Stretch Peak Research Articles

Microstructure changes in nanoparticulate gold films under different thermal atmospheres and the effects on bondability

Sintering in a furnace under different thermal atmospheres of air, nitrogen (N 2) or N 2 bubbled through formic acid (FA/N 2) was carried out for a spin-coated gold nanoparticle (NP) ink. Temperatures of 200, 250 and 290 °C were applied for each atmosphere. The size of the NPs was measured by transmission electron microscopy and the decomposition temperatures of the solvent and the organic capping molecules of the ink were determined by thermo-gravimetric analysis. The changes in the microstructure of Au NP films after sintering were studied using the field emission scanning electron microscopy, X-ray diffractometry, atomic force microscopy and focused ion beam analysis. Organic residues remaining on the film were detected by Fourier transform infrared spectroscopy and sheet resistance was measured using a four point probe for the calculation of resistivity. Wire bonding tests on the Au film were performed for bondability. The Au NP films sintered under air showed neck growth as temperature increased, while the films sintered under N 2 showed grain growth, except for the film sintered at 290 °C. Coalescence and grain growth as well as porosity were observed in the film sintered under FA/N 2. The infrared absorption peaks of stretch and deformation were found as organic residues, with C–O stretch peak only being detected in the film sintered under FA/N 2. All of the samples represented a preferred Au (1 1 1) orientation. The film sintered under N 2 showed good quality compared with those sintered under air or FA/N 2 and the resistivity was about twice the bulk value. Wire bonding tests were successful in all the films sintered under air, N 2 or FA/N 2 atmospheres.

Premature degradation of poly(α-hydroxyesters) during thermal processing of Bioglass®-containing composites

Bioactive, biodegradable composites are increasingly being explored as bone replacement materials and as scaffolds for tissue engineering. Their properties are not only dependent on the properties of the filler and matrix, but are also determined by their interaction. This study investigated the effect on poly(D,L-lactide) (PDLLA) matrix when processed at high-temperatures in the presence of Bioglass particulate filler. Composites with different filler contents were compounded at elevated temperatures by co-extrusion followed by compression moulding and compared with composites of similar composition prepared by thermally induced phase separation (TIPS), a low-temperature processing route. It was found that the inclusion of Bioglass in PDLLA under elevated temperatures resulted in the degradation of the matrix, leading to a reduction in the mechanical properties of the composites and in the molecular weight of the matrix. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy showed the presence of a peak at 1600 cm(-1) in the composite material, particularly when processed at elevated temperatures, whereas no peak at this wavelength was discernible for the pure PDLLA. Furthermore, time-based ATR-FTIR spectra taken at elevated temperatures on the TIPS-processed composites showed an increase in the intensity of the peak at 1600 cm(-1) and a concomitant reduction of the CO stretch peak at 1745 cm(-1) with time. This suggested the formation of a carboxylate salt by-products as a consequence of a reaction at the interface between the Bioglass filler and the PDLLA matrix. Therefore, the results confirmed that this degradation was not solely due to shear effects during the extrusion process. This work thereby supports the assertion that, in the presence of Bioglass filler particles, poly(alpha-hydroxyester)-based composites should not be processed at elevated temperatures.

Observation of water dangling OH bonds around dissolved nonpolar groups

We report the experimental observation of water dangling OH bonds in the hydration shells around dissolved nonpolar (hydrocarbon) groups. The results are obtained by combining vibrational (Raman) spectroscopy and multivariate curve resolution (MCR), to reveal a high-frequency OH stretch peak arising from the hydration shell around nonpolar (hydrocarbon) solute groups. The frequency and width of the observed peak is similar to that of dangling OH bonds previously detected at macroscopic air-water and oil-water interfaces. The area of the observed peak is used to quantify the number of water dangling bonds around hydrocarbon chains of different length. Molecular dynamics simulation of the vibrational spectra of water molecules in the hydration shell around neopentane and benzene reveals high-frequency OH features that closely resemble the experimentally observed dangling OH vibrational bands around neopentyl alcohol and benzyl alcohol. The red-shift of approximately 50 cm(-1) induced by aromatic solutes is similar to that previously observed upon formation of a pi-H bond (in low-temperature benzene-water clusters).

