2.2.1. Electrochemical Reaction in the Presence of Template Molecule Coordinated with Counteranion
Halide anions are well known to form anionic supramolecular assemblies having an infinite repeating structure by coordination with iodine-containing neutral molecules [
24]. When halide anions are counteranions of conducting cation radical salts of donor molecules, stacking structures of donor molecules are influenced by the shape of the anionic supramolecular assemblies. By choosing halide anions and iodine-containing neutral molecules in good combination, donor molecules in conducting cation radical salts are one-dimensionally stacked and molecular conductor nanowires are formed. Such examples are found in (
EDT–TTF)
4•BrI
2•(
TIE)
5 (
1), (
HMTSF)
2•Cl
2•(
TIE)
3 (
2), (
PT)
2•Cl•(
DFBIB)
2 (
3) and
TSF•Cl•
HFTIEB (
4), where
EDT–TTF,
HMTSF,
PT and
TSF are donor molecules, while
TIE,
DFBIB and
HFTIEB are iodine-containing neutral molecules (
Figure 29) [
25,
26,
27]. Their crystal structures are shown in
Figure 30(a)–(d), respectively. In addition, the van der Waals outlines are drawn for
EDT–TTF,
HMTSF,
PT and
TSF (
Figure 31(a)–(d)) and for the supramolecular assemblies of BrI
2•(
TIE)
5 (pentagonal), Cl
2•(
TIE)
3 (hexagonal), Cl•(
DFBIB)
2 (parallelogram) and Cl•(
HFTIEB) (parallelogram) (
Figure 32(a)–32(d)). From
Figure 31 and
Figure 32, it can be easily understood how compatibility is accomplished between the donor molecules and supramolecular assemblies in
1–
4.
Figure 29.
The chemical structures of donor molecules (EDT–TTF, HMTSF, and PT) and iodine-containing neutral molecules (TIE, DFBIB, and HFIEB).
Figure 29.
The chemical structures of donor molecules (EDT–TTF, HMTSF, and PT) and iodine-containing neutral molecules (TIE, DFBIB, and HFIEB).
Figure 30.
Crystal structures for (a)
1, (b)
2, (c)
3, and (d)
4. The dotted lines denote the “halogen bond” based on Lewis acidity of the neutral iodine atoms. [Reproduced with permission from [
27]
ACSNano 2008,
2, 143–155. ©2008, American Chemical Society].
Figure 30.
Crystal structures for (a)
1, (b)
2, (c)
3, and (d)
4. The dotted lines denote the “halogen bond” based on Lewis acidity of the neutral iodine atoms. [Reproduced with permission from [
27]
ACSNano 2008,
2, 143–155. ©2008, American Chemical Society].
The resistivity measurements were performed along each axis of the crystals of 1–4, and in all case semiconducting behavior was observed. For 1, the activation energies (27 meV) were identical for both the directions parallel and perpendicular to the stacking of EDT–TTF molecules, but the resistivity (0.1 Ω cm) at room temperature in the parallel direction was 2000-times higher than that in the perpendicular direction. Thus, there is a large anisotropy of 2000 in the resistivity between the two directions. Also for 2 the same activation energies (45 meV) were obtained between the directions parallel and perpendicular to the donor stacking. The anisotropy in the resistivity is about 100 (the room-temperature resistivity in the parallel direction is 1 Ω cm). For 3, the activation energies were about 300 meV, and the anisotropy was about 10. For 4, the resistivities at room temperature were 1 × 105Ω cm in the donor stacking direction, and 5 × 105 and 1 × 1013Ω cm in the two perpendicular directions, resulting in a resistivity anisotropy of 108. The activation energies were about 300–500 meV in every direction. The high anisotropy observed in these crystals originates from the molecular wire-bundle structures that prevent current flow perpendicular to the stacking direction of the donor molecules. Despite very anisotropic conduction, the activation energies are almost identical in the parallel and perpendicular directions to the donor stacking for 1 and 2. This coincidence of the same activation energies for the directions parallel and perpendicular to the donor stacking is not insignificant, because the band calculation predicts that the band filling is metallic along the donor stacking direction, while there is no effective transfer integral perpendicular to the donor stacking direction. This phenomenon is already known for K2Pt(CN)4•Br0.3•(H2O)n and is considered to be due to lattice defects that limit the conduction along the stacking direction, effectively cutting the nanowire.
