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Self assembled monolayers (SAMs) of n-alkanethiols of different chain length (4, 6, 8, 12, and 18 carbons in the chain) have been explored as corrosion inhibitors for copper exposed to humidified air containing formic acid, an environment used to mimic accelerated indoor atmospheric corrosion. Near-surface sensitive in-situ infrared reflection/absorption spectroscopy combined with interface sensitive vibrational sum frequency spectroscopy revealed unique molecular information on the role of each SAM during ongoing corrosion. All SAMs protect copper against corrosion, and this ability increases continuously with chain length. Their structural order is high prior to exposure, but an increased disorder is observed as a result of the corrosion process. The protection ability of the SAMs is attributed to a selective hindrance of the corrosion stimulators water, oxygen gas, and formic acid to reach the copper-SAM interface through each SAM, which results in different corrosion mechanisms on SAM protected copper and unprotected copper. This significantly retards the formation of the corrosion products copper hydroxide and copper formate, and results in essentially no formation of cuprite.

The influcence of the pulse duration on the emission characteristics of nearly debris-free laser-induced plasmas in the soft x-ray region (λ ≈1-5 nm) was investigated, using six different target gases from a pulsed jet. Compared to ns pulses of the same energy, a ps laser generates a smaller, more strongly ionized plasma, being about 10 times brighter than the ns laser plasma. Moreover, the spectra are considerably shifted towards shorter wavelengths. Electron temperatures and densities of the plasma are obtained by comparing the spectra with model calculations using a magneto-hydrodynamic code.

Laser-induced breakdown spectroscopy (LIBS) technology is an appealing technique compared with many other types of elemental analysis because of the fast response, high sensitivity, real-time, and noncontact features. One of the challenging targets of LIBS is the enhancement of the detection limit. In this study, the detection limit of gas-phase LIBS analysis has been improved by controlling the pressure and laser pulse width. In order to verify this method, low-pressure gas plasma was induced using nanosecond and picosecond lasers. The method was applied to the detection of Hg. The emission intensity ratio of the Hg atom to NO (I_Hg/ I_NO) was analyzed to evaluate the LIBS detection limit because the NO emission (interference signal) was formed during the plasma generation and cooling process of N₂ and O₂ in the air. It was demonstrated that the enhancement of I_Hg/I_NO arose by decreasing the pressure to a few kilopascals, and the I_Hg/I_NO of the picosecond breakdown was always much higher than that of the nanosecond breakdown at low buffer gas pressure. Enhancement of I_Hg/I_NO increased more than 10 times at 700 Pa using picosecond laser with 35 ps pulse width. The detection limit was enhanced to 0.03 ppm (parts per million). We also saw that the spectra from the center and edge parts of plasma showed different features. Comparing the central spectra with the edge spectra, I_Hg/I_NO of the edge spectra was higher than that of the central spectra using the picosecond laser breakdown process.

Luminescence upconversion nanocrystals capable of converting two low-energy photons into a single photon at a higher energy are sought-after for a variety of applications, including bioimaging and photovoltaic light harvesting. Currently available systems, based on rare-earth-doped dielectrics, are limited in both tunability and absorption cross-section. Here we present colloidal double quantum dots as an alternative nanocrystalline upconversion system, combining the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. By tailoring its composition and morphology, we form a semiconducting nanostructure in which excited electrons are delocalized over the entire structure, but a double potential well is formed for holes. Upconversion occurs by excitation of an electron in the lower energy transition, followed by intraband absorption of the hole, allowing it to cross the barrier to a higher energy state. An overall conversion efficiency of 0.1% per double excitation event is achieved.

Nanosecond timescale underwater electrical wire explosions of ring-shaped Cu wires were investigated using a pulsed generator with a current amplitude up to 50 kA. It was shown that this type of wire explosion results in the generation of a toroidal shock wave (SW). Time- and space-resolved optical diagnostics were used to determine azimuthal uniformity of the shock wave front and its velocity. It was found that the shock wave preserves its circular front shape in the range of radii 50 μm<r<5 mm. At r≤15μm, azimuthal irregularities of the SW front were obtained indicating the appearance of azimuthal instability. A surprising finding is that the shock wave propagates with a constant velocity of vsw=1.2M, where M is the Mach number. The dynamics of the leading part of the shock wave, based on the oblique shock wave theory, is presented, explaining the constant velocity of the shock wave.

