KR20110049568A - Diode comprising nitrogen-doped carbon nanotubes - Google Patents

Abstract

PURPOSE: A diode with nitrogen-doped carbon nano tubes is provided to make the structure of a carbon nano tube facing a diode in a pentagon carbon ring, thereby enhancing the current-voltage features of the diode. CONSTITUTION: A diode comprises first and second carbon nano tubes. One-ends of the first and second carbon nano tubes are caped. At least one nitrogen element is doped in the caped part. A carbon nano tube is a metallic carbon nano tube. The carbon nano tube has an arm chair structure or a zigzag type.

Description

Diodes containing carbon nanotubes doped with nitrogen atoms {Diode comprising Nitrogen-doped carbon nanotubes}

The present invention relates to a diode comprising a carbon nanotube doped with nitrogen atoms.

Silicon-based semiconductor technology, which has been the main technology in the electronics industry for the last half century, is approaching the limitation of technology due to the rapid increase in information throughput, high performance and high integration of electronic devices. According to Moore's law that the density of silicon-based semiconductor products will increase four times every three years, device technology with a minimum line width of 10 nm or less is expected within the next 10 years.

The miniaturization of line width in semiconductor technology is expected to bring technical limitations in all areas such as traditional manufacturing process technology, device characteristics and reliability. For example, the manufacturing process technology is a photolithography (Photo-lithograpy) process is a typical limitation technology, the light source currently applied to the semiconductor process can not provide the degree of miniaturization pattern required by the increased integration. As a light source having a smaller wavelength, an electron beam or X-ray, etc. has been studied, but it is inevitable to apply expensive technologies and equipments and reduce productivity. The crisis of the limitations of such technology is more serious in the field of device characteristics and reliability. Semiconductor circuits consist of transistors and metal interconnects connecting transistors. In conventional silicon transistors, leakage current caused by quantum mechanical tunneling and heat generated during operation are technical factors that limit integration. Even in metal wiring, the increase in current density resulting from the miniaturization of the line width exceeds the allowable range of existing metal materials (eg Al or Cu).

As an alternative for overcoming the limitations of such technology, electronic devices based on low-dimensional carbon allotrope such as carbon nanotubes are attracting attention. Carbon nanotubes can exhibit high quality semiconductor or metal properties in ultra-fine structures and can be free from the limitations of photolithography through partial or total self assembly processes. In addition, carbon nanotubes have potentials of 10 times greater electron mobility than conventional silicon-based transistors, thus reducing power consumption and heat generation in integrated circuits. A current density of more than 1,000 times can be tolerated.

As such, carbon nanotubes have excellent physical properties compared to conventional semiconductor or metal materials, and are highly attracted attention as an alternative to the existing technologies because they are likely to overcome the technical limitations of existing materials due to miniaturization.

An object of the present invention is to provide a diode comprising a carbon nanotube doped with nitrogen atoms.

The present invention as a means for solving the above problems, at least one end is capped, and includes a first and second carbon nanotubes doped with one or more nitrogen atoms in the capping portion,

The first and second carbon nanotubes provide diodes in which respective capping portions are disposed to face each other.

In the diode according to the present invention, nitrogen atoms doped in carbon nanotubes generate new energy levels near the Fermi level. The energy level produced by the nitrogen atoms in the diode of the invention acts as a conducting channel. Accordingly, tunneling current and negative differential resistance (NDR) behavior may appear between the carbon nanotubes disposed opposite to each other of the diode of the present invention.

The present invention includes at least one end capped and the first and second carbon nanotubes doped with one or more nitrogen atoms in the capping portion,

The first and second carbon nanotubes relate to diodes in which respective capping portions are disposed to face each other.

Hereinafter, the diode of the present invention will be described in more detail.

In the diode of the present invention, two capped carbon nanotubes, each of which is doped with one or more nitrogen atoms in each capping portion, are disposed to face each other. In the diode of the present invention, the doped nitrogen atom affects the molecular orbital (MO) of the carbon nanotubes. As a result, tunneling currnet and NDR (Negative Differential Resistance) behaviors appear between the two carbon nanotubes arranged oppositely. Accordingly, the diode of the present invention may exhibit, for example, the behavior of an Esaki diode (or tunneling diode).

