for high-performance transistors on an Si platform. We developed a rapid-melting-growth process for amorphous Ge (a-Ge) by optimizing the cooling rate and the underlying insulating materials. The effects of the solidification process for molten Ge on hole generation and spontaneous nucleation in Ge were determined. In addition, nucleation in the a-Ge matrix was found to be drastically suppressed by substituting SiO2 underlayers with SiN underlayers. By combining high cooling rates (10.5–11.5 °Cs−1) and SiN underlayers, we obtained ultra-long single crystal GOI strips (1 cm) with high hole mobilities (> 1000 cm2V−1s−1). This chip-size formation of high-quality GOI will facilitate the development of advanced high-speed Ge-based devices.
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85.30.Tv Field effect devices

Hot electron transmission in metals using epitaxial NiSi2/n-Si(111) interfaces

S. Parui, B. Wit, L. Bignardi, P. Rudolf, B. Kooi, B. J. van Wees, and T. Banerjee

Appl. Phys. Lett. 99, 032104 (2011); http://dx.doi.org/10.1063/1.3610458 (3 pages) | Cited 2 times

Online Publication Date: 21 July 2011

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We have investigated hot electron transmission across epitaxial metal-disilicide/n-Si(111) interfaces using ballistic electron emission microscopy (BEEM). Different crystal orientations of epitaxial NiSi2 were grown on a Si(111) substrate using molecular beam epitaxy. The presence of different interfaces of NiSi2 on Si(111) were confirmed by high resolution transmission electron microscopy. Electrical transport measurements reveal a clear rectifying Schottky interface with a barrier height of 0.69 eV. However, using BEEM, three different regions with different transmissions and Schottky barrier heights of 0.65 eV, 0.78 eV, and 0.71 eV are found. The addition of a thin Ni film on the NiSi2 layer strongly reduces the transmission in all the three regions and interestingly, almost equalizes the transmission across them.
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73.40.Ns Metal-nonmetal contacts
73.50.Mx High-frequency effects; plasma effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.Ht High-field and nonlinear effects
72.30.+q High-frequency effects; plasma effects
73.30.+y Surface double layers, Schottky barriers, and work functions

Sb-rich Si-Sb-Te phase change material for multilevel data storage: The degree of disorder in the crystalline state

Xilin Zhou, Liangcai Wu, Zhitang Song, Feng Rao, Yan Cheng, Cheng Peng, Dongning Yao, Sannian Song, Bo Liu, Songlin Feng, and Bomy Chen

Appl. Phys. Lett. 99, 032105 (2011); http://dx.doi.org/10.1063/1.3614553 (3 pages) | Cited 5 times

Online Publication Date: 22 July 2011

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The phase change memory with monolayer chalcogenide film (Si18Sb52Te30) is investigated for the feasibility of multilevel data storage. During the annealing of the film, a relatively stable intermediate resistance can be obtained at an appropriate heating rate. The transmission electron microscopy in situ analysis reveals a conversion of crystallization mechanism from nucleation to crystal growth, which leads a continuous reduction in the degree of disorder. It is indicated from the electrical properties of the devices that the fall edge of the voltage pulse is the critical factor that determines a reliable triple-level resistance state of the phase change memory cell.
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84.30.Sk Pulse and digital circuits
64.70.kg Semiconductors
73.61.Le Other inorganic semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Ratchet effect induced by linearly polarized near- and mid-infrared radiation in InAs nanowires patterned quasi two-dimensional electron system

Chongyun Jiang, Hui Ma, Jinling Yu, Yu Liu, and Yonghai Chen

Appl. Phys. Lett. 99, 032106 (2011); http://dx.doi.org/10.1063/1.3610966 (3 pages)

