Transformation of graphite into nanodiamond following extreme electronic excitations

Graphite targets have been irradiated at $90\mathrm{K}$ and $300\mathrm{K}$ with $850\mathrm{MeV}$ and $6\mathrm{GeV}$ lead ions and with $20–30\mathrm{MeV}$ fullerene cluster ions in a large range of fluences. Damage creation was studied both by transmission electron microscopy and Raman spectroscopy. The very strong energy density deposited in electronic processes generates a highly excited region around the projectile path. The relaxation of the deposited energy via hydrodynamic expansion and shock-wave propagation leads to the formation of small defective graphitic domains and of nanocrystalline diamond particles.

Figure 1

Transmission electron micrograph of graphite irradiated at $300\mathrm{K}$ and at normal incidence with $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions up to a fluence of $2\times {10}^{11}\text{ions}{\mathrm{cm}}^{-2}$.

Figure 2

Transmission electron micrograph of graphite irradiated at $300\mathrm{K}$ and at normal incidence with $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions up to a fluence of $2\times {10}^{11}\text{ions}{\mathrm{cm}}^{-2}$. The sample is tilted by 20° in the electron microscope. No reflection excited.

Figure 3

Latent tracks induced at $300\mathrm{K}$ in graphite, respectively, by (a) $30\mathrm{MeV}$ and (b) $20\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions. The samples were tilted by 20° in the electron microscope. The discontinuous lines are drawn to help the visualization of the disalignment of the tracks.

Figure 4

Electron diffraction pattern recorded on a massive graphite sample irradiated at $300\mathrm{K}$ with $20\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions up to a fluence of $8\times {10}^{11}\text{ions}{\mathrm{cm}}^{-2}$. Some of the main diffraction spots of graphite have been indexed.

Figure 5

Electron diffraction pattern recorded on a powdered graphite sample irradiated at $300\mathrm{K}$ with $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions up to a fluence of ${10}^{11}\text{ions}{\mathrm{cm}}^{-2}$. The original diffraction pattern shown in (a) is reproduced in (b) with circular lines lying on the new dotted diffraction spots induced by the irradiation. They correspond to interplanar distances: $0.085\mathrm{nm}<d_1<0.086\mathrm{nm}$, $0.097\mathrm{nm}<d_2<0.099\mathrm{nm}$, $0.161\mathrm{nm}<d_3<0.162\mathrm{nm}$, $0.106\mathrm{nm}<d_4<0.108\mathrm{nm}$.

Figure 6

Latent tracks induced at $300\mathrm{K}$ in graphite, respectively, by (a,b) $20\mathrm{MeV}$ and (c,d) $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions. Micrographs (a) and (c) were taken immediately after introducing the samples in the electron microscope, whereas micrographs (b) and (d) were registered after leaving a low current electron beam, respectively, during 2 or $5\text{minutes}$ on the samples.

Figure 7

Transmission electron micrographs of graphite irradiated at $300\mathrm{K}$ and at normal incidence with (a) $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions and (b) $20\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions. The samples were tilted by 20° in the electron microscope.

Figure 8

Transmission electron micrographs of graphite irradiated at $300\mathrm{K}$ and at normal incidence with $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions. The micrograph is taken after a few minutes observation in the TEM.

Figure 9

High resolution transmission electron micrograph of graphite irradiated by $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions at $300\mathrm{K}$.

Figure 10

Graphite sample deposited on a carbon covered TEM grid and irradiated at $300\mathrm{K}$ with $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ cluster ions up to a fluence of $5\times {10}^{10}\text{ions}{\mathrm{cm}}^{-2}$.

Figure 11

High resolution transmission electron micrograph of graphite irradiated by $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions at $300\mathrm{K}$ up to a fluence of $5\times {10}^9\text{ions}{\mathrm{cm}}^2$. The measured interplanar distances and angles are the following: $d_1=0.181\mathrm{nm}$, $d_2=0.334\mathrm{nm}$, $\theta (d_1,d_2)=60°$; $d_3=0.251\mathrm{nm}$, $d_4=0.247\mathrm{nm}$, $d_5=0.248\mathrm{nm}$, $d_6=0.250\mathrm{nm}$, $d_7=0.251\mathrm{nm}$, $\theta (d_4,d_5)=\theta (d_4,d_7)=60°$, $\theta (d_5,d_7)=\theta (d_6,d_7)=59°$.

