Papers by Michael Stadermann
Pnas, 2008
Biological pores regulate the cellular traffic of a large variety of solutes, often with high sel... more Biological pores regulate the cellular traffic of a large variety of solutes, often with high selectivity and fast flow rates. These pores share several common structural features: the inner surface of the pore is frequently lined with hydrophobic residues, and the selectivity filter regions often contain charged functional groups. Hydrophobic, narrow-diameter carbon nanotubes can provide a simplified model of membrane channels by reproducing these critical features in a simpler and more robust platform. Previous studies demonstrated that carbon nanotube pores can support a water flux comparable to natural aquaporin channels. Here, we investigate ion transport through these pores using a sub-2-nm, aligned carbon nanotube membrane nanofluidic platform. To mimic the charged groups at the selectivity region, we introduce negatively charged groups at the opening of the carbon nanotubes by plasma treatment. Pressure-driven filtration experiments, coupled with capillary electrophoresis analysis of the permeate and feed, are used to quantify ion exclusion in these membranes as a function of solution ionic strength, pH, and ion valence. We show that carbon nanotube membranes exhibit significant ion exclusion that can be as high as 98% under certain conditions. Our results strongly support a Donnan-type rejection mechanism, dominated by electrostatic interactions between fixed membrane charges and mobile ions, whereas steric and hydrodynamic effects appear to be less important.
Fusion Science and Technology, 2013
Journal of electroanalytical chemistry
Optimization of electrodeposition conditions produced Ni(OH)2 deposits chargeable up to 1.84 +/- ... more Optimization of electrodeposition conditions produced Ni(OH)2 deposits chargeable up to 1.84 +/- 0.02 e- per Ni on and the resulting nickel oxide/hydroxide active material could subsequently deliver 1.58 +/- 0.02 e- per Ni ion (462 mAhr/g) over a potential range < 0.2 V. The ability of the “NiOOH” active material to deliver an approximately ideal charge and discharge facilitated a coulometric and thermodynamic analysis through which the charge/discharge mechanisms were determined from known enthalpies of formation. The (dis)charge states were confirmed with in-situ Raman spectroscopy. The mechanisms were additionally evaluated with respect to pH and potential dependence, charge quantities, hysteresis, and fluoride ion partial inhibition of the charge mechanism. The results indicate that the “NiOOH” (dis)charges as a solid-state system with mechanisms consistent with known nickel and oxygen redox reactions. A defect chemistry mechanism known for the LiNiO2 system also occurs for “...
Scanning Probe Microscopy, 2007
Fusion Science and Technology, 2013
Physics of Plasmas, 2015
ABSTRACT Fusion targets imploded on the National Ignition Facility are subject to hydrodynamic in... more ABSTRACT Fusion targets imploded on the National Ignition Facility are subject to hydrodynamic instabilities. These have generally been assumed to be seeded primarily by surface roughness, as existing work had suggested that internal inhomogeneity was small enough not to contribute significantly. New simulations presented here examine this in more detail, and consider modulations in internal oxygen content in CH plastic ablators. The oxygen is configured in a way motivated by measurement of oxygen in the shells. We find that plausible oxygen nonuniformity, motivated by target characterization experiments, seeds instability growth that is 3-5× bigger than expected from surface roughness. Pertinent existing capsule characterization is discussed, which suggests the presence of internal modulations that could be oxygen at levels large enough to be the dominant seed for hydrodynamic instability growth. Oxygen-seeded growth is smaller for implosions driven by high-foot pulse shapes, consistent with the performance improvement seen with these pulse shapes. Growth is somewhat smaller for planned future pulse shapes that were optimized to minimize growth of surface ripples. A possible modified specification for oxygen modulations is discussed, which is about 1/5 of the current requirement.
ABSTRACT Measurement of contact resistance and electronic transport properties of carbon nanotube... more ABSTRACT Measurement of contact resistance and electronic transport properties of carbon nanotubes are typically performed with static contacts. Movable contacts provide many advantages over static contacts but difficulties arise from an inability to postion the probe precisely on a nanotube, and to control the exact position of the electrical measurement due to thermal drift and piezoelectric hysteresis. The technique presented here allows characterization of the conductivity of different parts of a surface by applying a small voltage to a conductive AFM-tip and then scanning the surface in non-contact mode. A tuning fork is used as a force sensor to allow for the employment of a solid metal tip. The resistance of the surface is determined from the current pulses flowing between tip and sample whenever the tip intermittently makes contact with the surface. The advantage of this technique is that electrical and topographical data are taken simultaneously and are therefore in registry. A further advantage is the high number and density of data points taken at constant contact force during a single scan. Progress on novel transport measurement on carbon nanotubes will presented.