Effect of Sintering Atmosphere on the Microstructure of Gold Nanoparticulate Film

AbstractOver the past few decades, metallic nanoparticles (NPs) have been of great interest due to their unique properties which distinguish them from those of bulk metals. Many attempts have been conducted to investigate the characteristics of NPs and their applications. However, the sintering process which converts metallic NPs to conductive film was not established yet. In this study, the microstructure evolution of Au NPs after sintering under different thermal condition was examined and the film quality was studied based on densification, organic residues and electrical resistivity. Au NP ink dispersed in a toluene were spin coated on Ni-plated FCCL or Si substrates and thermally treated in a furnace under different sintering profiles under various types of flows such as air, nitrogen (N2), or reducing atmosphere of formic acid (FA). The Au ink was consisted of Au NPs coated with an organic capping molecule. The capping molecules not only help NPs to disperse but prevent aggregation and precipitation of NPs out of solution. When the NPs are treated by thermal process, the surface ligands from capping molecule start to decompose and necking and melting of NPs occur producing the film with the electrical conductivity. The diameter of Au NPs was approximately between 5-7 nm with spherical shape. The Au film sintered under air showed only necking between neighboring Au NPs without further grain growth. When Au NPs films were sintered under N2 atmosphere, NPs fused together in clusters. Under sintering with flows of FA, a larger area of pores due to the volume shrinkage of the film was observed since an agglomeration and melting of NPs were considerably progressed compared to the film sintered under N2. Sintering with a flow of a single gas such as air or N2 showed organic residues in the film indicated by C-H or C-O stretch peaks. However, when mixed flows of FA and N2 were applied, there was no IR peaks from organic substances observed in the film. It is assumed that the organic capping molecules surrounding the Au NPs were removed significantly with sintering with two flows of FA and N2. The microstructure showed less pore distribution and lower level of organic residues compared to those sintered under air, N2, or FA atmospheres. The electrical resistivity was about twice of bulk value of 2.44 μΩ -cm. Overall Au NPs film sintered under FA and N2 resulted in a better sintering effect based on densification of the film and level of residual organics, translating into a relatively high electrical conductivity.

Visible-light Photodegradation of Higher Molecular Weight Organics on N-doped TiO2 Nanostructured Thin Films

Nitrogen doped titania nanoparticles were synthesized and deposited as thin films onto glass slides for photodecomposition studies of high molecular weight organics. The decomposition of stearic acid and polyethelyne glycol (PEG) on the nanostructured thin films under visible light irradiation were monitored using FTIR spectroscopy and a decrease in C–H stretch peak area in the 2,700–3,000 cm−1 range was monitored as the organic molecules were photocatalytically destroyed. Conversely, irradiation with visible light only or the whole Xenon lamp spectrum did not result in the degradation of the stearic or PEG coatings on glass in the absence of the nanocatalysts, which demonstrates for the first time visible light photoactivity of nitrogen-doped titania nanoparticle films.

Phenol-benzene complexation dynamics: Quantum chemistry calculation, molecular dynamics simulations, and two dimensional IR spectroscopy

Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared vibrational echo spectrum as a function of time, which directly displays the formation and dissociation of the complex through the growth of off-diagonal peaks, and the linear absorption spectrum, which displays two hydroxyl stretch peaks, one for the complex and one for the free phenol. The results of the simulations are compared to previously reported experimental data and are found to be in quite reasonable agreement. The electronic structure calculations show that the complex is T shaped. The classical potential used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level of the electronic structure calculations. A variety of other features is extracted from the simulations including the relationship between the structure and the projection of the electric field on the hydroxyl group. The fluctuating electric field is used to determine the hydroxyl stretch frequency-frequency correlation function (FFCF). The simulations are also used to examine the number distribution of benzene and CCl4 molecules in the first solvent shell around the phenol. It is found that the distribution is not that of the solvent mole fraction of benzene. There are substantial probabilities of finding a phenol in either a pure benzene environment or a pure CCl4 environment. A conjecture is made that relates the FFCF to the local number of benzene molecules in phenol's first solvent shell.

