Charles B. Mooney

Atomic-scale variations in contact potential difference on Au/Si(111) 7 × 7 surface in ultrahigh vacuum

Abstract The results of contact potential difference (CPD) imaging on Au-deposited p-type and n-type Si(111) 7×7 surfaces are discussed. The scanning Kelvin probe microscopy (SKPM) technique based on the gradient of the electrostatic force was used under ultrahigh vacuum (UHV) conditions to acquire the data presented. The CPD images of Au deposited on the Si(111) 7×7 surface show virtually identical features, irrespective of whether the Si is n- or p-type. In these images, it is believed that the atomically resolved potential difference does not originate from the intrinsic work function of the materials but reflects the local electron density on the surface. On the other hand, the average potentials corresponding to the DC levels in each CPD image reflects the work function value on the surface. The work function of p-type Si(111) 7×7 is found to be higher than that of n-type by about 0.45 eV, where both samples had the same resistivity of about 0.5 Ω cm and the same Au coverage. If the Au coverage is increased, the work function increases.

Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis

Firestone et al. sampled sedimentary sequences at many sites across North America, Europe, and Asia [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 106:16016–16021]. In sediments dated to the Younger Dryas onset or Boundary (YDB) approximately 12,900 calendar years ago, Firestone et al. reported discovery of markers, including nanodiamonds, aciniform soot, high-temperature melt-glass, and magnetic microspherules attributed to cosmic impacts/airbursts. The microspherules were explained as either cosmic material ablation or terrestrial ejecta from a hypothesized North American impact that initiated the abrupt Younger Dryas cooling, contributed to megafaunal extinctions, and triggered human cultural shifts and population declines. A number of independent groups have confirmed the presence of YDB spherules, but two have not. One of them [Surovell TA, et al. (2009) Proc Natl Acad Sci USA 104:18155–18158] collected and analyzed samples from seven YDB sites, purportedly using the same protocol as Firestone et al., but did not find a single spherule in YDB sediments at two previously reported sites. To examine this discrepancy, we conducted an independent blind investigation of two sites common to both studies, and a third site investigated only by Surovell et al. We found abundant YDB microspherules at all three widely separated sites consistent with the results of Firestone et al. and conclude that the analytical protocol employed by Surovell et al. deviated significantly from that of Firestone et al. Morphological and geochemical analyses of YDB spherules suggest they are not cosmic, volcanic, authigenic, or anthropogenic in origin. Instead, they appear to have formed from abrupt melting and quenching of terrestrial materials.

Specific photosynthetic rate enhancement by cyanobacteria coated onto paper enables engineering of highly reactive cellular biocomposite “leaves”

We describe a latex wet coalescence extrusive coating method that produces up to 10‐fold specific photosynthetic rate enhancements by nitrate‐limited non‐growing cyanobacteria deposited onto paper, hydrated and placed in the gas‐phase of small tube photobioreactors. These plant leaf‐like biocomposites were used to study the tolerance of cyanobacteria strains to illumination and temperature using a solar simulator. We report sustained CO2 absorption and O2 production for 500 h by hydrated gas‐phase paper coatings of non‐growing Synechococcus PCC7002, Synechocystis PCC6803, Synechocystis PCC6308, and Anabaena PCC7120. Nitrate‐starved cyanobacteria immobilized on the paper surface by the latex binder did not grow out of the coatings into the bulk liquid. The average CO2 consumption rate in Synechococcus coatings is 5.67 mmol m−2 h−1 which is remarkably close to the rate reported in the literature for Arabidopsis thaliana leaves under similar experimental conditions (18 mmol m−2 h−1). We observed average ratios of oxygen production to carbon dioxide consumption (photosynthetic quotient, PQ) between 1.3 and 1.4, which may indicate a strong dependence on nitrate assimilation during growth and was used to develop a non‐growth media formulation for intrinsic kinetics studies. Photosynthetic intensification factors (PIF) (O2 production by nitrate‐limited cyanobacteria in latex coatings/O2 produced by nitrate‐limited cell suspensions) in cyanobacteria biocomposites prepared from wet cell pellets concentrated 100‐ to 300‐fold show 7–10 times higher specific reactivity compared to cells in suspension under identical nitrate‐limited non‐growth conditions. This is the first report of changes of cyanobacteria tolerance to temperature and light intensities after deposition as a thin coating on a porous matrix, which has important implications for gas‐phase photobioreactor design using porous composite materials. Cryo‐fracture SEM and confocal microscopy images of cell coating distribution on the paper biocomposite suggest that the spatial arrangement of the cells in the coating can affect photoreactivity. This technique could be used to fabricate very stable, multi‐organism composite coatings on flexible microfluidic devices in the gas‐phase capable of harvesting light in a broader range of wavelengths, to optimize thermotolerant, desiccation tolerant, or halotolerant cyanobacteria that produce O2 with secretion of liquid‐fuel precursors synthesized from CO2. Biotechnol. Bioeng. 2014;111: 1993–2008.

Development of Low Temperature Ultrahigh Vacuum Atomic Force Microscope/Scanning Tunneling Microscope

A low temperature ultrahigh vacuum atomic force microscope (UHV-AFM) has been developed, which allows the sample to be cooled from room temperature to lower than 28 K during observation and can be attached to the conventional UHV-AFM. Atom resolved non-contact atomic force microscopy (NC-AFM) images of the Si(100) surface were obtained at 120 K and 50 K using the produced low temperature UHV-AFM/STM, and the Si(100) dimer structure was successfully observed for the first time by NC-AFM. It was found that the Si(100)-c(4×2) structure mainly covered the area at 120 K, but the p(2×2) structure area increased at 50 K.

