KR20100112727A - Spin current valve device using graphene nanoribbons - Google Patents

Abstract

PURPOSE: A spin current valve device using graphene nano ribbons is provided to use a current amount and spin of an atom through graphene nano ribbons which is an information medium. CONSTITUTION: A spin current valve device using graphene nano ribbons includes a graphene nano ribbon, an absorption material, and a side gate. The absorption material is adsorbed to a graphene nano ribbon. The absorption material is an atom or a molecule whose absorption energy in a zigzag edge of graphene is larger than absorption energy in other parts. A side gate(710) applies a voltage to both edges or one edge of a graphene nano ribbon to make absorption density of both edges of the absorption material absorbed to a nano ribbon.

Description

Spin current valve device using graphene nanoribbons

The present invention relates to a spin current valve device using a graphene nanoribbon (nanoribbon), and more specifically, the adsorption energy at different portions of the graphene zigzag-edge (Zigzag-edge) The present invention relates to a spin valve device using graphene nanoribbons having larger atoms or molecules adsorbed thereon.

In general, graphite (graphite) is a structure in which two-dimensional graphene sheets (plateene sheets) of carbon atoms connected in a hexagonal shape are stacked. Recently, one or more layers of graphene sheets were peeled off from graphite, and the properties of the sheets were examined to find very useful properties that differ from existing materials.

The most notable feature is that when an electron moves in the graphene sheet, it flows as if the mass of the electron is zero, which means that the electron flows at the speed of light movement in vacuum, that is, near the speed of light. The graphene sheet also has an abnormal half-integer quantum hall effect for electrons and holes.

It is also known that the electron mobility of the graphene sheet known to date has a high value of about 20,000 to 50,000 cm ² / Vs. Above all, in the case of carbon nanotubes similar to the graphene sheet, since the yield is very low after the synthesis after purification, the final product is expensive even if synthesized using cheap materials, while graphite is very cheap. In the case of single-walled carbon nanotubes, not only the metal and semiconductor properties vary depending on the curled direction and diameter, but also the band gaps are different even if they have the same semiconductor properties. In order to use semiconductor or metallic properties, it is necessary to separate each single-walled carbon nanotube, which is known to be very difficult.

On the other hand, in the case of the graphene sheet, the electrical characteristics change according to the crystal orientation of the graphene sheet having a given thickness, so that the user can express the electrical characteristics in the selection direction, so that the device can be easily designed. The characteristics of the graphene sheet can be used very effectively in the future carbon-based electrical devices or carbon-based electromagnetic devices.

In this regard, it is being sought to be used for new purposes in various fields using various properties of graphene.

An object of the present invention is to provide a spin current valve device using a graphene.

A spin current valve is formed by adsorbing atoms or molecules with a different density at a single layer or a multilayer graphene nanoribbon zigzag edge, where the adsorption energy at the edge is greater than that at other portions.

Spin current valve (spin current valve) according to the present invention has the effect that through the information medium called graphene nanoribbon in addition to the physical amount of the current amount, the physical amount of the spin of the electron can be used as information transfer means.

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

Hereinafter, the atoms or molecules adsorbed / adsorbed to the graphene nanoribbons will be referred to as adsorbents.

Figure 1 shows the appearance of zigzag-edge graphene nanoribbon (nanoribbon) in which metal atoms are adsorbed.

1 shows a case where metal atoms are adsorbed onto graphene nanoribbons (GNRs), but the type of adsorbent adsorbed on the graphene nanoribbons is not limited and the adsorption energy at the zigzag edge of graphene is different. Include all atoms or molecules that appear larger than the adsorption energy. Hereinafter, an example of the main metal atoms will be described as an adsorbent, but the atoms or molecules used as the adsorbent in the present invention are not limited to metal atoms.

