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Jacobs, Christopher B.

Publications and source records attributed to Jacobs, Christopher B..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Microbially-mediated method for synthesis of metal chalcogenide nanoparticles

A method for producing metal chalcogenide nanoparticles, the method comprising: (i) producing hydrogen chalcogenide-containing vapor from a microbial source, wherein said microbial source comprises: (a) chalcogen-reducing microbes capable of producing hydrogen chalcogenide vapor from a chalcogen-containing source; (b) a culture medium suitable for sustaining said chalcogen-reducing microbes; (c) at least one chalcogen-containing compound that can be converted to hydrogen chalcogenide vapor by said chalcogen-reducing microbes; and (d) at least one nutritive compound that provides donatable electrons to said chalcogen-reducing microbes during consumption of the nutritive compound by said chalcogen-reducing microbes; and (ii) directing said hydrogen chalcogenide-containing vapor into a metal-containing solution comprising a metal salt dissolved in a solvent to produce metal chalcogenide nanoparticles in said solution, wherein said chalcogen is sulfur or selenium, and said chalcogenide is sulfide or selenide, respectively. The invention is also directed to metal chalcogenide nanoparticle compositions produced as above and having distinctive properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Scalable processing of ZnS nanoparticles for high photoluminescence efficiency quantum dots

Nano Elements Source, LLC, a biotech startup has licensed the NanoFermentation technology from Oak Ridge National Laboratory to further commercialize low cost, cadmium free photoluminescent nanoparticles produced using affordable, environmentally-friendly. This project aimed to develop post chemical processing of biosynthesized ZnS quantum dots (QD) to improve their efficiency of luminescence to make them suitable for solid state lighting applications. Several post processing approached were proposed and tested using to biosynthesized of ZnS QD. Optical properties of ZnS nanoparticles including soft chemical etching, and photonic etching have been tested and quantified against standard materials. We applied the developed chemical modification approach to control quality of chemically synthetized ZnS QD’s, and to calculate the maximum achievable efficiency of photoluminescence. We estimated the cost of the proposed post-processing treatment of nanoFermented nanoparticles and proposed several approaches to further the development of low cost nanoparticles for electro-optical and other applications relevant to DOE mission.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Improved ZnS nanoparticle properties through sequential NanoFermentation

Sequential NanoFermentation (SNF) is a novel process which entails sparging microbially produced gas containing H 2 S from a primary reactor through a concentrated metal-acetate solution contained in a secondary reactor, thereby precipitating metallic sulfide nanoparticles (e.g., ZnS, CuS, or SnS). SNF holds an advantage over single reactor nanoparticle synthesis strategies, because it avoids exposing the microorganisms to high concentrations of toxic metal and sulfide ions. Also, by segregating the nanoparticle products from biological materials, SNF avoids coating nanoparticles with bioproducts that alter their desired properties. Herein, we report the properties of ZnS nanoparticles formed from SNF as compared with ones produced directly in a primary reactor (i.e., conventional NanoFermentation, or “CNF”), commercially available ZnS, and ZnS chemically synthesized by bubbling H 2 S gas through a Zn-acetate solution. The ZnS nanoparticles produced by SNF provided improved optical properties due to their smaller crystallite size, smaller overall particle sizes, reduced biotic surface coatings, and reduced structural defects. Furthermore, SNF still maintained the advantages of NanoFermentation technology over chemical synthesis including scalability, reproducibility, and lower hazardous waste burden.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Highly Permeable Oligo(ethylene oxide)- co -poly(dimethylsiloxane) Membranes for Carbon Dioxide Separation

Here, a series of cross–linked, freestanding oligo(ethylene oxide)– co –(polydimethylsiloxane–norbornene) membranes with varied composition is synthesized via in situ ring–opening metathesis polymerization. These membranes show remarkably high CO 2 permeabilities (3400 Barrer) and their separation performance approaches the Robeson upper bound. The excellent permeability of these copolymer membranes provides great potential for real–world applications where enormous volumes of gases must be separated. The gas transport properties of these films are found to be directly proportional to oligo(ethylene oxide) content incorporation, which stems from the increased solubility selectivity change within the copolymer matrix. This work provides a systematic study of how gas separation performance in rubbery membranes can be enhanced by tuning the CO 2 –philicity of their constituent monomeric subunits.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Multi-mode humidity sensing with water-soluble copper phthalocyanine for increased sensitivity and dynamic range

