Advanced Materials Interfaces

Published by Wiley
Online ISSN: 2196-7350
Publications
Article
Recent experiments have shown the potential of surface acoustic waves as a mean for transporting charge and spin in quantum wells. In particular, they have proven highly effective for the coherent transport of spin-polarized wave packets, suggesting their potential in spintronics applications. Motivated by these experimental observations, we have theoretically studied the spin and charge dynamics in a quantum well under surface acoustic waves. We show that the dynamics acquires a simple and transparent form in a reference frame co-moving with the surface acoustic wave. Our results, e.g., the calculated spin relaxation and precession lengths, are in excellent agreement with recent experimental observations.
 
Article
The epitaxial growth of crystalline oxides on semiconductors provides a pathway to introduce new functionalities to semiconductor devices. Key to electrically coupling crystalline oxides with semiconductors to realize functional behavior is controlling the manner in which their bands align at interfaces. Here we apply principles of band gap engineering traditionally used at heterojunctions between conventional semiconductors to control the band offset between a single crystalline oxide and a semiconductor. Reactive molecular beam epitaxy is used to realize atomically abrupt and structurally coherent interfaces between SrZr$_{x}$Ti$_{1-x}$O$_3$ and Ge, in which the band-gap of the former is enhanced with Zr content $x$. We present structural and electrical characterization of SrZr$_{x}$Ti$_{1-x}$O$_3$-Ge heterojunctions for $x$ = 0.2 to 0.75 and demonstrate the band offset can be tuned from type-II to type-I, with the latter being verified using photoemission measurements. The type-I band offset provides a platform to integrate the dielectric, ferroelectric and ferromagnetic functionalities of oxides with semiconducting devices.
 
Article
Carbon nanotube (CNT) fiber is formed by assembling millions of individual tubes. The assembly feature provides the fiber with rich interface structures and thus various ways of energy dissipation, as reflected by the non-zero loss tangent (>0.028--0.045) at low vibration frequencies. A fiber containing entangled CNTs possesses higher loss tangents than a fiber spun from aligned CNTs. Liquid densification and polymer infiltration, the two common ways to increase the interfacial friction and thus the fiber's tensile strength and modulus, are found to efficiently reduce the damping coefficient. This is because the sliding tendency between CNT bundles can also be well suppressed by the high packing density and the formation of covalent polymer cross-links within the fiber. The CNT/bismaleimide composite fiber exhibited the smallest loss tangent, nearly as the same as that of carbon fibers. At a higher level of the assembly structure, namely a multi-ply CNT yarn, the inter-fiber friction and sliding tendency obviously influence the yarn's damping performance, and the loss tangent can be tuned within a wide range, as similar to carbon fibers, nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow new applications ranging from high quality factor materials to dissipative systems.
 
Schematics of the mechanism of the giant switchable Rashba effect: (1) An external electric field is amplified and stored as a ferroelectric distortion, in particular Ti-O displacements. (2) These displacements entail via the oxygen octahedron network of the perovskite heterostructure, Os-O or (Ir,Ru)-O displacements. (3) As a consequence of the Os-O displacements the Os orbitals deform, which reflects the broken inversion symmetry. This orbital deformation and the strong SOC of Os finally lead to a giant Rashba spin splittings that is switchable by an electric-field.
Article
One of the most fundamental phenomena and a reminder of the electron's relativistic nature is the Rashba spin splitting for broken inversion symmetry. Usually this splitting is a tiny relativistic correction, hardly discernible in experiment. Interfacing a ferroelectric, BaTiO$_3$, and a heavy 5$d$ metal with a large spin-orbit coupling, Ba(Os,Ir)O$_3$, we show that giant Rashba spin splittings are indeed possible and even fully controllable by an external electric field. Based on density functional theory and a microscopic tight binding understanding, we conclude that the electric field is amplified and stored as a ferroelectric Ti-O distortion which, through the network of oxygen octahedra, also induces a large Os-O distortion. The BaTiO$_3$/BaOsO$_3$ heterostructure is hence the ideal test station for studying the fundamentals of the Rashba effect. It allows intriguing application such as the Datta-Das transistor to operate at room temperature.
 
