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The carbonaceous material possesses many kinds of structures and extensive applicability. For example, they are used for lithium battery and fuel cell electrode, printer¡¦s carbon powder, and for the reinforcement of tire. The carbon nanotube and carbon nanocapsule are the novel carbonaceous materials. Their unique property and applicability have attracted a lot of investigation. In this research, we attempt to understand the relationship between the structures and chemical properties of the carbonaceous material. Graphite is an ideal model for this study, and the temperature-programmed desorption method is applied in this investigation. XRD and TEM are also used to support the results of TPD method. Four kinds of exploration molecules are chosen. They are benzene-like molecules, cyclohexane-like molecules, long chain molecules and alcohol-like molecules, respectively. We attempt to find out the differences of the interaction between graphite and various kinds of molecules. The benzene-like molecules with alkyl branch are strongly adsorbed on graphite. The adsorption of long chain molecules on graphite is the next. There are more than one kind of adsorption site on graphite available for 1,3-hexadiene and alcohol-like molecules adsorption. The adsorption behavior of 1,3-hexadiene and alcohol molecules are more complicated. Although the desorption activation energy for different molecules on graphite with different coverages are different. The difference in the desorption activation energy are negligible. The tendency of change is similar for the same kind of molecules. The adsorbed molecules can also diffuse into graphite¡¦s interlayer structure. The interlayer distance of graphite can be changed by the diffusion process of the adsorbed molecules. The desorption activation energies may change when graphite¡¦s pore size changes or functional groups exist on graphite surface. The changes of the activation energy caused by the change of graphite¡¦s pore size or by the surface functional groups are more prominent than the changes induced by the coverage difference of adsorbed molecules on graphite.

Although silicon (Si) nanostructures exhibit size dependent light emission, which can be attributed to quantum confinement, the role of surface passivation is not yet fully understood. This understanding is central to the development of nanocrystal-based detectors. This study investigated the growth, surface chemistry, passivation with deuterium (D2), ammonia (ND3) and diborane (B2D6) and the resulting optical properties of Si nanostructures. Si nanocrystals less than 6 nm in diameter are grown on SiO2 surfaces in an ultra high vacuum chamber using hot-wire chemical vapor deposition and the as grown surfaces are exposed to atomic deuterium. Temperature programmed desorption (TPD) spectra show that that the nanocrystals surfaces are covered by a mix of monodeuteride, dideuteride and trideuteride species. The manner of filling of the deuteride states on nanocrystals differs from that for extended surfaces as the formation of the dideuteride and trideuteride species is facilitated by the curvature of the nanocrystal. No photoluminescence (PL) is observed from the as grown unpassivated nanocrystals. As the deuterium dose is increased, the PL intensity also begins to increase. This can be associated with increasing amounts of mono-, di- and trideuteride species on the nanocrystal surface, which results in better passivation of the dangling bonds and relaxing of the reconstructed surface. At high deuterium doses, the surface structure breaks down and amorphization of the top layer of the nanocrystal takes place. Amorphization reduces the PL intensity. Finally, as the nanocrystal size is varied, the PL peak shifts, which is characteristic of quantum confinement. The dangling bonds and the reconstructed bonds at the NC surface are also passivated and transformed with D and NDx by using deuterated ammonia (ND3), which is predissociated over a hot tungsten filament prior to adsorption. At low hot wire ND3 doses PL emission is observed at 1000 nm corresponding to reconstructed surface bonds capped by predominantly monodeuteride and Si-ND2 species. As the hot wire ND3 dose is increased, di- and trideuteride species form and intense PL is observed around 800 nm that does not shift with NC size and is associated with defect levels resulting from NDx insertion into the strained Si-Si bonds forming Si2=ND. The PL intensity at 800 nm increases as the ND3 dose is increased and the intensity increase is correlated to increasing concentrations of deuterides. At extremely high ND3 doses PL intensity decreases due to amorphization of the NC surface. In separate experiments, Si NCs were subjected to dissociative (thermal) exposures of ammonia followed by exposures to atomic deuterium. These NCs exhibited size dependent PL and this can be attributed to the prevention of the formation of Si2=ND species. Finally, deuterium-passivated Si NCs are exposed to BDx radicals formed by dissociating deuterated diborane (B2D6) over a hot tungsten filament and photoluminescence quenching is observed. Temperature programmed desorption spectra reveal the presence of low temperature peaks, which can be attributed to deuterium desorption from surface Si atoms bonded to subsurface boron atoms. The subsurface boron likely enhances nonradiative Auger recombination. / text