In the present invention, in particular, through the control of the number of nitrogen atoms doped and the doping position of the capping portion, the diode can, if necessary, provide a single switching current-voltage characteristic or a multi switching current-voltage characteristic. The characteristics can be controlled to show. The term "single switching current-voltage characteristic" used in the present invention, for example, as shown in the accompanying Figure 7, in the current-voltage curve (I-V curve) of the diode, according to the applied voltage It refers to the case where the NDR peak appears, and "multi-switching current-voltage characteristic" refers to the applied voltage in the diode's current-voltage curve IV curve, for example, as shown in FIG. 11 or 12. This means that more than one NDR peak appears. In the present invention, the diodes exhibiting the above characteristics may be referred to as single switching diodes or multi switching diodes, respectively.

In the present invention, it is preferable that the first and second carbon nanotubes included in opposing states are metallic CNTs. Carbon nanotubes, as shown in the accompanying Figure 1, the graphite sheet (graphite sheet) has a structure that is rounded to a nano size diameter. Such carbon nanotubes are single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT: double-walled CNT) and multi-walled carbon nanotubes (MWCNT: Multi) depending on the number of layers of graphite sheets rolled up. -walled CNTs, and may be classified into armchair, zigzag, and chiral structures depending on the curl angle. Carbon nanotubes have two structures having high asymmetry, specifically, an armchair structure (FIG. 2A) and a zigzag structure (FIG. 2B). Such a structure of carbon nanotubes may be represented by a chiral vector (C _h ) connecting two points on the graphite lattice in the graphite sheet. As shown in FIG. 3, in the chiral vector, an arbitrary origin O may be taken as a starting point of the vector, and a point that comes into contact with the origin when it is curled may be represented as an end point A of the vector. Meanwhile, when the carbon nanotubes are represented by chiral vector indices (m, n), their diameters and chiral angles may be represented by Equations 1 and 2 below.

[Equation 1]

[Equation 2]

In Formula 1, a _cc represents a bond distance between carbon and carbon in the carbon nanotube. Typically, the bond distance between carbon and carbon in graphite is about 1.421 kPa, about 1.44 kPa in C ₆₀ fullerene, and about 1.4 kPa in carbon nanotubes, but this value may vary depending on the diameter of the nanotube.

The chiral angle is an angle between the unit vector a ₁ and the chiral vector (C _h = n a ₁ + m a ₂ ), which represents the chirality of the carbon nanotubes. Specifically, when the chiral vector index is (n, 0), the chiral angle of the nanotube is 0 °, and this tube is defined as a zigzag structure. On the other hand, when the chiral vector index is (n, n), the chiral angle is 30 °, which is defined as the armchair structure, and the structure of the carbon nanotubes other than the zigzag and the armchair is defined as the chiral structure. .

The electrical properties of carbon nanotubes may vary depending on the diameter and chiral angle of the nanotubes. The electronic structure of the carbon nanotubes is based on a graphite structure having an electrically two-dimensional structure, and can be calculated by introducing a one-dimensional electrical structure considering only the axial direction of the nanotube, and specifically, a chiral vector index (n, m Can be classified into carbon nanotubes having metallicity and carbon nanotubes having semiconductivity. In other words, in the chiral vector index, when nm is a multiple of 3, the movement of free electrons is completely free, and carbon nanotubes react like metals, and when nm is not a multiple of 3, band gaps are formed like semiconductors. In order to move, energy must be supplied externally to overcome this.

In the present invention, it is preferable to use carbon nanotubes having metallic properties among the electrical properties of the carbon nanotubes as described above. When semiconducting carbon nanotubes are applied in the present invention, the desired current-voltage (I-V) characteristics may not be effectively exhibited. In the present invention, as long as the carbon nanotubes are metallic, the structure is not particularly limited, and armchair-type or zigzag-type carbon nanotubes can be used. Specifically, in the present invention, carbon nanotubes having a chiral vector index of (a, a) or (b, 0) can be used.

In addition, in the chiral vector index, a and b preferably satisfy the conditions of the following general formulas (1) and (2).

[Formula 1]

a = 5 to 16,

[Formula 2]

b = 3 × j

In the above, j represents an integer of 3 to 10.