Real-Time Investigation of Lung Surfactant Respreading with Surface Vibrational Spectroscopy

The respreading of a lung surfactant monolayer at the air-water interface is investigated with broad bandwidth sum frequency generation (BBSFG) spectroscopy. The lung surfactant mixture contains chain perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62), palmitoyloleoylphosphatidylglycerol (POPG), palmitic acid (PA), and KL4 (a 21-residue polypeptide analogue to the surfactant protein SP-B). DPPC-d62 serves as a probe molecule for the spectroscopic investigation. The BBSFG spectra of DPPC-d62 in the lung surfactant mixture are obtained in the C-D stretching region in real-time during film compression and expansion in a Langmuir trough. The BBSFG intensity of the CD3 stretch peak from DPPC-d62 terminal methyl groups is used as a measure of the interfacial density of DPPC-d62 after careful consideration of orientation effects. For the first time, the interfacial loss of DPPC in a complex lung surfactant mixture is quantified. Spectroscopic results reveal that there is an 18% DPPC-d62 interfacial loss during film respreading. However, the surface pressure-area isotherm measurements demonstrate that there is a rather large trough area reduction (37%) during film expansion. The relatively small interfacial loss of DPPC-d62 and the rather large trough area reduction indicate that the respreading of DPPC and non-DPPC components in the lung surfactant is not uniform and a surface refinement process exists during film compression and expansion. This refinement process results in a DPPC-enriched monolayer with a significant depletion of non-DPPC components after film respreading. Implication for replacement surfactant design from this work is discussed.

Oligomer Formation in Evaporating Aqueous Glyoxal and Methyl Glyoxal Solutions

Glyoxal and methyl glyoxal are common secondary atmospheric pollutants, formed from aromatic and terpene precursors. Both compounds are extremely water-soluble due to dihydrate formation and partition into cloudwater. In this work, FTIR-ATR and mass measurements indicate that both compounds remain primarily in the condensed phase due to oligomer formation when aqueous solution droplets are evaporated, regardless of concentration (> or = 1 mM) or, for glyoxal, droplet evaporation rate. FTIR spectral analyses suggestthat oligomer formation is triggered by conversion from dihydrate to monohydrate forms, which are still nonvolatile but contain reactive carbonyl groups. Methyl glyoxal hemiacetal formation is observed by changes in the C-0/C=0 stretch peak area ratio. The formation of glyoxal oligomers is detected by a dramatic shift of the C-0 stretching peak toward low frequencies. Glyoxal oligomer peaks at 1070 cm(-1), 950 cm(-1), and 980 cm(-1) are assigned to free C-OH stretch, dioxolane-linked C-OC asymmetric stretch, and tentativelyto non-dioxolane-linked C-OC stretches, respectively. Acids have little effect on glyoxal oligomer formation; however, base interrupts oligomer formation by catalyzing glyoxal hydration and disproportionation to glycolic acid. Since glyoxal and methyl glyoxal are commonly found in cloudwater and are expected to remain largely in the aerosol phase when cloud droplets evaporate, this process may be a source of secondary organic aerosol by cloud processing.

Secondary oxidation product on Si(111)-(7×7) characterized by isotope-labeled vibrational spectroscopy

The reaction of O(2) with Si(111)-(7 x 7) has been studied by electron energy-loss spectroscopy at 82 K. In addition to the losses due to Si-O-Si configurations, we observed two Si-O stretch modes depending on the coverage. A 146-meV peak appears at the initial reaction stage and was ascribed to a metastable product with one oxygen atom bonding on top of Si adatom and the other inserted into the backbond. The initial product is further oxidized to produce the second Si-O stretch peak at 150 meV. The secondary product was partially substituted with isotopes and analyzed with a simple model of coupled oscillators. The vibrational spectra reflect dynamical couplings between the isotopes, which is consistent with those predicted from the tetrahedral SiO(4) structure with one on top and three inserted oxygen atoms.

Reversible Hydrogenation of Surface N Atoms To Form NH on Pt(111)

The formation and dissociation chemistry of the NH species on Pt(111) was characterized with reflection absorption infrared spectroscopy and temperature programmed desorption. Irradiation of a chemisorbed bilayer of ammonia with a 100 eV electron beam at 85 K leads to a mixture of NH, N, and H on the surface. Annealing to temperatures in the range of 200-300 K leads to reaction of N and H to form additional NH. The NH species has an intense and narrow NH stretch peak at 3320 cm(-1), while no peak due to the PtNH bend is observed above 800 cm(-1). The NH species is stable up to a temperature of approximately 400 K. The surface N atoms produced from NH dissociation are readily hydrogenated back to NH by exposure of the surface to H2. However, NH cannot be further hydrogenated to generate adsorbed NH2 or to NH3 under the conditions used here. Exposure of the NH/Pt(111) surface to D2 at 380 K produces the ND species. Comparison with the results of density functional theory calculations based on small Pt clusters indicates that NH occupies three-fold hollow sites with the molecular axis perpendicular to the surface.

