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27 Jul 2009

Volume 95, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 043110 (2009); http://dx.doi.org/10.1063/1.3184784 (3 pages)

Felix Loske and Angelika Kühnle
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Electron spin quantum beats and room temperature g factor in GaAsN

H. M. Zhao, L. Lombez, B. L. Liu, B. Q. Sun, Q. K. Xue, D. M. Chen, and X. Marie

Appl. Phys. Lett. 95, 041911 (2009); http://dx.doi.org/10.1063/1.3186076 (3 pages) | Cited 4 times

Online Publication Date: 31 July 2009

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We report on the investigation of electron spin quantum beats at room temperature in GaAsN thin films by time-resolved Kerr rotation technique. The measurement of the quantum beats, which originate from the Larmor precession of electron spins in external transverse magnetic field, yields an accurate determination of the conduction electron g factor. We show that the g factor of GaAs1−xNx thin films is significantly changed by the introduction of a small nitrogen fraction.
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78.47.jm Quantum beats
68.55.ag Semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ls Magneto-optical effects
72.25.Dc Spin polarized transport in semiconductors
78.66.Fd III-V semiconductors

Tunability of the piezoelectric fields in strained III-V semiconductors

R. Garg, A. Hüe, V. Haxha, M. A. Migliorato, T. Hammerschmidt, and G. P. Srivastava

Appl. Phys. Lett. 95, 041912 (2009); http://dx.doi.org/10.1063/1.3194779 (3 pages) | Cited 5 times

Online Publication Date: 31 July 2009

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In this work we show that tetragonal strain can be used to create a sign reversal of the piezoelectric field in InAs/GaAs semiconductor heterostructures. The strain dependence of the internal displacement of the cation-anion pairs and of the bond polarity are taken into account, beyond the linear model, within an ab initio scheme. The reported tunability of the piezoelectric field is a concept that can be exploited in optoelectronic devices.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
77.65.Ly Strain-induced piezoelectric fields

Periodic supply of indium as surfactant for N-polar InN growth by plasma-assisted molecular-beam epitaxy

Yong-Zhao Yao, Takashi Sekiguchi, Takeshi Ohgaki, Yutaka Adachi, Naoki Ohashi, Hanako Okuno, and Masaki Takeguchi

Appl. Phys. Lett. 95, 041913 (2009); http://dx.doi.org/10.1063/1.3189262 (3 pages) | Cited 1 time

Online Publication Date: 31 July 2009

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We have investigated the self-surfactant effect of In for N-polar InN growth by plasma-assisted molecular-beam epitaxy. We found that InN quality was significantly improved if a thin In coverage (about 1.8 ML) was introduced before InN growth. However, this In coverage was slowly consumed during subsequent InN growth under N-rich condition. Periodically restoring In coverage for thick InN growth was proposed to solve this consumption problem. We suggest that the effect of In surfactant is to terminate the surface N dangling bonds and form an In adlayer, under which an efficient diffusion channel for lateral N adatom transport is created.
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68.55.ag Semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
66.30.-h Diffusion in solids
52.77.-j Plasma applications
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Improving thermoelectric performance of caged compounds through light-element filling

Y. Z. Pei, Jiong Yang, L. D. Chen, W. Zhang, J. R. Salvador, and Jihui Yang

Appl. Phys. Lett. 95, 042101 (2009); http://dx.doi.org/10.1063/1.3182800 (3 pages) | Cited 19 times

Online Publication Date: 27 July 2009

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Heavy elements filling have been considered the most effective way to improve the thermoelectric performance of caged compounds such as CoSb3 by reducing kL. Here, we show an opposite example of filling a light element, Na, into CoSb3 for obtaining high thermoelectric figure of merit ZT.ZT = 1.25 at 850 K for Na0.48Co4Sb12 is one of the highest values among all reported single-element-filled CoSb3. The Na-filling scatters phonons less effectively but it results in relatively high mobility thus large power factor. This most likely comes from the extra electronic states near the Fermi level induced by Na.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
71.20.Eh Rare earth metals and alloys
63.20.-e Phonons in crystal lattices

