Interfacial electron transfer (ET) between semiconductor nanomaterials and molecular adsorbates is an important fundamental process that is relevant to applications of these materials. Using femtosecond midinfrared spectroscopy, we have simultaneously measured the dynamics of injected electrons and adsorbates by directly monitoring the mid-IR absorption of electrons in the semiconductor and the change in adsorbate vibrational spectrum, respectively. We report on a series of studies designed to understand how the interfacial ET dynamics depends on the properties of the adsorbates, semiconductors, and their interaction. In Ru(dcbpy)2(SCN)2 (dcbpy = 2,2‘-bipyridine-4,4‘-dicarboxylate) sensitized TiO2 thin films, 400 nm excitation of the molecule promotes an electron to the metal-to-ligand charge transfer (MLCT) excited state, from which it is injected into TiO2. The injection process was characterized by a fast component, with a time constant of <100 fs, and a slower component that is sensitive to sample condition. Similar ultrafast electron injection times were measured in TiO2 films sensitized by Ru(dcbpy)2(X)2 (X2 = 2CN- and dcbpy). Electron injection in these systems was found to compete with the vibrational energy relaxation process within the excited state of the molecules, leading to an injection yield that depends on the excited-state redox potential of the adsorbate. The injection rate from Ru(dcbpy)2(SCN)2 to different semiconductors was found to obey the trend TiO2 > SnO2 > ZnO, indicating a strong dependence on the nature of the semiconductor. To understand these observations, various factors, such as electronic coupling, density of states, and driving force, that control the interfacial ET rate were examined separately. The effect of electronic coupling on the ET rate was studied in TiO2 sensitized by three adsorbates, Re(L n )(CO)3Cl [L n is a modified dcbpy ligand with n (=0, 1, 3) CH2 units between the bipyridine and carboxylate groups]. We found that the ET rate decreased with increasing number of CH2 units (or decreasing electronic coupling strength). The effect of driving force was investigated in Ru(dcbpy)2X2 (X2 = 2SCN-, 2CN-, and dcbpy) sensitized SnO2 thin films. In this case, we observed that the ET rate increased with the excited-state redox potential of the adsorbates, agreeing qualitatively with the theoretical prediction for a nonadiabatic interfacial ET process.

No abstract

To explore the potential for use of ligand-conjugated nanocrystals to target cell surface receptors, ion channels, and transporters, we explored the ability of serotonin-labeled CdSe nanocrystals (SNACs) to interact with antidepressant-sensitive, human and Drosophila serotonin transporters (hSERT, dSERT) expressed in HeLa and HEK-293 cells. Unlike unconjugated nanocrystals, SNACs were found to dose-dependently inhibit transport of radiolabeled serotonin by hSERT and dSERT, with an estimated half-maximal activity (EC(50)) of 33 (dSERT) and 99 microM (hSERT). When serotonin was conjugated to the nanocrystal through a linker arm (LSNACs), the EC(50) for hSERT was determined to be 115 microM. Electrophysiology measurements indicated that LSNACs did not elicit currents from the serotonin-3 (5HT(3)) receptor but did produce currents when exposed to the transporter, which are similar to those elicited by antagonists. Moreover, fluorescent LSNACs were found to label SERT-transfected cells but did not label either nontransfected cells or transfected cells coincubated with the high-affinity SERT antagonist paroxetine. These findings support further consideration of ligand-conjugated nanocrystals as versatile probes of membrane proteins in living cells.

Spoken language understanding system is traditionally designed as a pipeline of a number of components. First, the audio signal is processed by an automatic speech recognizer for transcription or n-best hypotheses. With the recognition results, a natural language understanding system classifies the text to structured data as domain, intent and slots for downstreaming consumers, such as dialog system, hands-free applications. These components are usually developed and optimized independently. In this paper, we present our study on an end-to-end learning system for spoken language understanding. With this unified approach, we can infer the semantic meaning directly from audio features without the intermediate text representation. This study showed that the trained model can achieve reasonable good result and demonstrated that the model can capture the semantic attention directly from the audio features.Index Terms-Spoken language understanding, end-toend training, recurrent neural networks