Aqueous solubility of copper phthalocyanine-3,4',4',4"'-tetrasulfonic acid tetrasodium salt (CuPcTs) enables fabrication of flexible electronic devices by low cost inkjet printing. We (1) investigate water adsorption kinetics on CuPcTs for better understanding the effects of relative humidity (RH) on hydrophilic phthalocyanines, and (2) assess CuPcTs as a humidity-sensing material. Reaction models show that H 2 O undergoes 2-site adsorption which can be represented by a pair of sequentially-occurring pseudo-first order reactions. Using high frequency (300–700 THz) and low frequency (1–8 MHz) dielectric spectroscopy combined with gravimetric measurements and principal component analysis, we observe that significant opto-electrical changes in CuPcTs occur at RH ≈ 60%. The results suggest that rapid H 2 O adsorption takes place at hydrophilic sulfonyl/salt groups on domain surfaces at low RH, while slow adsorption and diffusion of H 2 O into CuPcTs crystallites leads to a mixed CuPcTs-H 2 O phase at RH > 60%, resulting in high frequency dielectric screening of the film by water and dissociation of Na+ from CuPc(SO 3 -) 4 ions. Lastly, the CuPcTs-H 2 O interaction can be tracked using a combination of gravimetric, optical, and electrical sensing modes, enabling accurate ( ± 2.5%) sensing in the ~0–95% RH range with a detection limit of less than 0.1% RH.

36 MATERIALS SCIENCE↗
DOE OSTI2017

UV-activated ZnO films on a flexible substrate for room temperature O 2 and H 2 O sensing

Here, we demonstrate that UV-light activation of polycrystalline ZnO films on flexible polyimide (Kapton) substrates can be used to detect and differentiate between environmental changes in oxygen and water vapor. The in-plane resistive and impedance properties of ZnO films, fabricated from bacteria-derived ZnS nanoparticles, exhibit unique resistive and capacitive responses to changes in O 2 and H 2 O. We also propose that the distinctive responses to O 2 and H 2 O adsorption on ZnO could be utilized to statistically discriminate between the two analytes. Molecular dynamic simulations (MD) of O 2 and H 2 O adsorption energy on ZnO surfaces were performed using the large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) with a reactive force-field (ReaxFF). Furthermore, these simulations suggest that the adsorption mechanisms differ for O 2 and H 2 O adsorption on ZnO, and are governed by the surface termination and the extent of surface hydroxylation. Electrical response measurements, using DC resistance, AC impedance spectroscopy, and Kelvin Probe Force Microscopy (KPFM), demonstrate differences in response to O 2 and H 2 O, confirming that different adsorption mechanisms are involved. Statistical and machine learning approaches were applied to demonstrate that by integrating the electrical and kinetic responses the flexible ZnO sensor can be used for detection and discrimination between O 2 and H 2 O at low temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2017

New insights on electro-optical response of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) film to humidity

Understanding the relative humidity (RH) response of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is critical for improving the stability of organic electronic devices and developing selective sensors. In this work combined gravimetric sensing, nanoscale surface probing, and mesoscale optoelectronic characterization are used to directly compare the RH dependence of electrical and optical conductivities and unfold connections between the rate of water adsorption and changes in functional properties of PEDOT:PSS film. We report three distinct regimes where changes in electrical conductivity, optical conductivity, and optical bandgap are correlated with the mass of adsorbed water. At low (RH < 25%) and high (RH > 60%) humidity levels dramatic changes in electrical, optical and structural properties occur, while changes are insignificant in mid-RH (25% < RH < 60%) conditions. We associate the three regimes with water adsorption at hydrophilic moieties at low RH, diffusion and swelling throughout the film at mid-RH, and saturation of the film by water at high RH. Optical film thickness increased by 150% as RH was increased from 9% to 80%. Low frequency (1 kHz) impedance increased by ~100% and film capacitance increased by ~30% as RH increased from 9% to 80% due to an increase in the film dielectric constant. Finally, changes in electrical and optical conductivities concomitantly decrease across the full range of RH tested.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Stabilizing Ir(001) Epitaxy on Yttria-Stabilized Zirconia Using a Thin Ir Seed Layer Grown by Pulsed Laser Deposition