Ammonia: A source of hydrogen dopant for InN layers grown by metal organic vapor phase epitaxy

S. Ruffenach, M. Moret, O. Briot, and B. Gil

Appl. Phys. Lett. 95, 042102 (2009); http://dx.doi.org/10.1063/1.3189212 (3 pages) | Cited 11 times

Online Publication Date: 27 July 2009

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Thermal annealing of InN layers grown by metal organic vapor phase epitaxy (MOVPE) is investigated in nitrogen atmosphere for temperatures ranging from 400 to 550 °C and for heat treatment times up to 12 h. This treatment results in hydrogen outdiffusion, lowering significantly the residual n-type background doping. This mechanism is shown to be reversible through thermal annealing under ammonia atmosphere, responsible of hydrogen incorporation during growth. These results establish a MOVPE process allowing the obtention of InN samples, which exhibit similar electrical properties than molecular beam epitaxy grown samples: a key issue in view of future industrial production of InN based devices.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

High performance AlGaN/GaN power switch with HfO2 insulation

Junxia Shi, Lester F. Eastman, Xiaobin Xin, and Milan Pophristic

Appl. Phys. Lett. 95, 042103 (2009); http://dx.doi.org/10.1063/1.3190506 (3 pages) | Cited 18 times

Online Publication Date: 28 July 2009

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High performance AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistor was fabricated using HfO2 as the surface passivation and gate insulator. The gate and drain leakage currents are drastically reduced to tens of nanoamperes before breakdown. Without field plates, for 10 μm of gate-drain spacing, the off-state breakdown voltage is 1035 V with a specific on resistance of 0.9 mΩ cm2. In addition, there is no current slump observed from the pulse measurements. This is the best performance reported on GaN-based power-switching devices on sapphire up to now, which efficiently combines excellent device forward, reverse, and switching characteristics.
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85.30.Tv Field effect devices
81.05.Ea III-V semiconductors

Improvement of resistive switching characteristics in TiO2 thin films with embedded Pt nanocrystals

Wen-Yuan Chang (張文淵), Kai-Jung Cheng (鄭凱嶸), Jui-Ming Tsai (蔡濬名), Hung-Jen Chen (陳泓任), Frederick Chen (陳達), Ming-Jinn Tsai (蔡銘進), and Tai-Bor Wu (吳泰伯)

Appl. Phys. Lett. 95, 042104 (2009); http://dx.doi.org/10.1063/1.3193656 (3 pages) | Cited 24 times

Online Publication Date: 31 July 2009

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We have fabricated TiO2 thin films with embedded Pt nanocrystals (Pt-NCs) and investigated the resistive switching characteristics for nonvolatile memory application. Reversible and steady bistable resistance switching behavior was observed for the Pt/TiO2/Pt capacitors with Pt-NCs embedded in the TiO2 films. Moreover, an improvement in the stability of resistance switching and retention properties was also achieved from the embedding of uniform and fine Pt-NCs.
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73.40.Rw Metal-insulator-metal structures
73.61.Ng Insulators
84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
72.60.+g Mixed conductivity and conductivity transitions
81.16.-c Methods of micro- and nanofabrication and processing

Bipolar resistive switching behavior in Ti/MnO2/Pt structure for nonvolatile memory devices

Min Kyu Yang, Jae-Wan Park, Tae Kuk Ko, and Jeon-Kook Lee

Appl. Phys. Lett. 95, 042105 (2009); http://dx.doi.org/10.1063/1.3191674 (3 pages) | Cited 38 times