In the above, when the chiral vector index is represented by (a, a), the carbon nanotubes have an armchair structure. If the value of a is less than 5, carbon nanotubes may be difficult to produce. If it exceeds 16, the diameter of the carbon nanotubes is too large, there is a fear that the doping efficiency of nitrogen in the manufacturing process is reduced.

On the other hand, when the chiral vector index is represented by (b, 0), the carbon nanotubes have a zigzag structure. At this time, if j is less than 3, carbon nanotubes themselves may be difficult to produce. When it exceeds 10, the doping efficiency of nitrogen may decrease due to the increase in the diameter of the carbon nanotubes.

At least one end of each of the first and second carbon nanotubes included in the diode of the present invention is capped. In one aspect of the invention, the first and second carbon nanotubes may be capped by fullerene hemispheres. Fullerene is a spherical molecule composed of a plurality of carbon atoms, and is composed of a hexagonal carbon ring and a pentagonal carbon ring. Such fullerene is composed of an even number of carbons, such as 60, 70, 74, 76 and 78, in the present invention can be used fullerene hemispheres of various sizes depending on the size of the carbon nanotubes. In the present invention, carbon nanotubes are preferably capped with a fullerene hemisphere consisting of 60 carbon atoms.

In the present invention, various capping part structures are possible according to the structure of the carbon nanotubes. For example, in the present invention, when the carbon nanotube has an armchair structure, and the end thereof is capped by a C ₆₀ fullerene hemisphere, a pentagonal carbon ring is positioned at the top of the capping portion. In addition, in the present invention, when the carbon nanotubes have a zigzag structure and their ends are capped with C ₆₀ fullerene hemispheres, hexagonal carbon rings are positioned at the top of the capping portion.

In the present invention, it is possible to arrange a variety of nanotubes according to the structure of the capping portion of the carbon nanotubes as described above. For example, in one aspect of the present invention, the top ends of the first and second carbon nanotube capping portions disposed opposite to each other may have a pentagon facing carbon ring structure. In another aspect of the present invention, the top ends of the first and second carbon nanotube capping portions disposed opposite to each other may also have a hexagonal carbon ring structure (hexagon facing).

In the present invention, the opposite arrangement structure of the carbon nanotubes is not limited to the above-described structure. For example, in the present invention, it is also possible for the capping portions of the first and second carbon nanotubes to be disposed to have different structures (ex. Pentagon-hexagon facing).

In the present invention, it is particularly preferred that the structure of the uppermost capping portion of the first and second carbon nanotubes arranged opposite to each other is a pentagon facing carbon ring. By setting the structure of the oppositely arranged carbon nanotubes to the pentagonal carbon rings in this way, the current-voltage characteristics of the obtained diode can be further improved.

In the present invention, each of the capping sites of the first and second carbon nanotubes is doped with one or more nitrogen atoms. The Ezaki characteristics of the diode of the present invention are attributable to molecular intrinsic properties such as molecular energy level alignment with Fermi level and response to applied bias voltage. In other words, the nitrogen atom doped in the carbon nanotube in the present invention, affects the electronic structure, specifically the structural arrangement and electron transport properties. Accordingly, a new conducting channel is formed in the oppositely disposed carbon nanotubes, thereby increasing the NDR behavior and the tunneling current.

In the present invention, the amount of nitrogen atoms doped into the carbon nanotubes is not particularly limited as long as the amount of the nitrogen atoms doped in the carbon nanotubes to induce the NDR behavior and tunneling current between the carbon nanotubes arranged opposite. However, in consideration of the current-voltage characteristics of the finally formed diode, the doping level of the nitrogen atom is preferably as low as possible. Specifically, when a pentagonal carbon ring is present at the top of the capping portion of the carbon nanotubes, the capping portion may be doped with 10 or less, preferably 5 or less nitrogen atoms. In the above, the position of the doped nitrogen atoms may be one or more of the carbon atoms present in the first and second carbon layers, preferably one or more of the carbon atoms present in the second carbon layer, as described below. The specific meaning of a "first carbon layer" and a "second carbon layer" will be described later. In addition, when the hexagonal carbon ring is present at the top of the capping portion in the carbon nanotube of the present invention, the capping portion may be doped with 12 or less, preferably 6 or less nitrogen atoms. Even in this case, the doping position of the nitrogen atom may be at least one of the carbon atoms present in the first and second carbon layers, preferably at least one of the carbon atoms present in the second carbon layer. In the present invention, when the doping level of the nitrogen atom is excessively increased, there is a fear that the Ezaki characteristics of the final diode may not be effectively exhibited.

