Non-functionalized soluble diketopyrrolopyrrole: Simplest p-channel core for organic field-effect transistors

We report the synthesis, characterization and behavior in field-effect transistors of non-functionalized soluble diketopyrrolopyrrole (DPP) core with only a solubilizing alkyl chain (i.e. –C₁₆H₃₃ or –C₁₈H₃₇) as the simplest p-channel semiconductor. The characteristics were evaluated by UV–vis and fluorescence spectroscopy, X-ray diffraction, cyclic voltammetry (CV), thermal analysis, atomic force microscopy (AFM) and density functional theory (DFT) calculation. For top-contact field-effect transistors, two types of active layers were prepared either by a solution process (as a 1D-microwire) or thermal vacuum deposition (as a thin-film) on a cross-linked poly(4-vinylphenol) gate dielectric. All the devices showed typical p-channel behavior with dominant hole transports. The device made with 1D-microwiress of DPP-R18 showed field-effect mobility in the saturation region of 1.42 × 10^?2 cm²/V s with I_ON/I_OFF of 1.82 × 10³. These findings suggest that the non-functionalized soluble DPP core itself without any further functionalization could also be used as a p-channel semiconductor for low-cost organic electronic devices.     

Automatic Transformation of Membrane‐Type Electronic Devices into Complex 3D Structures via Extrusion Shear Printing and Thermal Relaxation of Acrylonitrile–Butadiene–Styrene Frameworks

This work demonstrates a means of automatic transformation from planar electronic devices to desirable 3D forms. The method uses a spatially designed thermoplastic framework created via extrusion shear printing of acrylonitrile–butadiene–styrene (ABS) on a stress‐free ABS film, which can be laminated to a membrane‐type electronic device layer. Thermal annealing above the glass transition temperature allows stress relaxation in the printed polymer chains, resulting in an overall shape transformation of the framework. In addition, the significant reduction in the Young's modulus and the ability of the polymer chains to reflow in the rubbery state release the stress concentration in the electronic device layer, which can be positioned outside the neutral mechanical plane. Electrical analyses and mechanical simulations of a membrane‐type Au electrode and indium gallium zinc oxide transistor arrays before and after transformation confirm the versatility of this method for developing 3D electronic devices based on planar forms.     

Gallium-nitride microwave Doherty power amplifier with 40 W PEP and 68% PAE

A 40 W gallium-nitride microwave Doherty power amplifier for WCDMA repeater applications is presented. The main amplifier and peaking amplifier are implemented using two 20 W PEP GaN HEMTs. Performance is evaluated for broadband gain, power efficiency and adjacent-channel-power-ratio (ACPR). Experimental results of the GaN Doherty amplifier yielded a power gain of over 11 dB from 1.8 to 2.5 GHz, 68% power added efficiency at 40 W peak power. Good linearity performance of -48 dBc ACPR is obtained at a peak-to-average ratio of 9.8 dB.     

Disclosing the Role of Defect-Engineered Metal–Organic Frameworks in Mixed Matrix Membranes for Efficient CO2 Separation: A Joint Experimental-Computational Exploration

Incorporation of defects in metal–organic frameworks (MOFs) offers new opportunities for manipulating their microporosity and functionalities. The so-called “defect engineering” has great potential to tailor the mass transport properties in MOF/polymer mixed matrix membranes (MMMs) for challenging separation applications, for example, CO₂ capture. This study first investigates the impact of MOF defects on the membrane properties of the resultant MOF/polymer MMMs for CO₂ separation. Highly porous defect-engineered UiO-66 nanoparticles are successfully synthesized and incorporated into a CO₂-philic crosslinked poly(ethylene glycol) diacrylate (PEGDA) matrix. A thorough joint experimental/simulation characterization reveals that defect-engineered UiO-66/PEGDA MMMs exhibit nearly identical filler–matrix interfacial properties regardless of the defect concentrations of their parental UiO-66 filler. In addition, non-equilibrium molecular dynamics simulations in tandem with gas transport studies disclose that the defects in MOFs provide the MMMs with ultrafast transport pathways mainly governed by diffusivity selectivity. Ultimately, MMMs containing the most defective UiO-66 show the most enhanced CO₂/N₂ separation performance—CO₂ permeability = 470 Barrer (four times higher than pure PEGDA) and maintains CO₂/N₂ selectivity = 41—which overcomes the trade-off limitation in pure polymers. The results emphasize that defect engineering in MOFs would mark a new milestone for the future development of optimized MMMs.     

Non‐Volatile Polymer Electroluminescence Programmable with Ferroelectric Field‐Induced Charge Injection Gate

Electroluminescence (EL) of organic and polymeric fluorescent materials programmable in the luminance is extremely useful as a non‐volatile EL memory with the great potential in the variety of emerging information storage applications for imaging and motion sensors. In this work, a novel non‐volatile EL memory in which arbitrarily chosen EL states are programmed and erased repetitively with long EL retention is demonstrated. The memory is based on utilizing the built‐in electric field arising from the remnant polarization of a ferroelectric polymer which in turn controls the carrier injection of an EL device. A device with vertically stacked components of a transparent bottom electrode/a ferroelectric polymer/a hole injection layer/a light emitting layer/a top electrode successfully emits light upon alternating current (AC) operation. Interestingly, the device exhibits two distinctive non‐volatile EL intensities at constant reading AC voltage, depending upon the programmed direct current (DC) voltage on the ferroelectric layer. DC programmed and AC read EL memories are also realized with different EL colors of red, green and blue. Furthermore, more than four distinguishable EL states are precisely addressed upon the programmed voltage input each of which shows excellent EL retention and multiple cycle endurance of more than 10⁵ s and 10² cycles, respectively.     

