John N. Russell

Hydrogen on polycrystalline diamond films: Studies of isothermal desorption and atomic deuterium abstraction

Studies of hydrogen isothermal desorption and abstraction from polycrystalline diamond surfaces are presented. The surface H and D coverages (θH and θD) are measured in real time by mass analyzing the recoiled ions generated in a time‐of‐flight scattering and recoil spectroscopy (TOF‐SARS) experiment. For surface temperatures (Ts) from 825 and 920 °C, isothermal H2 desorption is 1st order in θH with a measured activation energy, ET, of 69±6 kcal/mol and a pre‐exponential factor, ν, of 1010.5±0.9 s−1. For H2 desorption from diamond, the estimated ΔET based on bond energy calculations is ≊88 kcal/mol, substantially higher than the experimentally measured ET. This difference suggests π‐bonding of the surface after H2 desorption is involved. Using a simple bond order argument, the π‐bonding contribution is estimated to be ≊21 kcal/mol. The abstraction and replacement of absorbed H by atomic deuterium (Dat) is explained by three first‐order reactions. Under a constant Dat flux, the rate of abstraction of adsor...

Direct electrical detection of antigen-antibody binding on diamond and silicon substrates using electrical impedance spectroscopy.

The integration of biological molecules with semiconducting materials such as silicon and diamond has great potential for the development of new types of bioelectronic devices, such as biosensors and bioactuators. We have investigated the electrical properties of the antibody-antigen modified diamond and silicon surfaces using electrical impedance spectroscopy (EIS). Frequency dependent measurements at the open-circuit potential show: (a) significant changes in impedance at frequency >10(4) Hz when the surface immobilized IgG was exposed to anti-IgG, and (b) only little or no change when exposed to anti-IgM. Mott-Schottky measurements at high frequency (200 kHz) show that the impedance is dominated by the space charge layer of the semiconducting substrates. Silicon surfaces modified in a similar manner to the diamond surface are compared; n-type and p-type samples show complementary behavior, as expected for a field effect. We also show it is possible to directly observe antigen-antibody interaction at a fixed frequency in real time, and with no additional labeling.

Multiple internal reflection infrared spectroscopy of hydrogen adsorbed on diamond(110)

Multiple internal reflection infrared spectroscopy is used to investigate the reaction of atomic hydrogen with a polished, natural type IIa diamond (110) dehydrogenated surface held at 673 K. A single infrared absorption band at 2880 cm−1 is observed and is attributed to the C‐H stretching mode on an sp3 hybridized surface carbon. The band is stable up to surface temperatures between 1073 and 1173 K, and is absent when the dehydrogenated surface is exposed to atomic deuterium.

Adsorption and thermal decomposition of phenol on Ni(110)

Abstract The thermal decomposition of phenol on Ni(110) between 150 and 800 K was investigated with temperature programmed desorption (TPD), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES). After adsorption at 150 K, the phenol monolayer completely decomposed into H2, CO, and adsorbed carbon upon heating to 800 K. Molecular phenol desorbed from an unreactive state at 225 K and from the multilayer at 200 K. The saturated reactive monolayer resulted in four H2 desorption states, β1–β4. The β1-H2 state observed between 250 and 350 K, resulted from OH bond scission and demonstrated the formation of a phenoxy species. A deuterium kinetic isotope effect (DKIE) for β1-hydrogen desorption indicated that OH bond scission occurs between 250 and 350 K. However, the absence of a DKIE in the reactive adsorption at 290 K of OH/OD and CH/CD labeled phenol showed that phenol chemisorbed on Ni(110) via the π bonds of the ring. The β2–β4-H2 desorption states occurred in a continuum between 370 and 650 K and resulted from decomposition of the phenyl ring. The observation of a deuterium kinetic isotope effect for β2-H2 desorption from 2,4,6-d3-phenol, compared to h6-phenol, and 3,5-d2-phenol indicated that scission of the CH bond in either the (2,6) or the 4 position on the ring was the rate limiting step. CO desorption began near 400 K, and continued to about 650 K, exhibiting the same general thermal desorption distribution as the β2–β4-H2 desorption spectrum. In CO desorption, a DKIE indicated CH bond scission influenced the decomposition of the CC bonds in the ring which resulted in CO production. 13C labeling revealed that 60% of the CO bond units remained intact. At 650 K, the carbon residue had a graphitic Auger lineshape, and exhibited a LEED pattern that is consistent with graphite microcrystallites. The surface C dissolved into the bulk above 700 K.

Isothermal desorption of hydrogen from polycrystalline diamond films

The kinetics of isothermal H2 desorption from polycrystalline diamond are studied in real time. The surface H coverage (θH) is measured by mass analyzing the recoiled H+ ion signal during the desorption. We find that the H2 desorption is 1st order in θH with an activation energy of 69 ± 6 kcalmol and a prefactor of 1010.5 ± 0.9 s−1. We suggest that formation of a CC π-bond on the clean surface plays a key role in H2 desorption from diamond, a view consistent with previous theoretical calculations of H2 desorption from diamond.

Interaction of ammonia with hydrogen on Al(111)

Abstract The interaction of NH3 with clean and hydrogenated Al(111) surfaces is studied using temperature programmed desorption and infrared reflection absorption spectroscopy. On clean Al(111), NH3 adsorbs molecularly and desorbs by 200 K. In contrast, on the H-covered surface, a new NH3 desorption state (β) is seen at 225 K. The β-NH3 coverage tracks that of H, reaching a saturation coverage of about 0.58 NH 3 Al surface atom on the fully H-covered surface. Infrared spectroscopy shows that H causes appreciable change in NH3 adsorption geometry. NH3 preferentially adsorbs via a Lewis acid-base interaction at monohydride sites with the Al-N bond inclined away from the surface normal, whereas on the H-free surface this bond is essentially normal to the surface.

