MIMO-HFM: A MIMO System with Hyperbolic Frequency Modulation for Underwater Acoustic Communication

Reliable transmission and high data rate over underwater acoustic channels are considerably challenging. In this paper, we propose Multiple-Input and Multiple-Output (MIMO) scheme using a Hyperbolic Frequency Modulation (HFM) waveform. Our proposed system combines the advantages of both systems-special multiplexing of MIMO and immunity against Doppler shift of HFM. To increase the spectral efficiency, we employ M-ray HFM and overlapped sub-channels by leveraging the high temporal resolution characteristic. To verify effectiveness of our system, we have designed a theoretically enhanced acoustic simulator, which especially focuses on the reflection phenomenon by utilizing approved reflection loss models. Based on our acoustic simulator, we could verify that our system is robust against for multipath fading and Doppler shifting while keeping the multiplexing benefit of MIMO, while maintaining a very low complexity and system overhead. In addition, the results provide a useful insight for physical layer design in acoustic communication systems.     

Two-dimensional air-stable CrSe2 nanosheets with thickness-tunable magnetism

Since Geim et al.firstly separated graphene from graph-ite by mechanical exfoliation method in 2004,the research of two-dimensional (2D) van der Waals (vdW) layered materials has begun[1].Compared with three-dimensional materials,2D vdW layered materials exposing the most atoms to exterior are more sensitive to external control and have the great po-tential applications in electronic,optoelectronic and electro-chemical area[2].     

Digital Laser Micropainting for Reprogrammable Optoelectronic Applications

Structural coloration is closely related to the progress of innovative optoelectronic applications, but the absence of direct, on-demand, and rewritable coloration schemes has impeded advances in the relevant area, particularly including the development of customized, reprogrammable optoelectronic devices. To overcome these limitations, a digital laser micropainting technique, based on controlled thin-film interference, is proposed through direct growth of the absorbing metal oxide layer on a metallic reflector in the solution environment via a laser. A continuous-wave laser simultaneously performs two functions—a photothermal reaction for site-selective metal oxide layer growth and in situ real-time monitoring of its thickness—while the reflection spectrum is tuned in a broad visible spectrum according to the laser fluence. The scalability and controllability of the proposed scheme is verified by laser-printed painting, while altering the thickness via supplementary irradiation of the identical laser in the homogeneous and heterogeneous solutions facilitates the modification of the original coloration. Finally, the proof-of-concept bolometer device verifies that specific wavelength-dependent photoresponsivity can be assigned, erased, and reassigned by the successive application of the proposed digital laser micropainting technique, which substantiates its potential to offer a new route for reprogrammable optoelectronic applications.     

A Liquid Metal Based Multimodal Sensor and Haptic Feedback Device for Thermal and Tactile Sensation Generation in Virtual Reality

Virtual reality (VR) has been widely used for training, gaming, and entertainment, and the value of VR is continually increasing as a contact-free technology. For an immersive VR experience, measuring finger movements and providing appropriate feedback to the hand are as important as visual information, given the necessity of the hands for activities in daily life. Thus, a hand-worn VR device with motion sensors and haptic feedback is desirable. In this paper, a multimodal sensing and feedback glove is developed with soft, stretchable, lightweight, and compact sensor and heater sheets manufactured by direct ink writing (DIW) of liquid metal, eutectic gallium-indium (eGaIn). In the sensor sheet, ten sensors and three vibrators are embedded to measure finger movements and provide vibro-haptic feedback. The other heater sheet provides thermo-haptic sensation in accurate and rapid manner via model-based feedback control even under stretched conditions. The multimodal sensing and feedback glove allows users to feel the contact status and discriminate materials with different temperature. Performance of the proposed multimodal glove is verified under VR environments including touching and pushing two blocks of different materials and grabbing a heated metal ball submerged in hot water.     

Compact Quantum-Dot Microbeads with Sub-Nanometer Emission Linewidth

Fluorescent microbeads are widely used for applications in life sciences and medical diagnosis. The spectral contrast and sharpness of photoluminescence are critical in the utilities of microbeads for imaging and multiplexing. Here, microbeads capable of generating single-peak laser emission with a sub-nanometer linewidth are demonstrated. The microbeads are made of quantum dots that are tightly packed and crosslinked via ligand exchange for high optical gain and refractive index as well as material stability. Bright single-mode lasing with no photobleaching is achieved with particle diameters as small as 1.5 µm in the air. Sub-nm lasing emission is maintained even inside high-index surroundings, such as organic solvents and biological tissues. Feasibility of intracellular tagging and multi-color imaging in vivo is demonstrated.     

An Enhanced Link Adaptation Scheme Based on Cooperative Interference Prediction for MIMO-OFDM Systems

Dynamic inter-cell interference (ICI) causes channel quality indicator mismatch such that system throughput is reduced. In this paper, an enhanced link adaptation scheme based on cooperative interference prediction is proposed to reduce the mismatch. The scheme predicts the dynamic ICI within a cluster of base stations (BSs) for improving the link adaptation accuracy. With the dynamic ICI prediction, more accurate modulation and coding scheme can be selected without increasing the overhead over the air. System level simulations show that the proposed scheme significantly improves the system spectral efficiency (SE), especially the cell-edge SE.     

Hydrogen passivation effects under negative bias temperature instability stress in metal/silicon-oxide/silicon-nitride/silicon-oxide/silicon capacitors for flash memories

The paper presents the passivation effect of post-annealing gases on the negative bias temperature instability of metal/silicon-oxide/silicon-nitride/silicon-oxide/silicon (MONOS) capacitors. MONOS samples annealed at 850 °C for 30 s by a rapid thermal annealing (RTA) are treated by additional annealing in a furnace, using annealing gases N₂ and N₂-H₂ (2% hydrogen and 98% nitrogen gas mixture) at 450 °C for 30 min. MONOS samples annealed in an N₂-H₂ environment are found to have lowest oxide trap charge density shift, ΔN_ot = 8.56 × 10¹¹ cm⁻², and the lowest interface-trap density increase, ΔN_it = 4.49 × 10¹¹ cm⁻² among the three samples as-deposited, annealed in N₂ and N₂-H₂ environments. It has also been confirmed that the same MONOS samples have the lowest interface-trap density, D_it = 0.834 × 10¹¹ eV⁻¹ cm⁻², using small pulse deep level transient spectroscopy. These results indicate that the density of interface traps between the silicon substrate and the tunneling oxide layer are significantly reduced by the additional furnace annealing in the N₂-H₂ environment after the RTA.     

Effect of multiple reflows on interfacial reaction and shear strength of Sn-Ag electroplated solder bumps for flip chip package

The effect of displacement rate and intermetallic compound (IMC) growth on the shear strength of electroplated Sn-2.5Ag (in wt.%) flip chip solder with Cu under-bump metallization (UBM) were investigated after multiple reflows. Cu₆Sn₅ IMC was formed at the interface after one reflow. After five reflows, two different IMC layers, consisting of a scallop-shaped Cu₆Sn₅ phase and a planar Cu₃Sn phase, and their thicknesses increased with increasing reflow number up to 10. The shear strengths peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force. The tendency toward brittle fracture characteristics was intensified with increasing displacement rate and reflow number.     

Metalorganic Chemical Vapor Deposition of CdTe(133) Epilayers on Si(211) Substrates

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〉.