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Top 20 Most Read Articles
July 2007
The 20 articles with the most full-text downloads during the month, in descending order.
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Perpendicular recording media for hard disk drives J. Appl. Phys. 102, 011301 (2007); http://dx.doi.org/10.1063/1.2750414 (22 pages) Online Publication Date: 6 July 2007
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Perpendicular recording technology has recently been introduced in hard disk drives for computer and consumer electronics applications. Although conceptualized in the late 1970s, making a product with perpendicular recording that has competing performance, reliability, and price advantage over the prevalent longitudinal recording technology has taken about three decades. One reason for the late entry of perpendicular recording is that the longitudinal recording technology was quite successful in overcoming many of its problems and in staying competitive. Other reasons are the risks, problems, and investment needed in making a successful transition to perpendicular recording technology. Iwasaki and co-workers came up with many inventions in the late 1970s, such as single-pole head, CoCr alloy media with a perpendicular anisotropy, and recording media with soft magnetic underlayers [
S. Iwasaki and K. Takemura, IEEE Trans. Magn. 11, 1173 (1975)
;
S. Iwasaki and Y. Nakamura, IEEE Trans. Magn. 14, 436 (1978)
;
S. Iwasaki, Y. Nakamura, and K. Ouchi, IEEE Trans. Magn. 15, 1456 (1979)
]. Nevertheless, the research on perpendicular recording media has been intense only in the past five years or so. The main reason for the current interest comes from the need to find an alternative technology to get away from the superparamagnetic limit faced by the longitudinal recording. Out of the several recording media materials investigated in the past, oxide based CoCrPt media have been considered a blessing. The media developed with CoCrPt-oxide or CoCrPt–SiO2 have shown much smaller grain sizes, lower noise, and larger thermal stability than the perpendicular recording media of the past, which is one of the reasons for the success of perpendicular recording. Moreover, oxide-based perpendicular media have also overtaken the current longitudinal recording media in terms of better recording performance. Several issues that were faced with the soft underlayers have also been solved by the use of antiferromagnetically coupled soft underlayers and soft underlayers that are exchange coupled with an antiferromagnetic layer. Significant improvements have also been made in the head design. All these factors now make perpendicular recording more competitive. It is expected that the current materials could theoretically support areal densities of up to 500–600 Gbits/in.2. In this paper, the technologies associated with perpendicular recording media are reviewed. A brief background of magnetic recording and the challenges faced by longitudinal recording technology are presented first, followed by the discussions on perpendicular recording media. Detailed discussions on various layers in the perpendicular recording media and the recent advances in these layers have been made. Some of the future technologies that might help the industry beyond the conventional perpendicular recording technology are discussed at the end of the paper.
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A comprehensive review of ZnO materials and devices J. Appl. Phys. 98, 041301 (2005); http://dx.doi.org/10.1063/1.1992666 (103 pages) Online Publication Date: 30 August 2005
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The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60 meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by
Bunn [Proc. Phys. Soc. London 47, 836 (1935)
], studies of its vibrational properties with Raman scattering in 1966 by
Damen et al. [Phys. Rev. 142, 570 (1966)
], detailed optical studies in 1954 by
Mollwo [Z. Angew. Phys. 6, 257 (1954)
], and its growth by chemical-vapor transport in 1970 by
Galli and Coker [Appl. Phys. Lett. 16, 439 (1970)
]. In terms of devices, Au Schottky barriers in 1965 by
Mead [Phys. Lett. 18, 218 (1965)
], demonstration of light-emitting diodes (1967) by
Drapak [Semiconductors 2, 624 (1968)
], in which Cu2O was used as the p-type material, metal-insulator-semiconductor structures (1974) by
Minami et al. [Jpn. J. Appl. Phys. 13, 1475 (1974)
], ZnO/ZnSe n-p junctions (1975) by
Tsurkan et al. [Semiconductors 6, 1183 (1975)
], and Al/Au Ohmic contacts by
Brillson [J. Vac. Sci. Technol. 15, 1378 (1978)
] were attained. The main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO, as recently discussed by
Look and Claflin [Phys. Status Solidi B 241, 624 (2004)
]. While ZnO already has many industrial applications owing to its piezoelectric properties and band gap in the near ultraviolet, its applications to optoelectronic devices has not yet materialized due chiefly to the lack of p-type epitaxial layers. Very high quality what used to be called whiskers and platelets, the nomenclature for which gave way to nanostructures of late, have been prepared early on and used to deduce much of the principal properties of this material, particularly in terms of optical processes. The suggestion of attainment of p-type conductivity in the last few years has rekindled the long-time, albeit dormant, fervor of exploiting this material for optoelectronic applications. The attraction can simply be attributed to the large exciton binding energy of 60 meV of ZnO potentially paving the way for efficient room-temperature exciton-based emitters, and sharp transitions facilitating very low threshold semiconductor lasers. The field is also fueled by theoretical predictions and perhaps experimental confirmation of ferromagnetism at room temperature for potential spintronics applications. This review gives an in-depth discussion of the mechanical, chemical, electrical, and optical properties of ZnO in addition to the technological issues such as growth, defects, p-type doping, band-gap engineering, devices, and nanostructures.
