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15 Jan 2007

Volume 90, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 032108 (2007); http://dx.doi.org/10.1063/1.2431702 (3 pages)

D. Buca, B. Holländer, S. Feste, St. Lenk, H. Trinkaus, S. Mantl, R. Loo, and M. Caymax
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Improvement switching characteristics of toggle magnetic random access memory with dual polarity write pulse scheme

Yuan-Jen Lee, Chien-Chung Hung, Ding-Yeong Wang, Cheng-Tyng Yen, Wei-Chuan Chen, Shan-Yi Yang, Kuei-Hung Shen, Yung-Hung Wang, Yung-Hsiang Chen, Ming-Jer Kao, and Ming-Jinn Tsai

Appl. Phys. Lett. 90, 032503 (2007); http://dx.doi.org/10.1063/1.2431755 (3 pages)

Online Publication Date: 17 January 2007

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The writing probability of toggle magnetic random access memory (MRAM) at built-in bias field is studied by micromagnetic simulation and a dual polarity write pulse scheme has been proposed to enhance the toggle probability at low writing field. The critical writing field can be reduced to 19 Oe at strong built-in bias field from CoFe(1.0 nm)/CoFeB(2.0 nm)/Ru/CoFe(5.0 nm) pinned layer structure. From the simulation and experimental results, it is proven that the toggle MRAM can be operated at lower writing field by dual polarity write pulse scheme.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
84.30.Sk Pulse and digital circuits

Room-temperature ferromagnetism of Cu-implanted GaN

Jong-Han Lee, In-Hoon Choi, Sangwon Shin, Sunggoo Lee, J. Lee, Chungnam Whang, Seung-Cheol Lee, Kwang-Ryeol Lee, Jong-Hyeob Baek, Keun Hwa Chae, and Jonghan Song

Appl. Phys. Lett. 90, 032504 (2007); http://dx.doi.org/10.1063/1.2431765 (3 pages) | Cited 28 times

Online Publication Date: 17 January 2007

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1 MeV Cu2+ ion was implanted into GaN with a dose of 1×1017 cm−2 at room temperature. After implantation, the samples were subsequently performed by rapid thermal annealing at 700, 800, and 900 °C for 5 min. Both nonmagnetic Cu ion implanted samples annealed at 700 and 800 °C exhibit the ferromagnetism at room temperature, and the saturation magnetization of these samples is estimated to be 0.057μB and 0.27μB per Cu atom from M-H curve, respectively. However, the sample annealed at 900 °C does not show ferromagnetism due to clustering of Cu during the annealing process.
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81.05.Ea III-V semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.S- Impurities in crystals

Growth, structural, and magnetic characterizations of nanocrystalline γ′-FeNiN(220) thin films

P. Prieto, K. R. Pirota, J. M. Sanz, E. Jiménez, J. Camarero, F. Maccherozzi, and F. G. Panaccione

Appl. Phys. Lett. 90, 032505 (2007); http://dx.doi.org/10.1063/1.2430920 (3 pages) | Cited 2 times

Online Publication Date: 18 January 2007

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The authors have developed a fabrication process of nanocrystalline γ′-FeNiN[220] thin ferromagnetic films by using a dual ion beam sputtering system. The films show well defined in-plane magnetic uniaxial anisotropy, with high anisotropy field and high macroscopic saturation magnetization, requisites of crucial importance for high-frequency applications. The estimated ferromagnetic resonance frequency goes within the gigahertz regime, and the magnetic response can be tailored by the deposition conditions. Element-selective measurements reveal a reduction of the total Fe and Ni magnetic moments in γ′-FeNiN with respect to pure Fe and Ni due to hybridization between Fe and Ni 3d and N 2p states.
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75.70.Ak Magnetic properties of monolayers and thin films
81.07.Bc Nanocrystalline materials
81.15.Cd Deposition by sputtering
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Gw Magnetic anisotropy

