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11 Dec 2006

Volume 89, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 242109 (2006); http://dx.doi.org/10.1063/1.2405843 (3 pages)

Carlo R. da Cunha, Nobuyuki Aoki, Takahiro Morimoto, Yuichi Ochiai, Richard Akis, and David K. Ferry
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Widely tunable single-mode quantum cascade lasers with two monolithically coupled Fabry-Pérot cavities

S. Höfling, J. Heinrich, J. P. Reithmaier, A. Forchel, J. Seufert, M. Fischer, and J. Koeth

Appl. Phys. Lett. 89, 241126 (2006); http://dx.doi.org/10.1063/1.2404933 (3 pages) | Cited 6 times

Online Publication Date: 15 December 2006

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The authors report on tunable, miniaturized, two-segment coupled cavity quantum cascade lasers fabricated in a process with a single dry etch step. They observed controllable vernier-effect-based mode switching, induced by the spectral shift of the short cavity’s Fabry-Pérot mode comb due to Joule heating. With the help of this discontinuous tuning mechanism, single-mode operation with routinely ∼ 20 dB side mode suppression ratio was achieved over a broad spectral range. The authors measured a quasicontinuous tuning range of 12 cm−1 (138 nm) and an entire single-mode tuning range of 16.5 cm−1 (190 nm), centered around 933 cm−1 (10.7 μm).
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.60.Bt Optoelectronic device characterization, design, and modeling
42.82.Bq Design and performance testing of integrated-optical systems

Gain suppression phenomena observed in InxGa1−xN quantum well laser diodes emitting at 470 nm

K. Kojima, M. Funato, Y. Kawakami, S. Nagahama, T. Mukai, H. Braun, and U. T. Schwarz

Appl. Phys. Lett. 89, 241127 (2006); http://dx.doi.org/10.1063/1.2404971 (3 pages) | Cited 21 times

Online Publication Date: 15 December 2006

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Optical gain spectra were measured for InGaN-based laser diodes (LDs) emitting at 406 nm (LD406) and 470 nm (LD470) by employing the Hakki-Paoli method. The internal loss coefficient was as large as 35 cm−1 for the LD470 compared to 25 cm−1 for LD406. Moreover, gain saturation was observed at about 490 nm just below the lasing threshold, and a gain band appears at higher photon energies for further carrier injection resulting in lasing at 470 nm. Spontaneous emission peaks of electroluminescence were measured as a function of injection current density below threshold for both samples. The authors attribute the huge blueshift of the spontaneous emission of LD470 up to 450 meV to a filling of the localized tail states in addition to that caused by the screening of the piezoelectric field. The blueshift for the LD406 was as small as about 30 meV and can be interpreted as a result of the screening by both injected carriers and dopants.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Spectral and spatial dynamics in InGaN blue-violet lasers

G. Ropars, A. Le Floch, and G. P. Agrawal

Appl. Phys. Lett. 89, 241128 (2006); http://dx.doi.org/10.1063/1.2404974 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2006

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An angular differential analysis of the longitudinal modes associated with successive spectral substructures in InGaN lasers demonstrates a large increase in the mode widths towards the red side of the spectra because of the antiguiding lens effects occurring in such gain-guided lasers. A simple model predicts the growing asymmetrical triangular-shape spectral envelope with much higher powers in the red substructures with increasing excitation, in agreement with the high-resolution spectral measurements. Moreover, the observed 20% mode-width variations imply a critical stripe-width limitation of the active medium that would prevent oscillation of higher-order modes on the blue side of the laser spectrum.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Quantum key distribution at 1550 nm with twin superconducting single-photon detectors

Robert H. Hadfield, Jonathan L. Habif, John Schlafer, Robert E. Schwall, and Sae Woo Nam

Appl. Phys. Lett. 89, 241129 (2006); http://dx.doi.org/10.1063/1.2405870 (3 pages) | Cited 37 times

