Materials for emergent silicon-integrated optical computing.

Progress in computing architectures is approaching a paradigm shift: traditional computing based on digital complementary metal-oxide semiconductor technology is nearing physical limits in terms of miniaturization, speed, and, especially, power consumption. Consequently, alternative approaches are under investigation. One of the most promising is based on a "brain-like" or scheme.

Anodized Nickel Foam for Oxygen Evolution Reaction in Fe-Free and Unpurified Alkaline Electrolytes at High Current Densities.

To achieve practically high electrocatalytic performance for the oxygen evolution reaction (OER), the active surface area should be maximized without severely compromising electron and mass transport throughout the catalyst electrode. Though the importance of electron and mass transport has been studied using low surface area catalysts under low current densities (∼tens of mA/cm), the transport properties of large surface area catalysts under high operating current densities (∼500 mA/cm) for practical OER catalysis have rarely been explored. Herein, three-dimensional (3D) hierarchically porous anodized nickel foams (ANFs) with large and variable surface areas were synthesized electrochemical anodization of 3D nickel foam and applied as OER electrocatalysts in Fe-free and unpurified KOH electrolytes.

A Vacuum Ultraviolet-Enhanced Oxidation Mechanism for Pd: Near-Surface Oxidation for Atomic Layer Etching.

Density functional theory (DFT) is used to better understand the oxidation of Pd metal using vacuum ultraviolet (VUV) light co-exposed with O, which is known to produce O and O. The oxidation of Pd metal arising from O, O, and O is assessed on bare Pd, Pd with a 0.25 monolayer of adsorbed atomic O, and Pd with increasing O incorporation into the substrate.

Zintl layer formation during perovskite atomic layer deposition on Ge (001).

Using in situ X-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and density functional theory, we analyzed the surface core level shifts and surface structure during the initial growth of ABO perovskites on Ge (001) by atomic layer deposition, where A = Ba, Sr and B = Ti, Hf, Zr. We find that the initial dosing of the barium- or strontium-bis(triisopropylcyclopentadienyl) precursors on a clean Ge surface produces a surface phase that has the same chemical and structural properties as the 0.5-monolayer Ba Zintl layer formed when depositing Ba by molecular beam epitaxy.

Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition.

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods.

A Low-Leakage Epitaxial High-κ Gate Oxide for Germanium Metal-Oxide-Semiconductor Devices.

Germanium (Ge)-based metal-oxide-semiconductor field-effect transistors are a promising candidate for high performance, low power electronics at the 7 nm technology node and beyond. However, the availability of high quality gate oxide/Ge interfaces that provide low leakage current density and equivalent oxide thickness (EOT), robust scalability, and acceptable interface state density (D(it)) has emerged as one of the most challenging hurdles in the development of such devices. Here we demonstrate and present detailed electrical characterization of a high-κ epitaxial oxide gate stack based on crystalline SrHfO3 grown on Ge (001) by atomic layer deposition.

A silicon-based photocathode for water reduction with an epitaxial SrTiO3 protection layer and a nanostructured catalyst.

The rapidly increasing global demand for energy combined with the environmental impact of fossil fuels has spurred the search for alternative sources of clean energy. One promising approach is to convert solar energy into hydrogen fuel using photoelectrochemical cells. However, the semiconducting photoelectrodes used in these cells typically have low efficiencies and/or stabilities.

Highly controllable and stable quantized conductance and resistive switching mechanism in single-crystal TiO2 resistive memory on silicon.

TiO2 is being widely explored as an active resistive switching (RS) material for resistive random access memory. We report a detailed analysis of the RS characteristics of single-crystal anatase-TiO2 thin films epitaxially grown on silicon by atomic layer deposition. We demonstrate that although the valence change mechanism is responsible for the observed RS, single-crystal anatase-TiO2 thin films show electrical characteristics that are very different from the usual switching behaviors observed for polycrystalline or amorphous TiO2 and instead very similar to those found in electrochemical metallization memory.

Atomic Interdiffusion and Diffusive Stabilization of Cobalt by Copper During Atomic Layer Deposition from Bis(N-tert-butyl-N'-ethylpropionamidinato) Cobalt(II).

Electromigration of copper in integrated circuits leads to device failure. Potential solutions involve capping the copper with ultrathin cobalt films. We report the properties of cobalt films after deposition on polycrystalline Cu at 265 °C by atomic layer deposition from H2 and bis(N-tert-butyl-N'-ethylpropionamidinato) cobalt(II) (CoAMD).

Titration of free hydroxyl and strained siloxane sites on silicon dioxide with fluorescent probes.

A technique enabling the detection and quantification of low density sites on planar SiO2 surfaces is demonstrated. Fluorescent probes are used to titrate free hydroxyl and strained siloxane sites on the surface of amorphous SiO2 substrates in vacuum. The titration of free hydroxyl sites was performed to validate the method and to provide a reference for the measurement of the strained siloxane site density.

Improvement of solar energy conversion with Nb-incorporated TiO2 hierarchical microspheres.

