Kavalenka, et al. (2012) Ballistic and non-ballistic gas flow through ultrathin nanopores, Nanotechnology 23: 145706.
This paper explores the physics of gas flow through pnc-Si membranes. The manuscript first establishes that the flow thorugh the membrane pores is molecular in nature. This means that the distance between gas molecules is large compared to the pore dimensions so that collisions between the gas molecules can be ignored and only collisions with the pore walls change affect gas molecule trajectories. The manuscript further establishes that because the membranes are molecularly thin, many molecules pass through pores without contacting the walls at all. This ballisitic component of the flow serves to further enhance the permeance of pnc-Si to gas molecules. As with liquid transport through the membranes, the permeance of gas through pnc-Si is shown to be many orders of magnitude higher than through conventional thick nanoporous membranes.
Kavalenka, et al. (2012) Chemical capacitive sensing using ultrathin flexible nanoporous electrodes, Sensors & Actuators B: Chemical, 162: 22-26
Capacitive chemical sensors feature a chemically-sensitive polymer material sandwiched between two electrode plates. In the presence of the chemical to be sensed, the polymer swells, the spacing between the electrode plates increases, and the capacitance goes up. As electrodes are typically impermeable to the chemical to be detected, chemical access to the polymer is often a challenge. We address this challenge by using gold-plated pnc-Si as a permeable electrode. The paper illustrates the reversible detection of hexane, toluene and acetone
This paper develops analytical and computational models of diffusion through membranes with known pore distributions and illustrates that ultrathin membranes, but not conventional thick membranes, are capable of high resolution separations by diffusion far from equilibrium. While the theory is predictive of experiments with small molecules, large molecules are more hindered than theory predicts. The difference between theory and experiments may be explained by protein adsorption that reduces pores sizes.
Ishimatsu et al. (2010) Ion-Selective Permeability of UltrathinNanopore silicon Membrane as Studied Using Nanofabricated Micropipet Probes. Analytical Chemistry 82:7127-7134
Shigeru Amemiya’s laboratory at the University of Pittsburgh used a highly senstitive electrochemical probe to measure small ion diffusion through pnc-Si without interference from stagnant layers. The paper demonstrates that pnc-Si membranes have a permeability to small monovalent ions (< 1/10th of pore size) that is predictable from membrane geometry alone. By contrast, multivalent and/or large (>30% of pore size) ions experience hindrance from steric and electrostatic effects.
This paper reports a new method for carbon deposition on silicon that results in the growth of graphene layers inside of the pores of pnc-Si. Very precise control (~ nm resolution) of pore sizes is obtainable by the technique. Interestingly the modified membranes do not exhibit enhanced water flow despite similarities to carbon nanotube membranes that are known to exhibit enhanced flow. The manuscript also demonstrates that carbonized membranes exhibit high resolution separations and high hydraulic permeabilities as seen with unmodified pnc-Si in Gaborski et al.
This paper reports the extraordinary hydraulic permeabilty of pnc-Si membranes and illustrates that water flow rates are consistent with the predictions of classic fluid theory. The manuscript also demonstrates the ability of pnc-Si to separate nanoparticles, including proteins, with better than 5 nm resolution and with little loss or dilution of the filtrate. The work establishes the capacity of pnc-Si membranes to serve as dead-end filters for the high resolution, low loss separation of nanomaterials.
In this work we measure cell growth, adhesion and viability on pnc-Si and compare the values to standard cell culture substrates. Results show that pnc-Si has no detrimental effects on cells and actually enhances growth rates for some cell types. The manuscript also demonstrates pnc-Si dissolves in biological media in a non-toxic fashion at rates that can be controlled through surface treatments. The work establishes the viability of pnc-Si as a new platform for cell culture and tissue engineering.
Kim et al. (2008) A Structure-Permeability Relationship of Ultrathin Nanoporous Silicon Membrane: A Comparison with the Nuclear Envelope J. Am. Chem. Soc. 130:4230-4231.
Striemer, et al. (2007) Charge- and size-based separation of macromolecules using ultrathin silicon membranes. 2007 Nature. 445:749-753.