Assessment of the local supercurrent densities in long superconducting coated conductors

M. Zehetmayer, R. Fuger, M. Eisterer, F. Hengstberger, and H. W. Weber

Appl. Phys. Lett. 90, 032506 (2007); http://dx.doi.org/10.1063/1.2431472 (3 pages) | Cited 9 times

Online Publication Date: 18 January 2007

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The authors report on measurements of the local supercurrent density in long Y1Ba2Cu3O7−δ based coated conductors by the magnetoscan technique. Significant inhomogeneities were found, which are well resolved by the resulting magnetic field map. A single central line scan along the length of the conductor reflects the inhomogeneities over the entire width of the sample, thus offering the possibility of very fast characterization. Modifying the applied field leads to different results highlighting either the overall critical current or details of the defect structure. In addition, numerical simulations of the current dynamics were carried out for a qualitative and quantitative interpretation of the results.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.F- Transport properties

Determination of the entropy changes in the compounds with a first-order magnetic transition

G. J. Liu, J. R. Sun, J. Shen, B. Gao, H. W. Zhang, F. X. Hu, and B. G. Shen

Appl. Phys. Lett. 90, 032507 (2007); http://dx.doi.org/10.1063/1.2425033 (3 pages) | Cited 84 times

Online Publication Date: 18 January 2007

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Entropy changes in the compounds of La1−xPrxFe11.5Si1.5 (x = 0.3 and 0.4) have been experimentally studied. A tower-shaped entropy change of the height of ∼ 27 J/kg K is obtained based on the analyses of heat capacity, while the Maxwell relation predicts an extra entropy peak of the height of ∼ 99 J/kg K, slightly varying with Pr content. A careful study indicates that the Maxwell relation cannot be used in the vicinity of the Curie temperature because of the coexistence of paramagnetic and ferromagnetic phases, and the huge entropy peak is a spurious result. Similar conclusions are applicable to MnAs and Mn1−xFexAs, for which huge entropy changes have been reported. Appropriate methods for the determination of entropy change of the compound with phase separation are discussed based on the magnetic data.
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75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
65.40.G- Other thermodynamical quantities
65.40.Ba Heat capacity
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials

Studies on the cluster sizes in the mixed-phase thin films

Qing-li Zhou, Kui-juan Jin, Hui-bin Lu, Chun-lian Hu, Kun Zhao, Dong-yi Guan, and Guo-zhen Yang

Appl. Phys. Lett. 90, 032508 (2007); http://dx.doi.org/10.1063/1.2432945 (3 pages) | Cited 2 times

Online Publication Date: 19 January 2007

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Based on the phase separation scenario, by simulating the resistivity of La0.33Pr0.34Ca0.33MnO3 film with the known coexisting-phase sizes, the authors have obtained the theoretical ferromagnetic (FM) cluster sizes of La2/3Ca1/3MnO3 film, showing around 0.6 μm near Tc. Subsequently the insulator-metal transition occurs when the cluster grows up to 0.7 μm, and the abrupt drop in resistivity occurs when the size is around 0.9 μm. Furthermore, the FM cluster sizes grow with the magnetic field. The obtained results indicate that the model and method can be used to predict the critical size of the clusters at the phase transition for the mixed-phase materials.
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72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
75.50.Dd Nonmetallic ferromagnetic materials
64.75.-g Phase equilibria

Magnetic anisotropy in the ferromagnetic Cu-doped ZnO nanoneedles

T. S. Herng, S. P. Lau, S. F. Yu, H. Y. Yang, L. Wang, M. Tanemura, and J. S. Chen

Appl. Phys. Lett. 90, 032509 (2007); http://dx.doi.org/10.1063/1.2433028 (3 pages) | Cited 32 times

