The main goal of this research was to maintain the bulk charge carrier mobility of graphene, after deposition of the gate dielectric layer used for making transistor devices. The approach was introducing a thin film of deoxyribonucleic acid (DNA) nucleobase purine guanine, deposited by physical vapor deposition (PVD), onto layers of graphene that were transferred onto various flexible substrates. Several test platforms were fabricated with guanine as a standalone gate dielectric, as the control, and guanine as a passivation layer between the graphene and PMMA. It was found that the bulk charge carrier mobility of graphene was best maintained and most stable using guanine as a passivation layer between the graphene and PMMA. Other transport properties, such as charge carrier concentration, conductivity type and electrical resistivity were investigated as well. This is an important first step to realizing high performance graphene-based transistors that have potential use in bio and environmental sensors, computer-processing and electronics.
In this study, we investigated the effect of substrates on the electrical properties of transferred graphene. A wide range of substrates such as silicon carbide (SiC), glass, kapton, photo-print paper, polydimethylsiloxane (PDMS) and Willow glass were selected based on their surface properties, flexibility and lattice match. Four monolayers of graphene were transferred onto each of these substrates. A comparative study of the electrical characteristics of the transferred graphene film only and graphene/guanine film on the different substrates was undertaken.
We report transmission spectroscopy results from the mid- to far-infrared on graphene, grown by chemical vapor
deposition (CVD) on Cu. Similar results have been reported by several groups and their substrates of choice were
thermal Si dioxide, quartz, or SiC, where strong phonon absorption results in transmission blocking bands in midinfrared.
Silicon wafers (thickness ~ 500 μm), on the other hand, have transmission extending out to about 100 cm-1
when the doping level is low. Therefore, we choose to use Si wafers as the carrier substrates for transferred CVD
graphene. The complex refractive index of the Si substrate is measured by infrared spectroscopic ellipsometry. As a
result, continuous spectra (without blocking bands) in the range of 400 to 4000 cm-1 are obtained and they are modeled
by free carrier absorption (the Drude model) and interband transitions (considering the Pauli blocking.) From these, the
carrier density, carrier mobility, sheet resistivity, intraband scattering rate, and graphene layer number can be inferred. In
the far-infrared range, the absorption is dominated by the intraband free carrier absorption and it mainly results from the
interband transition in the mid-infrared range. Having continuous spectra using the Si substrates gives us the advantage
to model the whole spectral region (from far-infrared to mid-infrared) accurately.
The potential of DNA-based dielectrics for energy storage applications was explored via the incorporation of high
dielectric constant (ε) ceramics such as TiO2 (rutile) and BaTiO3 in the DNA bio-polymer. The DNA-Ceramic
hybrid films were fabricated from stable suspensions of the nanoparticles in aqueous DNA solutions. Dielectric
characterization revealed that the incorporation of TiO2 (rutile) in DNA resulted in enhanced dielectric constant
(14.3 at 1 kHz for 40 wt % TiO2) relative to that of DNA in the entire frequency range of 1 kHz-1 MHz. Variable
temperature dielectric measurements, in the 20-80°C range, of both DNA-TiO2 and DNA-BaTiO3 films, revealed
that the ceramic additive stabilizes DNA against large temperature-dependent variations in both ε and the dielectric
loss factor tan δ. The bulk resistivity of the DNA-Ceramic hybrid films, in the case of both TiO2 and BaTiO3
additives in DNA, was measured to be two to three orders of magnitude higher than that of the control DNA films,
indicating their potential for utilization as insulating dielectrics in capacitor applications. As a part of a baseline
study, results based on a comparison of the temperature-dependent dielectric behavior of DNA and DNA-CTMA
complex films as well as their frequency-dependent polarization behavior, are also discussed.
This work details a proof of concept study for vapor phase selective sensing using a strategy of biorecognition elements
(BRE) integrated into a zinc oxide field effect transistor (ZnO FET). ZnO FETs are highly sensitive to changes to the
environment with little to no selectivity. Addition of a biorecognition element retains the sensitivity of the device while
adding selectivity. The DNA aptamer designed to bind the small molecule riboflavin was covalently integrated into the
ZnO FET and detects the presence of 116 ppb of riboflavin in a nitrogen atmosphere by a change in current. The
unfunctionalized ZnO FET shows no response to this same concentrations of riboflavin, showing that the aptamerbinding
strategy may be a promising strategy for vapor phase sensing.
Biomaterials such as nucleic acids and proteins can be exploited to create higher order structures. The biomolecular
components such as DNA and peptides have been used to assemble nanoparticles with high fidelity. Here, we use DNA
and peptides, and their preferential interaction with inorganic and carbon nanomaterials to form homogeneous hybrids.
The enhanced binding of Pt ions to both DNA and peptide functionalized nanoparticles mediates the assembly of carbon
nanotubes functionalized with DNA with peptide coated gold nanoparticles.
In this paper we present our current research in developing non-conductive, optically transparent electromagnetic
interference (EMI) or radio frequency (RF) shielding. It uses metallic nanopowders blended with deoxyribonucleic acid
(DNA) based host materials. Recent results of this DNA-based EMI shielding demonstrate 18-27dB over a frequency
range of 18 - 6 GHz, respectively, with an electrical resistivity measuring > 20MΩ for a 20 μm dielectric spacing. These
films were optical transparent in the visible wavelength range.
In this work, we show the use of single stranded DNA aptamers as selective biorecognition elements in a sensor based
on a field effect transistor (FET) platform. Aptamers are chemically attached to the semiconducting material in the FET
through the use of linker molecules and confirmed through atomic force microscopy and positive target detection.
