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23 Dec 2002

Volume 81, Issue 26, pp. 4895-5074

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Two charge states of dominant acceptor in unintentionally doped GaN: Evidence from photoluminescence study

M. A. Reshchikov, H. Morkoç, S. S. Park, and K. Y. Lee

Appl. Phys. Lett. 81, 4970 (2002); http://dx.doi.org/10.1063/1.1531227 (3 pages) | Cited 29 times

Online Publication Date: 17 December 2002

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Photoluminescence of the dominant deep-level acceptor in high-purity freestanding GaN is studied over a wide range of excitation intensities. A yellow luminescence (YL) band at about 2.2 eV saturates with increasing excitation intensity, whereas a green luminescence (GL) band at about 2.5 eV increases as a square of the excitation intensity. The YL and GL bands are attributed to two charge states of the same defect, presumably a gallium vacancy-oxygen complex. © 2002 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.40.Fy Semiconductors

Simulation of interface states effect on the scanning capacitance microscopy measurement of p–n junctions

J. Yang and F. C. J. Kong

Appl. Phys. Lett. 81, 4973 (2002); http://dx.doi.org/10.1063/1.1532547 (3 pages) | Cited 14 times

Online Publication Date: 17 December 2002

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A two-dimensional numerical simulation model of interface states in scanning capacitance microscopy (SCM) measurements of p–n junctions is presented. In the model, amphoteric interface states with two transition energies in the Si band gap are represented as fixed charges to account for their behavior in SCM measurements. The interface states are shown to cause a stretch-out and a parallel shift of the capacitance–voltage characteristics in the depletion and neutral regions of p–n junctions, respectively. This explains the discrepancy between the SCM measurement and simulation near p–n junctions, and thus modeling interface states is crucial for SCM dopant profiling of p–n junctions. © 2002 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.De Semiconductor-device characterization, design, and modeling
07.79.-v Scanning probe microscopes and components
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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Superconducting single-electron transistor coupled to a locally tunable electromagnetic environment

W. Lu, A. J. Rimberg, and K. D. Maranowski

Appl. Phys. Lett. 81, 4976 (2002); http://dx.doi.org/10.1063/1.1530731 (3 pages) | Cited 5 times

Online Publication Date: 17 December 2002

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We have developed a system consisting of a superconducting single-electron transistor (S-SET) coupled to a two-dimensional electron gas (2DEG), for which the dissipation can be tuned in the immediate vicinity of the S-SET. Such tuning can be performed easily, and provides access to a significant range of environmental impedances. For temperatures above 100 mK, we find qualitative agreement between measured changes in the S-SET conductance versus dissipation and a model incorporating electromagnetic fluctuations in both the S-SET leads and the 2DEG. © 2002 American Institute of Physics.
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85.25.-j Superconducting devices
85.35.Gv Single electron devices
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.50.+r Tunneling phenomena; Josephson effects

Influence of LaAlO3 surface topography on rf current distribution in superconducting microwave devices

A. P. Zhuravel, A. V. Ustinov, K. S. Harshavardhan, and Steven M. Anlage

Appl. Phys. Lett. 81, 4979 (2002); http://dx.doi.org/10.1063/1.1530753 (3 pages) | Cited 15 times

Online Publication Date: 17 December 2002

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A laser scanning microscope with a thermal spot size of about 4 μm is used to measure a quantity proportional to the rf current density in an operating superconducting coplanar waveguide microwave resonator. The twinning of the LaAlO3 substrate produces a meandering of the current at the edges due to irregularities in the wet etching of the YBa2Cu3O7−δ film associated with substrate twin domain blocks, and an ( ∼ 20%) enhancement of the rf photoresponse at these locations. These irregularities are candidates for enhanced nonlinear response from the device. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Mm Grain and twin boundaries

Highly crystallized as-grown smooth and superconducting MgB2 films by molecular-beam epitaxy

A. J. M. van Erven, T. H. Kim, M. Muenzenberg, and J. S. Moodera

Appl. Phys. Lett. 81, 4982 (2002); http://dx.doi.org/10.1063/1.1530732 (3 pages) | Cited 38 times

