D. Casterman

The University of Sheffield, Sheffield, ENG, United Kingdom

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Publications (5)15.1 Total impact

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    ABSTRACT: A Pd-contacted dopant-free CNTFET with small-diameter (0.57 nm) carbon nanotube showing an anomalous n-type electrical characteristic is reported for the first time. This observed behaviour is attributed to a carbon nanotube work function higher than (or close to) palladium as well as a large hole-to-electron effective mass ratio of approximately 2.5 predicted by hybridization in small-diameter nanotubes. A variation of the conduction type with temperature is also observed and is attributed to an increase of the palladium work function and decrease of the CNT work function with increasing temperature.
    Nanotechnology 05/2010; 21(21):215202. · 3.84 Impact Factor
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    D. Casterman, M. M. De Souza
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    ABSTRACT: An efficient numerical method for the evaluation of the Green’s function used in the calculation of the Coulomb-limited electron mobility in high- κ metal oxide semiconductor field effect transistors is presented. This simple method is applicable to gate stacks with an arbitrary number of layers of varying dielectric permittivity. A charge profile with varying dielectric profile is demonstrated to show an increase in Coulomb-limited mobility of 16% in comparison to a point charge located at the interface. A metal gate reduces the scattering potential due to its infinite dielectric constant which leads to lesser impact of charge in comparison to a polysilicon gate. The Coulomb-limited mobility for devices having identical equivalent oxide thickness of 0.5–0.8 nm with (a) a hafnium silicate interfacial layer (IL) and (b) zero IL is presented.
    Journal of Applied Physics 04/2010; · 2.21 Impact Factor
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    ABSTRACT: The effects of gold deposition on monolayer graphene (MG) epitaxied on SiC (0001) substrate are examined via scanning tunneling microscopy and scanning tunneling spectroscopy (STS). Two types of surfaces with distinctive topography are demonstrated: (i) intercalated gold clusters having no interaction with graphene and (ii) 13×13-G reconstruction attributed to a Moiré pattern arising from the intercalation of 1 ML of gold between a MG and the underlying SiC substrate. This surface also displays a 2×2R30-Au (111) surface reconstruction interpreted as surface corrugation. The STS curve shows a possible hole-doping effect in the latter case.
    Applied Physics Letters 07/2009; 94(26):263115-263115-3. · 3.79 Impact Factor
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    ABSTRACT: The impact of hybridization on the Schottky barrier height (SBH) for holes at a metal/nanotube contact is investigated using ab initio density-functional theory. For small diameters, the impact of hybridization is a deviation of the SBH in comparison to that calculated using the “1/d” rule, where d is the diameter of the carbon nanotube (CNT). In the hybridization region, the SBH reduces with chiral angle, suggesting that CNTs in this region may well be suited to microelectronic applications due to small SBH and large band gaps. Hybridization also causes a difference between the effective mass of electrons and holes, supposed to be identical within the tight-binding approximation. A strongly patterned behavior of the effective mass dependent on chirality and diameter is also reported here.
    Physical review. B, Condensed matter 03/2009; 79(12). · 3.77 Impact Factor
  • D. Casterman, M. M. De Souza
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    ABSTRACT: The mechanism of charge transfer for doping p-type Palladium-contacted Carbon Nanotube Field Effect Transistors (CNTFETs) using SbCl6 is investigated via ab initio Density Functional Theory (DFT). The interaction of SbCl6 with a (100)-Pd surface leads to an adsorption of a Chlorine atom, which peels off from a rehybridized SbCl5, lowering the workfunction of Pd. The interaction of SbCl6 with carbon nanotube having different diameters shows that the molecule is repulsed from the surface of the nanotube, after acquiring an electron from the CNT for neutralization. The band structure calculation reveals that this exchange of charge enables the nanotube to be doped p-type. Hence both interactions serve to enhance injection of holes from Pd to the CNT.
    Journal of Materials Science Materials in Electronics 01/2007; 18(7):729-734. · 1.49 Impact Factor