Highly selective sensing of a small molecule, riboflavin is shown down to the nano-molar level in zinc oxide FET and
micro-molar level in a carbon nanotube FET. High selectivity is determined through the use of negative control target
molecules with similar molecular structures as the positive control targets with little to no sensor response. The goal of
this work is to develop a sensor platform where biorecognition elements can be used to functionalize an array of
transistors for simultaneous sensing of multiple targets in biological fluids.
Deoxyribonucleic acid (DNA)-based biopolymers posses unique electronic and self assembly properties that render them suitable organic semiconductors for organic field effect transistors. Doping DNA molecules with conductive guests has resulted in a significant decrease of the overall resistivity of the blend with effective free charge carrier mobilities comparable to other conductive polymers such as pentacene and poly(3-hexylthiophene) (P3HT). In this paper we discuss doping DNA with single wall carbon nanotubes (SWCNTs) and transistor behavior.
Organic field effect transistors (O-FETs) are of considerable interest for the development of flexible displays and a variety of other macro-electronic applications. We investigated a DNA-based biopolymer material as a gate dielectric for fabricating O-FET backplanes using the organic semiconductor material Pentacene having small geometry devices and improved performance characteristics required for high resolution displays. The results to date continue to show the potential of this approach for low-cost O-FET backplanes for the next generation flexible displays and other macro-electronic applications.
This paper demonstrates the use of DNA based biopolymers as semiconducting thin films in organic field effect
transistors. The "doping" of the DNA molecules with conductive polymers leads to a significant decrease of the
overall resistivity in the blend with effective free charge carrier mobilities comparable to other conductive polymers
such as Pentacene and P3HT. Baytron P as well as single wall carbon nanotubes (SWCNT) have been explored as "doping" conductive polymers.
This paper reports on the use of new DNA-based biopolymers as the semiconducting layer in field effect transistors. Thin-film field effect transistor (FET) structures are fabricated with two different DNA-biopolymers as semiconductor layers, and two different field effect transistor structures are studied. Current voltage characteristics of the FETs show that the devices are operating in depletion mode.
Organic field-effect transistors (OFETs) currently utilize organic semiconductor materials with low electron
mobilities and organic gate oxide materials with low dielectric constants. Compared to inorganic FETs, OFETs have
slow operating speeds and high operating voltages. In this paper we discuss blending the conductive polymer
polyethylene dioxythiophene (PEDOT) with deoxyribonucleic acid (DNA), with minimal optimization to produce a
new bio-conductive polymer complex potentially suitable for OFETs. The conductivity of this new bio-conductive
polymer complex is tunable, ranging from 10-10 S/cm to 10-3 S/cm at room temperature.
A new capacitive test structure is used to characterize biopolymers at microwave frequencies. The new test
structure is comprised of a parallel plate capacitor, combined with coplanar waveguide-based input and output feed
lines. This allows electrical measurements to be taken easily under an applied DC electric field and at various
temperatures. The dielectric properties are characterized for two biopolymer thin films: a deoxyribonucleic acid
(DNA)-based film and a bovine serum albumin (BSA)-based film. These bio-dielectric thin films are compared
with a standard commercial polymer thin film, poly[Bisphenol A carbonate-co-4,4'(3,3,5-trimethyl
cyclohexylidene) diphenol], also known as amorphous polycarbonate (APC).
A new capacitive test structure is used to characterize biopolymers at microwave frequencies. The new test structure is comprised of a parallel plate capacitor, combined with coplanar waveguide-based input and output feed lines. This allows microwave measurements to be taken easily under an applied DC electric field. The microwave dielectric properties are characterized for two biopolymer thin films: a deoxyribonucleic acid (DNA)-based film and a bovine serum albumin (BSA)-based film. These bio-dielectric thin-films are compared with a standard commercial polymer thin film, poly[Bisphenol A carbonate-co-4,4'(3,3,5-trimethyl cyclohexylidene) diphenol], or amorphous polycarbonate (APC).
A hallmark of biological systems is their ability to self-assemble. This self-assembly can occur on the molecular, macromolecular and mesoscale. In this work, we have chosen to exploit biology's ability to self-assemble by incorporating additional functionality within the final structure. Our research efforts have been directed at not only understanding how biological organisms control nucleation and growth of inorganic materials, but also how this activity can be controlled in vitro. In previous work, we have demonstrated how peptides can be selected from a combinatorial library that possesses catalytic activity with respect to inorganic nucleation and deposition. We have engineered some of these peptide sequences into self-assembling protein structures. The goal of the project was to create an organic/inorganic hybrid that retained the “memory” properties of the organic, but possessed the superior optical and electronic properties of the inorganic.
The diversity of biological sensing and biocatalysis is astounding. A considerable effort has been directed at not only understanding the mechanism of these biological processes, but also how this activity can be maintained or duplicated in an artificial environment. We will present work on the formation of functional optical devices that convert biological responses into optical signals through changes in diffraction efficiency and reflection angle. By incorporating biomolecules into monomer systems that can be cured using a two-photon polymerization mechanism, greater spatial resolution and increased biological viability can be achieved. The polymer can be nanopatterned using ultrafast nonlinear holography to create a functional BioMEMS device. Additionally, we will discuss the characterization of the biomolecules and the processing of the gratings that incorporate these functional proteins. This approach is a first step towards the development of a hybrid organic-inorganic composite device.
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