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Applied Physics Reviews — 2009

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Adaptive interferometry with photorefractive crystals

Alexei A. Kamshilin, Roman V. Romashko, and Yuri N. Kulchin

J. Appl. Phys. 105, 031101 (2009); http://dx.doi.org/10.1063/1.3049475 (11 pages)

Online Publication Date: 3 February 2009

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This work presents a review of progress and development in the field of adaptive laser interferometry. This method enables highly precise and reliable measurement of various physical parameters under unstable environmental conditions, which makes it very attractive for numerous industrial applications.
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42.40.Kw Holographic interferometry; other holographic techniques
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
07.60.Ly Interferometers

Ultrafast optics: Imaging and manipulating biological systems

Kraig E. Sheetz and Jeff Squier

J. Appl. Phys. 105, 051101 (2009); http://dx.doi.org/10.1063/1.3081635 (17 pages)

Online Publication Date: 3 March 2009

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The rapid evolution of ultrafast optics technology over the past two decades has opened the window to a broad range of applications in biology and medicine. Compact, reliable, and turn-key ultrafast laser systems are enabling cutting-edge science to take place in everyday laboratories and clinics. Led by the discovery of two-photon excitation fluorescence microscopy nearly 20 years ago, the biological imaging community is exploring unique image contrast mechanisms and pushing spatial and temporal resolution to new limits. Concurrent with advancements in imaging are developments in the precision application of extremely high peak intensities available in ultrashort pulses for disrupting or manipulating targeted locations in biological systems on the submicron scale while leaving surrounding tissue healthy. The ability for scientists to selectively discriminate structures of interest at the cellular and subcellular levels under relevant physiological conditions shows tremendous promise for accelerating the path to understanding biological functions at the most fundamental level.
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87.63.lt Laser imaging
87.64.M- Optical microscopy

Stressed multidirectional solid-phase epitaxial growth of Si

N. G. Rudawski, K. S. Jones, S. Morarka, M. E. Law, and R. G. Elliman

J. Appl. Phys. 105, 081101 (2009); http://dx.doi.org/10.1063/1.3091395 (20 pages)

Online Publication Date: 27 April 2009

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The study of the solid-phase epitaxial growth (SPEG) process of Si (variously referred to as solid-phase epitaxy, solid-phase epitaxial regrowth, solid-phase epitaxial crystallization, and solid-phase epitaxial recrystallization) amorphized via ion implantation has been a topic of fundamental and technological importance for several decades. Overwhelmingly, SPEG has been studied (and viewed) as a single-directional process where an advancing growth front between amorphous and crystalline Si phases only has one specific crystallographic orientation. However, as it pertains to device processing, SPEG must actually be considered as multidirectional (or patterned) rather than bulk in nature with the evolving growth interface having multiple crystallographic orientations. Moreover, due to the increasingly ubiquitous nature of stresses presented during typical Si-based device fabrication, there is great interest in specifically studying the stressed-SPEG process. This work reviews the progress made in understanding the multidirectional SPEG and, more importantly, stressed multidirectional SPEG process. For the work reviewed herein, (001) Si wafers with 〈110〉-aligned, intrinsically stressed Si3N4/SiO2 patterning consisting of square and line structures were used with unmasked regions of the Si substrate amorphized via ion implantation. It is revealed that the stresses generated in the Si substrate from the patterning, both in line and square structures, alter the kinetics and geometry of the multidirectional SPEG process and can influence the formation of mask-edge defects which form during growth to different degrees as per differences in the substrate stresses generated by each type of patterning. Likewise, it is shown that application of external stress from wafer bending during SPEG in specimens with and without patterning can also influence the geometry of the evolving growth interface. Finally, the effect of the addition of SPEG-enhancing impurities during multidirectional stressed growth is observed to alter the evolution of the growth interface, thus suggesting that stress influences on growth are much less than those from dopants. Within the context of prior work, attempts are made to correlate the prior observations in single-directional stressed SPEG with the observations from patterned stressed SPEG reviewed herein. However, as is argued in this review, it ultimately appears that much of the research performed on understanding the single-directional stressed-SPEG process cannot be reasonably extended to the multidirectional stressed-SPEG process.
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81.15.Np Solid phase epitaxy; growth from solid phases
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.ag Semiconductors
64.70.kg Semiconductors