Water is of interest for understanding the formation history and habitability of past and present solar system environments. It also has potential as a resource - when split to its constituent oxygen and hydrogen - both in space and on the Earth. Determining the sources, evolution, and eventual fate of water on bodies easily reachable from Earth, especially Earth's moon, is thus of high scientific and exploration value to the private sector and government space agencies. Understanding how to efficiently split water with solar energy has potential to launch a hydrogen economy here on Earth and to power spacecraft more sustainably to far away destinations. To address the fundamental interactions of water with important surfaces relevant to space exploration and technology development, temperature programmed desorption (TPD) and water photolysis experiments under well controlled adsorbate coverages have been carried out and are described in detail in this thesis. TPD experiments under ultra-high vacuum (UHV) conditions were conducted on lunar surrogate materials and genuine lunar samples brought to Earth by the Apollo program. The TPD's were conducted to determine the desorption activation energies of water chemisorbed directly to the powder surfaces, knowledge of which can improve existing models of water evolution on Earth's moon and aid in interpreting data collected by spacecraft-based investigations at the Moon. The TPD experiments of molecular water interacting with two lunar surrogates (micronized JSC-1A and albite) in ultra-high vacuum revealed water desorption during initial heating to 750 K under ultra-high vacuum. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) indicated possible water formation during the initial heating via recombinative desorption of native hydroxyls above 425 ± 25K. Dissociative chemisorption of water (i.e., formation of surface hydroxyl sites) was not observed on laboratory time scales after controlled dosing of samples (initially heated above 750 K) with 0.2 - 500 L exposures of water. However, pre-heated samples of both types of surrogates were found to have a distribution of molecular water chemisorption sites, with albite having at least twice as many as the JSC-1A samples by mass. A fit to the TPD data yields a distribution function of desorption activation energies ranging from ~0.45 eV to 1.2 eV. Using the fitted distribution function as an initial condition, the TPD process was simulated on the timescale of a lunation. A preview of these results and their context was published in Icarus (2011) 213, 64, doi: 10.1016/j.icarus.2011.02.015 by lead author Charles Hibbitts and the full treatment of the results from the TPD on lunar surrogates (presented here in Chapter 2) has been published in the Journal of Geophysical Research – Planets (2013) 118, 105, doi: 10.1002/jgre.20025 by lead author Michael J Poston. The desorption activation energies for water molecules chemisorbed to Apollo lunar samples 72501 and 12001 were determined by temperature programmed desorption (TPD) experiments in ultra-high vacuum. A significant difference in both the energies and abundance of chemisorption sites was observed, with 72501 retaining up to 40 times more water (by mass) and with much stronger interactions, possibly approaching 1.5 eV. The dramatic difference between the samples may be due to differences in mineralogy, surface exposure age, and contamination of sample 12001 with oxygen and water vapor before it arrived at the lunar sample storage facility. The distribution function of water desorption activation energies for sample 72501 was used as an initial condition to mathematically simulate a TPD experiment with the temperature program matching the lunar day. The full treatment of the TPD results from these two lunar samples (presented here in Chapter 3) has been submitted with the title "Water chemisorption interactions with Apollo lunar samples 72501 and 12001 by ultra-high vacuum temperature programmed desorption experiments" to Icarus for publication in the special issue on lunar volatiles by lead author