Online Publication Date: 17 December 2002

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We have investigated the growth of superconductive thin films of magnesium diboride (MgB2) by molecular-beam epitaxy. A Si(111) substrate with a seed layer of MgO was used for the growth of these films by varying parameters such as the growth temperature, Mg:B flux ratio and deposition rate as well as the background pressure. It was found that highly crystallized films could already form at 250 °C; however, only in a narrow window of growth parameters. The highest critical temperature of 35.2 K with a sharp transition (ΔTC of 0.5 K) was observed for films grown at 300 °C. Using a capping layer of MgO proved to be highly beneficial for the preservation and the smoothness of these films. Together with the fact that MgO proved to be a good seed layer for thin films of MgB2 makes it an ideal candidate for growing all epitaxial MgB2 Josephson junctions. © 2002 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.10.+v Occurrence, potential candidates

Field-induced anisotropic nitrogen distribution as the source of uniaxial magnetic anisotropy in (Fe0.98Al0.02)1−δNδ films

Y-K. Liu, M. H. Kryder, and V. G. Harris

Appl. Phys. Lett. 81, 4985 (2002); http://dx.doi.org/10.1063/1.1531224 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2002

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Extended x-ray absorption fine structure is employed to describe a physical fingerprint that distinguishes the easy and hard in-plane magnetic axes in (Fe0.98Al0.02)1−δNδ films. This fingerprint manifests as an anisotropic strain field about the Fe atom and is shown to scale with magnetic anisotropy energy as δ increases. We propose this effect is due to an anisotropic distribution of N atoms caused by the application of a magnetic field during growth. © 2002 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra

Charge redistribution in YBa2Cu3O7−d probed by Raman spectroscopy: CuO2-plane phonon as a probe of carrier dynamics in the CuO2 plane

Minoru Osada, Masato Kakihana, Mikael Käll, and Lars Börjesson

Appl. Phys. Lett. 81, 4988 (2002); http://dx.doi.org/10.1063/1.1529082 (3 pages)

Online Publication Date: 17 December 2002

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Raman-scattering spectra were investigated for the Y1−xCaxBa2Cu3−yCoyO7−d system which undergoes a metal-to-insulator transition under variation of carrier concentration. As the system approaches the metal-to-insulator phase boundary, the intensity of CuO2-plane phonon modes decreases. We found that the intensity of the CuO2-plane mode scales with the inverse of the hole concentration within the CuO2 conducting planes. A remarkable correlation is found between the CuO2-plane mode intensity and Tc for Y1−xCaxBa2Cu3−yCoyO7−d. We suggest that this correlation as well as the CuO2-plane mode intensity offer a simple and useful probe for metal-to-insulator transition and carrier dynamics in the CuO2 plane for substituted materials. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Jb Electronic structure (photoemission, etc.)
74.25.F- Transport properties
74.62.Yb Other effects
74.25.Gz Optical properties
74.25.Kc Phonons
74.10.+v Occurrence, potential candidates
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions

High-Curie-temperature Ga1−xMnxAs obtained by resistance-monitored annealing

K. W. Edmonds, K. Y. Wang, R. P. Campion, A. C. Neumann, N. R. S. Farley, B. L. Gallagher, and C. T. Foxon

Appl. Phys. Lett. 81, 4991 (2002); http://dx.doi.org/10.1063/1.1529079 (3 pages) | Cited 18 times

Online Publication Date: 17 December 2002

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We show that by annealing Ga1−xMnxAs thin films at temperatures significantly lower than in previous studies, and monitoring the resistivity during growth, an unprecedented high Curie temperature TC and conductivity can be obtained. TC is unambiguously determined to be 118 K for Mn concentration x = 0.05, 140 K for x = 0.06, and 120 K for x = 0.08. We also identify a clear correlation between TC and the room temperature conductivity. The results indicate that Curie temperatures significantly in excess of the current values are achievable with improvements in growth and post-growth annealing conditions. © 2002 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors

Effect of underlayers of laser-assisted magnetic recording media on high-density recording

Hiroyuki Katayama, Kosuke Watanabe, Kazuhisa Takayama, Jun-ichi Sato, Shintaro Miyanishi, Kunio Kojima, and Kenji Ohta

Appl. Phys. Lett. 81, 4994 (2002); http://dx.doi.org/10.1063/1.1530746 (3 pages) | Cited 4 times

Online Publication Date: 17 December 2002

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The effect of underlayers of laser-assisted magnetic recording media has been investigated from the view point of high-density magnetic recording. The frequency response of a carrier-to-noise ratio (C/N) was measured in the media with various kinds of underlayers. It was found that they affect the high-frequency recording capability; the C/N at higher frequencies has been drastically improved for an Al-underlayered recording medium and a C/N of 40 dB was obtained at a recording frequency of 45 MHz and a track width of 0.35 μm. These results are explained by the surface morphology of the underlayer and its pinning effect on the domain-wall motion that is considered to work well for recording smaller stable domains. © 2002 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ss Magnetic recording materials
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.47.De Metallic surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