Third-generation infrared photodetector arrays

A. Rogalski, J. Antoszewski, and L. Faraone

J. Appl. Phys. 105, 091101 (2009); http://dx.doi.org/10.1063/1.3099572 (44 pages)

Online Publication Date: 11 May 2009

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Hitherto, two distinct families of multielement detector arrays have been used for infrared (IR) imaging system applications: linear arrays for scanning systems (first generation) and two-dimensional arrays for staring systems (second generation). Nowadays, third-generation IR systems are being developed which, in the common understanding, provide enhanced capabilities such as larger numbers of pixels, higher frame rates, better thermal resolution, multicolor functionality, and/or other on-chip signal-processing functions. In this paper, fundamental and technological issues associated with the development and exploitation of third-generation IR photon detectors are discussed. In this class of detectors the two main competitors, HgCdTe photodiodes and quantum-well photoconductors, are considered. This is followed by discussions focused on the most recently developed focal plane arrays based on type-II strained-layer superlattices and quantum dot IR photodetectors. The main challenges facing multicolor devices are concerned with complicated device structures, thicker and multilayer material growth, and more difficult device fabrication, especially for large array sizes and/or small pixel dimensions. This paper also presents and discusses the ongoing detector technology challenges that are being addressed in order to develop third-generation infrared photodetector arrays.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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When group-III nitrides go infrared: New properties and perspectives

Junqiao Wu

J. Appl. Phys. 106, 011101 (2009); http://dx.doi.org/10.1063/1.3155798 (28 pages)

Online Publication Date: 1 July 2009

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Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼ 1.9 μm (0.64 eV for InN) to the ultraviolet at ∼ 0.36 μm (3.4 eV for GaN) or 0.2 μm (6.2 eV for AlN). The continuous range of bandgap energies now spans the near infrared, raising the possibility of new applications for group-III nitrides. In this article we present a detailed review of the physical properties of InN and related group III-nitride semiconductors. The electronic structure, carrier dynamics, optical transitions, defect physics, doping disparity, surface effects, and phonon structure will be discussed in the context of the InN bandgap re-evaluation. We will then describe the progress, perspectives, and challenges in the developments of new electronic and optoelectronic devices based on InGaN alloys. Advances in characterization and understanding of InN and InGaN nanostructures will also be reviewed in comparison to their thin film counterparts.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.20.Nr Semiconductor compounds
61.72.uj III-V and II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

Intracavity nonlinearities in quantum-cascade lasers

Jing Bai and D. S. Citrin

J. Appl. Phys. 106, 031101 (2009); http://dx.doi.org/10.1063/1.3180960 (14 pages)

Online Publication Date: 7 August 2009

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We discuss various intracavity optical nonlinearities up to the third order in quantum-cascade lasers. The discussions are based on two kinds of nonlinearities, each toward respective applications. The susceptibilities at the second-harmonic or third-harmonic frequencies lead to harmonic generation for multicolor emission; moreover, the third-order susceptibility at the fundamental frequency results in a nonlinear refractive index, i.e., the Kerr nonlinearity, which is associated with self-pulsations in quantum-cascade lasers. The review surveys the technology progression for the enhancement of nonlinear frequency generation as well as the investigation of the physics behind the multimode output of quantum-cascade lasers. In addition, a simulation model accounting for intracavity nonlinear interactions in quantum-cascade lasers is introduced, which can be used to evaluate and further optimize the nonlinear performance.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

