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6 May 2002

Volume 80, Issue 18, pp. 3247-3450

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Subwavelength-sized aperture fabrication in aluminum by a self-terminated corrosion process in the evanescent field

D. Haefliger and A. Stemmer

Appl. Phys. Lett. 80, 3397 (2002); http://dx.doi.org/10.1063/1.1476059 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2002

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We present a simple, one-step process to fabricate apertures of high quality for scanning near-field optical microscope probes based on aluminum-coated silicon-nitride cantilevers. An evanescent optical field at the glass–water interface is used to heat up the aluminum at the tip apex due to light absorption. The heat induces breakdown of the passivating oxide layer and corrosion of the metal. Apertures with a protruding silicon-nitride tip of up to 30 nm height and minimal diameter of 38 nm are fabricated. The diameter is predefined by the lateral dimension of the silicon-nitride tip while the tip height is controlled by the penetration depth of the evanescent field. The corrosion process proves to be self-terminating, yielding highly reproducible tip heights. Near-field optical resolution in the transmission mode of 85 nm is demonstrated. © 2002 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes

Apertureless optical near-field fabrication using an atomic force microscope on photoresists

Alvarado Tarun, Marlon Rosendo H. Daza, Norihiko Hayazawa, Yasushi Inouye, and Satoshi Kawata

Appl. Phys. Lett. 80, 3400 (2002); http://dx.doi.org/10.1063/1.1476956 (3 pages) | Cited 15 times

Online Publication Date: 29 April 2002

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We present an apertureless optical near-field fabrication using an atomic force microscope. With this technique, we can directly pattern 100 nm lines that are smaller than the diameter of the incident far-field diffraction spot on positive photoresist spin coated over glass substrate. The nanostructure fabrication was carried out by the field enhancement generated at the tip apex of an apertureless probe illuminated with a 403 nm laser light. Results also show that the amount of energy required to induce photolysis seems to decrease in the presence of the tip. © 2002 American Institute of Physics.
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81.16.Ta Atom manipulation
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Terahertz conductivity of anisotropic single walled carbon nanotube films

Tae-In Jeon, Keun-Ju Kim, Chul Kang, Seung-Jae Oh, Joo-Hiuk Son, Kay Hyeok An, Dong Jae Bae, and Young Hee Lee

Appl. Phys. Lett. 80, 3403 (2002); http://dx.doi.org/10.1063/1.1476713 (3 pages) | Cited 56 times

Online Publication Date: 29 April 2002

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Absorption and dispersion of singlewalled carbon nanotube films were measured using an optoelectronic THz beam system for THz time-domain spectroscopy. The anisotropically aligned nanotube films were prepared through simple mechanical squeezing with a bar coater. The angle-dependent absorption and dispersion values were then measured. Results indicate that the index of refraction decreases with increasing frequency (0.1–0.8 THz), whereas the real conductivity increases with increasing frequency. The real conductivity measured is not congruent with the simple Drude model, but it follows a Maxwell–Garnett model, where the nanotubes are embedded in a dielectric host. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
73.50.Mx High-frequency effects; plasma effects
73.25.+i Surface conductivity and carrier phenomena

Self-assembly of Si nanoclusters on 6H–SiC(0001)-(3×3) reconstructed surface

W. J. Ong, E. S. Tok, H. Xu, and A. T. S. Wee

Appl. Phys. Lett. 80, 3406 (2002); http://dx.doi.org/10.1063/1.1476398 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2002

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Scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS) were used to observe the formation of metastable (6×6)-Si nanoclusters (diameter ∼ 16.5±0.1 A) on 6H–SiC(0001)-(3×3) surface. STM and XPS data suggest that these clusters are derived from the ejection of the Si-tetracluster unit of the initial (3×3) reconstruction at elevated temperatures and occur in a less Si-rich environment than the initial surface. The observed surface restructuring is related to the reconfiguration of coplanar Si bonds within the (3×3) unit cell. The occurrence of these regularly sized “magic” clusters demonstrates the potential of nanostructure formation of Si on SiC. © 2002 American Institute of Physics.
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68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
81.16.Dn Self-assembly
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
79.60.Dp Adsorbed layers and thin films

Writing of high-density patterned perpendicular media with a conventional longitudinal recording head

M. Albrecht, A. Moser, C. T. Rettner, S. Anders, T. Thomson, and B. D. Terris

Appl. Phys. Lett. 80, 3409 (2002); http://dx.doi.org/10.1063/1.1476062 (3 pages) | Cited 35 times

