KR101692445B1 - Method of producing band gap in graphene and graphene with a band gap therefrom - Google Patents

Abstract

The present invention relates to the formation of a bandgap of graphene, and it forms a band gap necessary to make graphene an electronic device by adsorbing an ionized alkali metal (Na ⁺ ) having a low energy of 100 eV or less on the graphene without stimulation And the size of the adsorbent can be adjusted according to the adsorption amount.

Description

METHOD OF PRODUCING BAND GAP IN GRAPHENE AND GRAPHENE WITH A BAND GAP THEREFROM BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a graphene bandgap formation technique using low energy sodium ions, a graphene fabrication method, and a bandgap retained graphene produced therefrom. The present invention relates to an ionized alkali metal (Na ⁺ ) Is adsorbed on the surface of graphene to form a band gap necessary to make graphene an electronic device, and it is a technical method to adjust the band gap size according to the amount of adsorption.

Graphene is a two-dimensional carbon single atom layer thin film with excellent strength of more than 200 times that of steel, 50% better thermal conductivity than carbon nanotubes at room temperature, 100 times more electron mobility than silicon, and flexibility of up to 20% of area , And optical transparency of about 98%, it is expected to be a next-generation electronic device material to replace silicon-based electronic devices that are expected to reach the physical limit in the near future.

The momentum dispersion relation E (k) is a typical two-dimensional parabola of dependence ^{(α k 2) (α k} ) that is not linear, so-called Dirac band dependency of the magnetic field - above all surprising yes unique physical properties of the pin of the conduction electron energy And the Fermi speed corresponds to 10 ⁶ m / s, hundreds of times that of silicon (Non-Patent Document 1). For this reason, graphene is expected to emerge in the new high-speed electronics industry, such as new high-speed electronic devices and nano devices, chemical sensors, terahertz sources and detectors.

However, graphene has excellent electrical conductivity due to its linear energy-momentum dispersion around its Fermi energy, but it does not have the bandgap at the same time, so it does not have the on / off switching function required for the device And there has been a demand to solve this problem. According to this demand, many studies have been carried out to maintain the inherent physical properties of graphene, to form a band gap of a certain size, and to artificially control the size thereof.

These studies, a recent attempt to form E _g at the de-laction point (DP) of graphene, have shown three technical means: (1) electron confinement, (2) forming a bilayer graphene ), And (3) chemical functionalization. For example, the formation of band gaps with narrowly grafted nanoribbon lithographically patterned has difficulties with respect to lithographic limitations and non-uniform edges. In the case of bilayer graphene, an electric field can be vertically applied to the sample to form an adjustable bandgap, but the bandgap size is limited to a maximum of 0.4 eV. That is, it is difficult to synthesize graphene having a band gap of at least 0.5 eV with sufficient stability at room temperature, which is a practically usable condition. In the case of graphene functionalization, a periodic potential is generated on the graphene from the alignment of adsorbed or substituted atoms, which tends to induce asymmetry on the charge distribution between the two carbon sublattices of graphene, Can be formed. The adsorption of alkali metal (AM) atoms has been used for functionalization, which is an effective charge donor of the graphene π-band which causes a downshift that exhibits an n-doping effect or charge asymmetry that forms an AM atomic bandgap . Twisted sodium nano-strips on graphene exhibit a broad bandgap (0.74 eV), which is predominantly produced, for example, by uneven charge distribution on graphene. However, this principle of band gap has not yet been established due to the two possibilities, structural deformations due to adsorbates and many-body effects.

In the above research, a technique in which a graphene band gap of 0.5 eV or more is formed by patterning hydrogen and oxygen atoms on a graphene through an adsorption method using sputtering (Non-Patent Documents 2 and 3). However, the formation of graphene band gap through this method has problems such as decrease of electron mobility by affecting the honeycomb lattice of two dimensions which is a characteristic of graphene because hydrogen and oxygen atoms are covalently bonded to carbon of graphene (Non-Patent Document 4).

