S.R. Johnson

Polyelectrolyte and molecular host ion self-assembly to multilayer thin films: An approach to thin film chemical sensors

Multilayer molecular films of polyelectrolyte/calixarene and polyelectrolyte/cyclodextrin hosts were fabricated by alternating adsorption of charged species in aqueous solutions onto a substrate (quartz or silicon wafer). This layer-by-layer molecular deposition approach has been successfully used to integrate molecular recognition reagents into polymer films as chemically selective layers for surface acoustic wave (SAW) chemical sensing applications. The resulting sensors have high sensitivity and selectivity to the organic vapors studied. The films were characterized with SEM, infrared and UV-vis spectroscopy, and monitored by SAW devices. These measurements revealed that the deposition process is highly reproducible and the resulting films are uniform and stable.

Control of selected physical properties of MX solids: an experimental and theoretical investigation

Received 17 January 1995; accepted in final form 2 May 1995 Abstract A series of eight materials of stoichiometry [Pt(L-L)2X2][Pt(L-L)2]Y 4 (X is Cl, Br; L-L is 1,2-diaminoethane (en) or 1,2- diaminocyclohexane (chxn); Y is CIO4, X-) were synthesized. Crystal structures were determined for the compounds [Pt(chxn)zC12][Pt(chxn)2](C104) 4 1, [Pt(chxn)2Brz][Pt(chxn)2](CIO4)4 2, and [Pt(chxn)zBrz][Pt(chxn)z]Br 4 4. All three of these compounds crystallize in the orthorhombic space group I222. Compound 1 has a = 5.711(1) ,~, b = 7.804(1) A, c = 24.101(7) A,, Z = 1, dx = 2.033 g cm 3. Compound 2 has a = 5.781(1) A, b = 7.720(1) ,~, c = 24.036(5) ,~, Z = 1, d× = 2.174 g cm -3. Compound 4 has a = 5.379(1) ,~, b = 7.028(1) A, c = 23.884(4) ,~, Z = 1, dx = 2.440 g cm 3. These solids contain pseudo one-dimensional chains with a charge-density-wave (CDW) ground state structure: X-Pt(IV)- X...Pt(II)...X. Single crystal resonance Raman experiments were performed on all compounds to measure the sym- metric X Pt X stretching frequency u~ and the band edge. It is shown that the optical and electronic properties and, therefore, the CDW strength of these one-dimensional materials may be systematically varied over a wide range by employing different combinations of L-L and Y; templates composed of hydrogen bonded networks of L-L and Y were found to control the metal-metal separation, thereby controlling the X-Pt(IV)-X...Pt(II)...X chain geometry. Rela- tionships between the CDW strength, measured as the ratio of the short M(IV) X distance to the long M(II) X distance, the band gap energy ul and the Pt-Pt separation are developed. The reaction coordinate is found to be dominated by changes in the M-M and Pt(II)-X separations over most of the range studied, with contributions from changes in the ptlV-x bonds becoming important only at the smallest M-M separations. Direct evidence demonstrating that MX systems are true Peierls distorted systems is also presented. These results are consistent with modeling based on Peierls- Hubbard hamiltonians. This work explains the unusual pressure and temperature dependences that have been observed for the structures and optical properties of this class of materials and also provides a wealth of information to benchmark many-body theoretical calculations modeling electron electron and electron-phonon interactions in one-dimensional materials. 1. Introduction There has been recent interest in halogen bridged * Corresponding authors.

Molecular host siloxane thin films for surface acoustic wave chemical sensors

Cyclodextrin siloxane coatings on surface acoustic wave (SAW) devices have been studied as sensors for volatile organic compounds (VOCs). The in-situ formation of cyclodextrin siloxane multilayer thin films efficiently yield uniform coatings on SAW devices. The incorporation of molecular host reagents (cyclodextins and their derivatives) into thin films greatly enhance the sensitivity and selectivity of SAW sensors. The identification of VOCs based on SAW sensor arrays is discussed.

Pressure tuning of the charge-density wave in the halogen-bridged transition-metal solid Pt2Br6(NH3)4.

We report the pressure dependence up to 95 kbar of Raman-active stretching modes in the quasi-one-dimensional MX chain solid

Coulomb driven chain ordering phase transitions in the quasi-1-D electronic material d8-PtI/en/ClO4

{\mathrm{Pt}}_{2}

Neutron diffraction study of [Pt(en)2][Pt(en)2I2](ClO4)4 at 20 K: structure and evidence of a new phase transition

{\mathrm{Br}}_{6}

Time-resolved photoinduced absorption and raman scattering in the MX chain solid PtCl

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A structural study of charge-density-wave perturbations in mixed-halide MX solids

{\mathrm{NH}}_{3}