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Epitaxial growth, often termed “epitaxy”, is one of the most essential techniques underpinning semiconductor electronics, because crystallinities of the materials seriously dominate operation efficiencies of the electronic devices such as power gain/consumption, response speed, heat loss, and so on. In contrast to already well-established epitaxial growth methodologies for inorganic (covalent or ionic) semiconductors, studies on inter-molecular (van der Waals) epitaxy for organic semiconductors is still in the initial stage. In the present review paper, we briefly summarize recent works on the epitaxial inter-molecular junctions built on organic semiconductor single-crystal surfaces, particularly on single crystals of pentacene and rubrene. Experimental methodologies applicable for the determination of crystal structures of such organic single-crystal-based molecular junctions are also illustrated.

CH3NH3PbI3 perovskite films were grown epitaxially on rubrene single crystals using the laser deposition method for the supply of the source materials (PbI2 and CH3NH3I). An atomically smooth surface with step-and-terrace structures was observed. Several types of crystal orientation were observed, which were dependent on the growth temperature and deposition conditions. For room temperature growth, the crystal orientation was correlated with the orientation of PbI2, which was also found to be grown epitaxially on the rubrene single crystal. In contrast, for growth at elevated temperatures, the crystal orientation with the smallest mismatch between rubrene and perovskite is produced. The construction of atomically ordered ideal perovskite crystals was verified. Moreover, a novel phenomenon was revealed where the octahedral PbI6 unit of PbI2 rotates vertically while retaining its lateral orientation. This growth mechanism results in a layer-by-layer growth and the construction of epitaxial perovskite films with atomic-order flat surfaces.

In this communication, we report a new type of stimuli-responsive amino acid-derived polymer, whose enzyme-degradability can be controlled by pH-induced quantitative conversion of the polymer backbone structure from polyester to polypeptide. [ABSTRACT FROM AUTHOR]

The phase transition of organosilane monolayers on Si-wafer substrate surfaces prepared from octadecyltrichlorosilane (OTS) or docosyltrichlorosilane (DOTS) was investigated on the basis of grazing incidence X-ray diffraction (GIXD) at various temperatures. The OTS monolayer was prepared by a chemisorption method. The DOTS monolayer was prepared by a water-cast method (DOTS). The GIXD measurement clarified that the OTS monolayer also changed from hexagonal phase to amorphous state above a melting point of otadecyl groups. The GIXD measurements also clarified that the molecular aggregation state of the DOTS monolayer changes from an anisotropic phase to an isotropic phase with an increase in temperature. An estimated linear thermal expansion coefficient of the lattice lengths of aand bof the DOTS monolayer in the rectangular crystalline state assigned a similar value to those of bulk polyethylene with an orthorhombic crystalline lattice. The setting angle of the abplane of the rectangular DOTS monolayer also showed similar behavior to that of the abplane of bulk polyethylene. [ABSTRACT FROM AUTHOR]

Abstract The realization of room-temperature processes is an important factor in the development of flexible electronic devices composed of organic materials. In addition, a simple and cost-effective process is essential to produce stable working devices and to enhance the performance of a smart material for flexible, wearable, or stretchable-skin devices. Here, we present a soft friction transfer method for producing aligned polymer films; a glass substrate was mechanically brushed with a velvet fabric and poly(3-hexylthiophene) (P3HT) solution was then spin-coated on the substrate. A P3HT film with a uniaxial orientation was obtained in air at room temperature. The orientation factor was 17 times higher than that of a film prepared using a conventional friction transfer technique at a high temperature of 120 °C. In addition, an oriented film with a thickness of 40 nm was easily picked up and transferred to another substrate. The mechanism for orientation of the film was investigated using six experimental methods and theoretical calculation, and was thereby attributed to a chemical process, i.e., cellulose molecules attach to the substrate and act as a template for molecular alignment.

We experimentally prepared a ferromagnet with an L10-FeCo ordered structure by inserting a periodic buffer layer to suppress the B2 structural transition and to maintain the L10 structure. The sample was fabricated by utilizing a technique involving the deposition of alternating monoatomic layers using pulsed laser deposition (PLD). This technique was used to deposit a thin film of (7 ML-FeCo/3 ML-buffer)3, in which either Cu or Ni was utilized as buffer layer. We characterized the surface roughness, surface morphology, lattice structure, and magnetic properties of the specimens by RHEED, AFM, SR-XRD, and SQUID, respectively. As a result, we successfully confirmed the construction of the L10-FeCo superstructure with a periodic Ni buffer layer for the first time. Both the magnetic moment and magnetic anisotropy were also increased by replacing Cu with Ni.

The structural and electronic properties of interfaces composed of donor and acceptor molecules play important roles in the development of organic opto-electronic devices. Epitaxial growth of organic semiconductor molecules offers a possibility to control the interfacial structures and to explore precise properties at the intermolecular contacts. 5,6,11,12-tetraazanaphthacene (TANC) is an acceptor molecule with a molecular structure similar to that of pentacene, a representative donor material, and thus, good compatibility with pentacene is expected. In this study, the physicochemical properties of the molecular interface between TANC and pentacene single crystal (PnSC) substrates were analyzed by atomic force microscopy, grazing-incidence X-ray diffraction (GIXD), and photoelectron spectroscopy. GIXD revealed that TANC molecules assemble into epitaxial overlayers of the (010) oriented crystallites by aligning an axis where the side edges of the molecules face each other along the [1¯10] direction of the PnSC. No apparent interface dipole was found, and the energy level offset between the highest occupied molecular orbitals of TANC and the PnSC was determined to be 1.75 eV, which led to a charge transfer gap width of 0.7 eV at the interface.

