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30 Jul 2012

Volume 101, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 051103 (2012); http://dx.doi.org/10.1063/1.4738774 (4 pages)

Alec Rose, Da Huang, and David R. Smith
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Band gap tunability of molecular beam epitaxy grown lateral composition modulated GaInP structures by controlling V/III flux ratio

K. W. Park, C. Y. Park, and Y. T. Lee

Appl. Phys. Lett. 101, 051903 (2012); http://dx.doi.org/10.1063/1.4739835 (4 pages)

Online Publication Date: 31 July 2012

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Lateral composition modulated (LCM) GaInP structures were grown on (001) GaAs substrate by molecular beam epitaxy with different V/III flux ratios. Band gap of LCM structures could be tuned from 1.93 eV to 1.83 eV by decreasing flux ratio while maintaining the same photoluminescence intensity, enhanced light absorption, and widened absorption spectrum. It is shown that for band gap tuning of LCM structures, flux ratio adjustment is a more viable method compared to growth temperature adjustment.
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71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Three-dimensional graphoepitaxial alignment resulting from solid-state dewetting of Au films on surfaces with monoperiodic topography

Amanda L. Giermann and Carl V. Thompson

Appl. Phys. Lett. 101, 051904 (2012); http://dx.doi.org/10.1063/1.4740277 (3 pages)

Online Publication Date: 31 July 2012

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Polycrystalline gold films were deposited and annealed on oxidized silicon with flat surfaces and surfaces modified to have saw-tooth surface topography. Annealing led to solid-sate dewetting to form discrete islands. As-deposited films on flat surfaces had a strong (111) texture that became still stronger during dewetting. Films deposited on saw-tooth structures had a weak (100) texture with a weak [110] in-plane alignment along the grooves. This in-plane alignment became much more uniform during dewetting. It is proposed that graphoepitaxial alignment observed in both the as-deposited and annealed films on saw-tooth structures is the result of surface-energy-driven grain growth.
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81.15.Dj E-beam and hot filament evaporation deposition
68.08.Bc Wetting
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.40.Gh Other heat and thermomechanical treatments
68.35.bd Metals and alloys
68.55.aj Insulators

dc illusion and its experimental verification

Min Liu, Zhong Lei Mei, Xiang Ma, and Tie Jun Cui

Appl. Phys. Lett. 101, 051905 (2012); http://dx.doi.org/10.1063/1.4742133 (3 pages) | Cited 4 times

Online Publication Date: 1 August 2012

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Based on the transformation optics method, we propose a dc illusion device, which can transform a metallic object into a magnified dielectric object using anisotropic conducting materials. Utilizing the analogy between electric conductivities and resistor networks, we design and fabricate the device using metal film resistors. The practical measurement data agree very well with simulation results. The proposed dc illusion device is easy to process and measure, and thus has potential applications in various sectors.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
41.20.-q Applied classical electromagnetism
42.15.Eq Optical system design

Phase change behaviors of Zn-doped Ge2Sb2Te5 films

Guoxiang Wang, Qiuhua Nie, Xiang Shen, R. P. Wang, Liangcai Wu, Jing Fu, Tiefeng Xu, and Shixun Dai

Appl. Phys. Lett. 101, 051906 (2012); http://dx.doi.org/10.1063/1.4742144 (5 pages) | Cited 1 time

Online Publication Date: 1 August 2012

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Zn-doped Ge2Sb2Te5 phase-change materials have been investigated for phase change memory applications. Zn15.16(Ge2Sb2Te5)84.84 phase change film exhibits a higher crystallization temperature (∼258 °C), wider band gap (∼0.78 eV), better data retention of 10 years at 167.5 °C, higher crystalline resistance, and faster crystallization speed compared with the conventional Ge2Sb2Te5. The proper Zn atom added into Ge2Sb2Te5 serves as a center for suppression of the face-centered-cubic (fcc) phase to hexagonal close-packed (hcp) phase transition, and fcc phase has high thermal stability partially due to the bond recombination among Zn, Sb, and Te atoms.
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81.05.Gc Amorphous semiconductors
81.05.Kf Glasses (including metallic glasses)
84.30.Sk Pulse and digital circuits
64.70.kg Semiconductors
64.70.kj Glasses
73.61.Jc Amorphous semiconductors; glasses

