Abstract Nanotribological and electrochemical behavior of platinum-nanofluid interfaces are repor... more Abstract Nanotribological and electrochemical behavior of platinum-nanofluid interfaces are reported for aqueous suspensions of positively charged Al2O3 and negatively charged TiO2 nanoparticles, employing Quartz Crystal Microbalance (QCM) and cyclic voltammetry (CV) techniques. Tribotronic methods were employed to adjust the nanoparticles’ positions relative to Pt surface electrodes, and both voltammetry and tribological performance measures were observed to be highly sensitive to the adjustments. Interfacial friction levels were observed to be higher for both types of nanoparticles when electrostatically driven towards the surface. For electric fields of sufficient amplitude and duration, the TiO2 nanosuspension exhibited properties consistent with reversible electrophoretic deposition of the nanoparticles, accompanied by changes in the electrochemical attributes of the electrode itself. Overall, the study suggests a method for active tribological control and optimization of device performance in applications where suspensions of charged nanoparticles are present and can be exposed to external fields.
A frequency-agile 200 GHz/300 MHz DNP NMR spectrometer was constructed The spectrometer is based ... more A frequency-agile 200 GHz/300 MHz DNP NMR spectrometer was constructed The spectrometer is based on solid-state mm-wave devices and quasioptical components 200 GHz photonic band gap resonator was integrated into double-tuned NMR saddle coil 13 C DNP enhancement of ca.1,500 was obtained in synthetic diamond crystals at room temperature Resonator probehead provides the same electronic B 1 at up to 11 dB lower incident power using a quasioptical 200 GHz bridge and a Bruker Biospin Avance II spectrometer equipped with a standard Bruker 7 T wide-bore 89 mm magnet parked at 300.13 MHz 1 H NMR frequency. The mmW bridge built with all solid-state active components allows for the frequency tuning between ca. 190 to ca. 198 GHz with the output power up to 27 dBm (0.5 W) at 192 GHz and up to 23 dBm (0.2 W) at 197.5 GHz. Room temperature DNP experiments with a synthetic single crystal high-pressure high-temperature (HPHT) diamond (0.3×0.3×3.0 mm 3) demonstrated dramatic 1,500-fold enhancement of 13 C natural abundance NMR signal at full incident mmW power. Significant 13 C DNP enhancement (of about 90) have been obtained at incident mmW powers of as low as <100 μW. Further tests of the resonator performance have been carried out with a thin (ca. 100 μm thickness) composite polystyrene-microdiamond film by controlling the average mmW power at the optimal DNP conditions via a gated mode of operation. From these experiments, the PBG resonator with loaded Q≃250 and finesse provides up to 12-fold/11 db gain in the average mmW power vs. the non-resonant probehead configuration employing only a reflective mirror.
Addition of nanoparticles to liquid lubricants often leads to a reduction in both friction and we... more Addition of nanoparticles to liquid lubricants often leads to a reduction in both friction and wear rates for a wide range of solid-liquid-nanoparticle combinations. While the lubricating properties of nanoparticles are well documented, the detailed physical mechanisms remain to be fully explored. In a step toward such an understanding, the nano-tribological properties of gold surfaces immersed in aqueous suspensions of negatively charged SiO 2 nanoparticles were examined by means of Quartz Crystal Microbalance (QCM) and Atomic Force Microscopy methods. The SiO 2 nanoparticles were found to reduce the resistance to shear motion at the QCM's solid-liquid interface. The effect was observed to be concentration dependent, with ca. 1.5 wt% yielding the maximum reduction in shear. An electrokinetic mechanism is proposed whereby the loosely bound nanoparticles roll and/or slide on the surface, while upper layers of nanoparticles slip over the surface layer because of the repulsive electrostatic forces between the individual particles. The nanoparticles were observed to remove the electrode material from the gold surface and slightly increase the overall roughness with the major change happening within the first hour of the exposure. This study inherently provides insight into a complex interface of solid, liquid and nanoparticles at a nanometer scale.
