In this Letter, a novel modified anodization was utilized to synthesize high‐aspect‐ratio, top‐open and ultraflat‐surface TiO2 nanotubes. The interruption of voltage during anodization leads to the formation of a double‐layered structure. Due to the weak mechanical connection between the upper and the underlying layer, the two parts can be easily detached. Compared with the conventional ultrasonication method to remove the clusters of nanotubes where rough surfaces resulted, this efficient and reliable strategy may facilitate further applications of TiO2 nanotubes in diverse conditions.
A thermoplastic polymer solution was inkjet printed in a pre‐defined hexagonal pattern onto carbon fibre reinforced epoxy resin (CFRP), leading to a significant increase in strength, stiffness and toughness of the final aerospace grade compo‐site system. The approach consisted of depositing low‐viscosity polymer microdroplets having chemically and me‐chanically comparable properties to epoxy polymer, onto CFRP before curing and solidification. The microdroplets remained arrested between composite plies without direct contact with the neighbouring microdroplets ensuring preservation of the structural integrity of the new composite system after curing. The key to achieving this synergistic effect was in appropriately selected additive materials; however, the novel aspects also included the method itself, which enabled an accurate crack arrest mechanism.
ZnO thin films with a rippled surface structure were used as electron‐collecting layers of inverted organic photovoltaics (OPVs). Using additional ultrathin layers of ZnO and TiO2 fabricated using atomic layer deposition (ALD), not only the power‐conversion efficiency of the OPVs could be increased (up to 3.5%), but also the photovoltaic performance became nearly constant within 100 days without any additional encapsulations of the solar cells under ambient conditions.
An effective way to reduce the reflection of a multicrystalline solar cell is the use of a honeycomb structure, which can be generated by etching a mask isotropically. In this Letter, a directly printed hexagonal inkjet mask is presented. It results in a honeycomb texture with well developed and defined etch pits at an average distance of 50.1 μm and a weighted reflection of 18.4%. The major advantage of this mask is that the masking process is simple and that it has the potential of being fast and having low costs.
We present metal wrap through (MWT) silicon solar cells with passivated surfaces based on a simplified device structure. This so‐called HIP‐MWT structure (high‐performance metal wrap through) does not exhibit an emitter on the rear side and therefore simplifies processing. The confirmed peak efficiency of the fabricated solar cells with an edge length of 125 mm, screen printed contacts and solder pads is 20.2%. To our knowledge, this is the highest value reported for large‐area p‐type silicon solar cells to date.
This Letter presents studies on low‐field electrical conduction in the range of 4–300 K for an ultrafast material, i.e., InGaAs:ErAs grown by molecular beam epitaxy. The unique properties include nano‐scale ErAs crystallites in the host semiconductor InGaAs, a deep Fermi level and picosecond ultrafast photocarrier recombination. As the temperature drops, the conduction mechanisms are in the sequence of: thermal activation, nearest‐neighbor hopping, and variable‐range hopping. In the low‐temperature limit, finite‐con‐ductivity metallic behavior, not insulating, was observed. This unusual conduction behavior, related to the nanometer‐scale ErAs crystallite islands, is explained with the Abrahams scaling theory.
Metallic single‐walled carbon nanotubes (m‐SWCNTs) with excellent conductivity and transparency are considered to be eminent electrode materials. However, it still remains a challenge to separate m‐SWCNTs by their diameters. As reported in this Letter, by effective purification treatment of SWCNTs, we succeeded in achieving diameter separation of m‐SWCNTs using gel column chromatography. TEM and Raman characterizations revealed that metal catalysts and amorphous carbon on tube surfaces were largely reduced, which contributed to the diameter separation of m‐SWCNTs.
We present the synthesis of highly crystalline metallic rhenium trioxide (ReO3) nanowires via a simple physical vapor transport at 300 °C for the first time. Based on HRTEM, the ReO3 nanowires exhibit a core of perfect cubic perovskite‐type single crystal structure with a shell of thin amorphous and disordered structures of less than 2 nm in the near surface layers. Possibly this is due to proton intercalation induced by the surface reaction of single crystal ReO3 with water.
A passive micro‐displacement sensor (for ～μm displacement) was fabricated based on a magnetoelectric laminate, in which the displacement change can result in a change of the magnetic flux around the magnetoelectric sensor. The displacement measurement was realized by measuring the magnetoelectric output voltage. The displacement detecting coefficient was ～2.5 mV/μm at a frequency of ～1 kHz. This passive displacement sensor possesses the advantages of low cost, high resolution, low energy consumption and good linearity and has potential for application in future displacement detectors.
