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7 Mar 2011

Volume 98, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 104101 (2011); http://dx.doi.org/10.1063/1.3560505 (3 pages)

Zhongchang Wang, Susumu Tsukimoto, Rong Sun, Mitsuhiro Saito, and Yuichi Ikuhara
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Vertical subwavelength mode confinement in terahertz and mid-infrared quantum cascade lasers

E. Strupiechonski, D. Grassani, D. Fowler, F. H. Julien, S. P. Khanna, L. Li, E. H. Linfield, A. G. Davies, A. B. Krysa, and R. Colombelli

Appl. Phys. Lett. 98, 101101 (2011); http://dx.doi.org/10.1063/1.3560980 (3 pages) | Cited 4 times

Online Publication Date: 7 March 2011

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We exploit the modal confinement properties of metal-metal ridge waveguides to investigate the effect of reducing the thickness of the active laser cores in both terahertz and mid-infrared quantum cascade lasers. Devices with active regions over 55 times thinner than the free-space emission wavelength are demonstrated. They show only a modest increase in threshold current density compared with conventional-thickness devices. The limited increase in threshold is possibly due to a parasitic current channel in addition to the radiative current channel. These structures could be useful for the development of ultra-low volume lasers.
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42.50.Pq Cavity quantum electrodynamics; micromasers
42.60.By Design of specific laser systems
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
42.55.Px Semiconductor lasers; laser diodes

Gain enhancement in a terahertz quantum cascade laser with parylene antireflection coatings

R. Rungsawang, N. Jukam, J. Maysonnave, P. Cavalié, J. Madéo, D. Oustinov, S. S. Dhillon, J. Tignon, P. Gellie, C. Sirtori, S. Barbieri, H. E. Beere, and D. A. Ritchie

Appl. Phys. Lett. 98, 101102 (2011); http://dx.doi.org/10.1063/1.3562002 (3 pages) | Cited 3 times

Online Publication Date: 7 March 2011

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We study the effect of parylene antireflection coatings on the gain of a 2.8 THz quantum cascade laser using terahertz time-domain spectroscopy. With antireflection coatings the threshold current increases as the mirror losses are increased, and the gain clamps at 16 cm−1, compared to 10 cm−1 for an uncoated device. These values are consistent with a drop in reflectivity from 0.320 to 0.053 as a consequence of the coating deposition. Further improvements could reveal the bare cavity gain and permit the quantum cascade laser to be used as an efficient terahertz amplifier.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Wc Optical coatings
42.79.Bh Lenses, prisms and mirrors
42.70.Jk Polymers and organics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Reaction-controlled diffraction grating of photopolymer for use of phase stable holographic optical element

Yong-Cheol Jeong, Bokyung Jung, Jihye Lee, and Jung-Ki Park

Appl. Phys. Lett. 98, 101103 (2011); http://dx.doi.org/10.1063/1.3562032 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2011

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Herein we propose control of polymerization kinetics to prevent inherent scattering problem of holographic photopolymer system that is caused by a phase separation between matrix and photopolymerized grating polymers. To elucidate this, in this letter, phase stability of the photopolymer system was studied with molecular dynamic simulation of Flory–Huggins theory and was investigated in the respect of polymerization kinetics. It was controlled with the variables of monomer conversion and degree of polymerization by varying both reaction time and rates. In addition, volume grating fixing effect of post ultraviolet treatment on photopolymer was examined.
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42.70.Jk Polymers and organics
82.35.-x Polymers: properties; reactions; polymerization
42.40.Eq Holographic optical elements; holographic gratings

Pencil lead plasma for generating multimicrojoule high-order harmonics with a broad spectrum

Y. Pertot, L. B. Elouga Bom, V. R. Bhardwaj, and T. Ozaki

Appl. Phys. Lett. 98, 101104 (2011); http://dx.doi.org/10.1063/1.3558999 (3 pages) | Cited 6 times

Online Publication Date: 9 March 2011

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Using the plasma harmonic method, we show the generation of efficient and intense high-order harmonics from plasma of pencil lead. We demonstrate multimicrojoule energy in each harmonic order for the 11th to the 17th order of a Ti:sapphire laser. By analyzing the target morphology and the plasma composition, we conclude that these intense harmonics are generated from nanoparticles of graphitic carbon.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Modeling the lasing spectra of InAs/InP Quantum dash lasers