Paramagnetic triplet centers produced by e-beam irradiation of synthetic microcrystalline Ib-type... more Paramagnetic triplet centers produced by e-beam irradiation of synthetic microcrystalline Ib-type high-pressure high-temperature (HPHT) diamonds were studied by X-band (9.4 GHz) continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy at X-band (9.4 GHz), pulsed EPR at X-and Q-bands (34 GHz), and fluorescence spectroscopies as a function of radiation fluences up to 5×10 19 e-/cm 2. EPR spectra of mostly "forbidden" ∆m s = 2 electronic spin transitions observed at g ≈ 4 (i.e., so-called half-field EPR spectra) reveal the presence of the main W15 triplet defects associated with the fluorescent negatively charged nitrogen-vacancy (NV-) centers as well as additional triplet spin centers identified as W16, W17, W18, and W33 that appear upon increasing the e-beam fluence. Consequent annealing at 1,400 o C significantly reduces the content of W17, W18, and W33 but not W15 and W16 defects. The efficacy of NVcenter fabrication as a function of fluence dependent e-beam irradiation is also reported.
Anodic aluminum oxide (AAO) ceramic membranes with macroscopically aligned and hexagonally packed... more Anodic aluminum oxide (AAO) ceramic membranes with macroscopically aligned and hexagonally packed nanopore architecture are attractive substrates for forming nanotubular lipid bilayers as well as sorption and catalytic media because of a tunable pore diameter, robust pore structure, and low fabrication cost. Here we employed continuous wave X-band (9 GHz) EPR of two pH-sensitive nitroxide radicals to assess acid–base properties AAO membranes prepared from low-cost commercial grade aluminum and compared those with commercial Anodisc membranes from Whatman, Ltd. The AAO membranes with pore diameters ≥58 ± 8 nm showed essentially the same pH inside the pores, pHint, as the bulk external solution, pHext, over the 0.1–3.0 M range of ionic strength. However, the apparent pKa of nitroxide probes inside the pores deviated from the bulk values for the nanopores of smaller diameters of ca. 29 and 18 nm. Specifically, for the latter nanopores the values of pHint were found to be 0.5–0.8 pH unit lower than the bulk p...
The sign of nanodiamond surface charge is discovered to profoundly impact friction at both nanome... more The sign of nanodiamond surface charge is discovered to profoundly impact friction at both nanometer and macroscopic scales.
Abstract Nanotribological and electrochemical behavior of platinum-nanofluid interfaces are repor... more Abstract Nanotribological and electrochemical behavior of platinum-nanofluid interfaces are reported for aqueous suspensions of positively charged Al2O3 and negatively charged TiO2 nanoparticles, employing Quartz Crystal Microbalance (QCM) and cyclic voltammetry (CV) techniques. Tribotronic methods were employed to adjust the nanoparticles’ positions relative to Pt surface electrodes, and both voltammetry and tribological performance measures were observed to be highly sensitive to the adjustments. Interfacial friction levels were observed to be higher for both types of nanoparticles when electrostatically driven towards the surface. For electric fields of sufficient amplitude and duration, the TiO2 nanosuspension exhibited properties consistent with reversible electrophoretic deposition of the nanoparticles, accompanied by changes in the electrochemical attributes of the electrode itself. Overall, the study suggests a method for active tribological control and optimization of device performance in applications where suspensions of charged nanoparticles are present and can be exposed to external fields.
A frequency-agile 200 GHz/300 MHz DNP NMR spectrometer was constructed The spectrometer is based ... more A frequency-agile 200 GHz/300 MHz DNP NMR spectrometer was constructed The spectrometer is based on solid-state mm-wave devices and quasioptical components 200 GHz photonic band gap resonator was integrated into double-tuned NMR saddle coil 13 C DNP enhancement of ca.1,500 was obtained in synthetic diamond crystals at room temperature Resonator probehead provides the same electronic B 1 at up to 11 dB lower incident power using a quasioptical 200 GHz bridge and a Bruker Biospin Avance II spectrometer equipped with a standard Bruker 7 T wide-bore 89 mm magnet parked at 300.13 MHz 1 H NMR frequency. The mmW bridge built with all solid-state active components allows for the frequency tuning between ca. 190 to ca. 198 GHz with the output power up to 27 dBm (0.5 W) at 192 GHz and up to 23 dBm (0.2 W) at 197.5 GHz. Room temperature DNP experiments with a synthetic single crystal high-pressure high-temperature (HPHT) diamond (0.3×0.3×3.0 mm 3) demonstrated dramatic 1,500-fold enhancement of 13 C natural abundance NMR signal at full incident mmW power. Significant 13 C DNP enhancement (of about 90) have been obtained at incident mmW powers of as low as <100 μW. Further tests of the resonator performance have been carried out with a thin (ca. 100 μm thickness) composite polystyrene-microdiamond film by controlling the average mmW power at the optimal DNP conditions via a gated mode of operation. From these experiments, the PBG resonator with loaded Q≃250 and finesse provides up to 12-fold/11 db gain in the average mmW power vs. the non-resonant probehead configuration employing only a reflective mirror.