Figure 12

High resolution transmission electron micrograph of graphite irradiated by $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions at $300\mathrm{K}$ up to a fluence of $5\times {10}^9\text{ions}{\mathrm{cm}}^2$. The measured interplanar distances and angle are the following: $d_1=0.257\mathrm{nm}$, $d_2=0.250\mathrm{nm}$, $d_3=0.259\mathrm{nm}$, $d_4=0.253\mathrm{nm}$, $d_5=0.255\mathrm{nm}$, $\theta (d_4,d_5)=61°$.

Figure 13

: High resolution transmission electron micrograph of graphite irradiated by $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ ions at $300\mathrm{K}$ up to a fluence of ${10}^{10}\text{ions}∕{\mathrm{cm}}^2$. The measured interplanar distances and angle are the following: $d_1=0.252\mathrm{nm}$, $d_2=0.261\mathrm{nm}$, $\theta (d_1,d_2)=59°$, $d_3=0.250\mathrm{nm}$.

Figure 14

Transmission electron micrograph of cleaved graphite deposited on an amorphous carbon film and irradiated at $90\mathrm{K}$ with $6\mathrm{GeV}$ Pb ions up to a fluence of $3\times {10}^{12}\text{ions}{\mathrm{cm}}^{-2}$.

Figure 15

High resolution transmission electron micrograph of cleaved graphite deposited on an amorphous carbon film and irradiated at $90\mathrm{K}$ with $6\mathrm{GeV}$ Pb ions up to a fluence of $3\times {10}^{12}\text{ions}{\mathrm{cm}}^{-2}$. The interplanar distances measured in the redeposited material are $d_1=0.209\mathrm{nm}$, $d_2=0.259\mathrm{nm}$ with $\theta (d_1,d_2)=90°$.

Figure 16

High resolution transmission electron micrograph of cleaved graphite deposited on an amorphous carbon film and irradiated at $90\mathrm{K}$ with $6\mathrm{GeV}$ Pb ions up to a fluence of $3\times {10}^{12}\text{ions}{\mathrm{cm}}^{-2}$. The interplanar distances measured in the redeposited material are $d_1=0.259\mathrm{nm}$, $d_2=0.253\mathrm{nm}$ with $\theta (d_1,d_2)=90°$, $d_3=0.223\mathrm{nm}$, $d_4=0.201\mathrm{nm}$ with $\theta (d_3,d_4)=72°$.

Figure 17

Graphite irradiated at $90\mathrm{K}$ with $850\mathrm{MeV}$ Pb ions up to a fluence of $8\times {10}^{11}\text{ions}{\mathrm{cm}}^{-2}$. Tracks seen from above (a), and after tilting by 20° in the microscope (b).

Figure 18

Visible Raman spectrum of a graphite sample irradiated with $850\mathrm{MeV}$ Pb ions at a fluence of $8\times {10}^{11}{\mathrm{cm}}^{-2}$ (sample $A$ in the text).

Figure 19

(Color online) Visible Raman spectrum of a graphite sample irradiated with $850\mathrm{MeV}$ Pb ions at a fluence of $8\times {10}^{12}{\mathrm{cm}}^{-2}$ (sample $B$ in the text).

Figure 20

(Color online) Visible Raman spectrum of a not evidently damaged area of a graphite sample irradiated with $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ at a fluence of $2.7\times {10}^{11}{\mathrm{cm}}^{-2}$ (sample $C$ in the text). The inset shows the fit to the $D$ peak. Notice the small feature at $482{\mathrm{cm}}^{-1}$.

Figure 21

(Color online) Visible Raman spectrum from a near-center zone of a graphite sample irradiated with $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ at a fluence of $2.7\times {10}^{11}{\mathrm{cm}}^{-2}$ (sample $C$ in the text). The inset shows the fit to the $D$ peak.

Figure 22

(Color online) Visible Raman spectrum from the center of a graphite sample irradiated with $30\mathrm{MeV}$ ${\mathrm{C}}_{60}$ at a fluence of $2.7\times {10}^{11}{\mathrm{cm}}^{-2}$ (sample $C$ in the text). The inset shows the fit to the $D$ peak. Notice the features at 1100 and $1443{\mathrm{cm}}^{-1}$, indicating that graphite was heavily shocked.

Figure 23

(Color online) Pressure-temperature phase diagram of carbon (from Ref. 40).