In order for the adsorbent to adsorb on the graphene, electrons must be separated from the metal atoms and transferred to the graphene. At this time, energy equal to the difference between the ionization energy of the metal and the work function of the graphene is required. When the gap between ionized metal atoms and graphene decreases, Coulomb energy is generated between them. If the Coulomb energy is larger than the energy required for electron transfer between the metal atoms and graphene, adsorption occurs.

Adsorption energy has a large value when transferring a large number of electrons, when having a small ion radius, when having a small ionization energy, when the charge transferred to the graphene is distributed in a narrow space.

When graphene is made into a nanoribbon, the edge shape of the nanoribbon is an armchair shape, a zigzag shape, or two shapes alternately. And depending on the shape of the edge, the properties of the nanoribbons, such as conductivity (conductivity), magnetic properties and so on. In particular, zigzag edge-shaped nanoribbons have locally distributed electrons with different spins at both edges.

FIG. 2 is a graph of the structure of the armchair-shaped graphene nanoribbons (Armchair-edged GNRs) and the adsorption energy of metal atoms. In the graph of FIG. 2, the x axis represents the adsorption point of the metal atoms and the y axis represents the adsorption energy.

Referring to the graph of FIG. 2, the shapes of the graphs for the atoms of lithium (Li), sodium (Na), potassium (K), beryllium (Be), magnesium (Mg), and calcium (Ca) are almost identical to those of the x-axis. It can be seen that there is no parallel between the adsorption energy at the center of the graphene nanoribbons, i.e., not near the edges, and at the armchair-edge.

That is, since there is almost no difference in the adsorption energy at the non-edge portion and the edge of the armchair, there is no particular tendency toward the adsorption point when the metal is adsorbed onto the edge of the armchair.

3 is a diagram showing the energy band structure of the armchair nanoribbons near the Fermi level and the charge distribution of electrons from outside.

In the upper figure of FIG. 3, the pink shaded portion 300 represents a conduction band near the Fermi level and is a state in which electrons from the outside are filled. Referring to the figure at the bottom of Figure 3, it can be seen that in the armchair nanoribbons, the distribution of charge is evenly dispersed and adsorbed without any tendency.

Figure 4 shows the graph of the structure and metal atom adsorption energy of zigzag edge-shaped graphene nanoribbons (Zigzag-edged GNRs). In the graph of FIG. 4, the x axis represents the adsorption point of the metal atom and the y axis represents the adsorption energy.

Referring to the graph of FIG. 4, unlike the case of FIG. 2, the adsorption energy at the zigzag-edge portion (1 and 13 portions of the x-axis) has the greater value than that of the other portions for the same atoms. do.

FIG. 5 is a diagram showing an energy band structure of a zigzag nanoribbon near a Fermi level and a charge distribution of electrons from outside. In the upper figure of FIG. 5, the pink shaded portion 500 represents a conduction band near the Fermi level and is an area filled with electrons from outside.

Referring to the lower figure of FIG. 5, it can be seen that electrons are mainly adsorbed to the edges unlike in the case of FIG. 3. In this case, the charges transferred to the graphene are distributed in a narrow space, and thus the coulombic energy is increased. As a result, the adsorption energy at the edge of the zigzag nanoribbon has a large value.

FIG. 6 is a graph showing changes in current characteristics according to electron spin directions near the Fermi level of zigzag graphene nanoribbons due to metal atom adsorption. In the graphene structure of FIG. 6, the circular shading indicates that the metal atoms are adsorbed, and the graph of FIG. 6 shows an energy band structure according to the direction of electron spin in k-space. The pink shaded portions 600 and 620 in the middle represent the valence band near the Fermi level.

Referring to FIG. 6, the portion of zero energy is at the Fermi level, where the Fermi level is in the gap for the spin up electrons, and the fermi level is the conduction band in the spin down electrons. This implies a conduction band, which means that it is insulator for upspin electrons and conductor for down spin electrons. In other words, it can be used as a spin current valve that can flow only the current in a specific spin direction.