Abstract We researched how the chemical and physical properties of a plasma polymer fuel capsule ... more Abstract We researched how the chemical and physical properties of a plasma polymer fuel capsule change as they are exposed to ambient gases. The fuel capsules contain the deuterium fuel inside them, they serve as the outer shell for the fuel and act as a ablator ...
Science, 2003
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Review of Scientific Instruments, 2003
An atomic force microscopy-based method for line edge roughness measurement J. Appl. Phys. 113, 1... more An atomic force microscopy-based method for line edge roughness measurement J. Appl. Phys. 113, 104903 (2013) Atomic force microscope infrared spectroscopy on 15 nm scale polymer nanostructures Rev. Sci. Instrum. 84, 023709 (2013) Bias controlled capacitive driven cantilever oscillation for high resolution dynamic force microscopy Appl. Phys. Lett. 102, 073110 Friction measurement on free standing plates using atomic force microscopy Rev. Sci. Instrum. 84, 013702 A correlation force spectrometer for single molecule measurements under tensile load J. Appl. Phys. 113, 013503 Additional information on Rev. Sci. Instrum.
Physical Review B, 2004
We present local conductance measurements of carbon nanotube networks with nanometer scale resolu... more We present local conductance measurements of carbon nanotube networks with nanometer scale resolution and show that there are discrete drops in conductance that correspond to junctions of metallic nanotubes and semiconducting nanotubes. The anomalies of these networks compared to thin films are shown, and a new method of discerning between semiconducting and metallic single-wall carbon nanotubes is demonstrated.
Physical Review B, 2005
We have measured the decay of local conductance in single-wall carbon nanotubes directly using co... more We have measured the decay of local conductance in single-wall carbon nanotubes directly using conductance imaging atomic force microscopy. The decay lengths were in the range from 190 nm to well over 3 m. There are strong indications that these decay lengths are the result of depletion lengths around metallic/ semiconducting carbon nanotube junctions, and that they are related to defects in the tubes.
Journal of Electroanalytical Chemistry, 2014
Optimization of electrodeposition conditions produced Ni(OH) 2 deposits chargeable up to 1.84 ± 0... more Optimization of electrodeposition conditions produced Ni(OH) 2 deposits chargeable up to 1.84 ± 0.02 e À per Ni on and the resulting nickel oxide/hydroxide active material could subsequently deliver 1.58 ± 0.02 e À per Ni ion (462 mA h/g) over a potential range <0.2 V. The ability of the ''NiOOH'' active material to deliver an approximately ideal charge and discharge facilitated a coulometric and thermodynamic analysis through which the charge/discharge mechanisms were determined from known enthalpies of formation. The (dis)charge states were confirmed with in situ Raman spectroscopy. The mechanisms were additionally evaluated with respect to pH and potential dependence, charge quantities, hysteresis, and fluoride ion partial inhibition of the charge mechanism. The results indicate that the ''NiOOH'' (dis)charges as a solid-state system with mechanisms consistent with known nickel and oxygen redox reactions. A defect chemistry mechanism known for the LiNiO 2 system also occurs for ''NiOOH'' to cause both high activity and hysteresis. Similar to other cation insertion nickel oxides, the activity of the ''NiOOH'' mechanism is predominantly due to oxygen redox activity and does not involve the Ni 4+ oxidation state. The ''NiOOH'' was produced from cathodic electrodeposition of Ni(OH) 2 from nickel nitrate solutions onto highly oriented pyrolytic graphite at ideal electrodeposition current efficiencies and the deposition mechanism was also characterized.
Journal of Microelectromechanical Systems, 2000
ABSTRACT Suspended carbon nanotube devices are a promising platform for future bio-electronic app... more ABSTRACT Suspended carbon nanotube devices are a promising platform for future bio-electronic applications. Suspended carbon nanotube transistors have been previously fabricated in air; however all previous attempts to bring them into liquid failed. We analyze forces acting on the suspended nanotube devices during immersion into liquids and during device operation and show that surface tension forces acting on the suspended nanotubes during transfer into the liquid phase are responsible for the nanotube damage. We have developed a new strategy that circumvents these limitations by coating suspended nanotubes with a rigid inorganic shell in the gas phase. The coating reinforces the nanotubes and allows them to survive transfer through the interface. Subsequent removal of the coating in the solution phase restores pristine suspended nanotubes. We demonstrate that devices fabricated using this technique preserve their original electrical characteristics.
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Papers by Michael Stadermann