Non-Patent Document 1: KS Novoselov, AK Geim, SV Morozov, D. Jiang, Y. Zhang, SV Dubonos, IV Grigorieva, and AA Firsov., "Electric field effect in atomically thin carbon films," Science, 306, 666? 669 (2004) Non-Patent Document 2: R. Balog, B. Jorgensen, L. Nilsson, M. Andersen, E. Rienks, M. Bianchi, M. Fanetti, E. Laegsgaard, A. Baraldi, S. Lizzit, Z. Sljivancanin, F . Besenbacher, B. Hammer, TG Pedersen, P. Hofmann, and L. Hornekaer., "Bandgap opening in graphene induced by patterned hydrogen adsorption," Nat. Mater., 9, 315-319 (2010). Non-Patent Document 3: Toru Takahashi, Katsuaki Sugawara, Eiichi Noguchi, Takafumi Sato, Takashi Takahashi, "Band-gap tuning of monolayer graphene by oxygen adsorption," Carbon, 73, 141-145 (2014). Non-Patent Document 4: Manu Jaiswal, Candy Haley Yi Xuan Lim, Qiaoliang Bao, Chee Tat Toh, Kian Ping Loh and Barbaros Ozyimaz., "Controlled Hydrogenation of Graphene Sheets and Nanoribbons," ACS Nano., 5, 888-896 ).

 The object of the present invention is to maintain the inherent physical properties of graphene in formation of a band gap necessary for using graphene as an electronic device, to form a band gap of at least 0.5 eV and to provide sufficient stability and reproducibility even at room temperature I have left.

 Further, the present invention aims at artificially adjusting the band gap of graphene according to the adsorption amount of alkali metal ions, so that graphene has an on / off switching function which is a basic element of a logic element.

In an aspect of the present invention, bandgap retaining graphene is provided, which comprises graphene and alkali metal ions formed on the graphene.

In another embodiment of the present invention, the graphene is a crystalline graphene.

In another embodiment of the present invention, the crystalline graphene is provided on a substrate, wherein the crystalline graphene is raised by stepping up the substrate temperature by 50 DEG C to 100 DEG C to provide a bandgap retention graphene grown do.

In another embodiment of the present invention, a bandgap retained graphene is provided wherein the alkali metal ion is formed with an energy of 50 eV to 100 eV.

In another embodiment of the present invention, the alkali metal ion is maintained at an ion beam current density of 1 nA / cm ² to 2 nA / cm ² for the substrate and a vacuum pressure of 1 x 10 ^-10 Torr to 2 x 10 ^-10 Lt; RTI ID = 0.0 > Torr. ≪ / RTI >

In another embodiment of the present invention, the bandgap retention graphene is provided wherein the substrate is maintained at 200 DEG C to 250 DEG C during the alkali metal formation.

In another embodiment of the present invention, a bandgap retained graphene is provided wherein the alkali metal ion is present in an amount ranging from 0.1 x 10 ¹⁵ atoms / cm ² to 4.2 x 10 ¹⁵ atoms / cm ² .

In another embodiment of the present invention, there is provided a bandgap retaining graphene wherein the alkali metal ion is a sodium ion.

In another aspect of the present invention, there is provided a bandgap retention graphene fabrication method comprising: providing a graphene; And an alkaline metal forming step of forming an alkali metal ion on the graphene.

In another aspect of the present invention, a method of manufacturing a bandgap retained graphene is provided, wherein the graphene providing step comprises a crystalline graphene forming step.

In another embodiment of the present invention, the crystalline graphene forming step comprises the steps of: forming crystalline graphene on a substrate; And gradually raising the substrate temperature by 50 DEG C to 100 DEG C stepwise.

In another embodiment of the present invention, the alkali metal forming step comprises forming the alkali metal ion at an energy of 50 eV to 100 eV.

In yet another aspect of the invention, the alkali metal forming stage is the ion beam current density on the substrate ^{1 nA / cm 2 ~ 2 nA} / is maintained and the vacuum pressure in ^{cm 2 1 x 10 -10 Torr ~} 2 x 10 - Lt; ^{RTI ID = 0.0} > ¹⁰ < / ^RTI > Torr.

In another embodiment of the present invention, the alkali metal forming step comprises maintaining the substrate at 200 ° C to 250 ° C.

In another aspect of the present invention, there is provided a process for producing a bandgap retained graphene wherein the alkali metal ion is present in an amount ranging from 0.1 x 10 ¹⁵ atoms / cm ² to 4.2 x 10 ¹⁵ atoms / cm ² .

In another embodiment of the present invention, there is provided a process for producing a bandgap retained graphene wherein the alkali metal ion is a sodium ion.

In one aspect of the present invention, there is provided a method for determining the formation amount of an alkali metal ion, comprising the steps of: providing graphene formed with an alkali metal ion; And a step of calculating the formation amount of the alkali metal ion using a change in work function.