Magnetization reversal measurements in Gd/Fe multilayer antidot arrays by vector magnetometry using x-ray magnetic circular dichroism

D. R. Lee, Y. Choi, C.-Y. You, J. C. Lang, D. Haskel, G. Srajer, V. Metlushko, B. Ilic, and S. D. Bader

Appl. Phys. Lett. 81, 4997 (2002); http://dx.doi.org/10.1063/1.1532552 (3 pages) | Cited 12 times

Online Publication Date: 17 December 2002

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Fe K-edge x-ray magnetic circular dichroism (XMCD) was used as vector magnetometry to measure the magnetization rotation while field cycling Gd/Fe multilayer antidot arrays through a hysteresis loop. The measured XMCD hysteresis curves were then compared quantitatively with micromagnetic calculations to reconstruct the microscopic magnetization configurations. The best fit reveals the existence of three types of characteristic domains: two that rotate coherently during magnetization reversal and one that is strongly pinned. The behavior is explained by a simple three-domain energy model, including a phenomenological ansatz for a shape-induced demagnetization energy contribution. © 2002 American Institute of Physics.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
78.66.Bz Metals and metallic alloys
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Melt-textured YBa2Cu3O7 based material doped with Li and Zn: Comparison of high trapped fields and pinning

L. Shlyk, G. Krabbes, G. Fuchs, K. Nenkov, and P. Verges

Appl. Phys. Lett. 81, 5000 (2002); http://dx.doi.org/10.1063/1.1532530 (3 pages) | Cited 16 times

Online Publication Date: 17 December 2002

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The pinning forces and trapped fields obtained in bulk YBa2Cu3O7 (YBCO)-based material doped with Li are compared with results reported for melt-processed samples doped with Zn. The increase of the volume pinning force of Li doped material is twice that of Zn doped YBCO at 77 K. This leads to 20% higher magnetic fields trapped in the Li-doped sample at 77 K. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors

Highly aligned, spin polarized thin films of Sr2FeMoO6 by a chemical vapor process

J. Rager, A. V. Berenov, L. F. Cohen, W. R. Branford, Y. V. Bugoslavsky, Y. Miyoshi, M. Ardakani, and J. L. MacManus-Driscoll

Appl. Phys. Lett. 81, 5003 (2002); http://dx.doi.org/10.1063/1.1532752 (3 pages) | Cited 17 times

Online Publication Date: 17 December 2002

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Highly oriented films of Sr2FeMoO6 were fabricated by ultrasonic spray pyrolysis. A combined organic/inorganic solution was developed and the films were deposited on single-crystal LaAlO3 between 600 °C and 900 °C followed by postannealing at 850 °C or 1200 °C in Ar/5% H2. Optimum films showed a metallic resistivity behavior with less than a 0.25% magnetoresistive effect at 50 K, 1 T, indicative of highly quality intra- and intergranular material. At 4.2 K, the lower bound saturation magnetization, Ms was ∼ 2.5 μB/f.u. and the transport spin polarization was 60±3%. © 2002 American Institute of Physics.
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72.25.Ba Spin polarized transport in metals
81.15.Rs Spray coating techniques
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
71.30.+h Metal-insulator transitions and other electronic transitions
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Evidence of the relaxor-paraelectric phase transition in Pb(Fe2/3W1/3)O3 ceramics

Liliana Mitoseriu, Maria M. Carnasciali, Paolo Piaggio, and Paolo Nanni

Appl. Phys. Lett. 81, 5006 (2002); http://dx.doi.org/10.1063/1.1530711 (3 pages) | Cited 13 times

Online Publication Date: 17 December 2002

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The transition relaxor-paraelectric in Pb(Fe2/3W1/3)O3 ceramics was studied by x-ray diffraction and Raman scattering at temperatures in the range of 85–800 K. For high diffraction angles (160° and 162°), a slight difference between the two phases was found. Raman spectra show an evolution with temperature with anomalies of bands of 848 cm−1 and 147 cm−1 (shift and intensity) in the Curie range of temperatures. This behavior is interpreted as an experimental evidence of perturbations of the nanopolar ordering related to the phase transition. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
78.30.Hv Other nonmetallic inorganics
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Epitaxial growth and dielectric properties of homologous Srm−3Bi4TimO3m+3 (m = 3,4,5,6) thin films