Homoepitaxial growth of organic semiconductor single crystals is a promising methodology toward the establishment of doping technology for organic opto-electronic applications. In this study, both electronic and crystallographic properties of homoepitaxially grown single crystals of rubrene were accurately examined. Undistorted lattice structures of homoepitaxial rubrene were confirmed by high-resolution analyses of grazing-incidence X-ray diffraction (GIXD) using synchrotron radiation. Upon bulk doping of acceptor molecules into the homoepitaxial single crystals of rubrene, highly sensitive photoelectron yield spectroscopy (PYS) measurements unveiled a transition of the electronic states, from induction of hole states at the valence band maximum at an adequate doping ratio (10 ppm), to disturbance of the valence band itself for excessive ratios (≥ 1000 ppm), probably due to the lattice distortion.

In this communication, we demonstrate that significantly different aggregation morphologies are readily generated from a simple poly(£,benzyl L-glutamate)/polystyrene hybrid block copolymer in nonaqueous media. These nanostructural variations were governed basically by both the solubility of each block to solvents and the character of the polypeptide block such as helix rodcoil transition. [ABSTRACT FROM AUTHOR]

Widespread alterations in RNA alternative splicing (AS) have been identified in adult gliomas. However, their regulatory mechanism, biological significance, and therapeutic potential remain largely elusive. Here, using a computational approach with both bulk and single-cell RNA-Seq, we uncover a prognostic AS signature linked with neural developmental hierarchies. Using advanced iPSC glioma models driven by glioma driver mutations, we show that this AS signature could be enhanced by EGFRvIII and inhibited by in situ IDH1 mutation. Functional validations of 2 isoform switching events in CERS5 and MPZL1 show regulations of sphingolipid metabolism and SHP2 signaling, respectively. Analysis of upstream RNA binding proteins reveals PTBP1 as a key regulator of the AS signature where targeting of PTBP1 suppresses tumor growth and promotes the expression of a neuron marker TUJ1 in glioma stem-like cells. Overall, our data highlights the role of AS in affecting glioma malignancy and heterogeneity and its potential as a therapeutic vulnerability for treating adult gliomas. [ABSTRACT FROM AUTHOR]

The hole mobility of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) film was measured using the time-of-flight method. The hole mobility was enhanced 4-fold after annealing at around the glass transition temperature (Tg). Optical, atomic force, and Kelvin force microscopies, and grazing-incidence X-ray diffraction measurements indicate the enhancement can be attributed to a homogeneous film structure, a homogeneous Fermi level energy, and a face-on oriented structure, all of which were established by annealing at Tg.

We present new semiconducting polymers incorporating naphtho[1, 2-b:5, 6-b'] dithiophene (NDT3) and naphtho[2, 1-b:6, 5-b'] dithiophene (NDT4), which are linked at the naphthalene positions, in the polymer backbone. It is interesting that the trend in the ordering structure and thus charge transport properties are quite different from what were observed in the isomeric polymers where the NDT3 and NDT4 cores are linked at the thiophene α-positions. In the thiophene-linked NDT system, the NDT3-based polymer (PNDT3BT) gave the better ordering in thin films and thus the high charge carrier mobility compared to the NDT4-based polymer (PNDT4BT). In the meantime, in the naphthalene-linked NDT system, the NDT4-based polymer (PNDT4iBT) provided the superior properties. Considering that PNDT4iBT has relatively low highest occupied molecular orbital (HOMO) energy level (−5.2 eV) and moderately high mobilities in the order of 10−2 cm2 V−1 s−1, the NDT4 core, when linked at the naphthalene positions, can be a good building unit for the development of high-performance semiconducting polymers for both organic field-effect transistors and photovoltaic devices.

The magnetic structure of the double perovskite compound Sr2CuTeO6 was determined from neutron powder diffraction data. This material is magnetically described as an S=1/2 quasi-two-dimensional square-lattice Heisenberg model with antiferromagnetic nearest-neighbor and next-nearest-neighbor interactions. Sr2CuTeO6 undergoes a magnetic phase transition at TN≻29 K. The spin structure below TN is Néel antiferromagnetic on the square lattice, which means that the nearest-neighbor interaction (J1) is stronger than the next-nearest-neighbor interaction (J2), in contrast to other isostructural compounds such as Ba2CuWO6 and Sr2CuWO6, for which |J1|<|J2| is realized. [ABSTRACT FROM AUTHOR]

The electrochemical and electromechanical properties of actuators based on the polymer electrolyte poly(ethylene oxide) (PEO), fabricated using a single-walled carbon nanotube (SWCNT)-ionic liquid (IL)-based gel electrode, were compared with those of actuators based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF(HFP)). The ionic conductivity of the PEO/IL gel electrolyte layer was much smaller than that of the PVdF(HFP)/IL layer. This is likely because the interaction between the oxygen atoms of PEO and the cations of the IL was larger than that between the fluorine atom of PVdF(HFP) and the IL cations. The maximum strain of the PEO electrolyte layer was smaller than that of the PVdF(HFP) electrolyte layer. Further, the maximum strain of an EMI[TFSI]/PEO electrode-based actuator was approximately 1.3 times larger than that of an EMI[TFSI]/PVdF(HFP) electrode-based actuator, where EMI[TFSI] is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. These results indicated that the PEO electrode-based actuators exhibited better performances than those based on a PVdF(HFP) electrode. In the case of the PEO electrode-based actuators, it was also found that the ion size, and the self-diffusion coefficient, as well as the rate of ion transport in the electrodes and electrolyte, were of critical importance for realizing low-voltage actuators. Finally, a simple model for the actuation mechanism was also proposed. The model, which was based on the product of the ionic transport number and the ionic volume, was shown to successfully explain the actuator behavior. [ABSTRACT FROM AUTHOR]