Acoustic filter based on Helmholtz resonator array

Jyun-Hong Lu, Chung-Chun Kuo, Fu-Li Hsiao, and Chii-Chang Chen

Appl. Phys. Lett. 101, 051907 (2012); http://dx.doi.org/10.1063/1.4742773 (4 pages)

Online Publication Date: 3 August 2012

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We investigate theoretically and experimentally the absorption of a Helmholtz resonator (HR) array, an aluminum device operated in water. The HR array’s period is 2 mm. The operating frequency range is ∼0.2–0.7 MHz. We observed two transmission dips in both experimental and theoretical spectra. These dips are dominated by different resonance orders in the HR. The resonance behaviors are investigated with steady-fields simulation and can be represented by spring-mass models. This allows us to reduce the device’s footprint significantly.
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43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
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Metal-induced solid-phase crystallization of amorphous TiO2 thin films

Chang Yang, Yasushi Hirose, Shoichiro Nakao, Ngoc Lam Huong Hoang, and Tetsuya Hasegawa

Appl. Phys. Lett. 101, 052101 (2012); http://dx.doi.org/10.1063/1.4739934 (4 pages) | Cited 2 times

Online Publication Date: 30 July 2012

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Metal-induced solid-phase crystallization of amorphous TiO2 thin films was investigated by introducing metal contact layers such as Ni or Cu between the TiO2 film and substrate. The crystallization temperature of TiO2 was found to be lowered by 30 °C (from ∼250 to ∼220 °C) with the use of a Ni contact layer. Based on the fact that part of the Ni atoms diffused to the surface of the crystallized TiO2 film, we proposed a reaction-assisted crystallization model in which an intermediate complex containing Ti-O and Ni-O bonds decomposes to crystallize TiO2 at a relatively low temperature.
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64.70.kg Semiconductors
68.35.Fx Diffusion; interface formation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

P-type conductive amorphous oxides of transition metals from solution processing

Jinwang Li (李 金望), Toshihiko Kaneda (金田 敏彦), Eisuke Tokumitsu (徳光 永輔), Mikio Koyano (小矢野 幹夫), Tadaoki Mitani (三谷 忠興), and Tatsuya Shimoda (下田 達也)

Appl. Phys. Lett. 101, 052102 (2012); http://dx.doi.org/10.1063/1.4739936 (5 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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We report a series of solution-processed p-type conductive amorphous Ln-M-O (a-Ln-M-O, where M = Ru, Ir, and Ln is a lanthanide element except Ce) having low resistivities (10−3 to 10−2 Ω cm). These oxides are thermally stable to a high degree, being amorphous up to 800 °C, and processable below 400 °C. Their film surfaces are smooth on the atomic scale, and the process allows patterning simply by direct imprinting without distortion of the pattern after annealing. These properties have high potential for use in printed electronics. The electron configurations of these oxides are apparently different from existing p-type oxides.
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73.61.Jc Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.60.Dv Thermal stability; thermal effects
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Effects of Ga on the growth of InN on O-face ZnO(000math) by plasma-assisted molecular beam epitaxy

YongJin Cho, Maxim Korytov, Martin Albrecht, Henning Riechert, and Oliver Brandt

Appl. Phys. Lett. 101, 052103 (2012); http://dx.doi.org/10.1063/1.4739941 (4 pages)

Online Publication Date: 30 July 2012

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We compare the structural properties of InN and In0.95Ga0.05N films grown on O-face ZnO(000math) substrates at different temperatures. The small amount of Ga results in dramatic changes in the morphology and structural properties of InN. In particular, inversion domains start to appear at higher temperatures in the In0.95Ga0.05N film. This process is a consequence of the chemical reaction of ZnO with Ga which can be prevented by choosing the substrate temperature to be 450°C or below.
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68.55.ag Semiconductors
52.77.-j Plasma applications
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors

Enhanced absorption of graphene with one-dimensional photonic crystal

Jiang-Tao Liu, Nian-Hua Liu, Jun Li, Xiao Jing Li, and Jie-Hui Huang

Appl. Phys. Lett. 101, 052104 (2012); http://dx.doi.org/10.1063/1.4740261 (3 pages) | Cited 4 times