In another embodiment of the present invention, there is provided a method comprising: measuring a work function change with respect to a forming amount of a unit layer (1 ML: 1 Monolayer) unit; And converting the work function change into an alkali metal ion content to be formed.

In another embodiment of the present invention, there is provided a method for determining the amount of alkali metal ions formed, wherein the alkali metal ion is a sodium ion.

This technology has the disadvantage that since the existing neutral alkali metal has no effect on graphene except n-doping, the ionized sodium atom is already adsorbed on the graphene in a charged state, And can not be covalently bonded to carbon of graphene like hydrogen or oxygen. Therefore, it can be applied to electronic devices by forming a bandgap while maintaining excellent properties of graphene.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a method of forming a bandgap in graphene using the alkali ion of the present invention. Fig.
FIG. 2A is a graph showing the measurement result of an angularly resolved photoemission spectroscopy (ARPES) showing a gap formed in the dirac band of graphene in the present invention. FIG. This graph shows that the point changes.
FIGS. 3A and 3B are schematic diagrams of a high-resolution core-level spectroscopy (HRCLS) system capable of analyzing the structure of atoms appearing when alkali metal ions are adsorbed on graphene and the temperature of the substrate is changed. As a graph showing the measurement results, FIG. 3A shows C 1s and FIG. 3B shows Na 2p, respectively.
FIG. 4 is a graph showing the desorption temperature of alkali metal ion (Na ⁺ ) based on the results of the high resolution photoelectron spectroscopy (HRCLS) measurement in the present invention.
5 is a graph showing a result of measuring a change in work function with respect to an adsorption amount of an alkali metal ion, wherein the atom density of graphene is 1 unit layer (monolayer: ML, 1 ML = 3.82x10 ¹⁵ atoms / cm ² ) .
FIG. 6 is a graph showing the ion content of the actual graphene in relation to the alkali metal ion adsorption amount, which is a graph in which the work function change of FIG. 5 is converted into the content of the alkali metal ion.

The present invention selected crystalline graphene using a silicon carbide substrate to study the bandgap formation of graphene. This method of crystallinity formation of graphene has an advantage that it can synthesize graphene uniformly to a wafer size with higher crystallinity than conventional graphene grown by a mechanical peeling method or a chemical vapor deposition (CVD) method, Because of the growth of graphene by layer by layer method, it is suitable for graphene study of single layer which shows the best characteristics of dirac band. In addition, since the growth of graphene and the formation of adsorbed material are performed together under ultrahigh vacuum (~ 10 < ^-10 > Torr), growth can be achieved with minimal impurities due to graphene growth and without additional impurities.

의 구조임을 확인할 수 있다. 1050℃ 이상부터는

의 구조를 보이며 결정성 그래핀의 특징인 그래핀 구조는 동일하지만 기판과의 강한 결합으로 인해 그래핀의 특성을 보이지 않는 버퍼층(buffer layer)의 탄소 구조가 만들어지는 것을 확인할 수 있다. 1200℃ 이상부터는 더 이상의 표면의 원자 구조가 LEED 장치로 자세히 구별되지 않기 때문에 각 분해 광전자 분광 장치(ARPES) 및 고 분해능 광전자 분광 장치(HRCLS)를 통해 양질의 단층 그래핀 성장여부를 확인한다.The specific growth process proceeds with increasing the temperature of the silicon carbide substrate stepwise in the ultra-high vacuum chamber. The temperature is preferably raised stepwise by 50 ° C in the range of 50 ° C to 100 ° C, and more preferably by stepwise increasing by 100 ° C. When the substrate is heated at a temperature of 100 ° C or more at a time, the atomic structure of the surface due to the temperature change can not be confirmed step by step. As a result, crystallized high-quality graphene can not be obtained. Particularly, since the number of graphene layers is finely determined according to the temperature of the substrate at a temperature of 1000 ° C. or higher at which the silicon atoms are desorbed, a stepwise temperature rise is required from 50 to 100 ° C. Thereafter, the atomic structure change of the surface due to the temperature change of the substrate can be confirmed by using the low energy electron diffraction (LEED) apparatus. At the substrate temperature of around 850 ° C., the atomic arrangement structure of the surface becomes 3 × 3,

. At temperatures above 1050 ℃

And the carbon structure of the buffer layer, which does not show graphene characteristics due to strong bonding with the substrate, can be confirmed, although the graphene structure characteristic of crystalline graphene is the same. Since the atomic structure of the surface is not clearly distinguished from the LEED device beyond 1200 ° C, it is confirmed that the quality of the single-layer graphene is grown through the angular resolution optoelectronic spectroscopy (ARPES) and the high resolution optoelectronic spectrometer (HRCLS).