Online Publication Date: 22 July 2011

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In this letter, we studied the polarization dependent current excited by near- and mid-infrared radiations in InAs nanowires patterned quasi two-dimensional structures. We observed a current with a predominated direction along the wires at normal incidence of mid-infrared radiation and attributed it to the ratchet effect. Photogalvanic effect induced by obliquely incident excitation is also observed. Under near-infrared excitation, however, the normal incident ratchet effect becomes insignificant and the linear photogalvanic effect at oblique incidence dominantly contributes to the electric current.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.40.+w Photoconduction and photovoltaic effects
73.63.Nm Quantum wires
78.20.Jq Electro-optical effects
78.56.-a Photoconduction and photovoltaic effects
78.67.Uh Nanowires

Contact resistance in top-gated graphene field-effect transistors

Bo-Chao Huang, Ming Zhang, Yanjie Wang, and Jason Woo

Appl. Phys. Lett. 99, 032107 (2011); http://dx.doi.org/10.1063/1.3614474 (3 pages) | Cited 17 times

Online Publication Date: 22 July 2011

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The parasitic resistance of different source/drain metals for top-gated graphene field-effect transistors was extracted by fitting the measured ID-VG data with a resistance model and was found to be a significant part of the total resistance of graphene field-effect transistors. The results show that Ti/Au gives relatively large contact resistance, about 7500 Ω·μm. Ni/Au contact shows better result compared to Ti/Au, which is around 2100 Ω·μm. The lowest contact resistance was given by Ti/Pd/Au, which is around 750 Ω·μm. The contact resistivity for Ti/Pd/Au source/drain contact is around 2 × 10−6 Ω·cm2, close to state of the art GaAs technology.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors
73.40.Cg Contact resistance, contact potential
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Domain wall induced magnetoresistance in a superconductor/ferromagnet nanowire

G. X. Miao, M. D. Mascaro, C. H. Nam, C. A. Ross, and J. S. Moodera

Appl. Phys. Lett. 99, 032501 (2011); http://dx.doi.org/10.1063/1.3610947 (3 pages) | Cited 2 times

Online Publication Date: 18 July 2011

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In a nanowire consisting of a ferromagnet/insulator/superconductor multilayer structure, the superconductivity is shown to depend strongly on the configuration of the magnetic domain walls in the neighboring ferromagnetic layer, yielding a high magnetoresistance within a temperature range near the superconducting transition temperature TC. Micromagnetic simulations confirmed that out-of-plane stray magnetic fields from uncompensated magnetic poles play a dominant role in inducing magnetoresistance in this particular system.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Rw Metal-insulator-metal structures

Low current density spin-transfer torque effect assisted by in-plane microwave field

Jianbo Wang, Congpu Mu, Weiwei Wang, Bin Zhang, Haiyan Xia, Qingfang Liu, and Desheng Xue

Appl. Phys. Lett. 99, 032502 (2011); http://dx.doi.org/10.1063/1.3611446 (3 pages) | Cited 1 time

Online Publication Date: 19 July 2011

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A strategy is presented to greatly reduce both the critical spin polarized current density and the magnetization switching time in elliptical magnetic spin valve. This method is a combination of microwave field and spin polarized current. The numerical simulation at zero temperature shows that the critical current density and the magnetization switching time are sensitive to the frequency and the amplitude of microwave magnetic field. A 75% reduction in critical current density is observed when the frequency of microwave coincides with the natural ferromagnetic resonance frequency of free layer.
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75.76.+j Spin transport effects
72.25.-b Spin polarized transport
75.40.Mg Numerical simulation studies
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Enhancement of microwave emission in magnetic tunnel junction oscillators through in-plane field orientation

Z. M. Zeng, P. Upadhyaya, P. Khalili Amiri, K. H. Cheung, J. A. Katine, J. Langer, K. L. Wang, and H. W. Jiang

Appl. Phys. Lett. 99, 032503 (2011); http://dx.doi.org/10.1063/1.3613965 (3 pages) | Cited 7 times

