| 1. |
- Lee, SangWook, et al.
(author)
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Fabrication and mechanical properties of suspended one-dimensional polymer nanostructures: polypyrrole nanotube and helical polyacetylene nanofibre
- 2006
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 17, s. 992-996
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Journal article (peer-reviewed)abstract
- Mechanical properties of suspended quasi-one-dimensional polymer nanostructures were investigated using atomic force microscopy (AFM). A recently developed new acid-free etch method combined with electron beam lithography was used to fabricate suspended polypyrrole (PPy) nanotubes and helical polyacetylene (HPA) nanofibres. The elastic modulus of each suspended structure was obtained by AFM force–distance measurements. The estimated modulus value of the PPy nanotube (HPA nanofibre) was 0.96 GPa (0.5 GPa). Using this acid-free method, all-organic flexible NEMS devices can be fabricated in the future.
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| 2. |
- Yu, H.Y., et al.
(author)
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Current enhancement with alternating gate voltage in the Coulomb blockade regime of a single wall carbon nanotube
- 2004
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In: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 79, s. 1613-1615
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Journal article (peer-reviewed)abstract
- We investigated the current–voltage characteristics of a carbon nanotube in a single electron transistor structure with alternating gate voltage. A continuous current enhancement effect with increasing frequency of the applied gate voltage up to 13 MHz is reported. Assuming that I=nef, more than 1000 electrons are driven to flow across the source–drain channel at VDS=100 mV, 13 MHz of gate voltage (Vp-p=2 V) and T=1.8 K. The continuous current enhancement is explained by the broadening effect of the discrete energy levels of the finite-length carbon nanotube.
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| 3. |
- Alp, Dennis, et al.
(author)
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The 30 Year Search for the Compact Object in SN 1987A
- 2018
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In: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 864:2
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Journal article (peer-reviewed)abstract
- Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.
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| 4. |
- Arendt, Richard G., et al.
(author)
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JWST NIRCam Observations of SN 1987A : Spitzer Comparison and Spectral Decomposition
- 2023
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 959:2
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Journal article (peer-reviewed)abstract
- JWST Near Infrared Camera (NIRCam) observations at 1.5–4.5 μm have provided broadband and narrowband imaging of the evolving remnant of SN 1987A with unparalleled sensitivity and spatial resolution. Comparing with previous marginally spatially resolved Spitzer Infrared Array Camera (IRAC) observations from 2004 to 2019 confirms that the emission arises from the circumstellar equatorial ring (ER), and the current brightness at 3.6 and 4.5 μm was accurately predicted by extrapolation of the declining brightness tracked by IRAC. Despite the regular light curve, the NIRCam observations clearly reveal that much of this emission is from a newly developing outer portion of the ER. Spots in the outer ER tend to lie at position angles in between the well-known ER hotspots. We show that the bulk of the emission in the field can be represented by five standard spectral energy distributions, each with a distinct origin and spatial distribution. This spectral decomposition provides a powerful technique for distinguishing overlapping emission from the circumstellar medium and the supernova ejecta, excited by the forward and reverse shocks, respectively.
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| 5. |
- Axelsson, S., et al.
(author)
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Theoretical and experimental investigations of three-terminal carbon nanotube nanorelays
- 2005
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In: New J. Phys. - : IOP Publishing. - 1367-2630. ; 7
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Journal article (peer-reviewed)abstract
- We present theoretical and experimental investigations of three-terminal nanoelectromechanical relays based on suspended carbon nanotubes. A charge is induced in the nanotube by applying a voltage to an underlying gate electrode thus inducing the nanotube to bend and make contact with a drain electrode. Such devices have potential applications as fast switches, logic devices, memory elements and pulse generators. We describe two modes of operation: a contact mode where the nanotube makes physical contact with the drain electrode and a non-contact mode where electrical contact between the nanotube and the drain electrode is made via a field emission current.
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| 6. |
- Cigan, Phil, et al.
