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991.
Kwang-Chon Kim Hyun Jae Kim Sang-Hee Suh M. Carmody S. Sivananthan Jin-Sang Kim 《Journal of Electronic Materials》2010,39(7):863-867
Single-crystalline CdTe(133) films have been grown by metalorganic chemical vapor deposition on Si(211) substrates. We studied
the effect of various growth parameters on the surface morphology and structural quality of CdTe films. Proper oxide removal
from the Si substrate is considered to be the principal factor that influences both the morphology and epitaxial quality of
the CdTe films. In order to obtain single-crystalline CdTe(133) films, a two-stage growth method was used, i.e., a low-temperature
buffer layer step and a high- temperature growth step. Even when the low-temperature buffer layer shows polycrystalline structure,
the overgrown layer shows single-crystalline structure. During the subsequent high-temperature growth, two-dimensional crystallites
grow faster than other, randomly distributed crystallites in the buffer layer. This is because the capturing of adatoms by
steps occurs more easily due to increased adatom mobility. From the viewpoint of crystallographic orientation, it is assumed
that the surface structure of Si(211) consists of (111) terrace and (100) step planes with an interplanar angle of 54.8°.
This surface structure may provide many preferable nucleation sites for adatoms compared with nominally flat Si(100) or (111)
surfaces. The surface morphology of the resulting films shows macroscopic rectangular-shaped terrace—step structures that
are considered to be a (111) terrace with two {112} step planes directed toward 〈110〉. 相似文献
992.
In this paper, secure multicasting with the help of cooperative decode‐and‐forward relays is considered for the case in which a source securely sends a common message to multiple destinations in the presence of a single eavesdropper. We show that the secrecy rate maximization problem in the secure multicasting scenario under an overall power constraint can be solved using semidefinite programing with semidefinite relaxation and a bisection technique. Further, a suboptimal approach using zero‐forcing beamforming and linear programming based power allocation is also proposed. Numerical results illustrate the secrecy rates achieved by the proposed schemes under secure multicasting scenarios. 相似文献
993.
C.L. Canedy W.W. Bewley J.R. Lindle J.A. Nolde D.C. Larrabee C.S. Kim M. Kim I. Vurgaftman J.R. Meyer 《Journal of Electronic Materials》2008,37(12):1780-1785
We report an experimental investigation of four interband cascade lasers with wavelengths spanning the mid-infrared spectral
range, i.e., 2.9 μm to 5.2 μm, near room temperature in pulsed mode. One broad-area device had a pulsed threshold current density of only 3.8 A/cm2 at 78 K (λ = 3.6 μm) and 590 A/cm2 at 300 K (λ = 4.1 μm). The room-temperature threshold for the shortest-wavelength device (λ = 2.6 μm to 2.9 μm) was even lower, 450 A/cm2. A␣cavity-length study of the lasers emitting at 3.6 μm to 4.1 μm yielded an internal loss varying from 7.8 cm−1 at 78 K to 24 cm−1 at 300 K, accompanied by a decrease of the internal efficiency from 77% to 45%. 相似文献
994.
Im Deok Jung Min Kook Cho Kong Myeong Bae Sang Min Lee Phill Gu Jung Ho Kyung Kim Sung Sik Kim Jong Soo Ko 《ETRI Journal》2008,30(5):747-749
We introduce a pixel‐structured scintillator realized on a flexible polymeric substrate and demonstrate its feasibility as an X‐ray converter when it is coupled to photosensitive elements. The sample was prepared by filling Gd2O2S:Tb scintillation material into a square‐pore‐shape cavity array fabricated with polyethylene. For comparison, a sample with the conventional continuous geometry was also prepared. Although the pixelated geometry showed X‐ray sensitivity of about 58% compared with the conventional geometry, the resolving power was improved by about 70% above a spatial frequency of 3 mm?1. The spatial frequency at 10% of the modulation‐transfer function was about 6 mm?1. 相似文献
995.
