Application of Field Effect in Semiconductor-Electrolyte Interfaces for Studies of Surface Charge Layer Characteristics of Semiconductors and Semimetals

2021 ◽  
pp. 37-87
Keyword(s):  
Surface Charge ◽  
Field Effect ◽  
Charge Layer

Molecular Characterization of the Surface Excess Charge Layer in Droplets

2020 ◽  
Author(s):  
Victor Kwan ◽  
Styliani Consta
Keyword(s):  
Hydrogen Bonds ◽  
Surface Charge ◽  
Droplet Size ◽  
Chloride Ions ◽  
Total Charge ◽  
Excess Charge ◽  
Surface Excess ◽  
High Concentration ◽  
Dipole Orientation ◽  
Charge Layer

<div>Charged droplets play a central role in native mass spectrometry, atmospheric aerosols and in serving as micro-reactors for accelerating chemical reactions. The surface excess charge layer in droplets has often been associated with distinct chemistry. Using molecular simulations for droplets with Na+ and Cl- ions we have found that this layer is ≈ 1.5−1.7 nm thick and depending on the droplet size it includes 33%-55% of the total number of ions. Here, we examine the effect of droplet size and nature of ions in the structure of the surface excess charge layer by using molecular dynamics. We find that in the presence of simple ions the thickness of the surface excess charge layer is invariant not only with respect to droplet size but also with respect to the nature of the simple ions and it is not sensitive to fine details of different force fields used in our simulations.</div><div> In the presence of macroions the excess surface charge layer may extend to 2.0. nm. For the same droplet size, iodide and model hydronium ions show considerably higher concentration than the sodium and chloride ions. <br></div><div>We also find that differences in the average water dipole orientation in the presence of cations and anions in this layer are reflected in the charge distributions. Within the surface charge layer, the number of hydrogen bonds reduces gradually relative to the droplet interior where the number of hydrogen bonds is on the average 2.9 for droplets of diameter < 4 nm and 3.5 for larger droplets. The decrease in the number of hydrogen bonds from the interior to the surface is less pronounced in larger droplets. In droplets with diameter < 4 nm and high concentration of ions the charge of the ions is not compensated only by the solvent polarization charge but by the total charge that also includes the other free charge. This finding shows exceptions to the commonly made assumption that the solvent compensates the charge of the ions in solvents with very high dielectric constant. The study provides molecular insight into the bi-layer droplet structure assumed in the equilibrium partitioning model of C. Enke and assesses critical assumptions of the Iribarne-Thomson model for the ion-evaporation mechanism. <br></div>

Transport of Ions and Molecules in Nanofluidic Devices

2008 ◽  
Author(s):  
Rohit Karnik ◽  
Chuanhua Duan ◽  
Kenneth Castelino ◽  
Rong Fan ◽  
Peidong Yang ◽  
...  
Keyword(s):  
Surface Charge ◽  
Surface Area ◽  
Field Effect ◽  
Electrostatic Interactions ◽  
Surface Reactions ◽  
Molecular Transport ◽  
Large Surface Area ◽  
Ionic Concentrations ◽  
Nanofluidic Devices ◽  
Transport Of Ions

Interesting transport phenomena arise when fluids are confined to nanoscale dimensions in the range of 1–100 nm. We examine three distinct effects that influence ionic and molecular transport as the size of fluidic channels is decreased to the nanoscale. First, the length scale of electrostatic interactions in aqueous solutions becomes comparable to nanochannel size and the number of surface charges becomes comparable to the number of ions in the channel. Second, the size of the channel becomes comparable to the size of biomolecules such as proteins and DNA. Third, large surface area-to-volume ratios result in rapid rates of surface reactions and can dramatically affect transport of molecules through the channel. These phenomena enable us to control transport of ions and molecules in unique ways that are not possible in larger channels. Electrostatic interactions enable local control of ionic concentrations and transport inside nanochannels through field effect in a nanofluidic transistor, which is analogous to the metal-oxide-semiconductor field effect transistor. Furthermore, by controlling surface charge in nanochannels, it is possible to create a nanofluidic diode that rectifies ionic transport through the channel. Biological binding events result in partial blockage of the channel, and can thus be sensed by a decrease in nanochannel conductance. At low ionic concentrations, the effect of biomolecular charge is dominant and it can lead to an increase in conductance. Surface reactions can also be used to control transport of molecules though the channel due to the large surface area-to-volume ratios. Rapid surface reactions enable a new technique of diffusion-limited patterning (DLP), which is useful for patterning of biomolecules and surface charge in nanochannels. These examples illustrate how electrostatic interactions, biomolecular size, and surface reactions can be used for controlling ionic and molecular transport through nanochannels. These phenomena may be useful for operations such as analyte focusing, pH and ionic concentration control, and biosensing in micro- and nanofluidic devices.

Molecular Dopant‐Dependent Charge Transport in Surface‐Charge‐Transfer‐Doped Tungsten Diselenide Field Effect Transistors

2021 ◽  
pp. 2101598
Author(s):  
Jae‐Keun Kim ◽  
Kyungjune Cho ◽  
Juntae Jang ◽  
Kyeong‐Yoon Baek ◽  
Jehyun Kim ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Charge Transport ◽  
Surface Charge ◽  
Field Effect ◽  
Field Effect Transistors ◽  
Tungsten Diselenide

Nanofluidic Devices for Sensing and Flow Control

2006 ◽  
Author(s):  
Rohit Karnik ◽  
Kenneth Castelino ◽  
Chuanhua Duan ◽  
Rong Fan ◽  
Peidong Yang ◽  
...  
Keyword(s):  
Flow Control ◽  
Surface Charge ◽  
Gate Voltage ◽  
Field Effect ◽  
Electrostatic Interactions ◽  
Debye Length ◽  
Electrical Conductance ◽  
Nanofluidic Channels ◽  
Nanofluidic Devices ◽  
High Concentrations

Nanofluidics is concerned with fluidic channels that are typically 1–100 nm in size. We have fabricated nanofluidic devices using both 1-D silica nanotubes and 2-D nanochannels to explore transport phenomena at the nanoscale. Here we review our work on 2-D nanochannels that provide confinement in one dimension. Our work mainly deals with two aspects of nanofluidics (a) effects related to electrostatic interactions and (b) effects related to biomolecule size. Surface charge plays an important role in nanofluidic channels, when the channel size is comparable to the Debye length. Using both electrical conductance measurements and fluorescence imaging, we studied the effects of surface charge in our nanofluidic devices, and demonstrated that the environment in nanochannels is governed by surface charge. We modified the nanochannel surface and showed that these modifications can be sensed by measuring ionic conductance of the nanochannels. Further, binding reactions involving biomolecules can be sensed at both low and high ionic concentrations. Our results showed that at low concentrations, conductance is governed by biomolecule charge, while at high concentrations it is governed by biomolecule size. Based on electrostatic effects in nanochannels, we also developed a nanofluidic transistor for flow control. This metal-oxide-solution field effect transistor was fabricated by patterning a metal gate electrode over nanochannels, similar to a MOSFET. Just as the gate voltage of a MOSFET controls carrier concentration in the semiconductor, we demonstrated that the gate voltage in a nanofluidic transistor controls the concentration of ions and biomolecules in the nanochannel, and hence controls their transport. Our fabrication process uses standard lithography, and is amenable to making networks of nanochannels. It suggests that rationally designed nanofluidic networks could be developed using this process for applications in sample preparation, sensing and switching. We are currently studying flow control and switching using field-effect, as well as ionic transport using patterned surface charge in nanofluidic devices.

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