Synthesis and characterization of chelating resins with amino moieties and application on removal of copper(II) from EDTA complexes

Strong-field ligands (amino moieties) are introduced into a hydrogel resin to obtain a chelating resin via inversion suspension polymerization. The characteristics of chelating copolymers are measured by using Fourier transform IR spectroscopy (FTIR), elemental analysis (EA), and scanning electron microscopy (SEM). After chelating copolymers adsorb cupric ions, the absorption peak of stretch NH is shifted to higher frequency because of a coordination reaction from the FTIR spectra. Furthermore, the mechanism of metal complex adsorption on the chelating copolymer is that the strong-field chelating ligand decomposes the bonding of the metal complexes and recoordinates the cupric ion to a chelating polymer, which is examined via FTIR, SEM with EA, and ionic chromatography analysis. The maximum adsorption capacity of cupric ions is 1.08 mmol/g and the adsorption capacity increases with the increase of the pH of the solution. The stability constant of the Cu chelating copolymer is 1018.72, and it can have competition adsorption with EDTA in aqueous solution. These amino chelating copolymers can be used not only to recover metal ions but also to move anion pollution in wastewater. It is interesting that parts of the cupric ions adsorbed on the chelating copolymer are reduced into cupreous ions and/or copper atoms after electron spectroscopy for chemical analysis measurement. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2457–2468, 2005

Spectroscopic and Computational Studies of Aqueous Ethylene Glycol Solution Surfaces

The combination of Monte Carlo, ab initio, and DFT computational studies of ethylene glycol (EG) and EG-water hydrogen-bonding complexes indicate that experimental vibrational spectra of EG and EG-water solution surfaces have contributions from numerous conformations of both EG and EG-water. The computed spectra, derived from harmonic vibrational frequency calculations and a theoretical Boltzmann distribution, show similarity to the experimental surface vibrational spectra of EG taken by broad-bandwidth sum frequency generation (SFG) spectroscopy. This similarity suggests that, at the EG and aqueous EG surfaces, there are numerous coexisting conformations of stable EG and EG-water complexes. A blue shift of the CH2 symmetric stretch peak in the SFG spectra was observed with an increase in the water concentration. This change indicates that EG behaves as a hydrogen-bond acceptor when solvated by additional water molecules. This also suggests that, in aqueous solutions of EG, EG-EG aggregates are unlikely to exist. The experimental blue shift is consistent with the results from the computational studies.

Solid-state proton conduction: An ab initio molecular dynamics investigation of ammonium perchlorate doped with neutral ammonia

Abstract The charge-transport mechanism in solid ammonium perchlorate crystal exposed to an ammonia-rich environment is studied using ab initio molecular dynamics. Ammonium perchlorate is an ionic crystal composed of NH4 + and ClO4 - ; units that possesses an orthorhombic phase at T < 513 K and a cubic phase at T > 513 K. Exposure to an ammonia-rich atmosphere allows ammonia molecules to be absorbed into the crystal at interstitial sites. It has been proposed that these neutral ammonias can form short-lived N2H7 + complexes with the NH4 + ions allowing proton transfer between them, thereby enhancing the conductivity considerably. To date, however, there has been no direct evidence of this proposed mechanism. In this paper, ab initio molecular dynamics techniques are employed to explore this mechanism. By comparing computed infrared spectra of the pure and ammonia-doped crystals, we observe a significant broadening of the NH stretch peak into a lower frequency region, indicating through an experimentally verifiable observable, the formation of hydrogen bonds between NH3 and NH4 + units. This suggestion is confirmed by direct observation of N2H7 + complexes from the trajectory. Comparison of the diffusion constants of NH4 + in the pure and doped crystals yields a ratio that is comparable to the experimentally measured conductivity ratio and clearly shows an enhanced positive charge mobility. Finally, compelling evidence suggesting the possibility of an ammonia umbrella inversion following proton transfer from NH4 + and NH3 is obtained.

