Frank Kenneth Hopkins

Bio-organic-semiconductor-field-effect-transistor based on deoxyribonucleic acid gate dielectric

Organic-based field-effect transistors (OFETs) utilize organic semiconductor materials with low electron mobilities and organic gate oxide materials with low dielectric constants. These have rendered devices with slow operating speeds and high operating voltages, compared with their inorganic silicon-based counter parts. Using a deoxyribonucleic acid (DNA)-based biopolymer, derived from salmon milt and roe sac waste by-products, for the gate dielectric region, we have fabricated an OFET device that exhibits very promising current-voltage characteristics compared with using other organic-based dielectrics. With minimal optimization, using a thin film of DNA-based biopolymer as the gate insulator and pentacene as the semiconductor, we have demonstrated a bio-organic-FET, or BiOFET, in which the current was modulated over three orders of magnitude using gate voltages less than 10V.

Improved crystal quality and harmonic generation in GaSe doped with indium

GaSe crystals were doped with indium, and improvements in the mechanical properties and second-harmonic efficiency over pure crystals were obtained. Both effects are due to an improvement in the crystal quality of the material, and it was shown that doping with low levels of indium did not alter the intrinsic value of the nonlinear d coefficient.

Effect of conductivity and dielectric constant on the modulation voltage for optoelectronic devices based on nonlinear optical polymers

Presented is the effect of using various cladding materials with different conductivities and dielectric constants on the applied voltage for optoelectronic (OE) devices based on nonlinear optical (NLO) polymers. Using a conductive polymer, we have demonstrated a 3 to 13 times increase in the effective electro-optic (EO) coefficient of electrode- poled NLO polymers, compared to using passive polymer claddings. We have achieved the lowest poling voltage to date for maximum EO coefficient, 300 V, for a two-layer waveguide structure consisting of a 2-?m- thick NLO polymer layer and a 2-?m-thick conductive cladding layer. The dielectric constants of both the NLO polymer core and passive polymer cladding materials used for conventional polymer-based integrated optic devices are typically very similar in magnitude. This suggests that only a small fraction of the applied modulation voltage is reaching the NLO polymer core layer, requiring 4 to 5 times higher modulation voltage than the desired V?. We have demonstrated a factor-of-2 decrease in the modulation voltage using the same conductive polymer, due to its possessing a much higher dielectric constant than the core material at the modulation frequency tested. The results show promise for shorter, lower-operating-voltage devices.

ZnGeP2 grown by the liquid encapsulated Czochralski method

The growth of ZnGeP2 by the liquid encapsulated Czochralski method is reported for the first time herein. Large boules of ZnGeP2, with diameters up to 40 mm and weights up to 400 gm were grown by Czochralski pulling from B2O3 encapsulated melts under high pressure (20 atm Ar) using axial gradients ≤120 °C/cm. Boules pulled at ≤4 mm/h exhibited large (50×20×15 mm3) monocrystalline grains of α‐phase ZnGeP2 with room temperature electrical properties of p‐type conduction, carrier concentrations ranging from 1012 to 1016 cm−3, and mobilities of 20 cm2/V s or less. Optical samples exhibited broad IR transmission (0.7 to 12.5 μm), second harmonic generation at 4.7 μm with 7.2% conversion efficiency, a broad subband gap photoluminescence signature, and near band‐edge absorption similar to that observed in Bridgman‐grown ZnGeP2.

Infrared two-photon-excited visible lasing from a DNA-surfactant-chromophore complex

Infrared two-photon-pumped and cavity-enhanced frequency upconversion lasing has been achieved in a novel DNA-surfactant-chromophore complex (DSCC) gel system, which is a new step toward producing a biological laser. Once the focused intensity of the 150 fs and approximately 775 nm pump laser beam is higher than a certain threshold level, highly directional stimulated emission at approximately 582 nm wavelength can be observed from a 1 cm long DSCC complex gel cell. With cavity feedback provided by the two optical windows, the pump threshold can be further reduced, the highly directional output lasing can be greatly enhanced, and the output spectral linewidth can be reduced to less than 1/5 of the spontaneous fluorescence spectral bandwidth.