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Making waves: Kinetic processes controlling surface evolution during low energy ion sputtering J. Appl. Phys. 101, 121301 (2007); http://dx.doi.org/10.1063/1.2749198 (46 pages) Online Publication Date: 20 June 2007
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When collimated beams of low energy ions are used to bombard materials, the surface often develops a periodic pattern or “ripple” structure. Different types of patterns are observed to develop under different conditions, with characteristic features that depend on the substrate material, the ion beam parameters, and the processing conditions. Because the patterns develop spontaneously, without applying any external mask or template, their formation is the expression of a dynamic balance among fundamental surface kinetic processes, e.g., erosion of material from the surface, ion-induced defect creation, and defect-mediated evolution of the surface morphology. In recent years, a comprehensive picture of the different kinetic mechanisms that control the different types of patterns that form has begun to emerge. In this article, we provide a review of different mechanisms that have been proposed and how they fit together in terms of the kinetic regimes in which they dominate. These are grouped into regions of behavior dominated by the directionality of the ion beam, the crystallinity of the surface, the barriers to surface roughening, and nonlinear effects. In sections devoted to each type of behavior, we relate experimental observations of patterning in these regimes to predictions of continuum models and to computer simulations. A comparison between theory and experiment is used to highlight strengths and weaknesses in our understanding. We also discuss the patterning behavior that falls outside the scope of the current understanding and opportunities for advancement.
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Plasmonics: Localization and guiding of electromagnetic energy in metal/dielectric structures J. Appl. Phys. 98, 011101 (2005); http://dx.doi.org/10.1063/1.1951057 (10 pages) Online Publication Date: 11 July 2005
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We review the basic physics of surface-plasmon excitations occurring at metal/dielectric interfaces with special emphasis on the possibility of using such excitations for the localization of electromagnetic energy in one, two, and three dimensions, in a context of applications in sensing and waveguiding for functional photonic devices. Localized plasmon resonances occurring in metallic nanoparticles are discussed both for single particles and particle ensembles, focusing on the generation of confined light fields enabling enhancement of Raman-scattering and nonlinear processes. We then survey the basic properties of interface plasmons propagating along flat boundaries of thin metallic films, with applications for waveguiding along patterned films, stripes, and nanowires. Interactions between plasmonic structures and optically active media are also discussed.
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High-κ gate dielectrics: Current status and materials properties considerations J. Appl. Phys. 89, 5243 (2001); http://dx.doi.org/10.1063/1.1361065 (33 pages)
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Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward successful integration into the expected processing conditions for future CMOS technologies, especially due to their tendency to form at interfaces with Si (e.g. silicates). These pseudobinary systems also thereby enable the use of other high-κ materials by serving as an interfacial high-κ layer. While work is ongoing, much research is still required, as it is clear that any material which is to replace SiO2 as the gate dielectric faces a formidable challenge. The requirements for process integration compatibility are remarkably demanding, and any serious candidates will emerge only through continued, intensive investigation. © 2001 American Institute of Physics. |
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Electrical conduction and photoluminescence properties of solution-grown ZnO nanowires J. Appl. Phys. 102, 014305 (2007); http://dx.doi.org/10.1063/1.2751116 (7 pages) Online Publication Date: 9 July 2007
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We report on the optical and electrical properties of zinc oxide nanorods synthesized in solution using Oswald ripening of ZnO nanodots with the addition of ethylenediamene growth directing agent. This method results in high quality, single crystalline ZnO nanorods that extend up to 3 μm in length and have an average diameter of 25±7 nm, compared to ∼ 75 nm diameter for similarly prepared nanorods but without the addition of the growth directing agent. Furthermore, we find that the higher aspect ratio nanorods exhibit strong size-dependent electrical characteristics, with a critical diameter of about 27 nm delimiting nonconductive and conductive behaviors. Theoretical calculations indicate that the origin of this size-dependent conductivity is the presence of surface states that deplete the carriers in the smaller diameter nanorods, and an estimate of the density of these states is provided.