Online Publication Date: 31 July 2009

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This study examined the electrical properties of Ti/MnO2/Pt devices with stable and reproducible bipolar resistive switching behavior. The dependency of the memory behavior on the cell area and operating temperature suggest that the conducting mechanism in the low resistance states is due to the locally conducting filaments formed. X-ray photoelectron spectroscopy showed that nonlattice oxygen ions form at the MnO2 surface. The mechanism of resistance switching in the system examined involves the generation and recovery of oxygen vacancies with the nonlattice oxygen ions.
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77.80.Fm Switching phenomena
73.40.Rw Metal-insulator-metal structures
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.jd Vacancies
85.50.Gk Non-volatile ferroelectric memories
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Direct observation of the controlled magnetization reversal processes in Py/Al/Py asymmetric ring stacks

L. Huang, M. A. Schofield, and Y. Zhu

Appl. Phys. Lett. 95, 042501 (2009); http://dx.doi.org/10.1063/1.3187545 (3 pages) | Cited 3 times

Online Publication Date: 27 July 2009

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Electron holographic experiments were performed to study the magnetization reversal process of patterned Py/Al/Py (20nm/20nm/10nm) asymmetric ring stacks. By changing the in-plane field applied perpendicular to the ring’s symmetric axis, we directly observed the vortex-based magnetization reversal process through controlled domain wall motion and annihilation. The two magnetic layers were found to switch at different critical fields, leading to the existence of various distinct domain state combinations. Quantitative agreement was obtained between measured phase shifts and those derived from micromagnetic calculations, which allows us to resolve the layer-by-layer magnetic behavior as a function of applied external field.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.70.Ak Magnetic properties of monolayers and thin films

Long baseline planar superconducting gradiometer for biomagnetic imaging

C. Granata, A. Vettoliere, C. Nappi, M. Lisitskiy, and M. Russo

Appl. Phys. Lett. 95, 042502 (2009); http://dx.doi.org/10.1063/1.3189285 (3 pages) | Cited 1 time

Online Publication Date: 28 July 2009

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A niobium based dc-superconducting quantum interference device (SQUID) planar gradiometer with a long baseline (50 mm) for biomagnetic applications has been developed. The pickup antenna consists of two integrated rectangular coils connected in series and magnetically coupled to a dc-SQUID in a double parallel washer configuration by two series multiturn input coils. Due to a high intrinsic responsivity, the sensors have shown at T = 4.2 K a white magnetic flux noise spectral density as low as 3 μΦ0/Hz1/2. The spectral density of the magnetic field noise referred to one sensing coil, is 3.0 fT/Hz1/2 resulting in a gradient spectral noise of 0.6 fT/(cm Hz1/2). In order to verify the effectiveness of such sensors for biomagnetic applications, the magnetic response to a current dipole has been calculated and the results have been compared with those of an analogous axial gradiometer. The results show that there is no significant difference. Due to their high intrinsic balance and good performances, planar gradiometers may be the elective sensors for biomagnetic application in a soft shielded environment.
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87.85.Pq Biomedical imaging
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.25.Dq Superconducting quantum interference devices (SQUIDs)
87.57.-s Medical imaging

Superconducting double spin valve with extraordinary large tunable magnetoresistance

Francesco Giazotto

Appl. Phys. Lett. 95, 042503 (2009); http://dx.doi.org/10.1063/1.3190498 (3 pages)

Online Publication Date: 28 July 2009

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A superconducting double spin valve device is proposed. Its operation takes advantage of the interplay between the spin-filtering effect of ferromagnetic insulators and superconductivity-induced out-of-equilibrium transport. Depending on the degree of nonequilibrium, extraordinary large tunnel magnetoresistance as large as 102%–106% can be obtained for realistic material parameters, and it can be tuned over several orders of magnitude under proper voltage biasing and temperature. The relevance of this setup for low-temperature applications is further discussed.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
85.25.-j Superconducting devices

Fast Fourier transform spectrometer readout for large arrays of microwave kinetic inductance detectors