S. T. Zhang, Y. F. Chen, H. P. Sun, X. Q. Pan, Z. G. Liu, and N. B. Ming

Appl. Phys. Lett. 81, 5009 (2002); http://dx.doi.org/10.1063/1.1530741 (3 pages) | Cited 6 times

Online Publication Date: 17 December 2002

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The first four members of Bi-layered Srm−3Bi4TimO3m+3 homologous series with m = 3, 4, 5, and 6, i.e., Bi4Ti3O12, SrBi4Ti4O15, Sr2Bi4Ti5O18, and Sr3Bi4Ti6O21, were grown on SrTiO3 (001) single-crystal substrates by pulsed-laser deposition. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) reveal that the films grew epitaxially with in-plane epitaxial alignment of [1math0]Srm−3Bi4TimO3m+3‖[010]SrTiO3. HRTEM cross-sectional images show that the films with m = 3, 4, and 5 are nearly free of intergrowth, whereas a number of growth defects were observed in the film with m = 6. Using an evanescent microwave probe, the room-temperature dielectric constants of these epitaxial films are measured to be 221±13, 205±15, 261±29, and 249±17 for films with m = 3, 4, 5, and 6, respectively. © 2002 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
77.22.Ch Permittivity (dielectric function)

Effect of LaNiO3 interlayer on dielectric properties of (Ba0.5Sr0.5)TiO3 thin films deposited on differently oriented Pt electrodes

Ki Hyun Yoon, Ji-Hoon Sohn, Byoung Duk Lee, and Dong Heon Kang

Appl. Phys. Lett. 81, 5012 (2002); http://dx.doi.org/10.1063/1.1531218 (3 pages) | Cited 29 times

Online Publication Date: 17 December 2002

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The (Ba0.5Sr0.5)TiO3 (BST) thin films were deposited on the LaNiO3/Pt(111)/Ti/SiO2/Si [LNO/Pt(111)] and LaNiO3/Pt(200)/SiO2/Si [LNO/Pt(200)] substrates by metalorganic deposition process. The BST films directly grown on the Pt(200) and Pt(111) substrates exhibited random orientation. In case of the LNO/Pt(111) substrates, the BST film was also randomly oriented, but the insertion of LNO interlayer on the Pt(200) substrates caused the growth of (100) textured BST films. The dielectric constant of the 350-nm-thick BST films on LNO/Pt(200) was around 400, which was higher than that of the films on LNO/Pt(111) (around 340). This result was attributed to the fact that the polar axis of the (100) oriented film was more tilted away from the normal to the film surface than that of randomly oriented film. Also, the tunabilities of BST films deposited on the LNO/Pt(200) and LNO/Pt(111) substrates were nearly 60% and 51% at the applied electric field of 400 kV/cm, respectively. Improved tunability has been attributed to the (100) texture of the film leading to an enhancement of the in-plane oriented polar axis. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Graded ferroelectric thin films: Possible origin of the shift along the polarization axis

G. Poullain, R. Bouregba, B. Vilquin, G. Le Rhun, and H. Murray

Appl. Phys. Lett. 81, 5015 (2002); http://dx.doi.org/10.1063/1.1532771 (3 pages) | Cited 22 times

Online Publication Date: 17 December 2002

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Hysteresis measurements performed on graded Pt/lead zirconate titanate (PZT)/Pt structures with well oxygenated PZT films do not display any shift along the polarization axis (Voffset) as previously reported. On the other hand, when the PZT graded films were grown under low oxygen pressure, an offset voltage was measured. This shift was systematically enhanced after cycling the film as for fatigue measurements. It was also observed that the Voffset is independent of the value of the reference capacitor used in the Sawyer–Tower circuit. We propose an asymmetry in the leakage current of the structure to be at the origin of the shift along the polarization axis. © 2002 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.55.-g Dielectric thin films

Effects of Hf contamination on the properties of silicon oxide metal–oxide–semiconductor devices

Chang Seok Kang, Katsunori Onishi, Laegu Kang, and Jack C. Lee

Appl. Phys. Lett. 81, 5018 (2002); http://dx.doi.org/10.1063/1.1532755 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2002