(author)
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High Angular Resolution ALMA Images of Dust and Molecules in the SN 1987A Ejecta
- 2019
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 886:1
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Journal article (peer-reviewed)abstract
- We present high angular resolution (similar to 80 mas) ALMA continuum images of the SN.1987A system, together with CO J = 2 -> 1, J = 6 -> 5, and SiO J = 5 -> 4 to J = 7 -> 6 images, which clearly resolve the ejecta (dust continuum and molecules) and ring (synchrotron continuum) components. Dust in the ejecta is asymmetric and clumpy, and overall the dust fills the spatial void seen in H alpha images, filling that region with material from heavier elements. The dust clumps generally fill the space where CO J = 6 -> 5 is fainter, tentatively indicating that these dust clumps and CO are locationally and chemically linked. In these regions, carbonaceous dust grains might have formed after dissociation of CO. The dust grains would have cooled by radiation, and subsequent collisions of grains with gas would also cool the gas, suppressing the CO J = 6 -> 5 intensity. The data show a dust peak spatially coincident with the molecular hole seen in previous ALMA CO J = 2 -> 1 and SiO J = 5 -> 4 images. That dust peak, combined with CO and SiO line spectra, suggests that the dust and gas could be at higher temperatures than the surrounding material, though higher density cannot be totally excluded. One of the possibilities is that a compact source provides additional heat at that location. Fits to the far-infrared-millimeter spectral energy distribution give ejecta dust temperatures of 18-23 K. We revise the ejecta dust mass to M-dust = 0.2-0.4 M-circle dot for carbon or silicate grains, or a maximum of <0.7 M-circle dot for a mixture of grain species, using the predicted nucleosynthesis yields as an upper limit.
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| 7. |
- Jeong, Heesu, et al.
(author)
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Room-Temperature-Grown amorphous Indium-Tin-Silicon-Oxide thin film as a new electron transporting layer for perovskite solar cells
- 2022
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In: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 581
-
Journal article (peer-reviewed)abstract
- We report the amorphous quaternary oxide, indium-tin-silicon-oxide (ITSO), thin film as a new electron transport layer (ETL) for perovskite solar cells (PSCs). ITSO thin films are grown by magnetron co-sputtering indium-tin-oxide (ITO) and silicon oxide (SiO2) on commercial transparent conducting oxide (TCO) thin films at room temperature. As Si content increases (0-53.8 at%) the optical bandgap increases by approximately 1.3 eV and the electrical resistivity increases by six orders mainly because of the carrier concentration decrease. Consequently, the ITSO electronic structure depends largely on Si content. PSCs employing ITSO thin films as ETLs were fabricated to evaluate the effect of Si content on device performances. Si content influenced the shunt and series resistance. The optimized device was obtained using an ITSO film with 33.0 at% Si content, exhibiting 14.50% power-conversion efficiency. These results demonstrate that ITSO films are promising for developing efficient PSCs by optimizing the growing process and/or In/Sn/Si/O compositions. This approach can reduce PSC manufacturing process time and costs if ITO and ITSO are grown together by continuous sequential sputtering in a dual gun (ITO and SiO2) chamber.
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| 8. |
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| 9. |
- Jhang, SungHo, et al.
(author)
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Random telegraph noise in carbon nanotubes and peapods
- 2006
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In: Current Applied Physics. - : Elsevier BV. - 1567-1739. ; 6, s. 987-991
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Journal article (peer-reviewed)abstract
- The switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individual single-walled carbon nanotubes (SWNTs) and C60-filled SWNTs (the so-called peapods). The RTN has been studied as a function of bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three different types of RTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of the SWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelastic scattering with ballistic electrons. On the other hand, the noise for peapods can be attributed to the motion of C60 molecules in hollow space of SWNTs.
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| 10. |
- Lee, DongSu, et al.
(author)
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Extraction of semiconducting carbon nanotubes by repeated dielectrophoretic filtering
- 2005
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In: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 80, s. 5-8
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Journal article (peer-reviewed)abstract
- We have separated semiconducting carbon nanotubes from as-grown batch material (HiPco production). A special configuration of electrodes which generates a 3-dimensional electric field gradient was used to filter out and deposit metallic carbon nanotubes by the dielectrophoretic method, leaving the remaining dispersion enriched in semiconducting nanotubes. The efficiency of filtering was determined by Raman spectroscopy. Using repeated deposition cycles, the ratio of semiconducting to metallic tubes was increased. After seven cycles, the proportion of semiconducting tubes in the remaining dispersion reached 94%.
