Quantum and Carbon Nanomaterials
NREL remains at the forefront of quantum and carbon nanomaterials research, expanding into a broader effort that includes layered semiconducting and thermoelectric materials.
We aim our efforts at:
- Understanding the fundamental properties of quantum and carbon nanomaterials
- Tuning and controlling their optical and electronic properties
- Using these materials in thermoelectrics, photovoltaics, water splitting, hydrogen storage, batteries, and transistors.
Quantum and carbon nanomaterials activities are funded by the U.S. Department of Energy Office of Basic Energy Science and commercial partners.
In-house Material Synthesis and Purification
- Temperature-controlled pulsed laser vaporization of a graphite target for single-walled carbon nanotubes (SWCNT) synthesis
- Designer SWCNT syntheses, such as 13C-labeled, boron-doped, nitrogen-doped
- Arc discharge system for large-diameter SWCNT synthesis
- Multiple chemical vapor deposition (CVD) systems for synthesis of SWCNTs, graphene, or monolayer transition-metal dichalcogenides (TMDCs)
- Mechanical exfoliation of SWCNTs using ultrasonic tip or shear-force mixer
- Solution-phase chemical exfoliation of TMDCs
- Ultracentrifuge for purifying and separating exfoliated SWCNTs or TMDCs
Suite of Spectroscopic and Surface/Structural Characterization Tools
- Spectroscopic systems capable of steady-state and time-resolved spectroscopic characterization of nanoscale materials, spanning wavelengths from the ultraviolet to mid-infrared
- Surface characterization tools: X-ray photoelectron spectroscopy, Auger spectroscopy, transmission electron microscope, scanning tunneling spectroscopy and microscopy, scanning Kelvin probe microscopy, X-ray diffraction, and others
- In-situ growth characterization tools: including low-energy electron diffraction, reflection high-energy electron diffraction, and spectroscopic ellipsometry.
Transport Property Measurement Systems
We have a wide array of thermoelectric characterization capabilities, including a physical properties measurement system, a homebuilt method-of-four-coefficients system, and a thin-film transport measurement system based on an ultra-thin suspended silicon nitride bridge.
Carbon Nanoscience Research
We study the fundamental properties and applications of low-dimensional carbon-based materials, including single-walled carbon nanotubes and graphene.
Single-Walled Carbon Nanotubes
SWCNTs are cylindrical nanomaterials composed of a single sheet of sp2-bonded carbon rolled into a tube with a large aspect ratio. The diameter of commonly
synthesized SWCNTs ranges from about 0.7 to 2 nm, whereas the length can exceed tens
of microns. SWCNTs can have either a semiconducting or metallic electronic structure,
and the statistical ratio of most as-synthesized samples is 2:1 semiconducting:metallic.
We explore the fundamental chemistry and physics of SWCNTs as well as incorporate SWCNTs into high-performance energy-conversion applications. We synthesize our own SWCNTs in-house by techniques such as laser vaporization, arc discharge, and CVD. We also develop and use numerous methods for separating SWCNTs by electronic structure, diameter, and chiral angle, including: density gradient ultracentrifugation, aqueous two-phase extraction, and selective extraction with conjugated polymers. We develop and research a number of novel energy conversion materials and technologies based on SWCNTs, including thin-film photovoltaics, catalytic electrodes, battery electrodes, and thermoelectric materials.
Graphene is a one-atom-thick, two-dimensional, semi-metallic material composed entirely
of sp2-bonded carbon. Graphene's extremely high conductivity and optical transparency make
it a relevant material for several interesting renewable energy applications.
We synthesize monolayer graphene by CVD and also synthesize colloidal graphene by exfoliation of graphite. We examine the fundamental transport properties of graphene, and the use of graphene in novel energy-conversion technologies, such as transparent conducting electrodes for thin-film solar cells and interfacial layers in technologies such as smart windows.
Layered Semiconductors Research
We study the fundamental properties and applications of quantum-confined layered materials, including TMDCs.
A number of two-dimensional, layered semiconductors with variable electronic structure
(semiconducting to metallic) provide an interesting counterpoint to graphene. One
popular class of such materials—TMDCs (MoS2, MoSe2, WS2, and WSe2)—has gained increasing interest in the research community in recent years. The properties
of TMDCs can change abruptly from those of the bulk material when the semiconductor
is grown, or exfoliated, as a single monolayer.
We are interested in the fundamental photophysics of layered 2-D semiconductors, and how these properties change as a function of external stimuli (e.g., stress, strain, functionalization, doping). Another area of active research is understanding and manipulating surfaces and interfaces to control charge dynamics between the TMDCs and substrates or between TMDCs and solution. We synthesize TMDCs by either CVD or chemical exfoliation and are interested in how the optical and electrical properties of these interesting materials influence their behavior in applications such as thin-film photovoltaics, energy storage, and catalytic electrodes for hydrogen evolution.
Thermoelectric Materials Research
Thermoelectric devices directly convert temperature differences and electric voltage, allowing electricity generation from waste heat (via the Seebeck effect) or local cooling/heating (via the Peltier effect). The efficiency of thermoelectric electricity generation is related to the active material's electrical conductivity (σ), Seebeck coefficient (α), and thermal conductivity (κ), and it is typically captured in a figure of merit (zT) at a given temperature (T):
whereas the Peltier coefficient (Π) is directly related to the Seebeck coefficient (α) at a given temperature (T):
Because the three material properties (σ, α, and κ) are inter-related, a primary goal of thermoelectrics research is the rational control of the carrier density and interfaces within a material to optimize zT.
We develop and study thermoelectric materials primarily with a bottom-up approach, using nanomaterial building blocks to design and control the nano- and meso-scale morphology and interfaces of complex thermoelectric materials. Some of the material systems we explore include single-walled carbon nanotubes, semiconducting polymers, semiconductor nanocrystal arrays, and composite materials including some combination of these building blocks. The goal of our approach is to use nanoscale interfaces to increase α and decrease κ while maintaining high σ.
The Chemistry and Nanoscience Center is part of the Materials, Chemical, and Computational Science directorate, led by Associate Laboratory Director Bill Tumas.