Michael J Poston. A new ultra-high vacuum system (described in Chapter 4) was designed and constructed for planned experiments examining the possible formation of hydrated species, including water, from interaction of solar wind hydrogen with oxygen in the lunar regolith and to examine the effects of the active radiation environment on water adsorption and desorption behavior on lunar materials. This system has been designed in close collaboration with Dr. Chris J Bennett. An examination of a unique system for water photolysis - zirconia nanoparticles for hydrogen production from water with ultra-violet photons - was performed to better understand the mechanism and efficiency of water splitting on this catalyst. Specifically, formation of H₂ from photolysis of water adsorbed on zirconia (ZrO₂) nanoparticles using 254 nm (4.9 eV) and 185 nm (6.7 eV) photon irradiation was examined. The H₂ yield was approximately an order of magnitude higher using monoclinic versus cubic phase nanoparticles. For monoclinic particles containing 2 monolayers (ML) of water, the maximum H₂ production rate was ~0.4 µmole hr⁻¹ m⁻² using 185 + 254 nm excitation and a factor of 10 lower using only 254 nm. UV reflectance reveals that monoclinic nanoparticles contain fewer defects than cubic nanoparticles. A H₂O coverage dependence study of the H₂ yield is best fit by a sum of interactions involving at least two types of adsorbate-surface complexes. The first dominates up to ~0.06 ML and is attributed to H₂O chemisorbed at surface defect sites. The second dominates at coverages up to a bilayer. H₂ formation is maximum within this bilayer and likely results from efficient energy transfer from the particle to the interface. Energy transfer is more efficient for the monoclinic ZrO₂ nanoparticles and likely involves mobile excitons. These results (presented in Chapter 5) have been submitted with the title "UV Photon-Induced Water Decomposition on Zirconia Nanoparticles" for publication in the Journal of Physical Chemistry C by lead author Michael J Poston. This paper has been reviewed and will be accepted after minor modification.

There has been growing demands towards the efficient production of enantiopure compounds through either asymmetric synthesis or separation from racemic mixtures. Recent studies have examined numerous different methods that may address this challenge. One of these methods involved the interaction of chiral molecules on achiral metal surfaces such as copper to create chiral templates while another method utilizes the interaction of chiral molecules on intrinsically chiral surfaces. Earlier studies using nonhybrid Density Functional Theory (DFT) functional has provided some insights into the geometric structures and relative energies of some of these interactions, but it failed to achieve quantitative agreement with experimental studies. Using dispersion corrected DFT functionals, this thesis present a study of chemisorbed dense adlayers of glycine and alanine on Cu(110) and Cu(3,1,17), physisorbed R-3-methycyclohexanone (R-3MCHO) on Cu(100), Cu(110), Cu(111), Cu(221), and Cu(643)R, and the hydrogenation of formaldehyde and methoxide on Zn or Zr heteroatoms promoted Cu surfaces. In the dense glycine and alanine adlayer study, we have resolved a disagreement between experimental observation made on LEED, STM, and XPD, and we showed that heterochiral and homochiral glycine adlayer coexist on Cu(110). Our model failed to show the minute enantiospecificity for dense alanine adlayer on Cu(3,1,17) which indicated a numeric limitation for computational modeling of surface adsorption. In the physisorbed system, the dispersion corrected methods calculated adsorption energies were in better quantitative agreement with the experimentally observed values than the nonhybrid functionals, but it also created a significant overestimation of total adsorption energies. On the other hand, our model had indicated a previously unexpected adsorbate-induced surface reconstruction on Cu(110). This is promising news in term of computational modeling's capability in examining surface-adsorbate interaction on an atomic scale. As for the hydrogenation of formaldehyde and methoxide on copper surfaces, the model showed that the increased binding strength between the reaction intermediates and the heteroatom promoted copper surfaces to be the primary contributor of the increased reaction rates. Furthermore, our model had also indicated that while clustered heteroatoms are relatively rare, a significant portion of reaction takes place near these clustered structures. It is our hope that the results and techniques presented in this thesis can be used to better understand and predict the interaction of more complex surface-adsorbate interactions.

