KR20150017422A - Graphene/Silicon Nanowire Molecular Sensor and the Fabricating Method and Method of Identification Using thereof - Google Patents

Abstract

A silicon/graphene molecular nanosensor comprises: a silicon substrate; a silicon nanowire coupled to the silicon substrate; and a graphene layer arranged on an upper portion of the silicon nanowire. A method to manufacture a silicon/graphene molecular nanosensor comprises: a first step of fabricating a silicon nanowire from a silicon substrate using an electrochemical etching method; and a second step of bonding graphene onto the silicon nanowire formed on the silicon substrate. Moreover, a method to identify the type of molecule using a silicon/graphene molecular nanosensor comprises: a step of repeatedly supplying and interrupting a target molecule at a predetermined cycle while applying a voltage to the silicon/graphene molecular nanosensor; and the other step of measuring a trend in resistance change, in terms of time, when the target molecule is repeatedly supplied and interrupted at the predetermined cycle. According to an embodiment of the present invention, a graphene/silicon nanowire molecular sensor can identify restoration to its original resistance at a high rate when the resistance changes at a high rate and gas supply is suspended, and exhibits performance as a molecular sensor to the target molecule through waveform analysis of a specific resistance graph to the target molecule.

Description

TECHNICAL FIELD The present invention relates to a graphene / silicon nanowire molecular sensor, a method of manufacturing the same, and a molecular identification method using the graphene / silicon nanowire molecular sensor.

The present invention relates to a graphene / silicon nanowire molecular sensor, a method of manufacturing the same, and a molecular identification method using the same. More particularly, the present invention relates to a molecular sensor using graphene grafted onto silicon nanowire, Lt; / RTI >

In recent years, nanowires have received great interest in industrial applications as well as their high importance in basic science research. In particular, vertically aligned silicon nanowires are considered to be ideal nano-based materials for next generation devices that perform functions such as condensing, power generation, energy storage, and sensors due to their high volume-to-area ratio advantages obtained from their vertical structures.

In order to realize the physico-chemical properties necessary for practical application as a future device using silicon nanowires, it is necessary to realize smooth electrical contact between the vertically aligned nanowires and the electrode.

In order to realize the physico-chemical properties necessary for practical application as a future device using silicon nanowires, it is necessary to realize smooth electrical contact between the vertically aligned nanowires and the electrode. To date, molecular sensors have been used for the deposition of uniform electrodes on the top of the nanowire, followed by deposition of various dielectric or organic materials on top of the nanowire. However, these methods have disadvantages in that the insulator or the organic material covers a certain portion of the nanowires on the upper part, thereby reducing the surface area in contact with the molecules, thereby decreasing the efficiency. Also, when a dielectric material is used for uniform metal electrode deposition on the upper part, the driving voltage is increased, which causes thermal problems and the device performance and durability are reduced.

In addition, future devices require flexible, bendable, and wearable devices that limit the use of dielectrics. Organic materials used to solve these problems are in ohmic contact with silicon nanowires, which makes it difficult to observe the resistance change due to the adsorption of minute amounts of molecules by increasing the dark current of the molecular sensor.

In order to solve the above problem, a molecular sensor capable of lowering the dark current of the sensor and increasing the on / off ratio and the efficiency by using the graphen having high electrical conductivity and flexibility, which can contact with the vertically and uniformly aligned silicon nanowires, .

SUMMARY OF THE INVENTION Accordingly, Silicon nanowires; Graphene nanoparticles comprising a graphene layer and a silicon / graphene molecular nanosensor comprising a graphene layer.

A further object of the present invention is to provide a method of manufacturing a silicon / graphene molecular nanosensor comprising the steps of: preparing a silicon nanowire from a silicon substrate by electrochemical etching and bonding graphene to the silicon nanowire; To provide.

Another object of the present invention is to provide a silicon / graphene nanosensor comprising a step of measuring a change in resistance with time, which is observed when a target molecule is supplied and cut under a voltage applied to the silicon / And to provide a method for identifying the kind of a molecule using a molecular nanosensor.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing the same.

