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Adsorbate-induced broadband infrared reflectance changes on metal surfaces.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Adsorbate-induced broadband infrared reflectance changes on metal surfaces./
Author:	Lin, Keng-Ching.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 1996,
Description:	145 p.
Notes:	Source: Dissertations Abstracts International, Volume: 58-03, Section: B.
Contained By:	Dissertations Abstracts International58-03B.
Subject:	Condensation. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9631307
ISBN:	9798691251726

Adsorbate-induced broadband infrared reflectance changes on metal surfaces.
Lin, Keng-Ching.

Adsorbate-induced broadband infrared reflectance changes on metal surfaces. - Ann Arbor : ProQuest Dissertations & Theses, 1996 - 145 p.

Source: Dissertations Abstracts International, Volume: 58-03, Section: B.

Thesis (Ph.D.)--Michigan State University, 1996.

This item must not be sold to any third party vendors.

This research focuses on the broadband infrared reflectance changes of metal surfaces upon adsorption of foreign species. The 1-2% observed adsorbate-induced reflectance decrease is much larger than the 0.001% reflectance increase expected from the polarizability of the adsorbate itself. Therefore, this reflectance drop must result from changes in the dielectric properties of the substrate. This effect has received little attention since the signal is difficult to measure reliably, and most surface IR spectroscopy studies emphasize the vibrational modes of the adsorbate, which give rise to relative narrow absorption bands. By distinguishing the physical origin of these broadband changes, we can characterize the modification of electronic transport in the substrate by the adsorbate. This knowledge is important in understanding the fundamental physics of a wide range of technological subjects, such as mechanisms of chemical sensing and transport in thin films. I have done a series of experiments to investigate the broadband reflectance changes for different adsorption systems using two reflection-absorption infrared spectroscopy (RAIRS) systems, a synchrotron-based system at Brookhaven National Laboratory and a novel cryogenic spectrometer at Michigan State University. The experimental results provide a test of a proposed model of conduction-electron scattering from disordered adsorbates that incorporates nonlocal electrodynamics for the interactions of probing electric fields with conduction electrons. A direct relation between surface resistivity changes and reflectance changes is derived and discussed by comparing the measured reflectance changes and published resistivity changes on thin metallic films for CO on Cu, O on Cu, and CO on Ni. The results are consistent for CO and O on Cu. A discrepancy found for CO on Ni stimulates further discussion of the theory and experimental tests. For O on Cu(100) the reflectance change at different coverages were measured as a function of infrared frequency and fitted with a theoretical function. At coverages below 0.25 ML, the reflectance changes are well fitted by a universal form with a characteristic rolloff frequency that determines the transition between local and nonlocal optics. The coverage-dependence of the reflectance change is different from theoretical predictions. Possible explanations are investigated with reference to the adsorption systems of O on Cu(100), CO on Pt(111) and formate on oxygen-predosed Cu(100).

ISBN: 9798691251726Subjects--Topical Terms:

942542
Condensation.
Subjects--Index Terms:

thin films

Adsorbate-induced broadband infrared reflectance changes on metal surfaces.
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100 1 $a Lin, Keng-Ching. $3 3692571
245 1 0 $a Adsorbate-induced broadband infrared reflectance changes on metal surfaces.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 1996
300 $a 145 p.
500 $a Source: Dissertations Abstracts International, Volume: 58-03, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Advisor: Tobin, Roger G.
502 $a Thesis (Ph.D.)--Michigan State University, 1996.
506 $a This item must not be sold to any third party vendors.
506 $a This item must not be added to any third party search indexes.
520 $a This research focuses on the broadband infrared reflectance changes of metal surfaces upon adsorption of foreign species. The 1-2% observed adsorbate-induced reflectance decrease is much larger than the 0.001% reflectance increase expected from the polarizability of the adsorbate itself. Therefore, this reflectance drop must result from changes in the dielectric properties of the substrate. This effect has received little attention since the signal is difficult to measure reliably, and most surface IR spectroscopy studies emphasize the vibrational modes of the adsorbate, which give rise to relative narrow absorption bands. By distinguishing the physical origin of these broadband changes, we can characterize the modification of electronic transport in the substrate by the adsorbate. This knowledge is important in understanding the fundamental physics of a wide range of technological subjects, such as mechanisms of chemical sensing and transport in thin films. I have done a series of experiments to investigate the broadband reflectance changes for different adsorption systems using two reflection-absorption infrared spectroscopy (RAIRS) systems, a synchrotron-based system at Brookhaven National Laboratory and a novel cryogenic spectrometer at Michigan State University. The experimental results provide a test of a proposed model of conduction-electron scattering from disordered adsorbates that incorporates nonlocal electrodynamics for the interactions of probing electric fields with conduction electrons. A direct relation between surface resistivity changes and reflectance changes is derived and discussed by comparing the measured reflectance changes and published resistivity changes on thin metallic films for CO on Cu, O on Cu, and CO on Ni. The results are consistent for CO and O on Cu. A discrepancy found for CO on Ni stimulates further discussion of the theory and experimental tests. For O on Cu(100) the reflectance change at different coverages were measured as a function of infrared frequency and fitted with a theoretical function. At coverages below 0.25 ML, the reflectance changes are well fitted by a universal form with a characteristic rolloff frequency that determines the transition between local and nonlocal optics. The coverage-dependence of the reflectance change is different from theoretical predictions. Possible explanations are investigated with reference to the adsorption systems of O on Cu(100), CO on Pt(111) and formate on oxygen-predosed Cu(100).
590 $a School code: 0128.
650 4 $a Condensation. $3 942542
650 4 $a Molecules. $3 592642
650 4 $a Chemistry. $3 516420
650 4 $a Molecular physics. $3 3174737
650 4 $a Condensed matter physics. $3 3173567
650 4 $a Physical chemistry. $3 1981412
653 $a thin films
690 $a 0611
690 $a 0609
690 $a 0494
690 $a 0485
710 2 $a Michigan State University. $3 676168
773 0 $t Dissertations Abstracts International $g 58-03B.
790 $a 0128
791 $a Ph.D.
792 $a 1996
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9631307