P‐type tin‐oxide thin film transistors for blue‐light detection application

We reported the characteristics of p‐type tin‐oxide (SnO) thin film transistors (TFTs) upon illumination with visible light. Our p‐type TFT device using the SnO film as the active channel layer exhibits high sensitivity toward the blue‐light with a high light/dark read current ratio (I_light/I_dark) of 8.2 × 10³ at a very low driven voltage of <3 V. Since sensing of blue‐light radiation is very critical to our eyes, the proposed p‐type SnO TFTs with high sensitivity toward the blue‐light show great potential for future blue‐light detection applications.

     

A high efficiency 3D photovoltaic microwire with carbon nanotubes (CNT)‐quantum dot (QD) hybrid interface

An innovative hybrid QD sensitized photovoltaic carbon nanotubes microyarn has been developed using thermally‐stable and highly conductive carbon nanotubes yarns (CNYs). These CNYs are highly inter‐aligned, ultrastrong and flexible with excellent electrical conductivity, mechanical integrity and catalytic properties. The CNYs are coated with a QD‐incorporated TiO₂ microfilm and intertwined with a second set of CNYs as a counter electrode (CE). The maximum photon to current conversion efficiency (η_AM1.5) achieved with prolonged‐time stability was 5.93%. These cells are capable of efficiently harvesting incident photons regardless of direction and generating photocurrents with high efficiency and operational stability.

     

Whispering gallery modes in intrinsic TiO2 microspheres coupling to the defect‐related photoluminescence after visible excitation

Defect‐caused visible photoluminescence after visible excitation in anatase TiO₂ microresonators couples to whispering gallery modes (WGMs). Spherical anatase TiO₂ of a radius between 1.5 µm and 4 µm have been prepared by a sol–gel technique based on hydrolysis of titanium tetrabutoxide. The observation of WGMs in intrinsic anatase TiO₂ without additional dopant offers new perspectives for the localisation of light at TiO₂ surfaces for the design of photocatalysts.

WGMs show up as narrow peaks in the photoluminescence spectra of TiO₂ microparticles after visible excitation.     

Ag fractals formed on top of a porous TiO2 thin film

This work demonstrates the formation of Ag fractals on top of a Ag:TiO₂ thin film. The dendrite‐type objects emerged from a homogeneous and highly transparent Ag:TiO₂ nanocomposite, via the mechanism of diffusion‐limited‐aggregation of Ag atoms, during heat‐treatment at 500 °C. A porous TiO₂ matrix was also formed during this process, opening a wide range of possible applications, namely in sensing‐based ones, together with surface enhanced spectroscopies. Furthermore, fractals incorporate a wide range of shapes and spatial scales, inducing a potentially interesting optical response, over the whole visible range, presumably related with localized surface plasmon modes with very broad spectral distribution.

     

Microfocus X‐ray scattering and micro‐Raman spectroscopy: Transcrystallinity in isotactic polypropylene

Microfocus X‐ray scattering and micro Raman spectroscopy have been applied to study the β‐transcrystalline morphology in isotactic polypropylene. The transformation from the α‐ to the β‐form through the so‐called bifurcation of growth mechanism has been investigated with high spatial resolution. We found that the mixed α–β region does not present spatial correlation along the shearing direction, implying that there is no cooperative crystallization from the different β‐nucleation centres. In addition, a strong change in the lamellar orientation of the α‐form thin layer that induces the growth of the β‐crystallites has been observed for the first time. Finally, changes in the relative intensities of some selected Raman bands allowed the observation of the α–β transformation process at the molecular level.

     

Bulk superconductivity in single‐phase Bi3O2S3

We report the synthesis of single‐phase Bi₃O₂S₃ sample and confirm the occurrence of bulk superconductivity with transition temperature at 5.8 K. The Bi₃O₂S₃ superconductor is categorized as typical type‐II superconductor based on the results of both temperature and magnetic field dependences of magnetization. Hall coefficient measurements give evidence of a multiband character, with a dominant conduction mainly by electron‐like charge carriers. The charge carrier density is about 1.45 × 10¹⁹ cm^–3, suggesting that the system has very low charge carrier density.

     

First‐principle investigations of the peculiar magnetic behavior of Sr2FeOsO6

Structural, electronic and magnetic properties of Sr₂FeOsO₆ have been revisited by using the first‐principle calculations. Semiconducting behavior is reproduced. The band gap is 0.09 eV from generalized gradient approximation (GGA) and 0.30 eV by considering both SOC and U, a bit larger than the experimental observed 0.125 eV. In the C‐type antiferromagnetic configuration, spin frustration is found by analysing the magnetic exchange parameters, explaining the experimental observed magnetic complexity.