Figure 31.
The van der Waals outlines are drawn for (a)
EDT–TTF, (b)
HMTSF, and (c)
PT, and (d)
TSF. [Reproduced with permission from [
27]
ACSNano 2008,
2, 143–155. ©2008, American Chemical Society].
Figure 31.
The van der Waals outlines are drawn for (a)
EDT–TTF, (b)
HMTSF, and (c)
PT, and (d)
TSF. [Reproduced with permission from [
27]
ACSNano 2008,
2, 143–155. ©2008, American Chemical Society].
Figure 32.
The structures of supramolecular assemblies with van der Waals outlines. The assemblies show (a) pentagonal, (b) hexagonal, and (c and d) parallelogram-shaped channels in crystals
1,
2,
3, and
4, respectively. [Reproduced with permission from [
27]
ACSNano 2008,
2, 143–155. ©2008, American Chemical Society].
Figure 32.
The structures of supramolecular assemblies with van der Waals outlines. The assemblies show (a) pentagonal, (b) hexagonal, and (c and d) parallelogram-shaped channels in crystals
1,
2,
3, and
4, respectively. [Reproduced with permission from [
27]
ACSNano 2008,
2, 143–155. ©2008, American Chemical Society].
2.2.2. Electrochemical Deposition on Gold Wafer Electrode Coated with Porous Alumina Sheet
Porous alumina membranes prepared by anodizing Al in the presence of an acidic electrolyte have ordered honeycomb structure characterized by an excellent uniformity in diameter (20 nm to several hundred nm) and spacing of the holes [
28,
29]. A thin Au or Ag film was sputter-deposited on one side of the porous alumina membrane to serve as an electrode within nano-size reaction space. By electrochemical reactions using Au or Ag electrodes coated with nanoporous alumina membrane, Au and Bi
2Te
3 nanowires with a diameter of 40 to 280 ± 30 nm were deposited into the alumina holes [
30,
31,
32]. This method was applied to the preparation of molecule conductor nanowires and nanotubes. A CH
3CN solution of NMe
4•[Ni(dmit)
2] (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato) in the presence of NMe
4•ClO
4 as supporting electrolyte was electrochemically oxidized with a constant current of 5–10 μA cm
–2 using an Au film coated with nanoporous (diameter = 49 ± 2 nm) alumina membrane as the working electrode and Pt wire (diameter = 1 mm) as the counter electrode (
Figure 33) [
33].
The [Ni(dmit)
2]
– ion is oxidized to [Ni(dmit)
2]
δ– (0 < δ < –1) and deposited as a salt of NMe
4•[Ni(dmit)
2]
2 into the alumina pores of the anode.
Figure 34 shows SEM images of the top and side views of NMe
4•[Ni(dmit)
2]
2 nanowire arrays after the alumina membrane is partially dissolved by the treatment with 0.1 M NaOH aqueous solution. The top view (
Figure 34(a)) of the nanowire arrays shows that more than 95% of the pores are filled with the nanowires of NMe
4+ salts, which are densely packed with each other. The tips of the nanowires are almost at the same level and the average diameter of the nanowires is 49 ± 2 nm, which corresponds to the pore diameter of the alumina membrane. The side view (
Figure 34(b)) of the nanowires shows that they stand up straight on the Au substrate and separate from each other. The nanowires are about 30 μm long, which also corresponds to the thickness of the alumina membrane, and are continuous.
Figure 33.
Schematic illustration of the fabricating nanowire arrays of crystalline NMe
4•[Ni(dmit)
2]
2 using a porous alumina template. [Reproduced with permission from [
33]
J. Phys. Chem. B 2004,
108, 13638–13642. ©2004, American Chemical Society].
Figure 33.
Schematic illustration of the fabricating nanowire arrays of crystalline NMe
4•[Ni(dmit)
2]
2 using a porous alumina template. [Reproduced with permission from [
33]
J. Phys. Chem. B 2004,
108, 13638–13642. ©2004, American Chemical Society].