According to an aspect of the present invention, there is provided a silicon / graphene molecular nanosensor comprising: a silicon substrate; Silicon nanowires bonded to the silicon substrate; And a graphene layer disposed on top of the silicon nanowire.

According to another aspect of the present invention, there is provided a method of fabricating a silicon / graphene molecular nanosensor, comprising: a first step of fabricating a silicon nanowire from a silicon substrate using an electrochemical etching process; And a second step of bonding the graphene to the silicon nanowire formed on the silicon substrate.

According to another aspect of the present invention, there is provided a silicon / graphene molecular nanosensor for identifying the type of a molecule using a silicon / graphene molecular nanosensor according to an embodiment of the present invention. Repeatedly supplying and shutting off the battery in a cycle; And measuring a change in resistance with time when the target molecule is repeatedly supplied and cut off at a predetermined cycle.

Other specific details of the invention are included in the detailed description and drawings.

The embodiments of the present invention have at least the following effects.

In other words, graphene is applied to a silicon nanowire-based molecular sensor to enhance the function and efficiency, and thus it is possible to apply it to various sensors.

It can be seen that the graphene / silicon nanowire molecular sensor according to the embodiment of the present invention is restored to the original resistance at a high speed when the resistance changes rapidly and the gas supply is stopped, and a specific resistance Waveform analysis of the graph can show performance as a molecular sensor for the target molecule.

The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the specification.

1A is a perspective view of a SEM image of a silicon nanowire according to an embodiment of the present invention.
1B is a top view of an SEM image of a silicon nanowire according to an embodiment of the present invention.
2 is a schematic diagram of a method for producing a silicon / graphene junction molecule nanosensor.
3 is a microscope image of a gold contact electrode deposited on a graphene layer according to an embodiment of the present invention.
4 is a microscope image of a comparative example in which graphene is not deposited compared with the present invention.
5 is a graph of current-voltage curves at the time of reverse voltage in a p-doped silicon / graphene junction molecular nanosensor according to an embodiment of the present invention.
FIG. 6 is a graph of resistance versus time for hydrogen gas using a silicon / graphene junction molecular nanosensor, in accordance with an embodiment of the present invention. FIG.
7 is a graph of change in resistance versus time for oxygen gas using a silicon / graphene junction molecular nanosensor, in accordance with an embodiment of the present invention.
8 is a graph of the change in resistance versus time for argon gas using a silicon / graphene junction molecular nanosensor, according to one embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

It is to be understood that when an element or layer is referred to as being "on" or " on "of another element or layer, All included. On the other hand, when a device is referred to as "directly on" or "directly above ", it does not intervene another device or layer in the middle.

The terms spatially relative, "below", "beneath", "lower", "above", "upper" May be used to readily describe a device or a relationship of components to other devices or components. Spatially relative terms should be understood to include, in addition to the orientation shown in the drawings, terms that include different orientations of the device during use or operation. For example, when inverting an element shown in the figure, an element described as " below or beneath "of another element may be placed" above "another element. Thus, the exemplary term "below" can include both downward and upward directions. The elements can also be oriented in different directions, in which case spatially relative terms can be interpreted according to orientation.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

According to an aspect of the present invention, there is provided a silicon / graphene molecular nanosensor comprising: a silicon substrate; Silicon nanowires bonded to the silicon substrate; And a graphene layer disposed on top of the silicon nanowire.

1A and 1B are a perspective view and a plan view, respectively, of an SEM image of a silicon nanowire according to an embodiment of the present invention.

Silicon nanowires may be formed on a silicon substrate. The silicon nanowire may be a structure that is integrally bonded to the silicon substrate.

A plurality of silicon nanowires disposed on the silicon substrate may be provided. The plurality of silicon nanowires may be arranged at regular intervals, and the spacing and height may be arranged at a constant height and spacing. The plurality of silicon nanowires may be a structure in which the heads of the silicon nanowires are bundled together to form a bundle (Fig. 1B).

