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28 Apr 2003

Volume 82, Issue 17, pp. 2749-2924

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Appl. Phys. Lett. 82, 2957 (2003); http://dx.doi.org/10.1063/1.1571977 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, Suguru Sangu, and Motoichi Ohtsu
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Atomic-layer deposition of wear-resistant coatings for microelectromechanical devices

T. M. Mayer, J. W. Elam, S. M. George, P. G. Kotula, and R. S. Goeke

Appl. Phys. Lett. 82, 2883 (2003); http://dx.doi.org/10.1063/1.1570926 (3 pages) | Cited 55 times

Online Publication Date: 21 April 2003

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Friction and wear are major concerns in the performance and reliability of microelectromechanical systems (MEMS) devices employing sliding contacts. While many tribological coating materials are available, most traditional surface coating processes are unable to apply conformal coatings to the high aspect ratio (height/width) structures typical of MEMS devices. We demonstrate that thin, conformal, wear-resistant coatings can be applied to Si surface-micromachined structures by atomic-layer deposition (ALD). For this demonstration, we apply 10-nm-thick films of Al2O3 using a binary reaction sequence with precursors of trimethyl aluminum and water. Deposition is carried out in a viscous flow reactor at 1 Torr and 168 °C, with N2 as a carrier gas. Cross-section transmission electron microscopy analysis shows that films are uniform to within 5% on MEMS device structures with aspect ratio ranging from 0 to >100. Films are stoichiometric Al2O3, with no evidence of contamination from other species, and are amorphous. Preliminary friction and wear data show that ALD films have promising properties for application to MEMS devices. © 2003 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Nanobelts as nanocantilevers

William L. Hughes and Zhong L. Wang

Appl. Phys. Lett. 82, 2886 (2003); http://dx.doi.org/10.1063/1.1570497 (3 pages) | Cited 94 times

Online Publication Date: 21 April 2003

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Semiconducting oxide nanobelts of ZnO have been sectioned and manipulated, for microelectromechanical systems, using an atomic force microscopy probe. Structurally modified nanobelts demonstrate potential for nanocantilever based technologies. With dimensions ∼ 35–1800 times smaller than conventional cantilevers, the nanocantilevers are expected to have improved physical, chemical, and biological sensitivity for scanning probe microscopy and sensor applications. © 2003 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
81.16.Ta Atom manipulation

Structural and optical properties of coherent GaN islands grown on 6H-SiC(0001)-(√3×√3)

C.-W. Hu, A. Bell, L. Shi, F. A. Ponce, D. J. Smith, and I. S. T. Tsong

Appl. Phys. Lett. 82, 2889 (2003); http://dx.doi.org/10.1063/1.1570000 (3 pages) | Cited 6 times

Online Publication Date: 21 April 2003

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Coherent islands of GaN with base widths in the range of 100 to 500 nm were grown on 6H-SiC(0001)-(√3×√3) surfaces via the vapor–liquid–solid (VLS) mechanism. The microstructure of GaN islands was studied by high-resolution cross-sectional transmission electron microscopy. The morphological details of the islands were imaged by atomic force microscopy and the same assembly of islands was identified in a scanning electron microscope in which site-specific cathodoluminescence (CL) spectroscopy was conducted on individual islands. The broadening of the CL linewidths together with the shift to lower wave numbers in the E2 Raman mode detected by micro-Raman spectroscopy suggest the existence of tensile strain in the GaN islands. The strain is due to the heavy Si doping of the GaN islands by Si adatoms on the (√3×√3) substrate surface during the VLS growth process. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
78.30.Fs III-V and II-VI semiconductors
68.60.Bs Mechanical and acoustical properties
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Formation of lateral quantum dot molecules around self-assembled nanoholes

Rudeesun Songmuang, Suwit Kiravittaya, and Oliver G. Schmidt

Appl. Phys. Lett. 82, 2892 (2003); http://dx.doi.org/10.1063/1.1569992 (3 pages) | Cited 85 times

Online Publication Date: 21 April 2003

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We fabricate groups of closely spaced self-assembled InAs quantum dots (QDs)—termed lateral QD molecules—on GaAs (001) by a combination of molecular-beam epitaxy and AsBr3 in situ etching. An initial array of homogeneously sized nanoholes is created by locally strain-enhanced etching of a GaAs cap layer above InAs QDs. Deposition of InAs onto the nanoholes causes a preferential formation of the InAs QD molecules around the holes. The number of QDs per QD molecule ranges from 2 to 6, depending on the InAs growth conditions. By decreasing the substrate temperature, the number of QDs per QD molecule increases, but the statistical distribution is wider due to a reduced In atom diffusion length. Our photoluminescence investigation documents the nanohole and QD molecule formation step by step and confirms the high crystal quality of these structures. An analysis of the nanohole geometry as a function of annealing time and InAs filling allows us to propose a model for the QD molecule formation process. © 2003 American Institute of Physics.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.37.Ps Atomic force microscopy (AFM)
66.30.H- Self-diffusion and ionic conduction in nonmetals