Online Publication Date: 15 December 2006

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The authors report on the full implementation of a superconducting detector technology in a fiber-based quantum key distribution (QKD) link. Nanowire-based superconducting single-photon detectors (SSPDs) offer infrared single-photon detection with low dark counts, low jitter, and short recovery times. These detectors are highly promising candidates for future high key rate QKD links operating at 1550 nm. The authors use twin SSPDs to perform the BB84 protocol in a 1550 nm fiber-based QKD link clocked at 3.3 MHz. They exchange secure key over a distance of 42.5 km in telecom fiber and demonstrate that secure key can be transmitted over a total link loss exceeding 12 dB.
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03.67.Dd Quantum cryptography and communication security
03.67.Hk Quantum communication
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Submerged waveguide constructed by the implantation of math ions in electro-optic crystals

Har’el Ilan, Alexander Gumennik, Roei Fathei, Aharon J. Agranat, Igal Shachar, and Michael Hass

Appl. Phys. Lett. 89, 241130 (2006); http://dx.doi.org/10.1063/1.2408667 (3 pages) | Cited 7 times

Online Publication Date: 15 December 2006

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Waveguide structures were fabricated in potassium lithium tantalate niobate crystals by the implantation of high energy math ions. The implantation forms an amorphous layer with a lowered index of refraction within the depth of the crystal, which serves as the cladding of the waveguides. Two amorphous layers were fabricated at 18.8 and 25.6 μm below the surface of the crystal by implantation at 30 and 40 MeV, respectively. This formed a submerged slab waveguide sandwiched between the two amorphous layers and two slab waveguides that were formed between the surface of the crystal and each of the amorphous layers. Coupling between those waveguides was observed and investigated, and confinement of the light in the sandwiched waveguide was demonstrated.
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42.82.Et Waveguides, couplers, and arrays
61.72.up Other materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Continuous wave operation of a non-self-sustained electric discharge pumped oxygen-iodine laser

A. Hicks, Yu. G. Utkin, W. R. Lempert, J. W. Rich, and I. V. Adamovich

Appl. Phys. Lett. 89, 241131 (2006); http://dx.doi.org/10.1063/1.2408668 (3 pages) | Cited 26 times

Online Publication Date: 15 December 2006

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This letter discusses operation of an electric discharge excited oxygen-iodine laser using a high-pressure, non-self-sustained pulser-sustainer discharge. Small signal gain on the 1315 nm iodine atom transition and the laser output power are measured in the M = 3 supersonic cavity downstream of the discharge section. In a 15% O2–85% He mixture, at a discharge pressure of 60 torr and discharge power of 1.5 kW, the highest gain measured in the M = 3 cavity is 0.022%/cm, at the flow temperature of T = 100±10 K. At these conditions, the laser output power is 0.28 W.
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42.55.Ks Chemical lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Generation of argon-ion mixed silicon plasmas forming argon encapsulated silicon clusters

T. Kaneko, H. Takaya, and R. Hatakeyama

Appl. Phys. Lett. 89, 241501 (2006); http://dx.doi.org/10.1063/1.2404606 (3 pages)

Online Publication Date: 14 December 2006

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An inductively coupled argon (Ar) plasma is superimposed on a silicon (Si) plasma generated by an electron beam gun in order to realize the formation of gas-atom encapsulated Si cage clusters. The Si clusters, which are formed and deposited on a substrate, are analyzed by laser-desorption time-of-flight mass spectrometry and are found to have the mass spectra of not only pure Si cluster (Sin; n = 1–17) but also Si cluster doped with Ar atom (ArSin; n = 10–20) in the case that the large amount of Ar ions is generated in addition to the Si plasma. Together with the analysis of x-ray photoelectron spectroscopy, it is revealed that the Ar atom is included in the Si cluster, forming the structure of endohedral Ar@Sin complexes. Furthermore, the mass spectrum of Ar@Sin indicates the existence of the magic numbered cluster size n = 15, 16 similar to the metal encapsulated Si clusters.
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52.50.Dg Plasma sources
52.77.Dq Plasma-based ion implantation and deposition
81.05.Cy Elemental semiconductors
82.80.Rt Time of flight mass spectrometry
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.uf Ge and Si

Electron-drift detection using directional planar probes in a low-pressure coaxial surface-wave discharge

S. Letout, C. Boisse-Laporte, and L. L. Alves

Appl. Phys. Lett. 89, 241502 (2006); http://dx.doi.org/10.1063/1.2405411 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2006