S. J. C. Yates, A. M. Baryshev, J. J. A. Baselmans, B. Klein, and R. Güsten

Appl. Phys. Lett. 95, 042504 (2009); http://dx.doi.org/10.1063/1.3159818 (3 pages) | Cited 13 times

Online Publication Date: 29 July 2009

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Microwave kinetic inductance detectors have great potential for large, very sensitive detector arrays for use in, for example, submillimeter imaging. Being intrinsically readout in the frequency domain, they are particularly suited for frequency domain multiplexing allowing ∼ 1000 s of devices to be readout with one pair of coaxial cables. However, this moves the complexity of the detector from the cryogenics to the warm electronics. We present here the concept and experimental demonstration of the use of fast Fourier transform spectrometer readout, showing no deterioration of the noise performance compared to the low noise analog mixing while allowing high multiplexing ratios.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Josephson squelch filter for quantum nanocircuits

P. Forn-Díaz, R. N. Schouten, W. A. den Braver, J. E. Mooij, and C. J. P. M. Harmans

Appl. Phys. Lett. 95, 042505 (2009); http://dx.doi.org/10.1063/1.3186047 (3 pages) | Cited 1 time

Online Publication Date: 30 July 2009

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We fabricated and tested a squelch circuit consisting of a copper powder filter with an embedded Josephson junction connected to ground. For small signals (squelch ON), the small junction inductance attenuates strongly from dc to at least 1 GHz, while for higher frequencies dissipation in the copper powder increases the attenuation exponentially with frequency. For large signals (squelch OFF), the circuit behaves as a regular metal powder filter. The measured ON/OFF ratio is larger than 50 dB up to 50 MHz. This squelch can be applied in low temperature measurement and control circuitry for quantum nanostructures, such as superconducting qubits and quantum dots.
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85.35.-p Nanoelectronic devices
84.30.Vn Filters
84.71.Mn Superconducting wires, fibers, and tapes
85.25.Cp Josephson devices

Structural and electrical characterization of SiO2/MgO(001) barriers on Si for a magnetic transistor

A. Kohn, A. Kovács, T. Uhrmann, T. Dimopoulos, and H. Brückl

Appl. Phys. Lett. 95, 042506 (2009); http://dx.doi.org/10.1063/1.3182732 (3 pages) | Cited 3 times

Online Publication Date: 30 July 2009

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We report a structural and electrical study of sputter-deposited SiO2/MgO barriers for developing magnetic Si-based transistors. We propose that SiO2/MgO tunneling barriers may utilize spin-filtering by achieving crystalline MgO (001) while reducing spin-scattering due to the Si/SiO2 interface. We find that MgO (<3 nm thick) crystallizes with (001) preferred orientation on thermally oxidized Si(<2 nm). Typical processing temperatures do not cause significant intermixing with SiO2 or ferromagnetic electrode. Conversely, MgO on Si is amorphous up to 2 nm thick. Capacitance-voltage characteristics of MgO capacitors are influenced significantly by the density of interface-states, as high as 5×1013 cm−2 eV−1 while Si/SiO2/MgO structures are electrically beneficial by reducing to 6×1012 cm−2 eV−1.
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73.40.Gk Tunneling
85.30.Tv Field effect devices
84.32.Tt Capacitors
73.20.At Surface states, band structure, electron density of states
82.45.Fk Electrodes

Robust coupling of superconducting order parameter in a mesoscale NbN–Fe–NbN epitaxial structure

S. K. Bose and R. C. Budhani

Appl. Phys. Lett. 95, 042507 (2009); http://dx.doi.org/10.1063/1.3189284 (3 pages) | Cited 2 times

