Title

Metallic and semiconductor nanoparticulate films generated under monolayers and between Langmuir-Blodgett films

Date of Award

1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Janos H. Fendler

Keywords

semiconductor particles

Subject Categories

Analytical Chemistry

Abstract

Preparation and characterization of ultrasmall metallic silver (Ag), gold (Au), and semiconductor cadmium sulfide (CdS), zinc sulfide (ZnS), lead sulfide (PbS), cadmium selenide (CdSe), zinc selenide (ZnSe), lead selenide (PbSe), and mixed semiconductor particles and particulate films under monolayers and between Langmuir-Blodgett (LB) films are the subject of this dissertation. Monolayers and LB films were prepared from bis(2-n-hexadecanoyloxy ethyl) methyl-(vinylbenzyl)ammonium chloride (1), (N,N$\sp\prime$-2-aminoethyl)-2-hexadecyl-1,3-propanediamide (2), N,N$\sp\prime$-dioctadecyl-N,N$\sp\prime$-di(2$\sp\prime$-thioacetoxyethyl) ammonium bromide (3), octadecanoyl mercaptan (4), arachidic acid (5), dihexadecyl phosphate (6), dioctadecyldimethylammonium bromide (7), n-hexadecyl 11-(4-vinylbenzamido) undecyl hydrogen phosphate (8) and gramicidin (9).

CdS, ZnS, PbS, CdSe, ZnSe, and PbSe, semiconductor particles and particulate films were in situ generated by infusing $\rm{H\sb{2}S}$ or $\rm{H\sb{2}Se}$ into aqueous solutions of the appropriate semiconductor forming precursors which had been coated by monolayers prepared from 2, 3, 4, 5, and 7. The effects of monolayer structures, compositions, concentrations, pH of precursors on rates and structures of semiconductors formed have been investigated. The effect of electric fields on the formation of CdS particulate films under monolayers had also been examined. In general, longer exposure times to the gases and higher concentrations of ions in the subphase lead to the more rapid formation of larger semiconductor particles and particulate films. The growth of PbS and CdS under monolayers prepared from 5 was arrested by the addition of thiophenol. However, evidence was obtained in all systems for size quantization.

Mixed and composite PbS and ZnS semiconductor particles and particulate films were generated under monolayers prepared from 3. The absorption edge was found to shift to longer wavelengths with the increase of the PbS fraction in ZnS/PbS films, while the absorption edge was found to shift to shorter wavelengths in PbS/ZnS films. In ZnS/PbS and PbS/ZnS films, domain formation was observed. Composite PbS/ZnS semiconductor particulate films were found to be more efficient in mediating photoelectron transfer than either PbS or ZnS. Mixed semiconductor CdS and ZnS particulate films were also in situ generated under monolayers, prepared from 3 and floating on mixed subphase (Cd(ClO$\sb4$)$\sb2$: Zn(ClO$\sb4$)$\sb2$ = 1:1, 3:7 and 1:9 v/v), by the infusion of H$\sb2$S. The solubility products of PbS, ZnS and CdS governed the formation of these mixed semiconductor particles.

Size-quantized PbS, PbSe, CdS and ZnS particles were in situ generated between the surfactant headgroups of LB films formed from 2, 3, and 5. Photoelectron transfer to methylviologen in aqueous solutions mediated by the LB-film-incorporated semiconductor particles was also examined as a function of particle size. Smaller semiconductor particles were shown to mediate photoelectron transfer more efficiently than larger ones.

Nanosized metallic particulate films of silver and gold were in situ generated under monolayers, prepared from 2-9, and between the head groups of LB films, formed from 2 and 6, by chemical reduction (by HCHO and CO), by 308-nm laser pulses, and from the corresponding metal halide crystallites by photolysis.

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