Shi-Dong Liang

Chiral and quantum size effects of single-wall carbon nanotubes on field emission

The emission current of a single-wall carbon nanotube (SWNT) in field emission is studied by the tunneling theory with the tight-binding approach. The emission current is almost independent of the chiral angle of SWNT in low fields, but increases with increase of chiral angles in very high fields. We found a room-temperature quantum size effect of SWNT on field emission. As the diameters of SWNTs increase, the current densities decrease for metallic tubes, but increase for semiconducting tubes. When the diameters of SWNTs are larger than 2nm the current densities of metallic and semiconducting tubes are very close. These chiral and quantum size effects are originated from the energy band structure of nanotubes.

Ultrafast optical emission of nanodiamond induced by laser excitation

The ultrafast optical emission of nanosized (∼5nm) crystallites has been detected under the picosecond (ps) laser excitation of 300nm through ultrafast fluorescence spectroscopy. This optical emission, photoluminescence (PL), induced at a laser wavelength of 300nm confines blue light. The ultrafast PL spectrum deconvoluted by a Monte Carlo method shows that two fast emission processes with decaytimes of 60 and 350ps. This type of ultrafast emission has not been observed under the same experimental conditions from the samples of a natural single crystal and an impure natural single crystal diamond. The mechanism responsible for this visible ultrafast emission is proposed by taking into account the effect of surface states and large surface-to-volume ratio of nanoparticles. All of these findings demonstrate the feasibility of using large band-gap nanomaterials to generate ultrafast optical emission at various wavelengths.

Chirality effect of single-wall carbon nanotubes on field emission

The chirality effect of an opened-end single-wall carbon nanotube on field emission is studied by using the tunneling theory with the tight-binding approximation. The characteristic of the emission-current line density versus field is found to be dependence on the chirality of nanotubes. A metallic tube has a line density higher than that of a semiconducting one. Also, for semiconducting tubes, a tube of larger chiral angle has a line density higher than that of smaller chiral angle; a zigzag semiconducting tube has a smallest line density among the others. Further, the Fowler–Nordheim plots may have a nonlinear behavior in high current region. Finally, at temperature T<1000 K, the emission current is almost independent of temperature. Our results are explained by the energy band structure of nanotubes.

The influence of temperature and electric field on field emission energy distribution of an individual single-wall carbon nanotube

The influence of temperature and electric field on field emission energy distribution (FEED) is studied. It is found that higher temperature energizes more higher-energy electrons. FEED peaks shift toward low energy linearly with the increase in applied voltage because of the electric field penetration. The theoretic current-voltage characteristic is fitted to the experimental data by the density of states, field enhancement factor, and temperature, from which the average energy of emitted electrons and then Fermi level of the carbon nanotube (CNT) is ascertained. This research confirms that the electric field competes with temperature and provides a method to ascertain the Fermi level of CNT.

Energy band structure effect on the field-electron energy distribution from a single-walled carbon nanotube

The energy band structure effect on field emission energy distribution (FEED) from a single-walled carbon nanotube (SWNT) has been investigated theoretically. Both single-peak and multi-peak characteristics of FEED have been found, which positions correspond to the position of the peaks of density of state (DOS) except for the peak around the Fermi energy for a metallic nanotube. The number and the width of the peaks of FEED strongly depend on the applied field and temperature. Based on the FEED, we have also calculated the average energy of emitted electrons from SWNT.

Research on the influence of image potential on the field emission behaviors of SmB 6 nanowires

SmB6 is believed as an ideal candidate for FE applications because of their unique properties. Up to date, the effect of image potential on the field emission (FE) behaviors of one-dimensional nanostructures is still unclear in experiments, and thus it becomes a challenging issue for the researchers. In this paper, the effect of image potential on FE properties of SmB6 nanowires are detailed studied by combination of experimental results and the generalized Schottky-Nordheim (SN) model. The experimental results show that they have a turn-on field of 3.4 V/μm (at 10 μΑ/cm2). Meanwhile, the image potential factor of SmB6 nanowires is calculated to be equal to 1 based on our model, which is resemble to ideal metal plane.

How to identify the image potential in field emission from non-metallic emitters?

We study comparatively Fowler-Nordheim (FN) and Schottky-Nordheim (SN) models to give a criterion to identify the image potential effect in the field emission from non-metallic emitters, which can be applied to distinct the metallic and non-metallic properties of the field emission from the experimental data.

5.5: Theoretical hints of spin polarized electron field emission from carbon nanotubes

We study theoretically the spin polarized electron field emission from carbon nanotube (CN) within an axial magnetic field. It is found that the spin polarization of emission current can reach 0.05~0.08 with 0.1~1μA emission current in the magnetic field 6T and the electric field 9~12V/nm at room temperature. The spin polarizations of the energy distributions oscillate and the peaks reach to 0.15~0.3 near Fermi energy in the magnetic field 6T. In low temperature 50~100K, the spin polarization of the emission current can reach to 0.1~0.2 with 0.01~0.02μA emission current in the magnetic field 6T and the electric field 8V/nm. It decreases and remains 0.05 in the temperature ~400K. These properties of the spin polarization in CN field emission originate from the modification of the energy band structure by the magnetic field.

Theory of field and thermionic electron emissions of carbon nanotubes

Carbon nanotubes (CN) exhibit not only experimentally excellent field-emission features, low threshold field, high current density and thermal stability,1 but also the current-voltage (I-V) characteristic deviates from the Fowler-Nordheim (FN) type behavior2 at high current density, which induces theoretical interesting to understand new physics in CN field emission. In principle, the energy band structure should play an important role in the field emission for low-dimensional materials. Based on the low-energy band structure of CNs we develop a generalized FN theory of field emission of CNs, giving analytically different I-V characteristics3 and thermionic emission equation, which provide a physical understanding of novel phenomena in CN field and thermionic emissions.

Effect of Peierls Distortion ou Field Emission of Carbon Nanotubes

Using the quantum tunneling theory with the tight-binding approach, we study the effects of Peierls distortion and the magnetic field in the field emission of carbon nanotubes. The Peierls distortion opens an energy gap at Fermi level, which suppresses the emission current. The responses of the emission current to the magnetic field are quite different for the semiconducting and metallic tubes