     

High‐temperature ferroelectricity and strong magnetoelectric effects in a hybrid organic–inorganic perovskite framework

A Cu‐based organic–inorganic perovskite framework exhibits high‐temperature ferroelectricity with strong magnetoelectric effects. Both electric field control of magnetization and magnetic field control of polarization are realized. Theoretical calculations suggest that a new mechanism of hybrid improper ferroelectricity arising from the Jahn–Teller distortions of magnetic metal ions and tilting of the organic cations are responsible for the peculiar multiferroic behaviors.

     

Lead‐free mesoscopic Cs2SnI6 perovskite solar cells using different nanostructured ZnO nanorods as electron transport layers

Lead‐free and more air‐stable perovskite Cs₂SnI₆ absorber with a direct bandgap of 1.48 eV is synthesized via a modified solution process. Different nanostructured ZnO nanorod arrays as electron transport layers and hole blocking layers are grown by controlling the seed layer and used to fabricate mesoscopic perovskite solar cells with Cs₂SnI₆ as light absorber layer. The influences of ZnO seed layers and nanorod morphology on the device photovoltaic performance were also investigated. With careful control of ZnO nanorod length and pore size to ensure high loading of the Cs₂SnI₆ absorber, we achieved power conversion efficiency of near 1%.

     

Thermally‐activated post‐growth dewetting of fullerene C60 on mica

Understanding and controlling the growth and stability of molecular thin films on solid surfaces is necessary to develop nanomaterials with well‐defined physical properties. As a prominent model system in organic electronics, we investigate the post‐growth dewetting kinetics of the fullerene C₆₀ on mica with real‐time and in situ X‐ray scattering. After layer‐by‐layer growth of C₆₀, we find a thermally‐activated post‐growth dewetting, where the smooth C₆₀‐layer breaks up into islands. This clearly shows that growth is kinetically limited before the system moves over an activation barrier into an energetically favored configuration. From the temperature‐dependent dewetting kinetics we find an effective activation barrier of 0.33 eV, which describes both the temperature‐dependent macroscopic changes in the surface morphology and the microscopic processes of inter‐ and intralayer diffusion during dewetting.

     

High‐mobility pentacene OTFT with TaLaO gate dielectric passivated by fluorine plasma

Pentacene thin‐film transistor with high‐κ TaLaO as gate dielectric has been fabricated and shows a carrier mobility of 0.73 cm²/V s, much higher than that based on pure La₂O₃ (0.43 cm²/V s) due to the smoother surface of the TaLaO film and thus larger pentacene islands grown on it in the initial stage. Moreover, among various times for fluorine‐plasma treatment on the TaLaO gate dielectric, 100 seconds result in the highest carrier mobility of 1.12 cm²/V s due to (1) smoothest oxide surface achieved by fluorine passivation of oxide traps, as measured by AFM and supported by smallest sub‐threshold swing and lowest low‐frequency noise; (2) the largest pentacene grains grown on the smoothest oxide surface, as demonstrated by AFM.

     

First‐principles prediction of a novel hexagonal phosphorene allotrope

Phosphorus prefers three‐connected configurations due to its inequivalent sp³‐hybridization. In the past year, many quasi two‐dimensional three‐connected networks were proposed as possible phosphorene allotropes. In this Letter, a new quasi two‐dimensional three‐connected network is proposed as a new potential phosphorene allotrope (Hex‐star). Based on first‐principles method calculations, the structure, stability and electronic properties of Hex‐star were systematically investigated. Our results indicate that Hex‐star is dynamically stable and it is a semiconductor with quasi‐direct band gap of 1.81 eV based on HSE06 method. Perspective top view (left) and Magen–David‐like orthographic top view (right) of Hex‐star phosphorene.

     

Low leakage stoichiometric SrTiO3 dielectric for advanced metal–insulator–metal capacitors

Metal–insulator–metal capacitors (MIMCAP) with stoichiometric SrTiO₃ dielectric were deposited stacking two strontium titanate (STO) layers, followed by intermixing the grain determining Sr‐rich STO seed layer, with the Ti‐rich STO top layer. The resulted stoichiometric SrTiO₃ would have a structure with less defects as demonstrated by internal photoemission experiments. Consequently, the leakage current density is lower compared to Sr‐rich STO which allow further equivalent oxide thickness downscaling.

