Browsing by Subject "Dewetting"
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Item Open Access MIMIM photodetectors using plasmonically enhanced MIM absorbers(SPIE, 2017) Dereshgi, S. Abedini; Okyay, Ali KemalWe demonstrate super absorbing metal-insulator-metal (MIM) stacks and MIMIM photosensitive devices operating at visible and near-infrared (VIS-NIR) spectrum, where absorbing (top) MIM and photocollecting (bottom) MIM can be optimized separately. We investigate different bottom metals in absorbing MIM with nanoparticles realized by dewetting of silver thin film on top. While gold and silver have conventionally been considered the most appropriate plasmonic absorbers, we demonstrate different absorbing metals like aluminum and specifically chromium, with its plasma frequency happening at 850 nm, as more efficient layers for absorption. Absorption in chromium hits 82 percent around 1000 nm. We provide convincing evidences by doing reflection experiment and computational simulations for absorbing MIM part. We also suggest for the first time investigating electric loss tangent of metal or coherently, surface plasmon quality factor of absorbing metals which are reliable tools for engineering different metal layers. They reveal that despite the fact that gold and silver are good plasmonic scatterers in VIS-NIR and reliable absorbers in VIS region, they are not proper choices as absorbers for NIR applications. Once the most optimum absorbing design is pointed out, we integrate it on top of another metal-insulator to form an MIMIM photodetector with tunneling photocurrent path. The final optimized sample consisting of silver - hafnium oxide - chromium - aluminum oxide - silver nanoparticles (from bottom to top) has a dark current of 7nA and a photoresponsivity peak of 0.962 mA/W at 1000 nm and a full width at half maximum of 300 nm, while applied bias is 50 mV and device areas are 300 μm x 600 μm. This photoresponse shows 70 times enhancement compared to former reported spin coated rare nanoparticle MIMIMs.Item Open Access Organic light-emitting physically unclonable functions(Wiley-VCH Verlag GmbH & Co. KGaA, 2021-12-22) Kayacı, N.; Özdemir, R.; Kalay, M.; Kiremitler, N. B.; Usta, H.; Önses, Mustafa SerdarThe development of novel physically unclonable functions (PUFs) is of growing interest and fluorescent organic semiconductors (f-OSCs) offer unique advantages of structural versatility, solution-processability, ease of processing, and great tuning ability of their physicochemical/optoelectronic/spectroscopic properties. The design and ambient atmosphere facile fabrication of a unique organic light-emitting physically unclonable function (OLE-PUF) based on a green-emissive fluorescent oligo(p-phenyleneethynylene) molecule is reported. The OLE-PUFs have been prepared by one-step, brief (5 min) thermal annealing of spin-coated nanoscopic films (≈40 nm) at a modest temperature (170 °C), which results in efficient surface dewetting to form randomly positioned/sized hemispherical features with bright fluorescence. The random positioning of molecular domains generated the unclonable surface with excellent uniformity (0.50), uniqueness (0.49), and randomness (p > 0.01); whereas the distinctive photophysical and structural properties of the molecule created the additional security layers (fluorescence profile, excited-state decay dynamics, Raman mapping/spectrum, and infrared spectrum) for multiplex encoding. The OLE-PUFs on substrates of varying chemical structures, surface energies and flexibility, and direct deposition on goods via drop-casting are demonstrated. The OLE-PUFs immersed in water, exposed to mechanical abrasion, and read-out repeatedly via fluorescence imaging showed great stability. These findings clearly demonstrate that rationally engineered solution-processable f-OSCs have a great potential to become a key player in the development of new-generation PUFs.Item Open Access Physically unclonable surfaces via dewetting of polymer thin films(American Chemical Society, 2021-03-10) Torun, N.; Torun, İ.; Şakir, M.; Kalay, M.; Önses, Mustafa SerdarFrom anti-counterfeiting to biotechnology applications, there is a strong demand for encoded surfaces with multiple security layers that are prepared by stochastic processes and are adaptable to deterministic fabrication approaches. Here, we present dewetting instabilities in nanoscopic (thickness <100 nm) polymer films as a form of physically unclonable function (PUF). The inherent randomness involved in the dewetting process presents a highly suitable platform for fabricating unclonable surfaces. The thermal annealing-induced dewetting of poly(2-vinyl pyridine) (P2VP) on polystyrene-grafted substrates enables fabrication of randomly positioned functional features that are separated at a microscopic length scale, a requirement set by optical authentication systems. At a first level, PUFs can be simply and readily verified via reflection of visible light. Area-specific electrostatic interactions between P2VP and citrate-stabilized gold nanoparticles allow for fabrication of plasmonic PUFs. The strong surface-enhanced Raman scattering by plasmonic nanoparticles together with incorporation of taggants facilitates a molecular vibration-based security layer. The patterning of P2VP films presents opportunities for fabricating hybrid security labels, which can be resolved through both stochastic and deterministic pathways. The adaptability to a broad range of nanoscale materials, simplicity, versatility, compatibility with conventional fabrication approaches, and high levels of stability offer key opportunities in encoding applications.