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Directional planar probes are used to investigate the electron population in low-pressure (10–100 mTorr) coaxial surface-wave (2.45 GHz) discharges, considering the anisotropy possibly induced by a local plasma resonance. Probe characteristics exhibit a significant increase in the electronic current over a wide range of probe potentials, depending on radial position and direction of observation. Such behavior reveals the presence of highly anisotropic electrons. Experimental probe currents were simulated by considering multiple electron populations, with drifting Maxwellian velocity distributions. Results yield axial drift velocities corresponding to energies up to 30 eV for populations of only a few 10−2 below the thermal background density.
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52.70.Ds Electric and magnetic measurements
52.80.Pi High-frequency and RF discharges
52.25.Fi Transport properties

Quantitative determination of the O(math) density via visible cavity-enhanced spectroscopy

Manish Gupta, Thomas Owano, Douglas Baer, and Anthony O’Keefe

Appl. Phys. Lett. 89, 241503 (2006); http://dx.doi.org/10.1063/1.2408655 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2006

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A simple method has been developed to quantitatively measure the ground state oxygen atom, O(math), density. The technique exploits cavity-enhanced spectroscopy to probe the relatively weak O(math)←O(math) transition near 636 nm. O(math) densities of approximately 3.4×1014 at./cm3 were measured in an inductively coupled plasma produced within a high-finesse optical cavity, and a minimum detectable atom state density of 1.3×1012 at./cm3 was determined. The absorption profile yielded a translational temperature of 453 K. The technique can be readily extended to other atomic species.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
07.60.Rd Visible and ultraviolet spectrometers
52.50.Dg Plasma sources
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Experimental evidence of B clustering in amorphous Si during ultrashallow junction formation

D. De Salvador, G. Bisognin, M. Di Marino, E. Napolitani, A. Carnera, H. Graoui, M. A. Foad, F. Boscherini, and S. Mirabella

Appl. Phys. Lett. 89, 241901 (2006); http://dx.doi.org/10.1063/1.2402905 (3 pages) | Cited 9 times

Online Publication Date: 11 December 2006

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The authors have investigated ultrashallow p+/n-junction formation by solid-phase epitaxy, by using x-ray absorption near-edge spectroscopy measurements on the B K edge. A clear fingerprint of B–B clusters is detected in the spectra. The authors demonstrate that B clustering occurs during the very early stages of annealing-induced Si recrystallization, i.e., when B is still in an amorphous matrix. After complete regrowth the local structure around B remains the same as in the amorphous phase, implying that B clusters are transferred to the crystalline structure.
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61.43.Dq Amorphous semiconductors, metals, and alloys
64.70.K- Solid-solid transitions
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.70.Dm X-ray absorption spectra

Composite growth in highly undercooled Ni70.2Si29.8 eutectic alloy

Yiping Lu, Feng Liu, Gencang Yang, and Yaohe Zhou

Appl. Phys. Lett. 89, 241902 (2006); http://dx.doi.org/10.1063/1.2405875 (3 pages) | Cited 4 times

Online Publication Date: 11 December 2006

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High undercooling was achieved in eutectic Ni70.2Si29.8 alloy melt using glass fluxing combined with cyclic superheating. An unusual interlaced morphology is observed in the as-solidified microstructure. This composite structure is found for the first time. Its forming process can be ascribed to a composite growth concurring with recalescence.
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81.10.Fq Growth from melts; zone melting and refining
61.72.-y Defects and impurities in crystals; microstructure
64.70.D- Solid-liquid transitions
81.30.Fb Solidification

Surface pole figures by reflection high-energy electron diffraction

F. Tang, G.-C. Wang, and T.-M. Lu

Appl. Phys. Lett. 89, 241903 (2006); http://dx.doi.org/10.1063/1.2403916 (3 pages) | Cited 7 times