On the other hand, the doping position of the nitrogen atom in the present invention is also not particularly limited, but in consideration of the characteristics of the final diode, it is preferable that the doping position is near the capping portion of each carbon nanotube. Specifically, the doping position of the nitrogen atom is preferably at least one of the carbon atoms present in any one of the carbon layers of the first to eighth carbon layers based on the uppermost carbon ring of the nanotube capping portion.

The term "carbon layer" used in the present invention is defined as follows. First, a plane made of carbon atoms included in a carbon ring located at the top of the capping portion of the carbon nanotubes is defined as the first carbon layer. Subsequently, in the opposite direction of the capping portion in the carbon nanotube, an imaginary plane made of carbon atoms directly bonded to carbon atoms present in the first carbon layer is defined as a second carbon layer. Subsequently, in the same manner, an imaginary plane made up of carbon atoms directly bonded to carbon atoms present in the second carbon layer in the opposite direction to the capping portion of the carbon nanotubes is transferred to the third carbon layer and again to the third carbon layer. The hypothetical plane formed by the carbon atoms to which it belongs and carbon atoms directly bonded in the opposite direction to the capping portion is defined as the fourth carbon layer, and the fifth, sixth, seventh, eighth and ninth carbon layers are defined in the same manner.

Such details will be described below with reference to the accompanying drawings.

4A shows a state in which the armchair-type carbon nanotubes are capped by the fullerene (C ₆₀ ) hemisphere, in which a pentagonal carbon ring is formed at the top of the capping portion. exist. In this case, five carbon atoms (①) present in the uppermost pentagonal carbon ring are defined as belonging to the first carbon layer, and the five carbon atoms are directly bonded in the opposite direction to the capping portion. The imaginary plane formed by (②) is defined as the second carbon layer, and the carbon atom (②) existing in the second carbon layer and ten carbon atoms (③) directly bonded in the opposite directions to the capping part. The virtual plane formed is defined as a third carbon layer, and the fourth carbon layer ④, the fifth carbon layer ⑤, and the sixth carbon layer ⑥ are sequentially defined in the same manner. On the other hand, Figure 4 (b) is attached according to one aspect of the present invention, the zig-zag carbon nanotubes are shown capped by a C ₆₀ fullerene hemisphere, in this case a hexagonal carbon ring at the top of the capping portion Is present. Also in this case, the definition method of a carbon layer is the same as that of the case of FIG.

In the present invention, the doping position of the nitrogen atom may be one or more of the carbon atoms present in the first to eighth carbon layers among the carbon layers defined as above. In the present invention, more preferably, the doping position of the nitrogen atom may be at least one of the carbon atoms present in the first and second carbon layers, and more preferably at least one of the carbon atoms present in the second carbon layer. . That is, in the present invention, the doping position of the nitrogen atom may include: a carbon atom belonging to a carbon ring (first carbon layer) existing at the top of the carbon nanotube capping portion; And it may be one or more carbon atoms selected from the group consisting of carbon atoms (second carbon layer) directly bonded to the carbon atoms, more preferably a carbon ring (top carbon) present at the top of the capping portion of the carbon nanotubes One or more carbon atoms of the carbon atoms (second carbon layer) directly bonded to the carbon atoms belonging to the layer).

In the present invention, when the doping position of the nitrogen atom is too far from the capping portion, there is a fear that the I-V characteristics of the diode may not be effectively controlled.

However, in the present invention, the number of nitrogen atoms doped in the carbon nanotubes and their doping positions may be changed in consideration of the current-voltage characteristics of the desired diode.

For example, to implement a single switching diode in the present invention, each carbon nanotube may be doped with one nitrogen atom. In this case, the nitrogen atom is present in the capping portion of each of the first and second carbon nanotubes, preferably the carbon atoms present in each of the first and second carbon layers, more preferably in the second carbon layer. It may be doped with one of the carbon atoms. That is, in the present invention, when the single switching diode is to be implemented, the number of nitrogen atoms to be doped may be one, and the position may be any one of the carbon atoms present in the first and second carbon layers or the second carbon layer. It can be one.