Looking at the side-view in more detail, the nanowires have periodic corrugated structures with a period of about 30 nm, and look like straight pearl chains. This feature is due to the oscillation of voltage of about 2 mV with a period of about 25 s during the electrochemical deposition under a galvanostatic condition. It is conceivable that such an oscillation of electric current or voltage originates from the following process: the electrochemical deposition of the [Ni(dmit)2]δ– ions occurs in a confined one-dimensional environment, so the speed of the diffusion of the electric active species, [Ni(dmit)2]– ion is heavily reduced. As the electrochemical deposition is a diffusion-controlled process, the [Ni(dmit)2]– ion is rapidly consumed, and the concentration abruptly decreases in the front of the growing surface. The equilibrium electrode potential increases with decreasing the [Ni(dmit)2]– ion concentration. At this time the trace impurity of [Ni(dmit)2]2– competes with the reaction. During the consumption of [Ni(dmit)2]2–, the [Ni(dmit)2]– ion concentration adjusts itself in the front of the deposition interface and its electrochemical deposition is restarted. This process is repeated until the alumina pores are fully filled.
Figure 34.
(a) SEM image of the top view of NMe
4•[Ni(dmit)
2]
2 nanowire arrays after the template was partially dissolved. The average pore diameter of template: 49 ± 2 nm. (b) SEM image of the side view of nanowire arrays in the template with the pore diameter of 49 ± 2 nm. [Reproduced with permission from [
33]
J. Phys. Chem. B 2004,
108, 13638–13642. ©2004, American Chemical Society].
Figure 34.
(a) SEM image of the top view of NMe
4•[Ni(dmit)
2]
2 nanowire arrays after the template was partially dissolved. The average pore diameter of template: 49 ± 2 nm. (b) SEM image of the side view of nanowire arrays in the template with the pore diameter of 49 ± 2 nm. [Reproduced with permission from [
33]
J. Phys. Chem. B 2004,
108, 13638–13642. ©2004, American Chemical Society].
From the EDS measurement along the axis of a single nanowire, the compositions at different locations through the nanowire are all the same. The observed XRD peaks are indexed to NMe4•[Ni(dmit)2]2 in monoclinic crystal system with the same cell parameters to those of the corresponding single crystal obtained by the electrochemical oxidation with a conventional electrode under the same conditions. These results indicate that the nanowires incorporated into the alumina pores are crystalline NMe4•[Ni(dmit)2]2 salts.
The electrical conducting properties of the nanowires were investigated by conductive atomic force microscopy (C–AFM).
Figure 35 shows one example of the
I–
V curves obtained by the C–AFM data measured on the top of nanowire arrays with the average pore diameter of 49 ± 2 nm. Above ± 3 V the current goes beyond the limit, but in the narrow voltage range of ± (1–3) V the
I–
V curve is straight and gives electrical conductivities of 0.1–10 S cm
–1. This comparatively high electrical conductivity suggests that the long axis of the nanowire corresponds to the conduction direction, that is, the stacking direction of the [Ni(dmit)
2]
2– ions.
The use of Au film electrode coated with the porous alumina membrane was also applied to the preparation of nanotubes of β’’–(
BEDT–TTF)
4•[H
2O•Fe(C
2O
4)
3]•C
6H
5NO
2 [
34], whose bulk crystal exhibits metallic conductivity down to low temperature and superconductivity near 7 K [
35]. A nitrobenzene solution containing
BEDT–TTF, (NMe
4)
3•[Fe(C
2O
4)
3]•3H
2O and 18-crown-6-ether was electrochemically oxidized using an alumina/Au film as an anode and a Pt sheet as a cathode with a constant current of 1 μA cm
–1 for about 72 h. After the reaction completion the alumina membrane was dissolved in 2 M NaOH aqueous solution to get free standing arrays of nanotubes of the
BEDT–TTF salt on the Au film.
Figure 35.
The C–AFM data of the NMe
4•[Ni(dmit)
2]
2 nanowire arrays. After the template was partially dissolved, the C–AFM data was measured on the top of nanowire arrays with the average pore diameter of 49 ± 2 nm. [Reproduced with permission from [
33]
J. Phys. Chem. B 2004,
108, 13638–13642. ©2004, American Chemical Society].
Figure 35.
The C–AFM data of the NMe
4•[Ni(dmit)
2]
2 nanowire arrays. After the template was partially dissolved, the C–AFM data was measured on the top of nanowire arrays with the average pore diameter of 49 ± 2 nm. [Reproduced with permission from [
33]
J. Phys. Chem. B 2004,
108, 13638–13642. ©2004, American Chemical Society].
