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1 Oct 2012

Volume 101, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 141101 (2012); http://dx.doi.org/10.1063/1.4742864 (4 pages)

Po-Hsun Huang, Michael Ian Lapsley, Daniel Ahmed, Yuchao Chen, Lin Wang, and Tony Jun Huang
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Carbon-doped Ge2Sb2Te5 phase change material: A candidate for high-density phase change memory application

Xilin Zhou, Liangcai Wu, Zhitang Song, Feng Rao, Min Zhu, Cheng Peng, Dongning Yao, Sannian Song, Bo Liu, and Songlin Feng

Appl. Phys. Lett. 101, 142104 (2012); http://dx.doi.org/10.1063/1.4757137 (4 pages) | Cited 2 times

Online Publication Date: 2 October 2012

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Carbon-doped Ge2Sb2Te5 material is proposed for high-density phase-change memories. The carbon doping effects on electrical and structural properties of Ge2Sb2Te5 are studied by in situ resistance and x-ray diffraction measurements as well as optical spectroscopy. C atoms are found to significantly enhance the thermal stability of amorphous Ge2Sb2Te5 by increasing the degree of disorder of the amorphous phase. The reversible electrical switching capability of the phase-change memory cells is improved in terms of power consumption with carbon addition. The endurance of ∼2.1 × 104 cycles suggests that C-doped Ge2Sb2Te5 film will be a potential phase-change material for high-density storage application.
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84.30.Sk Pulse and digital circuits

Reversible ferromagnetism in rutile TiO2 single crystals induced by nickel impurities

Y. L. Zhao, M. Motapothula, N. L. Yakovlev, Z. Q. Liu, S. Dhar, A. Rusydi, Ariando, M. B. H. Breese, Q. Wang, and T. Venkatesan

Appl. Phys. Lett. 101, 142105 (2012); http://dx.doi.org/10.1063/1.4756799 (4 pages)

Online Publication Date: 3 October 2012

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We report a Ni impurity induced reversible ferromagnetism and surface conduction in rutile TiO2 crystals subjected to specific thermal annealing. For annealing in vacuum at 800 °C, a growing ferromagnetic signal is seen with time while for a similar annealing in air, the magnetism vanishes. The magnetism is concomitant with a surface conductivity which at low temperatures shows tunneling characteristics. Here, we show that Ni magnetic impurity (in TiO2 crystals at <100 ppm) under vacuum annealing segregates to the surface over a 50 nm layer where the Ni concentration exceeds 10%–20% and drops with subsequent air annealing.
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75.30.Hx Magnetic impurity interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Rf Surface magnetism
81.40.Gh Other heat and thermomechanical treatments
68.35.Dv Composition, segregation; defects and impurities
73.25.+i Surface conductivity and carrier phenomena

Electronically active defects in the Cu2ZnSn(Se,S)4 alloys as revealed by transient photocapacitance spectroscopy

D. Westley Miller, Charles W. Warren, Oki Gunawan, Tayfun Gokmen, David B. Mitzi, and J. David Cohen

Appl. Phys. Lett. 101, 142106 (2012); http://dx.doi.org/10.1063/1.4754834 (4 pages) | Cited 1 time

Online Publication Date: 3 October 2012

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Transient photocapacitance (TPC) spectra were obtained on a series of Cu2ZnSn(Se,S)4 absorber devices with varying Se:S ratios, providing bandgaps (Eg) between 1 eV and 1.5 eV. Efficiencies varied between 8.3% and 9.3% for devices with Eg ≤ 1.2 eV and were near 6.5% for devices with Eg ≥ 1.4 eV. The TPC spectra revealed a band-tail region with Urbach energies at or below 18 meV for the first group, but in the 25-30 meV range for the higher band-gap samples. A deeper defect band centered near 0.8 eV was also observed in most samples. We identified a correlation between the Urbach energies and the voltage deficit in these devices.
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71.55.Ak Metals, semimetals, and alloys
72.40.+w Photoconduction and photovoltaic effects
71.20.Gj Other metals and alloys

Intrinsic threshold mechanism of phase-change memory cells by pulsed current–voltage characterization