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| 11. |
- Lee, DongSu, et al.
(author)
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Fabrication of crossed junctions of semiconducting and metallic carbon nanotubes: A CNT-gated CNT-FET
- 2006
-
In: Journal of nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 0000-0000. ; 6, s. 1325-1330
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Journal article (peer-reviewed)abstract
- We have developed a method to fabricate crossed junctions between semiconducting (s) and metallic (m) carbon nanotubes (CNTs) combining electric field directed chemical vapor deposition growth and dielectrophoretic alignment. By separating the s- and m-CNTs with a thin dielectric an ultrasmall field effect transistor (FET) was fabricated. By using the m-CNT as a gate it was possible to modulate the source-drain current through the s-CNT FET channel. We have also used the m-CNT as an electrical lead. An off-state current lowering was observed when the m-CNT lead was used as a drain electrode.
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| 12. |
- Lee, Minho, et al.
(author)
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Thermal-assisted photo-annealed TiO2 thin films for perovskite solar cells fabricated under ambient air
- 2020
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In: Applied Surface Science. - : ELSEVIER. - 0169-4332 .- 1873-5584. ; 530
-
Journal article (peer-reviewed)abstract
- We report herein a facile process for the fabrication of amorphous TiO2 thin films under ambient atmosphere using thermal-assisted UV-annealing (similar to 125 degrees C). The TiO2 films were prepared via spin-coating titanium diisopropoxide bis(acetylacetonate) precursor and sequential photo-annealing at various temperatures. Additional soft annealing during the UV-annealing altered the surface chemical states and electrical band structures of the amorphous TiO2 films. The UV-annealing at room temperature leads to a higher conduction band minimum level of the film and a smaller amount of hydroxyl group at the film surface, compared to the thermal-assisted (100-250 degrees C) UV-annealing or the thermal-only annealing (500 degrees C). Effects of the temperature during the UV-annealing process on photovoltaic properties were investigated by fabricating planar heterojunction perovskite cells with methylammonium lead triiodide under ambient atmosphere. At higher temperature of 100-150 degrees C, compared to room temperature, fill factor and power conversion efficiency were enhanced, and hysteresis in current-voltage curves were reduced. Impedance analysis demonstrates that the capacitance is significantly reduced, leading to suppressed hysteresis of the perovskite solar cells. Finally, we achieved a power-conversion efficiency of 20.36% (for the reverse scan) and a stabilized power output of 18.57% from a 125 degrees C -photo-annealed TiO2-based device.
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| 13. |
- Lee, SangWook, et al.
(author)
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A three-terminal carbon nanorelay
- 2004
-
In: Nano letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 4:10, s. 2027-2030
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Journal article (peer-reviewed)abstract
- Three-terminal nanorelay structures were fabricated with multiwall carbon nanotubes (MWNTs). The nanotube relays were deflected by applying a gate voltage until contact (mechanical and/or electrical) was made with a drain electrode, thus closing the circuit. It was possible to achieve multiple switching cycles, showing that carbon nanotubes are suitable and practical systems for developing nanoelectromechanical devices of this kind.
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| 14. |
- Lee, SangWook, et al.
(author)
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Network analyses identify liver-specific targets for treating liver diseases
- 2017
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In: Molecular Systems Biology. - : EMBO. - 1744-4292. ; 13:8
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Journal article (peer-reviewed)abstract
- We performed integrative network analyses to identify targets that can be used for effectively treating liver diseases with minimal side effects. We first generated co-expression networks (CNs) for 46 human tissues and liver cancer to explore the functional relationships between genes and examined the overlap between functional and physical interactions. Since increased de novo lipogenesis is a characteristic of nonalcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC), we investigated the liver-specific genes co-expressed with fatty acid synthase (FASN). CN analyses predicted that inhibition of these liver-specific genes decreases FASN expression. Experiments in human cancer cell lines, mouse liver samples, and primary human hepatocytes validated our predictions by demonstrating functional relationships between these liver genes, and showing that their inhibition decreases cell growth and liver fat content. In conclusion, we identified liver-specific genes linked to NAFLD pathogenesis, such as pyruvate kinase liver and red blood cell (PKLR), or to HCC pathogenesis, such as PKLR, patatin-like phospholipase domain containing 3 (PNPLA3), and proprotein convertase subtilisin/kexin type 9 (PCSK9), all of which are potential targets for drug development.