Use of Mesoscopic Host Matrix to Induce Ferrimagnetism in Antiferromagnetic Spinel Oxide

Despite the advances in the methods for fabricating nanoscale materials, critical issues remain, such as the difficulties encountered in anchoring, and the deterioration in their stability after integration with other components. These issues need to be addressed to further increase the scope of their applicability. In this study, using epitaxial mesoscopic host matrices, materials are spatially confined at the nanoscale, and are supported, anchored, and stabilized. They also exhibit properties distinct from the bulk counterparts proving their high quality nanoscale nature. ZnFe₂O₄ and SrTiO₃ are used as the model confined material and host matrix, respectively. The ZnFe₂O₄ phases are spatially confined by the SrTiO₃ mesoscopic matrix and have strongly enhanced ferrimagnetic properties as compared to bulk and plain thin films of ZnFe₂O₄, with a Curie temperature of ≈500 K. The results of a series of control experiments and characterization measurements indicate that cationic inversion, which originates from the high interface‐to‐volume ratio of the ZnFe₂O₄ phase in the ZnFe₂O₄–SrTiO₃ nanocomposite film, is responsible for the magnetization enhancement. An exchange bias is observed, owing to the coexistence of ferrimagnetic and antiferromagnetic regions in the confined ZnFe₂O₄ phase. The magnetic properties are dependent on the ZnFe₂O₄ crystallite size, which can be controlled by the growth conditions.     

Polydopamine Encapsulation of Fluorescent Nanodiamonds for Biomedical Applications

Fluorescent nanodiamonds (FNDs) are promising bioimaging probes compared with other fluorescent nanomaterials such as quantum dots, dye‐doped nanoparticles, and metallic nanoclusters, due to their remarkable optical properties and excellent biocompatibility. Nevertheless, they are prone to aggregation in physiological salt solutions, and modifying their surface to conjugate biologically active agents remains challenging. Here, inspired by the adhesive protein of marine mussels, encapsulation of FNDs within a polydopamine (PDA) shell is demonstrated. These PDA surfaces are readily modified via Michael addition or Schiff base reactions with molecules presenting thiol or nitrogen derivatives. Modification of PDA shells by thiol terminated poly(ethylene glycol) (PEG‐SH) molecules to enhance colloidal stability and biocompatibility of FNDs is described. Their use as fluorescent probes for cell imaging is demonstrated; it is found that PEGylated FNDs are taken up by HeLa cells and mouse bone marrow‐derived dendritic cells and exhibit reduced nonspecific membrane adhesion. Furthermore, functionalization with biotin‐PEG‐SH is demonstrated and long‐term high‐resolution single‐molecule fluorescence based tracking measurements of FNDs tethered via streptavidin to individual biotinylated DNA molecules are performed. This robust polydopamine encapsulation and functionalization strategy presents a facile route to develop FNDs as multifunctional labels, drug delivery vehicles, and targeting agents for biomedical applications.     

Dependence of the linewidth enhancement factor on the number of compressively strained quantum well in lasers

We have systematically studied the well number dependence of the linewidth enhancement factor in strained quantum-well (QW) lasers and have demonstrated experimentally that the linewidth enhancement factor can be reduced from /spl sim/9.4 to /spl sim/2.0 by increasing the number of compressively strained QW's from 2 to 8. This behavior is primarily due to an increase in the differential gain with the number of QW's.     

In0.53Ga0.47As MSM photodiodes withtransparent CTO Schottky contacts and digital superlattice grading

Metal-semiconductor-metal (MSM) photodiodes with an In_0.53 Ga_0.47As active region were investigated using a transparent cadmium tin oxide (CTO) layer for the interdigitated electrodes to improve the low responsivity of conventional MSM photodiodes with opaque electrodes. CTO is suitable as a Schottky contact, an optical window and an anti-reflection (AR) coating. The transparent contact prevents shadowing of the active layer by the top electrode, thus allowing greater collection of incident light. Responsivity of CTO-based MSM photodiodes with 1-μm finger widths and 2-μm finger spacings and without an AR coating between the electrodes was twice (0.62 A/W) that of a similar MSM photodiodes with Ti/Au electrodes (0.30 A/W). A thin 800 Å In_0.52Al_0.48 As layer was inserted below the electrodes to elevate the electrode Schottky barrier height. A digitally graded superlattice region (660 A) was also employed to reduce carrier trapping at the In _0.53Ga_0.47As/In_0.52Al_0.48As heterointerface which acts to degrade photodiode bandwidth. Bandwidth of opaque electrode MSMs was elevated nearly an order of magnitude over a previous MSM photodiode design with an abrupt heterointerface, whereas the bandwidth of transparent electrode MSM's only improved about five times, indicating resistive effects may be intervening