W. Chen, Z. Li, J. H. Peng, Y. F. Deng, and X. S. Miao

Appl. Phys. Lett. 101, 142107 (2012); http://dx.doi.org/10.1063/1.4757280 (4 pages)

Online Publication Date: 3 October 2012

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A short pulsed current–voltage (I-V) measurement method is proposed for phase-change random access memory (PCRAM) to investigate the self-heating behavior. The pulse widths and periods are indispensable parameters to describe pulsed I-V characteristics of PCRAM cells. By comparing the difference between direct current I-V curves and pulsed I-V curves, the threshold voltages of pulsed I-V are much higher. It implies the existence of self-heating and energy accumulation. Assume that the heating of the active region causes the change of the electronic barrier and the electronic activity, the physical model dominated by the self-heating in PCRAM cells is proposed.
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84.30.Sk Pulse and digital circuits

Spin relaxation of negatively charged excitons in (In,Al)As/AlAs quantum dots with indirect band gap and type-I band alignment

D. Dunker, T. S. Shamirzaev, J. Debus, D. R. Yakovlev, K. S. Zhuravlev, and M. Bayer

Appl. Phys. Lett. 101, 142108 (2012); http://dx.doi.org/10.1063/1.4754619 (4 pages)

Online Publication Date: 4 October 2012

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Spin dynamics of negatively charged excitons is experimentally studied in (In,Al)As/AlAs quantum dots with indirect band gap and type-I band alignment. At low temperatures of 1.8 K, the spin relaxation time is 55 μs in a magnetic field of 3 T. It decreases with increasing magnetic field as B−5, which evidences that the spin relaxation of the negatively charged excitons is provided by an one-acoustic-phonon process.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ey III-V semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.35.-y Excitons and related phenomena

Compositionally graded relaxed AlGaN buffers on semipolar GaN for mid-ultraviolet emission

Erin C. Young, Feng Wu, Alexey E. Romanov, Daniel A. Haeger, Shuji Nakamura, Steven P. Denbaars, Daniel A. Cohen, and James S. Speck

Appl. Phys. Lett. 101, 142109 (2012); http://dx.doi.org/10.1063/1.4757423 (5 pages)

Online Publication Date: 4 October 2012

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In this Letter, we report on the growth and properties of relaxed, compositionally graded AlxGa1 − xN buffer layers on freestanding semipolar (20math1) GaN substrates. Continuous and step compositional grades with Al concentrations up to x = 0.61 have been achieved, with emission wavelengths in the mid-ultraviolet region as low as 265 nm. Coherency stresses were relaxed progressively throughout the grades by misfit dislocation generation via primary (basal) slip and secondary (non-basal) slip systems. Threading dislocation densities in the final layers of the grades were less than 106/cm2 as confirmed by plan-view transmission electron microscopy and cathodoluminescence studies.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

A simple method for the determination of doping type in nanomaterials based on electrical response to humidity

Jin-Woo Han, Beomseok Kim, Nobuhiko P. Kobayashi, Jing Li, and M. Meyyappan

Appl. Phys. Lett. 101, 142110 (2012); http://dx.doi.org/10.1063/1.4757609 (3 pages)

Online Publication Date: 4 October 2012

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A simple method to determine the doping type of inorganic nanomaterials is presented. The surface reaction with moisture results in distinctive electrical responses depending on the doping type of the material. The moisture acts as an electron donor, releasing electrons to the semiconductor materials. Thus, the resistance of p-type materials increases due to the withdrawal of holes, while that of n-type decreases due to electron donation. Compared to spectroscopy and Hall measurement techniques, the present method is a simple and fast approach for determining the doping types, enabling fast feedback in material research as well as in device prototyping.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.72.U- Doping and impurity implantation
73.63.-b Electronic transport in nanoscale materials and structures

Monolithic integration of high electron mobility InAs-based heterostructure on exact (001) Silicon using a GaSb/GaP accommodation layer

L. Desplanque, S. El Kazzi, C. Coinon, S. Ziegler, B. Kunert, A. Beyer, K. Volz, W. Stolz, Y. Wang, P. Ruterana, and X. Wallart