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Surface plasmon enhanced silicon solar cells J. Appl. Phys. 101, 093105 (2007); http://dx.doi.org/10.1063/1.2734885 (8 pages) Online Publication Date: 7 May 2007
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Thin-film solar cells have the potential to significantly decrease the cost of photovoltaics. Light trapping is particularly critical in such thin-film crystalline silicon solar cells in order to increase light absorption and hence cell efficiency. In this article we investigate the suitability of localized surface plasmons on silver nanoparticles for enhancing the absorbance of silicon solar cells. We find that surface plasmons can increase the spectral response of thin-film cells over almost the entire solar spectrum. At wavelengths close to the band gap of Si we observe a significant enhancement of the absorption for both thin-film and wafer-based structures. We report a sevenfold enhancement for wafer-based cells at λ = 1200 nm and up to 16-fold enhancement at λ = 1050 nm for 1.25 μm thin silicon-on-insulator (SOI) cells, and compare the results with a theoretical dipole-waveguide model. We also report a close to 12-fold enhancement in the electroluminescence from ultrathin SOI light-emitting diodes and investigate the effect of varying the particle size on that enhancement.
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Band parameters for III–V compound semiconductors and their alloys J. Appl. Phys. 89, 5815 (2001); http://dx.doi.org/10.1063/1.1368156 (61 pages)
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We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other. © 2001 American Institute of Physics. |
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J. Appl. Phys. 102, 013103 (2007); http://dx.doi.org/10.1063/1.2752582 (5 pages) Online Publication Date: 5 July 2007
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Light emitting field-effect transistors (LEFETs) were fabricated with a low work function metal (calcium) and a high work function metal (gold) as the source and drain electrodes. The gold electrode serves as the source for holes into the π band and the drain for electrons from the π* band; the calcium electrode serves as the source for electrons into the π* band and the drain for holes from the π band. For 65 V<VG<103 V, the LEFET operates in the ambipolar regime. The emission zone has been spatially resolved (as it is moved across the channel by sweeping the gate voltage) using confocal microscopy; the full width at half maximum is 2 μm. At the gate voltage extremes (VG = 0 or VG = 150 V), the electron (hole) density extends all the way across the 16 μm channel such that the electron (hole) accumulation layer functions as the cathode (anode) for a light-emitting diode, with opposite carrier injection by tunneling; i.e., the carrier densities are sufficiently high that the accumulation layer functions as a low resistance contact, implying near metallic transport.
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Ferroelectric thin films: Review of materials, properties, and applications J. Appl. Phys. 100, 051606 (2006); http://dx.doi.org/10.1063/1.2336999 (46 pages) Online Publication Date: 12 September 2006
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An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems’ applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems’ applications, and permittivity and loss in ferroelectric films—important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures.
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Small molecular weight organic thin-film photodetectors and solar cells J. Appl. Phys. 93, 3693 (2003); http://dx.doi.org/10.1063/1.1534621 (31 pages) Online Publication Date: 21 March 2003
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In this review, we discuss the physics underlying the operation of single and multiple heterojunction, vacuum-deposited organic solar cells based on small molecular weight thin films. For single heterojunction cells, we find that the need for direct contact between the deposited electrode and the active organics leads to quenching of excitons. An improved device architecture, the double heterojunction, is shown to confine excitons within the active layers, allowing substantially higher internal efficiencies to be achieved. A full optical and electrical analysis of the double heterostructure architecture leads to optimal cell design as a function of the optical properties and exciton diffusion lengths of the photoactive materials. Combining the double heterostructure with novel light trapping schemes, devices with external efficiencies approaching their internal efficiency are obtained. When applied to an organic photovoltaic cell with a power conversion efficiency of 1.0%±0.1% under 1 sun AM1.5 illumination, devices with external power conversion efficiencies of 2.4%±0.3% are reported. In addition, we show that by using materials with extended exciton diffusion lengths LD, highly efficient double heterojunction photovoltaic cells are obtained, even in the absence of a light trapping geometry. Using C60 as an acceptor material, double heterostructure external power conversion efficiencies of 3.6%±0.4% under 1 sun AM1.5 illumination are obtained. Stacking of single heterojunction devices leads to thin film multiple heterojunction photovoltaic and photodetector structures. Thin bilayer photovoltaic cells can be stacked with ultrathin (∼5 Å), discontinuous Ag layers between adjacent cells serving as efficient recombination sites for electrons and holes generated in the neighboring cells. Such stacked cells have open circuit voltages that are n times the open circuit voltage of a single cell, where n is the number of cells in the