Nanotube silicide

Field emission displays are VFDs that use field emission cathodes as the electron source. The cathodes can be molybdenum microtips,33-35 carbon films,36,37 carbon nanotubes,38" 16 diamond tips,47 or other nanoscale-emitting materials.48 Niobium silicide applied as a protective layer on silicon tip field emission arrays has been claimed to improve the emission efficiency and stability.49 ZnO Zn is used in monochrome field emission device (FED) displays but its disadvantage is that it saturates at over 200 V.29... 

The next step Ifom Silicon-based sheet polymers to tubular structures has been performed so far only on the computer. In Chapter 17, Th. Frauenheim et al. describe the structure and the electronic properties of silicide, silane and siloxane nanotubes. The structures can be understood in terms of conventional graphitic carbon nanotubes by replacing the flat hexagons by puckered rings. The electronic properties depend on the tube diameter. Potential applications are discussed. 

Figure 17.3. Examples of the structures of silicide and silane nanotubes with (8,0) (left panel) and (8,8) (right panel) chirality. From top to bottom are shown pure silicide (Si ) and the silanes (SiH-io) and (SiH-sf), in each case in top and side views (taken from ref...

Figure 17.4. Strain energies (left) and gap sizes (right) as functions of mean diameter are shown for all calculated (n,0) and (n,n) silicide and silane nanotubes. The gap sizes of planar reference structures are symbolized by a single line due to nearly equal gap widths of 2.49 eV and 2.50 eV for planar Si and SiH, respectively. (Taken from ref.

Analyzing the electronic properties of the investigated systems, the flat silicide and the SiH sheets, as well as all nanotubes considered here, were found to be semiconducting. Within our DFTB method, we obtain band gaps of 2.49 eV and 2.50 eV for Sf and SiH layers, respectively, agreeing quite nicely with that obtained by other calculations (2.48 eV) and experimental results... 

Additionally, the mechanical properties of silicide and silane nanotubes have been obtained by DFTB calculations. The data clearly indicate that Si-based nanotubes are less stiff than other nanotubes hitherto considered, such as those made of P, BN, or C. Compared with typical values of Young s moduli of about 1.2 TPa for CNTs, the values for Si-based tubes are of the order of the bulk modulus of crystalline silicon, 98 GPa, predicted with the same theoretical method. Depending on tube diameter and type, the Young s moduli vary between 55 and 80 GPa. 

Viewed from above the layer, the structure clearly resembles a graphenelike layer, although it is puckered in a similar way as in the silicide, silane, and phosphorus cases. Thus, the question arises as to whether siloxenes may form stable tubular structures as predicted for hypothetical silicides, silanes, and black phosphorus nanotubes. The experimentally synthesized siloxene consists of hexagonal puckered layers, in which the Si-Si bond distance is 2.34 A, the Si-H bond length is 1.54 A, and the Si-O bond length is 1.60 A. The Si-0-H bond angle is 115°. 

Eleetronieally, the flat sheet as well as all the nanotubes considered here were determined to be semieonducting. In Figure 17.7, the gap sizes of nanotubes are shown as a function of the mean diameter. The gap sizes grow from about 1.5 eV for the smallest (n,0) nanotube towards the value for flat siloxene sheets (1.9 eV) as the tube diameter increases, as in the case of silicides and silanes discussed above. 

Boron compounds with nonmetals, i.e., boron hydrides, carbides, nitrides, oxides, silicides, and arsenides, show simple atomic structures. For example, boron nitride (BN) can be found in layered hexagonal, rhombohedral, and turbostratic or denser cubic and wurtzite-like structures, as well as in the form of nanotubes and fullerenes. Boron compounds with metalloids also differ from borides by electronic properties being semiconductors or wide-gap insulators. 

CNT formation (although Au was shown to be able to nucleate nanotubes). In the case of Pd, the metallic nanoparticles demonstrated a pronounced metal-support interaction, resulting in Pd silicide formation. 

Mink JE, Rojas JP, Logan BE, Hussain MM (2012) Vertically grown multiwalled carbon nanotube anode and nickel silicide integrated high performance microsized (1.25 pL) microbial fuel cell. Nano Lett 12 791-795... 

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