Appl. Phys. Lett. 101, 142111 (2012); http://dx.doi.org/10.1063/1.4758292 (4 pages)

Online Publication Date: 5 October 2012

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We report on the epitaxial growth of high electron mobility AlSb/InAs heterostructure on exactly oriented (001) Si substrate, using a GaP interfacial layer. The growth conditions are first optimized on GaP substrates to achieve the highest electron mobility. The influence of the Sb flux during the early stage of the GaSb buffer layer is particularly emphasized. Using these optimized growth conditions, the AlSb/InAs heterostructure is grown on a GaP/Si template obtained by metal-organic vapor phase epitaxy. An electron mobility as high as 27 800 cm2 V−1 s−1 and 111 000 cm2 V−1 s−1, respectively, at 300 and 77 K is demonstrated.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Kk Vapor phase epitaxy; growth from vapor phase
72.20.Fr Low-field transport and mobility; piezoresistance

The effect of hydrogen on the surface segregation of phosphorus in epitaxially grown relaxed Si0.7Ge0.3 films by rapid thermal chemical vapor deposition

Jiun-Yun Li, Chiao-Ti Huang, and James C. Sturm

Appl. Phys. Lett. 101, 142112 (2012); http://dx.doi.org/10.1063/1.4757123 (4 pages)

Online Publication Date: 5 October 2012

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The surface segregation of phosphorus in relaxed Si0.7Ge0.3 epitaxial films grown on Si (100) substrates by rapid thermal chemical vapor deposition was investigated in this letter. The effect of the growth temperature on phosphorus segregation was studied experimentally and examined using a two-state model. As the growth temperature is reduced, phosphorus segregation is greatly suppressed, and we report an extremely sharp phosphorus turn-off slope of 6 nm/dec at 500 °C. The sharper slopes at low temperatures are explained by a modified two-state model which includes the effect of increased surface coverage of hydrogen at low temperatures.
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68.35.Dv Composition, segregation; defects and impurities
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
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Exchange bias and memory effect in double perovskite Sr2FeCoO6

R. Pradheesh, Harikrishnan S. Nair, V. Sankaranarayanan, and K. Sethupathi

Appl. Phys. Lett. 101, 142401 (2012); http://dx.doi.org/10.1063/1.4756792 (4 pages)

Online Publication Date: 1 October 2012

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We report on the observation of exchange bias (EB) and memory effect in double perovskite Sr2FeCoO6. Antiphase boundaries between the ferromagnetic and the antiferromagnetic regions in the disordered glassy phase are assumed as responsible for the observed effect, which reflects in the cooling field dependence and temperature evolution of exchange bias field and in training effect. The spin glass (SG) phase itself is characterized through memory, ageing, and magnetic relaxation experiments. The spin glass transition temperature, Tg, versus Hdc2/3 follows the Almeida-Thouless line yielding a freezing temperature, Tf = 73K. Time-dependent magnetic relaxation studies reveal the magnetization dynamics of the underlying glassy phase in this double perovskite.
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75.30.Et Exchange and superexchange interactions
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.-n Magnetization dynamics

Dynamic response of exchange bias in graphene nanoribbons

S. Narayana Jammalamadaka, S. S. Rao, J. Vanacken, V. V. Moshchalkov, Wei Lu, and J. M. Tour

Appl. Phys. Lett. 101, 142402 (2012); http://dx.doi.org/10.1063/1.4755840 (5 pages)

Online Publication Date: 1 October 2012

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The dynamics of magnetic hysteresis, including the training effect and the field sweep rate dependence of the exchange bias, is experimentally investigated in exchange-coupled potassium split graphene nanoribbons (GNRs). We find that, at low field sweep rate, the pronounced absolute training effect is present over a large number of cycles. This is reflected in a gradual decrease of the exchange bias with the sequential field cycling. However, at high field sweep rate above 0.5 T/min, the training effect is not prominent. With the increase in field sweep rate, the average value of exchange bias field grows and is found to follow power-law behavior. The response of the exchange bias field to the field sweep rate variation is linked to the difference in the time it takes to perform a hysteresis loop measurement compared with the relaxation time of the anti-ferromagnetically aligned spins. The present results may broaden our current understanding of magnetism of GNRs and would be helpful in establishing the GNRs-based spintronic devices.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Jn Dynamics of magnetic nanoparticles
75.30.Et Exchange and superexchange interactions