S. ChandramohanBeo Deul Ryu P. UthirakumarJi Hye Kang Hyun Kyu KimHyung Gu Kim Chang-Hee Hong 《Solid-state electronics》2011,57(1):90-92
We report on the spectral tunability of white light by localized surface plasmon (LSP) effect in a colour converting hybrid device made of CdSe/ZnS quantum dots (QDs) integrated on InGaN/GaN blue light-emitting diodes (LEDs). Silver (Ag) nanoparticles (NPs) are mixed with QDs for generating LSP effect. When the plasmon absorption of Ag NPs is synchronized to the QW emission at 448 nm, the NPs selectively absorb the blue light and subsequently enhance the QD emission. Using this energy transfer scheme, the (x, y) chromaticity coordinates of the hybrid white LED was tuned from (0.32, 0.17) to (0.43, 0.26), and thereby generated warm white light emission with correlated colour temperature (CCT) around 1800 K. Moreover, a 47% enhancement in the external quantum efficiency (EQE) was realized. 相似文献
996.
Layered Orthorhombic Nb2O5@Nb4C3Tx and TiO2@Ti3C2Tx Hierarchical Composites for High Performance Li‐ion Batteries 下载免费PDF全文
Chuanfang Zhang Seon Joon Kim Michael Ghidiu Meng‐Qiang Zhao Michel W. Barsoum Valeria Nicolosi Yury Gogotsi 《Advanced functional materials》2016,26(23):4143-4151
Engineering electrode nanostructures is critical in developing high‐capacity, fast rate‐response, and safe Li‐ion batteries. This study demonstrates the synthesis of orthorhombic Nb2O5@Nb4C3Tx (or @Nb2CTx) hierarchical composites via a one‐step oxidation —in flowing CO2 at 850 °C —of 2D Nb4C3Tx (or Nb2CTx) MXene. The composites possess a layered architecture with orthorhombic Nb2O5 nanoparticles decorated uniformly on the surface of the MXene flakes and interconnected by disordered carbon. The composites have a capacity of 208 mAh g?1 at a rate of 50 mA g?1 (0.25 C) in 1–3 V versus Li+/Li, and retain 94% of the specific capacity with 100% Coulombic efficiency after 400 cycles. The good electrochemical performances could be attributed to three synergistic effects: (1) the high conductivity of the interior, unoxidized Nb4C3Tx layers, (2) the fast rate response and high capacity of the external Nb2O5 nanoparticles, and (3) the electron “bridge” effects of the disordered carbon. This oxidation method was successfully extended to Ti3C2Tx and Nb2CTx MXenes to prepare corresponding composites with similar hierarchical structures. Since this is an early report on producing this structure, there is much room to push the boundaries further and achieve better electrochemical performance. 相似文献
997.
In Situ Formation of Copper‐Based Hosts Embedded within 3D N‐Doped Hierarchically Porous Carbon Networks for Ultralong Cycle Lithium–Sulfur Batteries 下载免费PDF全文
Qiuhong Yu Yang Lu Rongjie Luo Xianming Liu Kaifu Huo Jang‐Kyo Kim Jun He Yongsong Luo 《Advanced functional materials》2018,28(39)
Lithium–sulfur (Li–S) batteries are promising energy storage systems due to their large theoretical energy density of 2600 Wh kg?1 and cost effectiveness. However, the severe shuttle effect of soluble lithium polysulfide intermediates (LiPSs) and sluggish redox kinetics during the cycling process cause low sulfur utilization, rapid capacity fading, and a low coulombic efficiency. Here, a 3D copper, nitrogen co‐doped hierarchically porous graphitic carbon network developed through a freeze‐drying method (denoted as 3D Cu@NC‐F) is prepared, and it possesses strong chemical absorption and electrocatalytic conversion activity for LiPSs as highly efficient sulfur host materials in Li–S batteries. The porous carbon network consisting of 2D cross‐linked ultrathin carbon nanosheets provides void space to accommodate volumetric expansion upon lithiation, while the Cu, N‐doping effect plays a critical role for the confinement of polysulfides through chemical bonding. In addition, after sulfuration of Cu@NC‐F network, the in situ grown copper sulfide (CuxS) embedded within CuxS@NC/S‐F composite catalyzes LiPSs conversion during reversible cycling, resulting in low polarization and fast redox reaction kinetics. At a current density of 0.1 C, the CuxS@NC/S‐F composites' electrode exhibits an initial capacity of 1432 mAh g?1 and maintains 1169 mAh g?1 after 120 cycles, with a coulombic efficiency of nearly 100%. 相似文献
998.
