The integration of graphene and 2D materials into device technologies requires a detailed understanding of how intrinsic and extrinsic forces impact their properties, as well as the development of engineering strategies to vary their properties for a specific response. In this paper we describe and review our efforts for hybridizing graphene in different ways so as to modify or enhance a range of properties. This hybridization comes in the form of chemical or electronic modification for use in applications ranging from chem/bio sensors to nanoelectronics. We discuss results on exploiting chemistry and defects in graphene for chemical vapor sensing, on hybridizing graphene with fluorine atoms for potential use in nanoelectronics, and on electronically hybridizing graphene in multilayer stacks that give rise to new optical and surface properties.
Functional surfaces find application in a number of areas, such as designing flexible electronic devices and integrating electronic systems with biological ones. However, the preparation of functional surfaces entails processing that is destructive to fragile polymer or biological substrates. A benign transfer method is thus needed to move pre-functionalized surfaces from a stable substrate to a fragile one. Chemical hydrogenation of graphene weakens the adhesion force between the graphene and its substrate. We exploit this phenomenon to construct a method for transferring graphene with pre-formed chemical, physical, and electronic functionalities from a heat-, vacuum-, and chemical-stable substrate such as silicon to several less robust ones, including polymers and living cells. We also discuss reversibility of graphene hydrogenation and the implications for re-adhering graphene securely to new substrates.
Sensing devices based on Graphene Field Effect Transistors (G-FET) have been demonstrated by several groups to show excellent sensitivity for a variety of chemical agents. These devices are based on measuring changes in the electrical conductivity of graphene when exposed to various chemicals. However, because of its unique band structure, graphene also exhibits changes in its optical response upon chemical exposure. The conical intersection of the valence and conduction bands results in a low density of states near the Dirac point. At this point, chemical doping resulting from molecular binding to graphene can result in dramatic changes in graphene’s optical absorption. Here we will discuss our recent work in developing a graphene planar lightwave circuit (PLC) sensor which exploits these optical and electronic properties of graphene to demonstrate chemical sensitivity. The devices are based on a strong evanescent coupling of graphene via electrically gated silicon nanowire waveguides. A strong response in the form of a reversible optical attenuation change of 6 dB is shown when these devices interact with toxic industrial chemicals such as iodine and ammonia. The optical transition can also be tuned to the optical c-band (1530-1565 nm) which enables these devices to operate at telecom wavelengths.
We present progress towards scalable, high precision nanofabrication in a variety of materials using heated
Atomic Force Microscope (AFM) probes. Temperature control of a heated AFM tip allows nanometer scale thermochemical
patterning, deposition of thermoplastic polymers, and surface melting. The challenges that must be overcome to
scale such a technology to industrial-scale manufacturing include tip wear, thermal and mechanical control of the
cantilever, chemical reaction control at the tip-surface interface, and fabrication throughput. To mitigate tip wear, we
have integrated nanocrystalline diamond films onto our heated AFM probe tip. Such diamond tips are extremely resistant
to wear and fouling at a self-heating temperature of 400 C and load force of 200 nN over long distances. To improve
cantilever temperature control, a closed loop feedback control was designed to allow for 0.2 C precision temperature
control during nanolithography. Electrohydrodynamic jetting controls the deposition of polyethylene onto a heated probe
tip. Finally, to address throughput, we have fabricated cantilever arrays having independent temperature control and
integrated them into a commercial AFM system. We show these advances by patterning thousands of nanostructures of
polyethylene and poly(3-dodecylthiophene), with cumulative length more than 2 mm and patterning accuracy better than
50 nm.
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