In the present invention, when one nitrogen atom is doped in each of the first and second carbon nanotubes, various arrangements are possible according to the nitrogen atom doping position. For example, in the present invention, the first and second carbon nanotubes may be disposed with each of the doped nitrogen atoms facing each other (eclipsed conformation). 5 (a) and 5 (b), respectively, show a state in which five doped nitrogen atoms are disposed to face each other in an arrangement in which pentagonal and hexagonal carbon rings are arranged at the top of the capping unit.

In another aspect of the present invention, in the carbon nanotubes arranged opposite to each other, each of the nitrogen atoms doped may be arranged at a predetermined angle to each other. 6 (a) and 6 (b) are attached to carbon nanotubes in which pentagonal and hexagonal carbon rings are formed at opposite capping portions, respectively, when the doped nitrogen atoms form an angle of 180 ° with respect to each other. Indicates. In the present invention, in addition to the above-described arrangement, various nitrogen atoms may be arranged, and the specific arrangement form thereof is not particularly limited.

On the other hand, when implementing the multi-switching diode in the present invention, the carbon nanotube, two or more, preferably two, three or four, more preferably three or four nitrogen atoms may be doped. have. In this case, the nitrogen atom is at least two of the carbon atoms present in the capping portion of each of the first and second carbon nanotubes, preferably the second to fifth carbon layers, more preferably the second carbon layer, It may preferably be doped with two, three or four carbon atoms, more preferably two or three carbon atoms. That is, when the present invention intends to implement a multi-switching diode, the number of nitrogen atoms doped may be two or more, preferably two, three or four, more preferably three or four, The position may be selected from the second and fifth carbon layers, or carbon atoms present in the second carbon layer. In the present invention, in particular, by doping nitrogen atoms to three or four carbon atoms of the carbon atoms present in the second carbon layer of the capping portion of each carbon nanotube, it is possible to implement the multi-switching characteristics more effectively.

In order to more effectively implement the multi-switching characteristics of the diode in the present invention, the nitrogen atoms doped in the same carbon layer is preferably disposed adjacent to each other. The term "nitrogen atoms disposed adjacent to each other" used in the present invention means that when a nitrogen atom is doped to any one carbon atom belonging to a specific carbon layer, the nitrogen atom is located next to the carbon atom doped in the same carbon layer. It means the case where another nitrogen atom is doped by a carbon atom. For example, FIG. 9 shows a side view of a diode in which first and second carbon nanotubes each doped with three nitrogen atoms are disposed to face each other, and FIG. The diode is viewed from the axial direction of the carbon nanotubes. In addition, in FIG. 10, (a) shows the case where all three nitrogen atoms doped in the 2nd carbon layer are arrange | positioned adjacently, (b) is a state where nitrogen atoms are not adjacent, ie, it is arrange | positioned in the separated state. The case is shown.

In the present invention, when three or more nitrogen atoms are doped into the carbon nanotubes, as shown in FIG. 10 (a), all of the doped nitrogen atoms are preferably disposed adjacent to each other. As described above, in the present invention, since the nitrogen atoms are disposed adjacent to each other, the diode can more effectively exhibit the multi-switching characteristic.

In the present invention, the distance between the first and the second carbon nanotubes disposed opposite (ex. D of FIGS. 5 and 6), specifically, the distance between the carbon rings at the top of the capping portion is 1.0 kPa to 5.0 kPa, preferably May be about 2.0 kPa to 4.0 kPa, more preferably about 3.0 kPa. If the distance between the first and the second carbon nanotubes is outside the above range, there is a fear that the current-voltage characteristics of the diode may not be effectively implemented.

In the present invention, the method of manufacturing the diode is not particularly limited.

In the present invention, for example, by using a variety of techniques known in the art, by producing two carbon nanotubes doped with a nitrogen atom, at least one end is capped, and then disposed to face each other to produce a diode Can be.

Until now, a variety of methods for growing carbon nanotubes have been developed, and in the present invention, all of these methods can be used. Representative examples of the method for producing carbon nanotubes include the arc discharge method, laser ablation method, chemical vapor deposition (CVD), pyrolysis of Hydrocarbon or HiPCO (The High Pressure Carbon Monoxide Process).

In the present invention, two approaches are possible to prepare carbon nanotubes doped with nitrogen atoms. The first approach is to dope nitrogen directly during the synthesis of carbon nanotubes, and the second approach is to synthesize carbon nanotubes and then process them to introduce nitrogen atoms.