Schematic of MIMCAP with stoichiometric STO dielectric formed from bottom Sr‐rich STO and top Ti‐rich STO after intermixing during crystallization anneal.     

Using magnetic levitation for 2D and 3D self‐assembly of cubic silicon macroparticles

Today's micro‐ and nano‐fabrication is essentially two‐dimensional, with very limited possibilities of accessing the third dimension. The most viable way to mass‐fabricate functional structures at the nano‐scale, such as electronics or MEMS, with equal feature sizes in all directions, is by three‐dimensional self‐assembly. Up to now, three‐dimensional self‐assembly has mainly been restricted to crystals of polymer spheres. We report on two‐ and three‐dimensional self‐assembly of silicon cubes, levitated in a paramagnetic fluid. We demonstrate the benefits of templating and study the effect of a change in hydrophilicity of the cubes. These experiments bring us one step closer to three‐dimensional self‐assembly of anisotropic, semiconducting units, which is a crucial milestone in overcoming the scaling limits imposed by contemporary 2D microfabrication.

     

CuNi binary alloy catalyst for growth of nitrogen‐doped graphene by low pressure chemical vapor deposition

The CuNi binary alloy can be significant as a catalyst for nitrogen‐doped (N‐doped) graphene growth considering controllable solubility of both carbon and nitrogen atoms. Here, we report for the first time the possibility of synthesizing substitutional N‐doped bilayer graphene on the binary alloy catalyst. Raman spectroscopy, atomic force microscopy and transmission electron microscopy analysis confirm the growth of bilayer and few‐layer graphene domains. X‐ray photoelectron spectroscopy analysis shows the presence of around 5.8 at% of nitrogen. Our finding shows that large N‐doped bilayer graphene domains can be synthesized on the CuNi binary alloy.

     

Observation of negative refraction in the graphene/ferrite composite

An observation of negative refraction in the naturally obtained composition of graphene and barium ferrite is reported. The capacitance and inductance measurements revealed the electric and magnetic resonances accompanied with the negative values of permittivity and permeability in the overlapped frequency range. According to the “left‐handed” media approach such a material is characterized by negative refraction. The derived values of the real part of refractive index are negative at the frequencies above 500 MHz.

     

Al‐density variation as one driving force for void formation in PERC solar cells

The reduction of void formation in local Al contact structures is of high interest in studies dealing with passivated emitter and rear contact (PERC) solar cells. So far, several processing parameters and their impact on local contact formation were investigated in detail. However, up to now density variation of Al in dependence on temperature and Si content in the melt were not taken into account as a principal reason for void formation. In this context the current assumption of a constant volume of the Al paste particles is discussed in more detail. Based on the results of energy dispersive X‐ray spectroscopy, void formation implies either an expansion of paste particles or their burst during contact formation.

     

Graphene screen‐printed radio‐frequency identification devices on flexible substrates

Despite the great promise of printed flexible electronics from 2D crystals, and especially graphene, few scalable applications have been reported so far that can be termed roll‐to‐roll compatible. Here we combine screen printed graphene with photonic annealing to realize radio‐frequency identification devices with a reading range of up to 4 meters. Most notably our approach leads to fatigue resistant devices showing less than 1% deterioration of electrical properties after 1000 bending cycles. The bending fatigue resistance demonstrated on a variety of technologically relevant plastic and paper substrates renders the material highly suitable for various printable wearable devices, where repeatable dynamic bending stress is expected during usage. All applied printing and post‐processing methods are compatible with roll‐to‐roll manufacturing and temperature sensitive flexible substrates providing a platform for the scalable manufacturing of mechanically stable and environmentally friendly graphene printed electronics.

     

Exchange bias at low fields exhibited by the interface between epitaxial layers of ferromagnetic and charge‐ordered rare‐earth manganites

Epitaxial thin films of ferromagnetic La_0.7Sr_0.3MnO₃ (LSMO) and charge‐ordered, antiferromagnetic Y_0.5Ca_0.5MnO₃ (YCMO) were deposited on SrTiO₃ (100) substrates by pulsed laser deposition (PLD). The heterostructure undergoes tetragonal distortion due to strong biaxial tensile strain imposed by the substrate. The LSMO–YCMO bilayers exhibit significant exchange bias (EB) across the interface even in a very small remnant magnetic field (～5 Oe) present in the superconductor magnet. The unidirectional exchange anisotropy at the interface can be switched by reversing the polarity of the remnant magnetic field.