Double tungstate lasers: From bulk toward on-chip integrated waveguide devices

It has been recognized that the monoclinic double tungstates $KY{(WO_4)}_2$, $KGd{(WO_4)}_2$, and $KLu{(WO_4)}_2$ possess a high potential as rare-earth-ion-doped solid-state laser materials, partly due to the high absorption and emission cross sections of rare-earth ions when doped into these materials. Besides, their high refractive indexes make these materials potentially suitable for applications that require optical gain and high power in integrated optics, with rather high integration density. We review the recent advances in the field of bulk lasers in these materials and present our work toward the demonstration of waveguide lasers and their integration with other optical structures on a chip

Aerosol Jet Printing of 3D Pillar Arrays from Photopolymer Ink

An aerosol jet printing (AJP) printing head built on top of precise motion systems can provide positioning deviation down to 3 μm, printing areas as large as 20 cm × 20 cm × 30 cm, and five-axis freedom of movement. Typical uses of AJP are 2D printing on complex or flexible substrates, primarily for applications in printed electronics. Nearly all commercially available AJP inks for 2D printing are designed and optimized to reach desired electronic properties. In this work, we explore AJP for the 3D printing of free-standing pillar arrays. We utilize aryl epoxy photopolymer as ink coupled with a cross-linking “on the fly” technique. Pillar structures 550 μm in height and with a diameter of 50 μm were 3D printed. Pillar structures were characterized via scanning electron microscopy, where the morphology, number of printed layers and side effects of the AJP technique were investigated. Satellite droplets and over-spray seem to be unavoidable for structures smaller than 70 μm. Nevertheless, reactive ion etching (RIE) as a post-processing step can mitigate AJP side effects. AJP-RIE together with photopolymer-based ink can be promising for the 3D printing of microstructures, offering fast and maskless manufacturing without wet chemistry development and heat treatment post-processing

Molecular beam epitaxy of InN dots on nitrided sapphire

A series of self-assembled InN dots are grown by radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE) directly on nitrided sapphire. Initial nitridation of the sapphire substrates at 900 C results in the formation of a rough AlN surface layer, which acts as a very thin buffer layer and facilitates the nucleation of the InN dots according to the Stranski-Krastanow growth mode, with a wetting layer of {approx}0.9 nm. Atomic force microscopy (AFM) reveals that well-confined InN nanoislands with the greatest height/width at half-height ratio of 0.64 can be grown at 460 C. Lower substrate temperatures result in a reduced aspect ratio due to a lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN truncates the growth at T>500 C. The densities of separated dots vary between 1.0 x 10{sup 10} cm{sup -2} and 2.5 x 10{sup 10} cm{sup -2} depending on the growth time. Optical response of the InN dots under laser excitation is studied with apertureless near-field scanning optical microscopy and photoluminescence spectroscopy, although no photoluminescence is observed from these samples. In view of the desirable implementation of InN nanostructures into photonic devices, the results indicate that nitrided sapphire is a suitable substrate for growing self-assembled InN nanodots

Imaging of InGaN inhomogeneities using visible apertureless near-field scanning optical microscope

Received ( The optical properties of epitaxially grown islands of InGaN are investigated with nanometer-scale spatial resolution using visible apertureless near-field scanning optical microscopy. Scattered light from the tip-sample system is modulated by cantilever oscillations and detected at the third harmonic of the oscillation frequency to distinguish the near-field signal from unwanted scattered background light. Scattered near-field measurements indicate that the as-grown InGaN islanded film may exhibit both inhomogeneous In composition and strain-induced changes that affect the optical signal at 633 nm and 532 nm. Changes are observed in the optical contrast for large 3D InGaN islands (100's of nm) of the same height. Near-field optical mapping of small grains on a finer scale reveals InGaN composition or strain-induced irregularities in features with heights of only 2 nm, which exhibit different near-field signals at 633 nm and 532 nm incident wavelengths. Optical signal contrast from topographic features as small as 30 nm is detected

UV-protection of wood surfaces by controlled morphology fine-tuning of ZnO nanostructures