Elucidating the Origins of Subgap Tail States and Open‐Circuit Voltage in Methylammonium Lead Triiodide Perovskite Solar Cells 下载免费PDF全文
Tian Du Jinhyun Kim Jonathan Ngiam Shengda Xu Piers R. F. Barnes James R. Durrant Martyn A. McLachlan 《Advanced functional materials》2018,28(32)
Recombination via subgap trap states is considered a limiting factor in the development of organometal halide perovskite solar cells. Here, the impact of active layer crystallinity on the accumulated charge and open‐circuit voltage (Voc) in solar cells based on methylammonium lead triiodide (CH3NH3PbI3, MAPI) is demonstrated. It is shown that MAPI crystallinity can be systematically tailored by modulating the stoichiometry of the precursor mix, where small quantities of excess methylammonium iodide (MAI) improve crystallinity, increasing device Voc by ≈200 mV. Using in situ differential charging and transient photovoltage measurements, charge density and charge carrier recombination lifetime are determined under operational conditions. Increased Voc is correlated to improved active layer crystallinity and a reduction in the density of trap states in MAPI. Photoluminescence spectroscopy shows that an increase in trap state density correlates with faster carrier trapping and more nonradiative recombination pathways. Fundamental insights into the origin of Voc in perovskite photovoltaics are provided and it is demonstrated why highly crystalline perovskite films are paramount for high‐performance devices. 相似文献
999.
Multicasting is a useful communication method in wireless mesh networks (WMNs). Many applications in WMNs require efficient
and reliable multicast communications, i.e., high delivery ratio with low overhead among a group of recipients. In spite of
its significance, little work has been done on providing such multicast service in multi-channel WMNs. Traditional multicast
protocols for wireless and multi-hop networks tend to assume that all nodes, each of which is equipped with a single interface,
collaborate on the same channel. This single-channel assumption is not always true, as WMNs often provide nodes with multiple
interfaces to enhance performance. In multi-channel and multi-interface (MCMI) WMNs, the same multicast data must be sent
multiple times by a sender node if its neighboring nodes operate on different channels. In this paper, we try to tackle the
challenging issue of how to design a multicast protocol more suitable for MCMI WMNs. Our multicast protocol builds multicast
paths while inviting multicast members, and tries to allocate the same channel to neighboring members in a bottom-up manner.
By unifying fixed channels of one-hop multicast neighbors, the proposed algorithm can improve the performance such as reducing
multicast data transmission overhead and delay, while managing a successful delivery ratio. In order to prove such expectation
on the performance, we have implemented and evaluated the proposed solution on the real testbed having the maximum 24 nodes,
each of which is equipped with two IEEE 802.11a Atheros WLAN cards. 相似文献
1000.
Scaling the Aspect Ratio of Nanoscale Closely Packed Silicon Vias by MacEtch: Kinetics of Carrier Generation and Mass Transport 下载免费PDF全文
Jeong Dong Kim Parsian K. Mohseni Karthik Balasundaram Srikanth Ranganathan Jayavel Pachamuthu James J. Coleman Xiuling Li 《Advanced functional materials》2017,27(12)
Metal‐assisted chemical etching (MacEtch) has shown tremendous success as an anisotropic wet etching method to produce ultrahigh aspect ratio semiconductor nanowire arrays, where a metal mesh pattern serves as the catalyst. However, producing vertical via arrays using MacEtch, which requires a pattern of discrete metal disks as the catalyst, has often been challenging because of the detouring of individual catalyst disks off the vertical path while descending, especially at submicron scales. Here, the realization of ordered, vertical, and high aspect ratio silicon via arrays by MacEtch is reported, with diameters scaled from 900 all the way down to sub‐100 nm. Systematic variation of the diameter and pitch of the metal catalyst pattern and the etching solution composition allows the extraction of a physical model that, for the first time, clearly reveals the roles of the two fundamental kinetic mechanisms in MacEtch, carrier generation and mass transport. Ordered submicron diameter silicon via arrays with record aspect ratio are produced, which can directly impact the through‐silicon‐via technology, high density storage, photonic crystal membrane, and other related applications. 相似文献