The photon haystack and emerging radiation detection technology

Robert C. Runkle, L. Eric Smith, and Anthony J. Peurrung

J. Appl. Phys. 106, 041101 (2009); http://dx.doi.org/10.1063/1.3207769 (21 pages)

Online Publication Date: 24 August 2009

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The resources devoted to interdicting special nuclear materials have increased considerably over the last several years in step with growing efforts to counter nuclear proliferation and nuclear terrorism. This changing landscape has led to a large amount of research and development that aims to improve the effectiveness of technology now deployed worldwide. Interdicting special nuclear materials is most commonly addressed by detecting and characterizing emitted gamma rays, but modest signature emissions can be obscured by attenuating material and must be differentiated from large and highly variable environmental background emissions. It is a daunting technical challenge to identify special nuclear materials via gamma-ray detection, but a host of new detection technologies is now emerging. This challenge motivates our review of special nuclear material signatures, the physics of detection approaches, emerging technologies, and performance metrics. The use of benchmark gamma-ray sources aids our discussion.
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29.40.-n Radiation detectors

Three-dimensional microfabrication of materials by femtosecond lasers for photonics applications

Saulius Juodkazis, Vygantas Mizeikis, and Hiroaki Misawa

J. Appl. Phys. 106, 051101 (2009); http://dx.doi.org/10.1063/1.3216462 (14 pages)

Online Publication Date: 11 September 2009

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Femtosecond laser fabrication of three-dimensional structures for photonics applications is reviewed. Fabrication of photonic crystal structures by direct laser writing and holographic recording by multiple beam interference techniques are discussed. The physical mechanisms associated with structure formation and postfabrication are described. The advantages and limitations of various femtosecond laser microfabrication techniques for the preparation of photonic crystals and elements of microelectromechanical and micro-optofluidic systems are discussed.
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42.70.Qs Photonic bandgap materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Ln Holographic recording materials; optical storage media

Gas hydrates: Unlocking the energy from icy cages

Carolyn A. Koh, Amadeu K. Sum, and E. Dendy Sloan

J. Appl. Phys. 106, 061101 (2009); http://dx.doi.org/10.1063/1.3216463 (14 pages)

Online Publication Date: 24 September 2009

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Technological advancements to control gas hydrates in energy transportation, recovery, and storage require detailed knowledge of the structural properties of these materials, and the thermodynamic and kinetic mechanisms of gas hydrate formation and decomposition. Paradigm shifts are moving the energy industry from thermodynamic to kinetic control strategies of gas hydrates in gas and oil deepwater pipelines, and from exploration to production from hydrated arctic deposits. This review examines the recent research progress in molecular structural kinetic studies of gas hydrates, and the development of new strategies for detecting and producing energy from arctic and oceanic hydrated deposits, and producing new materials for hydrogen storage.
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84.60.-h Direct energy conversion and storage
89.30.-g Fossil fuels and nuclear power
01.30.Rr Surveys and tutorial papers; resource letters
33.15.Bh General molecular conformation and symmetry; stereochemistry
05.70.Fh Phase transitions: general studies

Defects in ZnO

M. D. McCluskey and S. J. Jokela

J. Appl. Phys. 106, 071101 (2009); http://dx.doi.org/10.1063/1.3216464 (13 pages)

Online Publication Date: 5 October 2009

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Zinc oxide (ZnO) is a wide band gap semiconductor with potential applications in optoelectronics, transparent electronics, and spintronics. The high efficiency of UV emission in this material could be harnessed in solid-state white lighting devices. The problem of defects, in particular, acceptor dopants, remains a key challenge. In this review, defects in ZnO are discussed, with an emphasis on the physical properties of point defects in bulk crystals. As grown, ZnO is usually n-type, a property that was historically ascribed to native defects. However, experiments and theory have shown that O vacancies are deep donors, while Zn interstitials are too mobile to be stable at room temperature. Group-III (B, Al, Ga, and In) and H impurities account for most of the n-type conductivity in ZnO samples. Interstitial H donors have been observed with IR spectroscopy, while substitutional H donors have been predicted from first-principles calculations but not observed directly. Despite numerous reports, reliable p-type conductivity has not been achieved. Ferromagnetism is complicated by the presence of secondary phases, grain boundaries, and native defects. The famous green luminescence has several possible origins, including Cu impurities and Zn vacancies. The properties of group-I (Cu, Li, and Na) and group-V (N, P, As, and Sb) acceptors, and their complexes with H, are discussed. In the future, doping of ZnO nanocrystals will rely on an understanding of these fundamental properties.
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71.55.Gs II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
61.72.jj Interstitials
61.72.jd Vacancies
61.72.Mm Grain and twin boundaries
75.50.Dd Nonmetallic ferromagnetic materials
72.20.Fr Low-field transport and mobility; piezoresistance