Then, low energy Na ⁺ ions are doped on a single layer graphene (SLG) formed on the substrate surface to form a graphene band gap. Specifically, alkali metal ions (for example, Na ⁺ ) are applied to the substrate at an ion beam current density of 1 nA / cm ² to 2 nA / cm ² , preferably about 1 nA / cm ² , And adsorbs it. When the beam current density is more than 2 nA / cm ^2, the change in the amount of sodium ion adsorption to graphene is increased, so that the change in graphene band gap due to the amount of sodium ion adsorption can not be observed in detail. Particularly, in the present invention, the graphene band gap size gradually increases with increasing sodium ion adsorption amount, and when it becomes one layer (1ML) compared to graphene, its size becomes maximum, so that the fine adjustment of sodium ion adsorption amount is required . In particular, the Na ⁺ ions in the range of 50 eV to 100 eV, preferably 100 eV, are adsorbed while maintaining the SLG sample in the range of 200 ° C to 250 ° C, preferably 200 ° C. When the sample is held at room temperature and sodium ion is adsorbed, the graphene surface may be broken by ion energy of 100 eV, and the adsorbed sodium ion also can not form a uniform structure on the graphene. The sample temperature above 300 ° C is the desorption condition of sodium ion on the graphene surface. Sodium ion energy above 100 eV can cause graphene damage because it acts to desorb the atoms on the surface like argon and nitrogen sputtering.

After the alkali metal ions were adsorbed, changes in the graphene? -Bands and the intrinsic energy levels (C 1s, Na 2p and Si 2p) produced by doped Na ⁺ ions were measured using ARPES and HRCLS using synchrotron photons, The presence or absence of band gap formation of graphene was confirmed.

As can be seen from the measurement results of the ARPES of each decomposition photoelectron spectrometer of FIG. 2 (a), it was confirmed that a single layer of graphene was formed through a linear energy dispersion relationship, and then sodium ion (Na ⁺ ) was adsorbed The linear graphene band structure disappears in the upper region of the conduction band, and at the same time, the electron density around the Fermi energy is remarkably reduced. This is not a simple doping effect, but a band gap formation of graphene. As shown in FIG. 2 (b), when the amount of sodium adsorption is one layer (1 ml) as compared with that of graphene, the band gap becomes about 0.7 eV on the basis of the Fermi energy It can be seen that the declamp point moves to the maximum.

The size of the band gap can be more easily controlled by changing the amount of adsorbed ions. Interestingly, a large bandgap is formed, but the novel electronic properties of graphene due to dirac fermions, such as linearity and mobility of the? -Bands, remain almost intact even during Na ⁺ ion doping. Also, the graphene bond of Na ⁺ ions was found to be weaker than the bond of neutral hydrogen or nitrogen atoms, which was to flash Na ⁺ doped graphene at a temperature lower than the desorption temperature of hydrogen or nitrogen to restore clean graphene It is because. Thus, it has been found that doping Na ⁺ ions on SLG is an effective way to form an adjustable bandgap in graphene without deteriorating the novel electrical properties of graphene.

In addition, the characteristics of the bandgap retained graphene can be confirmed in the C 1s, Na 2p spectrum through a high resolution photoemission spectrometer. As can be seen in Fig. 3 (a), before adsorption of Na ⁺ ions, C 1 s of clean SLG represents four well-known sub-peaks. This is from the SiC of the different source: SiC substrate, S ₁ and S ₂ of the zero layer, and G carbon atoms of the graphene. (B) to (f) of FIG. 2 (a) from Na ⁺ ions bonded with C atoms of graphene when adsorbing Na ⁺ ions of 50 to 100 eV, preferably 100 eV, As shown, a sub-peak of binding energy E _b = 285.9 eV appears. In this case, the damage on the graphene is almost the same as that in the case where the relative size of the G sub-peak of graphene and the SiC sub-peak of the SiC substrate is clean graphene (SiC / G? 0.7) in FIG. It can be confirmed that there is no. In addition, the Na ⁺ C subpixel remains at 450 ° C, which is much higher than the adsorption temperature of graphene on the graphene atom, T _d = 270 ° C. It can be seen that the bonding strength with the pin C carbon atom is high.