Online Publication Date: 11 December 2006

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The authors demonstrated that it is possible to construct a reflection high-energy electron diffraction (RHEED) pole figure of a polycrystalline film by recording multiple RHEED patterns as they rotate the substrate around the surface normal. Since electrons have limited penetration depth, the pole figure constructed is a surface pole figure. It is in contrast with the conventional x-ray pole figure which gives an average texture information of the entire film. Surface texture change, particularly the evolution of multiple preferred orientations, in polycrystalline Ru films grown by oblique angle vapor deposition has been observed using this RHEED surface pole figure technique.
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81.05.Bx Metals, semimetals, and alloys
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.47.De Metallic surfaces
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Hugoniot-compression curve of Zr-based bulk metallic glass

T. Mashimo, H. Togo, Y. Zhang, Y. Uemura, T. Kinoshita, M. Kodama, and Y. Kawamura

Appl. Phys. Lett. 89, 241904 (2006); http://dx.doi.org/10.1063/1.2403931 (3 pages) | Cited 10 times

Online Publication Date: 11 December 2006

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The Hugoniot-compression curves of the Zr-based bulk metallic glass (Zr55Al10Ni5Cu30 in at. %) and the metallic compound crystal with the same composition were measured by means of the inclined-mirror photographic technique. A kink was observed on the Hugoniot curve at 14 GPa for the glass probably due to phase transition, while no kink was observed for the crystal. The Hugoniot elastic limit stress (6.2 GPa) of the glass was comparable to one of the crystal.
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81.05.Kf Glasses (including metallic glasses)
64.30.-t Equations of state of specific substances
61.43.Fs Glasses
81.40.Lm Deformation, plasticity, and creep
64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids

Epitaxial growth of single-crystalline AlN films on tungsten substrates

Guoqiang Li, Tae-Won Kim, Shigeru Inoue, Koichiro Okamoto, and Hiroshi Fujioka

Appl. Phys. Lett. 89, 241905 (2006); http://dx.doi.org/10.1063/1.2404588 (3 pages) | Cited 5 times

Online Publication Date: 11 December 2006

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The authors have grown single-crystalline AlN(0001) films on W(110) substrates with an in-plane alignment AlN[11–20]‖W[001] at temperatures ranging from 450 to 600 °C by pulsed laser deposition. These AlN films have a clear sixfold symmetry without 30° rotational domains. When AlN films are grown at 450 °C, the interfacial reaction between AlN and W(110) is fully suppressed and a flat surface with a root-mean-square value as low as 0.20 nm for AlN films is obtained. These single-crystalline AlN films grown on W(110) open a good opportunity for the high performance film bulk acoustic wave resonators of the next generation.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
79.20.Kz Other electron-impact emission phenomena

Optical imaging of thin films with molecular depth resolution

R. Köhler, P. Lazar, and H. Riegler

Appl. Phys. Lett. 89, 241906 (2006); http://dx.doi.org/10.1063/1.2404601 (3 pages) | Cited 4 times

Online Publication Date: 11 December 2006

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Oxide layers of suitable thicknesses greatly enhance the reflectivity contrast from molecularly thin films deposited on silicon wafers. This interference enhancement can be used to visualize and to quantify film topologies with a thickness resolution well below 1 nm.
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68.55.-a Thin film structure and morphology
68.37.-d Microscopy of surfaces, interfaces, and thin films
78.66.Qn Polymers; organic compounds

Highly efficient GaN-based light emitting diodes with micropits

M. Hao, T. Egawa, and H. Ishikawa

Appl. Phys. Lett. 89, 241907 (2006); http://dx.doi.org/10.1063/1.2402219 (3 pages) | Cited 7 times

Online Publication Date: 12 December 2006

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Light emitting diodes (LEDs) on GaN templates with high-density V-shaped micropits have been grown and characterized by transmission electron microscopy, scanning electron microscopy, and photoluminescence. Higher emission efficiency has been obtained for the fabricated LEDs compared with those without V-shaped pits. The high efficiency of the LEDs is mainly attributed to the increase in light extraction efficiency due to the light extraction from the sidewalls of the V-shaped pits. The improved internal quantum efficiency of the device resulting from the reduction of the dislocation density in the light emitting area also contributes to the high efficiency of the LEDs.
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85.60.Jb Light-emitting devices

Three-dimensional size determination of particles with photoelectron emission microscopy

Liviu I. Chelaru and Frank-J. Meyer zu Heringdorf

Appl. Phys. Lett. 89, 241908 (2006); http://dx.doi.org/10.1063/1.2404968 (3 pages) | Cited 3 times