In this paper, we demonstrate the reproducible epitaxial growth of 100 nm thick Ir(001) films on a heteroepitaxial stack consisting of 5 nm Ir and 100 nm yttria-stabilized zirconia (YSZ) grown on Si(001) substrates. It is shown that a 5 nm thick Ir layer grown by pulsed laser deposition in the same chamber as the YSZ film without breaking the vacuum is the key to stabilizing Ir(001) epitaxial growth. Growth of the Ir seed layer with pure (001) orientation occurs only in a narrow growth temperature window from 550 to 750 °C, and the fraction of Ir(111) increases at substrate temperatures outside of this window. The Ir seed layer prevents exposure of the YSZ film to air during sample transfer and enables highly reproducible Ir(001) heteroepitaxy on YSZ buffered Si(001). In contrast, if Ir is grown directly on a bare YSZ layer that was exposed to ambient conditions, the films are prone to change orientation to (111). These results reveal that preserving the chemical and structural purity of the YSZ surface is imperative for achieving Ir(001) epitaxy. The narrow range of the mosaic spread values from eight experiments demonstrates the high yield and high reproducibility of Ir(001) heteroepitaxy by this approach. Lastly, the improved Ir(001) epitaxial growth method is of great significance for integrating a variety of technologically important materials such as diamond, graphene, and functional oxides on a Si platform.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Ultrafast dynamics of metal plasmons induced by 2D semiconductor excitons in hybrid nanostructure arrays

With the advanced progress achieved in the field of nanotechnology, localized surface plasmons resonances (LSPRs) are actively considered to improve the efficiency of metal-based photocatalysis, photodetection, and photovoltaics. Here, we report on the exchange of energy and electric charges in a hybrid composed of a two-dimensional tungsten disulfide (2D-WS 2 ) monolayer and an array of aluminum (Al) nanodisks. Femtosecond pump-probe spectroscopy results indicate that within ~830 fs after photoexcitation of the 2D-WS 2 semiconductor, energy transfer from the 2D-WS 2 excitons excites the plasmons of the Al array. Then, upon the radiative and/or nonradiative damping of these excited plasmons, energy and/or electron transfer back to the 2D-WS 2 semiconductor takes place as indicated by an increase in the reflected probe at the 2D exciton transition energies at later time-delays. This simultaneous exchange of energy and charges between the metal and the 2D-WS 2 semiconductor resulted in an extension of the average lifetime of the 2D-excitons from ~15 to ~58 ps in absence and presence of the Al array, respectively. Furthermore, the indirectly excited plasmons were found to live as long as the 2D-WS 2 excitons exist. Furthermore, the demonstrated ability to generate exciton-plasmons coupling in a hybrid nanostructure may open new opportunities for optoelectronic applications such as plasmonic-based photodetection and photocatalysis.

2D Materials↗
DOE OSTI2016

Morphology-defined interaction of copper phthalocyanine with O 2 /H 2 O

Copper phthalocyanine (CuPc) is an important hole transport layer for organic photovoltaics (OPVs), but its interaction with ambient gas/vapor may lead to changes in electronic properties of the material which subsequently limits the lifetime of OPV devices. CuPc films of thickness 25 nm and 100 nm were grown by thermal sublimation at 25°C, 150°C, and 250°C in order to vary morphology. Using a source-measure unit and a quartz crystal microbalance (QCM), we measured changes in electrical resistance and film mass in situ during exposure to controlled pulses of O 2 and H 2 O vapor. Mass loading by O 2 was enhanced by a factor of 5 in films deposited at 250 C, possibly due to the ~200° C CuPc -> transition which allows higher O 2 mobility between stacked molecules. While gas/vapor sorption occurred over timescales of < 10 minutes, resistance change occurred over timescales > 1 hour, suggesting that mass change occurs by rapid adsorption at active surface sites, whereas resistive response is dominated by slow diffusion of adsorbates into the film bulk. Resistive response generally increases with film deposition temperature due to increased porosity associated with larger crystalline domains. The 25 nm thick films exhibit higher resistive response than 100 nm thick films after an hour of O 2 /H 2 O exposure due to the smaller analyte diffusion length required for reaching the film/electrode interface. We found evidence of decoupling of CuPc from the gold-coated QCM crystal due to preferential adsorption of O 2 /H 2 O molecules on gold, which is consistent with findings of other studies.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Towards functional assembly of 3D and 2D nanomaterials

