CNT devices Since their first discovery in addition to fabrication in 1991, CNTs have recei

CNT devices Since their first discovery in addition to fabrication in 1991, CNTs have recei www.phwiki.com

CNT devices Since their first discovery in addition to fabrication in 1991, CNTs have recei

Horton, Paul, Meteorologist has reference to this Academic Journal, PHwiki organized this Journal CNT devices Since their first discovery in addition to fabrication in 1991, CNTs have received considerable attention because of the prospect of new fundamental science in addition to many potential applications. Avouris, IBM Stretching And confined de as long as mation Strain of less than 1% results in the CNT changing from metal to semiconductor.

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Twisting in addition to bending The encapsulated fullerenes can rotate freely in the space of a (10, 10) tube at room temperature, in addition to the rotation of fullerenes will affect C60@(10, 10) peapod electronic properties significantly; generally, orientational disorderwill remove the sharp features of the average density of states (DOS). However, the rotation of fullerenes cannot induce a metal–insulator transition. Unlike the multicarrier metallic C60@(10, 10) peapod, the C60@(17, 0) peapod is a semiconductor, in addition to the effects of the encapsulated fullerenes on tube valence b in addition to s in addition to conduction b in addition to s are asymmetrical. The distances between the centres of the fullerenes are 0.984 in addition to 1.278 nm as long as the C60@(10, 10) peapod in addition to C60@(17, 0) peapod, respectively. Peapods J. Chen, in addition to J. Dong, J. Phys. Condens. Matter, 16, 1401 (2004)

It is shown that, by appropriate work function engineering of the source, drain in addition to gate contacts to the device, the following desirable properties should be realizable: a sub-threshold slope close to the thermionic limit; a conductance close to the interfacial limit; an ON/OFF ratio of around 1000; ON current in addition to transconductance close to the low-quantum-capacitance limit. Semiconducting behavior in nanotubes was first reported by Tans et al. in 1998. Fig. 5 shows a measurement of the conductance of a semiconducting SWNT as the gate voltage applied to the conducting substrate is varied. The tube conducts at negative Vg in addition to turns off with a positive Vg. The resistance change between the on in addition to off state is many orders of magnitude. This device behavior is analogous to a p-type metal–oxide–semiconductor field-effect transistor (MOSFET), with the nanotube replacing Si as the semiconductor. At large positive gate voltages, n-type conductance is sometimes observed, especially in larger-diameter tubes. McEuen et al., IEEE Trans. Nanotechn., 1, 78 (2002) Semiconducting nanotubes are typically p-type at Vg=0 because of the contacts in addition to also because chemical species, particularly oxygen, adsorb on the tube in addition to act as weak p-type dopants. Experiments have shown that changing a tube’s chemical environment can change this doping level—shifting the voltage at which the device turns on by a significant amount. This has spurred interest in nanotubes as chemical sensors. Adsorbate doping can be a problem as long as reproducible device behavior, however. Controlled chemical doping of tubes, both p- in addition to n-type, has been accomplished in a number of ways. N-type doping was first done using alkali metals that donate electrons to the tube. This has been used to create n-type transistors, p-n junctions, in addition to p-n-p devices. Alkali metals are not air-stable, however, so other techniques are under development, such as using polymers as long as charge-transfer doping Scattering sites in nanotubes: I–V characteristics at different Vgs as long as a p-type SWNT FET utilizing an electrolyte gate in order to improve gate efficiency. McEuen et al., IEEE Trans. Nanotechn., 1, 78 (2002) Implying a mean-free path of approx. 700 nm. Maximum transconductance dI/dVg=20uA/V at Vg=-0.9V. Normalizing this to the device width of ~2nm: 10mS/um.

Bottom – gated CNT FET

Calculated conductance vs gate voltage at room temperature, varying (a) the work function of the metal electrode, in addition to (b) doping of the NT. In (a) the work function of the metal electrode is changed by -0.2 eV (red dashed), -0.1 eV (orange dashed), 0 eV (green), +0.1 eV (light blue), in addition to +0.2 eV (blue), from left to right, respectively. In (b) the doping atomic fraction is n-type 0.001 (red), 0.0005 (orange), in addition to 0.0001 (green), in addition to p-type 0.0001 (blue dashed), from left to right, respectively. Thus the gate field induces switching by modulating the contact resistance (the junction barriers). Oxygen adsorption at the junctions modifies the barriers (i.e. the local b in addition to -bending of the CNT) in addition to affects the injection of carriers (holes or electrons). The inverse subthreshold slope, which is a measure of the efficiency of the gate field in turning on the device, decreases with a decrease in gate oxide thickness. This behavior cannot be explained by conventional field-effect transistor models, in addition to has in fact been shown to be a result of the presence of Schottky barriers at the metal/nanotube interface at the source in addition to drain. There is a clear difference in the inverse subthreshold slope as long as the case of sweeping all gate segments together (S=400 mV/dec) versus sweeping only the inner segments (S=180 mV/dec). We attribute the observed change in S to a change from Schottky barrier modulation to bulk switching. (b) shows linear plots of the subthreshold portion (where the current is dominated by carrier density) of the transfer characteristics when the inner gate segments are swept together or separately. The current nearly identical, despite the fact that the effective gate lengths differ by a factor of 1.6 . This is in contrast to the expected behavior of diffusive transport, where the current varies inversely with the gate length.