When the edge shape of graphene nanoribbon is zigzag or the zigzag shape and the armchair shape exist together, it can be used as spin current valve by using the adsorption characteristic at the zigzag edge. It is preferable that the edge shape of the graphene nanoribbons are zigzag only, and when the zigzag shape and the armchair shape exist together, the more zigzag edges exist, the more advantageous the spin current valve.

On the other hand, in general, when the metal is sprinkled on the zigzag edge graphene nanoribbon, both edges are adsorbed, so that an external device capable of driving metal atoms to one edge is required to make the conductor act only for one spin current.

FIG. 7 illustrates a spin current valve structure capable of flowing only a current in a specific spin direction using a side gate.

Referring to FIG. 7, the nanoribbons on which metal is adsorbed and side gates 700 and 710 positioned at both sides thereof are included. The type of adsorbed atoms is not limited and may be used for both atoms or molecules in which the adsorption energy at the zigzag edge of the graphene is greater than that at other portions. For convenience of explanation, it is assumed that there is only one side gate located at both sides of the nanoribbons, but the present invention is not limited thereto, and a plurality of side gates at both ends of the nanoribbons may be symmetrically or asymmetrically installed as necessary. .

When sprinkling metal atoms on zigzag edge graphene nanoribbons, they are distributed evenly on the left and right sides of graphene on average. In this case, since both the spin-up current and the spin-down current flow, only the spin current in the spin direction must flow while only one metal atom is adsorbed. To this end, the structure includes side gates 700 and 710.

When a voltage is applied to both ends of the side gates 700 and 710 to have a potential difference, an electric field 720 is generated in a direction crossing the graphene nanoribbons, whereby the adsorption energy of metal atoms adsorbed at both edges is different. This causes + ionization As shown in FIG. 7, the metal atoms do not want to be adsorbed around the terminal 760 to which the + voltage is applied. The portions 740, 745, and 750 on which the metal atoms are adsorbed have a metallic property, and have a semiconductor (non-conductive at cryogenic) property around the terminal 760 to which the + voltage is applied. This makes it possible to form a spin valve that allows only one direction of spin current to flow.

1 shows a state in which a metal atom is adsorbed on one edge on a graphene having a zigzag edge shape.

Figure 2 is a graph of the structure and metal atoms adsorption energy of the armchair edge-shaped graphene nanoribbons (Armchair-edged GNRs).

3 is a diagram showing the energy band structure of the armchair nanoribbons near the Fermi level and the charge distribution of electrons from outside.

Figure 4 is a graph of the structure and metal atoms adsorption energy of zigzag edge-shaped graphene nanoribbons (Zigzag-edged GNRs).

5 is a diagram showing the energy band structure of the zigzag nanoribbons near the Fermi level and the charge distribution of electrons from outside.

FIG. 6 is a graph showing a change in current characteristics along the direction of electron spin current near the Fermi level of zigzag graphene nanoribbons due to metal atom adsorption.

FIG. 7 illustrates a spin current valve structure capable of flowing only a current in a specific spin direction using a side gate.

Claims (3)

Graphene nanoribbons; And Including the adsorbent adsorbed on the graphene nanoribbon, The adsorbent is an atom or molecule in which the adsorption energy at the edge of the graphene nanoribbon is greater than the adsorption energy at the other part, and is adsorbed at different edges of the graphene nanoribbon at different densities to the graphene nanoribbon. Spin current valve device using a graphene nano-ribbon characterized in that only one direction of the spin current can flow. The method of claim 1, The graphene nanoribbon further comprises a side gate (side gate) to vary the adsorption density of both edges of the adsorbent adsorbed on the nanoribbon by applying a voltage to both edges or one edge of the graphene nanoribbon Spin current valve device using. The method according to claim 1 or 2, The graphene nanoribbon is a graphene nanoribbon having a zigzag edge shape, and the adsorbent is any one of lithium, sodium, potassium, beryllium, magnesium, and calcium.

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