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Effects of hafnium (Hf) contamination on the properties of n+-polycrystalline-Si/SiO2/Si metal–oxide–semiconductor (MOS) devices were investigated using p-type Si substrates implanted by Hf ions. Flat-band voltages (Vfb) and substrate doping concentrations (NA) of the MOS capacitors were not dependent on the Hf dose levels of 1×1011–1×1013 atoms/cm2. Leakage current density of the MOS capacitor was also not affected by the implant conditions. Electron channel mobility of n-type MOS field-effect transistors with 45-Å-thick SiO2 as gate dielectrics was not degraded by the implantation of Hf ions into the Si substrates. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
85.30.Tv Field effect devices
68.35.Dv Composition, segregation; defects and impurities

Ultralow loss polycrystalline alumina

Jonathan D. Breeze, Xavi Aupi, and Neil McN. Alford

Appl. Phys. Lett. 81, 5021 (2002); http://dx.doi.org/10.1063/1.1532553 (3 pages) | Cited 8 times

Online Publication Date: 17 December 2002

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Polycrystalline alumina with extremely low microwave dielectric loss is reported with properties analogous to a theoretical ensemble of randomly oriented, single crystal sapphire grains. By avoiding deleterious impurities and by careful control of microstructure, we show that grain boundaries in aluminum oxide have only a limited influence on the dielectric loss. A method of measuring the electric permittivity and loss tangent of low-loss microwave ceramic dielectrics is reported. The electrical parameters such as relative permittivity and loss tangent are extracted using the radial mode matching technique. The measured values for ultralow loss polycrystalline aluminum oxide agree well with theoretical values modelled on an ensemble of randomly oriented anisotropic single crystal sapphire grains. © 2002 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
61.72.Mm Grain and twin boundaries
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Microstructure and field emission properties of coral-like carbon nanotubes

N. G. Shang, C. P. Li, W. K. Wong, C. S. Lee, I. Bello, and S. T. Lee

Appl. Phys. Lett. 81, 5024 (2002); http://dx.doi.org/10.1063/1.1527992 (3 pages) | Cited 14 times

Online Publication Date: 17 December 2002

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Coral-like carbon nanotubes (CNTs) have been synthesized by using chemical vapor deposition. Unlike conventional CNTs, the as-deposited CNT consisted of a high density of interlaced graphitic nanoflakes of about 5 nm in thickness. The CNTs had a bamboo-like internal structure with their outer walls consisting of many open graphite layers, and the nanoflakes stemming from the “bamboo knots.” The growth mechanism of CNTs was discussed. The field emission characteristics of CNT films showed a turn-on field as low as 4 V/μm. This special CNT might extend mechanical and electronic properties and applications of the CNTs. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Lp Transmission electron microscopy (TEM)

Electron-stimulated hydrogen desorption from diamond surfaces and its influence on the low-pressure synthesis of diamond

C. Goeden and G. Dollinger

Appl. Phys. Lett. 81, 5027 (2002); http://dx.doi.org/10.1063/1.1526460 (3 pages) | Cited 4 times

Online Publication Date: 17 December 2002

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A total cross section σD = (5±2.6)×10−18 cm2 is measured for electron-stimulated desorption (ESD) of deuterium from a boron-doped, deuterated diamond(100) surface at 5 eV incident electron energy. This large ESD cross section means a significant contribution of ESD to hydrogen abstraction reactions in microwave-driven chemical vapor deposition of diamond. The ESD cross section decreases when changing to a nitrogen-doped diamond. This change is suggested to be the reason for the reported influence of small concentrations of nitrogen or boron added to the process gas on diamond growth. © 2002 American Institute of Physics.
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68.43.Rs Electron stimulated desorption
81.05.U- Carbon/carbon-based materials
79.20.La Photon- and electron-stimulated desorption

Enhancing the resolution of scanning near-field optical microscopy by a metal tip grown on an aperture probe

Heinrich G. Frey, Fritz Keilmann, Armin Kriele, and Reinhard Guckenberger

Appl. Phys. Lett. 81, 5030 (2002); http://dx.doi.org/10.1063/1.1530736 (3 pages) | Cited 66 times

Online Publication Date: 17 December 2002

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We show improvement of the optical and topographical resolution of scanning near-field optical microscopy by introducing a “tip-on-aperture” probe, a metallic tip formed on the aperture of a conventional fiber probe. The tip concentrates the light passing through the aperture. Thus the advantages of aperture and apertureless scanning near-field optical microscopy are combined. Tips are grown by electron beam deposition and then covered with metal. Fluorescent beads are imaged with a resolution down to 25 nm (full width at half maximum) in the optical signal. The near-field appears strongly localized within 5 nm in z direction, thus promising even higher resolution with sharper tips. © 2002 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
68.37.Uv Near-field scanning microscopy and spectroscopy