Online Publication Date: 19 January 2007

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Copper-doped ZnO (ZnO:Cu) nanoneedles exhibiting room-temperature ferromagnetism were fabricated by an ion beam technique using Cu plate and ZnO film. A saturated magnetization moment of 0.698 emu/cm3 was found in the nanoneedles when a field of 10 kOe was applied perpendicular to the substrate, which was 15% larger than the field applied parallel to the substrate. The magnetic ordering of the nanoneedles was enhanced significantly to 0.968 emu/cm3 after annealing of 400 °C for 20 min. However, the magnetic anisotropy at high field is vanished but an “easy plane” ferromagnetism becomes apparent at low field region. The possible mechanisms of the magnetic ordering and anisotropy in the ZnO:Cu nanoneedles are discussed.
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75.30.Gw Magnetic anisotropy
61.72.Cc Kinetics of defect formation and annealing
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors

Irreversibility of magnetization rotation in exchange biased Fe/epitaxial-FeF2 thin films

Justin Olamit, Kai Liu, Zhi-Pan Li, and Ivan K. Schuller

Appl. Phys. Lett. 90, 032510 (2007); http://dx.doi.org/10.1063/1.2431784 (3 pages) | Cited 8 times

Online Publication Date: 19 January 2007

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Magnetization reversal via rotation is typical in ferromagnet/antiferromagnet exchange biased systems. The reversibility of the rotation is a manifestation of the microscopic reversal process. The authors have investigated the magnetization reversal in Fe/epitaxial-FeF2 thin films using vector magnetometry and first-order reversal curves. The reversal is predominantly by rotation as the applied field makes an angle with the antiferromagnet spin axis, mostly irreversible at small angles and reversible at larger angles. A modified Stoner-Wohlfarth model reproduces the overall trend of the irreversibility evolution. The remaining discrepancies between the modeled and measured irreversibilities may be attributed to local incomplete domain walls.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.60.Jk Magnetization reversal mechanisms
75.30.Et Exchange and superexchange interactions
75.60.Ch Domain walls and domain structure

Control of hole distribution through isovalent R-cation substitution in Cu2Ba2RCu2O8 superconductors

M. Karppinen, Y. Abe, I. Grigoraviciute, J. M. Chen, R. S. Liu, and H. Yamauchi

Appl. Phys. Lett. 90, 032511 (2007); http://dx.doi.org/10.1063/1.2431458 (3 pages)

Online Publication Date: 19 January 2007

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Superconductive Cu2Ba2RCu2O8 samples with R ranging from Gd to Tm have been synthesized through a sol-gel route. Both iodometric titration and Cu L-edge x-ray absorption near-edge structure (XANES) spectroscopy data indicate that the average Cu valence remains constant, whereas Tc increases with decreasing size of the R constituent. An explanation for this trend is revealed from O K-edge XANES spectra, which show that the smaller-for-larger R-cation substitution results in a shift of holes from the Cu2O2 charge reservoir to the superconductive CuO2 planes. Since Cu2Ba2RCu2O8 samples are underdoped, such a shift of holes raises the value of Tc.
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74.62.Dh Effects of crystal defects, doping and substitution
74.25.F- Transport properties
74.72.-h Cuprate superconductors
74.25.N- Response to electromagnetic fields
78.70.Dm X-ray absorption spectra
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Growth and electrical properties of large size Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals prepared by the vertical Bridgman technique

Guisheng Xu, Kai Chen, Danfeng Yang, and Junbao Li

Appl. Phys. Lett. 90, 032901 (2007); http://dx.doi.org/10.1063/1.2431706 (3 pages) | Cited 28 times