stack. In optimized structures, the short circuit photocurrent remains approximately constant upon stacking thin cells, leading to higher achievable power conversion efficiencies, as confirmed by modelling optical interference effects and exciton migration. A 2.5%±0.3% power efficiency under 100 mW/cm2 AM1.5 illumination conditions is obtained by stacking two ∼1% efficient devices. Alternatively, when the contact layers between the stacked cells are eliminated, a multilayer structure consisting of alternating films of donor and acceptor-type materials is obtained. Since the thicknesses of the individual layers (∼5 Å) can be substantially smaller than the exciton diffusion length, nearly 100% of the photogenerated excitons are dissociated, and the resulting free charges are detected. In addition, the ultrathin organic layers facilitate electron and hole transport through the multilayer stack by tunneling. When these devices are operated as photodetectors under applied fields >106 V/cm, the carrier collection efficiency reaches 80%, leading to external quantum efficiencies of 75%±1% across the visible spectrum in cells containing the thinnest layers. We find that due to the fast carrier tunneling process, the temporal response of these multilayer detectors is a direct measure of exciton dynamics. Response times of 720±50 ps are achieved, leading to a 3 dB bandwidth of 430±30 MHz. A summary of representative results obtained for both polymer and small molecule photovoltaic cells and photodetectors is included in this review. Prospects for further improvements in organic solar cells and photodetectors are considered. © 2003 American Institute of Physics. |
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J. Appl. Phys. 102, 013508 (2007); http://dx.doi.org/10.1063/1.2749281 (5 pages) Online Publication Date: 5 July 2007
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Comparative analysis of optical characteristics of In0.08Ga0.92N/In0.03Ga0.97N multiquantum well (MQW) laser diode structures grown on freestanding GaN and on sapphire substrates is reported. Higher quantum efficiency, higher thermal activation energy, smaller Stokes-like shift, and shorter radiative lifetime are observed for InGaN MQWs on GaN substrate than those of the same MQWs on sapphire substrate. From time-resolved optical analysis, we find that not only an increase in nonradiative lifetime due to reduced dislocation density but also a decrease in radiative lifetime caused by suppressed piezoelectric field play an important role in enhancing optical properties of InGaN MQWs on GaN substrates.
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Effect of different metal deposition methods on the growth behaviors of carbon nanotubes J. Appl. Phys. 102, 014301 (2007); http://dx.doi.org/10.1063/1.2750408 (4 pages) Online Publication Date: 2 July 2007
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It is generally known that the catalyst particles promote tip or base growth of carbon nanotubes depending on the contact force between the catalyst particles and the substrate. We have investigated the correlation between the growth modes of vertically aligned carbon nanotubes (CNTs) and the adhesion of Ni catalyst particles to the Si substrates. It is shown that Ni films (10 nm thick) deposited by pulsed laser deposition (PLD) and electron beam evaporation are broken up into nanoparticles and/or islands when pretreated in NH3 gas ambient at 850 °C for 20 min. It is found that CNT growth on the PLD substrate proceeds by base growth mode, whereas CNT growth on the electron-beam evaporated substrate is operated by tip growth mode. The different CNT growth behaviors are explained in terms of the difference of the adhesion between the Ni catalyst particles and the substrate due to the different kinetic energy of depositing Ni particles.
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Gallium-doped zinc oxide films as transparent electrodes for organic solar cell applications J. Appl. Phys. 102, 023501 (2007); http://dx.doi.org/10.1063/1.2750410 (5 pages) Online Publication Date: 16 July 2007
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We report microstructural characteristics and properties of gallium-doped ZnO films deposited on glass by pulsed laser deposition. The Zn0.95Ga0.05O film deposited at 200 °C and 1×10−3 Torr showed predominant 〈0001〉 orientation with a metallic behavior and a resistivity of 2×10−4 Ω cm at room temperature. Low resistivity of the ZnGaO films has been explained in terms of optimal combination of carrier concentration and minimized scattering, and is correlated with the microstructure and the deposition parameters. Power conversion efficiency comparable to indium tin oxide-based devices (1.25±0.05%) is achieved on a Zn0.95Ga0.05O/Cu-phthalocyanine/C60 double-heterojunction solar cell.
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J. Appl. Phys. 102, 013511 (2007); http://dx.doi.org/10.1063/1.2752783 (4 pages) Online Publication Date: 5 July 2007
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Temperature-dependent photoluminescence excitation (PLE) spectroscopy is used to study nominally undoped and indium-doped ZnO nanorods grown by thermal evaporation method. Clear differences in PLE features between the two samples are observed. We demonstrate that the first derivative of the PLE spectra can be used to determine the free exciton energy for both samples. The physics behind is understood either in terms of competing absorption and recombination to the green emission band being monitored, or based on the analogy between the first derivative of PLE and photoreflectance spectroscopy. Two residual donor levels located at about 37 and 120 meV below the conduction band minimum are identified from the PLE spectra.