Vacancy clustering model for Ti non-steady-state radiation-enhanced diffusion in MgO(100)

M. Lu, C. Lupu, and J. W. Rabalais

Appl. Phys. Lett. 81, 5033 (2002); http://dx.doi.org/10.1063/1.1531829 (3 pages) | Cited 4 times

Online Publication Date: 17 December 2002

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Ti diffusion in MgO(100) prebombarded by Ar+, Cl+, and Cr+ has been studied by secondary ion mass spectroscopy under conditions for non-steady-state radiation-enhanced diffusion. The Ti diffusion behaviors of these samples are different, although the ballistic behaviors of the implanting ions are similar. For short annealing periods, the Ti diffusion enhancements follow the order Cr+>Ar+>Cl+, while for long annealing periods the order is Cl+>Ar+>Cr+. A model based on a vacancy clustering mechanism during thermal relaxation of the energetic cascade is proposed to explain these trends. © 2002 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters
61.80.Jh Ion radiation effects
61.82.Ms Insulators
61.72.S- Impurities in crystals
61.72.up Other materials

Self-organized ZnO quantum dots on SiO2/Si substrates by metalorganic chemical vapor deposition

Sang-Woo Kim, Shizuo Fujita, and Shigeo Fujita

Appl. Phys. Lett. 81, 5036 (2002); http://dx.doi.org/10.1063/1.1527690 (3 pages) | Cited 65 times

Online Publication Date: 17 December 2002

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ZnO quantum dots (QDs) were fabricated on SiO2/Si substrates by metalorganic chemical vapor deposition. The densities and sizes of dots were investigated by atomic force microscopy. Photoluminescence at 10 K showed the broad spectra with band tails up to about 3.55 and 3.65 eV for the as-grown and the annealed ZnO QDs, respectively, which were located at the higher energy with respect to the free exciton emission of the ZnO thin film located at about 3.377 eV. These results indicate that the broad emission band results from the quantum size effect, reflecting the dot size inhomogeneity. © 2002 American Institute of Physics.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Et II-VI semiconductors
68.37.Ps Atomic force microscopy (AFM)
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)

Colloidal particle foams: Templates for Au nanowire networks?

J. N. O’Shea, M. A. Phillips, M. D. R. Taylor, P. Moriarty, M. Brust, and V. R. Dhanak

Appl. Phys. Lett. 81, 5039 (2002); http://dx.doi.org/10.1063/1.1526924 (3 pages) | Cited 9 times

Online Publication Date: 17 December 2002

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Spin coating a dilute solution of thiol-passivated Au nanoparticles onto silicon produces nanostructured cellular networks. Photoemission measurements, coupled with atomic force microscopy imaging and a statistical crystallography analysis, show that although annealing in the 500–600 K range removes the thiol surfactants surrounding the nanoparticles, the cellular morphology of the nanocrystal foam is preserved following annealing. Thus, self-assembled nanocrystal arrays may be exploited as templates for (bare) Au nanostructures on Si. Although appreciable particle diffusion during annealing does not occur, significant sintering of Au nanocrystals within the cellular network branches is observed. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.07.Vb Quantum wires
81.05.Bx Metals, semimetals, and alloys
81.16.Dn Self-assembly
61.46.-w Structure of nanoscale materials
82.70.Dd Colloids
61.72.Cc Kinetics of defect formation and annealing
82.70.Rr Aerosols and foams

Charge imaging and manipulation using carbon nanotube probes

S.-D. Tzeng, C.-L. Wu, Y.-C. You, T. T. Chen, S. Gwo, and H. Tokumoto

Appl. Phys. Lett. 81, 5042 (2002); http://dx.doi.org/10.1063/1.1530377 (3 pages) | Cited 14 times

Online Publication Date: 17 December 2002

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Due to their high aspect ratio, well-defined cylindrical structure, and good electrical conductivity, carbon nanotubes (CNTs) are ideal probes for “true” local imaging of electric domain structures at the nanoscale. By performing force–distance measurements and tip-shape profiling with a uniformly charged oxide square, we clearly demonstrate the local nature of the CNT tip for electrostatic force microscopy. We show that CNTs can be used to probe long-range electrostatic forces with a lateral resolution better than 5 nm. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
85.35.Kt Nanotube devices
68.37.Ps Atomic force microscopy (AFM)
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