1,721,095 research outputs found
Orientation and chemistry of alkoxides on copper(111)
No full textSurface analytical techniques have been used to study the interaction of straight-chain alcohols with a preoxidized single-crystal Cu(111) surface under ultra-high vacuum conditions. The adsorbed alcohols deprotonate to form stable alkoxides chemisorbed to the surface. These alkoxides decompose at elevated temperatures by -hydride elimination, desorbing as aldehydes. The influence of deuterium isotope labelling, selective fluorination, and chain length on this mechanism has been studied. Temperature Programmed Reaction (TPR) spectra for the reactions of ethoxides and 1-propoxides and their selectively deuterated counterparts reveal both primary kinetic isotope effects and measurable secondary isotope effects.Fourier Transform Infrared Reflection Absorption Spectra (FT-IRAS) have been obtained for ethoxide, selectively fluorinated and deuterated ethoxides, 1-propoxide and selectively deuterated 1-propoxides, at saturation coverages on the Cu(111) surface. Quantitative measurements of the absorption intensities of the absorbed alkoxides and the randomly oriented corresponding alcohols allowed determination of the orientation of the adsorbed ethoxide and trifluoroethoxide. Ethoxide on the Cu(111) surface has the C-C bond tilted 70 2\sp\circ from the surface normal while in trifluoroethoxide the C-C bond is oriented 50 5\sp\circ from the surface normal. In both species the plane of the molecule defined by the C-C-O atoms is tilted towards the surface. This tilt between the plane of the molecule and the plane of the surface normal is 17 2\sp\circ for ethoxide and 20 11\sp\circ for trifluoroethoxide. The FT-IRAS spectra of the 1-propoxides have been compared to the reflection infrared spectra of self-assembled monolayers containing long alkyl chains. The spectra show evidence for both crystalline-like packing and conformational disorder in the adlayer, suggesting the presence of both ordered and disordered domains of the alkoxides on the Cu(111) surface. Finally, the FT-IRAS spectra of propene and a set of fluorinated propenes have been obtained. These physisorbed molecules are shown to lie with their molecular C-C=C planes parallel to the metal surface.Made available in DSpace on 2011-05-07T12:24:05Z (GMT). No. of bitstreams: 2
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Previous issue date: 1995Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:40:34Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:17:25-05:00
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Group with Access UIUC Users [automated]
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Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
Thermal and dynamic processes in deposition, growth, and etching of materials: I. Thermal and collision-induced activation of alkyl intermediates on aluminum. II. Chemical vapor deposition and growth of silicide on copper
No full textChemical vapor deposition (CVD) is becoming an increasingly important manufacturing process for the fabrication of VLSI and ULSI devices. A major challenge in optimizing a CVD process is developing an understanding of the complex mechanistic pathways followed. The first section in this thesis reports studies on the thermal and dynamical activation of surface bound alkyl species which play a vital role in the form of intermediates in metal-organic chemical vapor deposition. The particular systems of interest are those of aluminum CVD precursors. Models of these intermediates are obtained by thermal decomposition of alkyl iodides. The results provide an insight into the complex reaction patterns involved in the thermal reactions and rate-structure sensitivities of the alkyl species in the presence of the coadsorbed halogen atom. Multiple reaction pathways including metal etching processes which bear direct implications to the synthesis of organometallics and metal etching, are identified.It is becoming apparent that chemistry at surfaces, whether it be heterogeneous catalysis, semiconductor etching, or chemical vapor deposition, is controlled by much more than the nature and structure of the surface. Also, nonthermal activation of autocatalytic reactions is often required for the nucleation and growth of thin films in devices so that the stability of the device structure is maintained. Dynamical pathways followed in these high pressure and energy processes have to be well understood. The second part of these studies describe an investigation of collision-induced reaction of alkyl intermediates using supersonic inert gas atomic beams. Selective activation of a thermodynamically favored unimolecular decomposition reaction is initiated by hyperthermal collisions. Quantitative estimations of the reaction cross sections are made using straightforward hard sphere energy transfer dynamics. This successful demonstration of collision-induced activation of large, multiatomic moieties has paved the way for proposed studies (now underway in our group) on actual CVD precursors with known barriers to nucleation and growth.In the second section, the reaction mechanisms and kinetics of competitive dissociation, disproportionation, and thin film growth processes involved in the chemical vapor deposition of metal-silicide thin films are investigated. Metal-silicides are widely used as interconnect and gate materials in devices and also as corrosion resistant materials. Reactivity of silane and disilane with copper is studied in detail using temperature programmed reaction, Auger electron, Fourier transform infrared reflection absorption spectroscopies and low energy electron diffraction. For both the precursors, the structural chemistry and product distributions of adsorbed intermediates found at low temperatures are quite rich but significantly differ at the mechanistic level. It is shown quantitatively that disilane is almost 2-3 orders of magnitude more reactive than silane due to its facile Si-Si bond dissociation. However, in both cases, kinetics of silicon deposition and silicide formation are limited by the site-blocking effect of surface bound hydrogen generated by the decomposition of the silyl fragments. An ordered silicide overlayer is readily formed at higher coverages effected above dihydrogen desorption temperatures. This bimolecular process has to compete with an associative reaction which leads to the formation of silane. The results obtained from the different spectroscopic data show that the growth process involves an intriguing set of coupled reactions in which deposition, island growth, and Si etching effectively compete in a complex manner. Understanding of these parameters and the reaction mechanisms involved, enables the application of this process for the vapor phase growth of silicide thin films.Made available in DSpace on 2011-05-07T13:22:33Z (GMT). No. of bitstreams: 2