Perpendicular magnetic anisotropy of cobalt films intercalated under graphene

N. Rougemaille, A. T. N'Diaye, J. Coraux, C. Vo-Van, O. Fruchart, and A. K. Schmid

Appl. Phys. Lett. 101, 142403 (2012); http://dx.doi.org/10.1063/1.4749818 (3 pages)

Online Publication Date: 2 October 2012

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Magnetic properties of nanometer-thick Co films intercalated at the graphene/Ir(111) interface are investigated using spin-polarized low-energy electron microscopy and Auger electron spectroscopy. We show that the graphene top layer promotes perpendicular magnetic anisotropy in the Co film underneath, even for relatively thick intercalated deposits. The magnetic anisotropy energy is significantly larger for the graphene/Co interface than for the free Co surface. Hybridization of the graphene and Co electron orbitals is believed to be at the origin of the observed perpendicular magnetic anisotropy.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
79.20.Fv Electron impact: Auger emission

Investigation of room temperature ferromagnetism of 3C-SiC by vanadium carbide doping

Hui Wang, Cheng-Feng Yan, Hai-Kuan Kong, Jian-Jun Chen, Jun Xin, and Er-Wei Shi

Appl. Phys. Lett. 101, 142404 (2012); http://dx.doi.org/10.1063/1.4756939 (4 pages) | Cited 3 times

Online Publication Date: 2 October 2012

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Undoped and vanadium carbide (VC) doped 3C-SiC powders have been prepared, and an in-depth study is performed on the VC-doping dependence of room temperature ferromagnetism (FM). It is demonstrated that the FM originates in vacancy defects. The saturation magnetization (Ms) of VC is about 800 times than that of undoped 3C-SiC, while the Ms of VC-doped 3C-SiC is even smaller than that of the undoped one. The increase of doping concentration would result in the decrease of vacancy concentration and the increase of carrier concentration, suggesting that the FM of 3C-SiC is related to both vacancy and carrier concentrations.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.up Other materials
72.20.Fr Low-field transport and mobility; piezoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials

Single particle demultiplexer based on domain wall conduits

A. Torti, V. Mondiali, A. Cattoni, M. Donolato, E. Albisetti, A. M. Haghiri-Gosnet, Paolo Vavassori, and R. Bertacco

Appl. Phys. Lett. 101, 142405 (2012); http://dx.doi.org/10.1063/1.4755785 (5 pages)

Online Publication Date: 2 October 2012

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multimedia

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The remote manipulation of micro and nano-sized magnetic particles carrying molecules or biological entities over a chip surface is of paramount importance for future on-chip applications in biology and medicine. In this paper, we present a method for the on-chip demultiplexing of individual magnetic particles using bifurcated magnetic nano-conduits for the propagation of constrained domain walls (DWs). We demonstrate that the controlled injection and propagation of a domain wall in a bifurcation allow capturing, transporting, and sorting a single magnetic particle between two predefined paths. The cascade of n levels of such building blocks allows for the implementation of a variety of complex sorting devices as, e.g., a demultiplexer for the controlled sorting among 2n paths.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Rs Nanotechnologies-applications

Bit error rate investigation of spin-transfer-switched magnetic tunnel junctions

Zihui Wang, Yuchen Zhou, Jing Zhang, and Yiming Huai

Appl. Phys. Lett. 101, 142406 (2012); http://dx.doi.org/10.1063/1.4756787 (4 pages) | Cited 1 time

Online Publication Date: 3 October 2012

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A method is developed to enable a fast bit error rate (BER) characterization of spin-transfer-torque magnetic random access memory magnetic tunnel junction (MTJ) cells without integrating with complementary metal-oxide semiconductor circuit. By utilizing the reflected signal from the devices under test, the measurement setup allows a fast measurement of bit error rates at >106, writing events per second. It is further shown that this method provides a time domain capability to examine the MTJ resistance states during a switching event, which can assist write error analysis in great detail. BER of a set of spin-transfer-torque MTJ cells has been evaluated by using this method, and bit error free operation (down to 10−8) for optimized in-plane MTJ cells has been demonstrated.
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75.70.Ak Magnetic properties of monolayers and thin films
02.50.-r Probability theory, stochastic processes, and statistics
02.60.-x Numerical approximation and analysis
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Magnetization of 2.6 T in gadolinium thin films