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Electrical and structural characterization of as-grown and annealed hydrothermal bulk ZnO J. Appl. Phys. 102, 014903 (2007); http://dx.doi.org/10.1063/1.2751413 (5 pages) Online Publication Date: 5 July 2007
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Hall effect measurements in the range 20–370 K on as-grown and annealed hydrothermal bulk ZnO have been performed. The bulk conductivity in the highly resistive as-grown sample was found to decrease and then increase after annealing at 550 °C and 930 °C, respectively. The conduction in the as-grown material is attributed to a deep donor which is replaced by a much shallower donor after annealing at 930 °C. Annealing at both temperatures also produced strong surface conduction effects. Nondegenerate low-mobility surface conduction dominated the electrical properties of the sample annealed at 550 °C, while a degenerate surface channel was formed after annealing at 930 °C. In addition, Rutherford backscattering and channeling spectrometry (RBS/C) was used to assess the effect of annealing on the crystalline quality of the samples. RBS/C measurements reveal that annealing at 930 °C leads to significant improvement of the crystalline quality of the material, while annealing at 550 °C results in the segregation of a nonchanneling impurity at the surface.
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J. Appl. Phys. 93, 793 (2003); http://dx.doi.org/10.1063/1.1524305 (26 pages) Online Publication Date: 27 December 2002
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Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid–solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime—experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3ω method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology. © 2003 American Institute of Physics. |
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J. Appl. Phys. 102, 024301 (2007); http://dx.doi.org/10.1063/1.2753589 (6 pages) Online Publication Date: 16 July 2007
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Aligned one-dimensional diluted magnetic semiconductor Zn1−xMnxO nanowires were synthesized from a reaction of metallic Zn foil and MnCl2⋅6H2O under oxygen environment at variant temperatures between 750 and 950 °C by a chemical vapor deposition method. The c-axis preferentially grown nanowire arrays are single crystalline wurtzite structure, of which the growing temperature has a significant influence on both morphology and magnetic ordering. Nanowires with the highest aspect ratios were grown at 850 °C, whereas nanowires presenting largest room-temperature ferromagnetism were formed at 950 °C. More Mn2+ substitution in the ZnO lattice was observed at 950 °C, resulting in strong room-temperature ferromagnetism with a saturation magnetization of 0.25 emu/g. At synthesis temperatures of 750 and 850 °C, formation of a ZnMn2O4 room-temperature paramagnetic second phase was found. The nanostructures with different aspect ratios were obtained with the variation of synthesis temperature. The temperature dependent growth of aligned Zn1−xMnxO nanowires reveals strong room-temperature ferromagnetism occurs in the nanowire arrays synthesized at high temperature. The nanowires with strong room temperature have great potential in spintronic nanodevice application.
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J. Appl. Phys. 97, 011101 (2005); http://dx.doi.org/10.1063/1.1819976 (28 pages) Online Publication Date: 9 December 2004
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This article reviews the history and current progress in high-mobility strained Si, SiGe, and Ge channel metal-oxide-semiconductor field-effect transistors (MOSFETs). We start by providing a chronological overview of important milestones and discoveries that have allowed heterostructures grown on Si substrates to transition from purely academic research in the 1980’s and 1990’s to the commercial development that is taking place today. We next provide a topical review of the various types of strain-engineered MOSFETs that can be integrated onto relaxed Si1−xGex, including surface-channel strained Si n- and p-MOSFETs, as well as double-heterostructure MOSFETs which combine a strained Si surface channel with a Ge-rich buried channel. In all cases, we will focus on the connections between layer structure, band structure, and MOS mobility characteristics. Although the surface and starting substrate are composed of pure Si, the use of strained Si still creates new challenges, and we shall also review the literature on short-channel device performance and process integration of strained Si. The review concludes with a global summary of the mobility enhancements available in the SiGe materials system and a discussion of implications for future technology generations.
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Single semiconductor nanocrystals: Physics and applications J. Appl. Phys. 101, 081727 (2007); http://dx.doi.org/10.1063/1.2723184 (5 pages) Online Publication Date: 27 April 2007
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Semiconductor nanocrystals are nanoscale light sources that received much attention in recent years. We will give an overview about semiconductor colloidal nanocrystals as active optical materials in photonic structures and hybrid colloidal-epitaxial devices, for realizations of cavity quantum electrodynamics (cavity QED) concepts, or for probing field intensities in coupled resonator optical waveguides.
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