Online Publication Date: 16 January 2007

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Relaxor-based ferroelectric single crystals Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIMNT) have been grown directly from their melt using the vertical Bridgman method, and their boules have reached the size of ϕ45×80 mm. The as-grown PIMNT28/40/32 crystals on the (001) cuts exhibit a dielectric constant ε ∼ 5200, dielectric loss tan δ ∼ 0.50%, piezoelectric strain constant d33 ∼ 1700–2200 pC/N, electromechanical coupling factors kt ∼ 0.61 and k33 ∼ 0.92, coercive field Ec ∼ 10.88 kV/cm, remanent polarization Pr ∼ 46 μC/cm2, Curie temperature TC ∼ 192 °C, and rhombohedral to tetragonal phase transition temperature Trt ∼ 119 °C. Moreover, their piezoelectric properties show good thermal stability under the heat treatment at 105 °C.
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81.10.Fq Growth from melts; zone melting and refining
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ej Polarization and depolarization
77.80.B- Phase transitions and Curie point

Plasmalike negative capacitance in nanocolloids

J. Shulman, S. Tsui, F. Chen, Y. Y. Xue, and C. W. Chu

Appl. Phys. Lett. 90, 032902 (2007); http://dx.doi.org/10.1063/1.2431782 (3 pages) | Cited 6 times

Online Publication Date: 17 January 2007

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A negative capacitance has been observed in a nanocolloid between 0.1 and 10−5 Hz. The response is linear over a broad range of conditions. The low-ω dispersions of both the resistance and capacitance are consistent with the free-carrier plasma model, while the transient behavior demonstrates a possible energy storage mechanism. A collective excitation, therefore, is suggested.
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73.63.-b Electronic transport in nanoscale materials and structures
72.30.+q High-frequency effects; plasma effects
82.70.Dd Colloids

Investigation of effective internal field in congruent lithium niobate crystal by digital holographic interferometry

Ya’nan Zhi, De’an Liu, Weijuan Qu, Zhu Luan, and Liren Liu

Appl. Phys. Lett. 90, 032903 (2007); http://dx.doi.org/10.1063/1.2432236 (3 pages) | Cited 1 time

Online Publication Date: 17 January 2007

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The phase contrast across the crystal thickness induced by the internal field is measured by the digital holographic interferometry just after the congruent lithium niobate crystal is partially poled. The direction of applied external field is antiparallel to that of internal field, and the measured phase contrast varies linearly with the applied external field. A new internal field is obtained by this method and named effective internal field. The distinct discrepancy between effective and equivalent internal fields is observed. The authors attribute this effect to the new macroscopic representation of elastic dipole components of defect complex in the crystal.
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42.70.Gi Light-sensitive materials
42.40.Kw Holographic interferometry; other holographic techniques
07.60.Ly Interferometers
78.20.Jq Electro-optical effects

Epitaxial growth of BaTiO3 films on TiN/Si substrates by a hydrothermal-galvanic couple method

Yu-Chih Chieh, Chin-Chih Yu, and Fu-Hsing Lu

Appl. Phys. Lett. 90, 032904 (2007); http://dx.doi.org/10.1063/1.2431572 (3 pages) | Cited 5 times

Online Publication Date: 18 January 2007

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Highly (111)- and (200)-oriented cubic BaTiO3 films with dense and hemispherelike morphology have been synthesized on different oriented TiN-coated silicon substrates in barium contained concentrated alkaline solutions at temperatures below 100 °C. An unconventional hydrothermal technique combining a hydrothermal method with a galvanic couple setup was used to prepare the films. Resultant BaTiO3 films could grow easily and epitaxially on the TiN seeding layer over Si substrates. Compared to the conventional hydrothermal method, such a hydrothermal-galvanic couple technique could significantly enhance the growth rate of BaTiO3.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.A- Nucleation and growth
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Anisotropy of domain switching in prepoled lead titanate zirconate ceramics under multiaxial electrical loading

Yuan-Ming Liu, Fa-Xin Li, and Dai-Ning Fang

Appl. Phys. Lett. 90, 032905 (2007); http://dx.doi.org/10.1063/1.2426925 (3 pages) | Cited 2 times