Functional assemblies of materials can be realized by tuning the work function and band gap of nanomaterials by rational material selection and design. Here we demonstrate the structural assembly of 2D and 3D nanomaterials and show that layering a 2D material monolayer on a 3D metal oxide leads to substantial alteration of both the surface potential and optical properties of the 3D material. A 40 nm thick film of polycrystalline NiO was produced by room temperature rf-sputtering, resulting in a 3D nanoparticle assembly. Chemical vapor deposition (CVD) grown 10-30 μm WS2 flakes (2D material) were placed on the NiO surface using a PDMS stamp transfer technique. The 2D/3D WS2/NiO assembly was characterized using confocal micro Raman spectroscopy to evaluate the vibrational properties and using Kelvin probe force microscopy (KPFM) to evaluate the surface potential. Raman maps of the 2D/3D assembly show spatial non-uniformity of the A1g mode (~418 cm-1) and the disorder-enhanced longitudinal acoustic mode, 2LA(M) (~350 cm-1), suggesting that the WS2 exists in a strained condition on when transferred onto 3D polycrystalline NiO. KPFM measurements show that single layer WS2 on SiO2 has a surface potential 75 mV lower than that of SiO2, whereas the surface potential of WS2 on NiO is 15 mV higher than NiO, indicating that WS2 could act as electron donor or acceptor depending on the 3D material it is interfaced with. Thus 2D and 3D materials can be organized into functional assemblies with electron flow controlled by the WS2 either as the electron donor or acceptor.

Jacobs, Christopher B.↗
DOE OSTI2016

Imaging of electrical response of NiO x under controlled environment with sub-25-nm resolution

The spatially resolved electrical response of rf-sputtered polycrystalline NiO x films composed of 40 nm crystallites was investigated under different relative humidity levels (RH). The topological and electrical properties (surface potential and resistance) were characterized using Kelvin probe force microscopy (KPFM) and conductive scanning probe microscopy at 0%, 50%, and 80% relative humidity with sub 25nm resolution. The surface potential of NiO x decreased by about 180 mV and resistance decreased in a nonlinear fashion by about 2 G when relative humidity was increased from 0% to 80%. The dimensionality of surface features obtained through autocorrelation analysis of topological, surface potential and resistance maps increased linearly with increased relative humidity as water was adsorbed onto the film surface. Spatially resolved surface potential and resistance of the NiO x films were found to be heterogeneous, with distinct features that grew in size from about 60 nm to 175 nm between 0% and 80% RH levels, respectively. Here, we find that the changes in the heterogeneous character of the NiO films are consistent through the topological, surface potential, and resistance measurements, suggesting that the nanoscale surface potential and resistance properties converge with the mesoscale properties as water is adsorbed onto the NiO x film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Multimodal probing of oxygen and water interaction with metallic and semiconducting carbon nanotube networks under ultraviolet irradiation

In this study, carbon nanotube (CNT) networks composed of semiconducting single wall nanotubes (s-SWNTs), metallic single wall nanotubes (m-SWNTs), and multiwall nanotubes (MWNTs) were exposed to O 2 and H 2 O vapor in the dark and under UV irradiation. Changes in film resistance and mass were measured in situ . In the dark, resistance of metallic nanotube networks increases in the presence of O 2 and H 2 O, whereas resistance of s-SWNT networks decreases. We find that UV irradiation increases the sensitivity of CNT networks to O 2 and H 2 O by more than an order of magnitude. Under UV irradiation, the resistance of metallic nanotube networks decreases in the presence of O 2 and H 2 O likely through the generation of free charge carriers. UV irradiation increases the gas/vapor sensitivity of s-SWNT networks by nearly a factor of 2 compared to metallic nanotube networks. Networks of s-SWNTs show evidence of delamination from the gold-plated QCM crystal, possibly due to preferential adsorption of O 2 and H 2 O on gold.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Effect of UV irradiation on the dynamics of oxygen and water interaction with carbon nanotubes

