Enhanced Optical and Electrical Properties of Organic Field Effect Transistor using Metal Nanoparticles

Organic field effect transistors (OFETs) have several advantages over the conventional inorganic field effect transistor such as easy fabrication process, low-cost mass production capability and low temperature process that enables flexible substrate based device. Many applications using polymer based transistor devices are demonstrated. Successful demonstrations of Logic-gate operation, visible-IR detection and various sensor operations and the advantages discussed above show its great potential as a next generation device technology and attract many researchers to delve to improve the device properties. However, there are several disadvantages on the organic materials such as short lifetime, disability to operate under severe conditions and low carrier mobility. Among those the low carrier mobility is a critical hurdle to develop high performance device operation. Its low mobility limits the operation speed of the device, efficient amplification and carrier transport in a detector device. In this thesis, hybrid organic transistors using Poly(3-hexylthiophene-2,5-diyl)(P3HT) and metal nanostructure are introduced. The metal nanostructure has a unique localized surface plasmon resonance property that can be tailored by adjusting the shape and size of the metal structures. Therefore, the hybridization using polymer semiconducting materials and metal nanoparticles can provide plasmon based optical response and improved mobility due to the free electron concentration in the metal nanostructure. We fabricated organic thin film transistor on a highly doped silicon substrate and characterized its electrical properties as a transistor operation and optical detection properties as a field effect transistor based detector. Then, metal nanoparticles have been deposited by vacuum evaporation of small molecules on the surface of the OFETs. The electrical and optical properties have been investigated to compare with a device without plasmonic nanostructure. We successfully demonstrated the improved optical properties of the OFETs are due to surface plasmon resonance of the metal nanoparticles. The metal nanoparticles incorporated in organic transistor shows improved drain current due to the increased conductivity assisted by the free electrons in the metal nanoparticles. In addition, we observed enhanced photo responsivity (A/W) in its optical detector operation. A slight change of the spectral response was observed and we believe that this is originated from the contribution of the plasmon induced hot electrons in the metal nanoparticles. Further studies to have better understandings on metal nanoparticle incorporated in organic transistor were discussed in this thesis

Study on Ultra Wideband Spectral Response and Efficient Hot Electron Detection using Plasmon Field Effect Transistor

Plasmon based field effect transistors (FET) can be used to convert energy induced by incident optical radiation to electrical energy. Plasmonic FETs can efficiently detect incident light and amplify it by coupling to resonant plasmonic modes thus improving selectivity and signal to noise ratio. The spectral responses can be tailored both through optimization of nanostructure geometry as well as constitutive materials. In this paper, we studied various plasmonic nanostructures using gold for a wideband spectral response from visible to near IR. We show using empirical data and simulation results that detection loss exponentially increases as the volume of metal nanostructure increases and also a limited spectral response is possible using gold nanostructures in a plasmon to electric conversion device. Finally, we demonstrate a plasmon field effect transistor that offers a broadband spectral response from visible to telecommunication wavelengths

Computational study for optimization of a plasmon FET as a molecular biosensor

Surface Plasmon Resonance (SPR) is currently being widely studied as it exhibits sensitive optical properties to changes in in the refractive index of the surrounding medium. As novel devices using SPR have been developing rapidly there is a necessity to develop models and simulation environments that will allow for continued development and optimization of these devices. A biological sensing device of interest is the Plasmon FET which has been proven experimentally to have a limit of detection (LOD) of 20pg/ml while being immune to the absorption of the medium. The Plasmon FET is a metal-semiconductor-metal detector which employ functionalized gold nanostructures on a semi-conducting layer. This direct approach has the advantages of not requiring readout optics reducing size and allowing for point-of -care measurements. Using Lumerical FDTD and Device numerical solvers, we can report an advanced simulation environment illustrating several key sensor specifications including LOD, resolution, sensitivity, and dynamic range, for a variety of biological markers providing a comprehensive analysis of a Direct Plasmon-to-Electric conversion device designed to function with colored mediums (eg.whole blood). This model allows for the simulation and optimization of a plasmonic sensor that already o ers advantages in size, operability, and multiplexing-capability, with real time monitoring

Efficient hot electron collection, detection, and amplification in plasmon field-effect transistor

