The Nanoelectronics and Nanophotonics group uses a combination of experiment, theory, and modeling to discover and exploit the unique properties of nanomaterials for electronics, photonics, and optoelectronics.
In addition to addressing scientific and technical challenges from nanoscience to nanotechnology, our team of materials scientists, physicists, and chemists enjoys pondering the quirkier side of science, as can be seen in the Entropyman website created by postdoctoral researcher Edward Feng.
Our group also likes to spend time together outside of the research environment. We frequently take advantage of the many recreational opportunities available in the Bay Area, especially water skiing, orienteering, and scuba diving.
We present the first demonstration of thermoelectricity in a metal-organic framework (MOF) material. We find a large Seebeck coefficient at room temperature and low thermal conductivity, two important properties for making efficient thermoelectric devices. This work opens a path towards new types of thermoelectric materials based on molecular, long-range ordered, nanoporous materials.
In most materials, the photocurrent usually depend linearly or sub-linearly on light intensity due to conventional recombination processes. Several decades ago, a few exotic materials displayed an unusual superlinear increase of the photocurrent with increasing light intensity, which stumped theorists for a long time. We report the experimental observation of this intriguing regime in novel two-dimensional transition-metal dichalcogenides. This behavior is observed in monolayer alloys spanning the compositional range from MoS2 to MoSe2, and is suggested to arise from the non-equilibrium photophysics of multiple recombination centers. See the paper in Nano Letters.
Topological insulators possess unique electronic and optical properties of interest for novel devices. To realize this promise, it is important to achive high-performance electrical contacts. In a recent paper, we employ large-scale ab initio calculations to demonstrate the many features of such contacts. In particular, we find that strong interaction between the metal and the TI destroys spin-momentum locking, in contrast to the commonly accepted view that TI states are robust.
In a collaboration with Rice University and Tokyo Tech, we demonstrated a macroscopic, antenna-free, terahertz detector based on thin films of carbon nanotubes. The detector is broadband, does not require power to operate, and shows performance approaching that of established uncooled technologies. Additional details can be found in the journal Nano Letters and in this video.
In a new paper in Science, our group demonstrates for the first time electrical conductivity in a metal-organic framework (MOF). By infiltrating the HKUST MOF with guest molecules, we tuned the electrical conductivity over six orders of magnitude in thin film MOF devices. In addition to creating a new class of conducting nanoporous materials, this work opens up new avenues for applications in sensors, electronics, and optoelectronics.
We developed a novel approach to create macroscopic carbon nanotube p-n junction photodetectors based on the photothermoelectric effect which shows polarization sensitivity up to the mid-infrared. The experimental work in conjunction with theory establishes the working principles and performance attributes of this class of devices. The paper was recently published in ACS Nano DOI: 10.1021/nn402679u.
In a recent paper in Nature’s Scientific Reports, we present a broadband photodetector based on thin films of aligned carbon nanotubes. The detector shows good linearity from the visible to the mid-infrared, and because of the unique aligned-nanotube material, opens a new path for polarimetry.
Electronic and optoelectronic devices based on carbon nanotubes are limited by the presence of metallic nanotubes in addition to the desirable semiconducting nanotubes. Our group, in collaboration with Rice University, devised an approach to physically remove the metallic nanotubes from devices post-fabrication using functionalization combined with a thermal and fluidic process. Details can be found in the journal Nanotechnology.
The thermoelectric efficiency of materials is usually considered at high doping where the electronic transport is ohmic, leading to the conventional ZT factor. In a new theoretical paper published in Physical Review B Journal, we derive the equivalent thermoelectric efficiency for low doping where the electronic transport is dominated by space-charge-limited effects. Application to specific systems shows that nanowires are the most promising to harness this regime.
Call for papers: MRS Spring 2013 symposium on
Electrical Contacts to Nanomaterials and Nanodevices.
Submit your abstracts on the MRS website.
Abstract deadline: November 1, 2012.
The performance of field-effect transistors degrades as the channel length is reduced unless the gate oxide thickness is aggressively scaled. In a recent paper in ACS Nano we demonstrate that these scaling issues can be overcome in short channel carbon nanotube transistors by allowing the gate to modulate the contacts. Enhanced Performance of Short-Channel Carbon Nanotube Field-Effect Transistors Due to Gate-Modulated Electrical Contacts.
A recent paper in J. Phys.: Condens. Matter 23, 465301 (2011), discussed the impact that crystallographic orientation has on the strength of the intrinsic spin Hall effect in GaAs quantum wires. An image from this paper was featured on the cover of the journal's November 23 issue.
Electrical contacts play a critical role in many technology areas, and understanding contacts to nanomaterials is essential to fully harness their technology potential. A review article from our group details the unique issues associated with such nanocontacts. Nature Nanotechnology 6, 773 (2011).
As detailed in a recent paper in Nano Letters 11, 3074 (2011), the electronic properties of heterojunctions are significantly different in core/shell nanowires as compared to their bulk form, leading to the formation of quasi-one-dimensional electron gases.
A project from our group titled “Energy Conversion Using Chromophore-Functionalized Carbon Nanotubes” was recently awarded a 2010 LDRD Award for Excellence for its embodiment of “National Laboratory Challenge, Risk and Creativity,” and “National Laboratory Relevance and Impact.”
We studied the impact of doping on the electronic and optical properties of semiconducting carbon nanotubes, as discussed in Phys. Rev. Lett. 104, 177402 (2010).
We developed a new approach to calculate the high frequency properties of nanoelectronic devices, as described in Phys. Rev. Lett. 103, 026601 (2009).
Our group recently demonstrated that chromophores/nanotube hybrid devices can detect different colors of light. See this featured in Nature Photonics.
“ the definitive text on the topic”
—ScienceDaily, May 29, 2008
This book explains the basic physics of carbon nanotube devices for multiple applications including electronics, nano-electro-mechanical systems (NEMS), and optoelectronics.