Online Publication Date: 30 July 2009

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We report an unconventional and promising route to self-assemble distributed superconductor-ferromagnet-superconductor (S-F-S) Josephson junctions on single crystal [100] MgO. These structures consist of [110] epitaxial nanoplaquettes of Fe covered with superconducting NbN films of varying thickness. The S-F-S structures are characterized by a strong magnetoresistance (MR) anisotropy for the in-plane and out-of-plane magnetic fields. The stronger in-plane MR suggests decoherence of S-F-S junctions whose critical current follows a (1−T/Tc) and (1−T/Tc)1/2 dependence for T ≈ Tc and T⪡Tc, respectively, in accordance with the theory of supercurrent transport in such junctions.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
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Oxygen passivation of vacancy defects in metal-nitride gated HfO2/SiO2/Si devices

E. Cartier, M. Hopstaken, and M. Copel

Appl. Phys. Lett. 95, 042901 (2009); http://dx.doi.org/10.1063/1.3186075 (3 pages) | Cited 16 times

Online Publication Date: 27 July 2009

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We show that oxygen can be diffused through thin TiN layers to correct flatband voltage offsets in HfO2/SiO2/Si structures, achieving nearly band-edge capacitance voltage characteristics without undue growth of parasitic SiO2. Photoemission reveals that the TiN remains conductive despite mild oxidation, although over-oxidation results in insulating layers. Secondary ionization mass spectroscopy of samples treated with isotopically labeled 18O was used to assess how much oxygen is required to fully passivate the defects caused by thermal processing of metallized HfO2/SiO2/Si devices.
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81.65.Rv Passivation
61.72.jd Vacancies
79.60.Jv Interfaces; heterostructures; nanostructures
81.65.Mq Oxidation
84.32.Tt Capacitors
85.30.Tv Field effect devices

Polarization rotation contributions to dielectric nonlinearity in 65Pb(Mg1/3Nb2/3)O3–35PbTiO3 single crystals

Ashley Bernal and Nazanin Bassiri-Gharb

Appl. Phys. Lett. 95, 042902 (2009); http://dx.doi.org/10.1063/1.3187916 (3 pages) | Cited 5 times

Online Publication Date: 27 July 2009

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The dielectric response of 65Pb(Mg1/3Nb2/3)O3–35PbTiO3 (PMN-35PT) single crystals is reported for ac field amplitudes up to ∼ 3.5 kV/cm over a frequency range from 3 Hz to 1 kHz. The nonlinear dielectric response is described by a Rayleigh-like analysis, indicating extrinsic contributions from nonlinear and hysteretic motion of internal interfaces (phase boundaries and domain walls). Furthermore, the extrinsic contributions are more than five times higher in the [110]- and [001]-poled crystals than crystals poled along the [111] axis. This is attributed to the ease of the polarization vector rotation along the MC mirror plane between orthorhombic and tetragonal phases of PMN-35PT.
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77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point

Changes in the structure of an atomic-layer-deposited HfO2 film on a GaAs (100) substrate as a function of postannealing temperature

C. Y. Kim, S. W. Cho, M.-H. Cho, K. B. Chung, D. C. Suh, D.-H. Ko, C.-H. An, H. Kim, and H. J. Lee

Appl. Phys. Lett. 95, 042903 (2009); http://dx.doi.org/10.1063/1.3182702 (3 pages) | Cited 6 times

Online Publication Date: 28 July 2009

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The effects of postannealing temperature on the crystal structure and energy band gap (Eg) values of atomic-layer-deposited HfO2 films grown on a GaAs (100) substrate were investigated. In postannealed HfO2 films prepared using a rapid thermal annealing (RTA) process in a N2 ambient at temperatures over 600 °C, the initially produced, partially crystallized HfO2 film changed into a well-ordered crystalline structure with no detectable interfacial layer between the film and the GaAs substrate. In the case of a RTA prepared at 700 °C, the thickness of the film was relatively increased compared to that of an as-grown film. Changes in the depth profile data related to stoichiometry and electronic structure after the annealing treatment indicated that Ga oxide is formed within the HfO2 film during the RTA. The formation of Ga oxide in the film significantly affected the Eg values, i.e., the Eg changed from 5.5 for an as-grown film to 4.7 eV for a film annealed at 700 °C.
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77.55.-g Dielectric thin films
68.55.aj Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
71.20.Ps Other inorganic compounds
61.72.Cc Kinetics of defect formation and annealing