Carbon nanotube (CNT) films composed of semiconducting single wall nanotubes (s-SWNTs), metallic single wall nanotubes (m-SWNTs), and multiwall nanotubes (MWNTs) were exposed to O2 and H2O vapor in the dark and under UV irradiation. Changes in the film conductivity and mass were measured in situ. We find that UV irradiation increases the resistive response of CNT films to O2 and H2O by more than an order of magnitude. In m-SWNT and MWNT films, UV irradiation changes the sign of the resistive response to O2 and H2O by generating free charge carriers. S-SWNTs show the largest UV-induced resistive response and exhibit weakening of van der Waals interactions with the QCM crystal when exposed to gas/vapor.

adsorption↗
DOE OSTI2015

Carbon nanotubes grown on metal microelectrodes for the detection of dopamine

Microelectrodes modified with carbon nanotubes (CNTs) are useful for the detection of neurotransmitters because the CNTs enhance sensitivity and have electrocatalytic effects. CNTs can be grown on carbon fiber microelectrodes (CFMEs) but the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult. Metal wires are highly conductive and many metals have no intrinsic electrochemical activity for dopamine, so we investigated CNTs grown on metal wires as microelectrodes for neurotransmitter detection. In this work, we successfully grew CNTs on niobium substrates for the first time. Instead of planar metal surfaces, metal wires with a diameter of only 25 μm were used as CNT substrates; these have potential in tissue applications due to their minimal tissue damage and high spatial resolution. Scanning electron microscopy shows that aligned CNTs are grown on metal wires after chemical vapor deposition. By use of fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes exhibit higher sensitivity and lower ΔE p value compared to CNTs grown on carbon fibers or other metal wires. The limit of detection for dopamine at CNT-Nb microelectrodes is 11 ± 1 nM, which is approximately 2-fold lower than that of bare CFMEs. Adsorption processes were modeled with a Langmuir isotherm, and detection of other neurochemicals was also characterized, including ascorbic acid, 3,4-dihydroxyphenylacetic acid, serotonin, adenosine, and histamine. CNT-Nb microelectrodes were used to monitor stimulated dopamine release in anesthetized rats with high sensitivity. This research demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb microelectrodes, are useful for monitoring neurotransmitters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Carbon nanospikes grown on metal wires as microelectrode sensors for dopamine

Carbon nanomaterials are advantageous as electrodes for neurotransmitter detection, but the difficulty of nanomaterials deposition on electrode substrates limits the reproducibility and future applications. In our study, we used plasma enhanced chemical vapor deposition (PECVD) to directly grow a thin layer of carbon nanospikes (CNS) on cylindrical metal substrates. No catalyst is required and the CNS surface coverage is uniform over the cylindrical metal substrate. We characterized the CNS growth on several metallic substrates including tantalum, niobium, palladium, and nickel wires. Using fast-scan cyclic voltammetry (FSCV), bare metal wires could not detect 1 mu M dopamine while carbon nanospike coated wires could. Moreover, the highest sensitivity and optimized S/N ratio was recorded from carbon nanospike-tantalum (CNS-Ta) microwires grown for 7.5 minutes, which had a LOD of 8 +/- 2 nM for dopamine with FSCV. CNS-Ta microelectrodes were more reversible and had a smaller Delta E-p for dopamine than carbon-fiber microelectrodes, suggesting faster electron transfer kinetics. The kinetics of dopamine redox were adsorption controlled at CNS-Ta microelectrodes and repeated electrochemical measurements displayed stability for up to ten hours in vitro and over a ten day period as well. The oxidation potential was significantly different for ascorbic acid and uric acid compared to dopamine. Finally, growing carbon nanospikes on metal wires is a promising method to produce uniformly-coated, carbon nanostructured cylindrical microelectrodes for sensitive dopamine detection.

36 MATERIALS SCIENCE↗
DOE OSTI2015

In situ capping for size control of monochalcogenides (ZnS, CdS, and SnS) nanocrystals produced by anaerobic metal-reducing bacteria

Metal monochalcogenide quantum dot nanocrystals of ZnS, CdS and SnS were prepared by anaerobic, metal-reducing bacteria using in situ capping by oleic acid or oleylamine. Furthermore, the capping agent preferentially adsorbs on the surface of the nanocrystal, suppressing the growth process in the early stages, thus leading to production of nanocrystals with a diameter of less than 5 nm.

77 NANOSCIENCE AND NANOTECHNOLOGY↗