We demonstrate the self‐catalyst growth of vertically aligned InAs nanowires on bare Si(111) by droplet epitaxy. The growth conditions of indium droplets suitable for nucleation and growth of nanowires have been identified. We have then realized vertically aligned and non‐tapered InAs nanowires on bare Si(111) substrates through optimal indium droplets. It was found that the lateral dimensions and density of nano‐wires are defined by the indium droplets. This technique unravels a controllable, cost‐effective and time‐efficient route to fabricating functional monolithic hybrid structures of InAs nanowires on silicon.
We report a stacked Y2O3/TiOx resistive random access memory (RRAM) device, showing good high‐temperature switching characteristics of extremely low reset current of 1 μA at 150 °C, large off/on resistance window (>200) at 150 °C, large rectification ratio of ～300 at 150 °C and good current distribution at 85 °C. The good rectifying property, lower high‐temperature sneak current and tighter high‐temperature current distribution can be attributed to the combined results of the oxygen vacancies in TiOx and the related carrier depletion effect.
Persistent layer‐by‐layer growth is demonstrated for pulsed‐laser homoepitaxy of ZnO thin films on $(000\bar 1)$ ZnO single crystals. Employing interval pulsed‐laser deposition (PLD), RHEED oscillations are stabilized over a film thickness of about 90 nm. For interval pulsed laser deposited films a considerably decreased root‐mean‐square surface roughness of 0.26 nm was found, in comparison to 0.74 nm for conventional PLD. A small asymmetry in the X‐ray diffraction (XRD) 2θ –ω scan reveals compressive strain in the thin film being slightly larger for interval PLD as compared to conventional PLD. The FWHM of the photoluminescence (PL) I6 line is higher with about 500 µeV as compared to 350 µeV for the conventional PLD. Consequently, both XRD as well as PL indicate a slightly higher amount of charged defects for the interval PLD.
Steady‐state and time‐resolved photoluminescence of silicon nanoparticles dispersed in low‐polar liquids at above room temperature is studied. The roles of low‐polar liquids as well as mechanisms responsible for their temperature‐dependent photoluminescence are discussed. The thermal sensitivity of the photoluminescence is estimated and application of the nanoparticles as nanothermometers is proposed.
A high‐efficiency bulk heterojunction organic photovoltaic cell (OPV) was achieved by the electrospray deposition method. The surface roughness of the P3HT:PCBM thin film can be reduced using the mixed solvent consisting of o‐dichlorobenzene (o‐DCB) and acetone. The effect of acetone concentration is related to its dielectric constant. Under an optimized concentration of acetone in o‐DCB (20 vol%), the P3HT/PCBM active layer with a smooth surface can be formed, and the power conversion efficiency of the OPV was 1.9%.
A facile metal catalyst free route to synthesize boron doped (0.6%–1.0%) carbon nanotubes via ceramic nanowires in which the formation of the nanowires (probably serving as templates), the carbon nanotubes and their doping all occur unanimously in the reaction, is presented.
We report enhanced anomalous photovoltaic effects and switchable photovoltage generation in pure and Pr–Cr co‐doped BiFeO3 (BFO) nanotubes (NTs). Influence of metal doping on short circuit current, open circuit voltage, power conversion efficiency and fill factor are investigated. The power conversion efficiency of pure BFO NTs (～0.207%) is found to be enhanced by several orders of magnitude in comparison with the reported bulk effect. Pr‐doped NTs provide highest values of power conversion efficiency (～0.5%).
We report on solution‐processible polymer solar cells (PSCs) fabricated on a papery substrate using carton. Highly conductive PEDOT:PSS was used as a bottom anode and planarization layer, and a semi‐transparent top cathode was applied. This research could be an important approach to the development of all‐solution‐processible papery PSCs as well as paper electronics.
Dip‐coating of a colloidal suspension is investigated in situ with microbeam grazing incidence small‐angle X‐ray scattering. We focus on the real‐time monitoring of a vertical dip‐coating process yielding insights into structural changes during pattern formation of the thin film. With the selected configuration a fixed spot on the sample surface is probed and the structural information at the time the contact line passes this spot is obtained, hence revealing the structure at the vicinity of the flowing meniscus owing to the microfocused beam. After dip‐coating the morphology is analyzed with atomic force microscopy, yielding real space information about the arrangement of individual nanoparticles at the film surface.
