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We report the interface structures of CdO thin films on 001 -MgO and 0001 -Al 2 O 3 substrates. Using aberration corrected scanning transmission electron microscopy, we show that epitaxial growth of (001)-CdO ∥ (001)-MgO occurs with a lattice misfit greater than 10%. A high density of interface misfit dislocations is found to form. In combination with molecular dynamics simulations, we show that dislocation strain fields form and overlap in very thin heterostructures of CdO and MgO (< 3 nm). On the c-Al 2 O 3 substrate, we find that CdO grows with a surface normal of 025. We show that three rotation variants form due to the symmetry of the sapphire surface. These results contribute insights into the epitaxial growth of these rock-salt oxides. [ABSTRACT FROM AUTHOR]

We demonstrate the use of anomalous x-ray scattering of constituent cations at their absorption edge, in a conventional Bragg-Brentano diffractometer, to measure absolutely and quantitatively the polar orientation and polarity fraction of unipolar and mixed polar wurtzitic crystals. In one set of experiments, the gradual transition between c+ and c- polarity of epitaxial ZnO films on sapphire as a function of MgO buffer layer thickness is monitored quantitatively, while in a second experiment, we map the polarity of a lateral polar homojunction in GaN. The dispersion measurements are compared with piezoforce microscopy images, and we demonstrate how x-ray dispersion and scanning probe methods can provide complementary information that can discriminate between polarity fractions at a material surface and polarity fractions averaged over the film bulk. [ABSTRACT FROM AUTHOR]

Chemical solution deposition is used to grow biaxially textured NiFe2O4 (NFO) thin films on (0001) sapphire substrates; a high degree of out-of-plane orientation in the <111> direction is confirmed by θ-2θ X-ray diffraction and pole figures. X-ray φ-scanning indicates in-plane texture and an epitaxial relationship between NFO (111) and Al2O3 (0001) in two crystallographic variants. The out-of-plane magnetization exhibits improved Mr/Ms from 0.5 in 110 nm-thick films to 0.8 in 60 nm-thick films. Compared to uniaxially textured NFO films on platinized silicon, the out-of-plane coercivity is reduced by 20%. The improved out-of-plane magnetic anisotropy is comparable to epitaxial NFO films of similar thickness deposited by pulsed laser deposition and sputtering. [ABSTRACT FROM AUTHOR]

Polycrystalline NiFe2O4 (NFO) thin films are grown on (111) platinized Si substrates via chemical solution processing. θ-2θ x-ray diffraction, x-ray pole figures and electron diffraction indicate that the NFO has a high degree of <111> uniaxial texture normal to the film plane. The texturing is initiated by nucleation of (111) planes at the Pt interface and is enhanced with decreasing film thickness. As the NFO magnetic easy-axis is <111>, the out-of-plane magnetization exhibits improved Mr/Ms and coercivity with respect to randomly oriented films on silicon substrates. The out-of-plane Mr/Ms ratio for (111) textured NFO thin film is improved from 30% in 150 nm-thick films to above 70% in 50 nm-thick films. The improved out-of-plane magnetic anisotropy is comparable to epitaxial NFO films of comparable thickness deposited by pulsed laser deposition and sputtering. [ABSTRACT FROM AUTHOR]

The field of infrared surface plasmon resonance (IR-SPR) spectroscopy has the potential to enable unique applications and technologies in chemical sensing, heat harvesting, and infrared detectors. Finding an ideal material that can support a surface plasmon in the IR region has been a challenge for more than a decade. High carrier mobility, μ ＞ 200 cm2 V−1 s−1, and tunable carrier concentration in the range 1019 ＜ n ＜ 1021 cm−3 are two necessary criteria for a spectrally narrow tunable plasmon resonance band in the IR. The ideal material would also be easy to prepare and robust in water and under ambient conditions. In this review, we highlight the development of the field over the last decade. We also provide a guide to explain the extension of visible plasmonics to the infrared region and the evolution of IR-SPR using conducting metal oxides (CMOs). CMOs are free electron conductors and most of them have no interfering electronic or vibrational transitions in the range of interest. Therefore, these materials also provide an excellent test of the fundamental physics of SPR, including the effects of surface fields, enhancement phenomena and the relationship between thin film epsilon near zero (ENZ) mode and the localized surface plasmon resonance (LSPR) in nanocrystals. In summary, we discuss the materials challenges and prospects for this field of research. [ABSTRACT FROM AUTHOR]

A two-step homoepitaxial growth process producing step-free surfaces on low dislocation density, Ga-polar ammonothermal GaN single crystals is described. Growth is conducted under very low supersaturation conditions where adatom incorporation occurs predominantly at step edges, and lateral growth is strongly preferred. The achievable step-free area is limited by the substrate dislocation density. For ammonothermal crystals with an average dislocation density of ∼1 × 104 cm−2, step-free mesas up to 200 × 200 μm2 in size are achieved. These remarkable surfaces create a unique opportunity to study the effect of steps on the properties and performance of semiconductor heterostructures. [ABSTRACT FROM AUTHOR]

