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We report experimental and theoretical analysis of the plasmonic resonances of Al nanoparticles and nanorods. Ordered nanoparticle arrays with well-defined shapes and narrow size distributions are fabricated on quartz substrates over large areas using extreme ultraviolet interference lithography. The structures, which have sizes down to 40 nm, exhibit strong and sharp particle plasmon resonances in the near and deep-UV ranges. A comprehensive theoretical analysis carried out using dipolar approximation and finite-difference time-domain methods shows good overall agreement with measurements while revealing the dependence of the optical response of Al structures on the fabrication conditions. The results demonstrate the suitability of using Al as a plasmonic material in the UV range and the feasibility of extending applications of plasmonics, such as surface-enhanced Raman spectroscopy, down to the deep-UV range. [ABSTRACT FROM AUTHOR]

The mass spectra in the range of 2(D+)–38(D19+) amu of clusters formed in a supersonic free-jet expansion of normal D2 are investigated as functions of source temperature in the range of 95–220 K and of source pressure in the range of 10–120 bars. For some of the small ion fragments, time-of-flight distributions are also measured. For large clusters (n>200) the intensities of the odd-numbered ion fragments exhibit magic numbers at D9+ and D15+ in accordance with previous experiments and calculations. The even-numbered ion fragments have much smaller intensities and exhibit new magic numbers at D10+ and D14+. For source conditions such that large clusters are formed, the intensities of the various different ion fragments are observed to saturate beyond a certain source pressure. At lower source pressures, where only small clusters are formed, the terminal mole fractions of the neutral dimers are analyzed in the light of available theories which take into account both the thermodynamics and the kinetics of the expansion. At higher source pressures and lower temperatures, where larger clusters are formed, the sizes of the neutral clusters are estimated using scaling laws and are found to be consistent with the mass spectra and measured time-of-flight distributions. By using a variety of techniques it has been possible to obtain reliable conclusions about the neutral cluster sizes for the present free-jet expansion conditions. [ABSTRACT FROM AUTHOR]

The mass spectra in the range of 2(D+)–38(D19+) amu of clusters formed in a supersonic free-jet expansion of normal D2 are investigated as functions of source temperature in the range of 95–220 K and of source pressure in the range of 10–120 bars. For some of the small ion fragments, time-of-flight distributions are also measured. For large clusters (n>200) the intensities of the odd-numbered ion fragments exhibit magic numbers at D9+ and D15+ in accordance with previous experiments and calculations. The even-numbered ion fragments have much smaller intensities and exhibit new magic numbers at D10+ and D14+. For source conditions such that large clusters are formed, the intensities of the various different ion fragments are observed to saturate beyond a certain source pressure. At lower source pressures, where only small clusters are formed, the terminal mole fractions of the neutral dimers are analyzed in the light of available theories which take into account both the thermodynamics and the kinetics of the expansion. At higher source pressures and lower temperatures, where larger clusters are formed, the sizes of the neutral clusters are estimated using scaling laws and are found to be consistent with the mass spectra and measured time-of-flight distributions. By using a variety of techniques it has been possible to obtain reliable conclusions about the neutral cluster sizes for the present free-jet expansion conditions. [ABSTRACT FROM AUTHOR]

Microstructure and origin of the orange photoluminescence (PL) band of visible luminescing spark-processed germanium (sp-Ge) has been studied using simultaneous micro-Raman and -PL spectroscopy and scanning electron microscope. Instability of the sp-Ge film to energetic electron beams (>=5 keV) during SEM measurements suggested that sp-Ge is not composed exclusively of purely Ge–Ge bonded material (elemental Ge) but also of other form(s) of material(s) of different chemistry. Indeed, micro-Raman spectra of the films showed that sp-Ge is composed of mainly substoichiometric germanium oxides (GeO[sub x]s) and elemental Ge (in the form of nano- or micro-crystals). Further, it is proposed that the Ge particles were embedded in thick GeO[sub x] (0

Seminal field ionization detection of a supersonic helium beam is reported, including intensity measurements on a continuous beam and time-of-flight measurements on a chopped beam. Also unique to these experiments is the care with which the field ionization tip was prepared and characterized prior to its use. Comparative measurements on a static helium gas are presented and the effective detection area of the field ionization tip is extracted for both beam and static gas. These areas are much smaller than those reported in previous experiments, suggesting that detection efficiency depends strongly on energy and momentum transfer during the initial atom–tip collision. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report a high-throughput method for the fabrication of metallic nanogap arrays with high-accuracy over large areas. This method, based on shadow evaporation and interference lithography, achieves sub-10 nm gap sizes with a high accuracy of ±1.5 nm. Controlled fabrication is demonstrated over mm2 areas and for periods of 250 nm. Experiments complemented with numerical simulations indicate that the formation of nanogaps is a robust, self-limiting process that can be applied to wafer-scale substrates. Surface-enhanced Raman scattering (SERS) experiments illustrate the potential for plasmonic sensing with an exceptionally low standard-deviation of the SERS signal below 3% and average enhancement factors exceeding 1 × 106. [ABSTRACT FROM AUTHOR]

High probabilities of energy transfer from translation to molecular rotations are observed in the scattering of n-D(2) from LiF(001) at an incident beam energy of 85.3 meV. For the 100 incidence direction, close-coupling calculations yield ratios of the rotationally inelastic (j=0-->2) and (j=1-->3) peaks to the rotationally elastic specular peaks (G=0) that are in reasonable agreement with experiment, as are the ratios of the rotationally elastic diffraction peak intensities to the specular peak intensities. The agreement between theory and experiment is also quite good for the rotationally inelastic diffractive (-1-1) transitions for (j=1-->3), but rather poor for (j=0-->2). The calculations show that the interaction between the electrostatic field of the surface ions and the quadrupole moment of the D(2) molecule efficiently promotes the (j=0-->2) and (j=1-->3) transitions. If this electrostatic interaction is excluded from the potential model, the ratios of the (j=0-->2) and (j=1-->3) rotationally inelastic peaks to the corresponding specular peaks show a large discrepancy with experiment, underlining the importance of this interaction. The close-coupling calculations show a somewhat worse agreement with experiment for the 110 incidence direction. In particular, the sharp peaks observed experimentally in the ratios of the peak intensities of the rotationally inelastic G=0 (j=0-->2) and (j=1-->3) to the rotationally elastic G=0 transitions as a function of incident angle are not reproduced by the calculations. The theoretical ratios of the peak intensities of the rotationally elastic diffraction to G=0 transitions are shifted to lower incidence angles with respect to experiment. The rotationally inelastic diffractive (-10) transitions present an interesting resonance phenomenon for the (j=0-->2) rotational transition. This resonance is predicted by both theory and experiment, although at rather different incident angles.