Online Publication Date: 19 July 2011

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We observe giant enhancement of microwave emission in MgO-based magnetic tunnel junction nano-oscillators through in-plane magnetic field orientation. At an optimal in-plane field angle, the output power reaches up to 240 nW, two orders of magnitude higher compared to the vicinity of the easy axis (∼1 nW). Moreover, in this condition, the linewidth is significantly narrowed (<100 MHz) and the additional precession modes are suppressed. Analysis of the data indicates that the optimal field angle is influenced by the field-like torque. The results demonstrate that controlling the in-plane magnetic field orientation can be an important strategy for developing high-power spin-torque oscillators.
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84.30.Ng Oscillators, pulse generators, and function generators
85.35.-p Nanoelectronic devices

Alternating current magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a micro superconducting quantum interference device

M. J. Martínez-Pérez, E. Bellido, R. de Miguel, J. Sesé, A. Lostao, C. Gómez-Moreno, D. Drung, T. Schurig, D. Ruiz-Molina, and F. Luis

Appl. Phys. Lett. 99, 032504 (2011); http://dx.doi.org/10.1063/1.3609859 (3 pages) | Cited 2 times

Online Publication Date: 20 July 2011

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We report the controlled integration, via dip pen nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 μB) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 102, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Xx Molecular magnets
81.16.Nd Micro- and nanolithography
75.75.Cd Fabrication of magnetic nanostructures

Spin resolved photoelectron microscopy using a two-dimensional spin-polarizing electron mirror

C. Tusche, M. Ellguth, A. A. Ünal, C.-T. Chiang, A. Winkelmann, A. Krasyuk, M. Hahn, G. Schönhense, and J. Kirschner

Appl. Phys. Lett. 99, 032505 (2011); http://dx.doi.org/10.1063/1.3611648 (3 pages) | Cited 9 times

Online Publication Date: 21 July 2011

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We report on an imaging spin-filter for electrons. The specular reflection of low-energy electrons at the surface of a tungsten single crystal is used to project a spin-filtered two-dimensional image onto a position sensitive detector. Spin-filtering is based on the spin-dependent reflectivity of electrons due to spin-orbit coupling in the scattering target, while a two-dimensional field of view, encoded in the angle of incidence, is conserved in the outgoing beam. We characterize the efficiency of the spin-filter by recording photoelectron emission microscopy images of the magnetic domain structure of 8 monolayers cobalt grown on copper (100).
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ch Domain walls and domain structure
78.20.Ls Magneto-optical effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.25.Ba Spin polarized transport in metals

Superconducting quantum interference devices with submicron Nb/HfTi/Nb junctions for investigation of small magnetic particles

J. Nagel, O. F. Kieler, T. Weimann, R. Wölbing, J. Kohlmann, A. B. Zorin, R. Kleiner, D. Koelle, and M. Kemmler

Appl. Phys. Lett. 99, 032506 (2011); http://dx.doi.org/10.1063/1.3614437 (3 pages) | Cited 7 times

Online Publication Date: 21 July 2011

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We investigated, at temperature 4.2 K, electric transport, flux noise, and resulting spin sensitivity of miniaturized Nb direct current superconducting quantum interference devices (SQUIDs) based on submicron Josephson junctions with HfTi barriers. The SQUIDs are either of the magnetometer-type or gradiometric in layout. In the white noise regime, for the best magnetometer we obtain a flux noise SΦ1/2 = 250nΦ0/Hz1/2, corresponding to a spin sensitivity Sμ1/2 ≥ 29μB/Hz1/2. For the gradiometer we find SΦ1/2 = 300nΦ0/Hz1/2 and Sμ1/2 ≥ 44μB/Hz1/2. The devices can still be optimized with respect to flux noise and coupling between a magnetic particle and the SQUID, leaving room for further improvement towards single spin resolution.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices

Noise properties of a resonance-type spin-torque microwave detector

Oleksandr Prokopenko, Gennadiy Melkov, Elena Bankowski, Thomas Meitzler, Vasil Tiberkevich, and Andrei Slavin

Appl. Phys. Lett. 99, 032507 (2011); http://dx.doi.org/10.1063/1.3612917 (3 pages) | Cited 3 times