Online Publication Date: 30 July 2012

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The optical absorption of graphene layers prepared on top of a one-dimensional photonic crystal (1DPC) is investigated theoretically. The absorption of graphene with 1DPC is enhanced greatly over a broad spectral range due to photon localization. The absorption of graphene can also be tuned by varying either the incident angle or the distance between the graphene and the 1DPC.
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78.67.Wj Optical properties of graphene
78.40.Ri Fullerenes and related materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Analysis of an anomalous hump in gate current after dynamic negative bias stress in HfxZr1-xO2/metal gate p-channel metal-oxide-semiconductor field-effect transistors

Szu-Han Ho, Ting-Chang Chang, Chi-Wei Wu, Wen-Hung Lo, Ching-En Chen, Jyun-Yu Tsai, Hung-Ping Luo, Tseung-Yuen Tseng, Osbert Cheng, Cheng-Tung Huang, and Simon M. Sze

Appl. Phys. Lett. 101, 052105 (2012); http://dx.doi.org/10.1063/1.4739525 (4 pages) | Cited 3 times

Online Publication Date: 30 July 2012

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This letter investigates a hump in gate current after dynamic negative bias stress (NBS) in HfxZr1-xO2/metal gate p-channel metal-oxide-semiconductor field-effect transistors. By measuring gate current under initial through body floating and source/drain floating, it shows that hole current flows from source/drain. The fitting of gate current-gate voltage characteristic curve demonstrates that Frenkel-Poole mechanism dominates the conduction. Next, by fitting the gate current after dynamic NBS, in the order of Frenkel-Poole then tunneling, the Frenkel-Poole mechanism can be confirmed. These phenomena can be attributed to hole trapping in high-k bulk and the electric field formula Ehigh-k εhigh-k = Q + Esio2εsio2.
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85.30.Tv Field effect devices

A silicon-on-insulator complementary-metal-oxide-semiconductor compatible flexible electronics technology

Hongen Tu and Yong Xu

Appl. Phys. Lett. 101, 052106 (2012); http://dx.doi.org/10.1063/1.4739937 (4 pages)

Online Publication Date: 31 July 2012

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This paper reports a simple flexible electronics technology that is compatible with silicon-on-insulator (SOI) complementary-metal-oxide-semiconductor (CMOS) processes. Compared with existing technologies such as direct fabrication on flexible substrates and transfer printing, the main advantage of this technology is its post-SOI-CMOS compatibility. Consequently, high-performance and high-density CMOS circuits can be first fabricated on SOI wafers using commercial foundry and then be integrated into flexible substrates. The yield is also improved by eliminating the transfer printing step. Furthermore, this technology allows the integration of various sensors and microfluidic devices. To prove the concept of this technology, flexible MOSFETs have been demonstrated.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Bulk and interfacial deep levels observed in In0.53Ga0.47As/GaAs0.5Sb0.5 multiple quantum well photodiode

Wenjie Chen, Baile Chen, Jinrong Yuan, Archie Holmes, and Patrick Fay

Appl. Phys. Lett. 101, 052107 (2012); http://dx.doi.org/10.1063/1.4740275 (5 pages) | Cited 1 time

Online Publication Date: 31 July 2012

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Multiple quantum well (MQW) photodiodes based on the InGaAs/GaAsSb material system are emerging as viable candidates for mid infrared detection. A critical issue for these devices is dark current caused by defects within the material. In this work, low frequency noise spectroscopy and random telegraph signal characterization were used to characterize defect levels in MQW photodiodes. Three traps, located at 0.14 eV (Ea), 0.34 eV (Eb), and 0.43 eV (Ec), were identified from the measured noise. Ea is associated with bulk InGaAs, Eb may be associated with bulk GaAsSb, and Ec is localized at the InGaAs/GaAsSb heterointerface.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

ZnO-based graphite-insulator-semiconductor diode for transferable and low thermal resistance high-power devices

ZhiKun Zhang, Jiming Bian, Jingchang Sun, Zhenhe Ju, Yuxin Wang, Fuwen Qin, Dong Zhang, Yingmin Luo, and Hongzhu Liu

Appl. Phys. Lett. 101, 052108 (2012); http://dx.doi.org/10.1063/1.4742150 (4 pages)