The silicon nanowires disposed on the silicon substrate may be vertically aligned, but the present invention is not limited to the perpendicular angle of 90 degrees, and may include a case where the silicon nanowires are arranged obliquely.

Silicon nanowires may include silicon nanowires in which impurities are absent, but may be p-type or n-type silicon nanowires. The p-type silicon nanowires are doped with p-type impurities and the n-type silicon nanowires are doped with n-type impurities.

The n-type impurity may include a Group 5 chemical element such as phosphorus (P), arsenic (As). The p-type impurity may include a group III chemical element such as boron (B) and aluminum (Al).

The silicon / graphene molecular nanosensor according to an embodiment of the present invention is capable of responding to molecules, and is particularly sensitive to gas molecules. Gaseous molecules may be various gas molecules and may be, but are not necessarily limited to, hydrogen, oxygen, argon, carbon monoxide, carbon dioxide, nitrogen, ammonia, helium, neon, methane, ethane, propane or butane.

A graphene layer may be disposed over the silicon nanowires disposed on the silicon. Graphene is a conductive material with a thickness of one layer of atoms, with carbon atoms forming a honeycomb arrangement in two dimensions. Graphene is structurally and chemically very stable and is an excellent conductor with a faster charge mobility than silicon and can carry more current than copper.

The graphene disposed on the silicon nanowire may be a single layer graphene in the form of a thin film or a two layer graphene.

The silicon / graphene molecular nanosensor may further include contact electrodes on the silicon substrate and the graphene layer, respectively. The contact electrode may be a metal electrode, and the metal may include silver (Ag), gold (Au), copper (Cu), aluminum (Al), platinum (Pt)

The silicon / graphene molecular nanosensor according to an embodiment of the present invention may exhibit Schottky diode characteristics. Silicon / graphene molecular nanosensors with Schottky diode characteristics do not exhibit the accumulation effect unlike ordinary diodes, and their threshold voltages are relatively low, resulting in high efficiency in terms of the power of the circuit, resulting in less signal distortion, There is a characteristic that the efficiency can be increased.

A method of fabricating a silicon / graphene molecular nanosensor according to an embodiment of the present invention includes: a first step of fabricating a silicon nanowire from a silicon substrate using an electrochemical etching method; And a second step of bonding the graphene to the silicon nanowire formed on the silicon substrate.

2 is a schematic diagram of a method for producing a silicon / graphene junction molecule nanosensor.

More specifically, the first step of the electrochemical etching method comprises: (a) a step of treating a silicon substrate with silver nitrate and a hydrofluoric acid mixture in an air atmosphere to coat silver particles on the silicon surface;

(B) treating deionized water on the silver-coated silicon substrate to remove the remaining mixed solution on the silicon substrate; And

(C) of immersing and etching the silver-coated silicon substrate in a mixed solution of hydrofluoric acid, hydrogen peroxide and deionized water. When silver nitrate and hydrofluoric acid mixture is treated on a silicon substrate, phosphorus metal can be used as a catalyst in silicon etching. The silver nitrate has a concentration of 0.001 to 0.05 M, and the concentration of hydrofluoric acid can be mixed in the range of 1 to 10 M.

The silver particles placed on the silicon have a high electric affinity property, so they take the electrons from the silicon surface in contact with the silver particles rather than the silicon surface exposed to the solution, and the hydrogen peroxide in the solution is reduced to water by the electrons, . At the same time as the electrons are taken away, the silicon that acquires the holes is oxidized and the oxidized silicon can be removed by hydrofluoric acid. In this continuous reaction, the thin film coated with the silver particles etches the silicon and forms silicon nanowires between the silver foil pores. For example, when a mixed solution having a volume ratio of 1 / 0.2 / 2 of HF / H ₂ O ₂ / H ₂ O to silicon nanowires is etched at room temperature for 10 minutes, the length of the silicon nanowires may be about 17 μm have. Through the plan view, it can be seen that the head of the silicon nanowires is bundled together. However, if the volume ratio of HF / H ₂ O ₂ / H ₂ O is varied, the length of the finally formed silicon nanowires can be controlled. The degree of porosity can be controlled according to the concentration of hydrogen peroxide, and the arrangement of silicon nanowires can be controlled by adjusting the number of porous structures to be large.