Online Publication Date: 29 April 2002

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We have fabricated arrays of magnetic islands in perpendicular CoCrPt media with ∼100 nm lateral dimension using a focused ion beam. A quasistatic write/read tester was used to study aspects of the recording physics of these patterned media. We present results on the variation of the readback signal as the phase of the written square wave changes with respect to the patterned array as a function of island size and write current. Using an analytic near-field expression for head field we are able to model how the observed dependence between phase shift and readback signal as a function of write current arises. This analysis allows us to gain an insight into the role of the island switching field distribution and the write head magnetic field gradient in the patterned media writing process. © 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

Mapping strain fields in ultrathin bonded Si wafers by x-ray scattering

M. Nielsen, M. Poulsen, O. Bunk, C. Kumpf, R. Feidenhans’l, R. L. Johnson, F. Jensen, and F. Grey

Appl. Phys. Lett. 80, 3412 (2002); http://dx.doi.org/10.1063/1.1476702 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2002

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X-ray scattering reveals the atomic displacements arising from rotational misalignment in ultrathin silicon bonded wafers. For a 4.3 nm top wafer, the strain field penetrates from the bonded interface to the surface and produces distinctive finite-size oscillations in x-ray data. Analytical calculations permit the atomic displacements throughout the thin top wafer to be modeled. © 2002 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
61.05.cf X-ray scattering (including small-angle scattering)

Absorption spectra and chirality of single-walled 4 Å carbon nanotubes

WanZhen Liang, GuanHua Chen, Zhaoming Li, and Zi-Kang Tang

Appl. Phys. Lett. 80, 3415 (2002); http://dx.doi.org/10.1063/1.1478155 (3 pages) | Cited 23 times

Online Publication Date: 29 April 2002

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Absorption spectrum of recently discovered single-walled 4 Å carbon nanotubes is measured. The semiempirical PM3 localized-density-matrix method is employed to evaluate the absorption spectra of three possible 4 Å single-walled carbon nanotubes, (3,3), (4,2), and (5,0). Both experimental and calculated results reveal that these nanotubes have finite optical gaps and strong anisotropic optical responses. When the electric field is perpendicular to the nanotubes, they are transparent to visible lights; and this is confirmed and explained by the calculations. Compared to the measured absorption spectrum, calculated absorption spectra are used to determine the chirality of the nanotubes synthesized in the channels of porous zeolites. © 2002 American Institute of Physics.
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78.67.Ch Nanotubes
61.46.-w Structure of nanoscale materials
78.40.Ri Fullerenes and related materials
31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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High-sensitivity quantum Hall far-infrared photodetector integrated with log-periodic antenna

Y. Kawaguchi, K. Hirakawa, and S. Komiyama

Appl. Phys. Lett. 80, 3418 (2002); http://dx.doi.org/10.1063/1.1476061 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2002

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We have developed a high sensitivity far-infrared (FIR) photodetector by using the two-dimensional electron gas system in modulation-doped Al0.3Ga0.7As/GaAs heterojunctions. A FIR-sensitive channel was formed by applying a negative bias voltage to the split gates which were integrated with a log-periodic antenna. Although the area of sensitivity was small (850×850 μm2), the responsivity reached as high as 5.8×104 V/W. It is also demonstrated that the responsivity can be modulated by a factor of 10 by changing the split-gate voltages. The capability of ON/OFF switching of photoresponsivity suggests that this detector is suitable for realizing high sensitivity FIR imaging arrays. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.43.-f Quantum Hall effects

Charge retention in metal–oxide–semiconductor capacitors on SiC used as nonvolatile-memory elements

Sima Dimitrijev, Kuan Yew Cheong, Jisheng Han, and H. Barry Harrison

Appl. Phys. Lett. 80, 3421 (2002); http://dx.doi.org/10.1063/1.1476060 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2002

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In this letter, the possibility of using metal–oxide–semiconductor capacitors on SiC as nonvolatile random-access memory elements has been experimentally investigated. Because of the wide energy gap and the very low minority-carrier generation rate in SiC, it should be possible to achieve very long retention times. The investigations show that charge leakage through the gate oxide may prevent the use of SiC metal–oxide–semiconductor (MOS) capacitors as memory elements. Importantly, the experiments demonstrate that both the charge leakage and carrier-generation rate are low in the case of nitrided SiO2–SiC interfaces. The retention time extrapolated to room temperature is in the order of 109 years for the case of MOS capacitors on 4H–SiC, which is approximately equal to the theoretical limit. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Piezoelectric and electrostrictive strain behavior of Ce-doped BaTiO3 ceramics

Chen Ang, Zhi Yu, Zhi Jing, Ruyan Guo, A. S. Bhalla, and L. E. Cross

Appl. Phys. Lett. 80, 3424 (2002); http://dx.doi.org/10.1063/1.1473871 (3 pages) | Cited 29 times