Donor dopedCdO thin films on c-plane sapphire are prepared by reactive co-sputtering from Cd-metal and Y-metal targets which are driven using pulsed-dc and RF power respectively. Intrinsic CdO exhibits a carrier density of 1.8 × 1019 cm-3 and a mobility of 330 cm² V-1 s-1. By increasing the Y-flux, carrier density values can be increased smoothly and reproducibly to a maximum value of 3.3 × 1020 cm-3. Mobility increases with Y flux, and exhibits a broad plateau between approximately 5 × 1019 cm-3 and 2 × 1020 cm-3. Higher carrier concentrations produce a sharp drop in mobility. The increase in mobility is attributed to a reduction of intrinsic donors (i.e., oxygen vacancies) with increasing carrier density while the ultimate decrease in mobility results from a combination of factors including cadmium vacancies, reduced crystal quality, and smaller crystallite sizes, all of which accompany carrier density values greater than the mid 1020 cm-3 range. This work demonstrates that CdO thin films can be prepared by magnetron sputtering with transport properties and crystal quality that are comparable to those grown using molecular beam epitaxy. [ABSTRACT FROM AUTHOR]

Ultrafast control of the polarization state of light may enable a plethora of applications in optics, chemistry and biology. However, conventional polarizing elements, such as polarizers and waveplates, are either static or possess only gigahertz switching speeds. Here, with the aid of high-mobility indium-doped cadmium oxide (CdO) as the gateway plasmonic material, we realize a high-quality factor Berreman-type perfect absorber at a wavelength of 2.08 μm. On sub-bandgap optical pumping, the perfect absorption resonance strongly redshifts because of the transient increase of the ensemble-averaged effective electron mass of CdO, which leads to an absolute change in the p-polarized reflectance from 1.0 to 86.3%. By combining the exceedingly high modulation depth with the polarization selectivity of the perfect absorber, we experimentally demonstrate a reflective polarizer with a polarization extinction ratio of 91 that can be switched on and off within 800 fs. [ABSTRACT FROM AUTHOR]

Selective area growth of thin films reduces the number of steps in microfabrication processing and enables novel device structures. Here, we report, for the first time, selective area epitaxy of an oxide material on a GaN surface. Chlorination of the GaN surface via wet chemical processing is found effective to disrupt Mg adsorption and selectively prevent molecular beam epitaxy growth of MgO. MgO films grown on neighboring, nonchlorinated surfaces are epitaxial with a (111) MgO||(0001) GaN crystallographic relationship. Better than 3 μm lateral resolution for the selective area growth of MgO on GaN is demonstrated. [ABSTRACT FROM PUBLISHER]

Understanding the impact and complex interaction of thermal carrier scattering centers in functional oxide systems is critical to their progress and application. In this work, we study the interplay among electron and phonon thermal transport, mass-impurity scattering, and phononvacancy interactions on the thermal conductivity of cadmium oxide. We use time domain thermoreflectance to measure the thermal conductivity of a set of CdO thin films doped with Dy up to the saturation limit. Using measurements at room temperature and 80 K, our results suggest that the enhancement in thermal conductivity at low Dy concentrations is dominated by an increase in the electron mobility due to a decrease in oxygen vacancy concentration. Furthermore, we find that at intermediate doping concentrations, the subsequent decrease in thermal conductivity can be ascribed to a large reduction in phononic thermal transport due to both point defect and cationvacancy scattering. With these results, we gain insight into the complex dynamics driving phonon scattering and resulting thermal transport in functional oxides. [ABSTRACT FROM AUTHOR]

The interest in plasmonic technologies surrounds many emergent optoelectronic applications, such as plasmon lasers, transistors, sensors and information storage. Although plasmonic materials for ultraviolet-visible and near-infrared wavelengths have been found, the mid-infrared range remains a challenge to address: few known systems can achieve subwavelength optical confinement with low loss in this range. With a combination of experiments and ab initio modelling, here we demonstrate an extreme peak of electron mobility in Dy-doped CdO that is achieved through accurate 'defect equilibrium engineering'. In so doing, we create a tunable plasmon host that satisfies the criteria for mid-infrared spectrum plasmonics, and overcomes the losses seen in conventional plasmonic materials. In particular, extrinsic doping pins the CdO Fermi level above the conduction band minimum and it increases the formation energy of native oxygen vacancies, thus reducing their populations by several orders of magnitude. The substitutional lattice strain induced by Dy doping is sufficiently small, allowing mobility values around 500 cm2 V−1 s−1 for carrier densities above 1020 cm−3. Our work shows that CdO:Dy is a model system for intrinsic and extrinsic manipulation of defects affecting electrical, optical and thermal properties, that oxide conductors are ideal candidates for plasmonic devices and that the defect engineering approach for property optimization is generally applicable to other conducting metal oxides. [ABSTRACT FROM AUTHOR]

Controllable Ge doping in GaN is demonstrated for carrier concentrations of up to 2.4 × 1020 cm-3. Low temperature luminescence spectra from the highly doped samples reveal band gap renormalization and band filling (Burstein-Moss shift) in addition to a sharp transition. Infrared ellipsometry spectra demonstrate the existence of electron plasma with an energy around 3500 cm-1 and a surface plasma with an energy around 2000 cm-1. These findings open possibilities for the application of highly doped GaN for plasmonic devices. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) in semiconducting materials at mid-infrared (mid-IR) energies offers the potential for new plasmonic functionalities and integration schemes. Mainstream semiconductors are transparent to mid-IR energies, thus a tightly integrated monolithic package for SPR sensing becomes feasible. We report mid-IR surface plasmon resonance in zinc oxide as a model material for semiconductors with 4 × 1019 to 8 × 1019 cm-3 carriers. The surface plasmon modes were characterized using spectroscopic IR-ellipsometry and compared to a reflectivity simulation. The data confirm the feasibility of mid-IR SPR, show a generic ability for plasmon tuning, and demonstrate the predictive power of the reflectivity model. [ABSTRACT FROM AUTHOR]