Method of obtaining a silicon carbide-graphene composite with a controlled surface morphology

Abstract

A method of obtaining a SiC-graphene composite with a controlled surface morphology having a surface covered with terraces or a network of pits where the method comprises providing a SiC substrate, annealing in an external beam of silicon atoms, and then cooling in an external beam of silicon atoms is disclosed.

Claims

1. A method of obtaining a silicon carbide (SiC) graphene surface composite with a controlled surface morphology, comprising the steps of: (a) providing a silicon carbide (SiC) substrate, (b) annealing the SiC substrate at a temperature of 1573 K to 2090 K, at a pressure of not more than 510.sup.7 mbar, in a first beam of silicon atoms from an external source of silicon atoms, (c) cooling, wherein in step (c) the SiC substrate from step b) is cooled at a rate of 0.23 K/s to 1.43 K/s, in a second beam of silicon atoms from the external source of silicon atoms, to obtain a surface covered with terraces, or cooled at a rate of >100 K/s in a third beam of silicon atoms from the external source of silicon atoms, to obtain a surface covered with a network of pits.

2. The method according to claim 1, characterized in that the second beam of silicon atoms from the external source of silicon atoms during cooling ranges from 7.010.sup.13 cm.sup.2s.sup.1 to 2.510.sup.14 cm.sup.2s.sup.1.

3. The method according to claim 1, characterized in that the first beam of silicon atoms from the external source of silicon atoms during the annealing ranges from 7.010.sup.13 cm.sup.2s.sup.1 to 2.510.sup.14 cm.sup.2s.sup.1.

4. The method according to claim 1, characterized in that the third beam of silicon atoms from the external source of silicon atoms during cooling ranges from 5.010.sup.13 cm.sup.2s.sup.1 to 2.510.sup.14 cm.sup.2s.sup.1.

5. The method according to claim 1, characterized in that the external source of silicon atoms is a sublimation source.

6. The method of claim 1, wherein the SiC substrate has a crystalline structure.

7. The method of claim 1, wherein the SiC substrate has a polycrystalline structure.

Description

(1) Embodiments of the invention are illustrated in the Figures, where

(2) FIG. 1a-1b is an image of the SiC surface with a graphene layer for a cooling speed of 0.45 K/s,

(3) FIG. 2a-2b is an image of a SiC surface with a graphene layer for a cooling speed of 0.45 K/s,

(4) FIG. 3 is an image of the SiC surface with a graphene layer for a cooling speed of 0.45 K/s,

(5) FIG. 4 is an image of a SiC surface with a graphene layer for a cooling speed of 0.23 K/s,

(6) FIG. 5 is an image of a SiC surface with a graphene layer for a cooling speed of 1.43 K/s,

(7) FIG. 6 is an image of the SiC surface with a graphene layer for a cooling speed of 100 K/s,

(8) FIG. 7 is an image of a SiC surface with a graphene layer for a cooling speed of 100 K/s and a graphitization temperature of 1549 K,

(9) FIG. 8 is an ARPES spectrum of a SiC surface covered with four-layer graphene,

(10) FIG. 9 is an ARPES spectrum of SiC surface covered with two-layer graphene,

(11) FIG. 10 is a graphene on SiC surface obtained with a cooling rate of 0.3 K/s without silicon beam,

(12) FIG. 11 is an exemplary pit profile,

(13) FIG. 12-14 are a comparison of surface profile of the samples shown in FIG. 4 and

(14) FIG. 15 and FIG. 16, respectively, FIG. 17 is an image of the SiC surface with a graphene layer for a cooling rate of 0.45 K/s and a process temperature of 2090K,

(15) FIG. 18a is an image of the sample surface obtained at the cooling rate 100 K/s and the value of the beam of silicon atoms of 2.510.sup.14 cm.sup.2s.sup.1, FIG. 18b is a three-dimensional image of the surface of the sample according to example 12.

