Tin doped indium oxide (ITO) films are highly transparent in the visible region, exhibiting high reflectance in the infrared region, and having nearly metallic conductivity. Owing to this unusual combination of electrical and optical properties, this material is widely applied in optoelectronic devices. The association of these properties in a single material explains the vast domain of its applicability and the diverse production methods which have emerged. Although the different properties of tin doped indium oxide in the film form are interdependent, this article mainly focuses on the electrical aspects. Detailed description of the conduction mechanism and the main parameters that control the conductivity is presented. On account of the large varieties and differences in the fabrication techniques, the electrical properties of ITO films are discussed and compared within each technique.

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Tin doped indium oxide thin films: Electrical properties

Transition-metal oxide nanocrystals are interesting candidates for localized surface plasmon resonance hosts because they exhibit fascinating properties arising from the unique character of their outer-d valence electrons. WO3−δ nanoparticles are known to have intense visible and near-IR absorption, but the origin of the optical absorption has remained unclear. Here we demonstrate that metallic phases of WO3−δ nanoparticles exhibit a strong and tunable localized surface plasmon resonance, which opens up the possibility of rationally designing plasmonic tungsten oxide nanoparticles for light harvesting, bioimaging, and sensing.

Tunable localized surface plasmon resonances in tungsten oxide nanocrystals.

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the functi...

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation.

We present a review on the emerging materials for novel plasmonic colloidal nanocrystals. We start by explaining the basic processes involved in surface plasmon resonances in nanoparticles and then discuss the classes of nanocrystals that to date are particularly promising for tunable plasmonics: non-stoichiometric copper chalcogenides, extrinsically doped metal oxides, oxygen-deficient metal oxides and conductive metal oxides. We additionally introduce other emerging types of plasmonic nanocrystals and finally we give an outlook on nanocrystals of materials that could potentially display interesting plasmonic properties.

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New materials for tunable plasmonic colloidal nanocrystals

In femtosecond pump-probe measurements, the appearance of coherent phonon oscillations at 4.5 and 6.0 THz indicating the rutile metal phase of ${\mathrm{VO}}_{2}$ does not occur simultaneously with the first-order metal-insulator transition (MIT) near $68\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The monoclinic and correlated metal (MCM) phase between the MIT and the structural phase transition (SPT) is generated by a photoassisted hole excitation, which is evidence of the Mott transition. The SPT between the MCM phase and the rutile metal phase occurs due to subsequent Joule heating. The MCM phase can be regarded as an intermediate nonequilibrium state.

https://arxiv.org/pdf/cond-mat/0608085.pdf

Monoclinic and correlated metal phase in VO(2) as evidence of the Mott transition: coherent phonon analysis.

We study the ultrafast insulator-to-metal transition in nanoparticles of VO2, obtained by ion implantation and self-assembly in silica. The nonmagnetic, strongly correlated compound VO2 undergoes a reversible phase transition, which can be photoinduced on an ultrafast time scale. In the nanoparticles, prompt formation of the metallic state results in the appearance of surface-plasmon resonance. We achieve large, ultrafast enhancement of optical absorption in the near-infrared spectral region that encompasses the wavelength range for optical-fiber communications. One can further tailor the response of the nanoparticles by controlling their shape.

http://qcmd.mpsd.mpg.de/files/qcmd-theme/publications/2003-2009/2005_lbnl_rini-etal-OL_30.pdf

Photoinduced phase transition in VO2 nanocrystals: ultrafast control of surface-plasmon resonance.

Z-scan and pump-probe measurements with ultrafast, 800nm laser pulses were used to compare the ultrafast optical nonlinearities of VO2 nanoparticles and thin films in both semiconducting and metallic states. In the metallic state, both the nanocrystals and thin films exhibit a positive, intensity-dependent nonlinear index of refraction. However, the nonlinear effects are relatively larger in the VO2 nanocrystals, which also reveal a saturable nonlinear absorption. When the semiconductor-to-metal phase transition is induced by the laser pulse, VO2 thin films exhibit a negative equivalent nonlinear index of refraction while the nanocrystals exhibit a smaller but still positive index. Both the VO2 nanocrystals and thin films undergo the phase transition within 120fs.

Optical nonlinearities in VO2 nanoparticles and thin films

Extended defects from 5-, 2-, and 1-keV Si+ ion implantation are investigated by transmission electron microscopy using implantation doses of 1 and 3×1014 cm−2 and annealing temperatures from 750 to 900 °C. Despite the proximity of the surface, {311}-type defects are observed even for 1 keV. Samples with a peak concentration of excess interstitials exceeding ∼1% of the atomic density also contain some {311} defects which are corrugated across their width. These so-called zig-zag {311} defects are more stable than the ordinary {311} defects, having a dissolution rate at 750 °C which is ten times smaller. Due to their enhanced stability, the zig-zag {311} defects grow to lengths that are many times longer than their distance from the surface. It is proposed that zig-zag {311} defects form during the early stages of annealing by coalescence the high volume density of {311} defects confined within a very narrow implanted layer. These findings indicate that defect formation and dissolution will continue to con...

Interstitial defects in silicon from 1–5 keV Si+ ion implantation

We investigate the formation of nanoparticles of Au in SiO2 by multiple ion implantation steps and intermediate anneals to isolate nucleation and growth, thereby producing a narrow particle size distribution. We discuss the effects of varying the initial nucleation dose and the growth temperature and establish guidelines for synthesizing nanoparticles with improved size uniformity. By this method, we have obtained a standard deviation of 16% on an average diameter of 1.68 nm, compared to 28% when no attempt is made to isolate nucleation and growth.

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Synthesis of Nearly Monodisperse Embedded Nanoparticles by Separating Nucleation and Growth in Ion Implantation

The rates of solid-phase epitaxy (SPE) in unstrained ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ alloys have been measured by time-resolved reflectivity for eight different alloy compositions, including both Si-rich and Ge-rich layers. Amorphous layers 300--400 nm thick were first formed in 8-\ensuremath{\mu}m-thick, relaxed, epitaxial ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ layers (0.02\ensuremath{\le}x\ensuremath{\le}0.87) by ion implantation of ${\mathrm{Si}}^{+}$. For each composition, the measured SPE rates spanned approximately two orders of magnitude. The alloy SPE rates are shown to be related to the regrowth rates of the two pure elements by a simple equation expressed in terms of the composition parameter x and having no adjustable parameters. The form of this equation implies that crystallization occurs by a serial attachment process at the amorphous-crystal interface and that the rate of attachment of each individual atom is determined by the identities of its four nearest neighbors. Such a process is consistent with the dangling-bond model proposed by Spaepen and Turnbull [in Laser-Solid Interactions and Laser Processing, edited by S. D. Ferris, H. J. Leamy, and J. M. Poate, AIP Conf. Proc. No. 50 (AIP, New York, 1979)] if the SPE rate is limited by the migration rate of dangling bonds rather than by their formation rate. Based on this analysis, an interpretation is proposed for the anomalously large activation energies that have been measured for SPE in some Si-rich compositions.

T. E. Haynes

Papers

Photoinduced phase transition in VO2 nanocrystals: ultrafast control of surface-plasmon resonance.

Optical nonlinearities in VO2 nanoparticles and thin films

Interstitial defects in silicon from 1–5 keV Si+ ion implantation

Synthesis of Nearly Monodisperse Embedded Nanoparticles by Separating Nucleation and Growth in Ion Implantation

Composition dependence of solid-phase epitaxy in silicon-germanium alloys: Experiment and theory.