Online Publication Date: 22 July 2011

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We analyze performance of a resonance-type spin-torque microwave detector (STMD) in the presence of noise and reveal two distinct regimes of STMD operation. In the high-frequency regime, the minimum detectable microwave power Pmin is limited by the low-frequency Johnson-Nyquist noise and the signal-to-noise ratio (SNR) of STMD is proportional to the input microwave power PRF. In the low-frequency regime, Pmin is limited by the magnetic noise, and the SNR is proportional to math. The developed formalism can be used for the optimization of the practical noise-handling parameters of a STMD.
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85.75.Mm Spin polarized resonant tunnel junctions
84.40.Dc Microwave circuits
02.60.Pn Numerical optimization

Modeling of the spin-transfer torque switching in FePt/MgO-based perpendicular magnetic tunnel junctions: A combined ab initio and micromagnetic simulation study

Wanjiao Zhu, Yaowen Liu, and Chun-Gang Duan

Appl. Phys. Lett. 99, 032508 (2011); http://dx.doi.org/10.1063/1.3615664 (3 pages) | Cited 3 times

Online Publication Date: 22 July 2011

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Combined ab initio and micromagnetic simulations are carried out to build up a direct relationship between critical switching current Jc and geometric structure (in-plane lattice constant a and film thickness) of FePt in magnetic tunnel junctions. Ab initio calculations predict that the strain effect can significantly influence the uniaxial magnetic anisotropy constant Ku, whereas the thickness has less significant impact on Ku. Micromagnetic simulations show that Jc linearly increases with the increasing Ku (the decreasing a) and the switching time decreases with the increasing current at a fixed Ku and is sensitive to the perpendicular spin-torque factor at negative current.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.78.Jp Ultrafast magnetization dynamics and switching
75.76.+j Spin transport effects
75.78.Cd Micromagnetic simulations

Electric field control of magnetism without magnetic bias field in the Ni/Pb(Mg1/3Nb2/3)O3-PbTiO3/Ni composite

H. C. Xuan, L. Y. Wang, Y. X. Zheng, Y. L. Li, Q. Q. Cao, S. Y. Chen, D. H. Wang, Z. G. Huang, and Y. W. Du

Appl. Phys. Lett. 99, 032509 (2011); http://dx.doi.org/10.1063/1.3616137 (3 pages)

Online Publication Date: 22 July 2011

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This paper reports on the electric field control of magnetism without magnetic bias field in a Ni/Pb(Mg1/3Nb2/3)O3-PbTiO3/Ni composite prepared by electrochemical deposition. The converse magnetoelectric effect, which was measured by an induction method, shows a peak value of 0.45 G/V at the resonance frequency of 102 kHz. Without magnetic bias field, the magnetization of the Ni layers can be controlled by an applied dc electric field in a reversible and reproducible way and shows an analogous on-off behavior with the electric field switching on and off alternatively.
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75.85.+t Magnetoelectric effects, multiferroics
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Microwave coupled electron tunneling measurement of Co nanoparticles

W. Jiang, F. Tijiwa Birk, and D. Davidović

Appl. Phys. Lett. 99, 032510 (2011); http://dx.doi.org/10.1063/1.3614554 (3 pages) | Cited 1 time

Online Publication Date: 22 July 2011

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We study electron tunneling through Co nanoparticles in the presence of repeated microwave pulses at 4.2 K. While individual pulses are too weak to affect the magnetic switching field, repeated microwave pulses start to reduce the magnetic switching field at 10 μs spacing. We use I-V curve as a thermometer to show that the microwave pulses do not heat the sample, showing that magnetization in Co nanoparticles is directly excited by microwave pulses, and the relaxation time of the excitation energy is in the range of microsecond.
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73.63.Bd Nanocrystalline materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
73.40.Gk Tunneling

Proximity effect in electron-doped cuprate Josephson junctions

S. Charpentier, G. Roberge, S. Godin-Proulx, and P. Fournier

Appl. Phys. Lett. 99, 032511 (2011); http://dx.doi.org/10.1063/1.3613999 (3 pages)