One of the most significant limitations for a wider utilisation of the renewable and CO2-storing resource wood is its low ultraviolet (UV) light stability. The protection of the wood surface without altering its aesthetic appeal requires an optically transparent but UV protective coating which should be strongly attached to the rough and inhomogeneous substrate. For this purpose, ZnO nanostructures were deposited onto the wood surface via a chemical bath deposition process. The morphology of crystalline ZnO was controlled by aluminium nitrate or ammonium citrate in the growth step resulting in nanorod arrays or platelet structures, respectively. Detailed structural, chemical and mechanical characterisations as well as accelerated weathering exposure revealed the effective performance of the platelet structure, which formed a dense and thin ZnO coating on spruce. The total colour change (ΔE in the CIE system) was calculated to be 20.5 for unmodified wood, while it was about three for the modified samples after 4 weeks accelerated weathering test. Moreover, the ZnO coating also suppressed crack initiation and propagation indicating a substantial increase in durability

Fabrication, Characterization and Simulation of Sputtered Pt/In-Ga-Zn-O Schottky Diodes for Low-Frequency Half-Wave Rectifier Circuits

Amorphous In-Ga-Zn-O (IGZO) is a high-mobility semiconductor employed in modern thin-film transistors for displays and it is considered as a promising material for Schottky diode-based rectifiers. Properties of the electronic components based on IGZO strongly depend on the manufacturing parameters such as the oxygen partial pressure during IGZO sputtering and post-deposition thermal annealing. In this study, we investigate the combined effect of sputtering conditions of amorphous IGZO (In:Ga:Zn=1:1:1) and post-deposition thermal annealing on the properties of vertical thin-film Pt-IGZO-Cu Schottky diodes, and evaluated the applicability of the fabricated Schottky diodes for low-frequency half-wave rectifier circuits. The change of the oxygen content in the gas mixture from 1.64% to 6.25%, and post-deposition annealing is shown to increase the current rectification ratio from 10 5 to 10 7 at ±1 V, Schottky barrier height from 0.64 eV to 0.75 eV, and the ideality factor from 1.11 to 1.39. Half-wave rectifier circuits based on the fabricated Schottky diodes were simulated using parameters extracted from measured current-voltage and capacitance-voltage characteristics. The half-wave rectifier circuits were realized at 100 kHz and 300 kHz on as-fabricated Schottky diodes with active area of 200 μm × 200 μm, which is relevant for the near-field communication (125 kHz - 134 kHz), and provided the output voltage amplitude of 0.87 V for 2 V supply voltage. The simulation results matched with the measurement data, verifying the model accuracy for circuit level simulation

Optical waveguides in laser crystals

This article reviews the recent research on different types of planar and channel crystalline optical waveguides, fabrication methods such as liquid phase epitaxy, pulsed laser deposition, thermal bonding, reactive ion or ion beam etching, wet chemical etching, ion in-diffusion, proton exchange, ion beam implantation, and femtosecond laser writing, as well as waveguide laser operation of rare-earth and transition-metal ions in oxide crystalline materials such as $Al_{2}O_{3}$, $Y_{3}Al_{5}O_{12}$, $YAlO_{3}$, $KY(WO_{4})_{2}$, and $LiNbO_{3}$

Deep-UV-Enhanced Approach for Low-Temperature Solution Processing of IZO Transistors with High-k AlOx/YAlOx Dielectric

Solution processing is an attractive alternative to standard vacuum fabrication techniques for the large-area manufacturing of metal oxide (MOx)-based electron devices. Here, we report on thin-film transistors (TFTs) based on a solution-processed indium zinc oxide (IZO) semiconductor utilizing a deep-ultraviolet (DUV)-enhanced curing, which enables a reduction of the annealing temperature to 200 degrees C. The effects of the DUV light exposure and the subsequent post-annealing parameters on the chemical composition of the IZO films have been investigated using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The semiconductor layer has been combined with an high-lc aluminum oxide/yttrium aluminum oxide (AlOx/YAlOx) dielectric stack to realize fully solution-processed MOx TFTs at low temperature. The IZO/AlOx/YAlOx TFTs treated for 20 min DUV followed by 60 min at 200 degrees C exhibited I-on/I-off of >10(8), a subthreshold slope (SS) of 10(8), a SS <100 mV dec(-1), and mu(sat) of 2.83 +/- 1.4 cm(2 )V(-1) s(-1). The TFTs possess high operational stability under gate bias stress, exhibiting low shifts in the threshold voltage of <1 V after 1000 s. The DUV-enhanced approach reduces the thermal budget required for the curing of solution-processed IZO semiconductors films, paving the way for its further implementation on temperature-sensitive substrates in future