C-Met expression and mechanical activation of satellite cells on cultured muscle fibers.

Single-fiber cultures can be used to model satellite cell activation in vivo. Although technical deficiencies previously prevented study of stretch-induced events, here we describe a method developed to study satellite cell gene expression by in situ hybridization (ISH) using protocol modifications for fiber adhesion and fixation. The hypothesis that mechanical stretching activates satellite cells was tested. Fiber cultures were established from normal flexor digitorum brevis muscles and plated on FlexCell dishes with a layer of Vitrogen. After 2 hr of stretch in the presence of BrdU, satellite cells on fibers attached to Vitrogen were activated above control levels. In the absence of activating treatments or mechanical stretch, ISH studies showed 0-6 c-Met+ satellite cells per fiber. Time course experiments demonstrated stable quiescence in the absence of stretch and significant peaks in activation after 30 min and 2 hr of stretch. Frequency distributions for unstretched fiber cultures showed a significantly greater number of quiescent c-Met+ satellite cells than were activated by stretching, suggesting that typical activation stimuli did not trigger cycling in the entire c-Met+ population of satellite cells. These methods have a strong potential to further dissect the nature of stretch-induced activation and gene expression among characterized populations of individual quiescent and activated satellite cells.

Direct evidence of an anomalous charge transport mechanism in ammonium perchlorate crystal in an ammonia-rich atmosphere from first-principles molecular dynamics

The charge transport mechanism in solid ammonium perchlorate (AP) crystal exposed to an ammonia-rich environment is studied using ab initio molecular dynamics (AIMD). Ammonium perchlorate is an ionic crystal composed of NH 4 + and ClO 4 − units that possesses an orthorhombic phase at T<513 K and a cubic phase at T>513 K. Exposure to an ammonia-rich atmosphere allows ammonia molecules to be absorbed into the crystal at interstitial sites. It has been proposed that these neutral ammonias can form short-lived N 2H 7 + complexes with the NH 4 + ions allowing proton transfer between them, thereby enhancing the conductivity considerably. To date, however, there has been no direct evidence of this proposed mechanism. In this paper, ab initio molecular dynamics techniques are employed to explore this mechanism. By comparing computed infrared spectra of the pure and ammonia-doped crystals, we observe a significant broadening of the NH stretch peak into a lower frequency region, indicating through an experimentally verifiable observation, the formation of hydrogen bonds between NH 3 and NH 4 + units. This suggestion is confirmed by direction observation of N 2H 7 + complexes from the trajectory. Comparison of the diffusion constants of NH 4 + in the pure and doped crystals yields a ratio that is comparable to the experimentally measured conductivity ratio and clearly shows an enhanced positive charge mobility. Finally, compelling evidence suggesting the possibility of an ammonia umbrella inversion following proton transfer from NH 4 + and NH 3 is obtained.

Raman spectroscopy ofCo(OH)2at high pressures: Implications for amorphization and hydrogen repulsion

Raman spectra of cobalt hydroxide $\mathrm{Co}(\mathrm{OH}{)}_{2}$ were recorded to 31 GPa using a diamond anvil cell. In contrast to a previous infrared (IR) spectroscopic study, our Raman data show no sharp change in the O-H stretch peak width near 11 GPa, ruling out the possibility of abrupt hydrogen sublattice amorphization at this pressure. This is consistent with neutron diffraction data for $\mathrm{Co}(\mathrm{OD}{)}_{2}$ to 16 GPa which shows no evidence for such amorphization but instead indicates a possible change in local D ordering in response to $D\ensuremath{\cdot}\ensuremath{\cdot}\ensuremath{\cdot}D$ repulsion. However, in agreement with the IR work, we find that the peak width of the OH stretch mode increases significantly over a broad pressure interval from 10 to 25 GPa and reaches $\ensuremath{\sim}200{\mathrm{cm}}^{\ensuremath{-}1}$ at 25 GPa. An energy dispersive x-ray diffraction study carried out to 48 GPa indicates that $\mathrm{Co}(\mathrm{OH}{)}_{2}$ remains crystalline to at least this pressure, although evidence for some anomalous broadening of x-ray peaks is observed at $\ensuremath{\sim}26\mathrm{GPa}.$ The peak widths $(g200{\mathrm{cm}}^{\ensuremath{-}1})$ of both the Raman and infrared stretching vibration of $\mathrm{Co}(\mathrm{OH}{)}_{2}$ are indicative of a high degree of disorder of the H positions while only minimal disordering of the Co-O substructure is allowed by the x-ray data. Thus, the possibility of substructure amorphization remains viable, but through a process of continuous disordering over a broad pressure interval rather than as a discrete discontinuity. Repulsion between neighboring H atoms is likely to be an important driving force for this disordering as suggested by previous neutron and theoretical studies, but it remains uncertain whether such a model can quantitatively describe the range of observed peak widths at high pressures.