Article
The grain boundary resistivity problem of highly conductive bulk Li0.34La0.55TiO3 perovskite has been investigated by means of impedance spectroscopy and solid-state NMR of samples processed in controlled atmospheres. The samples were sintered in air, synthetic air, and oxygen, in which the level of moisture varied. A dry atmosphere is critical to obtain dense ceramics with a low grain boundary resistivity. The grain boundary conductivity is five times higher for samples sintered in oxygen atmosphere due to the suppression of Li2CO3 secondary phase formation, which is responsible for low lithium ion diffusion at the grain boundary.
 
Article
The In2O3(111) surface can be transformed from an oxidized bulk termination to one that is covered by single In adatoms. As each adatom sits at one specific site within the surface unit cell they form a well-ordered (1 × 1) superstructure. Annealing at 500°C in O2 or in ultrahigh vacuum results in a fully reversible conversion between these two surface terminations; this transformation and intermediate stages were followed with Scanning Tunneling Microscopy (STM). Formation of this novel surface structure under reducing conditions is corroborated by Density Functional Theory (DFT). The reduced adatom-covered and the oxidized In2O3(111) surfaces are expected to exhibit different chemical and electronic properties, which can easily be exploited by the facile and reversible switching between the two terminations.
 
Article
In the early stage of corrosion of Al or Al alloys (i.e., during the initiation of localized corrosion), an oxide film is generally present on the surface. This work investigates the possibility for a cathodic reaction to occur on these oxide films. We discuss realistic models of supported oxide films on Al(111) in order to disentangle the factors determining the reactivity towards O2. Three components of the complex film formed on Al(111) can be identified: an ultrathin under-stoichiometric AlxOy interface layer, an intermediate Al2O3 phase with γ-alumina structure, and an hydroxylated AlOOH surface termination with boehmite structure. The electron transfer to O2 molecules depends on the workfunction, Φe, of the metal/oxide interface and on the thickness of the inner Al2O3 phase. The electron transfer takes place both from the metal-oxide interface and the oxide surface to the adsorbed O2 molecule. Very important is the role of the hydroxyl groups at the surface: they eliminate the Al surface states and stabilize the surface; they allow the reduced O2− species to capture protons and transform into hydrogen peroxide in a non-activated process. H2O2 is further reduced to two water molecules, in a series of two-electron mechanisms. These reactions take place only when the internal alumina phase is ultrathin (here 0.2 nm). As soon as an Al2O3 inner layer develops (film thickness of about 1 nm), the film becomes unreactive and passivates the Al(111) surface. The results help to shed light on the complex reactions responsible for metal corrosion.
 
Article
Functionalized gold nanoparticle films are wellknown to act as chemically-sensitive resistors (i.e., passive electrical components). B. Raguse, E. Chow, and co-workers report in article 1400062 that such nanoparticle films are also capable of being used as chemically-sensitive, active (transistor-like) components by applying an external gate potential in the presence of hydrophobic ions. An immediate application is the development of highly sensitive sensors where the sensitivity towards charged molecules is improved by several orders of magnitude.
 
Article
In article 1300125, M. Sun and co-workers demonstrate that both linear Plasmon enhancement and plasmonic gradient enhancement have significant contributions to SEM-based high vacuum Tip-enhanced Raman spectroscopy (SEM-HV-TERS). They strongly enhance Raman and IR-active modes, respectively, in the SEM-HV-TER spectra. In principle, all of the “3N-6” vibrational modes can be simultaneously observed in situ by means of this ultrasensitive spectral analysis at the nanoscale, which opens a new pathway for surface spectral analysis.
 
Article
A rare ferroic transition in A-site ordered LaScO3/BiScO3 superlattices is displayed on the back cover. In article 201400042, J. M. Rondinelli and G. Gou report that switching the layer polarization, arising from each A-cation sublattice with strain, produces an isosymmetric transition from a ferrielectric (FiE) to ferroelectric (FE) state. FiE-to-FE transitions are a new route to design piezoelectric responses in complex oxide heterostructures.
 
Article
Photoinduced charge distributions for single Au nanoparticles deposited on single crystalline TiO2 are visualized in situ by Kelvin probe force microscopy. Under UV light, the electrons in excited TiO2 transfer to the Au nanoparticles. In contrast, when the Au nanoparticles are selectively excited by visible-infrared light, electrons are injected from the nanoparticles to TiO2, resulting in plasmon-induced charge separation.
 
