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81.
O‐Pil Kwon Seong‐Ji Kwon Mojca Jazbinsek Fabian D. J. Brunner Jung‐In Seo Christoph Hunziker Arno Schneider Hoseop Yun Yoon‐Sup Lee Peter Günter 《Advanced functional materials》2008,18(20):3242-3250
We investigate a configurationally locked polyene (CLP) crystal 2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna21 (point group mm2) exhibit large second‐order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1 crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1–3 THz by optical rectification of 160 fs pulses has been demonstrated. 相似文献
82.
Veronika Kondratieva Seung-Woo Seo 《Communications Letters, IEEE》2007,11(2):149-151
Authentication based on the Merkle tree has been proposed as an energy efficient approach in a resource constrained sensor network environment. It replaces complicated certificate verification with more power efficient hash computations. While previous works assumed complete binary Merkle tree structures, which can be used efficiently only in sensor networks with a specific number of sensor nodes, we investigate incomplete Merkle trees to support any number of sensors. For the incomplete Merkle tree, we demonstrate that an optimal structure can be found through mathematical analysis and simulation. A novel tree indexing scheme is also proposed to reduce communication overhead and save sensors resources during authentication 相似文献
83.
Yoonseok Ka Eungkyu Lee Si Yun Park Jaewon Seo Dae-Gyeon Kwon Hyun Hwi Lee Yongsup Park Youn Sang Kim Changsoon Kim 《Organic Electronics》2013,14(1):100-104
We investigate the effects of ZnO annealing temperature (TA) on the performance of inverted polymer solar cells with ZnO electron-selective layers deposited by spin coating aqueous solutions of an ammine-hydroxo zinc complex. The inverted solar cells based on poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester with TA as low as 80 °C exhibit power-conversion efficiencies of 3.6%, which is equal to those of devices with higher TA. Characterizations of the ZnO films using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, grazing incidence wide-angle X-ray scattering, and optical transmittance measurements show that the abrupt improvement of device performance from TA = 60 to 80 °C is due to the improvement of energy-level alignment arising from the increases in the relative amount and the crystallinity of ZnO. 相似文献
84.
Wireless Networks - The Wi-Fi fingerprint, which can be used on existing wireless networks, is one of the main indoor positioning techniques that utilizes the received signal strength (RSS). In... 相似文献
85.
The impact of semiconductor technology scaling on CMOS RF and digital circuits for wireless application 总被引:1,自引:0,他引:1
Kwyro Lee Nam I. Ickjin Kwon Gil J. Kwangseok Han Park S. Bo-Ik Seo 《Electron Devices, IEEE Transactions on》2005,52(7):1415-1422
The impact of CMOS technology scaling on the various radio frequency (RF) circuit components such as active, passive and digital circuits is presented. Firstly, the impact of technology scaling on the noise and linearity of the low-noise amplifier (LNA) is thoroughly analyzed. Then two new circuits, i.e., CMOS complementary parallel push-pull (CCPP) circuit and vertical-NPN (V-NPN) circuit for direct-conversion receiver (DCR), are introduced. In CCPP, the high RF performance of pMOS comparable to nMOS provides single ended differential RF signal processing capability without the use of a bulky balun. The use of parasitic V-NPN bipolar transistor, available in triple well CMOS technology, has shown to provide more than an order of magnitude improvement in 1/f noise and dc offset related problems, which have been the bottleneck for CMOS single chip integration. Then CMOS technology scaling for various passive device performances such as the inductor, varactor, MIM capacitor, and switched capacitor, is discussed. Both the forward scaling of the active devices and the inverse scaling of interconnection layer, i.e., more interconnection layers with effectively thicker total dielectric and metal layers, provide very favorable scenario for all passive devices. Finally, the impact of CMOS scaling on the various digital circuits is introduced, taking the digital modem blocks, the various digital calibration circuits, the switching RF power amplifier, and eventually the software defined radio, as examples. 相似文献
86.
Cheolwoo You Gilsang Yoon Changwoo Seo Sherlie Portugal Gihwan Park Taejin Jung Huaping Liu Intae Hwang 《Wireless Personal Communications》2011,59(4):789-806
IMT-Advanced mobile communication systems make it possible for any devices to access high-speed networks anytime and anywhere.