G. Scheunert, W. R. Hendren, C. Ward, and R. M. Bowman

Appl. Phys. Lett. 101, 142407 (2012); http://dx.doi.org/10.1063/1.4757126 (4 pages) | Cited 3 times

Online Publication Date: 3 October 2012

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There is renewed interest in rare-earth elements and gadolinium in particular for a range of studies in coupling physics and applications. However, it is still apparent that synthesis impacts understanding of the intrinsic magnetic properties of thin gadolinium films, particularly for thicknesses of topicality. We report studies on 50 nm thick nanogranular polycrystalline gadolinium thin films on SiO2 wafers that demonstrate single-crystal like behavior. The maximum in-plane saturation magnetization at 4 K was found to be 4πMS4 K = (2.61 ± 0.26) T with a coercivity of HC4 K = (160 ± 5) Oe. A maximum Curie point of TC = (293 ± 2) K was measured via zero-field-cooled–field-cooled magnetization measurements in close agreement with values reported in bulk single crystals. Our measurements revealed magnetic transitions at T1 = (12 ± 2) K (as deposited samples) and T2 = (22 ± 2) K (depositions on heated substrates) possibly arising from the interaction of paramagnetic face-centred cubic grains with their ferromagnetic hexagonal close-packed counterparts.
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75.70.Ak Magnetic properties of monolayers and thin films
75.75.Cd Fabrication of magnetic nanostructures
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Interdependence of reversal asymmetry and training effect in Ir22Mn78/Ni81Fe19 bilayers probed with magnetoresistance

Himanshu Fulara, Sujeet Chaudhary, and Subhash C. Kashyap

Appl. Phys. Lett. 101, 142408 (2012); http://dx.doi.org/10.1063/1.4757603 (5 pages) | Cited 1 time

Online Publication Date: 4 October 2012

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Using magnetoresistance as a probe we demonstrate the correlation between reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. During the training procedure, both exchange bias field and the degree of asymmetry decrease monotonically following a very similar trend. The analysis of the magnetoresistance behaviour establishes that the two distinct training mechanisms are operative. The first one is exhibited by an abrupt single cycle training effect and an accompanying pronounced reversal asymmetry, attributed to the presence of biaxial anisotropy in the IrMn layer. The second one displays a gradual cycling dependence due to thermal depinning of uncompensated antiferromagnetic spins.
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75.60.Jk Magnetization reversal mechanisms
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
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Real-time measurement of picosecond THz pulses by an ultra-fast YBa2Cu3O7−d detection system

P. Thoma, A. Scheuring, M. Hofherr, S. Wünsch, K. Il'in, N. Smale, V. Judin, N. Hiller, A.-S. Müller, A. Semenov, H.-W. Hübers, and M. Siegel

Appl. Phys. Lett. 101, 142601 (2012); http://dx.doi.org/10.1063/1.4756905 (4 pages) | Cited 1 time

Online Publication Date: 3 October 2012

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The temporal evolution of picosecond THz pulses generated at ANKA, the electron storage ring of the Karlsruhe Institute of Technology, has been measured in real-time using an ultra-fast YBa2Cu3O7−δ detection system. YBa2Cu3O7−δ thin-film detectors with 30 nm thickness were patterned to microbridges (2 μm long, 4.5 μm wide) and embedded into a planar log-spiral THz antenna. The detectors were glued on a silicon lens and installed in an ultra-fast readout system with a temporal resolution of 15 ps (full width at half maximum). Detector responses as short as 17 ps were recorded showing very good agreement with the expected storage ring bunch lengths.
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85.25.-j Superconducting devices

A titanium-nitride near-infrared kinetic inductance photon-counting detector and its anomalous electrodynamics