Characterization of defect-related optical absorption in ZnGeP2

A broad optical absorption band with a peak near 1 μm is present in most single crystals of ZnGeP2. These same crystals have an electron paramagnetic resonance (EPR) signal which has been assigned to singly ionized zinc vacancies. A direct correlation between the intensity of the optical absorption at 1 μm and the intensity of the EPR signal has been established using a set of ZnGeP2 crystals where this absorption varied widely. These results suggest that the singly ionized zinc vacancy acceptor plays a direct role in the electronic transition(s) responsible for the 1 μm optical absorption. In separate experiments, it was found that illuminating the ZnGeP2 crystals with a He–Ne laser (632.8 nm) while at temperatures near 25 K produces an increase in the absorption at 1 μm and an increase in the zinc vacancy EPR spectrum. These latter results provide further evidence that the absorption at 1 μm is associated with the singly ionized zinc vacancy acceptor.

Growth and characterization of gallium selenide crystals for far-infrared conversion applications

Abstract We have developed a method to synthesize large batch sizes of GaSe and have grown single crystals by the Bridgman method. Our results show a d value of 75 pV/m for GaSe. GaSe crystals were tested at a fluence of 1.6 J/cm 2 and 140 MW/cm 2 without damage. The 2 mm thick crystal was used in a high-power test where a crystal with an AR coating was able to operate at 30 kHz with an average power of 21 W into the crystal, equivalent to 32 kW/cm 2 CW in a 100 μm spot.

Deoxyribonucleic acid (DNA) cladding layers for nonlinear-optic-polymer-based electro-optic devices

Nonlinear optic (NLO) polymer based electro-optic devices have been achieving world record low half wave voltages and high frequencies over the last 2-3 years. Part of the advancement is through the use of relatively more conductive polymers for the cladding layers. Based on the current materials available for these cladding materials, however, the desired optical and electromagnetic properites are being balanced for materials processability. One does not want the solvent present in one layer to dissovle the one deposited underneath, or be dissolved by the one being deposited on top. Optimized polymer cladding materials, to further enhance device performance, are continuing to be investigated. Thin films of deoxyribonucleic acid (DNA), derived from salmon sperm, show promise in providing both the desired optical and magnetic properties, as well as the desired resistance to various solvents used for NLO polymer device fabrication. Thin films of DNA were deposited on glass and silicon substrates and the film quality, optical and electromagnetic properties and resistance to various solvents were characterized.

Microwave dielectric properties of DNA based polymers between 10 and 30 GHz

Deoxyribonucleic acid (DNA) based polymer thin-films were characterized at microwave frequencies for the first time. The dielectric properties of the film were extracted from comparison of the propagation constants of the co-planar waveguide (CPW) lines on bare MgO substrates and the DNA based films on MgO substrates. The insertion loss introduced by the DNA film is only 0.1 dB at 10 GHz and 0.5 dB at 30 GHz. The relative dielectric constant of the DNA based film averages to four at microwave frequencies, and the loss-tangent was below 0.1 up to 30 GHz.

Development of chemical sensors using polymer optical waveguides fabricated with DNA

A number of studies are currently focused on using polymers derived from salmon DNA as the primary ingredient in the design of optical waveguide devices. Although the long term goal is to develop optical devices for rapid chemical and biosensing, this work was aimed specifically at studying the response of a planar DNA waveguide to ammonia in nitrogen and air with controlled amounts of humidity at ambient temperatures. This follows the work of S. S. Sarkisov et al. who used PMMA and other polymer films doped with the indicator dye bromocresol purple (BCP). These devices are characterized by absorption sensitivities of the order 0.1 dB attenuation of the transmitted light signal per 100 ppm change in the NH3 concentration with response times of better than 1 ms and can be recycled with no loss of sensitivity. The performances of waveguide devices using films fabricated with high and low molecular weight DNA with BCP are compared to BCP-doped PMMA devices.