Online Publication Date: 31 July 2012

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ZnO-based graphite-insulator-semiconductor (GIS) diode was fabricated on the high thermal and electrical conductive graphite substrate, with a SiO2 thin layer employed as the insulator layer. The current-voltage characteristics exhibit an excellent rectifying diode-like behavior with an obvious turn on voltage of 2.0 V and rather low leakage current of ∼10−4 A. An interesting negative capacitance phenomenon was also observed from the GIS diode. The excellent heat dissipation performance of the GIS diode compared with conventional sapphire based devices was experimentally demonstrated, which was of special interest for the development of high-power semiconductor devices with sufficient power durability.
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85.30.Tv Field effect devices

Valence band offset of n-ZnO/p-MgxNi1−xO heterojunction measured by x-ray photoelectron spectroscopy

Y. M. Guo, L. P. Zhu, J. Jiang, L. Hu, C. L. Ye, and Z. Z. Ye

Appl. Phys. Lett. 101, 052109 (2012); http://dx.doi.org/10.1063/1.4742172 (3 pages) | Cited 1 time

Online Publication Date: 1 August 2012

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The valence band offset (VBO) of a n-ZnO/p-MgxNi1−xO heterojunction grown by pulsed laser deposition was investigated by x-ray photoelectron spectroscopy. From the directly measured VBO of 1.64 ± 0.05 eV, a −2.26 ± 0.05 eV conduction band offset was derived. This indicates that the ZnO/MgxNi1−xO heterojunction has a type-II (staggered) band alignment. The conduction band minimum (CBM) of the n-ZnO/p-MgxNi1−xO heterojunction shifts to higher energy with Mg doping relative to the n-ZnO/p-NiO heterojunction. Thus, the position of the CBM can be controlled by the Mg concentration.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Fg Pulsed laser ablation deposition
61.72.up Other materials

Metal silicide Schottky barriers on Si and Ge show weaker Fermi level pinning

L. Lin, Y. Guo, and J. Robertson

Appl. Phys. Lett. 101, 052110 (2012); http://dx.doi.org/10.1063/1.4742861 (4 pages)

Online Publication Date: 3 August 2012

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Experimental data and ab-initio calculations find that metal silicide–silicon interfaces have weaker Fermi level pinning than simple metal-Si interfaces, which is incompatible with standard metal induced gap state (MIGS) model of Schottky barriers. We show that this arises because the MIGS in silicide interfaces are not derived from Si surface dangling bonds, but from metal “dangling bond” states in the silicide, whose energies vary with the metal. Calculations predict that rare-earth germinides will have very small barriers on n-Ge.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states

Study of polarity effect in SiOx-based resistive switching memory

Yao-Feng Chang, Pai-Yu Chen, Yen-Ting Chen, Fei Xue, Yanzhen Wang, Fei Zhou, Burt Fowler, and Jack C. Lee

Appl. Phys. Lett. 101, 052111 (2012); http://dx.doi.org/10.1063/1.4742894 (4 pages) | Cited 1 time

Online Publication Date: 3 August 2012

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The SiOx-based resistive switching memory was realized by a simple TaN/SiO2/n++ Si-substrate structure. Post-deposition annealing treatment not only reduced operational variation but also stabilized electrical reliability during repeated switching. The relationship between applied voltage polarity and reset switching parameters is investigated and may indicate that resistive switching occurs at the cathode side. Oxygen-vacancy clustering and asymmetrical thermal-dissipation of the electrodes are discussed as possible causes for the polarity dependence of reset switching parameters. Data retention in high- and low-resistance states was measured for over 104 s, indicating promising potential for future nonvolatile memory applications.
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84.30.Sk Pulse and digital circuits
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Observation of magnetocapacitance in ferromagnetic nanowires

Kulothungasagaran Narayanapillai, Mahdi Jamali, and Hyunsoo Yang

Appl. Phys. Lett. 101, 052401 (2012); http://dx.doi.org/10.1063/1.4739848 (3 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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The authors have investigated magnetic domain wall induced capacitance variation as a tool for the detection of magnetic reversal in magnetic nanowires for in-plane (NiFe) and out-of-plane (Co/Pd) magnetization configurations. The switching fields in the capacitance measurements match with that of the magnetoresistance measurements in the opposite sense. The origin of the magnetocapacitance has been attributed to magnetoresistance. This magnetocapacitance detection technique can be useful for magnetic domain wall studies.
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75.75.Fk Domain structures in nanoparticles
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Transversal magneto-resistance in epitaxial Fe3O4 and Fe3O4/NiO exchange biased system