The morphology of the nanotube arrays are characterized by SEM and TEM.
Figure 36(a)–(c) show SEM images of the nanotube arrays prepared by the electrochemical deposition into the alumina pores with a diameter of 200 nm. From the cross-section image in
Figure 36(a), the average length of the nanotube is about 30 μm. The top view of the nanotube arrays in
Figure 36(b) shows that all of the nanotubes have open ends and a dense arrangement. The details of the ends of the nanotubes are shown in
Figure 36(c) and also by the TEM image in
Figure 36(d). The outer diameter of the nanotubes is about 200 nm and the thickness is 29 ± 5 nm. No macroscopic defect is observed in all of the nanotubes. The diameter of the nanotubes can be tuned by changing the diameter of the alumina pore, and the length can be controlled by changing the electrochemical oxidation time.
The nanotubes have the same molecular composition to that of the single crystal of β’’–(BEDT–TTF)4•[H2O•Fe(C2O4)3]•C6H5NO2 as shown by the EDX measurement result and from the comparison of Raman spectra and XRD patterns between the nanotube and single crystal. In particular, the presence of mainly (00l) reflections in the XRD pattern indicates that the c–axis of the crystal of this BEDT–TTF salt is directed perpendicular to the Au film.
The electrical conductivities of the nanotubes were measured.
Figure 37(a) and
Figure 37(b) show the representative
I–
V characteristics of the nanotube arrays and single nanotubes measured at room temperature, respectively. From the slope of the straight line in the
I–
V curve in
Figure 37(a), the electrical conductivity of the nanotube array is estimated to be about 1.4 × 10
–5 S cm
–1. To measure the electrical conductivity of the single nanotube, a device based on an individual nanotube was fabricated on a SiO
2/Si substrate with a method based on an Au–wire mask (inset in
Figure 37(b)). The slope of the straight line in the
I–
V curve (
Figure 37(b)) gives the electrical conductivity of about 2.9 × 10
–5 S cm
–1. The temperature dependence of the normalized resistivity measured along the length direction of the nanotube arrays shows a metallic behavior in the temperature range of 10 K to room temperature (
Figure 37(c)).
Figure 36.
SEM images (a–c), and TEM image (d) of the nanotube arrays. [Reproduced with permission from [
34]
Adv. Mater. 2006,
18, 2753–2757. ©2006, Wiley-VCH Verlag GmbH & Co. KGaA].
Figure 36.
SEM images (a–c), and TEM image (d) of the nanotube arrays. [Reproduced with permission from [
34]
Adv. Mater. 2006,
18, 2753–2757. ©2006, Wiley-VCH Verlag GmbH & Co. KGaA].
Figure 37.
I–V characteristics of (a) nanotube arrays and (b) a single nanotube. The inset of (a) shows schematically the circuit used in the measurement and the inset of (b) shows an optical image of the single-nanotube device. The bar length is 10 μm. (c) The temperature dependence of the normalized resistance of nanotube arrays. [Reproduced with permission from [
34]
Adv. Mater. 2006,
18, 2753–2757. ©2006, Wiley-VCH Verlag GmbH & Co. KGaA].
Figure 37.
I–V characteristics of (a) nanotube arrays and (b) a single nanotube. The inset of (a) shows schematically the circuit used in the measurement and the inset of (b) shows an optical image of the single-nanotube device. The bar length is 10 μm. (c) The temperature dependence of the normalized resistance of nanotube arrays. [Reproduced with permission from [
34]
Adv. Mater. 2006,
18, 2753–2757. ©2006, Wiley-VCH Verlag GmbH & Co. KGaA].
Almost the same electrical conductivities between the nanotube array and the single nanotube are observed. This implies that the nanotube array is composed of many single nanotubes being connected to both electrodes in parallel, so their electrical conductivities are simply cumulative. However, the electrical conductivity measured by either the nanotube array or the single nanotube is 106-times lower than that of the single crystal. Two main reasons are considered to explain this feature. Firstly, since the length direction of the nanotube is parallel to the c–axis, the I–V characteristics are measured along the c–axis, which is the direction of low electrical conductivity (the highly-conducting direction is on the ab–plane). Secondly, the crystalline nature of the nanotubes is not as perfect as that of a single crystal, and this may lower the conductivity across the grain boundaries. Furthermore, some effects of the measurement set-up may also be responsible for the decreasing conductivity.
