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      • Graphene nanoribbon devices at high bias

        Philip Kim,Melinda Y Han 나노기술연구협의회 2014 Nano Convergence Vol.1 No.1

        We present the electron transport in graphene nanoribbons (GNRs) at high electric bias conduction. When graphene is patterned into a few tens of nanometer width of a ribbon shape, the carriers are confined to a quasi-one-dimensional (1D) system. Combining with the disorders in the system, this quantum confinement can lead into a transport gap in the energy spectrum of the GNRs. Similar to CNTs, this gap depends on the width of the GNR. In this review, we examine the electronic properties of lithographically fabricated GNRs, focusing on the high bias transport characteristics of GNRs as a function of density tuned by a gate voltage. We investigate the transport behavior of devices biased up to a few volts, a regime more relevant for electronics applications. We find that the high bias transport behavior in this limit can be described by hot electron scattered by the surface phonon emission, leading to a carrier velocity saturation. We also showed an enhanced current saturation effect in the GNRs with an efficient gate coupling. This effect results from the introduction of the charge neutrality point into the channel, and is similar to pinch-off in MOSFET devices. We also observe that heating effects in graphene at high bias are significant.

      • Mechanical properties of paraformaldehyde-treated individual cells investigated by atomic force microscopy and scanning ion conductance microscopy

        Kim Seong-Oh,Kim Joonhui,Okajima Takaharu,Cho Nam-Joon 나노기술연구협의회 2017 Nano Convergence Vol.4 No.5

        Background Cell fixation is an essential step to preserve cell samples for a wide range of biological assays involving histochemical and cytochemical analysis. Paraformaldehyde (PFA) has been widely used as a cross-linking fixation agent. It has been empirically recognized in a gold standard protocol that the PFA concentration for cell fixation, C PFA, is 4%. However, it is still not quantitatively clear how the conventional protocol of C PFA is optimized. Methods Here, we investigated the mechanical properties of cell fixation as a function of C PFA by using atomic force microscopy and scanning ion conductance microscopy. The goal of this study is to investigate the effect of C PFA (0–10 wt%) on the morphological and mechanical properties of live and fixed mouse fibroblast cells. Results We found that both Young’s modulus, E, and the fluctuation amplitude of apical cell membrane, a m, were almost constant in a lower C PFA (<10−4%). Interestingly, in an intermediate C PFA between 10−1 and 4%, E dramatically increased whereas a m abruptly decreased, indicating that entire cells begin to fix at C PFA = ca. 10−1%. Moreover, these quantities were unchanged in a higher C PFA (>4%), indicating that the cell fixation is stabilized at C PFA = ca. 4%, which is consistent with the empirical concentration of cell fixation optimized in biological protocols. Conclusions Taken together, these findings offer a deeper understanding of how varying PFA concentrations influence the mechanical properties of cells and suggest new avenues for establishing refined cell fixation protocols. Background Cell fixation is an essential step to preserve cell samples for a wide range of biological assays involving histochemical and cytochemical analysis. Paraformaldehyde (PFA) has been widely used as a cross-linking fixation agent. It has been empirically recognized in a gold standard protocol that the PFA concentration for cell fixation, C PFA, is 4%. However, it is still not quantitatively clear how the conventional protocol of C PFA is optimized. Methods Here, we investigated the mechanical properties of cell fixation as a function of C PFA by using atomic force microscopy and scanning ion conductance microscopy. The goal of this study is to investigate the effect of C PFA (0–10 wt%) on the morphological and mechanical properties of live and fixed mouse fibroblast cells. Results We found that both Young’s modulus, E, and the fluctuation amplitude of apical cell membrane, a m, were almost constant in a lower C PFA (<10−4%). Interestingly, in an intermediate C PFA between 10−1 and 4%, E dramatically increased whereas a m abruptly decreased, indicating that entire cells begin to fix at C PFA = ca. 10−1%. Moreover, these quantities were unchanged in a higher C PFA (>4%), indicating that the cell fixation is stabilized at C PFA = ca. 4%, which is consistent with the empirical concentration of cell fixation optimized in biological protocols. Conclusions Taken together, these findings offer a deeper understanding of how varying PFA concentrations influence the mechanical properties of cells and suggest new avenues for establishing refined cell fixation protocols.

