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FIGURE 1. Scanning electron (SEM) micrographs of (a) a MWNT deposit and (b) a mat of SWNTs after purification. A few nanoparticles and embedded catalyst particles, respectively, are still present.

Figure 1 Scanning electron (SEM) micrographs of (a) a MWNT deposit and (b) a mat of SWNTs after purification. A few nanoparticles and embedded catalyst particles, respectively, are still present.

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FIGURE 2. Resistivity as a function of temperature for a purified SWNT film before and after heating and gvacuating the sample stage; (a) room temperature region (b) whole temperature range as log(R) vs po (2-D variable range hopping representation). at a “T*” of 255K. After the sample space was evacuated (bottom trace) there was only a slight minimum in the resistivity versus temperature curve which was shifted by more than 20K. Furthermore, this measurement has shown that even the slope of the log R vs T "3 had changed (see Fig. 2(b)), demonstrating the importance of the tube-tube contacts in the hopping process.
FIGURE 2. Resistivity as a function of temperature for a purified SWNT film before and after heating and gvacuating the sample stage; (a) room temperature region (b) whole temperature range as log(R) vs po (2-D variable range hopping representation). at a “T*” of 255K. After the sample space was evacuated (bottom trace) there was only a slight minimum in the resistivity versus temperature curve which was shifted by more than 20K. Furthermore, this measurement has shown that even the slope of the log R vs T "3 had changed (see Fig. 2(b)), demonstrating the importance of the tube-tube contacts in the hopping process.
FIGURE 3. (a) AFM image of aMW NT adhered on the polished ultrafiltration alumina membrane, with a portion bridging a pore of the membrane; (b) cross-sectional profiles of the nanotube (A) and corresponding pore (B) depicted in image (a). RENN hy MEARE Ne RINE RRR, AF SEENON L BLE DONA REN NEE 8 Once a suspended nanotube is located with the AFM, we determine its diameter, suspended length, and deflection midway along the suspended length from data like those of Fig. 3(b). The apparent tube width is a convolution of the tube diameter and the tip radius. Height remains a reliable measure of the tube diameter. The reversibility of the tube deflection and the linearity of the 6-F curve show that the nanotube response is linear and elastic. The slope of the curve, typically ~0.5m/N, directly gives the Young modulus of the MWNT once L and Ro are known.
FIGURE 3. (a) AFM image of aMW NT adhered on the polished ultrafiltration alumina membrane, with a portion bridging a pore of the membrane; (b) cross-sectional profiles of the nanotube (A) and corresponding pore (B) depicted in image (a). RENN hy MEARE Ne RINE RRR, AF SEENON L BLE DONA REN NEE 8 Once a suspended nanotube is located with the AFM, we determine its diameter, suspended length, and deflection midway along the suspended length from data like those of Fig. 3(b). The apparent tube width is a convolution of the tube diameter and the tip radius. Height remains a reliable measure of the tube diameter. The reversibility of the tube deflection and the linearity of the 6-F curve show that the nanotube response is linear and elastic. The slope of the curve, typically ~0.5m/N, directly gives the Young modulus of the MWNT once L and Ro are known.
According to the Fowler Nordheim theory (F-N theory, i.e., elastic tunneling through a triangular barrier, with the electron distribution described by Fermi-Dirac statistics [22]), the energy distribution oof the emitted electrons is Jpn(E) « exp((E - E-)/b(F/o!/2))£(E - Ep), where E is the electron energy, E¢ the Fermi energy, @ the work function, F the electric field, and f(E) the Fermi-Dirac distri- bution. We show in Fig. 4(a) a field electron energy spectra obtained on a MWNT film, along with the best fit obtained with the F-N distribution. Obviously, the distribution doesn’t match the measured spectra. The F-N theory predicts exponential slopes or both sides of the distribution which arise from the tail of the Fermi-Dirac distribution and from the increase of the barrier width, respectively.
According to the Fowler Nordheim theory (F-N theory, i.e., elastic tunneling through a triangular barrier, with the electron distribution described by Fermi-Dirac statistics [22]), the energy distribution oof the emitted electrons is Jpn(E) « exp((E - E-)/b(F/o!/2))£(E - Ep), where E is the electron energy, E¢ the Fermi energy, @ the work function, F the electric field, and f(E) the Fermi-Dirac distri- bution. We show in Fig. 4(a) a field electron energy spectra obtained on a MWNT film, along with the best fit obtained with the F-N distribution. Obviously, the distribution doesn’t match the measured spectra. The F-N theory predicts exponential slopes or both sides of the distribution which arise from the tail of the Fermi-Dirac distribution and from the increase of the barrier width, respectively.
We observed luminescence induced by electron field emission on single- and mul- tiwall nanotubes films as well as on single MWNT emitters. The light emission occurred in the visible part of the spectrum, and could sometimes be seen with the naked eye. No light emission was detected without applied potential. The emitted light intensity followed furthermore closely the variations in emitted cur- rent, as can be assessed in Fig. 5(a), where the emitted current and emitted light intensity have been simultaneously measured. Actually, the emitted intensity depends critically on the current, since the relative variations are 3-4 times higher for the lumi- nescence as compared to the current.
We observed luminescence induced by electron field emission on single- and mul- tiwall nanotubes films as well as on single MWNT emitters. The light emission occurred in the visible part of the spectrum, and could sometimes be seen with the naked eye. No light emission was detected without applied potential. The emitted light intensity followed furthermore closely the variations in emitted cur- rent, as can be assessed in Fig. 5(a), where the emitted current and emitted light intensity have been simultaneously measured. Actually, the emitted intensity depends critically on the current, since the relative variations are 3-4 times higher for the lumi- nescence as compared to the current.
FIGURE 6. Sequence of field emission patterns obtained on a SWNT film. The FEM | patterns observed on the screen reflect directly the emitted current distribu- tion. Since the tunneling electrons have very small kinetic energy, they follow the lines of forces, which diverge in first approximation radially from the emitter surface. The emission pattern at the tip, reflecting the spatial distribution of the emitted density, is thus enlarged before hitting the screen. A pattern detected by FEM on carbon nanotubes can be induced either by adsorbates, by local changes in the emitted current due to preferential emission sites (surface steps that result in a locally enhanced field amplifi- cation, protusions of amorphous carbon present on the tip surface, or atomic wires), or spatial variations of the electronic density.
FIGURE 6. Sequence of field emission patterns obtained on a SWNT film. The FEM | patterns observed on the screen reflect directly the emitted current distribu- tion. Since the tunneling electrons have very small kinetic energy, they follow the lines of forces, which diverge in first approximation radially from the emitter surface. The emission pattern at the tip, reflecting the spatial distribution of the emitted density, is thus enlarged before hitting the screen. A pattern detected by FEM on carbon nanotubes can be induced either by adsorbates, by local changes in the emitted current due to preferential emission sites (surface steps that result in a locally enhanced field amplifi- cation, protusions of amorphous carbon present on the tip surface, or atomic wires), or spatial variations of the electronic density.
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