Article
A new method for integrating metal-organic frameworks (MOFs) on polymer fibers is developed based on an oxide nucleation layer via atomic layer deposition (ALD). As G. N. Parsons and co-workers report in article 1400040, ALD coating enables uniform MOF coverage on fibers, high MOF loading, and large BET surface area. NH3 breakthrough tests demonstrate high adsorption capacity of the MOF-fiber mats for toxic gas. The synthesis approach is also generally applicable to a wide range of polymer fibers and MOFs. This work represents a breakthrough in the deployment of MOFs for technical applications.
 
Experimental scheme (not in scale). (A) OM molecules are spread over aqueous subphase containing Au(SCN)4−. (B) After incubation, the monolayer is isothermally compressed resulting in the formation of aligned OM/gold micro-wires. (C) The micro-wires are transferred onto a solid substrate; plasma treatment and gold enhancement produce highly conductive, transparent gold micro-wire films.
Micro-wire formation at the air/water interface. Surface-pressure/area isotherm of OM monolayer compressed upon a water subphase containing soluble Au(SCN)4−; BAM images above the isotherm were recorded at the surface pressures indicated by the arrows.
Spectroscopic confirmation that the micro-wires comprise of metallic Au. (A) x-ray photoelectron spectroscopy (XPS) spectrum of micro-wires transferred from the air/water interface onto solid substrate. (B) x-ray diffraction (XRD) pattern of the micro-wires after gold enhancement.
Optical transparency and electrical conductance of gold micro-wire films. (A) Transmittance spectrum. The inset shows a picture of the Au film deposited on glass and placed upon a text feature; (B) Current/voltage (I/V) curves recorded for thermally evaporated square electrodes at distances of 100 μm and 1 mm, respectively; (C) Current/voltage curves recorded for pasted silver electrodes parallel (top picture on the right), and vertical (bottom picture on the right) to the aligned Au micro-wires, respectively. Electrode distance was 2 cm.
Article
“Bottom-up” technologies are based upon the premise that organized systems – from the nano-scale up to the macro-scale – can be assembled spontaneously from basic building blocks in solution. We demonstrate a simple strategy for the generation of extremely long (up to several centi­meters), horizontally-aligned gold micro-wires, produced through a surfactant monolayer template deposited from gold thiocyanate [Au(SCN)4−] aqueous solution. Specifically, we show that the surfactant, octyl-maleimide (OM), spontaneously forms oriented micro-wires at the air/water interface, which constitute a template for deposition of metallic gold through binding and crystallization of the soluble gold complex. The Au micro-wires can be subsequently transferred onto solid substrates, and following plasma treatment and gold enhancement exhibit excellent conductivity even at electrode spacings of several centimeters. Importantly, the micro-wire alignment determines the direction of electrical current, demonstrating that long-range ordering of the micro-wires can be accomplished, significantly affecting the physical properties of the system. The new approach is simple, robust, and can be readily exploited for bottom-up fabrication of micro-wire assemblies and transparent conductive electrodes.
 
Article
Chemical vapor deposition (CVD) of polymer films represent the marriage of two of the most important technological innovations of the modern age. CVD as a mature technology for growing inorganic thin films is already a workhorse technology of the microfabrication industry and easily scalable from bench to plant. The low cost, mechanical flexibility, and varied functionality offered by polymer thin films make them attractive for both macro and micro scale applications. This review article focuses on two energy and resource efficient CVD polymerization methods, initiated Chemical Vapor Deposition (iCVD) and oxidative Chemical Vapor Deposition (oCVD). These solvent-free, substrate independent techniques engineer multi-scale, multi-functional and conformal polymer thin film surfaces and interfaces for applications that can address the main sustainability challenges faced by the world today.
 
