Surface‐enhanced Raman spectroscopy (SERS) is a powerful analytical technique commonly used in the detection of traces of organic molecules. The mechanism of SERS is of a dual nature, with Raman scattering enhancements due to a combination of electromagnetic (EM) and chemical contributions. In conventional SERS, the EM component is largely responsible for the enhancement, with the chemical contribution playing a less significant role. An alternative technique, called photo‐induced enhanced Raman spectroscopy (PIERS) has been recently developed, using a photo‐activated semiconductor substrate to give additional chemical enhancement of Raman bands over traditional SERS. This enhancement is assigned to surface oxygen vacancies (V
o) formed upon pre‐irradiation of the substrate. In this work, the exceptional chemical contribution in PIERS allows for the evaluation of atomic V
o dynamics in metal oxide surfaces. This technique is applied to study the formation and healing rates of surface‐active V
o in archetypical metal‐oxide semiconductors, namely, TiO2, WO3, and ZnO. Contrary to conventional analytical tools, PIERS provides intuitive and valuable information about surface stability of atomic defects at ambient pressure and under operando conditions, which has important implications in a wide range of applications including catalysis and energy storage materials.
In honour of Professor John Brown's 65 th birthday festschrift __________________________________________ Using tunable vacuum-UV radiation from a synchrotron, the threshold photoelectron spectrum, threshold photoelectron photoion coincidence spectrum and ion breakdown diagram of the 1,1, cis-1,2 and trans-1,2 isomers of C 2 H 2 Cl 2 have been recorded in the range 9−23 eV. The energies of the peaks in the threshold photoelectron spectrum are in good agreement with outer-valence Greens function caculations. The major difference between the isomers, both predicted and observed experimentally is that the F and G states of
We demonstrate that temperature gradients can be investigated in evaporating volatile water/alcohol droplets by characterising the volume averaged temperature by laser induced fluorescence and the near-surface temperature by cavity enhanced Raman scattering. In the former technique, the fluorescence spectrum from Rhodamine B can be used to determine the droplet temperature with an accuracy of +/-1 K. The latter technique uses the band width of the OH stretching Raman band to determine the temperature change within the near-surface volume in which whispering gallery modes propagate with an accuracy of +/-4 K. We demonstrate that the temperatures measured with varying evaporation time, buffer gas pressure, droplet size and composition are consistent with the predictions from a quasi-steady theoretical treatment of the evaporation rate and can be used to investigate temperature gradients within evaporating droplets.
Shortwave infrared barriode detectors were grown by molecular beam epitaxy. An absorption layer composition of In 0.28 Ga 0.72 As 0.25 Sb 0.75 allowed for lattice matching to GaSb and cutoff wavelengths of 2.9 lm at 250 K and 3.0 lm at room temperature. Arrhenius plots of the dark current density showed diffusion limited dark currents approaching those expected for optimized HgCdTe-based detectors. Specific detectivity figures of around 7 Â 10 10 Jones and 1 Â 10 10 Jones were calculated, for 240 K and room temperature, respectively. Significantly, these devices could support focal plane arrays working at higher operating temperatures. V
We report the first, to the best of our knowledge, femtosecond-laser-pumped optical parametric oscillator (OPO) based on the newly developed nonlinear crystal, CdSiP₂. The OPO was synchronously pumped by a mode-locked Yb:KYW/Yb:fiber master-oscillator power amplifier, providing 1.053 μm pump pulses with durations of 130 fs at a repetition rate of 100 MHz. The 0.5-mm-thick CdSiP₂ crystal was cut for a type-I noncritical interaction, providing a broad phase-matching bandwidth and ensuring excellent temporal overlap among the pump, signal, and idler pulses. The OPO generated signal pulses with a spectral coverage over 1260-1310 nm and mid-infrared idler pulses with a broad spectral coverage at 5.8-6.6 μm (6.2 THz). With a 2% output coupler (OC), the threshold pump power was 600 mW. At the maximum pump power of 1.6 W, 0.55 W was absorbed due to two-photon absorption and residual linear absorption in the CdSiP₂ crystal, 0.75 W was transmitted, and 53 mW signal power was extracted through the OC. We estimate that the generated idler power was 24 mW.
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