Materials Research

Two-Dimensional Graphene/h-BN Heterostructures for Nanoelectronics

posted Jun 14, 2013, 8:34 AM by Timothy Fisher   [ updated Jun 24, 2013, 7:40 PM by Nick Glavin ]

Student: Nicholas Glavin

Faculty: Tim Fisher

Sponsor: Air Force Research Laboratory

Summary:  Atomically thin two-dimensional materials including graphene and hexagonal-boron nitride are attracting significant interest in the research community due to their intrinsic optical and electronic properties.  In particular, graphene, a two dimensional atomically thin sheet of sp2 bonded carbon atoms, has been shown to exhibit ambipolar transport and the highest electron mobilities of any material to date.  However, the lack of a significant band gap limits graphene for use in transistor applications.  Hexagonal-BN sheets stacked on graphene as well as h-BN domains substituted within the graphene lattice have been investigated as two potential techniques to engineer and control the band structure without significantly altering the mobility. Ideally, transistors fabricated from a bottom-up growth and/or controlled levels of BN substitution could lead to precise control of film thickness and quality, the reduction of interfacial electron scattering upon stacking, enable for better scale-up potential in future devices, and produce a significant band gap for transistor functionality.  This work focuses on growth and characterization of stackable and substituted graphene/h-BN heterostructures by means of Pulsed Laser Deposition (PLD), Molecular Beam Epitaxy (MBE), and microwave annealing techniques, with a focus on the understanding of electron and phonon transport at the nanoscale domain. 

Graphene-Decorated Substrates and Interfacial Properties

posted Jun 14, 2013, 8:33 AM by Timothy Fisher   [ updated Jun 16, 2013, 5:51 AM by Tim Fisher ]

Student: Anurag Kumar

Faculty: Tim Fisher

Sponsor: Raytheon

Summary: Microwave plasma CVD (MPCVD) growth of graphene and graphene based nanostructures has been developed. Very short growth time makes MPCVD an attractive process for large scale graphene growth. The same process can be also be used to produce doped graphene. Catalyst-free MPCVD synthesis of multi-layer graphene extensions from carbon fiber offers a unique possibility of minimizing interfacial losses in transport applications. Effect on thermal interface resistance is being studied using the 3ω method. Graphene sheets grown on CNTs also increase the mechanical stiffness and elastic recoverability of a vertically aligned CNT array.  Further, vertically oriented 2D graphene sheets on flat substrates serve as a unique template for high density nanoparticle deposition. Such substrates have found promising application in surface enhanced Raman spectroscopy (using Au and Ag nanoparticles) and electrochemical sensing (using Pt nanoparticles).

Representative Papers:

Hierarchical Carbon-Boron Nitride Foam for Thermal Storage

posted Jun 14, 2013, 8:28 AM by Timothy Fisher   [ updated Jun 18, 2013, 12:31 PM by Rajib Paul ]

Postdoctoral Researcher: Dr. Rajib Paul

Faculty: Tim Fisher

Sponsor: Air Force Office of Scientific Research

Summary: A facile microwave chemical treatment was performed for surfacial chemical modification of macroporous carbon foam with boron and nitrogen. The resulting surfaces of the foam exhibit distinct BN and carbon domains based on chemical and microscopic analysis, in agreement with theoretical predictions. The resultant materials are shown to exhibit exceptionally high methanol desorption enthalpy and thermal stability in comparison to untreated carbon foam, and subsequently are suggested as candidate materials for sorption cooling and thermal storage applications with methanol as the adsorbate. To increase the inferior surface area of carbon foam, petal-like structures made of few layer graphene were deposited over its entire surface by MPCVD technique. Further experiments with this material are on-going. In order to realize real hierarchical structure, we also synthesized a unique 3D material made of graphene-petals for tunable 3D nano-architecture for electronic cooling technology.

Representative Paper: 1002/adfm.201200325/abstract

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