Online Publication Date: 18 January 2007

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The authors report an observation of anisotropic domain switching process in prepoled lead titanate zirconate (PZT) ceramics under multiaxial electrical loading. Prepoled PZT blocks were obliquely cut to apply an electric field at discrete angles θ (0°–180°) to the initial poling direction. Both the coercive field and switchable polarization are found to decrease significantly when sin θ increases from zero to unity. The measured strain curves show that most domains that accomplished 180° domain switching actually experienced two successive 90° switching. The oriented domain texture after poling plus the induced nonuniform stress are used to explain the observed domain switching anisotropy.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Large scale ab initio molecular dynamics simulations of hydrogen-induced degradation of Ta diffusion barriers in ultralow-k dielectric systems

Ling Dai, V. B. C. Tan, Shuo-Wang Yang, Ping Wu, and Xian-Tong Chen

Appl. Phys. Lett. 90, 032906 (2007); http://dx.doi.org/10.1063/1.2432948 (3 pages) | Cited 1 time

Online Publication Date: 19 January 2007

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In ultralow-k dielectric systems, the porous dielectrics are normally sealed by a SiC film before the deposition of a Ta diffusion barrier layer. However, the Ta barrier effects are negated when the SiC films are fabricated by plasma-enhanced chemical vapor deposition (PECVD). Through large scale ab initio molecular dynamics simulations, the authors found that the barrier degradation is due to H atoms introduced during PECVD. The H impurities diffuse into and transform an otherwise dense Ta layer into a loose amorphous phase which is ineffective as a diffusion barrier.
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77.55.-g Dielectric thin films
68.35.Fx Diffusion; interface formation
85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Enhanced tunable properties of Ba0.6Sr0.4TiO3 thin films grown on Pt/Ti/SiO2/Si substrates using MgO buffer layers

Weicheng Zhu, Jinrong Cheng, Shengwen Yu, Jia Gong, and Zhongyan Meng

Appl. Phys. Lett. 90, 032907 (2007); http://dx.doi.org/10.1063/1.2433029 (3 pages) | Cited 13 times

Online Publication Date: 19 January 2007

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Ba0.6Sr0.4TiO3 (BST) thin films were prepared on MgO buffered Pt(111)/Ti/SiO2/Si substrates by pulsed laser deposition. The crystallographic structure, interface characteristics, and dielectric properties of BST thin films are strongly dependent on MgO thickness. BST thin films exhibit (111) preferred orientation when MgO layer is thicker than 5 nm. The MgO layer can mitigate the interdiffusion between BST and Pt, causing the dielectric loss and leakage current of BST thin films to decrease significantly. The dielectric loss, tunability, and the largest figure of merit of BST thin films on 10 nm MgO achieve 0.009, 30%, and 33.4, respectively.
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77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.66.Fn Inorganic compounds
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Enhanced luminescence from catalyst-free grown InP nanowires

M. Mattila, T. Hakkarainen, H. Lipsanen, H. Jiang, and E. I. Kauppinen

Appl. Phys. Lett. 90, 033101 (2007); http://dx.doi.org/10.1063/1.2431711 (3 pages) | Cited 17 times

Online Publication Date: 16 January 2007

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The surface effects in the optical properties of catalyst-free grown InP nanowires are investigated. Both as-grown nanowires and nanowires treated with hydrofluoric acid are studied using low- and room-temperature continuous-wave and time-resolved photoluminescence measurements and transmission electron microscopy. It is shown that the room-temperature photoluminescence intensity is increased by two orders of magnitude after the surface treatment, and that there is also a significant increase in the double-exponential photoluminescence decay time.
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78.67.Lt Quantum wires
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
68.65.La Quantum wires (patterned in quantum wells)
81.65.-b Surface treatments
68.37.Lp Transmission electron microscopy (TEM)

Sliding of zinc oxide nanowires on silicon substrate

A. V. Desai and M. A. Haque

Appl. Phys. Lett. 90, 033102 (2007); http://dx.doi.org/10.1063/1.2431712 (3 pages) | Cited 13 times