Developing a fundamental understanding of the interactions of chemical warfare agents (CWAs) with surfaces is essential for the rational design of new sorbents, sensors, and decontamination strategies. The interactions of chemical warfare agent simulants, molecules which retain many of the same chemical or physical properties of the agent without the toxic effects, with amorphous silica were conducted to investigate how small changes in chemical structure affect the overall chemistry. Experiments investigating the surface chemistry of two classes of CWAs, nerve and blister agents, were performed in ultrahigh vacuum to provide a well-characterized system in the absence of background gases. Transmission infrared spectroscopy and temperature-programmed desorption techniques were used to learn about the adsorption mechanism and to measure the activation energy for desorption for each of the simulant studied. In the organophosphate series, the simulants diisopropyl methylphosphonate (DIMP), dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), dimethyl chlorophosphate (DMCP), and methyl dichlorophosphate (MDCP) were all observed to interact with the silica surface through the formation of a hydrogen bond between the phosphoryl oxygen of the simulant and an isolated hydroxyl group on the surface. In the limit of zero coverage, and after defect effects were excluded, the activation energies for desorption were measured to be 57.9 ± 1, 54.5 ± 0.3, 52.4 ± 0.6, 48.4 ± 1, and 43.0 ± 0.8 kJ/mol for DIMP. DMMP, TMP, DMCP, and MDCP respectively. The adsorption strength was linearly correlated to the magnitude of the frequency shift of the ν(SiO-H) mode upon simulant adsorption. The interaction strength was also linearly correlated to the calculated negative charge on the phosphoryl oxygen, which is affected by the combined inductive effects of the simulants' different substituents. From the structure-function relationship provided by the simulant studies, the CWA, Sarin is predicted to adsorb to isolated hydroxyl groups of the silica surface via the phosphoryl oxygen with a strength of 53 kJ/mol. The interactions of two common mustard simulants, 2-chloroethyl ethyl sulfide (2-CEES) and methyl salicylate (MeS), with amorphous silica were also studied. 2-CEES was observed to adsorb to form two different types of hydrogen bonds with isolated hydroxyl groups, one via the S moiety and another via the Cl moiety. The desorption energy depends strongly on the simulant coverage, suggesting that each 2-CEES adsorbate forms two hydrogen bonds. MeS interacts with the surface via a single hydrogen bond through either its hydroxyl or carbonyl functionality. While the simulant work has allowed us to make predictions agent-surface interactions, actual experiments with the live agents need to be conducted to fully understand this chemistry. To this end, a new surface science instrument specifically designed for agent-surface experiments has been developed, constructed, and tested. The instrument, located at Edgewood Chemical Biological Center, now makes it possible to make direct comparisons between simulants and agents that will aid in choosing which simulants best model live agent chemistry for a given system. These fundamental studies will also contribute to the development of new agent detection and decontamination strategies. / Ph. D.