      • Nanostructured plasmonic substrates for use as SERS sensors

        Jeon Tae Yoon,Kim Dong Jae,Park Sung-Gyu,Kim Shin-Hyun,Kim Dong-Ho 나노기술연구협의회 2016 Nano Convergence Vol.3 No.18

        Plasmonic nanostructures strongly localize electric fields on their surfaces via the collective oscillations of conducting electrons under stimulation by incident light at a certain wavelength. Molecules adsorbed onto the surfaces of plasmonic structures experience a strongly enhanced electric field due to the localized surface plasmon resonance (LSPR), which amplifies the Raman scattering signal obtained from these adsorbed molecules. This phenomenon is referred to as surface-enhanced Raman scattering (SERS). Because Raman spectra serve as molecular fingerprints, SERS has been intensively studied for its ability to facilely detect molecules and provide a chemical analysis of a solution. Further enhancements in the Raman intensity and therefore higher sensitivity in SERS-based molecular analysis have been achieved by designing plasmonic nanostructures with a controlled size, shape, composition, and arrangement. This review paper focuses on the current state of the art in the fabrication of SERS-active substrates and their use as chemical and biosensors. Starting with a brief description of the basic principles underlying LSPR and SERS, we discuss three distinct nanofabrication methods, including the bottom-up assembly of nanoparticles, top-down nanolithography, and lithography-free random nanoarray formation. Finally, typical applications of SERS-based sensors are discussed, along with their perspectives and challenges.

      • Enhanced viscoelastic property of iron oxide nanoparticle decorated organoclay fluid under magnetic field

        Son You-Hwan,Jung Youngsoo,Roh Heesuk,이중건 나노기술연구협의회 2017 Nano Convergence Vol.4 No.22

        Stable hydrophobic nanocomposites of magnetic nanoparticles and clay are prepared by the self-assembly of magnetite (Fe3O4) nanoparticles on surfaces of exfoliated clay platelets. Due to the attractive interaction between hydrophobic groups, oleic acid coated nanoparticles are strongly attached to the surface of cetyl trimethylammonium cation coated clay platelets in organic media. Crystal structure and magnetic property of composite particles are examined using electron microscopy, x-ray diffractometer and vibration sample magnetometer. In addition, composite particles are dispersed in mineral oil and rheological properties of composite particle suspensions are characterized using steady-state and oscillatory measurements. Magnetite nanoparticle decorated organoclay forms a tunable network in mineral oil. When a magnetic field is applied, the composite particle fluid exhibits higher storage modulus and maintains a solid-like property at larger strain. Our results show that the viscoelastic property of the magnetite nanoparticle decorated organoclay fluid is controlled by applying external magnetic field.

      • Mechanical test method and properties of a carbon nanomaterial with a high aspect ratio

        Jeon Sang Koo,Jang Hoon-Sik,Kwon Oh Heon,남승훈 나노기술연구협의회 2016 Nano Convergence Vol.3 No.29

        Superior nanomaterials have been developed and applied to many fields, and improved characteristic of nanomaterials have been studied. Measurement of the mechanical properties for nanomaterials is important to ensure the reliability and predict the service life times of products containing nanomaterials. However, it is challenging to measure the mechanical properties of nanomaterials due to their very small dimensions. Moreover, macro-scale measurement systems are not suitable for use with nanomaterials. Therefore, various methods have been developed and used to in an effort to measure the mechanical properties of nanomaterials. This paper presents a review of various evaluation systems and the measurement methods which are used to determine the mechanical properties of carbon nanotube (CNT) and carbon nanofiber (CNF), representatively. In addition, we measured the tensile strength and elastic modulus of the CNT and CNF in the scanning electron microscope (SEM) installed the nano-manipulator and the force sensor and this measurement system and results would be introduced in detail.

      • Polymeric nanoparticles containing diazepam: preparation, optimization, characterization, in-vitro drug release and release kinetic study

        Bohrey Sarvesh,Chourasiya Vibha,Pandey Archna 나노기술연구협의회 2016 Nano Convergence Vol.3 No.3

        Nanoparticles formulated from biodegradable polymers like poly(lactic-co-glycolic acid) (PLGA) are being extensively investigated as drug delivery systems due to their two important properties such as biocompatibility and controlled drug release characteristics. The aim of this work to formulated diazepam loaded PLGA nanoparticles by using emulsion solvent evaporation technique. Polyvinyl alcohol (PVA) is used as stabilizing agent. Diazepam is a benzodiazepine derivative drug, and widely used as an anticonvulsant in the treatment of various types of epilepsy, insomnia and anxiety. This work investigates the effects of some preparation variables on the size and shape of nanoparticles prepared by emulsion solvent evaporation method. These nanoparticles were characterized by photon correlation spectroscopy (PCS), transmission electron microscopy (TEM). Zeta potential study was also performed to understand the surface charge of nanoparticles. The drug release from drug loaded nanoparticles was studied by dialysis bag method and the in vitro drug release data was also studied by various kinetic models. The results show that sonication time, polymer content, surfactant concentration, ratio of organic to aqueous phase volume, and the amount of drug have an important effect on the size of nanoparticles. Hopefully we produced spherical shape Diazepam loaded PLGA nanoparticles with a size range under 250 nm with zeta potential −23.3 mV. The in vitro drug release analysis shows sustained release of drug from nanoparticles and follow Korsmeyer-Peppas model.