Degenerate rhombohedral and orthorhombic states in Ca-substituted Na0.5Bi0.5TiO3

Rajeev Ranjan, V. Kothai, Rohini Garg, Anupriya Agrawal, Anatoliy Senyshyn, and Hans Boysen

Appl. Phys. Lett. 95, 042904 (2009); http://dx.doi.org/10.1063/1.3193658 (3 pages) | Cited 6 times

Online Publication Date: 31 July 2009

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Neutron powder diffraction and temperature dependent dielectric studies were carried out on Ca-substituted Na0.5Bi0.5TiO3, i.e., (Na0.5Bi0.5)1−xCaxTiO3. Stabilization of an orthorhombic phase even at a low Ca concentration (0.05<x ≤ 0.10) suggests that Na0.5Bi0.5TiO3 (NBT) is susceptible to orthorhombic distortion. The orthorhombic and rhombohedral phases coexist for x = 0.10, suggesting these phases to be nearly degenerate. The orthorhombic distortion favoring tendency of Ca assists in promoting the inherent instability with regard to this structure in pure NBT, which was reported recently.
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77.22.Ch Permittivity (dielectric function)
61.66.Fn Inorganic compounds
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.05.fm Neutron diffraction
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
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Improved photovoltaic performance of bilayer heterojunction photovoltaic cells by triplet materials and tetrapod-shaped colloidal nanocrystals doping

Yanqin Li, Rosanna Mastria, Kechang Li, Angela Fiore, Yue Wang, Roberto Cingolani, Liberato Manna, and Giuseppe Gigli

Appl. Phys. Lett. 95, 043101 (2009); http://dx.doi.org/10.1063/1.3186074 (3 pages) | Cited 6 times

Online Publication Date: 27 July 2009

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The aim of this work is to investigate the photovoltaic properties of indium tin oxide/poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) / poly(3-hexylthiophene-2,5-diyl) /fullerene/aluminum bilayer heterojunction solar cells when the active polymer layer is doped with triplet organic molecules (a platinum porphyrin complex) and tetrapod-shaped colloidal CdTe nanocrystals. In both cases, the device photovoltaic responses are greatly improved due to the enhanced triplet exciton population, in the case of molecular doping, and due to the improved charge transport and charge separation characteristics, for nanocrystal doping. The latter are related both to the relatively large nanostructured interface and to the high intrinsic carrier mobilities of nanocrystals.
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84.60.Jt Photoelectric conversion
61.72.up Other materials
81.16.-c Methods of micro- and nanofabrication and processing
82.70.Dd Colloids
71.35.-y Excitons and related phenomena
72.20.Fr Low-field transport and mobility; piezoresistance

Local temperature control of photonic crystal devices via micron-scale electrical heaters

Andrei Faraon and Jelena Vučković

Appl. Phys. Lett. 95, 043102 (2009); http://dx.doi.org/10.1063/1.3189081 (3 pages) | Cited 17 times

Online Publication Date: 27 July 2009

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We demonstrate a method to locally control the temperature of photonic crystal devices via micron-scale electrical heaters. The method is used to control the resonant frequency of InAs quantum dots strongly coupled to GaAs photonic crystal resonators. This technique enables independent control of large ensembles of photonic devices located on the same chip at tuning speed as high as hundreds of kilohertz.
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42.82.-m Integrated optics
42.70.Qs Photonic bandgap materials
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Single ricin detection by atomic force microscopy chemomechanical mapping

Guojun Chen, Jianfeng Zhou, Bosoon Park, and Bingqian Xu

Appl. Phys. Lett. 95, 043103 (2009); http://dx.doi.org/10.1063/1.3190197 (3 pages) | Cited 1 time