Han-Chun Wu, R. Ramos, R. G. S. Sofin, Zhi-Min Liao, M. Abid, and I. V. Shvets

Appl. Phys. Lett. 101, 052402 (2012); http://dx.doi.org/10.1063/1.4739951 (5 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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We have investigated transversal magneto-resistance (MR) in epitaxial Fe3O4 and Fe3O4/NiO exchange biased systems. It was found that the magnetic field dependence and the magnitude of the transversal MR in both systems strongly depend on the bias current density which suggests that the transversal MR in metal oxide with anti-phase boundaries (APBs) cannot be described by the conventional transversal MR for a single magnetic domain. The effect of electron scattering at the APBs may have to be considered. Angular dependence of the transversal MR at low temperature further indicates that the current explanation of the origin of transversal MR on the basis of anisotropic MR alone may not be sufficient for a system experiencing charge ordering.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Lx Magnetic oxides

Direct imaging of spin relaxation in stepped α-Fe2O3/Ni81Fe19 bilayers using x-ray photoemission electron microscopy

R. Bali, H. Marchetto, A. Barcza, M. G. Blamire, and S. S. Dhesi

Appl. Phys. Lett. 101, 052403 (2012); http://dx.doi.org/10.1063/1.4738781 (4 pages)

Online Publication Date: 31 July 2012

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The magnetic domain structure of stepped ferromagnetic Ni81Fe19 films, exchange coupled to antiferromagnetic α-Fe2O3, has been studied using x-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism. Annealing the α-Fe2O3/Ni81Fe19 bilayers in a magnetic field, applied parallel or perpendicular to the step edges, results in a significant increase in the domain size compared to the as-grown bilayer. Subsequent zero-field annealing induces spin-relaxation along the crystallographic axes of the α-Fe2O3. The spin-relaxation process is found to depend on the magnetic field direction during annealing with the domain structure determined by a competition between the step-induced uniaxial anisotropy and the exchange anisotropy.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Ee Antiferromagnetics
75.60.Ch Domain walls and domain structure
78.20.Ls Magneto-optical effects
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy

Generating wave vector specific Damon-Eshbach spin waves in Py using a diffraction grating

J. Sklenar, V. S. Bhat, C. C. Tsai, L. E. DeLong, and J. B. Ketterson

Appl. Phys. Lett. 101, 052404 (2012); http://dx.doi.org/10.1063/1.4737438 (3 pages)

Online Publication Date: 31 July 2012

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A patterned square silver antidot lattice on a thin uniform permalloy film facilitates direct coupling of a quasi-uniform microwave field to short wavelength magnetic modes. The resulting modes are studied as a function of both the magnitude and orientation (relative to the symmetry axes of the array) of an in-plane, external DC magnetic field. The observed modes are identified as surface spin waves with wavelengths matching the Fourier components of the silver array.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Ds Spin waves

Antiferromagnetic interaction in coupled CdSe/ZnMnSe quantum dot structures

D. Dagnelund, Q. J. Ren, I. A. Buyanova, A. Murayama, and W. M. Chen

Appl. Phys. Lett. 101, 052405 (2012); http://dx.doi.org/10.1063/1.4739852 (5 pages)

Online Publication Date: 1 August 2012

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Spin polarization of nonmagnetic CdSe quantum dots (QDs) coupled to adjacent ZnMnSe diluted magnetic semiconductor (DMS) is investigated by CW and time-resolved magneto-optical spectroscopy under tunable laser excitation. Efficient enhancement in the degree of σ− circular polarization of photoluminescence from the CdSe QDs is observed under optical excitation at the σ+-active exciton state of the DMS. The fact that the enhancement persists much longer than the exciton lifetime of the DMS rules out a role of the DMS excitons. A possible explanation is discussed in terms of antiferromagnetic coupling between the excitons in QDs and aligned Mn ions in DMS.
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75.70.Ak Magnetic properties of monolayers and thin films
78.55.Et II-VI semiconductors
78.66.Fd III-V semiconductors
78.47.da Excited states
75.50.Ee Antiferromagnetics
75.50.Pp Magnetic semiconductors