J. Gao, M. R. Vissers, M. O. Sandberg, F. C. S. da Silva, S. W. Nam, D. P. Pappas, D. S. Wisbey, E. C. Langman, S. R. Meeker, B. A. Mazin, H. G. Leduc, J. Zmuidzinas, and K. D. Irwin

Appl. Phys. Lett. 101, 142602 (2012); http://dx.doi.org/10.1063/1.4756916 (4 pages) | Cited 1 time

Online Publication Date: 5 October 2012

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We demonstrate single-photon counting at 1550 nm with titanium-nitride (TiN) microwave kinetic inductance detectors. Full-width-at-half-maximum energy resolution of 0.4 eV is achieved. 0-, 1-, 2-photon events are resolved and shown to follow Poisson statistics. We find that the temperature-dependent frequency shift deviates from the Mattis-Bardeen theory, and the dissipation response shows a shorter decay time than the frequency response at low temperatures. We suggest that the observed anomalous electrodynamics may be related to quasiparticle traps or subgap states in the disordered TiN films. Finally, the electron density-of-states is derived from the pulse response.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
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Improved performances of polymer-based dielectric by using inorganic/organic core-shell nanoparticles

W. Benhadjala, I. Bord-Majek, L. Béchou, E. Suhir, M. Buet, F. Rougé, V. Gaud, B. Plano, and Y. Ousten

Appl. Phys. Lett. 101, 142901 (2012); http://dx.doi.org/10.1063/1.4756785 (4 pages)

Online Publication Date: 1 October 2012

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BaTiO3/hyperbranched polyester/methacrylate core-shell nanoparticles were studied by varying the shell thickness and the methacrylate ratio. We demonstrated that coalescence typically observed in traditional composites employing polymer matrices is significantly reduced. By modifying the shell thickness, the equivalent filler fraction was tuned from 7 wt. % to 41 wt. %. Obtained permittivities were compared with reported models for two-phase mixtures. The nonlinear behavior of the dielectric constant as a function of the equivalent filler fraction has been fitted with the Bruggeman equation. Methacrylate groups reduce by a decade the loss factor by improving nanoparticles adhesion. The permittivity reaching 85 at 1 kHz makes core-shell nanoparticles a promising material for embedded capacitors.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Inference of oxygen vacancies in hydrothermal Na0.5Bi0.5TiO3

Aoife O'Brien, David I. Woodward, Kripasindhu Sardar, Richard I. Walton, and Pam A. Thomas

Appl. Phys. Lett. 101, 142902 (2012); http://dx.doi.org/10.1063/1.4755882 (4 pages)

Online Publication Date: 1 October 2012

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A high-resolution x-ray powder diffraction study has been made of pseudo-rhombohedral and tetragonal phases in Na0.5Bi0.5TiO3 (NBT), produced via hydrothermal and conventional solid-state methods. Hydrothermal NBT exhibits significantly greater structural distortion at room temperature than solid-state NBT. Peak widths and superstructure peak intensities show a phase transition at ∼305 °C, with trends suggesting that the structure tends towards cubic symmetry at this temperature. Structural refinements indicate that the transition occurs via a phase coexistence region with no clear intermediate phase. Piezoelectric data show evidence of polarisation pinning in hydrothermal NBT, interpreted as a high proportion of oxygen vacancies.
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61.72.jd Vacancies
64.70.K- Solid-solid transitions
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
81.10.Dn Growth from solutions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Leakage current mechanisms in high performance alumina-silicone nanolaminate dielectrics

S. K. Sahoo, R. P. Patel, and C. A. Wolden

Appl. Phys. Lett. 101, 142903 (2012); http://dx.doi.org/10.1063/1.4756788 (4 pages) | Cited 1 time

Online Publication Date: 2 October 2012

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Alumina-silicone nanolaminates deposited by plasma-enhanced chemical vapor deposition were explored as dielectrics in metal-insulator-metal capacitors. Temperature-dependent current versus voltage (I-V) measurements were used to investigate the conduction mechanisms contributing to the leakage current in these structures. It is observed that space charge limited current mechanism is the dominant conduction process in the high field region. The estimated shallow trap level energies (Et) are 0.16 eV and 0.33 eV for 50% and 83.3% Al2O3 nanolaminates, respectively.
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73.40.Rw Metal-insulator-metal structures
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
84.32.Tt Capacitors