In addition, a new spectrum (Na-C) due to adsorption of sodium ions and a change in the size thereof can be predicted for each structural change. For example, the fact that the gray spectrum (SiC) scarcely shifts to the temperature change of the substrate means that the adsorbed sodium ions do not enter into the graphene. This is comparable to the previous studies in which hydrogen and lithium migrate by 0.7 eV and 2 eV, respectively. In addition, the gray spectrum shows an increase in size up to 450 ° C compared to other spectra, indicating that the surface structure of graphene has changed due to the adsorption of sodium ions.

This analysis can also be confirmed by the Na 2p spectrum. As shown in FIG. 3 (b), it can be seen that the yellow spectrum, which occupies the most part, changes abruptly with temperature, that is, And it can be seen that its size is almost equal to the remaining spectrum at around 450 ° C. As a result, it can be seen that the atomic structure corresponding to the remaining spectrum except for the yellow spectrum is bonded to the graphene more strongly than the structure corresponding to the yellow spectrum, and this structure is the structure resulting from the formation of the band gap in the graphene Able to know.

In the case of hydrogen and oxygen, the desorption temperatures of the graphene are 900 ° C. and 1000 ° C., respectively. As shown in FIG. 4, since the sodium ion is 450 ° C. or less, It is not the same covalent bond. In particular, Na ⁺ ion doped graphenes do not exhibit such decay in dirac fermions, although some graphene functionalized with external atoms at high adsorption temperatures often exhibit degraded electrical properties such as reduced charge carrier mobility. Accordingly, a graphene functionalization method which is easy and effective to control and form the band gap by controlling the amount of ion adsorption is disclosed.

That is, according to the present invention, it can be confirmed that the result is almost the same as that of the single-layer graphene when the Fermi speed is compared with that of the single layer by the slope analysis according to the energy dispersion relation when forming the band gap of FIG. It can be seen that the gap is adjustable while maintaining the inherent characteristics of the graphene.

In addition, the adsorption amount of sodium ions on the graphene of one of the adsorption layers is defined by a change in work function with the adsorption time. The change in work function can be explained by the change of state density of secondary electrons through photoelectron measurement. Especially, when the sodium ion adsorption amount on graphene is one layer (1ML), this work function change saturation, The condition at this time can be defined as 1 ML. More specifically, the content of alkali ions adsorbed on the graphene was determined by firstly determining the ion adsorption amount according to the amount of adsorption, with the atom density of graphene being 1 monolayer (ML, 1 ML = 3.82x10 ¹⁵ atoms / cm ² ) By measuring the change in work function (see FIG. 5). The data thus measured are converted to a function of the ion content deposited on the actual graphene for the adsorption amount as shown in FIG. The range of ion content used is 0.1 x 10 ¹⁵ atoms / cm ² to 4.2 x 10 ¹⁵ atoms / cm ² . Within this range, a bandgap is formed and the bandgap increases up to 0.7 eV as the ion content increases. At an ion content higher than this range, the amount of graphene-based alkali ion adsorption becomes one unit or more, so that the band gap is in a saturated deposition state, as shown in Fig. 2 (a).

Example

A sample of 6H-SiC (0001) substrate on which an epitaxial graphene is formed is provided. Then, ARPES data for the graphene electron band of graphene was obtained at beamline 4A2 of Korea Pohang Accelerator Laboratory (PAL) using a synchrotron photon of 34 eV energy. In addition, the internal state level spectrum (C 1s, Na 2p, Si 2p) of the substrate sample was measured with a photon energy of 130 eV or 510 eV at a PAL beamline 8A2 of an energy-resolution of 200 meV. The instruments used for the measurements were a hemispherical Scientific R4000 analyzer (ARPES) and a Scientific SES100 (HRCLS) with a total resolution of less than 100 meV.

Measuring the pressure in the chamber was maintained at 1 x 10 ^-10 Torr, Na ⁺ ions are ion beam current density to the target generation, and using a low energy ion gun alkali metal (Kimball Physics) is adjusted to 1 nA cm ^-2 Respectively. The sample was held at 200 DEG C and Na ⁺ ions of 100 eV energy were adsorbed. The amount of adsorbed Na ⁺ ions on SLG was calibrated by measuring the work function versus exposure curve taking into account a single layer (1 ml). The momentum (k _∥ ) in the direction perpendicular to Γ → K of the Brillouin zone of the surface was varied to yield a series of electron-to-image images from the Na ⁺ doped sample. Subsequently, the changes in the inner level (C 1s, Na 2p and Si 2p) were measured by using SIE100 (Scienta SES100) (HRCLS), and the presence or absence of bandgap formation of graphene was confirmed.

