Sensitivity of Second Harmonic Generation to Space Charge Effects at Si(111)/Electrolyte and Si(111)/SiO\u3csub\u3e2\u3c/sub\u3e/Electrolyte Interfaces

The potential dependence in the surface second harmonic response from hydrogen terminated n‐Si(111) and oxidized n‐Si(111) surfaces has been examined in aqueous NH4F and H2SO4 solutions. The relative phase of the nonlinear response as measured by rotational anisotropy experiments is found to be highly sensitive to the presence of the oxide and the field applied across the Si(111)/oxide/electrolyte interface. These observations are attributed to field effects within the space–charge region of the semiconductor which vary with the presence and thickness of the insulating oxide layer on the Si(111) surface

Phenomena of g-u symmetry-breakdown in HD

Phenomena associated with the breakdown of inversion symmetry in the HD molecule are reviewed and discussed. A distinction is made between three kinds of physical effects observed in HD spectra. The existence of a small electric dipole moment in the ground state gives rise to vibrational and pure rotational transitions following selection rules of electric dipole transitions. Coupling between electronic states of g and u symmetry occurs, which is associated with the appearance of forbidden lines in the electronic spectrum. This effect occurs predominantly at near coincidences between levels of opposite inversion symmetry and a recently observed example of strongly interacting states (H̄ ′

Climate change, the Great Barrier Reef and the response of Australians

© 2016, Palgrave Macmillan Ltd. All rights reserved. Inspiration, aspirations, attitudes, and perception of threats play a pivotal role in the way that individuals associate themselves with natural environments. These sentiments affect how people connect to natural places, including their behaviours, perceived responsibility, and the management interventions they support. World Heritage Areas hold an important place in the lives of people who visit, aspire to visit, or derive a sense of security and well-being from their existence. Yet, the connection between people and special places is rarely quantified and policymakers find it difficult to incorporate these human dimensions into decision-making processes. Here we describe the personal concern and connection that Australians have with the Great Barrier Reef and discuss how the results may help with its management. We utilize a statistically representative sample of Australian residents (n = 2,002) and show empirically that climate change is perceived to be the biggest threat to the Great Barrier Reef, and that the Great Barrier Reef inspires Australians, promotes pride, and instills a sense of individual identity and collective responsibility to protect it. An increased understanding of the high levels of personal connection to iconic natural resources may help managers to enhance public support for protecting climate-sensitive systems within Australia and around the world

Mapping Molecular Orientation with Phase Sensitive Vibrationally Resonant Sum-Frequency Generation Microscopy

We demonstrate a phase sensitive, vibrationally resonant sum-frequency generation (PSVR-SFG) microscope that combines high resolution, fast image acquisition speed, chemical selectivity, and phase sensitivity. Using the PSVR-SFG microscope, we generate amplitude and phase images of the second-order susceptibility of collagen I fibers in rat tail tendon tissue on resonance with the methylene vibrations of the protein. We find that the phase of the second-order susceptibility shows dependence on the effective polarity of the fibril bundles, revealing fibrous collagen domains of opposite orientations within the tissue. The presence of collagen microdomains in tendon tissue may have implications for the interpretation of the mechanical properties of the tissue. [Image: see text

Probing the Intermolecular Hydrogen Bonding of Water Molecules at the CCl\u3csub\u3e4\u3c/sub\u3e/Water Interface in the Presence of Charges Soluble Surfactant

The molecular structure and hydrogen bonding of water molecules at the CCl4/water interface in the presence of a charged soluble surfactant has been explored in this study using vibrational sum frequency generation. By examining OH stretching modes that are highly sensitive to the local hydrogen bonding environment it is found that water molecules at the CCl4/water interface both in the presence and absence of a charged soluble surfactant are predominantly in a tetrahedral arrangement much like the structure ofice. Isotopic dilution studies have been employed to further characterize this icelike interfacial structure. Ablueshift ofapproximately120 cm-1 of the icelike OH stretching mode is observed upon dilution with D2O. The first vibrational spectra of the OH stretching mode from uncoupled HOD molecules at the CCl4/water interface is also reported

Tunable Picosecond Infrared Laser System Based on Parametric Amplification in KTP with a Ti:Sapphire Amplifier

A picosecond laser system that will generate high-power tunable IR pulses with bandwidths suitable for spectroscopic applications is discussed. The system is based on white-light continuum generation in ethylene glycol and optical parametric amplification in potassium titanyl phosphate. The nonlinear-optical processes are driven by a regeneratively amplified Ti:sapphire laser that produces 1.7-ps pulses at a repetition rate of 1 kHz. Energies as high as 40 and 12 µJ have been achieved over the signal (1.02–1.16-µm) and idler (2.6–3.7-µm) tuning ranges, respectively. The IR beam temporal and spatial characteristics are also presented

Induced Changes in Solvent Structure by Phospholipid Monolayer Formation at a Liquid–Liquid Interface

Vibrational sum frequency spectroscopy has been used in conjunction with dynamic surface tension measurements to study formation of a 1,2-dilauroyl-sn-phosphatidylcholine (DLPC) monolayer at a water–carbon tetrachloride interface. Surface tension measurements show that an aqueous solution of liquid crystalline phosphocholine vesicles (4.5 μM DLPC) requires several hours to form a tightly packed, fully equilibrated monolayer of DLPC monomers. Vibrational spectra of the interfacial region at different stages in the monolayer formation process indicate that the solvent structure undergoes dramatic re-organization as the monolayer forms. Initial adsorption of DLPC monomers severely disrupts the interfacial hydrogen bonding. Intensity in the OH stretching region oscillates in a systematic fashion during the first 2 h of monolayer formation before finally settling to a level characteristic of the fully equilibrated monolayer. Frequency shifts of the OH stretching vibration show that water molecules with their C2 axes aligned parallel to the interface experience a markedly different environment than those water molecules aligned perpendicular to the interface. This difference is attributed to the effect of the adsorbed, zwitterionic DLPC head-groups which, if aligned parallel to the interface, can stabilize in-plane water molecules

High-Power Broadly Tunable Picosecond IR Laser System for Use in Nonlinear Spectroscopic Applications

We developed a high-power tunable picosecond IR laser system suitable for nonlinear spectroscopic investigations. We employ a Ti:sapphire regenerative amplifier that produces 1.9-ps, 17-cm−1, 800-nm pulses at 1 kHz as a pump source. White-light generation in ethylene glycol and optical parametric amplification in potassium titanyl phosphate are used to produce the IR pulses. The tuning range extends from 2.4 to 3.8 μm in the idler and 1.0 to 1.2 μm in the signal. A total efficiency (signal plus idler) as high as 20% was achieved. The spatial, spectral, and temporal characteristics of the IR beam are presented along with vibrational sum-frequency spectra from a glass/octadecyltrichlorosilane/air interface