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Previous issue date: 1996Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:53:57Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:25:00-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
Thermal and dynamic processes in deposition, growth, and etching of materials: I. Thermal and collision-induced activation of alkyl intermediates on aluminum. II. Chemical vapor deposition and growth of silicide on copper
No full textChemical vapor deposition (CVD) is becoming an increasingly important manufacturing process for the fabrication of VLSI and ULSI devices. A major challenge in optimizing a CVD process is developing an understanding of the complex mechanistic pathways followed. The first section in this thesis reports studies on the thermal and dynamical activation of surface bound alkyl species which play a vital role in the form of intermediates in metal-organic chemical vapor deposition. The particular systems of interest are those of aluminum CVD precursors. Models of these intermediates are obtained by thermal decomposition of alkyl iodides. The results provide an insight into the complex reaction patterns involved in the thermal reactions and rate-structure sensitivities of the alkyl species in the presence of the coadsorbed halogen atom. Multiple reaction pathways including metal etching processes which bear direct implications to the synthesis of organometallics and metal etching, are identified.It is becoming apparent that chemistry at surfaces, whether it be heterogeneous catalysis, semiconductor etching, or chemical vapor deposition, is controlled by much more than the nature and structure of the surface. Also, nonthermal activation of autocatalytic reactions is often required for the nucleation and growth of thin films in devices so that the stability of the device structure is maintained. Dynamical pathways followed in these high pressure and energy processes have to be well understood. The second part of these studies describe an investigation of collision-induced reaction of alkyl intermediates using supersonic inert gas atomic beams. Selective activation of a thermodynamically favored unimolecular decomposition reaction is initiated by hyperthermal collisions. Quantitative estimations of the reaction cross sections are made using straightforward hard sphere energy transfer dynamics. This successful demonstration of collision-induced activation of large, multiatomic moieties has paved the way for proposed studies (now underway in our group) on actual CVD precursors with known barriers to nucleation and growth.In the second section, the reaction mechanisms and kinetics of competitive dissociation, disproportionation, and thin film growth processes involved in the chemical vapor deposition of metal-silicide thin films are investigated. Metal-silicides are widely used as interconnect and gate materials in devices and also as corrosion resistant materials. Reactivity of silane and disilane with copper is studied in detail using temperature programmed reaction, Auger electron, Fourier transform infrared reflection absorption spectroscopies and low energy electron diffraction. For both the precursors, the structural chemistry and product distributions of adsorbed intermediates found at low temperatures are quite rich but significantly differ at the mechanistic level. It is shown quantitatively that disilane is almost 2-3 orders of magnitude more reactive than silane due to its facile Si-Si bond dissociation. However, in both cases, kinetics of silicon deposition and silicide formation are limited by the site-blocking effect of surface bound hydrogen generated by the decomposition of the silyl fragments. An ordered silicide overlayer is readily formed at higher coverages effected above dihydrogen desorption temperatures. This bimolecular process has to compete with an associative reaction which leads to the formation of silane. The results obtained from the different spectroscopic data show that the growth process involves an intriguing set of coupled reactions in which deposition, island growth, and Si etching effectively compete in a complex manner. Understanding of these parameters and the reaction mechanisms involved, enables the application of this process for the vapor phase growth of silicide thin films.U of I OnlyETDs are only available to UIUC Users without author permissio
Transfer printing by kinetic control of adhesion to an elastomeric stamp
No full textAn increasing number of technologies require large-scale integration of disparate classes of separately fabricated objects into spatially organized, functional systems(1-9). Here we introduce an approach for heterogeneous integration based on kinetically controlled switching between adhesion and release of solid objects to and from an elastomeric stamp. We describe the physics of soft adhesion that govern this process and demonstrate the method by printing objects with a wide range of sizes and shapes, made of single-crystal silicon and GaN, mica, highly ordered pyrolytic graphite, silica and pollen, onto a variety of substrates without specially designed surface chemistries or separate adhesive layers. Printed p-n junctions and photodiodes fixed directly on highly curved surfaces illustrate some unique device-level capabilities of this approach.The authors thank A. Shim for helpful discussions, A. Jerez for help generating schematic cartoons,
J. Rinne for supplying silica microspheres, J. Lyding for the use of his AFM, and C. J. Hubert for the use
of her African Violets. This work was supported by DARPA-funded AFRL-managed Macroelectronics
ProgramContract FA8650-04-C-7101, the US Department of Energy under grant
DEFG02-91-ER45439, the National Science Foundation under grant DMII-0328162, and a graduate
fellowship from the Fannie and John Hertz Foundation.