After forming a silicon nanowire from a silicon substrate, graphene can be deposited and placed on the silicon nanowire.

The graphene can be manufactured by using a mechanical stripping method, a chemical vapor deposition method (CVD), an epitaxy method, or the like. The manufacturing process of graphene is described in a previous study [J. Appl. Phys. 113, 064305]

In order to transfer the graphene produced on the metal surface to another substrate, a supporting film which is a moving means can be used, which may be polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS) or the like, but not always limited thereto . PMMA, PDMS, etc., which are supporting films, are placed on the graphene / metal layer grown on the metal, and the metal can be removed by immersing the graphene / metal layer on the graphene / metal layer before transferring them to the silicon nanowire.

Illustratively, the graphene produced by the chemical vapor deposition method can be supported on PMMA, transferred to deionized water, and transferred onto the silicon nanowire. A sample that has been transferred to silicon nanowire is dried at room temperature to bond the graphene to the silicon nanowire.

Further comprising depositing a contact electrode on the silicon nanowire with the graphene transferred thereto.

The contact electrode may be a metal electrode, and the metal may include silver (Ag), gold (Au), copper (Cu), aluminum (Al), platinum (Pt)

A thermal deposition method, an electron beam deposition method, a sputtering deposition method, or the like may be used for depositing the contact electrode on the silicon nanowire to which the graphen is transferred, but the present invention is not limited thereto.

A method for identifying the type of a molecule using a silicon / graphene molecular nanosensor according to an embodiment of the present invention includes repeatedly supplying and blocking a target molecule at a predetermined cycle while a voltage is applied to the silicon / ; And measuring a change in resistance with time when the target molecule is repeatedly supplied and cut off at a predetermined cycle.

A forward voltage or an inverse voltage can be applied to the silicon / graphene molecular nanosensor. When a gas molecule to be measured as a target molecule is processed in a sensor, the type of gas molecule is judged by the tendency of resistance change with time .

Gaseous molecules may be various gas molecules and may be, but are not necessarily limited to, hydrogen, oxygen, argon, carbon monoxide, carbon dioxide, nitrogen, ammonia, helium, neon, methane, ethane, propane or butane.

When the target molecule is treated on the sensor by the on / off method at a constant cycle, a resistance graph according to the gas characteristic time appears. For example, there is a different resistance graph that appears when treating hydrogen, treating oxygen, or treating argon gas. Therefore, after confirming the reference to a specific gas, it is possible to confirm which gas is to be measured by comparing the graphs showing the resistance to the unknown gas.

Example

One. Manufacturing example  1: Silicon Nano-ray  making

The silicon to be used for the etching was a p-type Si wafer doped with boron and having a resistance of 1-10 Ohm / cm and a crystal orientation. Organic matters on the surface of the silicon wafer were removed with a 3: 1 mixture of sulfuric acid and hydrogen peroxide and rinsed with deionized water. As a first step to fabricate silicon nanowires, silicon wafers were immediately added to a mixed solution of 0.005 M of AgNO ₃ and 5 M of hydrofluoric acid at a slow rate for 1 minute in order to form phosphorus particles as an etch catalyst on the silicon surface Air atmosphere. The remaining solution on the prepared silicon wafer was sufficiently diluted with deionized water and removed. In the second step, the silicon wafer with the silver particles on the surface was immersed in a mixture of hydrofluoric acid, hydrogen peroxide and deionized water and etched at room temperature for 10 minutes. The concentration of the etching solution was adjusted so that the volume ratios of HF / H ₂ O ₂ / H ₂ O were 1 / 0.2 / 2, 1 / 0.5 / 2, 1 / 0.75 / 2 and 1/1/2.

