J. Bohandy

Metal deposition from a supported metal film using an excimer laser

A method for the direct writing of metal features from a metal film supported on an optically transparent substrate using a single pulse from a high‐energy excimer laser (193 nm) is presented. The technique eliminates the need for gas‐phase precursors in many cases and is an inherently clean process. Results of copper depositions onto silicon substrates are shown to exemplify the technique and a mechanism for the process is proposed.

Metal deposition at 532 nm using a laser transfer technique

The laser‐induced forward transfer technique in which material is ablatively transferred from a thin film to a target substrate by a pulsed excimer laser has been extended to 532 nm using a frequency‐doubled YAG laser. Cu and Ag have been deposited on fused silica substrates using microscope objectives for focusing, resulting in reductions in feature size over that obtainable with the multimode excimer laser. The photothermal deposition process has been modeled using the one‐dimensional thermal diffusion equation, including a moving solid‐melt boundary, with good agreement between theoretical and experimental results.

A novel microwave technique for detection of superconductivity

A new technique for detection of superconductivity which is based upon microwave resistivity is described. This method is similar in both its implementation and execution to the technique of electron‐spin resonance, and, as a consequence, exhibits high sensitivity. An additional benefit of this method is the fact that metal‐insulator phase transitions of materials are recorded only if they have a magnetic field dependence.

Site selective optical spectra of free base porphin in anthracene

Abstract The low temperature optical spectra of free base porphin in crystalline anthracene have been observed in the visible region of the spectrum. Quasilines and broad components were observed in the region of the forbidden Q bands. Site selection techniques were used to separate the spectra of inequivalent site species, and vibronic frequencies were assigned in the ground state and excited Q states. The relative strengths of the broad and quasiline components of the spectra in the Q x and Q y states indicated that the host lattice may affect the relative transition strengths of Q x and Q y . These results indicated that the strength of the transition to Q x is greater than that of Q y for a free porphin molecule.

ESR investigation of the photoisomerization of OClO to ClOO in an H2SO4 glass: Magnetophotoselection and kinetics

The photoisomerization of OClO (ClO2) to ClOO in a sulfuric acid glass at 20 to 77 K has been reinvestigated using electron spin resonance (ESR) to observe the reactant and product and to quantitatively determine their relative concentrations. Polarized light photolysis yields a partial orientation of the remaining ClO2 molecules (magnetophotoselection) and shows that the optical transition dipole moment lies in the molecular plane and is perpendicular to the ClO2 rotational symmetry axis, as expected for the well known A(2A2)←X(2B1) transition of ClO2. Here, however, the photolysis yields only ClOO, in contrast to the gas phase where ClO is observed suggesting photodissociation. The photoisomerization kinetics are nonexponential and suggest that random variations among the ClO2 trapping sites in the H2SO4 glass have a considerable effect on the probability that a photoexcited ClO2 molecule will isomerize.

Temperature dependence of Mg porphin, Cu porphin, and Pd porphin luminescence

Fluorescence spectra of MgP in triphenylene and phosphorescence spectra of CuP and PdP in triphenylene have been obtained from room temperature down to 10u2009°K. Analysis of the temperature dependence of the MgP spectra shows that the coupling between the Mg porphin guest and the triphenylene host is weak. A temperature‐dependent splitting of the 0–0 phosphorescence band of PdP, previously observed in nonane, was also observed in triphenylene but our attempt to verify a suggested explanation was inconclusive. For CuP in triphenylene, a TD–TQ separation of 267 cm−1 has been measured.

Detection of weak link superconductivity by magnetically modulated electrical resistance

Abstract A new technique, based on observing the effect of magnetic field modulation on the DC resistance of superconductors, sensitively detects the presence of weak links in granular high temperature superconductors. The phase detected response to the magnetic modulation shows a peak at T c for both metallic and ceramic superconductors, analogous to that observed in magnetically modulated microwave absorption. A second peak, attributed to weak links, is observed below T c in the ceramic oxide superconductors when tailing is present in the resistance vs. temperature curve.

On distinguishing intrinsic and weak-link responses in magnetically-modulated dissipation in high Tc superconductors

It is noted that, contrary to a recent report, magnetic-field modulation of electromagnetic dissipation in superconductors yields both an intrinsic response indicative of the superconducting transition and extrinsic responses indicative of weak links. Ways of distinguishing between these difference responses are also noted.

Conventional and dye laser optical spectra of zinc porphin in anthracene

Abstract Conventional polarized optical absorption spectra and fluorescence spectra of single crystal and polycrystalline samples of zinc porphin in anthracene have been obtained at 4.2 K. Narrow band excitation of fluorescence using a tunable dye laser was used for site selection to eliminate ambiguities due to impurities and multiple sites. The spectra are compared to those of zinc porphin in a different aromatic host (triphenylene) and in n-octane. Some of the vibronic energies are assigned to calculated vibrations of a similar metalloporphin, copper porphin.

Single site spectra of Zn porphin in triphenylene

Abstract Single site spectra of Zn porphin in triphenylene have been recorded at low temperature. There were three principal site species, each of which had slightly different fluorescence and absorption spectra. Because the spectra of each site were separately recorded, the confusion which resulted from the spectra of multiple site species in previous studies was eliminated. Vibrational assignments in the ground and excited electronic states were made, and relative intensities of the spectral lines recorded. The general pattern of intensity of the spectra was in qualitative agreement with the theory of vibronic borrowing in the cyclic polyene model.