EXAMPLE 1

Preparation of Graphene on a SiC Surface with a Cooling Rate of 0.45 K/s (Sample 1 18.7.c)

(16) The SiC crystal with the (0001) orientation is introduced into the vacuum chamber, then the chamber is pumped down to a pressure of <110.sup.9 mbar and the sample is annealed at a temperature gradually increasing from 373 K to 1123 K (degassing) and then the samples are annealed at a temperature of 1223 K under vacuum conditions in silicon atoms beam of a value of 6.010.sup.12 cm.sup.2s.sup.1. This ensures a silicon growth rate of 1 /min. Then the surface prepared in this way is subjected to the graphitization process at the temperature of 2024 K in a beam of silicon atoms from an external sublimation source corresponding to the nominal growth rate of silicon layers of 30 /min, which corresponds to a silicon beam of 1.810.sup.14 cm.sup.2s.sup.1 at a pressure in the vacuum chamber not exceeding 510.sup.7 mbar. After completion of the graphitization step, the sample is cooled down at the rate of 0.45 K/s in a beam of silicon atoms of 1.810.sup.14 cm.sup.2s.sup.1. FIG. 8 shows the spectrum obtained by the angle-resolved photoelectron spectroscopy (ARPES) technique, confirming the presence of four-layer graphene on the SiC surface (Dirac cone-shaped spectrum). The number of layers is equal to the number of dispersion relations visible in the spectrum (marked with arrows). The spectrum is characteristic for the four-layer ABC-stacked graphene, which is especially visible for the part of the spectrum located close to the Fermi energy, which is shown in FIG. 8. The surface image of the sample obtained in this way is shown in FIG. 1a. 1b. The samples cooled at a very slow rate (in this case 0.45 K/s) are characterized by an ordered, almost perfectly flat surface with a well-developed structure of low terraces.

EXAMPLE 2

Preparation of Graphene on a SiC Surface with a Cooling Rate of 0.45 K/s (Sample 2)

(17) The preparation of graphene on the SiC surface is carried out according to example 1, with the difference that the graphitization step is carried out at the temperature of 1973K. The surface image of the thus obtained sample is shown in FIGS. 2a-2b. FIG. 9 shows the spectrum obtained by the angle-resolved photoelectron spectroscopy (ARPES) technique, confirming the presence of two-layer graphene on the SiC surface.

EXAMPLE 3

Preparation of Graphene on a SiC Surface with a Cooling Rate of 0.45 K/s (Sample 3)

(18) The preparation of graphene on the SiC surface is carried out according to example 1, with the difference that the graphitization step is carried out at the temperature of 1600K, while the second and third beam of silicon atoms (the beam used during graphitization and during cooling) is 7.010.sup.13 cm.sup.2s.sup.1. The surface image of the sample thus obtained is shown in FIG. 3.

EXAMPLE 4

Preparation of Graphene on a SiC Surface with a Cooling Rate of 0.23 K/s (Sample 4)

(19) The preparation of graphene on the SiC surface is carried out according to example 1, with the difference that the graphitization step is carried out at the temperature of 1975K, and after completion of the graphitization step, the sample is cooled down at a rate of 0.23 K/s. The surface image of the sample thus obtained is shown in FIG. 4.

EXAMPLE 5

Preparation of Graphene on a SiC Surface with a Cooling Rate of 1.43 K/s (Sample 5)

(20) The preparation of graphene on the SiC surface is carried out according to example 1, with the difference that the graphitization step is carried out at the temperature of 1831K, and after completion of the graphitization step, the sample is cooled down at a rate of 1.43 K/s. The surface image of the sample thus obtained is shown in FIG. 5.

EXAMPLE 6

Preparation of Graphene on a SiC Surface with a Cooling Rate of 100 K/s (Sample 6)

(21) The preparation of graphene on the SiC surface is carried out according to example 1, with the difference that the graphitization step is carried out at the temperature of 1975K, and after completion of the graphitization step, the sample is cooled down at a rate of 100 K/s. The surface image of the sample thus obtained is shown in FIG. 6a. The sample is characterized by the presence of numerous pits on the surface, which is especially visible in three-dimensional images (FIG. 6b).