M. Z. M. Khan, T. K. Ng, U. Schwingenschlogl, P. Bhattacharya, and B. S. Ooi

Appl. Phys. Lett. 98, 101105 (2011); http://dx.doi.org/10.1063/1.3560052 (3 pages) | Cited 1 time

Online Publication Date: 9 March 2011

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We report a theoretical model for InAs/InP quantum-dash (Qdash) lasers incorporating a coupled set of rate equations taking into account the inhomogeneous broadening due to Qdash size fluctuation, the homogeneous broadening due to optical gain of a single Qdash, and the longitudinal cavity modes. The role of cavity length on the Qdash lasing characteristics, particularly the redshift in the peak lasing wavelength, is analyzed and compared with the experimental results by attributing it to the active region inhomogeneity.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Biaxial tensile strain effects on photoluminescence of different orientated Ge wafers

H.-S. Lan, S.-T. Chan, T.-H. Cheng, C.-Y. Chen, S.-R. Jan, and C. W. Liu

Appl. Phys. Lett. 98, 101106 (2011); http://dx.doi.org/10.1063/1.3562589 (3 pages) | Cited 5 times

Online Publication Date: 9 March 2011

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The enhanced photoluminescence of direct transition is observed on (100), (110), and (111) Ge under biaxial tensile strain. The enhancement is caused by the increase in electron population in the Γ valley. The shrinkage of energy difference between the lowest L valleys and the Γ valley is responsible to the population increase on (100) and (110) Ge. For (111) Ge, the energy difference increases under biaxial tensile strain but the strain decreases energy difference between the electron quasi-Fermi level and the Γ valley due to the small density of state of the lowest L valleys, and thus enhances direct recombination.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High-speed nanometer-resolved imaging vibrometer and velocimeter

Ata Mahjoubfar, Keisuke Goda, Ali Ayazi, Ali Fard, Sang Hyup Kim, and Bahram Jalali

Appl. Phys. Lett. 98, 101107 (2011); http://dx.doi.org/10.1063/1.3563707 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2011

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Conventional laser vibrometers are incapable of performing multidimensional vibrometry at high speeds because they build on single-point measurements and rely on beam scanning, significantly limiting their utility and precision. Here we introduce a laser vibrometer that performs high-speed multidimensional imaging-based vibration and velocity measurements with nanometer-scale axial resolution without the need for beam scanning. As a proof-of-concept, we demonstrate real-time microscopic imaging of acoustic vibrations with 1 nm axial resolution, 1200 image pixels, and 30 ps dwell time at 36.7 MHz scan rate.
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07.10.-h Mechanical instruments and equipment
06.60.Jn High-speed techniques (microsecond to femtosecond)
06.30.Gv Velocity, acceleration, and rotation

Ultrafast cross saturation dynamics in inhomogeneously broadened InAs/InP quantum dash optical amplifiers

A. Capua, G. Eisenstein, and J. P. Reithmaier

Appl. Phys. Lett. 98, 101108 (2011); http://dx.doi.org/10.1063/1.3564901 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2011

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We describe multiwavelength pump probe characterization of an inhomogeneously broadened semiconductor nanostructure gain medium. An InAs/InP quantum-dash optical amplifier is perturbed by a 100 fs pulse and the response is measured at wavelengths outside the homogeneously broadened spectral region. Energy dependent carrier cross relaxation as well as capture and escape processes are investigated and quantified.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Experimental cross-polarization detection of coupling far-field light to highly confined plasmonic gap modes via nanoantennas

J. Wen, P. Banzer, A. Kriesch, D. Ploss, B. Schmauss, and U. Peschel

Appl. Phys. Lett. 98, 101109 (2011); http://dx.doi.org/10.1063/1.3564904 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2011