2. Manufacturing example  2: Grapina  making

Generally, a large area of graphene was produced by using a well-known chemical vapor deposition (CVD) method. First, copper to be used as a catalyst layer is deposited on the substrate, and a methane-hydrogen mixed gas is reacted at a high temperature of about 1000 ° C. so that an appropriate amount of carbon is dissolved or adsorbed in the catalyst layer. After cooling, the carbon atoms contained in the catalyst layer are crystallized on the surface to form a graphene crystal structure. The graphene thus synthesized can be separated from the substrate by removing the catalyst layer and then used for a desired application. Detailed manufacturing and transcription processes are described in previous studies [J. Appl. Phys. 113, 064305 (2013).

3. Manufacturing example  3: Silicon Narrow - Grapina  Fabrication of bonding structure

A large area of graphene fabricated by chemical vapor deposition (CVD) was supported on PMMA, floated in deionized water, and transferred onto silicon nanowires. The transferred sample on the silicon nanowire was placed on a hot plate, dried at room temperature for 1 hour or more, and then further dried at 60 to 100 degrees for 3 hours or more.

4. Manufacturing example  4: Silicon Narrow - Grapina  Bonded structure Contact electrode  making

A contact electrode (Au, Ag, Pt, etc.) was deposited on the graphene by thermal evaporation, electron beam evaporation, sputtering or the like on the dried silicon nanowire-graphene. In one embodiment of the present invention, gold (Au) is deposited on the top and silver (Ag) is deposited on the bottom contact electrode.

FIG. 3 is a microscope image of a gold contact electrode deposited on a graphene layer according to an embodiment of the present invention, and FIG. 4 is a microscope image of a comparative example in which graphene is not deposited, compared with the present invention.

It can be seen that when the graphene is deposited, the gold contact electrode can be placed on the graphene. That is, a uniform and flat Au thin film is formed at the portion where graphen is present. On the other hand, when graphene was not deposited, it was confirmed that the gold was not arranged in a plane shape but arranged in a lump form on the silicon nanowire head. Graphene acts as a support membrane to prevent gold from penetrating into the silicon nanowires on the head of the silicon nanowire, helping the silicone head to evenly contact the metal. On the other hand, in the case where graphene is not present, it is difficult to expect uniform electrical contact since it is non-uniformly arranged on the silicon nanowire head.

4. Experimental Example  One: Grapina /silicon Narrow  Current-voltage characteristics of junction structure

As shown in FIG. 5, a junction structure of graphene / silicon nanowires with upper and lower electrodes formed and a current-voltage curve when voltage was applied are shown. Due to the metallic nature of graphene, it was confirmed that the current-voltage curve shows the characteristics of a schottky diode when it is bonded to a semiconductor silicon nanowire. The present invention exemplifies p-type silicon nanowires. The graphene / silicon nanowire molecular sensor, a p-type silicon nanowire, observed no current flow at forward voltage and rectified current flow only at reverse voltage.

As shown in the right panel diagram of FIG. 5, electrons are difficult to move due to a high potential barrier between the graphene and the p-type silicon nanowire at the forward voltage, and when the reverse voltage is applied, So that the intensity of the current increases.

4. Experimental Example  2: Depending on the type of gas Grapina / Measurement of resistance change in silicon molecule nanosensor

(1) Measurement of resistance change during hydrogen gas treatment

First, the applied voltage to the graphene / silicon nanowire molecular sensor manufactured by the methods of Production Examples 1 to 4 was -10 V, and hydrogen gas was periodically treated to evaluate the change rate of the sensor over time.

Referring to FIG. 6, it can be seen that the resistance of the graphene / silicon nanowire increased about 11 times when the hydrogen gas was supplied, and it took about 12 seconds for the 30% resistance increase to take place. When the supply of the hydrogen gas is stopped again, the time required for the 30% resistance to return to the original state takes about 0.15 second, and the time taken for the resistance to return to the original state takes 1 second at the maximum value of the resistance.