Colossal low-frequency resonant magnetomechanical and magnetoelectric effects in a three-phase ferromagnetic/elastic/piezoelectric composite

Guoxi Liu, Xiaotian Li, Jianguo Chen, Huaduo Shi, Wenlei Xiao, and Shuxiang Dong

Appl. Phys. Lett. 101, 142904 (2012); http://dx.doi.org/10.1063/1.4756919 (4 pages) | Cited 2 times

Online Publication Date: 2 October 2012

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Colossal low-frequency resonant magnetomechanical (MM) and magnetoelectric (ME) coupling effects have been found in a three-phase composite made of Pb(Zr,Ti)O3 ceramic fibers/phosphor copper-sheet unimorph and NdFeB magnets. The experimental results revealed that the ferromagnetic/elastic/piezoelectric three-phase composite with a cantilever beam structure could show huge bending MM coefficient of ∼145.9 × 10−3/Oe (unit in bending radian per Oe) and ME voltage coefficient of ∼16 000 V/cm·Oe at the first-order bending resonance frequency of ∼5 Hz. The achieved results related to ME effect are at least one order of magnitude higher over those of other ME materials and devices reported ever. The extremely strong MM and ME couplings in the three-phase composite are due to strong magnetic force moment effect induced by the interaction between NdFeB magnets and the applied magnetic field, and further resonant enhancement via the strain-mediated phosphor copper-sheet with a relatively high mechanical quality factor.
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75.80.+q Magnetomechanical effects, magnetostriction
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
75.85.+t Magnetoelectric effects, multiferroics
75.30.Cr Saturation moments and magnetic susceptibilities
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Nanoscale ferroelectric tunnel junctions based on ultrathin BaTiO3 film and Ag nanoelectrodes

X. S. Gao, J. M. Liu, K. Au, and J. Y. Dai

Appl. Phys. Lett. 101, 142905 (2012); http://dx.doi.org/10.1063/1.4756918 (5 pages) | Cited 2 times

Online Publication Date: 3 October 2012

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In this work, Ag nanoisland electrodes (nanoelectrodes) have been deposited on top of ultrathin ferroelectric BaTiO3 (BTO) films to form a nanoscale metal-ferroelectric-metal tunnel junction by integrating growth techniques of nanocluster beam source and laser-molecular beam epitaxy. The ultrathin BTO films (∼3 nm thick) exhibit both apparent ferroelectric polarization reversal and ferroelectric tunneling related resistive switching behaviors. The introducing of Ag nanoislands (∼20 nm in diameter) as top electrode substantially enhances the tunneling current and alters the symmetry of I-V hysteresis curves. The enhanced tunneling current is likely due to the reduction in tunneling barrier height and an increase in effective tunneling area by Ag nano-electrodes, while the improved symmetric in I-V curve may be attributed to the variation of electrode-oxide contact geometry.
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73.40.Gk Tunneling
77.80.-e Ferroelectricity and antiferroelectricity
82.45.-h Electrochemistry and electrophoresis
77.55.fe BaTiO3-based films
42.62.-b Laser applications
61.46.-w Structure of nanoscale materials

Minimum domain size and stability in carbon nanotube-ferroelectric devices

C. Blaser and P. Paruch

Appl. Phys. Lett. 101, 142906 (2012); http://dx.doi.org/10.1063/1.4757880 (5 pages)

Online Publication Date: 5 October 2012

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Ferroelectric domain switching in c-axis-oriented epitaxial Pb(Zr0.2Ti0.8)O3 thin films was studied using different field geometries and compared to numerical simulations and theoretical predictions. With carbon nanotubes as electrodes, continuous nanodomains as small as 9 nm in radius in a 270 nm thick film could be switched, remaining stable for over 20 months. Defect pinning of domain walls appears to play a key role in stabilizing such domains, below the predicted thermodynamic size limit.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
85.35.Kt Nanotube devices
02.60.-x Numerical approximation and analysis
77.80.-e Ferroelectricity and antiferroelectricity
77.80.Dj Domain structure; hysteresis
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