Molecular and Nanostructures
|Cover image generated by Ben Grosser (ITG, Beckman Institute, UIUC) on the results of modeling by SV. Rotkin (Lehigh) for the book "Applied Physics of Carbon Nanotubes: Fundamentals of Theory, Optics and Transport Devices", SV.Rotkin, S.Subramoney, Eds.; Nanoscience and Nanotechnology Series, Springer Verlag GmbH & Co. KG, (2005).||
Setup of an armchair SWNT METFET using the STM tip as a modulation gate.
The armchair [10,10] SWNT is on the SiO2 substrate. The Pt tip of
the Scanning Tunneling Microscope (STM) generates a strong and nonuniform
electric field at the surface of the SWNT. The image charges in the
dielectric substrate further enhance the nonuniformity of the field.
This breaks the symmetry of the SWNT and allows band gap opening in the
primarily metallic tube. Further device applications of this fundamental
effect are expected.
(Cover image for Slava V. Rotkin, and Karl Hess, "Possibility of a Metallic Field-Effect Transistor", Applied Physics Letters vol. 84 (16), p.3139-3141, 19 April 2004. See also another paper on the same topic Yan Li, Slava V. Rotkin, and Umberto Ravaioli, "Metal-Semiconductor Transition in Armchair Carbon Nanotubes by Symmetry Breaking", Applied Physics Letters, vol. 85 (18), 4178-4180 (Nov 2004). )
|Nanotube may be used for making ultra-small Nanoelectromechanical system (NEMS) device. The SWNT cantilever is shown in two positions (overlayed): Off - when the tube is straight and On - when the tube is bent by the electrostatic force applied to the substrate electrode (not shown). The color on the tube shows the charge density (modeled quantum-mechanically) which is due to the polarization of the SWNT in the external potential of the substrate electrode. (See Slava V. Rotkin, Vaishali Shrivastava, Kirill A. Bulashevich, and Narayan R. Aluru, "Atomistic Capacitance of a Nanotube Electromechanical Device", International Journal of Nanoscience vol. 1, No. 3/4, 337-346, 2002.)||Being a natural ultra-sharp tip, the SWNT may be used for Near-Field Optical Microscopy (NSOM). The picture shows a typical setup where the armchair metallic SWNT probes the (example) butan molecule at the quartz substrate. The strong enhancement of the electric field of the light shined at the surface (not shown) near the apex of the SWNT allows to detect the objects that have a lateral size smaller than the light wavelength, which may not happen in a classical optical microscopy. Image generated by Ben Grosser at ITG, Beckamn Institute and SV. Rotkin (data).|
|Simulation of the edge reconstruction of a double layer of graphite. The resulting structure is shaped as a sleeve along the edge. The sleeve diameter and chirality correspondes to the most abundant [10,10] SWNT (on the right).||Simulation of the armchair single wall nanotube. The [10,10] SWNT has a diameter ~ 1.4 nm. The simulated fragment is 4.5 nm long.|
|Simulation of the edge reconstruction of Graphite Polyhedral Crystal surface. Single wall Nano-arches are formed after the lip-lip bond formation of the free edges of neibghor graphite layers.||Same as on the left, excepting the Nano-Arches contain double walls. The formation of this structure is due to van der Waals forces between graphene sheets, very similar to formation of MWNTs.|
|Simulation of the bandstructure modification of a single-wall nanotube due to the SiO2 substrate surface image charges. (See Alexey G. Petrov, Slava V. Rotkin, "Breaking of Nanotube Symmetry by Substrate Polarization", Nano Letters 3(6), 701-705, 2003. )||A "rider" organic molecule at the nanotube surface. This small molecule
can gently attach to the nanotube surface by the van der Waals forces and
modify its electronic structure by the field of a "tail" charge, shown in
If your browser supports gif animation you will see switching of the rider between ON and OFF positions. In the OFF position the tail charge is closer to the nanotube channel and can block the transport. (See Slava V. Rotkin, Ilya Zharov, "Nanotube Light-Controlled Electronic Switch", in International Journal of Nanoscience vol. 1, No. 3/4, 347-355, 2002.)
Courtesy Dr. Slava V. Rotkin.