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We experimentally demonstrate the coupling of far-field light to highly confined plasmonic gap modes via connected nanoantennas. The excitation of plasmonic gap modes is shown to depend on the polarization, position, and wavelength of the incident beam. Far-field measurements performed in crossed polarization allow for the detection of extremely weak signals re-emitted from gap waveguides and can increase the signal-to-noise ratio dramatically.
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73.22.Lp Collective excitations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Theoretical study of polarization-doped GaN-based light-emitting diodes

L. Zhang, K. Ding, N. X. Liu, T. B. Wei, X. L. Ji, P. Ma, J. C. Yan, J. X. Wang, Y. P. Zeng, and J. M. Li

Appl. Phys. Lett. 98, 101110 (2011); http://dx.doi.org/10.1063/1.3565173 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2011

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Insufficient hole injection is a major impediment to the luminescence efficiency of III-nitride light-emitting diodes (LEDs). In our previous work by Zhang et al. [Appl. Phys. Lett. 97, 062103 (2010)] , high-density mobile three-dimensional hole gas is obtained in Mg-doped Al composition graded AlGaN layer with Al composition linearly decreasing from a certain value to 0. In this paper, it is revealed by a theoretical study that the hole injection efficiency in blue-light GaN-based LEDs can be greatly enhanced by using this polarization-doped method. An increase in the electroluminescence intensity and the internal quantum efficiency in polarization-doped GaN-based LEDs is observed, in comparison with a conventional LED.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

Multiple Bragg diffraction in magnetophotonic crystals

Seungmin Baek, Alexander V. Baryshev, and Mitsuteru Inoue

Appl. Phys. Lett. 98, 101111 (2011); http://dx.doi.org/10.1063/1.3560256 (3 pages) | Cited 1 time

Online Publication Date: 11 March 2011

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We demonstrate properties of magnetophotonic crystals (MPCs) with quasi-two-dimensional structure. Crystals were bismuth-substituted yttrium iron garnet/silicon dioxide (Bi:YIG/SiO2) multilayers sputtered on top of one-dimensional structured substrates. Parameters of these MPCs were such that two spectrally neighboring stop bands overlapped in their spectra. For MPCs in this multiple Bragg diffraction regime, we observed a strong dispersion of their magneto-optical responses—an enhancement of the polarization rotation and an alteration of the rotation sign.
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42.79.Dj Gratings
42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Ls Magneto-optical effects
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Substrate heating influence on the deposition rate of oxides during pulsed laser deposition in ambient gas

S. Amoruso, C. Aruta, R. Bruzzese, X. Wang, and U. Scotti di Uccio

Appl. Phys. Lett. 98, 101501 (2011); http://dx.doi.org/10.1063/1.3565157 (3 pages) | Cited 5 times

Online Publication Date: 10 March 2011

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We investigate the effects of ambient pressure and substrate temperature on the deposition rate of oxides grown by pulsed laser deposition in oxygen atmosphere. The deposition rate of LaGaO3 (LGO) and LaAlO3 (LAO) is studied at room temperature by means of a quartz crystal microbalance and at 800 °C by exploiting reflection high energy electron diffraction. We observe a clear dependence of the deposition rate on temperature for an oxygen pressure between 10−2 and 1 mbar. A simple model based on multiple-elastic-scattering processes thoroughly describes the observed dependence of the deposition rate on the pressure/density of the background gas.
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81.15.Fg Pulsed laser ablation deposition

A high-power high-efficiency klystronlike relativistic backward wave oscillator with a dual-cavity extractor

Renzhen Xiao (肖仁珍), Changhua Chen (陈昌华), Jun Sun (孙钧), Xiaowei Zhang (张晓微), and Lijun Zhang (张黎军)

Appl. Phys. Lett. 98, 101502 (2011); http://dx.doi.org/10.1063/1.3562612 (3 pages) | Cited 11 times

Online Publication Date: 11 March 2011

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A klystronlike relativistic backward wave oscillator (RBWO) with a dual-cavity extractor is presented. The phase of the axial electric field component Ez varies by 0° in the dual-cavity extractor, and a larger electric field appears in the second extraction cavity, in comparison with a single-cavity extractor. Such an improved field distribution is beneficial for converting modulated beam power into microwave power. The particle in cell simulation results reveal that microwaves with power of 10 GW, frequency of 4.3 GHz are generated, and conversion efficiency is 48% when diode voltage is 1.2 MV and beam current 17.3 kA.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
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Indefinite permittivity and negative refraction in natural material: Graphite