The lack of understanding of the temporal effects and the restricted ability to control experimental conditions in order to obtain intrinsic spectral lineshapes in surface sum-frequency generation vibrational spectroscopy (SFG-VS) have limited its applications in surface and interfacial studies. The emergence of high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) with sub-wavenumber resolution [Velarde et al., J. Chem. Phys., 2011, 135, 241102] offers new opportunities for obtaining and understanding the spectral lineshapes and temporal effects in SFG-VS. Particularly, the high accuracy of the HR-BB-SFG-VS experimental lineshape provides detailed information on the complex coherent vibrational dynamics through direct spectral measurements. Here we present a unified formalism for the theoretical and experimental routes for obtaining an accurate lineshape of the SFG response. Then, we present a detailed analysis of a cholesterol monolayer at the air/water interface with higher and lower resolution SFG spectra along with their temporal response. With higher spectral resolution and accurate vibrational spectral lineshapes, it is shown that the parameters of the experimental SFG spectra can be used both to understand and to quantitatively reproduce the temporal effects in lower resolution SFG measurements. This perspective provides not only a unified picture but also a novel experimental approach to measuring and understanding the frequency-domain and time-domain SFG response of a complex molecular interface.

Dye-sensitized solar cells are a promising alternative to traditional inorganic semiconductor-based solar cells. Here we report an open-circuit voltage of over 1,000 mV in mesoscopic dye-sensitized solar cells incorporating a molecularly engineered cobalt complex as redox mediator. Cobalt complexes have negligible absorption in the visible region of the solar spectrum, and their redox properties can be tuned in a controlled fashion by selecting suitable donor/acceptor substituents on the ligand. This approach offers an attractive alternate to the traditional I₃⁻/I⁻ redox shuttle used in dye-sensitized solar cells. A cobalt complex using tridendate ligands [Co(bpy-pz)₂]^3+/2+(PF₆)_3/2 as redox mediator in combination with a cyclopentadithiophene-bridged donor-acceptor dye (Y123), adsorbed on TiO₂, yielded a power conversion efficiency of over 10% at 100 mW cm⁻². This result indicates that the molecularly engineered cobalt redox shuttle is a legitimate alternative to the commonly used I₃⁻/I⁻ redox shuttle.

We present a visible-infrared sum-frequency spectroscopic technique that is capable of simultaneously determining the magnitude and phase of the sample response from a single set of experimental conditions. This is especially valuable in cases where the phase stability is high, as in collinear beam geometries, as it enables multiple experiments to be performed without re-measuring the local oscillator phase or the reference phase. After illustrating the phase stability achievable with such a geometry, we provide a technique for quantitatively determining the magnitude and phase from a single set of two-dimensional spectral-temporal interference fringes. A complete demonstration is provided for the C–H stretching frequency region at the surface of an octadecyltricholosilane film.

The Pan-STARRS1 survey is collecting multi-epoch, multi-color observations of the sky north of declination −30° to unprecedented depths. These data are being photometrically and astrometrically calibrated and will serve as a reference for many other purposes. In this paper, we present our determination of the Pan-STARRS1 photometric system: g_P1, r_P1, i_P1, z_P1, y_P1, and w_P1. The Pan-STARRS1 photometric system is fundamentally based on the Hubble Space Telescope Calspec spectrophotometric observations, which in turn are fundamentally based on models of white dwarf atmospheres. We define the Pan-STARRS1 magnitude system and describe in detail our measurement of the system passbands, including both the instrumental sensitivity and atmospheric transmission functions. By-products, including transformations to other photometric systems, Galactic extinction, and stellar locus, are also provided. We close with a discussion of remaining systematic errors.