A high gas fraction, reduced power, syngas bioprocessing method demonstrated with a Clostridium ljungdahlii OTA1 paper biocomposite.

We propose a novel approach to continuous bioprocessing of gases. A miniaturized, coated‐paper strip, high gas fraction, biocomposite absorber has been developed using slowly shaken horizontal anaerobic tubes. Concentrated Clostridium ljungdahlii OTA1 was used as a model system. These gas absorbers demonstrate elevated CO mass transfer with low power input, reduced liquid requirements, elevated substrate consumption, and increased product secretion compared to shaken suspended cells. Concentrated OTA1 cell paste was coated by extrusion onto chromatography paper. The immobilized system shows high, constant reactivity immediately upon rehydration. Cell adhesion was by adsorption to the cellulose fibers; visualized by SEM. The C. ljungdahlii OTA1 coated paper mounted above the liquid level absorbs CO and H2 from a model syngas secreting acetate with minimal ethanol. At 100 rpm shaking speed (7.7 Wm−3) the optimal cell loading is 6.5 gDCW m−2 to maintain high CO absorbing reactivity without the cells coming off of the paper into the liquid phase. Reducing the medium volume from 10 mL to 4 mL (15% of tube volume) did not decrease CO reactivity. The reduced liquid volume increased secreted product concentration by 80%. The specific CO consumption by paper biocomposites was higher at all shaking frequencies <100 rpm than suspended cells under identical incubation conditions. At 25 rpm the biocomposite outperforms suspended cells for CO absorption by 2.5‐fold, with an estimated power reduction of 97% over the power input at 100 rpm. The estimated minimum kLa for miniaturized biocomposite gas‐absorbers is ∼100 h−1, 10 to 104 less power input than other syngas fermentation systems reported in the literature at similar kLa. Specific consumption rates in a biocomposite were ∼14 mmol gDCW−1 h−1. This work intensified CO absorption and reactivity by 14‐fold to 94 mmol CO m−2 h−1 over previous C. ljungdahlii OTA1 work by our group. Specific acetate production rates were 23 mM h−1 or 46 mmol m−2 h−1. The specific rates and apparent kLa scaled linearly with biocomposite coating area. Biotechnol. Bioeng. 2016;113: 1913–1923.

AC Mode Feedback and Gate Pulse Acquisition Methods for Scanning Near-Field Optical Microscope

A scanning near-field optical microscope (SNOM) with a nanometer-size aperture cantilever is a new powerful tool for investigating the optical characteristics of specimen surfaces. We applied the AC-mode feedback and gate pulse acquisition methods in illumination/reflection-mode SNOM. The application of the AC-mode feedback method increased the optical intensity of reflected light from two-to seven fold that obtained by the contact-mode feedback method. The use of the gate pulse acquisition method reduced optical imaging artifacts originating from the topographical features of surfaces.

Blending Measurements in Mixtures with Reclaimed Asphalt: Use of Scanning Electron Microscopy with X-Ray Analysis

A major impediment to the widespread use of asphalt concrete with a high content of reclaimed asphalt pavement (RAP) is uncertainty in the degree of blending between the RAP and the fresh binder. Furthering knowledge concerning the blending between RAP and fresh binder has been difficult because of the lack of an experimental method to quantify the degree of blending in asphalt concrete. This study introduces energy dispersive X-ray spectroscopy (EDS) scanning electron microscopy (SEM) as a means to analyze the degree of blending between RAP and fresh materials in asphalt concrete. EDS allows for mapping the distribution and relative proportion of elements in a sample, hence, allowing for the detection of the distribution of elements in an asphalt concrete specimen. Fresh and RAP binders will have a similar elemental composition. Therefore, titanium dioxide in a fine powder form (0.15-µm particles) is blended with the fresh binder as a tracer before the production of asphalt concrete to enable delineation of the RAP and fresh binders using EDS SEM. The efficacy of EDS SEM for quantifying the degree of blending between RAP and fresh binders in asphalt concrete is demonstrated with two high RAP content mixtures.

Reply to Boslough: Prior studies validating research are ignored

In PNAS, M. Boslough (1) raises issues about carbon spherules and nanodiamonds unrelated to our magnetic spherule focused research (2). Boslough should instead address the questions he raises to the appropriate investigators.

Mapping Contact Potential Differences with Noncontact Atomic Force Microscope Using Resonance Frequency Shift versus Sample Bias Voltage Curves

We have measured cantilever resonance frequency versus sample bias voltage and generated frequency vs bias ( f–V) curves using an ultrahigh-vacuum noncontact atomic force microscope (UHV NC-AFM). Using the f–V data, we calculated the contact potential difference (CPD) between the tip and the sample. These CPD measurements were compared with those that were directly observed with a scanning Kelvin probe force microscope (SKPM) on the same atomically resolved area of the sample using a UHV-AFM. The CPD values obtained by both methods were similar, however, it was difficult to obtain CPD values that agreed precisely on the atomic scale.

In‐Situ Observation of Freeze Fractured and Deep Etched Red Blood Cells with a High‐Vacuum Low‐Temperature Atomic Force Microscope

A high-vacuum low-temperature atomic force microscope (AFM) for the direct observation of freeze-fracture samples has been developed. This AFM has a freeze-fracture mechanism inside the vacuum chamber. With this AFM it is possible to observe the fractured surface directly without both fabricating a replica and exposure to the ambient atmosphere. Both sandwich and knife fracture methods have been achieved to obtain freeze-fracture surfaces and after deep etching. A fine structure of the fractured red blood cell membrane has been observed using both methods. These are relatively quick and easy methods for the observation of freeze-fracture surfaces without introducing replica artifacts.