Refractory carbide layer

1 . A chemical vapor deposition (CVD) method for preparing a layer comprising silicon carbide crystals, wherein at least part of the layer is formed from a gas mixture containing a silicon source and an aromatic carbon source, wherein the molar C/Si ratio in said gas mixture is from about 0.85 to about 1.45;

wherein in SEM image analysis of a cross section of the layer, at most about 20% of the surface of the cross section area has a pattern of parallel lines tilted by more than 15° with respect to a portion of a surface of the layer which is closest to the respective image;

wherein a surface of the layer has a mean linear intercept surface grain size in a range of 0.2-25 μm;

wherein the surface of the layer comprises refractory carbide crystal tops having a regular hexagonal pyramid shape;

wherein a distribution of silicon carbide crystal orientations is such that an orientational quality Q is at least about 0.95,

wherein the orientational quality Q is calculated from maximum peak intensities of an X-ray diffractogram detected with Cu k-alpha radiation at 1.5406 Å wavelength, according to the following formula

Q

=

I

111

+

I

2

⁢

2

⁢

2

+

I

3

⁢

3

⁢

3

/

5

⁢

1

⁢

1

I

1

⁢

1

⁢

1

+

I

2

⁢

0

⁢

0

+

I

2

⁢

2

⁢

0

+

I

311

+

I

2

⁢

2

⁢

2

+

I

4

⁢

0

⁢

0

+

I

3

⁢

3

⁢

1

+

I

4

⁢

2

⁢

0

+

I

3

⁢

3

⁢

3

/

5

⁢

1

⁢

1

+

I

4

⁢

2

⁢

2

wherein

I 111 is the maximum intensity at 2θ ranging from 34.6° to 36.6°,

I 200 is the maximum intensity at 2θ ranging from 40.4° to 42.4°,

I 220 is the maximum intensity at 2θ ranging from 59.0° to 61.0°,

I 311 is the maximum intensity at 2θ ranging from 70.8° to 72.8°,

I 222 is the maximum intensity at 2θ ranging from 74.5° to 76.5°,

I 400 is the maximum intensity at 2θ ranging from 89.0° to 91.0°,

I 331 is the maximum intensity at 2θ ranging from 99.8° to 101.8°,

I 420 is the maximum intensity at 2θ ranging from 103.4° to 105.4°,

I 333/511 is the maximum intensity at 2θ ranging from 132.4° to 134.4°,

I 422 is the maximum intensity at 2θ ranging from 119.0° to 121.0°.

2 . The chemical vapor deposition method of claim 1 , wherein the aromatic carbon source is a C 6 to C 30 aromatic compound selected from the group consisting of benzene, a C 1 -C 6 -alkyl benzene, a di-C 1 -C 6 -alkyl benzene, a tri-C 1 -C 6 -alkyl benzene, a tetra-C 1 -C 6 -alkyl benzene, a biphenyl derivative, a diphenylmethane derivative and a naphthalene derivative.

3 . The chemical vapor deposition method of claim 1 , wherein the reaction temperature is from about 900 to about 1800° C.

4 . The chemical vapor deposition method of claim 1 , wherein the reaction is carried out under a reduced pressure of from about 0 to about 300 mbar; and/or

wherein the gas mixture further comprises an inert carrier gas comprising H 2 or Ar, and said inert gas carrier is present in a molar ratio of the inert carrier gas to Si of from about 10 to about 40.

5 . The chemical vapor deposition method of claim 1 , wherein the method yields a free-standing layer or wherein the layer is deposited onto a carbonaceous substrate, onto a siliconaceous substrate, or onto a layer comprising refractory metal carbides.