Addition of nanoparticles to liquid lubricants often leads to a reduction in both friction and we... more Addition of nanoparticles to liquid lubricants often leads to a reduction in both friction and wear rates for a wide range of solid-liquid-nanoparticle combinations. While the lubricating properties of nanoparticles are well documented, the detailed physical mechanisms remain to be fully explored. In a step toward such an understanding, the nano-tribological properties of gold surfaces immersed in aqueous suspensions of negatively charged SiO 2 nanoparticles were examined by means of Quartz Crystal Microbalance (QCM) and Atomic Force Microscopy methods. The SiO 2 nanoparticles were found to reduce the resistance to shear motion at the QCM's solid-liquid interface. The effect was observed to be concentration dependent, with ca. 1.5 wt% yielding the maximum reduction in shear. An electrokinetic mechanism is proposed whereby the loosely bound nanoparticles roll and/or slide on the surface, while upper layers of nanoparticles slip over the surface layer because of the repulsive electrostatic forces between the individual particles. The nanoparticles were observed to remove the electrode material from the gold surface and slightly increase the overall roughness with the major change happening within the first hour of the exposure. This study inherently provides insight into a complex interface of solid, liquid and nanoparticles at a nanometer scale.
Paramagnetic triplet centers produced by e-beam irradiation of synthetic microcrystalline Ib-type... more Paramagnetic triplet centers produced by e-beam irradiation of synthetic microcrystalline Ib-type high-pressure high-temperature (HPHT) diamonds were studied by X-band (9.4 GHz) continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy at X-band (9.4 GHz), pulsed EPR at X-and Q-bands (34 GHz), and fluorescence spectroscopies as a function of radiation fluences up to 5×10 19 e-/cm 2. EPR spectra of mostly "forbidden" ∆m s = 2 electronic spin transitions observed at g ≈ 4 (i.e., so-called half-field EPR spectra) reveal the presence of the main W15 triplet defects associated with the fluorescent negatively charged nitrogen-vacancy (NV-) centers as well as additional triplet spin centers identified as W16, W17, W18, and W33 that appear upon increasing the e-beam fluence. Consequent annealing at 1,400 o C significantly reduces the content of W17, W18, and W33 but not W15 and W16 defects. The efficacy of NVcenter fabrication as a function of fluence dependent e-beam irradiation is also reported.
Anodic aluminum oxide (AAO) ceramic membranes with macroscopically aligned and hexagonally packed... more Anodic aluminum oxide (AAO) ceramic membranes with macroscopically aligned and hexagonally packed nanopore architecture are attractive substrates for forming nanotubular lipid bilayers as well as sorption and catalytic media because of a tunable pore diameter, robust pore structure, and low fabrication cost. Here we employed continuous wave X-band (9 GHz) EPR of two pH-sensitive nitroxide radicals to assess acid–base properties AAO membranes prepared from low-cost commercial grade aluminum and compared those with commercial Anodisc membranes from Whatman, Ltd. The AAO membranes with pore diameters ≥58 ± 8 nm showed essentially the same pH inside the pores, pHint, as the bulk external solution, pHext, over the 0.1–3.0 M range of ionic strength. However, the apparent pKa of nitroxide probes inside the pores deviated from the bulk values for the nanopores of smaller diameters of ca. 29 and 18 nm. Specifically, for the latter nanopores the values of pHint were found to be 0.5–0.8 pH unit lower than the bulk p...
The sign of nanodiamond surface charge is discovered to profoundly impact friction at both nanome... more The sign of nanodiamond surface charge is discovered to profoundly impact friction at both nanometer and macroscopic scales.
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Papers by Alex Smirnov