Article
In this contribution, a novel method for practical uses in the fabrication of the top contact electrode in a metal/organic monolayer/metal device is presented. The procedure involves the thermally induced decomposition of an organometallic compound, abbreviated as the TIDOC method. Monolayers incorporating the metal organic compounds (MOCs) [[4-{(4-carboxy)ethynyl}phenyl]ethynyl]-(triphenylphosphine)-gold, 1, or [1-isocyano-4-methoxybenzene]-[4-amino-phenylethynyl]-gold, 2, were annealed at moderate temperatures (1: 150 °C for 2h and 2: 100 °C for 2 h), resulting in cleavage of the Au-P or Au-C bond and reduction of Au(I) to Au(0) as metallic gold nanoparticles (GNPs). These particles are distributed on the surface of the film resulting in formation of metal/molecule/GNP sandwich structures. Electrical properties of these nascent devices were determined by recording I–V curves with a conductive-AFM. The I–V curves collected from these metal/organic monolayer/GNPs sandwich structures are typical of metal-molecule-metal junctions, with no low resistance traces characteristic of metallic short circuits observed over a wide range of set-point forces. The TIDOC method is therefore an effective procedure for the fabrication of molecular junctions for the emerging area of molecular electronics.
 
Article
Cell motions are driven by coordinated actions of the intracellular cytoskeleton – actin, microtubules (MTs) and substrate/focal adhesions (FAs). This coordination is altered in metastatic cancer cells resulting in deregulated and increased cellular motility. Microfabrication tools, including photolithography, micromolding, microcontact printing, wet stamping and microfluidic devices have emerged as a powerful set of experimental tools with which to probe and define the differences in cytoskeleton organization/dynamics and cell motility patterns in non-metastatic and metastatic cancer cells. In this review, we discuss four categories of microfabricated systems: (i) micropatterned substrates for studying of cell motility sub-processes (for example, MT targeting of FAs or cell polarization); (ii) systems for studying cell mechanical properties, (iii) systems for probing overall cell motility patterns within challenging geometric confines relevant to metastasis (for example, linear and ratchet geometries), and (iv) microfluidic devices that incorporate co-cultures of multiple cell types and chemical gradients to mimic in vivo intravasation/extravasation steps of metastasis. Together, these systems allow for creating controlled microenvironments that not only mimic complex soft tissues, but are also compatible with live cell high-resolution imaging and quantitative analysis of single cell behavior.
 
Article
In article 1400093 H.-Y. Chen and co-workers demonstrate that vapor-based thiol-reactive coatings which are composed of maleimide and vinyl anchoring groups can effectively tailor surface properties through specific conjugation reactions. Thermal stability tests and mechanical adhesion tests have shown robustness for these coatings on various substrates. Suppressed protein fouling property and controlled endothelial cell attachment is demonstrated by using the advanced coating technique.
 
Article
The use of conductive frameworks as the host scaffold to obtain nanostructured sulfur cathodes is an efficient way to increase the sulfur utilization for redox reaction in Li-S batteries with large discharge capacity and high energy density. However, due to dynamical interfaces driven by phase evolution between the conductive hosts and S-containing guests during cycling, the cathode still faces poor stability. Herein, the use of O-/N-containing nanocarbon as the conductive host sheds a light on the role of the dynamic interface between the carbon host and S-containing guest for a stable Li-S cell. The outstanding reversibility and stability of N-doped C/S cathodes are attributed to the favorable guest-host interaction at the electron-modified interface, manifesting as (i) a chemical gradient to adsorb polar polysulfides and (ii) ameliorative deposition and recharging of Li2S on the region of electron-rich pyridinic N and a graphene domain surrounding quaternary N. Highly reversible, efficient and stable Li storage properties such as mitigated polarization and charge barrier, high capacity of 1370 and 964 mAh g−1 at 0.1 and 1.0 C, respectively, and 70% of capacity retention after 200 cycles are achieved. Mechanistic insight into the capacity fading inspires the rational design on electrodes for high-performance electrochemical systems.
 
Article
Generally, it is very difficult to detect the precise location of specific amino acids in a 3D self-assembled structure. F. Besenbacher, M. Dong, and co-workers reveal in article 1400133 the possibility to find the position of cysteines exposed on cysteine-rich peptide fibers' surfaces. Gold nanoparticles (Au NPs) are employed as a probe to sense the presence of cysteines. In fact, the positions of the Au NPs along the fibers are correlated to the position of the exposed cysteines on the fiber surface.
 
