Low‐Power Nonvolatile Charge Storage Memory Based on MoS2 and an Ultrathin Polymer Tunneling Dielectric

Low‐power, nonvolatile memory is an essential electronic component to store and process the unprecedented data flood arising from the oncoming Internet of Things era. Molybdenum disulfide (MoS₂) is a 2D material that is increasingly regarded as a promising semiconductor material in electronic device applications because of its unique physical characteristics. However, dielectric formation of an ultrathin low‐k tunneling on the dangling bond‐free surface of MoS₂ is a challenging task. Here, MoS₂‐based low‐power nonvolatile charge storage memory devices are reported with a poly(1,3,5‐trimethyl‐1,3,5‐trivinyl cyclotrisiloxane) (pV3D3) tunneling dielectric layer formed via a solvent‐free initiated chemical vapor deposition (iCVD) process. The surface‐growing polymerization and low‐temperature nature of the iCVD process enable the conformal growing of low‐k (≈2.2) pV3D3 insulating films on MoS₂. The fabricated memory devices exhibit a tunable memory window with high on/off ratio (≈10⁶), excellent retention times of 10⁵ s with an extrapolated time of possibly years, and an excellent cycling endurance of more than 10³ cycles, which are much higher than those reported previously for MoS₂‐based memory devices. By leveraging the inherent flexibility of both MoS₂ and polymer dielectric films, this research presents an important milestone in the development of low‐power flexible nonvolatile memory devices.     

Surface modification of polydimethylsiloxane (PDMS) induced proliferation and neural-like cells differentiation of umbilical cord blood-derived mesenchymal stem cells

Stem cell-based therapy has recently emerged for use in novel therapeutics for incurable diseases. For successful recovery from neurologic diseases, the most pivotal factor is differentiation and directed neuronal cell growth. In this study, we fabricated three different widths of a micro-pattern on polydimethylsiloxane (PDMS; 1, 2, and 4 microm). Surface modification of the PDMS was investigated for its capacity to manage proliferation and differentiation of neural-like cells from umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs). Among the micro-patterned PDMS fabrications, the 1 microm-patterned PDMS significantly increased cell proliferation and most of the cells differentiated into neuronal cells. In addition, the 1 microm-patterned PDMS induced an increase in cytosolic calcium, while the differentiated cells on the flat and 4 microm-patterned PDMS had no response. PDMS with a 1 microm pattern was also aligned to direct orientation within 10 degrees angles. Taken together, micro-patterned PDMS supported UCB-MSC proliferation and induced neural like-cell differentiation. Our data suggest that micro-patterned PDMS might be a guiding method for stem cell therapy that would improve its therapeutic action in neurological diseases.     

Single‐Walled Carbon‐Nanotube Networks on Large‐Area Glass Substrate by the Dip‐Coating Method

Highly uniform and large‐area single‐walled carbon‐nanotube (SWNT) networks are realized by the dip‐coating method, which is based on fundamental fluid‐dynamic phenomena such as capillary condensation and surface tension. The changes in the polarity and hydration properties of the substrate affect the morphology of the SWNT networks and result in nonlinear growth of the networks in the repetitive dip‐coating process. The density and the thickness of the SWNT networks are controlled by processing variables including number of dip coatings, concentration of SWNT colloidal solution, and withdrawal velocity. The networks have uniform sheet resistances and high optical transmittance in the visible wavelength range.     

Narrating emotional events in schizophrenia.

Research has indicated that schizophrenia patients report similar amounts of experienced emotion in response to emotional material compared with nonpatients. However, less is known about how schizophrenia patients describe and make sense of their emotional life events. We adopted a narrative approach to investigate schizophrenia patients' renderings of their emotional life experiences. In Study 1, patients' (n = 42) positive and negative narratives were similarly personal, tellable, engaged, and appropriate. However, negative narratives were less grammatically clear than positive narratives, and positive narratives were more likely to involve other people than negative narratives. In Study 2, emotional (positive and negative) narratives were less tellable and detached, yet more linear and social compared with neutral narratives for both schizophrenia patients (n = 24) and healthy controls (n = 19). However, patients' narratives about emotional life events were less appropriate to context and less linear, and patients' narratives, whether emotional or not, were less tellable and more detached compared with controls' narratives. Although schizophrenia patients are capable of recounting life events that trigger different emotions, the telling of these life events is fraught with difficulty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multi-wavelength emitting InGan/GaN quantum well grown on V-shaped gan(1101) microfacet

InGaN/GaN multiple quantum wells (MQWs) were successfully grown on the inclined GaN(1101) microfacets. Conventional photolithography and subsequent growth of GaN were employed to generate the V-shaped microfacets along (1120) direction. The well-developed microfacets observed by scanning electron microscopy and the clear transmission electron microscope interfacial images indicated that the MQW was successfully grown on the GaN microfacets. Interestingly, cathodoluminescence (CL) spectra measured on the microfacets showed a continuous change in the luminescence peak positions. The CL peaks were shifted to a longer wavelength from 420 nm to 440 nm as the probing points were changed along upward direction. This could be attributed to the nonuniform distribution of the In composition and/or the wavefunction overlapping between adjacent wells. Present works thus propose a novel route to fabricate a monolithic white light emitting diode without phosphors by growing the InGaN/GaN MQWs on (1101) facet.     