Phenol decomposition on Al(111)

The reaction of phenol on Al(111) was investigated between 100 and 800 K with temperature programmed desorption and Auger electron spectroscopy. Molecular phenol desorbed at 200 K from the multilayer. The first monolayer of phenol decomposed into hydrogen, benzene, and adsorbed oxygen and carbon as the surface was heated. The sequence of bond scission was determined using deuterium labeling. Three H2 desorption peaks were observed. The first H2 desorption peak was from the dissociation of the hydroxyl group and was observed around 380 K. The second H2 desorption peak, which started around 450 K and reached a maximum at 510 K, resulted from the scission of the CH bonds in the 2 or 6 positions on the ring. The third H2 desorption peak was observed at 680 K and was from scission of the CH bonds on the remaining hydrocarbon fragments on the surface. Benzene desorption occurred between 450 and 700 K with maxima at 490 and 630 K resulting from hydrogen addition to the phenyl group from OH and CxHy moieties, respectively. HD exchange with the hydrogen on the phenyl ring also was observed. However, there was no evidence for hydrogenation (saturation) of any of the double bonds of the ring. After heating to 800 K. some O and C remained on the surface.

Carbon Catabolite Repression and Impranil Polyurethane Degradation in Pseudomonas protegens Strain Pf-5

ABSTRACT Polyester polyurethane (PU) coatings are widely used to help protect underlying structural surfaces but are susceptible to biological degradation. PUs are susceptible to degradation by Pseudomonas species, due in part to the degradative activity of secreted hydrolytic enzymes. Microorganisms often respond to environmental cues by secreting enzymes or secondary metabolites to benefit their survival. This study investigated the impact of exposing several Pseudomonas strains to select carbon sources on the degradation of the colloidal polyester polyurethane Impranil DLN (Impranil). The prototypic Pseudomonas protegens strain Pf-5 exhibited Impranil-degrading activities when grown in sodium citrate but not in glucose-containing medium. Glucose also inhibited the induction of Impranil-degrading activity by citrate-fed Pf-5 in a dose-dependent manner. Biochemical and mutational analyses identified two extracellular lipases present in the Pf-5 culture supernatant (PueA and PueB) that were involved in degradation of Impranil. Deletion of the pueA gene reduced Impranil-clearing activities, while pueB deletion exhibited little effect. Removal of both genes was necessary to stop degradation of the polyurethane. Bioinformatic analysis showed that putative Cbr/Hfq/Crc-mediated regulatory elements were present in the intergenic sequences upstream of both pueA and pueB genes. Our results confirmed that both PueA and PueB extracellular enzymes act in concert to degrade Impranil. Furthermore, our data showed that carbon sources in the growth medium directly affected the levels of Impranil-degrading activity but that carbon source effects varied among Pseudomonas strains. This study uncovered an intricate and complicated regulation of P. protegens PU degradation activity controlled by carbon catabolite repression. IMPORTANCE Polyurethane (PU) coatings are commonly used to protect metals from corrosion. Microbiologically induced PU degradation might pose a substantial problem for the integrity of these coatings. Microorganisms from diverse genera, including pseudomonads, possess the ability to degrade PUs via various means. This work identified two extracellular lipases, PueA and PueB, secreted by P. protegens strain Pf-5, to be responsible for the degradation of a colloidal polyester PU, Impranil. This study also revealed that the expression of the degradative activity by strain Pf-5 is controlled by glucose carbon catabolite repression. Furthermore, this study showed that the Impranil-degrading activity of many other Pseudomonas strains could be influenced by different carbon sources. This work shed light on the carbon source regulation of PU degradation activity among pseudomonads and identified the polyurethane lipases in P. protegens.

Preparation and Electrochemical Characterization of DNA-modified Nanocrystalline Diamond Films

Nanocrystalline diamond thin films of sub-micron thickness have been covalently modified with DNA oligonucleotides. Quantitative studies of hybridization of surface-bound oligonucleotides with fluorescently tagged complementary and non-complementary oligonucleotides were performed. The results show no detectable nonspecific adsorption, with extremely good selectivity between matched and mismatched sequences. Impedance spectroscopy measurements were made of DNA-modified boron-doped nanocrystalline diamond films. The results show that exposure to non-complementary sequences induce only small changes in impedance, while complementary DNA sequences produce a pronounced decrease in impedance. The combination of high stability, selectivity, and the ability to directly detect DNA hybridization via electrical means suggest that diamond may be an ideal substrate for continuously-monitoring biological sensors.

Hydrogen Chemistry on Diamond Surfaces

Surface chemical reactions of hydrogen with diamond are important events in the complex processes leading to diamond chemical vapor deposition (CVD). Our ongoing research addresses the surface reactions related to diamond growth. Studies were performed on single crystals, C(100) and C(110), and large grained polycrystalline CVD diamond films using a diverse array of ultra-high vacuum surface analytical techniques. Surface vibrational spectroscopies, high resolution electron energy loss spectroscopy (HREELS) and multiple internal reflection infrared spectroscopy (MIRIRS), were principal probes of surface structure, while HREELS and temperature programmed desorption (TPD) were used to investigate hydrogen adsorption, abstraction, and desorption. We found: (1) the C(100), C(110) and polycrystalline diamond surfaces are terminated primarily with CH species; (2) the ratio of H atom abstraction to adsorption is 0.05 ± 0.01; (3) hydrogen desorbs molecularly from C(110) peaking at 892 C and exhibits first order desorption kinetics with an activation energy of 75 kcal/mole; and (4) both clean and hydrogen-saturated C(100) surfaces display a 2x1 surface reconstruction.