Online Publication Date: 12 December 2006

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We show that the aspect ratio and the size of particles at surfaces can be estimated with photoelectron emission microscopy when both linear and nonlinear processes are utilized. As the width of the particles is known from regular photoemission microscopy, a complete determination of the particles’ dimensions becomes possible by two-photon photoemission microscopy. Here, the light diffraction pattern of the illuminating light around the particles is emphasized by the nonlinear dependence of the photoemission yield on the electric field components at the surface. This allows the quantitative measurement of the aspect ratio of the particles. The results are in agreement with theory and atomic force microscopy measurements.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
79.60.-i Photoemission and photoelectron spectra

Ablation of solids using a femtosecond extreme ultraviolet free electron laser

N. Stojanovic, D. von der Linde, K. Sokolowski-Tinten, U. Zastrau, F. Perner, E. Förster, R. Sobierajski, R. Nietubyc, M. Jurek, D. Klinger, J. Pelka, J. Krzywinski, L Juha, J. Cihelka, A. Velyhan, et al.

Appl. Phys. Lett. 89, 241909 (2006); http://dx.doi.org/10.1063/1.2405398 (3 pages) | Cited 12 times

Online Publication Date: 12 December 2006

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The ablation of solids by high energy femtosecond pulses from an extreme ultraviolet (XUV) free electron laser has been investigated using picosecond optical imaging. The time-resolved measurements are supplemented by an analysis of the permanent structural surface modifications. Compared with femtosecond optical excitation, distinct differences in the material response are found which are attributed to the increased penetration depth of the XUV radiation and the absence of any absorption nonlinearities.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.38.Mf Laser ablation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
41.60.Cr Free-electron lasers

High resolution measurements of strain and tilt distributions in SiGe mesas using electron backscatter diffraction

Angus J. Wilkinson

Appl. Phys. Lett. 89, 241910 (2006); http://dx.doi.org/10.1063/1.2403904 (3 pages) | Cited 6 times

Online Publication Date: 12 December 2006

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Electron backscatter diffraction allows the elastic strain and rotation tensors to be determined at high spatial resolution and with a strain sensitivity of ∼ 10−4. The technique is used to investigate variations of strains and rotations near the surface of 200 nm thick epitaxial layers of Si0.85Ge0.15 grown on a Si substrate patterned with mesa stripes. In wide mesa stripes the strain relaxation and lattice curvature are confined to the outer edges of the mesa. While in narrower mesas the relaxation extends across the entire mesa width. Measured stress levels confirm earlier predictions of the extent of relaxation with mesa width.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity

Defect and stress characterization of AlN films by Raman spectroscopy

Vanni Lughi and David R. Clarke

Appl. Phys. Lett. 89, 241911 (2006); http://dx.doi.org/10.1063/1.2404938 (3 pages) | Cited 12 times

Online Publication Date: 13 December 2006

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Raman spectroscopy was used to characterize the residual stress and defect density of AlN thin films reactively sputtered on silicon (100). The authors studied the correlation between the shift of the E2 (high) phonon of AlN at 658 cm−1 and the film biaxial stress and obtained a biaxial piezospectroscopic coefficient of 3.7 GPa/cm−1. A correlation was found between the width of the Raman line, the oxygen concentration measured by secondary ion mass spectroscopy, and acoustic losses. This work lays the basis for the nondestructive assessment of two key thin film properties in microelectromechanical systems applications, namely, acoustic attenuation and residual stress.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
77.65.Bn Piezoelectric and electrostrictive constants
78.30.Fs III-V and II-VI semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Growth and thermal stability of GaPO4 epitaxial thin films

J. D. Pedarnig, S. Roither, and M. Peruzzi

Appl. Phys. Lett. 89, 241912 (2006); http://dx.doi.org/10.1063/1.2404970 (3 pages) | Cited 2 times