Enhanced heat transfer performance of alumina sponge-like nano-porous structures through surface wettability control in nucleate pool boiling

For several decades, a porous surface has been recognized as an efficient medium to increase boiling performance in a nucleate boiling regime. Most feasible porous surfaces have been studied in millimeter and micron-sized domains. It has been believed that a higher wall superheat is required to commence incipient nucleate boiling under a submicron regime. In this study, we demonstrate that a significantly enhanced pool boiling heat transfer is observed in a submicron regime through three dimensionally interconnected hybrid pores: the Alumina sponge-like nano-porous structure (ASNPS). The structural uniqueness of the ASNPS leads to an enlarged surface area, increases the potential number of the active nucleation site density, and improves the vapor–liquid menisci through the reentrant pore. Simultaneously, by changing the surface wettability with a hydrophobic self-assembled monolayer (SAM) coating, the number of active nucleation site density is improved. Eventually, the combination of the ASNPS and hydrophobic SAM coating can achieve substantial heat transfer coefficient (HTC) enhancement in the nucleate boiling. Also, the thickness of the ASNPS is a critical issue to adequately augment the HTC in pool boiling. The thickness of the ASNPS is optimized by examining the boiling performance of the ASNPS fabricated in different amounts of anodizing times. A classical mechanistic model from literature was modified and compared with the experimentally obtained data. The modified mechanistic model – with the combination of forced-convection and thin liquid film evaporation – showed reasonable predictions.     

NIR luminescent Er/Yb co-doped SiO2–ZrO2 nanostructured planar and channel waveguides: Optical and structural properties

Optical and structural properties of planar and channel waveguides based on sol–gel Er³⁺ and Yb³⁺ co-doped SiO₂–ZrO₂ are reported. Microstructured channels with high homogeneous surface profile were written onto the surface of multilayered densified films deposited on SiO₂/Si substrates by a femtosecond laser etching technique. The densification of the planar waveguides was evaluated from changes in the refractive index and thickness, with full densification being achieved at 900 °C after annealing from 23 up to 500 min, depending on the ZrO₂ content. Crystal nucleation and growth took place together with densification, thereby producing transparent glass ceramic planar waveguides containing rare earth-doped ZrO₂ nanocrystals dispersed in a silica-based glassy host. Low roughness and crack-free surface as well as high confinement coefficient were achieved for all the compositions. Enhanced NIR luminescence of the Er³⁺ ions was observed for the Yb³⁺-codoped planar waveguides, denoting an efficient energy transfer from the Yb³⁺ to the Er³⁺ ion.     

Twistable and bendable actuator: a CNT/polymer sandwich structure driven by thermal gradient

We demonstrate a novel configuration of an electrothermal actuator (ETA), which is based on a polydimethylsiloxane (PDMS) slab sandwiched by upper and lower active layers of CNT-PDMS composite. When only one active layer of a single sandwich structure ETA is heated and the other is not, there exists a thermal gradient in the direction of the slab thickness, resulting in bending motion toward the unheated side. Moreover, a dual sandwich structure ETA, consisting of two parallel assembled sandwich structures on the same body, has the unique ability to act with a twisting motion as the two ETAs bend in opposite directions. We expect the advent of the bendable and twistable actuator to break new ground in ETAs.     

Numerical study for laminar wavy motions of liquid film flow on vertical wall

Film flows are classified into non-wavy laminar, wavy laminar and turbulence along the Reynolds number or the flow stability. Since the wavy motions of the film flows are so intricate and nonlinear, the studies have largely been dependent upon the experimental way. The numerical approaches have been limited on the non-wavy flow regime. To track the free surface position, various numerical techniques such as the VOF (Volume of Fluids), the MAC (Marker and Cell) and the moving grid have been adopted. However those were for a more accurate estimation of the average film thickness and not for capturing the wavy motion. Because the wavy motion highly affects the heat transfer in the film flow, the profound concern for the wavy motion is significant. In this study, the wavy motions of the laminar wavy film flow with the Reynolds number 200–1000 are successfully found by the VOF and PLIC (Piecewise Linear Interface Calculation) method. The numerical results, including the average film thickness, and the wave’s amplitude, frequency and velocity, are compared with the experimental results.     

A computational study on optimal design for organic tandem solar cells

A new model is developed by combining the optical model and the drift-diffusion model to optimize the thicknesses of active layers of individual sub-cells for high performance of organic tandem solar cell. When the photovoltaic properties of tandem organic solar cells based on poly(2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta (2,1-b;3,4-b′) dithiophene)-alt-4,7-(2,1,3-benzo-thiadiazole))/(6,6)-phenyl C71-butyric acid methyl ester and poly(3-hexylthiophene)/(6,6)-phenyl C61-butyric acid methyl ester are calculated as functions of thicknesses of individual sub-cells using the new model, it is found that the optimum thickness pair of active layers is 150 and 120 nm for the front and back sub-cell, respectively. Comparison of simulation with experiment reveals that the simulated results are very consistent with experimental ones.