Online Publication Date: 27 July 2009

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The authors report on a study of detecting ricin molecules immobilized on chemically modified Au (111) surface by chemomechanically mapping the molecular interactions with a chemically modified atomic force microscopy (AFM) tip. AFM images resolved the different fold-up conformations of single ricin molecule as well as their intramolecule structure of A- and B-chains. AFM force spectroscopy study of the interaction indicates that the unbinding force has a linear relation with the logarithmic force loading rate, which agrees well with calculations using one-barrier bond dissociation model.
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87.15.B- Structure of biomolecules
36.20.Hb Configuration (bonds, dimensions)
82.37.Rs Single molecule manipulation of proteins and other biological molecules
87.14.E- Proteins
87.64.Dz Scanning tunneling and atomic force microscopy
87.15.Fh Bonding; mechanisms of bond breakage

Production of size-controlled Si nanocrystals using self-organized optical near-field chemical etching

Takashi Yatsui and Motoichi Ohtsu

Appl. Phys. Lett. 95, 043104 (2009); http://dx.doi.org/10.1063/1.3193536 (3 pages) | Cited 4 times

Online Publication Date: 28 July 2009

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We demonstrate the selective photochemical etching of Si in a self-organized manner, which strongly depends on the distribution of the optical near field. This dependence was described by the virtual exciton-phonon-polariton model. The photoluminescence (PL) spectra from the etched Si exhibited a blueshifted PL peak at 1.8 eV, corresponding to Si nanocrystals of 2.8 nm diameter.
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81.16.Dn Self-assembly
78.55.Ap Elemental semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
81.07.De Nanotubes
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.35.-y Excitons and related phenomena
82.50.-m Photochemistry

Ion engineering of embedded nanostructures: From spherical to facetted nanoparticles

G. Rizza, E. A. Dawi, A. M. Vredenberg, and I. Monnet

Appl. Phys. Lett. 95, 043105 (2009); http://dx.doi.org/10.1063/1.3186030 (3 pages) | Cited 8 times

Online Publication Date: 28 July 2009

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We show that the high-energy ion irradiation of embedded metallic spherical nanoparticles (NPs) is not limited to their transformation into prolate nanorods or nanowires. Depending on their pristine size, the three following morphologies can be obtained: (i) nanorods, (ii) facettedlike, and (iii) almost spherical nanostructures. Planar silica films containing nearly monodisperse gold NPs (8–100 nm) were irradiated with swift heavy ions (5 GeV Pb) at room temperature for fluences up to 5×1013 cm−2. The experimental results are accounted for by considering a liquid-solid transformation of the premelted NP surface driven by the in-plane stress within the ion-deformed host matrix. This work demonstrates the interest of using ion-engineering techniques to shape embedded nanostructures into nonconventional configurations.
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61.82.Rx Nanocrystalline materials
64.70.kd Metals and alloys
64.70.Nd Structural transitions in nanoscale materials
64.70.D- Solid-liquid transitions
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Jh Ion radiation effects

Magnetic dead layer in ferromagnetic manganite nanoparticles

J. Curiale, M. Granada, H. E. Troiani, R. D. Sánchez, A. G. Leyva, P. Levy, and K. Samwer

Appl. Phys. Lett. 95, 043106 (2009); http://dx.doi.org/10.1063/1.3187538 (3 pages) | Cited 16 times

Online Publication Date: 28 July 2009

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We present experimental evidence on the physical origin of a magnetic dead layer (MDL) in manganite nanoparticles. The studied nanoparticles constitute the wall of La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3 manganite nanotubes. Magnetic properties analysis and high resolution transmission electron microscopy show a shell of approximately 2 nm thickness with different properties from the core. In this shell the atoms are in a noncrystalline array that perfectly explains the 50% reduction of the magnetization compared to the bulk. Moreover, we present experimental evidence that the internal magnetic structure of the MDL is constituted by small ferromagnetic clusters in a frustrated configuration.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
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