Online Publication Date: 16 January 2007

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Adhesion and friction forces between zinc oxide nanowires and silicon substrate were studied in situ inside a scanning electron microscope. A procedure for measuring these forces from the bending profiles of the nanowires was developed and the van der Waals and friction forces were found to be about 81.05 pN and 7.7 nN, respectively. The pronounced friction was explained using nanoscale adhesion-friction coupling mechanisms. Immediate implication of the findings is on the accuracy of nanomechanical characterization using bending experiments.
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68.65.La Quantum wires (patterned in quantum wells)
68.35.Np Adhesion
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

Coulomb blockade and Kondo effect in a few-electron silicon/silicon-germanium quantum dot

Levente J. Klein, Donald E. Savage, and Mark A. Eriksson

Appl. Phys. Lett. 90, 033103 (2007); http://dx.doi.org/10.1063/1.2431760 (3 pages) | Cited 15 times

Online Publication Date: 16 January 2007

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Transport measurements at cryogenic temperatures through a few-electron top gated quantum dot fabricated in a silicon/silicon-germanium heterostructure are reported. Variations in gate voltage induce a transition from an isolated dot toward a dot strongly coupled to the leads. In addition to Coulomb blockade, when the dot is strongly coupled to the leads, the authors observe the appearance of a zero bias conductance peak due to the Kondo effect. The Kondo peak splits in a magnetic field, and the splitting scales linearly with the applied field. They also observe a transition from pure Coulomb blockade to peaks with a Fano line shape.
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73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
72.25.Dc Spin polarized transport in semiconductors

Low-temperature growth of ZnO nanorods in anodic aluminum oxide on Si substrate by atomic layer deposition

Ching-Jung Yang, Shun-Min Wang, Shih-Wei Liang, Yung-Huang Chang, Chih Chen, and Jia-Min Shieh

Appl. Phys. Lett. 90, 033104 (2007); http://dx.doi.org/10.1063/1.2431786 (3 pages) | Cited 19 times

Online Publication Date: 16 January 2007

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Low-temperature growth of self-organized ZnO nanorods on Si substrate is achieved using anodic aluminum oxide and atomic layer deposition at 250 °C without catalyst or seed layer. Photoluminescence spectrum indicates that the ZnO nanorod arrays exhibit a blue∕green luminescence at 480 nm. In addition, the nanorod arrays demonstrate excellent field-emission properties with a turn-on electric field of 6.5 V μm−1 and a threshold electric field of 9.8 V μm−1, which are attributed to the perfectly perpendicular alignment of ZnO nanorods to the Si substrate.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Et II-VI semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.16.Dn Self-assembly
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials

Complete suppression of large InAs island formation on GaAs by metal organic chemical vapor deposition with periodic AsH3 interruption

Youngsoo Lee, Eungjin Ahn, Jungsub Kim, Pilkyung Moon, Changjae Yang, Euijoon Yoon, Hyunjin Lim, and Hyeonsik Cheong

Appl. Phys. Lett. 90, 033105 (2007); http://dx.doi.org/10.1063/1.2432285 (3 pages) | Cited 9 times

Online Publication Date: 16 January 2007

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Self-assembled InAs quantum dots (QDs) on GaAs substrates were grown by metal organic chemical vapor deposition with periodic AsH3 interruption. In contrast to the conventional InAs QD growth method, AsH3 was interrupted periodically while TMIn was introduced into the reactor continuously. By interrupting AsH3 periodically, the growth surface is modulated between As-stabilized surface and In-stabilized one, resulting in complete suppression of relaxed large island formation and significant improvement in photoluminescence intensity. With further optimization of growth parameters, the authors obtained the emission at 1.32 μm and narrow linewidth of 32 meV at room temperature.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