Online Publication Date: 22 July 2011

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We study the proximity effect in Josephson junctions made of electron-doped cuprates Pr2–xCexCuO4 (PCCO). With superconducting electrodes at a fixed doping x = 0.15, we explore the variation of the Josephson coupling with the doping and the thickness of the barrier. We observe Josephson coupling for any type of barrier: antiferromagnetic (AF) metal, AF insulator, or paramagnetic metal. For an x = 0.05 barrier, we can estimate the normal coherence length, ξn = 12 ± 3 nm. Comparing this value with the theoretical prediction, ξn,max = 4.5 nm, we conclude that the proximity effect through a barrier of PCCO x = 0.05 is stronger than expected.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.72.Ek Electron-doped
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Complete set of material properties of single domain 0.24Pb(In1/2Nb1/2)O3-0.49Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystal and the orientation effects

Enwei Sun, Wenwu Cao, Wenhua Jiang, and Pengdi Han

Appl. Phys. Lett. 99, 032901 (2011); http://dx.doi.org/10.1063/1.3615684 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2011

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Multidomain relaxor-based single crystals have intrigued the enthusiasm of many researchers due to their superior electromechanical properties. In order to understand the physical origin of multidomain properties, one must know the complete set of material coefficients in single domain state. Previous published single domain data were all measured under bias because single domain state is unstable. Here, we report a set of single domain data without bias for rhombohedral 0.24Pb(In1/2Nb1/2)O3-0.49Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystal. Comparing rotated coefficients from single domain data with measured multidomain material coefficients, we concluded that the orientation effects account for more than 90% of the observed multidomain properties.
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77.80.Jk Relaxor ferroelectrics
77.84.Cg PZT ceramics and other titanates

Energetics of hydrogen in GeO2, Ge, and their interfaces

Ka Xiong, Liang Lin, John Robertson, and Kyeongjae Cho

Appl. Phys. Lett. 99, 032902 (2011); http://dx.doi.org/10.1063/1.3610463 (3 pages) | Cited 4 times

Online Publication Date: 21 July 2011

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The energetics of interstitial hydrogen in GeO2, Ge, and their interfaces are calculated using a hybrid density functional. We find that interstitial atomic hydrogen unexpectedly behaves as a donor in GeO2, like H in ZnO but unlike H in SiO2. At Ge:GeO2 interfaces, the donor electron can transfer to the lower lying Ge conduction band, which stabilises the O-H bond/donor complex. This reduces the probability of passivating Ge dangling bond (Pb) centers at Ge:GeO2 interfaces.
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71.55.Ht Other nonmetals
61.72.jj Interstitials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Experimental and theoretical investigation on the high frequency dielectric properties of Ag/Al2O3 composites

Z. C. Shi, R. H. Fan, Z. D. Zhang, H. Y. Gong, J. Ouyang, Y. J. Bai, X. H. Zhang, and L. W. Yin

Appl. Phys. Lett. 99, 032903 (2011); http://dx.doi.org/10.1063/1.3608156 (3 pages) | Cited 6 times

Online Publication Date: 21 July 2011

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The impedance and dielectric properties of Ag/Al2O3 composites are investigated experimentally in the frequency range from 100 MHz to 1 GHz. Besides, equivalent circuit analysis and numerical simulations were carried out. For the composites with sufficiently high silver loading, current paths were formed and negative permittivity appeared. The negative permittivity can be well described by lossy Drude model. Moreover, the negative permittivity sample manifests inductive characteristic and shunt inductors are added to its equivalent circuit. Numerical simulations show that the interconnection of silver particles results in negative permittivity, hence the serious attenuation of electromagnetic waves.
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77.22.Ch Permittivity (dielectric function)
72.30.+q High-frequency effects; plasma effects

Effect of domain walls on the electrocaloric properties of Pb(Zr1−x,Tix)O3 thin films

J. Karthik and L. W. Martin

Appl. Phys. Lett. 99, 032904 (2011); http://dx.doi.org/10.1063/1.3614453 (3 pages) | Cited 8 times