Jingbo Sun, Ji Zhou, Bo Li, and Feiyu Kang

Appl. Phys. Lett. 98, 101901 (2011); http://dx.doi.org/10.1063/1.3562033 (3 pages) | Cited 3 times

Online Publication Date: 7 March 2011

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In this work, we report a nature indefinite permittivity in crystalline graphite that exhibits negative group refraction at ultraviolet region. A hyperbolic equifrequency contour was obtained from ellipsometry data at 254 nm and an all angle negative refraction was verified experimentally. The indefinite permittivity is attributed to extremely strong anisotropy in the crystal structure and the hybrid electronic transitions. This result not only explores a route toward natural negative-index materials, but also holds a promise for ultraviolet hyperlens, which may lead to a breakthrough in nanolithography for the next generation of electronics.
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81.05.uf Graphite
78.40.Ri Fullerenes and related materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
61.66.Bi Elemental solids

Distribution of bismuth atoms in epitaxial GaAsBi

D. L. Sales, E. Guerrero, J. F. Rodrigo, P. L. Galindo, A. Yáñez, M. Shafi, A. Khatab, R. H. Mari, M. Henini, S. Novikov, M. F. Chisholm, and S. I. Molina

Appl. Phys. Lett. 98, 101902 (2011); http://dx.doi.org/10.1063/1.3562376 (3 pages) | Cited 4 times

Online Publication Date: 7 March 2011

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The distribution of Bi atoms in epitaxial GaAs(1−x)Bix is analyzed through aberration-corrected Z-contrast images. The relation between the atomic number and the intensity of the images allows quantifying the distribution of Bi atoms in this material. A bidimensional map of Bi atoms is extracted showing areas where nanoclustering is possible and evidencing the location of Bi at As-substitutional positions in the lattice. The distribution of Bi atoms differs from a random spatial pattern of Bi atoms in the material.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.Nq Composition and phase identification
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Electronic origin of the phase transition in ternary alloy Mo(Si1−x,Alx)2

Zhengzheng Chen, Bin Shan, and Rong Chen

Appl. Phys. Lett. 98, 101903 (2011); http://dx.doi.org/10.1063/1.3562593 (3 pages)

Online Publication Date: 7 March 2011

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The structural stability of the ternary alloy Mo(Si1−x,Alx)2 with different x has been investigated using first-principles pseudopotential plane wave method. The electronic origin of the C11b→C40 phase transition is revealed by analyzing the density of states and d-band splitting induced by the crystal field. We further propose the feasibility of controlling the microscopic structure by adding a quaternary component according to the mechanism presented in this work.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
71.15.-m Methods of electronic structure calculations
71.20.Gj Other metals and alloys

Thermal conductivity of chalcogenide material with superlatticelike structure

H. Tong, X. S. Miao, X. M. Cheng, H. Wang, L. Zhang, J. J. Sun, F. Tong, and J. H. Wang

Appl. Phys. Lett. 98, 101904 (2011); http://dx.doi.org/10.1063/1.3562610 (3 pages) | Cited 5 times

Online Publication Date: 7 March 2011

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Thermal conductivity of chalcogenide material with superlatticelike (SLL) structure is investigated using the 3ω method and the molecular dynamics method. Both the measured and calculated results show that the thermal conductivity of SLL is lower than those of conventional chalcogenide materials and will decrease to a minimum as the number of interfaces increases. The Raman spectrum is introduced to study the phonon behavior of SLL and the “phonon mode vanishing” is proposed to explain its lower thermal conductivity. Finite-element analysis and phase change memory cell testing confirm the enhancement of cell performance for SLL with minimum thermal conductivity.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.30.Hv Other nonmetallic inorganics
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

A simple theoretical approach to analyze polarization properties in semipolar and nonpolar InGaN quantum wells

Atsushi A. Yamaguchi and Kazunobu Kojima

Appl. Phys. Lett. 98, 101905 (2011); http://dx.doi.org/10.1063/1.3561761 (3 pages) | Cited 3 times