Online Publication Date: 13 December 2006

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Thin epitaxial films of gallium orthophosphate (GaPO4) are grown on α-quartz (SiO2) substrates. Here, amorphous stoichiometric precursor layers fabricated by pulsed-laser deposition on (001) SiO2 substrates are transformed to crystalline GaPO4 by postannealing in air at 650–950 °C. Epitaxial films with thicknesses up to 300 nm exhibit strong in-plane and out-of-plane textures (angular widths <0.6°). Long-term annealing in air at temperatures above the α- to β-phase transition of the quartz substrate (573 °C) does not degrade the films.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions

Quantifying stacking faults and vacancies in thin convectively assembled colloidal crystals

H. Wei, L. Meng, Y. Jun, and D. J. Norris

Appl. Phys. Lett. 89, 241913 (2006); http://dx.doi.org/10.1063/1.2404973 (3 pages) | Cited 7 times

Online Publication Date: 13 December 2006

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The authors determine the concentration and distribution of stacking faults and vacancies in colloidal crystals between 3 and 11 layers thick grown via convective assembly. The average stacking parameter 〈α〉 rises from 0.1 for samples 3 layers thick to 0.8 for ≥ 6 layers. For samples ≥ 6 layers, the authors also find that the stacking faults are less likely to be near the substrate. The average vacancy concentration is 2.1×10−3 per unit cell. Surprisingly, the layer-averaged vacancy concentration is lowest in the layer nearest the substrate and highest in the next nearest layer.
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82.70.Dd Colloids
61.72.Nn Stacking faults and other planar or extended defects
61.72.J- Point defects and defect clusters

Athermal crystallization induced by electronic excitations in ion-irradiated silicon carbide

A. Benyagoub, A. Audren, L. Thomé, and F. Garrido

Appl. Phys. Lett. 89, 241914 (2006); http://dx.doi.org/10.1063/1.2405410 (3 pages) | Cited 18 times

Online Publication Date: 13 December 2006

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Silicon carbide single crystals were irradiated at room temperature with low energy I ions and high energy Pb ions. It is found that the damaged layer formed by the elastic collisions generated during low energy I ion irradiation can readily be removed by the electronic excitations induced by swift Pb ions. This effect occurs at a temperature quite below that at which the conventional ion-beam induced crystallization process is generally achieved by nuclear energy loss. This finding is interesting both from a fundamental point of view for the understanding of the interaction of swift heavy ions with solids and for a large number of technological applications.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
64.70.D- Solid-liquid transitions

Thermodynamic model for growth mechanisms of multiwall carbon nanotubes

F. H. Kaatz, M. P. Siegal, D. L. Overmyer, P. P. Provencio, and D. R. Tallant

Appl. Phys. Lett. 89, 241915 (2006); http://dx.doi.org/10.1063/1.2405847 (3 pages) | Cited 4 times

Online Publication Date: 13 December 2006

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Multiwall carbon nanotubes are grown via thermal chemical vapor deposition between temperatures of 630 and 830 °C using acetylene in nitrogen as the carbon source. This process is modeled using classical thermodynamics to explain the total carbon deposition as a function of time and temperature. An activation energy of 1.60 eV is inferred for nanotube growth after considering the carbon solubility term. Scanning electron microscopy shows growth with diameters increasing linearly with time. Transmission electron microscopy and Raman spectroscopy show multiwall nanotubes surrounded by a glassy-carbon sheath, which grows with increasing wall thickness as growth temperatures and times rise.
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81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
61.46.Fg Nanotubes
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
78.30.Na Fullerenes and related materials

Thin film interference in the optomechanical response of micromechanical silicon cantilevers

Paul R. Wilkinson and James K. Gimzewski

Appl. Phys. Lett. 89, 241916 (2006); http://dx.doi.org/10.1063/1.2405887 (3 pages) | Cited 3 times

Online Publication Date: 13 December 2006

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The mechanical response of uncoated silicon microcantilevers is shown to modulate as a function of incident wavelength. Cantilever motion is measured interferometrically, using phase sensitive detection in response to a mechanically chopped excitation source. Thin film interference modeling shows that the fraction of absorbed light within the cantilever varies periodically over the range of 450–1000 nm, in excellent agreement with the measurements. The results show that the optomechanical responsivity of these cantilevers can be tuned due to the effect via an appropriate selection of incident wavelength, incidence angle, lever thickness, and optical constants of the lever.
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07.10.Cm Micromechanical devices and systems
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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