Size-tunable infrared (1000–1600 nm) electroluminescence from PbS quantum-dot nanocrystals in a semiconducting polymer

L. Bakueva, S. Musikhin, M. A. Hines, T.-W. F. Chang, M. Tzolov, G. D. Scholes, and E. H. Sargent

Appl. Phys. Lett. 82, 2895 (2003); http://dx.doi.org/10.1063/1.1570940 (3 pages) | Cited 133 times

Online Publication Date: 21 April 2003

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Nanocomposites consisting of PbS nanocrystals in a conjugated polymer matrix were fabricated. We report results of photo- and electroluminescence across the range of 1000 to 1600 nm with tunability obtained via the quantum-size effect. The intensity of electroluminescence reached values corresponding to an internal quantum efficiency up to 1.2%. We discuss the impact of using different-length capping ligands on the transfer of excitations from polymer matrix to nanocrystals. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
78.67.Hc Quantum dots
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials

Interfacial reaction during the epitaxial growth of yttrium on CaF2(111)

A. Borgschulte, S. Weber, and J. Schoenes

Appl. Phys. Lett. 82, 2898 (2003); http://dx.doi.org/10.1063/1.1569998 (3 pages) | Cited 5 times

Online Publication Date: 21 April 2003

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By means of Auger electron spectroscopy and in situ reflection high-energy electron diffraction (RHEED) the interfacial reaction during the epitaxial growth of yttrium on CaF2(111) has been studied. The RHEED patterns confirm a smooth Volmer–Weber growth mode. Auger electron spectroscopy evidences a strong interdiffusion of the film and substrate, leading to a compressive in-plane strain of the growing film. Using RHEED, we can follow the strain relaxation via misfit glides during growth. The development and crystalline orientation of the glides are characterized. © 2003 American Institute of Physics.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
79.20.Fv Electron impact: Auger emission
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.60.Bs Mechanical and acoustical properties

Surface nanostructuring of borosilicate glass by femtosecond nJ energy pulses

Egidijus Vanagas, Igor Kudryashov, Dmitrii Tuzhilin, Saulius Juodkazis, Shigeki Matsuo, and Hiroaki Misawa

Appl. Phys. Lett. 82, 2901 (2003); http://dx.doi.org/10.1063/1.1570514 (3 pages) | Cited 25 times

Online Publication Date: 21 April 2003

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We report on a feature, that of hillock-shaped damage, formed on a glass surface by femtosecond pulses of tp = 180 fs [full width at half maximum (FWHM) value] duration produced by a recording beam focus with energy of 5 nJ/pulse at 800 nm wavelength (the corresponding irradiance of about 7.6 TW/cm2 was evaluated for a 0.68 μm FWHM spot size). Single hillocks of 40–50 nm height were recorded reproducibly in single-pulse irradiation. Surface nanopatterning over a large, curved area (over 200 μm2) can be achieved by implementing a confocal surface curvature tracking method that utilizes the reflection of a supplementary cw-laser beam. The ablation pattern achieved by this method is consistent with that of a Coulomb explosion. © 2003 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.43.Fs Glasses

Electron emission from diamond nanoparticles on metal tips

T. Tyler, V. V. Zhirnov, A. V. Kvit, D. Kang, and J. J. Hren

Appl. Phys. Lett. 82, 2904 (2003); http://dx.doi.org/10.1063/1.1570498 (3 pages) | Cited 20 times

Online Publication Date: 21 April 2003

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Single-crystalline diamond nanoparticles (∼5 nm in scale) have been deposited onto molybdenum needles (with radii <100 nm), and their effects on field emission behavior were measured. Combined transmission electron microscopy observations, field emission measurements, and diamond depositions allowed for direct comparison of the effects of various amounts of nanodiamond coating on the field emission properties of a coated metal field emitter. In the limit, field emission from a single isolated diamond nanoparticle is compared here with that from an uncoated metal emitter and from a coating comprised of several layers of nanoparticles. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Lp Transmission electron microscopy (TEM)
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