As a result, the same graph as FIGS. 2A and 2B and FIGS. 3A and 3B was calculated. When the graphene formed a band gap of 0.7 eV, the Fermi speed was found to be 0.8 x 10 ⁶ m / s, The velocity was slightly reduced from 1.0 x 10 ⁶ m / s, but as shown in the linear dirac band, the change in inherent properties was considered to be little. As a result, it was confirmed that graphenes retaining band gap formation and graphene specific characteristics as described above.

Since graphene exhibits superior properties compared to other materials with the characteristics of dirac bands, it can be used not only as a substitute for silicon based on the present invention, but also as a material for semiconductors, transparent electrodes, secondary batteries, It can be used in various industrial fields such as business. Although graphene has been evaluated as a material for transparent electrodes, it is expected to show rapid growth in the electrode materials for energy and heat-dissipating materials such as secondary batteries. However, as described above, There are still a lot of things to solve. Therefore, development of material properties and related technology of graphene nanomaterial through the present invention can pioneer new industrial field and become a source of national new growth power material and device industry.

10: Grain Fins
20: silicon carbide substrate
30: alkali metal ion (Na ⁺ )

Claims (19)

As a bandgap retaining graphene,
Graphene, and
An alkali metal ion formed in the graphene in a content ranging from 0.1 x 10 ¹⁵ atoms / cm ² to 4.2 x 10 ¹⁵ atoms / cm ²
Gt; graphene < / RTI > The bandgap retained graphene of claim 1, wherein the graphene is crystalline graphene. 3. The bandgap retained graphene according to claim 2, wherein the crystalline graphene is provided on a substrate and the crystalline graphene is grown by stepping up the substrate temperature by 50 DEG C to 100 DEG C. The bandgap retaining graphene according to claim 1, wherein the alkali metal ion is formed at an energy of 50 eV to 100 eV. The method of claim 1, wherein the alkali metal ions are maintained at an ion beam current density of 1 nA / cm ² to 2 nA / cm ² with respect to the substrate and a vacuum pressure of 1 x 10 ^-10 Torr to 2 x 10 ^-10 Torr Bandgap retained graphene. 4. The bandgap retained graphene of claim 3 wherein the substrate is maintained at 200 DEG C to 250 DEG C during alkali metal formation. delete The bandgap retaining graphene according to claim 1, wherein the alkali metal ion is a sodium ion. As a band gap-holding graphene fabrication method,
Providing a graphene; And
An alkali metal forming step of forming an alkali metal ion in the graphene in a content ranging from 0.1 x 10 ¹⁵ atoms / cm ² to 4.2 x 10 ¹⁵ atoms / cm ²
≪ / RTI > 10. The method of claim 9, wherein the providing of the graphene comprises forming a crystalline graphene. 11. The method of claim 10, wherein the crystalline graphene forming step comprises: forming crystalline graphene on a substrate; And raising the substrate temperature step by step from 50 ° C to 100 ° C. 10. The method of claim 9, wherein the step of forming an alkali metal comprises forming the alkali metal ion at an energy of 50 eV to 100 eV. Claim 9 wherein the alkali metal forming stage is the ion beam current density on the substrate ^{1 nA / cm 2 ~ 2 nA} / a 1 x maintained and vacuum pressure to the ^{cm 2 10 -10 Torr ~ 2 x} 10 -10 Torr in Wherein the step of forming the bandgap retained graphene comprises: 12. The method of claim 11, wherein the alkali metal forming step comprises maintaining the substrate at 200 [deg.] C to 250 [deg.] C. delete 10. The method of claim 9, wherein the alkali metal ion is a sodium ion. As an alkali metal ion formation amount confirmation method,
Providing graphene in which alkali metal ions are formed in a content ranging from 0.1 x 10 ¹⁵ atoms / cm ² to 4.2 x 10 ¹⁵ atoms / cm ² ; And
Calculating a formation amount of the alkali metal ion using a change in work function
Wherein the alkaline metal ion forming amount is determined based on the alkali metal ion formation amount. 18. The method of claim 17,
Measuring a work function change with respect to a forming amount of a unit layer (1 ML: 1 Monolayer) unit; And
Converting the work function change into an alkali metal ion content;
Wherein the alkaline metal ion forming amount is determined based on the alkali metal ion formation amount. 18. The method according to claim 17, wherein the alkali metal ion is a sodium ion.

Images