Browsing by Author "Swaraj, Sufal"
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- Electron Donating Functional Polymer Dielectrics to Reduce the Threshold Voltage of n-Type Organic Thin-Film Transistors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-08) Ronnasi, Bahar; King, Benjamin; Brixi, Samantha; Swaraj, Sufal; Niskanen, Jukka; Lessard, Benoît H.Low-cost and high-performance electronics based on synthetically simple materials are required to fuel the deployment of smart packaging and wearable electronics. Metal phthalocyanines (MPcs) are promising semiconductors for use in n-type organic thin film transistors (OTFTs) but often require high operating voltages. The first silicon phthalocyanine-based OTFT with a polymer dielectric is reported as an alternative to traditional metal oxide dielectrics. Incorporating poly(methyl methacrylate) (PMMA) as the dielectric successfully reduces the threshold voltage (VT) of bispentafluorophenoxy SiPc (F10-SiPc) from 14.9V to 7.3V while retaining high mobility. Further reduction in VT is obtained by using copolymers and blends of PMMA and dimethylamino ethyl methacrylate (DMAEMA)-containing polymers, where a higher molar fraction of DMAEMA leads to a consistent drop in VT to -0.7 V. The electron-donating groups of the tertiary amines in the DMAEMA show clear interfacial doping of the semiconductor, reducing the voltage required to populate the dielectric/semiconductor interface with charge carriers and turn on the device. Blending trace amounts of DMAEMA-containing copolymers with PMMA proves to be an effective strategy for reducing the VT while keeping the charge mobility high, unlike when using pure copolymers with elevated DMAEMA content. Time of flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) demonstrate that the DMAEMA-containing copolymer is floating to the surface of the PMMA blend at the dielectric–semiconductor interface, which explains the reduced VT. Synchrotron scanning transmission X-ray microscopy (STXM) demonstrates that PMMA promotes a more edge-on orientation of F10-SiPc films, compared to the more face-on orientation when deposited on the DMAEMA containing copolymer. This study demonstrates a straightforward process for designing dielectric polymers and their blends for the reduction in VT for n-type OTFTs. - Lignans in knotwood of Norway spruce: Localisation with soft x-ray microscopy and scanning transmission electron microscopy with energy dispersive x-ray spectroscopy
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-07) Mansikkala, Tuomas; Patanen, Minna; Kärkönen, Anna; Korpinen, Risto; Pranovich, Andrey; Ohigashi, Takuji; Swaraj, Sufal; Seitsonen, Jani; Ruokolainen, Janne; Huttula, Marko; Saranpää, Pekka; Piispanen, RiikkaLignans are bioactive compounds that are especially abundant in the Norway spruce (Picea abies L. Karst.) knotwood. By combining a variety of chromatographic, spectroscopic and imaging techniques, we were able to quantify, qualify and localise the easily extractable lignans in the xylem tissue. The knotwood samples contained 15 different lignans according to the gas chromatography-mass spectrometry analysis. They comprised 16% of the knotwood dry weight and 82% of the acetone extract. The main lignans were found to be hydroxymatairesinols HMR1 and HMR2. Cryosectioned and resin-embedded ultrathin sections of the knotwood were analysed with scanning transmission X-ray microscopy (STXM). Cryosectioning was found to retain only lignan residues inside the cell lumina. In the resin-embedded samples, lignan was interpreted to be unevenly distributed inside the cell lumina, and partially confined in deposits which were either readily present in the lumina or formed when OsO4 used in staining reacted with the lignans. Furthermore, the multi-technique characterisation enabled us to obtain information on the chemical composition of the structural components of knotwood. A simple spectral analysis of the STXM data gave consistent results with the gas chromatographic methods about the relative amounts of cell wall components (lignin and polysaccharides). The STXM analysis also indicated that a torus of a bordered pit contained aromatic compounds, possibly lignin.