      • The use of nanocrystal quantum dot as fluorophore reporters in molecular beacon-based assays

        Adegoke Oluwasesan,EnochY.Park 나노기술연구협의회 2016 Nano Convergence Vol.3 No.32

        The utilization of molecular beacon (MB) biosensor probes to detect nucleic acid targets has received enormous interest within the scientific community. This interest has been stimulated by the operational qualities of MB-based probes with respect to their unique sensitivity and specificity. The design of MB biosensors entails not only optimizing the sequence of the loop to hybridize with the nucleic acid target or optimization of the length of the stem to tune the sensitivity but also the selection of the appropriate fluorophore reporter to generate the signal transduction read-out upon hybridization of the probe with the target sequence. Traditional organic fluorescent dyes are mostly used for signal reporting in MB assays but their optical properties in comparison to semiconductor fluorescent quantum dot (Qdot) nanocrystals are at a disadvantage. This review highlights the progress made in exploiting Qdot as fluorophore reporters in MB-based assays with the aim of instigating further development in the field of Qdot-MB technology. The development reported to date indicates that unparalleled fluorescence signal reporting in MB-based assays can be achieved using well-constructed Qdot fluorophores.

      • In situ synthesis of silver nanoparticles on the surface of PDMS with high antibacterial activity and biosafety toward an implantable medical device

        Kim Joong Hyun,Park HyeungWoo,서수원 나노기술연구협의회 2017 Nano Convergence Vol.4 No.33

        We developed a straightforward method to fabricate antibacterial silicon films via the in situ synthesis of silver nanoparticles (AgNPs) on a polydimethylsiloxane (PDMS) film. To grow AgNPs attached on the film, AgNP seeds were synthesized through the reduction of silver ions electrostatically bound to hydroxyl groups formed on the surface of the film after treatment with air plasma. In the growth reaction, silver ions were reduced on the seeds of AgNPs by sodium citrate in a solution of AgNO3, which allowed for the formation of AgNPs with sizes of up to ~ 500 nm, which The formed AgNPs on the films were characterized using UV–vis spectrophotometer, scattering electron microscope and induced coupled mass spectrometer. The amount of AgNPs was estimated to be less than 0.05% of the total film weight. Even though it was coated with a small amount of AgNPs, the PDMS film exhibited reduction of E. coli and S. aureus with values of log10 4.8 and log10 5.7, respectively. The biosafety of the AgNP-attached PDMS film was examined by contact of cells with the film or film eluent. Counting of viable cells revealed no significant cytotoxicity of the in situ-fabricated AgNPs on the PDMS film.

      • Colloidal quantum dot based solar cells: from materials to devices

        Song Jung Hoon,Jeong Sohee 나노기술연구협의회 2017 Nano Convergence Vol.4 No.21

        Colloidal quantum dots (CQDs) have attracted attention as a next-generation of photovoltaics (PVs) capable of a tunable band gap and low-cost solution process. Understanding and controlling the surface of CQDs lead to the significant development in the performance of CQD PVs. Here we review recent progress in the realization of low-cost, efficient lead chalcogenide CQD PVs based on the surface investigation of CQDs. We focus on improving the electrical properties and air stability of the CQD achieved by material approaches and growing the power conversion efficiency (PCE) of the CQD PV obtained by structural approaches. Finally, we summarize the manners to improve the PCE of CQD PVs through optical design. The various issues mentioned in this review may provide insight into the commercialization of CQD PVs in the near future.

      • White light emitting diode based on purely organic fluorescent to modern thermally activated delayed fluorescence (TADF) and perovskite materials

        Parameswar Krishnan Iyer 나노기술연구협의회 2019 Nano Convergence Vol.6 No.31

        White organic/polymer light emitting diode (WOLED/WPLED) processed from solution has attracted significant research interest in recent years due to their low device production cost, device flexibility, easy fabrication over large area including roll to roll and ability to print in various designs and shapes providing enormous design possibilities. Although WOLEDs fabricated using solution process lack their thermally evaporated counterparts in terms of device efficiency, remarkable progress has been made in this regard in recent years by utilizing new materials and device structures. In the present review, we have summarized and extrapolated an excellent association of old and modern concept of cost-effective materials and device structure for realization of white light. In particular, this article demonstrated and focused on design, and development of novel synthesis strategy, mechanistic insights and device engineering for solution process low cost WOLEDs device. Herein, an overview of the prevailing routes towards white light emitting devices (WLEDs) and corresponding materials used, including polymer based WLED, small molecules emitters based thermally activated delayed fluorescence (TADF), perovskite light-emitting diodes (PeLEDs) and hybrid materials based LEDs, color down-converting coatings with corresponding best efficiencies ever realized. We presume that this exhaustive review on WLEDs will offer a broad overview of the latest developments on white SSL and stonework the approach en route for innovations in the immediate future.

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