Plasmon field-effect transistor is a hybrid device using nanostructures to detect the plasmonic energy. This device efficiently transfers plasmonic hot electrons from the metal nanostructures to the semiconductor. The transported hot electrons to the electron channel increases transistor drain current. We investigate the efficiency of plasmonic hot carrier harvesting between metal and semiconductor. We analyzed the effect of gold nanoparticle (NP) density and distribution on plasmon FET spectral response. Then, we studied electric field-assisted hot electron transfer and transport using different device structures. The position of plasmonic structures plays an important role in plasmonic energy detection efficiency because the gradient of electric field seen by induced hot electrons varies depending on the distance between drain and source. Both the experimental and simulation results confirm that by fabricating the gold NPs close to source the spectral response increases by 31% in comparison with having gold NPs close to the drain. Our simulation and experimental data suggest important design considerations to improve hot electron collection and conversion using metallic nanostructures for plasmonic energy harvesting

Efficient broadband energy detection from the visible to near-infrared using a plasmon FET

Plasmon based field effect transistors (FETs) can be used to convert energy induced by incident optical radiation to electrical energy. Plasmonic FETs can efficiently detect incident light and amplify it by coupling to resonant plasmonic modes thus improving selectivity and signal to noise ratio. The spectral responses can be tailored both through optimization of nanostructure geometry as well as constitutive materials. In this paper, we studied various plasmonic nanostructures using gold for a wideband spectral response from visible to near-infrared. We show, using empirical data and simulation results, that detection loss exponentially increases as the volume of metal nanostructure increases and also a limited spectral response is possible using gold nanostructures in a plasmon to electric conversion device. Finally, we demonstrate a plasmon FET that offers a broadband spectral response from visible to telecommunication wavelengths

Mutational spectrum of type I collagen genes in Korean patients with osteogenesis imperfecta

Mutations in the type I collagen genes COL1A1 and COL1A2 are responsible for the dominantly inherited connective tissue disorder osteogenesis imperfecta (OI). The severity of OI is diverse, ranging from perinatal lethality to a very mild phenotype that is characterized by normal stature and the absence of deformities. Although there have been several studies on the mutational spectra of COL1A1 and/or COL1A2 in Western populations, very few cases have been reported from Asia. In this study, we investigated 67 unrelated Korean probands with OI and used nucleotide sequence analysis to detect COL1A1 and COL1A2 mutations. Thirty-five different mutations were identified in the two genes, including 24 novel mutations. Among the 35 kinds of detected mutations, 15 were glycine substitutions (seven in COL1A1 and eight in COL1A2), one was a nonsense mutation, four were frameshift mutations in COL1A1, three were in-frame duplications in COL1A2, and 12 were splice site mutations (seven in COL1A1 and five in COL1A2). Until now, mutations in the COL1A1 and COL1A2 genes known to cause OI were unique and rarely repeated in other families. Interestingly, the c.982G>A (p.Gly328Ser) mutation in COL1A2 was found recurrently and was the causative mutation in five independent OI probands. Haplotype analysis of the COL1A2 gene revealed that four probands from five independent OI probands with c.982G>A (p.Gly328Ser) had a common haplotype. Our clinical data showed the heterogeneity even within a specific genotype, which suggested the complex expression of this disease.Research grant from the National Institute of Health, Korea; Grant number: 347-6111-211-207

Intracellular amyloid beta interacts with SOD1 and impairs the enzymatic activity of SOD1: implications for the pathogenesis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease caused by the degeneration of motor neurons. Mutations in Cu/Zn superoxide dismutase (SOD1), including G93A, were reportedly linked to familial ALS. SOD1 is a key antioxidant enzyme, and is also one of the major targets for oxidative damage in the brains of patients suffering from Alzheimer's disease (AD). Several lines of evidence suggest that intracellular amyloid beta (Aβ) is associated with the pathogenesis of AD. In this report we demonstrate that intracellular Aβ directly interacts with SOD1, and that this interaction decreases the enzymatic activity of the enzyme. We observed Aβ-SOD1 aggregates in the perinuclear region of H4 cells, and mapped the SOD1 binding region to Aβ amino acids 26-42. Interestingly, intracellular Aβ binds to the SOD1 G93A mutant with greater affinity than to wild-type SOD1. This resulted in considerably less mutant enzymatic activity. Our study implicates a potential role for Aβ in the development of ALS by interacting with the SOD1 G93A mutant