Niobium-modified TiO2 hierarchical spherical micrometer-size particles, which consist of many nanowires, are synthesized by solvothermal synthesis and studied as photoelectrodes for water photo-oxidation and dye-sensitized solar cell (DSSC) applications. Incorporation of Nb leads to a rutile-to-anatase TiO2 phase transition in the TiO2 hierarchical spheres (HSs), with the anatase percentage increasing from 0% for the pristine TiO2 HSs to 47.6% for the 1.

Pretreatment of yellow pine in an acidic ionic liquid: extraction of hemicellulose and lignin to facilitate enzymatic digestion.

The acidic ionic liquid 1-H-3-methylimidazolium chloride can effectively pretreat yellow pine wood chips under mild conditions for enzymatic saccharification. Wood samples were treated at temperatures between 110 and 150°C for up to 5 h in the ionic liquid and three fractions collected; a cellulose rich fraction, lignin, and an aqueous fraction. This treatment caused the hemicellulose and the lignin to be degraded and dissolved from the cell walls of the pine wood.

Depolymerization of oak wood lignin under mild conditions using the acidic ionic liquid 1-H-3-methylimidazolium chloride as both solvent and catalyst.

Oak wood lignin, which was separated from the wood using dissolution in the ionic liquid 1-methyl-3-ethylimidazolium acetate and subsequent precipitation, was successfully depolymerized in the acidic ionic liquid 1-H-3-methylimidazolium chloride under mild conditions (110-150 °C). Based on gel permeation chromatography results, an increase in temperature from 110 to 150 °C increased the rate of reaction, but did not significantly change the final size of the lignin fragments. Nuclear magnetic resonance and infrared spectroscopy were utilized to demonstrate that the depolymerization proceeded via a hydrolysis reaction that cleaved the alkyl-aryl ether linkages.

Cleaving the β--O--4 bonds of lignin model compounds in an acidic ionic liquid, 1-H-3-methylimidazolium chloride: an optional strategy for the degradation of lignin.

The hydrolysis of β--O--4 bonds in two lignin model compounds was studied in an acidic ionic liquid, 1-H-3-methylimidazolium chloride. The β--O--4 bonds of both guaiacylglycerol-β-guaiacyl ether and veratrylglycerol-β-guaiacyl ether underwent catalytic hydrolysis to produce guaiacol as the primary product with more than 70 % yield at 150 °C. Up to 32 wt % substrate concentration could be treated in the system without a decrease in guaiacol production.

Experimental and theoretical investigation on surfactant segregation in imprint lithography.

The effects of template surface composition on fluorinated surfactant segregation were investigated for imprint lithography with photopolymerizable vinyl ether formulations. Heptadecafluoro-1,1,2,2-tetrahydrodecyl vinyloxy-methyloxy dimethylsilane, containing a vinyl ether group, was employed as the surfactant, and blanket templates were pressed onto the liquid and illuminated with UV radiation from below. The extent of surfactant segregation to the vinyl ether-template interface before polymerization was characterized using contact angle measurements and angle-resolved X-ray photoelectron spectroscopy after removing the template from the cured vinyl ether polymer.

Growth of ultrathin films of amorphous ruthenium-phosphorus alloys using a single source CVD precursor.

Thin films ( approximately 30 nm) of amorphous RuP alloys (P approximately 15-20%) can be grown by CVD from the single source precursor cis-H2Ru(PMe3)4 at 250-300 degrees C and 200 mTorr pressure on native SiO2.

Surface hydration and its effect on fluorinated SAM formation on SiO2 surfaces.

Substrate hydration is demonstrated to be crucial to film quality during self-assembled (SA) film deposition of tridecafluoro-1,1,2,2,-tetrahydrooctyltrichlorosilane (FOTS) from the vapor phase. The surface hydration was studied by thermogravimetric analysis, and a model was developed to predict the conditions necessary to desorb all of the water adsorbed on a fused silica surface without significantly altering the concentration of the surface hydroxyl groups. The nature of the SA film was investigated as a function of the degree of rehydration of the dehydrated silica surface.

Optical second harmonic spectroscopy of boron-reconstructed Si(001).

Optical second harmonic generation (SHG) spectroscopy is used to probe Si(001) following thermal decomposition of diborane at the surface. Incorporation of boron (B) at second layer substitutional sites at H-free Si(001) intensifies and redshifts the E1 SHG spectral peak, while subsequent H termination further intensifies and blueshifts E1, in sharp contrast to the effect of bulk B doping or nonsubstitutional B. Ab initio pseudopotential and semiempirical tight binding calculations independently reproduce these unique trends, and attribute them to the surface electric field associated with charge transfer to electrically active B acceptors, and rehybridization of atomic bonds.

Direct absorption of gas-phase atomic hydrogen by si(100): A narrow temperature window.

Absorption of thermal-energy gaseous hydrogen atoms by Si(100), exceeding by far the dopant and other impurity concentrations, occurs within a narrow substrate temperature (T(s)) window centered at approximately 460 K. The absorbed hydrogen persists in the crystalline bulk as highly mobile species before migrating out and desorbing as molecular hydrogen at T(s) as high as 900 K, well above the recombinative desorption temperatures of surface-adsorbed H. Developing and sustaining atomic-scale surface roughness, by H-induced silicon etching, is a prerequisite for H absorption and determines the T(s) window.