Online Publication Date: 29 April 2002

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The ferroelectric and strain behavior of the Ba(Ti1−yCey)O3 solid solutions was studied. Three phase transition temperatures were shifted with increasing Ce concentration, and pinched at y = 0.06. The samples could be structurally indexed by x-ray diffraction in a tetragonal symmetry at y ⩽ 0.06; and in a pseudo-cubic symmetry at y>0.06. The strain levels in the range of 0.15–0.19% at ∼60 kV/cm with small hysteresis were obtained for the samples with low content Ce. With increasing Ce concentration, the tetragonality decreases, the strain level decreases, and becomes less hysteretic. The physical mechanism of the electrostrictive, piezoelectric, and ferroelectric-relaxor behavior is briefly discussed. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Ly Strain-induced piezoelectric fields
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
61.66.Fn Inorganic compounds

Tunable, monochromatic x rays using the internal beam of a betatron

V. V. Kaplin, S. R. Uglov, O. F. Bulaev, V. J. Goncharov, A. A. Voronin, M. A. Piestrup, C. K. Gary, N. N. Nasonov, and M. K. Fuller

Appl. Phys. Lett. 80, 3427 (2002); http://dx.doi.org/10.1063/1.1475360 (3 pages) | Cited 1 time

Online Publication Date: 29 April 2002

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Tunable, monochromatic x rays from thin radiators mounted inside a betatron have been observed. Parametric x-ray radiation (PXR) was generated by 33-MeV electrons passing multiple times through three radiators: a 43-μm-thick Si crystal, a 400-μm-thick graphite crystal, or a 310-layered-pair (W and B4C, d = 14.86 Å) multilayer. The pulse-height spectrum of the radiation (5 to 30 keV) was obtained and was tuned by rocking the crystal or multilayer relative to the electron-beam direction. The experimental results appear to follow theoretical predictions for PXR emission with some modification required for the curved trajectory of the electrons. © 2002 American Institute of Physics.
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29.20.df Betatrons
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
41.75.Fr Electron and positron beams
29.27.Eg Beam handling; beam transport
41.85.-p Beam optics

Influence of temperature and drive current on degradation mechanisms in organic light-emitting diodes

Masahiko Ishii and Yasunori Taga

Appl. Phys. Lett. 80, 3430 (2002); http://dx.doi.org/10.1063/1.1476704 (3 pages) | Cited 39 times

Online Publication Date: 29 April 2002

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We measured luminance decay and half life for green organic light-emitting diodes composed of materials with high glass transition temperature. The devices were driven at dc, constant current density ranging from 3.8 to 130 mA/cm2 at 25, 85, and 120 °C. The shapes of the luminance decay curves were compared by redrawing the curves on a time scale normalized by each half life. Temperature and drive current shortened the half life. However, the normalized decay curve of the device driven at 120 °C had the same shape as that of the device driven at 25 °C. Drive current also left the shape of the decay curves unchanged. Therefore, we conclude that the temperature and drive current do not change the relative contribution of multiple degradation mechanisms. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
73.61.Ph Polymers; organic compounds
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Resonant detection of subterahertz radiation by plasma waves in a submicron field-effect transistor

W. Knap, Y. Deng, S. Rumyantsev, J.-Q. Lü, M. S. Shur, C. A. Saylor, and L. C. Brunel

Appl. Phys. Lett. 80, 3433 (2002); http://dx.doi.org/10.1063/1.1473685 (3 pages) | Cited 73 times

Online Publication Date: 29 April 2002

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The resonant detection of subterahertz radiation by two-dimensional electron plasma confined in a submicron gate GaAs/AlGaAs field-effect transistor is demonstrated. The results show that the critical parameter that governs the sensitivity of the resonant detection is ωτ, where ω is the radiation frequency and τ is the momentum scattering time. By lowering the temperature and hence increasing τ and increasing the detection frequency ω, we reached ωτ ∼ 1 and observed resonant detection of 600 GHz radiation in a 0.15 μm gate length GaAs field-effect transistor. The evolution of the observed photoresponse signal with temperature and frequency is reproduced well within the framework of a theoretical model. © 2002 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.30.Tv Field effect devices
72.40.+w Photoconduction and photovoltaic effects

Effects of wet-oxidation treatment on Al0.45Ga0.55As/GaAs graded-like superlattice-emitter bipolar transistor with low turn-on voltage

Wen-Shiung Lour, Yen-Wei Wu, Shih-Wei Tan, Ming-Kwen Tsai, and Ying-Jay Yang

Appl. Phys. Lett. 80, 3436 (2002); http://dx.doi.org/10.1063/1.1473861 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2002