Correspondence and requests for materials should be addressed to J.A.R
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Kinetic and Mechanistic Studies of Chemical Vapor Deposition Processes on Metal Surfaces
No full textRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I OnlyMetal deposition from hexafluoroacetylacetonate complexes is also examined on Cu(111) and Pt(100) surfaces single crystal surfaces. In the case of the Rh(hfac)(C2H4)2 and Pt(hfac)2 on a copper surface, the transfer of the hfac ligands takes place below ∼220 K and this species subsequently either decomposes or reacts with the substrate to form Cu(hfac)2. This latter reaction is promoted by the presence of platinum on the copper surface but not by the presence of rhodium. In the reaction of Pt(hfac)2 on Pt(100), ligand dissociation begins ∼400 K and the resultant CFx surface fragments recombine to form a fluorocarbon species. This pathway is more strongly promoted in the presence of hydrogen as a reducing agent.Made available in DSpace on 2015-09-25T22:14:44Z (GMT). No. of bitstreams: 2
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Previous issue date: 2000Embargo set by: Seth Robbins for item 85759
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Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs169 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2000
Microfluidic Devices for Bioanalytical Applications
No full textPoly(dimethylsiloxane) (PDMS) based microfluidic devices have a wide range of applications in chemistry, biology, environmental science and drug delivery. PDMS devices, fabricated using soft lithography were utilized in fabrication and optimization of biotin-avidin protein bioassay. In order to optimize the performance of protein bioassay, various substrates and protein blocking reagents have been tested. Silicon dioxide substrate with proper thickness provide a great option for build biotin-avidin bioassay on with fluorescence detection. The resist abilities of bovine serum albumin (BSA), methoxy-poly(ethylene glycol)-succinimidyl propionate (PEG), poly(acrylamide-co-N-acryloxysuccinimide) (PAN) and further modified PAN were compared and analyzed on fluorescence images. Except fluorescence, secondary electron microscopy (SEM) has been used to quantify the microcontact printed protein arrays on gold surface. A mechanism for image formation is proposed and protein absorptions on both gold and self assembly monolayer are characterized quantitatively. A physical patterning method based on PDMS called decal transfer lithography is applied to fabricate the open channel patterns for biocompatible soft materials. Agarose gel and alginate gel are both patterned via this method. Atomic force microscope is used to character elastic moduli of both hydrogel surfaces including bulk and pattern surfaces. Three dimensional reconstructions of confocal images of those patterns is shown. Fibroblast cells are cultured on fibronectin immobilized gel surface to study cell attachment and growth.Made available in DSpace on 2015-09-25T22:13:38Z (GMT). No. of bitstreams: 2
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Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only161 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006
Poly(dimethylsiloxane)-Based Microfluidic Electrochemical Devices
No full textIn another application, the devices can be operated as passive microfluidic fuel cells incorporating high surface area/porous metal and metal alloy electrodes that are embedded and fully immersed in liquid electrolyte confined in the channels of a PDMS-based microfluidic network. A hydrogen-air fuel cell of the latter design exhibits exceptional durability and high performance, most notably yielding stable output power (>100 days) without the use of an anode-cathode separator membrane. The stability of the device for long-term operation was modeled using a stack of three fuel cells as a power supply for a portable display that otherwise uses a 3 V battery.Made available in DSpace on 2015-09-25T22:13:34Z (GMT). No. of bitstreams: 2
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Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only126 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006
Additive Soft-Lithographic Patterning of Submicrometer- and Nanometer-Scale Large-Area Resists on Electronic Materials
No full textWe describe a novel soft-lithographic technique possessing broad utility for the fabrication of large area, nanoscale (100 nm) multilayer resist structures on electronic material substrates. This additive patterning method transfers ultrathin poly(dimethylsiloxane) (PDMS) decals to an underlying SiO2-capped organic planarazation layer. The PDMS patterns serve as a latent image through which high-quality multilayer resist structures can be developed using reactive ion-beam etching
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