Online Publication Date: 9 March 2011

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By using a simple theoretical approach, the previously reported experimental results of the polarization properties in semipolar and nonpolar InGaN quantum wells (QWs) were analyzed. On the basis of the k⋅p-perturbation theory, we derived a useful analytical expression for describing the polarization properties of these QWs, and used this expression to analyze experimental data reported from various research groups. Based on these analyses, we predicted that the negative polarization degree, which is favorable for laser diodes with cleaved-facet cavity mirrors, would appear in the blue- or green-InGaN QWs on the lower-angle semipolar planes (30°–40° inclined from the c-plane).
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
42.55.Px Semiconductor lasers; laser diodes

Polarity effects in the x-ray photoemission of ZnO and other wurtzite semiconductors

M. W. Allen, D. Y. Zemlyanov, G. I. N. Waterhouse, J. B. Metson, T. D. Veal, C. F. McConville, and S. M. Durbin

Appl. Phys. Lett. 98, 101906 (2011); http://dx.doi.org/10.1063/1.3562308 (3 pages) | Cited 5 times

Online Publication Date: 9 March 2011

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Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al Kα (1486.6 eV) and synchrotron radiation (150 to 1486 eV). In particular, photoemission from the lowest binding energy valence band states was found to be significantly more intense on the Zn-polar face compared to the O-polar face. This is a consistent effect that can be used as a simple, nondestructive indicator of crystallographic polarity in ZnO and other wurtzite semiconductors.
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71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.15.Nc Total energy and cohesive energy calculations

Detection of a ZnSe secondary phase in coevaporated Cu2ZnSnSe4 thin films

Alex Redinger, Katja Hönes, Xavier Fontané, Victor Izquierdo-Roca, Edgardo Saucedo, Nathalie Valle, Alejandro Pérez-Rodríguez, and Susanne Siebentritt

Appl. Phys. Lett. 98, 101907 (2011); http://dx.doi.org/10.1063/1.3558706 (3 pages) | Cited 21 times

Online Publication Date: 9 March 2011

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Cu2ZnSnSe4 (CZTSe) thin films are grown by coevaporation. Composition depth profiles reveal that a Zn rich phase is present at the CZTSe/Mo interface. Raman measurements on the as grown films are used to study the near surface region and the CZTSe/Mo interface, after mechanically removing the thin film from the Mo coated glass. These measurements provide direct experimental evidence of the formation of a ZnSe phase at the CZTSe/Mo interface. While the Raman spectra at the surface region are dominated by CZTSe modes, those measured at the CZTSe/Mo interface are dominated by ZnSe and MoSe2 modes.
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81.05.Hd Other semiconductors
81.15.Dj E-beam and hot filament evaporation deposition
68.55.ag Semiconductors
68.35.Ct Interface structure and roughness
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics

In situ strain relaxation comparison between GaAsBi and GaInAs grown by molecular-beam epitaxy

R. France, C.-S. Jiang, and A. J. Ptak

Appl. Phys. Lett. 98, 101908 (2011); http://dx.doi.org/10.1063/1.3562952 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2011

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The strain relaxation of GaAsBi is studied in order to determine both the maximum thickness before dislocations form for various misfits and the potential of GaAsBi for usage in the compositionally graded buffer of lattice-mismatched devices. Low-misfit GaAsBi epilayers are grown and compared with GaInAs, a well-studied material currently used in compositional grades. Relaxation behavior and dislocation energetics are compared using in situ wafer curvature. Samples are grown using molecular-beam epitaxy under similar conditions with misfit up to –0.81%. GaAsBi begins to relax at a lower thickness than GaInAs of the same mismatch. This leads to the majority of GaAsBi strain relaxation occurring with less material growth than comparable GaInAs. However, GaAsBi has greater residual strain than GaInAs after 2 μm of growth. These results indicate that GaAsBi requires less elastic energy to form dislocations and more elastic energy to either encourage glide or multiply dislocations than GaInAs. GaAsBi shows less surface roughness than GaInAs for all samples, ruling out roughness as a source of dislocations and hindered glide in these alloys.
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68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.60.Bs Mechanical and acoustical properties
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Picosecond time-resolved x-ray refectivity of a laser-heated amorphous carbon film

