Mira Baraket

Manipulating Thermal Conductance at Metal−Graphene Contacts via Chemical Functionalization

Graphene-based devices have garnered tremendous attention due to the unique physical properties arising from this purely two-dimensional carbon sheet leading to tremendous efficiency in the transport of thermal carriers (i.e., phonons). However, it is necessary for this two-dimensional material to be able to efficiently transport heat into the surrounding 3D device architecture in order to fully capitalize on its intrinsic transport capabilities. Therefore, the thermal boundary conductance at graphene interfaces is a critical parameter in the realization of graphene electronics and thermal solutions. In this work, we examine the role of chemical functionalization on the thermal boundary conductance across metal/graphene interfaces. Specifically, we metalize graphene that has been plasma functionalized and then measure the thermal boundary conductance at Al/graphene/SiO(2) contacts with time domain thermoreflectance. The addition of adsorbates to the graphene surfaces are shown to influence the cross plane thermal conductance; this behavior is attributed to changes in the bonding between the metal and the graphene, as both the phonon flux and the vibrational mismatch between the materials are each subject to the interfacial bond strength. These results demonstrate plasma-based functionalization of graphene surfaces is a viable approach to manipulate the thermal boundary conductance.

High-quality uniform dry transfer of graphene to polymers.

In this paper we demonstrate high-quality, uniform dry transfer of graphene grown by chemical vapor deposition on copper foil to polystyrene. The dry transfer exploits an azide linker molecule to establish a covalent bond to graphene and to generate greater graphene-polymer adhesion compared to that of the graphene-metal foil. Thus, this transfer approach provides a novel alternative route for graphene transfer, which allows for the metal foils to be reused.

The functionalization of graphene using electron-beam generated plasmas

A plasmas-based, reversible functionalization of graphene is discussed. Using electron-beam produced plasmas, oxygen and fluorine functionalities have been added by changing the processing gas mixtures from Ar/O2 to Ar/SF6, respectively. The reversibility of the functionalization was investigated by annealing the samples. The chemical composition and structural changes were studied by x-ray photoelectron spectroscopy and Raman spectroscopy.

Aminated graphene for DNA attachment produced via plasma functionalization

We demonstrate the use of a unique plasma source to controllably functionalize graphene with nitrogen and primary amines, thereby tuning the chemical, structural, and electrical properties. Critically, even highly aminated graphene remains electronically conductive, making it an ideal transduction material for biosensing. Proof-of-concept testing of aminated graphene as a bio-attachment platform in a biologically active field-effect transistor used for DNA detection is demonstrated.

Plasma-Based Chemical Modification of Epitaxial Graphene

In this work, the treatment of epitaxial graphene on SiC using electron beam generated plasmas produced in mixtures of argon and oxygen is demonstrated. The treatment imparts oxygen functional groups on the surface with concentrations ranging up to about 12 at.%, depending on treatment parameters. Surface characterization of the functionalized graphene shows incorporation of oxygen to the lattice by disruption of ∏-bonds, and an altering of bulk electrical properties.

Characterization of Light Emission From Electron-Beam-Generated Plasmas in Oxygen

In this paper, characterization of light emission from pulsed electron-beam plasmas in oxygen is presented. High-speed CCD images reveal light intensity evolution during a pulse. From the individual frames, averaged light intensities were calculated and compared with current measurements. As expected, the comparison suggests that excited species are produced mainly during the pulse. Optical emission spectrum indicates the type of excited species being produced.