More specifically, in one aspect of the present invention, one or more nitrogen atoms are doped and at least one end is capped by a high temperature synthesis method to produce carbon nanotubes.

Examples of the high temperature synthesis method include an arc discharge method or a laser ablation method. In this method, carbon nanotubes are grown after evaporating a carbon source (usually graphite) at a high temperature. For example, in the case of using the arc discharge method, the carbon source (e.g. graphite rod) is evaporated using an arc (electric-arc), for example, under a helium gas atmosphere in the presence of a catalyst. Nanotubes can be prepared. In this method, for example, carbon nanotubes doped with nitrogen atoms can be produced by evaporating a catalyst including a graphite rod while the atmosphere in the arc discharge device is controlled to a nitrogen-helium atmosphere (ex. R Droppa, Jr., et al., J. Non-Crystalline Solids 299, 874 (2002)). In addition, the synthesis of carbon nanotubes doped with nitrogen atoms is also possible by using a composite electrode (anode) containing a nitrogen-containing precursor in a helium atmosphere (M. Glerup, J., et al., Chem. Phys. Lett . 387, 193 (2004).

In the case of laser ablation, a pulsed laser is used to ablate the catalyst including the graphite target, and to rapidly remove the vaporization product with a gas such as nitrogen. Doped carbon nanotubes can be synthesized.

In addition, it is possible to prepare carbon nanotubes doped with nitrogen atoms through a low temperature synthesis method such as chemical vapor deposition (CVD), and in particular, this method produces multi-walled carbon nanotubes doped with nitrogen atoms. Suitable for doing Through low temperature synthesis, methods for preparing nitrogen doped carbon nanotubes are described in various literatures (ex. R. Sen, BC, et al., Chem. Phys. Lett. 287, 671 (1998); M. Glerup, M. Castignolles). , et al., Chem. Commun. 20. 2542 (2003); M. Terrones, et al., Appl. Phys. Lett. 75, 3932 (1999); M. Yudasaka, et al., Carbon 35, 195 ( 1997); C. Tang, et al., Carbon 42, 2625 (2004), and the like.

In the field to which the present invention pertains, in addition to the above manner, various methods of preparing carbon nanotubes doped with nitrogen atoms are known (ex. Bobby G. Sumpter, et al., " Nitrogen-Mediated Carbon Nanotube Growth: Diameter Reduction". , Metallicity Bundle Dispersability, and Bamboo-like Structure Formation ", ACSNANO, Vol. 1, No. 4, 369-375 (2007); F. Villalpando-Paez, et al.," Synthesis and characterization of long strands of nitrogen- doped single-walled carbon nanotubes ", Chem. Phys. Lett. 424, 345-352 (2006); Brett L. Allen, et al.," Synthesis, Characterization, and Manipulation of Nitrogen-Doped Carbon Nanotube Cups ", ACSNANO, 2, No. 9 (2008), etc.).

In the present invention, the existing methods as described above may be applied as they are or with appropriate modifications according to the purpose. In the present invention, in applying the above-described methods, by controlling the amount of nitrogen or its precursor used with the carbon source (carbon soruce), the dimensions of the resulting carbon nanotubes (radius), etc. (Nano Lett., 2009, 9, 2009), it is possible to control the doping amount and the doping position of nitrogen atoms to the carbon nanotubes.

As described in various documents (ex. ACSNANO, Vol. 1, No. 4, 369-375 (2007)), when growing a carbon nanotube containing a nitrogen atom, the nitrogen atom is the end of the carbon nanotube While trying to be located at, there is a property to induce capping at the end. Therefore, by using such characteristics, when the amount of nitrogen is properly controlled during the growth of the carbon nanotubes, it is possible to control the amount and the doping position of the nitrogen atoms to be doped.

In addition, the method of disposing the carbon nanotubes prepared as described above in the present invention is not particularly limited. For example, a predetermined pattern is formed on a predetermined substrate (eg, a metal surface), and carbon nanotubes are formed using the same. Or other methods such as self-aligning the tube (Angew, Chem. Int. Ed. 2002, 41, 353; Science 2003, 300, 112; or Science 2001, 291, 630, etc.).