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We report an AlxGa1−xAs/GaAs heterojunction bipolar transistor (HBT) with a high Al mole fraction of x = 0.45. A digital graded superlattice emitter, forming a step-wise graded composition, is used to smooth out the potential spike resulting from a large conduction-band offset. HBT’s with such a digital graded emitter as a passivation layer exhibit a small offset voltage of 55 mV, a low turn-on voltage of 0.87 V and a current gain as high as 400. Effects of wet-oxidation treatment on fabricated HBT’s are also investigated. Experimental results reveal that the studied HBT’s exhibit reduced collector currents at a fixed base current in the early stage of the wet-oxidation treatment. However, better surface passivation and higher current gain are available after an appropriate wet-oxidation treatment is used to reduce base current. We qualitatively modeled these behaviors by introducing a concept of built-in field along the graded emitter. © 2002 American Institute of Physics.
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85.30.Pq Bipolar transistors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Cd Superlattices
81.65.Mq Oxidation
81.65.Rv Passivation
85.30.De Semiconductor-device characterization, design, and modeling
81.07.-b Nanoscale materials and structures: fabrication and characterization

Electrical properties of amorphous silicon carbide films

N. Biswas, X. Wang, and S. Gangopadhyay

Appl. Phys. Lett. 80, 3439 (2002); http://dx.doi.org/10.1063/1.1476389 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2002

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The interfacial properties of silicon carbide films on silicon substrate, using capacitance–voltage (C–V) and conductance–voltage techniques have been studied. The C–V characteristics observed largely depended on processing conditions. An interface state density of 2.38×1010 eV−1 cm−2 at the midgap was calculated for this sample. When CF4 was added to the precursors, the C–V curves were observed to have a “ledge” at the end of the accumulation region, indicative of the presence of additional localized defect states that respond to the applied ac signal. An interface state density of 2.11×1011 eV−1 cm−2 at the midgap was observed for this sample. However fluorination in plasma caused the etching of the weak bond, and hence a reduction in the fixed charge density and hysteresis. © 2002 American Institute of Physics.
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73.61.Jc Amorphous semiconductors; glasses
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Near-field ultrasonic scattering from surface-breaking cracks

James L. Blackshire and Shamachary Sathish

Appl. Phys. Lett. 80, 3442 (2002); http://dx.doi.org/10.1063/1.1476722 (3 pages) | Cited 14 times

Online Publication Date: 29 April 2002

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The near-field scattering of ultrasonic Rayleigh waves from surface-breaking cracks has been studied using scanning heterodyne interferometry. Distinct two-dimensional, localized displacement patterns were observed in the near field of the scattering sites, which provide an effective tool for detecting and characterizing the defects. The observed patterns showed a dramatic increase (2×–4×) in the ultrasonic displacement levels near the crack faces, allowing the cracks to be easily distinguished from background levels. A simple explanation for the increased near-field displacement amplitudes is presented that is based on wave propagation and free-boundary reflection arguments. © 2002 American Institute of Physics.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
68.35.Iv Acoustical properties
43.58.-e Acoustical measurements and instrumentation
43.20.Fn Scattering of acoustic waves
62.65.+k Acoustical properties of solids
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Solid-state soft actuator exhibiting large electromechanical effect

Mohsen Shahinpoor and Kwang J. Kim

Appl. Phys. Lett. 80, 3445 (2002); http://dx.doi.org/10.1063/1.1477276 (3 pages) | Cited 10 times

Online Publication Date: 29 April 2002

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This letter deals with the discovery of large low-voltage electromechanical actuation effects in an electroactive polymer made with poly(ethylene oxide) and poly(ethylene glycol). The experimental observations and robust performance of the solid-state polymer actuators in the form of a strip, which is suitably surface electroded and cation doped, are reported herein. Recent laboratory discovery shows that such solid-state actuators are polymeric materials capable of exhibiting large motion actuation capabilities (>1% bending strain) in a low electric field imposed across the strip (<10 V/mm) with considerable stress (>10 MPa) and fast responses (>10 Hz). Moreover, a stable operation over ten millions of cycles in air is achieved with nearly no performance degradation. © 2002 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
77.65.-j Piezoelectricity and electromechanical effects
73.61.Ph Polymers; organic compounds
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Surface-force measurement with a laser-trapped microprobe in solution

Taisuke Ota, Tadao Sugiura, and Satoshi Kawata

Appl. Phys. Lett. 80, 3448 (2002); http://dx.doi.org/10.1063/1.1468267 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2002

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Surface force between a micron-sized polystyrene and dielectric substrate in solution has been analyzed by measuring the displacement of the laser-trapped probe. The amount of displacement is measured by detecting the intensity of light scattering at the probe illuminated by evanescent field. The sensitivity of 27 fN and the range of 5.2 pN have been achieved in the experiment with various concentrations of electrolyte trisaminomethane. The distribution of the surface force of 3-aminopropyltriethoxysilane coated on the glass substrate was also detected. © 2002 American Institute of Physics.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
87.80.Cc Optical trapping
07.10.Pz Instruments for strain, force, and torque
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
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