As a result, it was confirmed that the hydrogen gas was repeatedly flown and cut off repeatedly.

(2) Measurement of resistance change during oxygen gas treatment

Referring to FIG. 7, when oxygen gas was flowed in the same manner as hydrogen gas, the resistance of the graphene / silicon nanowire junction structure tended to decrease by 1.37 times (37). It was confirmed that it takes 3.5 seconds to reduce the resistance by 30%. When the supply of the oxygen gas was stopped again, it was confirmed that the resistance of 30% took about 0.15 seconds to return to the original state. In addition, when judging the graph waveform, it was confirmed that the resistance value is lower than hydrogen gas.

(3) Measurement of resistance change during argon gas treatment

Referring to FIG. 8, when the argon gas is flowed in the same manner as the hydrogen gas, the resistance of the graphene / silicon nanowire junction structure is reduced by 1.4 times (40%). 1.5 seconds was consumed. When the supply of the argon gas was stopped again, it was confirmed that the resistance of 30% takes about 0.07 seconds to return to the original state. A graphical waveform similar to that of oxygen gas is shown, but it can be seen that there is a difference in the difference between the widths at which the resistance value drops and the maximum value that increases when oxygen is supplied.

Claims (18)

A silicon substrate;
Silicon nanowires bonded to the silicon substrate; And
And a graphene layer disposed above the silicon nanowire. The method according to claim 1,
A silicon / graphene molecular nanosensor comprising a plurality of silicon nanowires. The method according to claim 1,
The silicon nanowires are vertically aligned silicon / graphene molecular nanosensors. The method according to claim 1,
The silicon nanowires are p-type or n-type doped silicon / graphene molecular nanosensors. The method according to claim 1,
Wherein the molecule is a gas molecule. The method according to claim 1,
Wherein the gas is hydrogen, oxygen, or argon. The method according to claim 1,
And a contact electrode on the silicon substrate and the graphene layer, respectively. 8. The method of claim 7,
Wherein the contact electrode is Ag, Au or Al. The method according to claim 1,
Wherein the graphene is a single-layer or two-layer graphene. The method according to claim 1,
Wherein the silicon / graphene molecular sensor exhibits schottky diode characteristics. A first step of fabricating a silicon nanowire from a silicon substrate by using an electrochemical etching method; And
A second step of bonding graphene to a silicon nanowire formed on the silicon substrate;
/ RTI > of claim < RTI ID = 0.0 > 1, < / RTI > 12. The method of claim 11,
The first step of electrochemical etching comprises: (a) treating a silicon substrate with silver nitrate and hydrofluoric acid in an air atmosphere to coat silver particles on the silicon surface;
(B) treating deionized water on the silver-coated silicon substrate to remove the remaining mixed solution on the silicon substrate; And
A step (c) of immersing and etching the silver-coated silicon substrate in a mixed solution of hydrofluoric acid, hydrogen peroxide and deionized water,
/ RTI > of claim < RTI ID = 0.0 > 1, < / RTI > 13. The method of claim 12,
Wherein the concentration of silver nitrate is 0.001 to 0.05 M in the step (a), and the concentration of hydrofluoric acid is 1 to 10 M in the step (a). 12. The method of claim 11,
And a third step of depositing a contact electrode on the silicon nanowire to which the graphene is transferred after the second step. 15. The method of claim 14,
Wherein the contact electrode is gold, silver or platinum. Repeatedly supplying and blocking target molecules at a predetermined cycle while a voltage is applied to the silicon / graphene molecular nanosensor; And
And measuring the change in resistance with time when the target molecules are repeatedly supplied and blocked at a predetermined cycle. 17. The method of claim 16,
Wherein the target molecule is a target gas, wherein the target gas is a silicon / graphene molecular nanosensor. 18. The method of claim 17,
Wherein the molecule of interest is hydrogen, oxygen, or argon.

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