3 research outputs found
Contactless Characterization of Electronic Properties of Nanomaterials Using Dielectric Force Microscopy
Characterization of electronic properties of nanomaterials usually
involves fabricating field effect transistors and deriving materials
properties from device performance measurements. The difficulty in
fabricating electrical contacts to extremely small-sized nanomaterials
as well as the intrinsic heterogeneity of nanomaterials makes it a
challenging task to measure the electronic properties of large numbers
of individual nanomaterials. Here, we utilize a scanning probe technique,
the dielectric force microscopy (DFM) to address the challenges. The
DFM technique measures the low frequency dielectric response of nanomaterials,
which is intrinsically related to their electrical conductivity. The
incorporation of a gate bias voltage in DFM measurements allows for
charge carrier density modulation, which is exploited to determine
the carrier type in nanomaterials such as semiconducting single-walled
carbon nanotubes (SWNTs) and ZnO nanowires (ZnO NWs). This technique
avoids the need of electrical contacts and inherits the spatial mapping
capability of scanning probe microscopy, as manifested in the imaging
of intratube metallic/semiconducting junctions in SWNTs. We expect
the DFM technique to find broad applications in the characterization
of various nanoelectonic materials and nanodevices
Probing Electronic Doping of Single-Walled Carbon Nanotubes by Gaseous Ammonia with Dielectric Force Microscopy
The electronic properties of single-walled carbon nanotubes
(SWNTs)
are sensitive to the gas molecules adsorbed on nanotube sidewalls.
It is imperative to investigate the interaction between SWNTs and
gas molecules in order to understand the mechanism of SWNT-based gas-sensing
devices or the stability of individual SWNT-based field effect transistors
(FETs). To avoid the Schottky barrier at the metal/SWNT contact, which
dominates the performance of SWNT-based FETs, we utilize a contactless
technique, dielectric force microscopy (DFM), to study the intrinsic
interaction between SWNTs and gaseous ammonia molecules. Results show
that gaseous ammonia affects the conductivity of semiconducting SWNTs
but not metallic SWNTs. Semiconducting SWNTs, which are p-type doped
in air, show suppressed hole concentration in ammonia gas and are
even inverted to n-type doping in some cases
Electronic Transport Properties of Epitaxial Si/SiGe Heterostructures Grown on Single-Crystal SiGe Nanomembranes
To assess possible improvements in the electronic performance of two-dimensional electron gases (2DEGs) in silicon, SiGe/Si/SiGe heterostructures are grown on fully elastically relaxed single-crystal SiGe nanomembranes produced through a strain engineering approach. This procedure eliminates the formation of dislocations in the heterostructure. Top-gated Hall bar devices are fabricated to enable magnetoresistivity and Hall effect measurements. Both Shubnikov-de Haas oscillations and the quantum Hall effect are observed at low temperatures, demonstrating the formation of high-quality 2DEGs. Values of charge carrier mobility as a function of carrier density extracted from these measurements are at least as high or higher than those obtained from companion measurements made on heterostructures grown on conventional strain graded substrates. In all samples, impurity scattering appears to limit the mobility