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Diborane (B2H6) is a hydride gas often employed in high-purity industrial surface processes such as chemical vapor deposition or epitaxial layer growth. The use of diborane at industrial scales is complicated by the formation of higher-order borane contaminants in pure diborane gas via a complex series of gas-phase reactions. An advanced, rationally designed sorbent could stabilize diborane through interfacial interactions, dramatically reducing the decomposition rate without permanently trapping the molecule. However, the design of such a sorbent would require a nuanced understanding of diborane's fundamental surface chemistry, about which little is known. In the work presented in this thesis, a novel ultra-high vacuum (UHV) system was designed and employed to characterize the fundamental interactions of diborane with a variety of surfaces. In situ Fourier-transform infrared (FTIR) spectroscopy and temperature-programmed desorption (TPD) experiments were used in conjunction with density-functional theory (DFT) calculations to elucidate binding geometries and interaction mechanisms. On non-functionalized model surfaces such as CaF2 or amorphous carbon, diborane adsorbed only at cryogenic temperatures. Hydroxylated surfaces such as amorphous silica (SiO2) adsorbed significantly more diborane, which remained at slightly higher temperatures. FTIR spectra indicated the presence of hydrogen bonding between diborane and surface hydroxyl groups. DFT calculations revealed that the interaction takes the form of a novel bifurcated dihydrogen bond. In contrast with previous reports, diborane exhibited only weak interactions with the surface hydroxyl groups of silica. DFT calculations further elucidated that the irreversible reaction of diborane with surface hydroxyls is only possible in the presence of a second nucleophile (such as adventitious water). On the metal-organic framework (MOF) UiO-66 NH2, unique chemistry was observed in which diborane reacted with the –NH2 groups of the MOF linkers, yielding stable surface-bound products. DFT calculations determined the reaction mechanism to be dissociative adsorption of diborane, resulting in two amine-bound –BH3 moieties. Importantly, it was found that these fragments persisted at room temperature and could only leave the surface via the reverse reaction. The discovery that diborane can be stored as separate fragments that re-combine to yield the parent molecule has important implications for the development of new diborane sorbents. We hypothesize that surfaces designed with fixed, precisely spaced nucleophiles could enable the reversible storage of diborane. / Doctor of Philosophy / Diborane (B2H6) is a useful but hazardous gas employed in both academia and industry, often in processes that require ultra-high-purity source gases. However, diborane reacts with itself at room temperature, making the contamination of pure diborane very difficult to avoid. This problem could potentially be solved with a specially designed solid material that would sequester diborane without destroying it, but the design of such a material would require a much better understanding of diborane's chemistry with surfaces than currently exists. In this work, we employed ultra-high vacuum (UHV) methods to study the interactions between diborane and a variety of surfaces, with the ultimate goal of determining guiding principles for the design of diborane-stabilizing sorbents. Among the materials we studied were inorganic carbon, silica (SiO2), and a class of advanced microporous materials known as metal-organic frameworks (MOFs). Inorganic materials were found not to interact meaningfully with diborane. A novel hydrogen bond was discovered between diborane and the surface of silica, but the interaction was found to be too weak to provide significant stabilization. Most MOFs behaved similarly to silica. The MOF UiO-66-NH2, however, was found to react with diborane. Through a combination of computer simulations and UHV experiments, the precise nature of the reaction was determined. On the surface of UiO 66 NH2, diborane splits into two surface-bound BH3 molecules, where it is trapped until the reaction reverses. Importantly, it was found that BH3 can only leave the surface by recombining into diborane—effectively storing diborane on the surface to be released later. We hypothesize that this useful chemistry is due to the fixed distance between chemical groups on the MOF surface. This discovery suggests a promising strategy for the design of advanced diborane sorbents.

Metal oxide and metal oxide-supported metal nanoparticles can adsorb and decompose chemical warfare agents (CWAs) and their simulants. Nanoparticle activity depends on several factors including chemical composition, particle size, and support, resulting in a vast number of materials with potential applications in CWA decontamination. Current instrumentation in our laboratory used to investigate fundamental gas-surface interactions require extensive time and effort to achieve operating conditions. This thesis describes the design and construction of a high-throughput, high vacuum surface analysis instrument capable of studying interactions between CWA simulants and nanoparticulate surfaces. The new instrument is small, relatively inexpensive, and easy to use, allowing for expeditious investigations of fundamental interactions between gasses and nanoparticulate samples. The instrument maintains the sample under high vacuum (10?⁷-10?⁹ torr) and can reach operating pressures in less than one hour. Thermal control of the sample from 150-800 K enables sample cleaning and thermal desorption experiments. Infrared spectroscopic and mass spectrometric methods are used concurrently to study gas-surface interactions. Temperature programmed desorption is used to estimate binding strength of adsorbed species. Initial studies were conducted to assess the performance of the instrument and to investigate interactions between the CWA simulant dimethyl methylphosphonate (DMMP) and nanoparticulate silicon dioxide. / Master of Science