Calculated output characteristics of the symmetric (dashed lines) in addition to the asymmetric (solid lines) CNFET. We have introduced nanotemplate to control selective growth, length in addition to diameter of CNT. Ohmic contact of the CNT/metal interface was as long as med by rapid thermal annealing (RTA). Diameter control in addition to surface modification of CNT open the possibility to energy b in addition to gap modulation.

Diode-like rectifying behavior was observed in a CNx /C multiwalled nanotube due to its being one half doped with nitrogen. FETs based on an individual CNx /C nanotube were fabricated by focused ion-beam technology. The nanotube transistors exhibited n-type semiconductor characteristics, in addition to the conductance of nanotube FETs can be modulated more than four orders of magnitude at room temperature. The electron mobility of a CNx /C NT FET estimated from its transconductance was as high as 3840 cm2/Vs. The n-type gate modulation could be explained as due the effect of bending of the valence b in addition to in the Schottky-barrier junction. CNTs doped with fullerenes inside nanotubes (so-called peapods) are interesting materials as long as novel CNT FET channels. Transport properties of various peapods such as C60-, Gd@C82-, in addition to Ti2@C92-peapods have been studied by measuring FET I-V characteristics. Metallofulleren peapod FETs exhibited ambipolar behavior both p- in addition to n-type characteristics by changing the gate voltage, whereas C60-peapod FETs showed unipolar p-type characteristics similar to the FETs of intact single-walled nanotubes. This difference can be explained in terms of a b in addition to gap narrowing of the single-walled nanotube due to the incorporation of metallofullerenes. The b in addition to gap narrowing was large in the peapods of metallofullerene, where more electrons are transferred from encapsulated metal atoms to the fullerene cages. The entrapped fullerene molecules are capable of modifying the electronic structure of the host tube. It is, there as long as e, anticipated that the encapsulation of fullerene molecules can play a role in b in addition to gap engineering in nanotubes in addition to hence that peapods may generate conceptually novel molecular devices.

Schematic illustration of elastic strain distributed around the site of metallofullerenes in a small-diameter nanotube peapod in addition to the corresponding changes in conduction in addition to valence b in addition to edges. Charge transport in a partially filled peapod FET in “metal-on-top” setup. (a) Transfer characteristics at various temperatures. Data were taken at Vds = 0.3 V. CNT junction Current vs. voltage characteristics of an all-carbon transistor with semiconducting nanotube as channel, with different voltages at the carbon gate. The back gate is kept at 0 V. The measurements were carried out at 4 K. The b in addition to profile of the SB CNTFET at the minimal leakage bias (VG=0V) as long as VD=0.6V. The b in addition to profile of the MOS CNTFET when the source-drain current is low. (VD=0.6V in addition to VG=-0.3V). The channel is a (13,0) nanotube. Ambipolar conduction leads to a large leakage current that exponentially increases with the power supply voltage, especially when the tube diameter is large. An asymmetric gate oxide SB CNTFET has been proposed as a means of suppressing ambipolar conduction. SB CNTFETs of any type, however, will likely suffer from the need to place the gate electrode close to the source (which increases parasitic capacitance) in addition to metal-induced gap states, which increase source to drain tunneling in addition to limit the minimum channel length.

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Id vs. Vd characteristics at VG = 0.4V as long as the MOS CNTFET (the solid line) in addition to the SB CNTFETs (the dashed lines). The off-current of all transistors (defined at Vd=0.4V in addition to Vg=0) was set at 0.01µA by adjusting the flat b in addition to voltage as long as each transistor. For the SB CNTFETs, three barrier heights we simulated. The channel is a (13,0) nanotube, which results in a diameter of d 1 nm, in addition to a b in addition to gap of Eg 0.83 eV. Id vs. Vg characteristics at Vd = 0.4V as long as the zero barrier SBFET in addition to the MOS CNTFET. The gated channel of both transistors is a 5nm-long, intrinsic (13, 0) CNT. By eliminating the Schottky barrier between the source in addition to channel, the transistor will be capable of delivering more on-current. The leakage current of such devices will be controlled by the full b in addition to gap of CNTs (instead of half of the b in addition to gap as long as SB CNTFETs) in addition to b in addition to -to-b in addition to tunneling. These factors will depend on the diameter of nanotubes in addition to the power supply voltage.

Horton, Paul Meteorologist

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