R. Nüske, A. Jurgilaitis, H. Enquist, S. Dastjani Farahani, J. Gaudin, L. Guerin, M. Harb, C. v. Korff Schmising, M. Störmer, M. Wulff, and J. Larsson

Appl. Phys. Lett. 98, 101909 (2011); http://dx.doi.org/10.1063/1.3562967 (3 pages) | Cited 3 times

Online Publication Date: 10 March 2011

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We demonstrate thin film x-ray reflectivity measurements with picosecond time resolution. Amorphous carbon films with a thickness of 46 nm were excited with laser pulses characterized by 100 fs duration, a wavelength of 800 nm, and a fluence of 70 mJ/cm2. The laser-induced stress caused a rapid expansion of the thin film followed by a relaxation of the film thickness as heat diffused into the silicon substrate. We were able to measure changes in film thickness as small as 0.2 nm. The relaxation dynamics are consistent with a model which accounts for carrier-enhanced substrate heat diffusivity.
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81.07.Bc Nanocrystalline materials
81.05.U- Carbon/carbon-based materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties

Analysis of interband, intraband, and plasmon polariton transitions in silver nanoparticle films via in situ real-time spectroscopic ellipsometry

S. A. Little, R. W. Collins, and S. Marsillac

Appl. Phys. Lett. 98, 101910 (2011); http://dx.doi.org/10.1063/1.3564894 (3 pages) | Cited 3 times

Online Publication Date: 10 March 2011

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The dielectric function of Ag nanoparticle films, deduced from an analysis of in situ real-time spectroscopic ellipsometry (RTSE) measurements, is found to evolve with time during deposition in close consistency with the film structure, deduced in the same RTSE analysis. In the nucleation regime, the intraband dielectric function component is absent and plasmon polariton behavior dominates. Only at nuclei contact, does the intraband amplitude appear, increasing above zero. Both intraband and plasmon amplitudes coexist during surface smoothening associated with coalescence. The intraband relaxation time increases rapidly after surface smoothening is complete, also in consistency with the thin film structural evolution.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Elastic stiffness of L10 FePt thin film studied by picosecond ultrasonics

N. Nakamura, A. Uranishi, M. Wakita, H. Ogi, M. Hirao, and M. Nishiyama

Appl. Phys. Lett. 98, 101911 (2011); http://dx.doi.org/10.1063/1.3562031 (3 pages) | Cited 1 time

Online Publication Date: 11 March 2011

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The elastic stiffness of epitaxial and polycrystalline L10 FePt films is studied by picosecond ultrasonics coupled with x-ray reflectivity analysis, and we find that C33 of L10 FePt is 309 GPa. The morphology of FePt films shows dependence on the film thickness; as the film thickness increases the mazelike structure changes to a continuous film. The elastic stiffness correlates with the morphology change, and it increases as the film thickness increases. When the film thickness exceeds 40 nm, the elastic stiffness becomes independent of the film thickness, and we define the saturated value as C33 of L10 FePt.
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68.55.A- Nucleation and growth
68.55.J- Morphology of films
61.66.-f Structure of specific crystalline solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Surfactant mediated growth of Ti/Ni multilayers

Mukul Gupta, S. M. Amir, Ajay Gupta, and Jochen Stahn

Appl. Phys. Lett. 98, 101912 (2011); http://dx.doi.org/10.1063/1.3565161 (3 pages) | Cited 2 times

Online Publication Date: 11 March 2011

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The surfactant mediated growth of Ti/Ni multilayers is studied. They were prepared using ion beam sputtering at different adatom energies. It was found that the interface roughness decreased significantly when the multilayers were sputtered with Ag as surfactant at an ion energy of 0.75 keV. On the other hand, when the ion energy was increased to 1 keV, it resulted in enhanced intermixing at the interfaces and no appreciable effect of Ag surfactant could be observed. On the basis of the obtained results, the influence of adatom energy on the surfactant mediated growth mechanism is discussed.
Show PACS
81.15.Cd Deposition by sputtering
68.65.Ac Multilayers
68.35.Ct Interface structure and roughness
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