AgInSe2 nanorods: A semiconducting material for saturable absorber

Hendry I. Elim, Wei Ji, Meng-Tack Ng, and Jagadese J. Vittal

Appl. Phys. Lett. 90, 033106 (2007); http://dx.doi.org/10.1063/1.2429030 (3 pages) | Cited 5 times

Online Publication Date: 16 January 2007

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AgInSe2 nanorods (NRs) with a diameter of 15 nm have been investigated for their nonlinear optical responses by using Z-scan and transient absorption techniques with femtosecond laser pulses of photon energy greater than the band gap. At excitation irradiance of 20 GW/cm2, AgInSe2 NRs reveal saturation in the nonlinear absorption and optical Kerr nonlinearity with a recovery time determined to be a few tens of picoseconds. Such large saturable absorption and Kerr nonlinearity exhibit a third-order susceptibility of 1.2×10−8 esu and a figure of merit of 0.04 esu cm s−1, making AgInSe2 NRs a promising candidate for saturable absorption devices.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Epitaxial growth of ZnO nanowall networks on GaN/sapphire substrates

Sang-Woo Kim, Hyun-Kyu Park, Min-Su Yi, Nae-Man Park, Jong-Hyurk Park, Sang-Hyeob Kim, Sung-Lyul Maeng, Chel-Jong Choi, and Seung-Eon Moon

Appl. Phys. Lett. 90, 033107 (2007); http://dx.doi.org/10.1063/1.2430918 (3 pages) | Cited 29 times

Online Publication Date: 17 January 2007

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Heteroepitaxy of vertically well-aligned ZnO nanowall networks with a honeycomblike pattern on GaN/c-Al2O3 substrates by the help of a Au catalyst was realized. The ZnO nanowall networks with wall thicknesses of 80–140 nm and an average height of about 2 μm were grown on a self-formed ZnO thin film during the growth on the GaN/c-Al2O3 substrates. It was found that both single-crystalline ZnO nanowalls and catalytic Au have an epitaxial relation to the GaN thin film in synchrotron x-ray scattering experiments. Hydrogen-sensing properties of the ZnO nanowall networks have also been investigated.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Size-dependent piezoelectricity in zinc oxide nanofilms from first-principles calculations

Chun Li, Wanlin Guo, Yong Kong, and Huajian Gao

Appl. Phys. Lett. 90, 033108 (2007); http://dx.doi.org/10.1063/1.2430686 (3 pages) | Cited 11 times

Online Publication Date: 17 January 2007

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The size dependence of the piezoelectricity in ZnO nanofilms is investigated using ab initio density-functional theory calculations. The effective piezoelectric constant of ZnO nanofilms increases monotonically with increasing film thickness in the nanoscale simulated in the present work, and surprisingly, exceeds that of the bulk ZnO when the thickness is greater than 2.4 nm. The enhancement over the bulk value reaches 11% when the film thickness is 2.9 nm.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Bn Piezoelectric and electrostrictive constants
61.46.-w Structure of nanoscale materials

Buckling characterization of vertical ZnO nanowires using nanoindentation

Liang-Wen Ji, Sheng-Joue Young, Te-Hua Fang, and Chien-Hung Liu

Appl. Phys. Lett. 90, 033109 (2007); http://dx.doi.org/10.1063/1.2431785 (3 pages) | Cited 26 times

Online Publication Date: 17 January 2007

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Nanomechanical characterization of vertical well-aligned single-crystal ZnO nanowires on ZnO:Ga/glass templates was performed by nanoindentation technique. The buckling loads were found to be 1465 and 215 μN for the ZnO nanowires of 100 and 30 nm diameters, respectively. Furthermore, the buckling energies for the ZnO nanowires of 100 and 30 nm diameters were 3.62×10−10 and 3.69×10−11 J, respectively. Based on the Euler buckling model, Young’s modulus of the individual ZnO nanowire has been derived from two possible modes in this work.
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68.65.La Quantum wires (patterned in quantum wells)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations
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