Hereinafter, the present invention will be described in more detail through examples according to the present invention, but the scope of the present invention is not limited to the following examples.

Example. 1 to 10

The nitrogen-doped metallic carbon nanotubes, one end of which was capped by a fullerene hemisphere and the other end of which was passivated by a hydrogen atom, were evaluated as described below for their current-voltage characteristics and the like. In this case, the preparation of carbon nanotubes is described in Bobby G. Sumpter, et al., " Nitrogen-Mediated Carbon Nanotube Growth: Diameter Reduction, Metallicity Bundle Dispersability, and Bamboo-like Structure Formation ", ACSNANO, Vol. 1, No. 4, 369-375 (2007) may be employed by appropriate modification of the method, but by reducing the supply of nitrogen atoms as much as possible. In addition, the opposite arrangement of the manufactured carbon nanotubes may be performed by forming a predetermined pattern on the substrate and using the same to self-align the carbon nanotubes (Angew, Chem. Int. Ed. 2002, 41, 353). Science 2003, 300, 112; or Science 2001, 291, 630, etc.).

One type of carbon nanotubes used for the evaluation of the properties of Test Examples 1 and 2 was a carbon nanotube having a female chair structure having a chiral vector index of (5, 5), and another type of zigzag type having a chiral vector index of (9, 0). It was a carbon nanotube, and both nitrogen atoms were doped in any one of carbon atoms (carbon atoms present in the second carbon layer) directly bonded to the carbon atoms constituting the uppermost carbon ring of the capping portion.

In Test Example 3, three nitrogen atoms belonging to the second carbon layer of the carbon nanotube capping portion having an armchair structure having a chiral vector index of (5, 5) were doped with three nitrogen atoms, and the doping positions thereof were adjacent to each other. The diode 55Mb3A including the first and second carbon nanotubes disposed opposite to each other and four carbon atoms belonging to the second carbon layer of the capping portion are doped with nitrogen atoms, and each nitrogen atom is disposed adjacent to each other. The current-voltage characteristics of the diodes 55Mb4A including the first and second carbon nanotubes disposed opposite to each other were measured.

Test Example 1.

Of the carbon nanotubes, two carbon nanotubes (chiral vector index: (5, 5)) having an armchair structure are disposed to face each other (J1) so that the carbon rings (pentagonal carbon rings) located at the top of the capping part face each other. The current-voltage characteristics according to the distances (2.5 kW, 3.0 kW, 3.5 kW, 4.0 kW) between oppositely arranged carbon rings were evaluated. The evaluation was performed based on Density Functional Theory (DFT) and Non-equilibrium Green's Function Formalism (NEGF), with limited bias. The electrical structure was evaluated using the exchange-correlation functional of GGA parameterized by Perdew-Burke-Ernzerhof (PBE). Core electrons are represented by improved Troullier-Martins pseudopotentials, and valence electrons are described by a single-ζ numerical atomic orbital basis set (Atomistix ToolKit). (ATK) software package (version: 2.0.4)). In NEGF, the Surface Green's function describing the semi-infinite electrodes attached to the carbon nanotube junction J1 is a Hamiltonian and overlap matrices according to the carbon nanotube junction. Derived using The applied bias creates two contact chemical potentials (μ _1,2 = E _f ± eV / 2), and the current through the carbon nanotube junction (J1) is the bias window near the Fermi level ( The transmission coefficient in μ ₁ -μ ₂ ) was calculated by integrating.

FIG. 7 shows current-voltage characteristics measured by the above-described method for the carbon nanotube junction J1. As shown in FIG. 7, in the carbon nanotube junction according to the present invention, a large tunneling current is generated between the first and second carbon nanotubes, and the characteristics thereof show NDR behavior. This NDR behavior is a unique feature observed in Ezaki diodes (or tunneling diodes). That is, a slight change was observed depending on the distance between the carbon nanotubes, but in the current-voltage curve of the junction J1, a steep current peak was observed within the applied bias range of about 0.0 V <V <about 0.8 V. The current was relatively low around 1.0 V <V <1.5 V. In addition, the peak-to-valley ratio (PVR) according to the distance between carbon nanotubes (d = 2.5 kW, 3.0 kW, 3.5 kW, 4.0 kW) was 2.45, 4,62, 15.03 and 24.12, respectively.