The Curie temperature distribution of FePt granular magnetic recording media

O. Hovorka, S. Devos, Q. Coopman, W. J. Fan, C. J. Aas, R. F. L. Evans, Xi Chen, G. Ju, and R. W. Chantrell

Appl. Phys. Lett. 101, 052406 (2012); http://dx.doi.org/10.1063/1.4740075 (4 pages) | Cited 1 time

Online Publication Date: 1 August 2012

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We present atomistic calculations of the magnetic phase transition behavior in an L10 FePt system to study the effect of grain size distribution on the Curie temperature (Tc) dispersion with relevance to heat assisted magnetic recording. Identifying the relation between the size and Tc of a grain by means of finite size scaling analysis of the differentiated magnetization versus T data allows to show that a lognormal size distribution transforms into a lognormal Tc distribution with moments dependent on the critical exponents. We also address the question of the universality class of FePt.
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81.05.Bx Metals, semimetals, and alloys
81.05.Rm Porous materials; granular materials
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetocrystalline anisotropy behavior in the multiferroic BiMnO3 examined by Lorentz transmission electron microscopy

T. Asaka, M. Nagao, T. Yokosawa, K. Kokui, E. Takayama-Muromachi, K. Kimoto, K. Fukuda, and Y. Matsui

Appl. Phys. Lett. 101, 052407 (2012); http://dx.doi.org/10.1063/1.4742747 (4 pages)

Online Publication Date: 3 August 2012

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We investigated magnetic domain structures of a multiferroic manganite, BiMnO3, by Lorentz transmission electron microscopy. Ferromagnetic domains were observed below ∼105 K, close to the ferromagnetic Curie temperature, TC. The spontaneous magnetization aligns distinctly along the [010] direction, suggesting that the magnetic easy direction is along the b axis. Inflection and merging of the domain walls was observed at twin boundaries. This indicates pinning of the magnetic domain walls at crystallographic twin boundaries. Furthermore, we observed narrow magnetic domain walls, suggesting strong magnetocrystalline anisotropy.
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75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ch Domain walls and domain structure
75.85.+t Magnetoelectric effects, multiferroics
75.30.Cr Saturation moments and magnetic susceptibilities
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Energy-resolved detection of single infrared photons with λ = 8 μm using a superconducting microbolometer

Boris S. Karasik, Sergey V. Pereverzev, Alexander Soibel, Daniel F. Santavicca, Daniel E. Prober, David Olaya, and Michael E. Gershenson

Appl. Phys. Lett. 101, 052601 (2012); http://dx.doi.org/10.1063/1.4739839 (5 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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We report on the detection of single photons with λ = 8 μm using a superconducting hot-electron microbolometer. The sensing element is a titanium transition-edge sensor with a volume ∼0.1 μm3 fabricated on a silicon substrate. Poisson photon counting statistics including simultaneous detection of 3 photons was observed. The width of the photon-number peaks was 0.11 eV, 70% of the photon energy, at 50–100 mK. This achieved energy resolution is one of the best figures reported so far for superconducting devices. Such devices can be suitable for single-photon calorimetric spectroscopy throughout the mid-infrared and even the far-infrared.
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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

Direct current superconducting quantum interferometers with asymmetric shunt resistors

M. Rudolph, J. Nagel, J. M. Meckbach, M. Kemmler, M. Siegel, K. Ilin, D. Koelle, and R. Kleiner

Appl. Phys. Lett. 101, 052602 (2012); http://dx.doi.org/10.1063/1.4739850 (4 pages)

Online Publication Date: 30 July 2012

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We have investigated asymmetrically shunted Nb/Al-AlOx/Nb direct current (dc) superconducting quantum interference devices (SQUIDs). While keeping the total resistance R identical to a comparable symmetric SQUID with R−1 = R1−1+R2−1, we shunted only one of the two Josephson junctions with R = R1,2/2. Simulations predict that the optimum energy resolution ϵ and thus also the noise performance of such an asymmetric SQUID can be 3–4 times better than that of its symmetric counterpart. Experiments at a temperature of 4.2 K yielded ϵ ≈ 32 ℏ for an asymmetric SQUID with an inductance of 22 pH. For a comparable symmetric device, ϵ = 110 ℏ was achieved, confirming our simulation results.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
85.25.Cp Josephson devices
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