2.2.3. Electrochemical Deposition on Silicon Wafer Electrode Coated with Phospholipid Membrane
The use of silicon wafer electrode could occasionally lead to the formation of micro/nano-wires of molecular conductors, as described in 2.1.3. However, a reliable silicon wafer-based method favoring the selective growth of nanowires was necessary. Li and his colleagues modified one-side surface of a silicon wafer with a photochemically-bridged multi-lamellar membrane of phospholipid molecules having two conjugated carbon-carbon triple bonds in each long alkyl chain, 1,2-bis(10,12-tricosadiynoyl)-
sn-glycero-3-phosphocholine
(DC8,9PC) (
Figure 38) and succeeded in the formation of Ni(OH)
2-based nano-size sublayers incorporated in the open space between the lamellar layers by the electrochemical reduction of an Ni(NO
3)
2 aqueous solution using this modified silicon wafer as an electrode [
36].
Figure 38.
The chemical structure of 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC).
Figure 38.
The chemical structure of 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC).
As is obvious from the SEM image in
Figure 39, this multi-lamellar membrane coated on the silicon wafer possesses nano-size voids surrounded by
DC8,9PC molecules, which can be utilized as the reaction space for an electrochemical oxidation of donor molecules such as to give molecular conductor nanowires selectively. This was actually realized by the electrochemical oxidation of two bent donor molecules, ethylenedithio- and ethylenedioxy-tetrathiafulvalenoquinone-1,3-dithiolemethides (
EDT–TTFVO [
16] and
EDO–TTFVO [
37]) (
Figure 40) in the presence of a supporting electrolyte of NBu
4•FeCl
4 or NBu
4•FeBr
4.
The electrochemical oxidation of a PhCl–EtOH (9:1, v/v) solution of
EDT–TTFVO and NBu
4•FeCl
4 and of a dichloroethane (DCE) solution of
EDO–TTFVO and NBu
4•FeBr
4 was performed using both electrodes of the as above modified silicon wafer and a native silicon wafer as a reference, respectively. By using the modified silicon wafer electrode nanowires were obtained in the former case and nanosticks in the latter case.
Figure 41 and
Figure 42 show their SEM images. The diameter of the nanowires is ţ20 nm and that of the nanosticks is about 100 nm. On the other hand, the use of a native silicon wafer gave thin plate-shaped crystals with molecular formulas of (
EDT–TTFVO)
4•(FeCl
4)
2 and (
EDO–TTFVO)
2•FeBr
4•(DCE)
0.5, respectively. Their crystal structures are shown in
Figure 43 and
Figure 44. In (
EDT–TTFVO)
4•(FeCl
4)
2, all columns along the
a–axis are built on the repeated units of one trimer and one monomer, all of which have a head-to-tail stacking mode to each other. Several short S•••S contacts (<3.80 Å of van der Waals contact distance) between donors of neighboring stacks along the
b–axis, resulting in a two-dimensional network of S•••S interactions. The crystal of (
EDO–TTFVO)
2•FeBr
4•(DCE)
0.5 contains donor molecules alternating with (FeBr
4– ion + DCE molecule) layers. The two crystallographically-independent donor molecules form side-by-side arrays along the
c–axis with several short S•••S(O) contacts, suggesting a strong intermolecular interaction along this direction. In the
bc–plane the donor molecules construct two identical diagonal stacks along the [0 2 1] and [0 2 –1] directions. This donor array resembles a
β’’–type packing motif. The calculated Fermi surface is two-dimensional and has a closed-ellipse.
Figure 39.
SEM image of
DC8,9PC multilayers coated on a (001)–oriented silicon wafer. [Reproduced with permission from [
16]
New J. Chem. 2007,
31, 519–527. ©2007, the Royal Society of Chemistry and the Centre National de la Recherche Scientifique].
Figure 39.
SEM image of
DC8,9PC multilayers coated on a (001)–oriented silicon wafer. [Reproduced with permission from [
16]
New J. Chem. 2007,
31, 519–527. ©2007, the Royal Society of Chemistry and the Centre National de la Recherche Scientifique].