EXAMPLE 7

The Preparation of Graphene on a SiC Surface with a Cooling Rate of 100 K/s (Sample 7)

(22) The preparation of graphene on the SiC surface is carried out according to example 1, with the difference that the graphitization step is carried out at the temperature of 1549K, and after completion of the graphitization step, the sample is cooled at a rate of 100 K/s in a beam of silicon atoms of 5.010.sup.13 cm.sup.2s.sup.1. The surface image of the sample thus obtained is shown in FIG. 7a. The sample is characterized by the presence of numerous pits on the surface, which is especially visible in three-dimensional images (FIG. 7b).

EXAMPLE 8

Comparison with Commercial Samples (Sample 8 and 9, Comparative Example)

(23) FIGS. 13 and 15 (Sample 5), and FIGS. 14 and 16 (Sample 6) show surface cross sections of commercial graphene samples on a SiC surface taken with an atomic force microscope. In both cases, high terraces are clearly visible, which is additionally visible in FIGS. 13-14. The comparison with the profile of sample 4 (FIG. 4 and FIG. 12), obtained according to the invention, clearly shows that the terraces are much lower in relation to the graphene obtained with the methods used so far.

(24) The samples of commercially available graphene on SiC differ significantly from graphene produced by means of annealing in a beam of silicon and very slow cooling. The most important characteristic of commercial graphene is the presence of very high terraces on the surfacewith a height of approx. 10 nm for sample 5 and approx. 15 nm for sample 6. In the case of graphene produced with the use of slow cooling (sample 4), there are only narrow and low terraces on the surface, the surface is therefore very flat.

EXAMPLE 9

Preparation of Graphene on a SiC Surface with a Cooling Rate of 0.3 K/s, without a Beam of Silicon (Comparative Example)

(25) The preparation of graphene on the SiC surface is carried out according to example 2, with the difference that the sample is cooled without the presence of a beam of silicon. The surface image of the sample thus obtained is shown in FIG. 10. The image shows that the surface prepared in this way is disordered, the structure of the terraces is disturbed, and defects and pits appear on the surface. This shows that to obtain a surface with an almost perfectly flat morphology, covered only with low terraces, it is necessary, in addition to the slow cooling rate of the sample, to place it in the beam of silicon atoms during cooling.

EXAMPLE 10

Determination of the Surface Density of Pits and the Depth of Pits

(26) The depth of pits was determined on the basis of the AFM studies. An exemplary profile of the pit (sample 6, part of the image of example 6) is shown in FIG. 11. The depth of the pit is 2 nm=210.sup.9 m. The maximum depth of pits for samples annealed at high cooling rate is 3.510.sup.9 m. The surface density of the pits was determined by counting them in the AFM images. The pit is understood as the difference in height determined by the image recognition algorithm from the obtained images of the surface of the samples using the AFM method.

EXAMPLE 11

Preparation of Graphene on a SiC Surface with a Cooling Rate of 0.45 K/s (Sample 10)

(27) The preparation of graphene on the SiC surface is carried out according to example 1, with the difference that the graphitization step is carried out at a temperature of 2090K, the first and second beam of silicon atoms are equal to 2.510.sup.14 cm.sup.2s.sup.1, and after the graphitization step is completed, the sample is cooled down at the speed of 0.45 K/s. The surface image of the sample thus obtained is shown in FIG. 17.

EXAMPLE 12

Preparation of Graphene on a SiC Surface with a Cooling Rate of 100 K/s (Sample 11)

(28) The preparation of graphene on the SiC surface is carried out according to example 1, with the difference that the graphitization step is carried out at a temperature of 1670K, and after the graphitization step is completed, the sample is cooled at the rate of 100 K/s in a beam of silicon atoms of 2.510.sup.14 cm.sup.2s.sup.1. The surface image of the sample thus obtained is shown in FIG. 18a. The sample is characterized by the presence of numerous pits on the surface, which is especially visible in three-dimensional images (FIG. 18b).