To meet the needs of IMT-Advanced systems, cellular systems must solve the problem of intercell interference caused by frequency
reuse. Intercell interference problems become severe when orthogonal frequency division multiplexing (OFDM) transmission,
which is a key technology for 4G communication systems, is used in a cellular system. In this paper, a zone-based intercell
interference coordination (ICIC) scheme with high flexibility and low cost is proposed, and its performance is evaluated through
multicell system-level simulations carried out according to the simplified 3GPP (3rd Generation Partnership Project) Long
Term Evolution (LTE) system parameters. In the proposed algorithm, each cell is divided into several regions based on threshold
values. Each region reuses frequencies in different ways, and the regions have different maximum transmit (TX) powers according
to the interference environment. Even though the proposed scheme can be implemented with low complexity by using only the
existing user equipment (UE) measurement, simulation results have confirmed that it provides significant improvements in geometry
distribution. 相似文献
87.
Charge‐Generating Mode Control in High‐Performance Transparent Flexible Piezoelectric Nanogenerators
Hyun‐Kyu Park Keun Young Lee Ju‐Seok Seo Jin‐A Jeong Han‐Ki Kim Dukhyun Choi Sang‐Woo Kim 《Advanced functional materials》2011,21(6):1187-1193
In this work, we demonstrate the mode transition of charge generation between direct‐current (DC) and alternating‐current (AC) from transparent flexible (TF) piezoelectric nanogenerators (NGs), which is dependent solely on the morphology of zinc oxide (ZnO) nanorods without any use of an AC/DC converter. Tilted ZnO nanorods grown on a relatively low‐density seed layer generate DC‐type piezoelectric charges under a pushing load, whereas vertically aligned ZnO nanorods on a relatively high‐density seed layer create AC‐type charge generation. The mechanism for the geometry‐induced mode transition is proposed and characterized. We also examine the output performance of TF‐NGs which employ an indium zinc tin oxide (IZTO) film as a TF electrode. It is demonstrated that an IZTO film has improved electrical, optical, and mechanical properties, in comparison with an indium tin oxide (ITO) film. Enhanced output charge generation is observed from IZTO‐based TF‐NGs when TF‐NGs composed of only ITO electrodes are compared. This is attributed to the higher Schottky barrier and the lower series resistance of the IZTO‐based TF‐NGs. Thus, by using IZTO, we can expect TF‐NGs with superior mechanical durability and power generating performance. 相似文献
88.
Shahid Iqbal Le Thai Duy Hyunwoo Kang Ranveer Singh Mohit Kumar Jucheol Park Hyungtak Seo 《Advanced functional materials》2021,31(46):2102567
To realize the potential of Mott transition of multiphasic vanadium oxides (VOx) for memory applications, the development of VOx memtransistors on SiO2 wafer is introduced. Through electrical characterizations, the volatile memory behaviors of the VOx memtransistors are observed in both two- and three-terminal measurements. Their capacitive memory and resistive switching mechanisms are strongly related to the mixed VOx/SiO2 interface (called VSiOx). VSiOx supports the Mott transition in VOx at low bias voltages (<0.5 V), leading to the low power consumption of the memtransistor. Moreover, the fast switching time (≈35 ns) and tunable memory retention with the synaptic functions (potentiation and depression) of the memtransistors (by using the gate and drain biases) are demonstrated. Overall, the findings open up major opportunities for constructing ultrafast and femto-joule power-consuming neuromorphic devices. 相似文献
89.
Batteries: In Situ Formation of Conductive Metal Sulfide Domain in Metal Oxide Matrix: An Efficient Way to Improve the Electrochemical Activity of Semiconducting Metal Oxide (Adv. Funct. Mater. 31/2015) 下载免费PDF全文
In Young Kim Jiyoon Seo Seung Mi Oh Sharad B. Patil Seong‐Ju Hwang 《Advanced functional materials》2015,25(31):4921-4921
90.
G. Lucovsky H. Seo L.B. Fleming M.D. Ulrich J. Lüning P. Lysaght G. Bersuker 《Microelectronics Reliability》2006,46(9-11):1623-1628
Gate dielectrics comprised of nanocrystalline HfO2 in gate stacks with thin SiO2/SiON interfacial transition regions display significant asymmetries with respect to trapping of Si substrate injected holes and electrons. Based on spectroscopic studies, and guided by ab initio theory, electron and hole traps in HfO2 and other transition metal elemental oxides are assigned to O-atom divacancies, clustered at internal grain boundaries. Three engineering solutions for defect reduction are identified: i) deposition of ultra-thin, <2 nm, HfO2 dielectric layers, in which grain boundary formation is suppressed by effectively eliminating inter-primitive unit cell π-bonding interactions, ii) chemically phase separated high HfO2 silicates in which inter-primitive unit cell p-bonding interactions are suppressed by the two nanocrystalline grain size limitations resulting from SiO2 inclusions, and iii) non-crystalline Zr/Hf Si oxynitrides without grain boundary defects. 相似文献