Photonic guiding structures in lithium niobate crystals produced by energetic ion beams

Feng Chen

J. Appl. Phys. 106, 081101 (2009); http://dx.doi.org/10.1063/1.3216517 (29 pages)

Online Publication Date: 21 October 2009

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A range of ion beam techniques have been used to fabricate a variety of photonic guiding structures in the well-known lithium niobate (LiNbO3 or LN) crystals that are of great importance in integrated photonics/optics. This paper reviews the up-to-date research progress of ion-beam-processed LiNbO3 photonic structures and reports on their fabrication, characterization, and applications. Ion beams are being used with this material in a wide range of techniques, as exemplified by the following examples. Ion beam milling/etching can remove the selected surface regions of LiNbO3 crystals via the sputtering effects. Ion implantation and swift ion irradiation can form optical waveguide structures by modifying the surface refractive indices of the LiNbO3 wafers. Crystal ion slicing has been used to obtain bulk-quality LiNbO3 single-crystalline thin films or membranes by exfoliating the implanted layer from the original substrate. Focused ion beams can either generate small structures of micron or submicron dimensions, to realize photonic bandgap crystals in LiNbO3, or directly write surface waveguides or other guiding devices in the crystal. Ion beam-enhanced etching has been extensively applied for micro- or nanostructuring of LiNbO3 surfaces. Methods developed to fabricate a range of photonic guiding structures in LiNbO3 are introduced. Modifications of LiNbO3 through the use of various energetic ion beams, including changes in refractive index and properties related to the photonic guiding structures as well as to the materials (i.e., electro-optic, nonlinear optic, luminescent, and photorefractive features), are overviewed in detail. The application of these LiNbO3 photonic guiding structures in both micro- and nanophotonics are briefly summarized.
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42.86.+b Optical workshop techniques
42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
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On the shock response of cubic metals

N. K. Bourne, G. T. Gray, III, and J. C. F. Millett

J. Appl. Phys. 106, 091301 (2009); http://dx.doi.org/10.1063/1.3218758 (14 pages)

Online Publication Date: 6 November 2009

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The response of four cubic metals to shock loading is reviewed in order to understand the effects of microstructure on continuum response. Experiments are described that link defect generation and storage mechanisms at the mesoscale to observations in the bulk. Four materials were reviewed; these were fcc nickel, the ordered fcc intermetallic Ni3Al, the bcc metal tantalum, and two alloys based on the intermetallic phase TiAl; Ti–46.5Al–2Cr–2Nb and Ti–48Al–2Cr–2Nb–1B. The experiments described are in two groups: first, equation of state and shear strength measurements using Manganin stress gauges and, second, postshock microstructural examinations and measurement of changes in mechanical properties. The behaviors described are linked through the description of time dependent plasticity mechanisms to the final states achieved. Recovered targets displayed dislocation microstructures illustrating processes active during the shock-loading process. Reloading of previously shock-prestrained samples illustrated shock strengthening for the fcc metals Ni and Ni3Al while showing no such effect for bcc Ta and for the intermetallic TiAl. This difference in effective shock hardening has been related, on the one hand, to the fact that bcc metals have fewer available slip systems that can operate than fcc crystals and to the observation that the lower symmetry materials (Ta and TiAl) both possess high Peierls stress and thus have higher resistances to defect motion in the lattice under shock-loading conditions. These behaviors, compared between these four materials, illustrate the role of defect generation, transport, storage, and interaction in determining the response of materials to shock prestraining.
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81.40.Lm Deformation, plasticity, and creep
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
62.50.Ef Shock wave effects in solids and liquids
62.20.fq Plasticity and superplasticity
61.72.Lk Linear defects: dislocations, disclinations
64.30.-t Equations of state of specific substances
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
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