Figure 40.
The chemical structure of ethylenedithio- and ethylenedioxy-tetrathiafulvalenoquinone-1,3-dithiolemethides (EDT–TTFVO and EDO–TTFVO).
Figure 40.
The chemical structure of ethylenedithio- and ethylenedioxy-tetrathiafulvalenoquinone-1,3-dithiolemethides (EDT–TTFVO and EDO–TTFVO).
The nanowires and nanosticks show the same Raman spectra to those of the corresponding single crystals (
Figure 45(a) and (b)), so their molecular formulas also apply to the nano-size materials. The growth of the nano-size materials is considered to occur by the following process: the donor molecules migrate from the solution/membrane interface to the silicon electrode surface via the nano-size channels delimited by the long alkyl chains of
DC8,9PC molecules. They are oxidized on the silicon electrode surface to produce the conducting salts by combination with FeCl
4– or FeBr
4– ions, being largely present in the vicinity of the hydrophilic silicon surface. As the growing salt is in contact with FeCl
4– or FeBr
4– ions located in inter-headgroup areas, the growth can continue but should adapt to nano-size channels. Even when the growing salt reaches the membrane surface, the growth still continues towards the formation of long nanowires lying parallel to the membrane surface, as evidenced by SEM images.
Figure 41.
SEM image of (
EDT–TTFVO)
4•(FeCl
4)
2 nanowires. [Reproduced with permission from [
16]
New J. Chem. 2007,
31, 519–527. ©2007, the Royal Society of Chemistry and the Centre National de la Recherche Scientifique].
Figure 41.
SEM image of (
EDT–TTFVO)
4•(FeCl
4)
2 nanowires. [Reproduced with permission from [
16]
New J. Chem. 2007,
31, 519–527. ©2007, the Royal Society of Chemistry and the Centre National de la Recherche Scientifique].
Figure 42.
SEM image of (EDO–TTFVO)2•FeBr4•(DCE)0.5 nanosticks.
Figure 42.
SEM image of (EDO–TTFVO)2•FeBr4•(DCE)0.5 nanosticks.
Figure 43.
Stacking views of (EDT–TTFVO)4•(FeCl4)2 along the (a) a− and (b) b−axes.
Figure 43.
Stacking views of (EDT–TTFVO)4•(FeCl4)2 along the (a) a− and (b) b−axes.
Figure 44.
Stacking views of (EDO–TTFVO)2•FeBr4•(DCE)0.5 (X = Cl, Br) along the (a) b− and (b) c−axes.
Figure 44.
Stacking views of (EDO–TTFVO)2•FeBr4•(DCE)0.5 (X = Cl, Br) along the (a) b− and (b) c−axes.
Figure 45.
Raman spectra of nanowires or nanosticks (A) and single crystals (B) for (a) (EDT–TTFVO)4•(FeCl4)2 and (b) (EDO–TTFVO)2•FeBr4•(DCE)0.5.
Figure 45.
Raman spectra of nanowires or nanosticks (A) and single crystals (B) for (a) (EDT–TTFVO)4•(FeCl4)2 and (b) (EDO–TTFVO)2•FeBr4•(DCE)0.5.
As expected from the stacking structures above, the room-temperature conductivity of (EDT–TTFVO)4•(FeCl4)2 is very low (10–3–10–1 S cm–1) and the conducting behavior is semiconducting (activation energy is about 35 meV). On the other hand, (EDO–TTFVO)2•FeBr4•(DCE)0.5 shows high room-temperature conductivity (1.8 S cm–1) and metallic behavior down to 4 K. The conducting properties of the nano-size materials, in particular, (EDO–TTFVO)2•FeBr4•(DCE)0.5 nanosticks, which are expected to be also metallic down to low temperature, are of much interest. The conductivity measurement was done by contacting two probes with the nano-size materials sticking out of the membrane surface, but it was not successful because of resistivity drift. To know the intrinsic conducting properties of a single nanowire or nanostick, it is necessary to fabricate the following device: the part stuck out of the membrane is removed by an appropriate method, and the fattened surface is covered with a gold film. The resistivity of nanowires or nanosticks incorporated into the membrane between the silicon and gold electrodes should be measured, which corresponds to the resistivity of a single nanowire or nanostick separated from each other by insulating phospholipid molecules.