Online Publication Date: 22 July 2011

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The electrocaloric properties of polydomain epitaxial Pb(Zr1-x,Tix)O3 thin films are investigated using a Ginzburg-Landau-Devonshire thermodynamic model as a function of strain, temperature, and composition for 0.65 ≤ x ≤ 1. Polarization transitions driven by epitaxial strain and extrinsic contributions from domain wall displacements are found to dramatically impact the electrocaloric response. Careful choice of epitaxial misfit strain and composition allows one to harness the intrinsic and extrinsic contributions to obtain large adiabatic temperature changes much below the Curie temperature of the material.
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77.70.+a Pyroelectric and electrocaloric effects
77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point
77.84.Cg PZT ceramics and other titanates
77.55.Kt Pyroelectric films
77.55.Px Epitaxial and superlattice films

The investigation of depoling mechanism of densified KNbO3 piezoelectric ceramic

Haiyan Ge, Yudong Hou, Xue Rao, Mankang Zhu, Hao Wang, and Hui Yan

Appl. Phys. Lett. 99, 032905 (2011); http://dx.doi.org/10.1063/1.3614541 (3 pages) | Cited 4 times

Online Publication Date: 22 July 2011

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Thermal depoling phenomena determine the upper temperature limit of the piezoelectric ceramics in application. In this paper, high-densified KNbO3 ceramics derived from single-crystalline nanostructures exhibited favorable piezoelectric constants d33, which varied from 105 to 80 pC/N over a broad temperature range from 25 to 225 °C. In situ x-ray diffraction combined with Raman spectra demonstrate clearly the transition sequence of crystallographic orientations during thermal depoling process. The interaction between defect dipoles D and spontaneous polarization inside domains Ps favored to preserve piezoelectric activity, while the spontaneous rotation of Ps induced by the phase transition resulted in the deliquesce of d33.
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77.84.Ek Niobates and tantalates
73.63.Bd Nanocrystalline materials
77.22.Ej Polarization and depolarization
77.65.Bn Piezoelectric and electrostrictive constants
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
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Effect of microstructure on the thermal conductivity of disordered carbon

I. Suarez-Martinez and N. A. Marks

Appl. Phys. Lett. 99, 033101 (2011); http://dx.doi.org/10.1063/1.3607872 (3 pages) | Cited 1 time

Online Publication Date: 18 July 2011

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Computational methods are used to control the degree of structural order in a variety of carbon materials containing primarily sp2 bonding. Room-temperature thermal conductivities are computed using non-equilibrium molecular dynamics. Our results reproduce experimental data for amorphous and glassy carbons and confirm previously proposed structural models for vitreous carbons. An atomistic model is developed for highly oriented thin films seen experimentally, with a maximum computed thermal conductivity of 35 W m−1 K−1. This value is much higher than that of the amorphous and glassy structures, demonstrating that the microstructure influences the thermal conductivity more strongly than the density.
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61.43.Bn Structural modeling: serial-addition models, computer simulation
61.72.-y Defects and impurities in crystals; microstructure
68.55.-a Thin film structure and morphology
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Physical origin of the incubation time of self-induced GaN nanowires

V. Consonni, A. Trampert, L. Geelhaar, and H. Riechert

Appl. Phys. Lett. 99, 033102 (2011); http://dx.doi.org/10.1063/1.3610964 (3 pages) | Cited 10 times

Online Publication Date: 19 July 2011

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The nucleation process of self-induced GaN nanowires grown by molecular beam epitaxy has been investigated by reflection high-energy electron diffraction measurements. It is found that stable nuclei in the form of spherical cap-shaped islands develop only after an incubation time that is strongly dependent upon the growth conditions. Its evolution with the growth temperature and gallium rate has been described within standard island nucleation theory, revealing a nucleation energy of 4.9 ± 0.1 eV and a very small nucleus critical size. The consideration of the incubation time is critical for the control of the nanowire morphology.
Show PACS
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
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