Article
The inside cover image is a 2D pattern of water surface-tension-confined channels formed on an array of hydrophilic spots (“digits”) surrounded by hydrophobic barriers. This method, called digital liquid patterning (DLP), allows for the formation of liquid patterns of arbitrary and easily variable geometries without the need for the fabrication of new photomasks for every pattern with a different geometry. Further details can be found in article 1300075 by P. A. Levkin and co-workers.
 
Schematics of the catalyst structure and the experimental procedure. (a) The structure of the tri-layered catalyst system. (b) The catalyst system is annealed at high temperatures, which promotes diffusion of the catalyst material to the surface. (c) The nucleated catalyst nanoparticles are then able to induce the SWCNT growth.
SEM images of the as-grown SWCNTs with the varied thickness in the Al2O3 top layer (labeled on each panel). The scale bars correspond to 2 μm in all images. The SWCNT networks are designated as rare, medium or dense according to their density.
The density of SWCNT networks plotted as a function of the thickness of Al2O3 top layer.
Raman spectra showing the RBM band. (b) D and G features corresponding to the as-grown SWCNT networks produced with different catalyst structures. The spectra are normalized to the respective G-peak and the Si background contribution is subtracted.
Plots of (a) the average SWCNT diameter with error bars depicting standard deviations and (b) the metallic SWCNT fraction as a function of the thickness of Al2O3 top layer.
Article
Single-walled carbon nanotubes are promising for many applications due to their unique mechanical, electrical and optical properties. However, their application has been hampered so far by the lack of controllability in the direct growth process, in particular the size and chirality distributions which inevitably lead to a large variability of their electronic structures. Here we demonstrate the effect of catalyst interfacial diffusion using a tri-layered Al2O3/Fe(Mo)/Al2O3 catalyst and achieve the effective control of density, diameter, and conductivity of the as-grown nanotube networks. This method modulates the thickness of the top Al2O3 layer which affects the diffusion of Fe atoms and subsequently the formation of catalyst nanoparticles. We show that the tri-layered catalyst allows one to vary the density of networks from 0.18 to 35 tubes/μm2, the diameter from 1.36 to 1.72 nm, and the metallic fraction from 20% to 45%. It may thus represent a promising strategy for tailoring the properties of as-grown carbon nanotube networks for their proposed applications.
 
Article
By means of the investigation of dynamic adhesion behaviors of the water-oil interfaces, Y. L. Song and co-workers reveal in article 1400080 the underlying mechanism of adhesion phenomena in the lithographic printing process. The oil-water interfacial separation during the printing process is highly velocity-dependent. By controlling the printing velocity in a proper range, ink catch-up and wash-off phenomena can be prevented avoiding the vast waste of paper caused by unqualified printing.
 
Article
SrTiO3 to modern oxide electronics is like silicon to the entire semiconductor industry. Z. Q. Liu, Ariando, and co-workers show in article 1400155 that the bandgap of SrTiO3 can be 20% larger in thin films than in the bulk. Such bandgap enhancement can change several properties. For example, it can vary the electronic and magnetic phases of SrTiO3-based interface systems.
 
Article
The spatial arrangement of cells in their microenvironment is known to significantly influence cellular behavior, thus making the control of cellular organization an important parameter of in vitro co-culture models. However, recent advances in micropatterning co-culture methods within biochips do not address the simultaneous cultivation of anchorage-dependent and non-adherent cells. To address this methodological gap we combine S-layer technology with microfluidics to pattern co-cultures to study the cell-to-cell and cell-to-surface interactions under physiologically relevant conditions. We exploit the unique self-assembly properties of SbpA and SbsB S-layers to create an anisotropic protein nanobiointerface on-chip with spatially-defined cytophilic (adhesive) and cytophobic (repulsive) properties. While microfluidics control physical parameters such as shear force and flow velocities, our anisotropic protein nanobiointerface regulates the biological aspects of the co-culture method including biocompatibility, biostability, and affinity to non-adherent cells. The reliability and reproducibility of our microfluidic co-culture strategy based on laminar flow patterned protein nanolayers is envisioned to advance in vitro models for biomedical research.
 
