New results

Samples of nanodiamond sheets surrounded by amorphous carbon sheets have been taken from my MSc thesis. These samples contained diamond layer of width 7.1 A (8 layers of carbon atoms). The samples with other width of nanodiamond layer were obtained by inserting (cutting) a new diamond layers into the center of the sample like it shown on the picture (yellow atoms are initially frozen diamond and inserting diamond layers, green atoms are heated and cooled layers (the "green" part is the same for each sample)). An amorphous envelope remained the same therefore an influence of amorphous layers on the band gap of whole sample were also the same. In order to check quantum confinement effects the band gap of each sample was measured with accuracy of 0.15 eV.

Quanum confinement effects was not found in the band gap of these samples. The samples with the same amorphous envelope but different width of diamond layers showed the same value of band gap (within an accuracy of 0.15 eV) (see tables and Fig. 1).

Local densities of states of atoms in the center of diamond layers showed band gap of perfect bulk diamond 5.5 eV. For the atoms in diamond layer which were closer to an amorphous layer band gap was thinner. Local densities of states of atoms in the center of amorphous layers showed the value of a band gap which is very close to the band gap of the whole sample. (see Fig. 2).

So we can deduce that an influence of amorphous layer on the electronic properties of whole sample and a part of diamond region is so strong, that a quantum confinement effects are neglected. The system of nanodiamonds layers sandwitched between amorphous carbon layers is not suitable for studyind of quantum confinement effects.

                                          Sample 1

There are 19% sp2 bonded atoms in amorphous layers.

Number of atoms
Width of diamond layer (A)
band gap
160
0.9
1.25
192
1.25
1.37
224
1.6
1.38
288
2.3
1.38

Figure 1

Black line is for the sample with 160 atoms, green line is for the sample with 224 atoms, yellow line is for the sample with 288 atoms.


Figure 2

Local densities of states of atoms from the sample with 288 atoms. Red line is for abn atom which is located in the center of diamond layer, its band gap is 5.5 eV, black line is for the atom which is located on the edge between amorphos and diamond layers, green line is for the atom from center of amorphous layer.

                                          Sample 2


There are only 5% of sp2 atoms in amorphous layers.

Number of atoms
Width of diamond layer
band gap
160
1.5
5.2
192
1.85
5.35
224
2.2
5.32



                                        Sample 3

There are 26% sp2 bonded atoms in amorphous layers.

Number of atoms
Width of diamond layer (A)
band gap
224
1.03
0.89
256
1.4
0.87
288
1.74
0.89