Test Example 2

Of the prepared carbon nanotubes, two carbon nanotubes having a zigzag structure (chiral vector index: (9, 0)) are disposed to face each other so that the carbon rings (hexagonal carbon rings) located at the top of the capping part face each other. , The current-voltage characteristic according to the distance (2.5 kW, 3.0 kW, 3.5 kW, 3.8 kW, 4.0 kW) between the oppositely disposed carbon rings was evaluated in the same manner as in Test Example 1, and the results are shown in FIG. . As can be seen from the results of FIG. 8, in the case of the junction J2 in which the zigzag-type carbon nanotubes are disposed oppositely, they are relatively weak compared to the junction J1 of the armchair-type carbon nanotubes, but still have tunneling current and NDR behavior. This was observed. In the case of the zigzag carbon nanotube junction (J2), the PVR values according to the carbon nanotube distances (d = 2.5 kW, 3.0 kW, 3.5 kW, 3.8 kW, 4.0 kW) are 1.02, 1.12, 5.62 and 7.12, respectively. And 6.50.

Test Example 3.

The current-voltage characteristics of the two kinds of diodes 55Mb3A and 55Mb4A described above were evaluated in the same manner as in Test Examples 1 and 2, and the results are shown in FIGS. 11 and 12. As can be seen from the result of FIG. 11, when three or four nitrogen atoms are doped adjacent to the second carbon layer, two NDR peaks are shown according to the applied voltage. Accordingly, it can be seen that the diode of the present invention can be effectively applied to a multi switching device (see FIG. 12).

1 is a schematic diagram illustrating a structure of a general carbon nanotube.

Figure 2 is a schematic diagram showing the side of the carbon nanotubes of the armchair structure and zigzag structure.

3 is a view for explaining a chiral vector index of carbon nanotubes in a graphite sheet.

4 is a view for explaining the doping position of nitrogen atoms to carbon nanotubes in the present invention.

5, 6, 9 and 10 are views for explaining the arrangement of carbon nanotubes according to the doping position of nitrogen atoms.

7, 8, 11 and 12 are diagrams showing the current-voltage characteristics of the diode of the embodiment of the present invention.

Claims (17)

At least one end is capped and includes first and second carbon nanotubes doped with one or more nitrogen atoms in the capping part, The first and second carbon nanotubes are diodes each disposed with the capping portion facing each other. The diode of claim 1, wherein the carbon nanotubes are metallic carbon nanotubes. The diode of claim 1, wherein the carbon nanotubes have an armchair structure or a zigzag structure. The diode of claim 1, wherein the carbon nanotubes have a chiral vector index of (a, a) or (b, 0), and a and b in the chiral vector index satisfy the conditions of the following general formula (1) or (2): [Formula 1] a = 5 to 16, [Formula 2] b = 3 × j In the above, j represents an integer of 3 to 10. The diode of claim 1, wherein the first and second carbon nanotubes are capped by fullerene hemispheres. The diode of claim 1, wherein each of the first and second carbon nanotubes has a pentagonal carbon ring at the top of each capping portion. The diode of claim 1, wherein each of the first and second carbon nanotubes has a hexagonal carbon ring at the top of each capping portion. The diode of claim 1, wherein the carbon nanotubes are doped with one nitrogen atom. The method of claim 8, wherein the nitrogen atom comprises: a first carbon layer of each carbon nanotube capping portion; And a diode doped with one of the carbon atoms belonging to the second carbon layer. The diode according to claim 8, wherein the nitrogen atom is doped with one of the carbon atoms belonging to the second carbon layer. 9. The diode of claim 8 having a single switching current-voltage characteristic. The diode of claim 1, wherein the carbon nanotubes are doped with two or more nitrogen atoms. The diode according to claim 12, wherein the nitrogen atom is doped with two or more of the carbon atoms belonging to the second to fifth carbon layers. 13. The diode of claim 12 wherein the nitrogen atom is doped to at least two of the carbon atoms belonging to the second carbon layer. 13. The diode of claim 12 wherein the nitrogen atoms doped with carbon atoms are disposed adjacent to each other. 13. The diode of claim 12 having a multi switching current-voltage characteristic. The diode of claim 1, wherein a distance between the capping portions of the first and second carbon nanotubes is 1.0 kW to 5.0 kW.

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