Overcoming the Leakage and Contact Resistance Challenges in Highly Scaled PMOS and NMOS Carbon Nanotube Transistors.

In this work, we address the off-state leakage current challenge, while simultaneously demonstrating high drive current per CNT, in NMOS and PMOS carbon nanotube field-effect transistors (CNFETs). Increasing the bandgap from 0.6 to 0.

Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs.

Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics because of their exceptional charge transport properties and one-dimensional electrostatics. Ballistic transport approaching the quantum conductance limit of 2G 0 = 4e (2)/h has been achieved in field-effect transistors (FETs) containing one CNT. However, constraints in CNT sorting, processing, alignment, and contacts give rise to nonidealities when CNTs are implemented in densely packed parallel arrays such as those needed for technology, resulting in a conductance per CNT far from 2G 0.

Evolution, kinetics, energetics, and environmental factors of graphene degradation on silicon dioxide.

Recent studies have qualitatively shown that the oxidative stability of monolayer graphene integrated on oxides is relatively poor. Here, the evolution, kinetics, and energetics of this degradation are quantified. Specifically, the deterioration of graphene on SiO2 is studied in grain interiors and at grain boundaries in ambient air, dry air and nitrogen between 473 and 673 K, using spatially and temporally resolved in situ Raman spectroscopy in addition to electron microscopy and charge transport measurements.

Transfer of pre-assembled block copolymer thin film to nanopattern unconventional substrates.

In this work, we demonstrate that a preassembled block copolymer (BCP) thin film can be floated, transferred, and utilized to effectively nanopattern unconventional substrates. As target substrates, we chose Cu foil and graphene/Cu foil since they cannot be nanopatterned via conventional processes due to the high surface roughness and susceptibility to harsh processing chemicals and etchants. Perpendicular hexagonal PMMA cylinder arrays in diblock copolymer poly(styrene-block-methyl methacrylate) [P(S-b-MMA)] thin films were preassembled on sacrificial SiO2/Si substrates.

Orientation of a monolayer of dipolar molecules on graphene from X-ray absorption spectroscopy.

Recently, single-walled carbon nanotubes as well as graphene functionalized with azobenzene chromophores have drawn attention for applications in optoelectronics due to their ability to undergo cis-trans isomerization when exposed to light. The electronic properties of the nanocarbon materials at these unconventional interfaces can be tailored by gaining structural insight into the organic monolayers at the molecular level. In this work, we use polarization-dependent X-ray absorption spectroscopy to probe the orientation of three chromophores on graphene, all identical except for their terminal groups.

Highly stretchable carbon nanotube transistors with ion gel gate dielectrics.

Field-effect transistors (FETs) that are stretchable up to 50% without appreciable degradation in performance are demonstrated. The FETs are based on buckled thin films of polyfluorene-wrapped semiconducting single-walled carbon nanotubes (CNTs) as the channel, a flexible ion gel as the dielectric, and buckled metal films as electrodes. The buckling of the CNT film enables the high degree of stretchability while the flexible nature of the ion gel allows it to maintain a high quality interface with the CNTs during stretching.

Electronic transport and Raman scattering in size-controlled nanoperforated graphene.

We demonstrate the fabrication and study of the structure-property relationships of large-area (>1 cm(2)) semiconducting nanoperforated (NP) graphene with tunable constriction width (w = 7.5-14 nm), derived from CVD graphene using block copolymer lithography. Size-tunable constrictions were created while minimizing unintentional doping by using a dual buffer layer pattern-transfer method.

Barrier-guided growth of micro- and nano-structured graphene.

A novel approach for the rational synthesis of low-defect density, patterned graphene from the bottom up, called barrier-guided chemical vapor deposition, is introduced. A patterned barrier layer impedes the growth of graphene in selected areas of the copper substrate, guiding the growth of graphene into desired micro- and nano- structures with control over placement, orientation, and spatial and lateral extent.

Light-driven reversible modulation of doping in graphene.

We report a route to noncovalently latch dipolar molecules on graphene to create stable chromophore/graphene hybrids where molecular transformation can be used as an additional handle to reversibly modulate doping while retaining high mobilities. A light switchable azobenzene chromophore was tethered to the surface of graphene via π-π interactions, leading to p-doping of graphene with an hole concentration of ~5 × 10(12) cm(-2). As the molecules switch reversibly from trans to cis form the dipole moment changes, and hence the extent of doping, resulting in the modulation of hole concentration up to ~18% by alternative illumination of UV and white light.

Semiconducting two-dimensional graphene nanoconstriction arrays.

The fabrication and characterization of two-dimensional nanoconstriction arrays consisting of sub-20-nm graphene constrictions and interconnecting graphene islands are reported. The arrays are fabricated in a scalable top-down fashion using self-assembled close-packed polystyrene nanospheres as lithographic templates and characterized using electron microscopy, Raman spectroscopy, and charge transport measurements. At room temperature, the arrays behave as semiconductors with a field-effect conductance modulation of up to 450 and charge mobilities of ~1 cm(2) V(-1) s(-1) .

Dissociating excitons photogenerated in semiconducting carbon nanotubes at polymeric photovoltaic heterojunction interfaces.

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have strong near-infrared and visible absorptivity and exceptional charge transport characteristics, rendering them highly attractive semiconductor absorbers for photovoltaic and photodetector technologies. However, these applications are limited by a poor understanding of how photogenerated charges, which are bound as excitons in s-SWCNTs, can be dissociated in large-area solid-state devices. Here, we measure the dissociation of excitons in s-SWCNT thin films that form planar heterojunction interfaces with polymeric photovoltaic materials using an exciton dissociation-sensitive photocapacitor measurement technique that is advantageously insensitive to optically induced thermal photoconductive effects.

Fabrication and characterization of large-area, semiconducting nanoperforated graphene materials.

We demonstrate the fabrication of nanoperforated graphene materials with sub-20-nm features using cylinder-forming diblock copolymer templates across >1 mm(2) areas. Hexagonal arrays of holes are etched into graphene membranes, and the remaining constrictions between holes interconnect forming a honeycomb structure. Quantum confinement, disorder, and localization effects modulate the electronic structure, opening an effective energy gap of 100 meV in the nanopatterned material.