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| 15. |
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| 16. |
- Morjan, Raluca Elena, 1976, et al.
(author)
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Selective growth of individual multiwalled carbon nanotubes
- 2004
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In: Current Applied Physics. - : Elsevier BV. - 1567-1739. ; 4:6, s. 591-594
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Journal article (peer-reviewed)abstract
- Growth of individual, vertically aligned multiwalled carbon nanotubes (VACNT) on patterned Si wafers using dc plasma-enhanced CVD is described. The selective growth of individual VACNT within larger holes etched in Si is demonstrated for the first time.
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| 17. |
- Park, Jeewoong, et al.
(author)
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Acousto-microfluidics for screening of ssDNA aptamer
- 2016
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Journal article (peer-reviewed)abstract
- We demonstrate a new screening method for obtaining a prostate-specific antigen (PSA) binding aptamer based on an acoustofluidic separation (acoustophoreis) technique. Since acoustophoresis provides simultaneous washing and separation in a continuous flow mode, we efficiently obtained a PSA binding aptamer that shows high affinity without any additional washing step, which is necessary in other screening methods. In addition, next-generation sequencing (NGS) was applied to accelerate the identification of the screened ssDNA pool, improving the selecting process of the aptamer candidate based on the frequency ranking of the sequences. After the 8 th round of the acoustophoretic systematic evolution of ligands by exponential enrichment (SELEX) and following sequence analysis with NGS, 7 PSA binding ssDNA aptamer-candidates were obtained and characterized with surface plasmon resonance (SPR) for affinity and specificity. As a result of the new SELEX method with PSA as the model target protein, the best PSA binding aptamer showed specific binding to PSA with a dissociation constant (K d) of 0.7 nM.
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| 18. |
- Sveningsson, Martin, 1977, et al.
(author)
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Field emission from multiwalled carbon nanotubes – its application in NEMS
- 2005
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In: AIP COnference Proceedings. - 0094-243X .- 1551-7616. ; 786, s. 620-623
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Journal article (peer-reviewed)abstract
- Nanoelectromechanical systems (NEMS) are a rapidly growing area of research. We discuss here the fabrication of two different three terminal nanorelay structures based on multi-walled carbon nanotubes (MWNT). Using a gate voltage the whole MWNT can be deflected and the tip of the carbon nanotube can be moved closer to a drain electrode making physical contact. In another device structure the carbon nanotubes are shorter so they never can get real physical contact with the drain electrode, instead this device is based on the process of electron field emission from the MWNT.
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| 19. |
- Zanardo, Giovanna, et al.
(author)
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SPECTRAL AND MORPHOLOGICAL ANALYSIS OF THE REMNANT OF SUPERNOVA 1987A WITH ALMA AND ATCA
- 2014
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 796:2
-
Journal article (peer-reviewed)abstract
- We present a comprehensive spectral and morphological analysis of the remnant of supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and thermal components of the radio emission are investigated in images from 94 to 672 GHz (lambda 3.2 mm to 450 mu m), with the assistance of a high-resolution 44 GHz synchrotron template from the ATCA, and a dust template from ALMA observations at 672 GHz. An analysis of the emission distribution over the equatorial ring in images from 44 to 345 GHz highlights a gradual decrease of the east-to-west asymmetry ratio with frequency. We attribute this to the shorter synchrotron lifetime at high frequencies. Across the transition from radio to far infrared, both the synchrotron/dust-subtracted images and the spectral energy distribution (SED) suggest additional emission beside the main synchrotron component (S-nu proportional to nu(-0.73)) and the thermal component originating from dust grains at T similar to 22 K. This excess could be due to free-free flux or emission from grains of colder dust. However, a second flat-spectrum synchrotron component appears to better fit the SED, implying that the emission could be attributed to a pulsar wind nebula (PWN). The residual emission is mainly localized west of the SN site, as the spectral analysis yields -0.4 less than or similar to alpha less than or similar to -0.1 across the western regions, with alpha similar to 0 around the central region. If there is a PWN in the remnant interior, these data suggest that the pulsar may be offset westward from the SN position.
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