Sum-frequency spectroscopic studies of ice interfaces

Sum-frequency vibrational spectroscopy was used to study the (0001) surface of hexagonal ice (I h ) in contact with: air, a hydrophobic substrate, and a hydrophilic substrate. The spectra in the O-H stretch frequency rangewere obtained at various temperatures. For the air/ice interface, the degree of orientational order of the dangling OH bonds at the surface was measured as a function of temperature. Surface disordering appears to set in around 200 K and increases dramatically with temperature, which is a strong indication of the presence of surface melting of ice. For the hydrophobic and hydrophilic ice interfaces, a similar temperature dependence of the hydrogen-bonded OH stretch peak was observed. The free OH stretch mode, however, appears to be different from that of the air/ice interface due to the interactions with substrates at the interfaces.

Effects of calcium modulation on percutaneous absorption of a model drug.

To investigate the effect of modulation of the calcium gradient in the skin on the percutaneous absorption of nicotinic acid (NA). A skin model with an altered calcium gradient was produced by pretreatment with A23187 (25 microg/ml). The immunohistochemistry was used to evaluate the change in phosphoprotein Elk-1. ATR-FTIR spectroscopy was employed to investigate the changes in lipid conformation in the skin. The permeation profiles of the model drug were studied and the distribution profile of the model drug in the skin layer was evaluated using the cryostat micro-sectioning method. The immunohistochemistry demonstrated that modulation of the calcium gradient increased phosphorylated Elk-1 in the dermis. The FTIR study showed a shift of the asymmetric stretch peak, implying an increase in lipid fluidity in the epidermis. The amount of NA permeated through the A23187-pretreated skin was significantly lower than that of the control (2.2714 +/- 0.6040 vs. 3.1895 +/- 0.2456 microg/cm2/h). The Cryostat micro-sectioning study showed that there are concentration gradients of the model drug across the skin layers with a higher gradient in the control than in the A23187-pretreated skin. The alteration in the calcium gradient significantly decreased the permeation rate of a hydrophilic drug, such as nicotinic acid.

Resonance Raman spectroscopic investigation of the mechanism and kinetics of the degradation of N,N-hexamethylene bishexamide, a Nylon 6,6 model compound

We report a mechanistic study of the photo-oxidative degradation of N,N-hexamethylene bishexamide, a Nylon 6,6 model compound. Resonant Raman intensities of the amide and its previously identified enal degradation product are recorded as a function of the duration of the irradiation of the amide with 266nm laser pulses. The time dependences of the Raman intensities are consistent with those predicted by a kinetic mechanism for photo-oxidation. In particular, the rate of formation of the enal, probed by monitoring the Raman intensity of its CO stretch peak at 1680cm−1, agrees well with the rate of cleavage of the C–N bond in the amide, revealed by the time dependence of the intensity of the Am II (C–N stretch) vibration at 1537cm−1. Rate constants for important steps in the degradation mechanism are obtained from the analysis.

Sum-frequency generation spectroscopic study of CO adsorption and dissociation on Pt(111) at high pressure and temperature

Surface vibrational spectroscopy using infrared–visible sum-frequency generation was applied to the study of CO adsorption on the Pt(111) surface under high CO pressure at various temperatures. The temperature variation of the spectrum is reversible below 623 K. At ∼673 K, the spectrum changes with time, showing that most CO is thermally desorbed from the surface, some dissociated leaving carbon on the surface, and the platinum surface is presumably modified. A roughened platinum surface is effectively annealed under high CO pressure at room temperature. CO co-adsorbed with carbon on the surface causes a downshift in the frequency of the CO stretch peak.