The core of a nuclear reactor presents exceptionally stringent requirements for structuralmaterialsduetoitshightemperatureandintenseradiationaswellasitsneed for unfailing mechanical integrity [1][2][3][4] . Thus, candidate materials for nuclear applications must possess excellent irradiation tolerance, high strength, and thermal stability.However,thesepropertiesaredifficulttorealizesimultaneouslyinonematerialbecause of apparently intrinsic tradeoffs between them. Here we report a novel interface engineering strategy that simultaneously achieves superior irradiation tolerance, high strength, and high thermal stability in bulk nanolayered (NL) Cu-Nb composites. By synthesizing bulk NL Cu-Nb composites containing interfaces with controlled sink efficiencies, we design a material in which nearly all irradiation-induced defects are

A review is presented of the fabrication, operation, and applications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs emit light due to impact excitation of the rare earth (RE) ions by hot carriers followed by radiative RE relaxation. By appropriately choosing the RE dopant, narrow linewidth emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out by solid-source molecular beam epitaxy, and a plasma N 2 source. Growth mechanisms and optimization of the GaN layers for RE emission are discussed based on RE concentration, growth temperature, and V/III ratio. The fabrication processes and electrical models for both dc-and ac-biased devices are discussed, along with techniques for multicolor integration. Visible emission at red, green, and blue wavelengths from GaN doped with Eu, Er, and Tm has led to the development of flat-panel display (FPD) devices. The brightness characteristics of thick dielectric EL (TDEL) display devices are reviewed as a function of bias, frequency, and time. High contrast TDEL devices using a black dielectric are presented. The fabrication and operation of FPD prototypes are described. Infrared emission at 1.5 m from GaN:Er ELDs has been applied to optical telecommunications devices. The fabrication of GaN channel waveguides by inductively coupled plasma etching is also reviewed, along with waveguide optical characterization. Index Terms-Channel waveguides, electroluminescent devices, flat-panel displays, gallium nitride, molecular beam epitaxy, optical telecommunications, rare earths. GaN thin-film growth by CVD and MBE, focused ion beam fabrication of photonic components and circuits, rare-earth-doped luminescent devices for flat-panel displays, and communications. He has authored over 290 published articles and over 300 conference and seminar presentations.766

Femtosecond infrared spectroscopy was used to study the excited-state dynamics of Re(CO)3Cl(dcbpy) in DMF solution and on the surface of ZrO2 and TiO2 nanocrystalline thin films. For Re(CO)3Cl(dcbpy) in DMF solution, we observed a long-lived 3MLCT state with a lifetime of >1 ns. The frequencies for the CO stretching bands were blue-shifted compared to those in the ground state, consistent with the metal-to-ligand charge-transfer nature of the excited state. Rapid spectral evolution of the excited-state CO stretching bands was observed within the first 12 ps. For Re(CO)3Cl(dcbpy) on ZrO2 thin films, a similar 3MLCT state was observed. However, the spectral blue shift was much less pronounced and occurred on a faster time scale. We suggest that vibrational relaxation is the primary contribution to the spectral evolution of Re(CO)3Cl(dcbpy) on the ZrO2 film, whereas both vibrational relaxation and solvation of the MLCT state contribute to the spectral evolution in DMF solution. The excited-state decay rate of Re(CO)3Cl(dcbpy) on ZrO2 films was faster than the rate in DMF and increased with higher excitation power. The faster excited-state decay is attributed to the occurrence of an excited-state quenching process between neighboring excited molecules on the film. For Re(CO)3Cl(dcbpy)-sensitized TiO2 thin films, broad mid-IR absorption of injected electrons was observed. The rise time of the electron absorption signal in TiO2 was found to be less than 100 fs. In addition, the adsorbate CO stretching bands were also observed. We discuss the detailed information about the electron-injection process that can be obtained from the adsorbate vibrational spectra.

With the use of neutron reflectometry, we have determined the thickness and chemistry of the solid-electrolyte interphase (SEI) layer grown on a silicon anode as a function of state of charge and during cycling. We show the chemistry of this SEI layer becomes more LiF like with increasing lithiation and more Li−C−O−F like with delithiation. More importantly, the SEI layer thickness appears to increase (about 250 Å) as the electrode becomes less lithiated and thins to 180 Å with increasing Li content (Li 3.7 Si). We attribute this "breathing" to the continual consumption of electrolyte with cycling.