Article
Toward high-performance and stable inverted polymer solar cells, Y. Zhou, B. Song, and co-workers demonstrate in article 1400397 a facile method to prepare covalently bonded and uniform surface modifications on ITO substrates. Applying surface grafting of aziridine as the interlayer effectively lowers the surface work function of ITO which in turn dramatically improves the device performance and stability.
 
Article
Scanning Electrochemical Microscopy (SECM) is introduced as a promising technique to probe localized interfacial kinetics at the interface of electrolyte/supercapacitor electrode based on polyaniline (PANI) by measuring approach curves from which heterogeneous charge transfer rate constants (k eff) are extracted. The values correlate with the effectiveness of the electrode material for supercapacitor application. Specifically, measurements on PANI films of different thicknesses show that potential-dependent rate constants are observed only for PANI films of up to 5 μm thickness. In addition to the thickness of PANI, k eff is also found to be affected by the applied potential and surface morphology of PANI electrodes. These findings correlate with the macroscopic electrochemical performance of PANI electrodes which shows enhanced specific charge storage ability when their thickness is below 5 μm. Under these conditions, they deliver a specific capacitance of 486 F g−1 and a rate capability of 89%. The observed correlation between microscopic kinetic data determined by SECM and macroscopic device characteristics provides rational guidelines for the optimization of the physical and structural properties of high performance supercapacitor electrodes.
 
Article
A technique developed to self assemble solid colloidal particles under a sinusoidal electric field (AC field) is adapted to soft W/O/W double-emulsion globules, and is exploited for surface patterning. Double-emulsions containing cupric ions are prepared, placed between two planar ITO electrodes and submitted to a transversal AC field which induced their ordering into hexagonal 2D-arrays. The characteristic spacing is monitored by varying the globule volume fraction. Such self-assembly is used to fabricate copper-depleted arrays, using globules as both a metal precursor reservoir/provider and as a mask. The ordered globule monolayer is then submitted to a DC field to induce metal precursor leakage and its reduction onto the electrode. The organized, oily and dielectric globules generate arrays of holes (c.a. 7 μm) into a thin copper deposit (thickness of 12 nm). Holes are shown to be formed below the globules, and their separation (from 10 to 30 μm) can be tuned as deduced from direct observations using optical and atomic force microscopy.
 
An SEM image of a self-assembled AgMy monolayer on a 1-dodecanethiol-modifi ed gold substrate. The AgMy are composed of 5 nm silver cores and myristate capping ligands that are 2 nm thick. The average grain size of the gold substrate is ∼ 100 nm. 
A. Experimental set-up of AFM-based local oxidation lithography (LON) (a) and a schematic surface potential diagram of a AgMy monolayer on an alkanethiol SAM-modifi ed gold substrate (b). B. Line patterns fabricated by LON on a AgMy monolayer using a tip bias of-10.0 V, a scan speed of 10 nm/s and a relative humidity between 40 and 60%; (a) Height image, (b) KPFM surface potential image, and (c) profi les of the height and surface potential images.
A. A schematic illustration of a 1-dodecanethiol SAM on a gold surface (Au+SAM) (a) and the same substrate with a AgMy monolayer (Au+SAM+1 L) (b) and a AgMy multi-layer (Au+SAM+3 L) (c). B. AFM (a) and KPFM (b) images of the multi-layered AgMy sheets on a gold substrate modifi ed with a 1-dodecanethiol SAM. C. AFM (a) and KPFM (b) images of multi-layer AgMy sheets on a 1-dodecanethiol SAM-modifi ed silver substrate. 
(a) CPD changes resulting from the deposition of AgMy multi-layers on the 1-dode- 
Article
Nanometer scale patterning on 2D self-assembled silver nanoparticle sheets using local oxidation nanolithography (LON) is successfully conducted. The patterns written by means of this method exhibit not only topological changes but also changes in the contact potential difference. The silver nanoparticle sheet as an adjusted work function film, which is patternable by LON, has great potential for nano-optoelectronic device applications.
 
Article
By first-principles calculations we investigate the structural, electronic, and magnetic properties of the (LaMnO3)2/(SrTiO3)2 superlattice. We find that a monoclinic C2h symmetry is energetically favorable and that the spins order ferromagnetically. Under both compressive and tensile uniaxial strain the electronic structure of the superlattice shows a half-metallic character. In particular, a fully spin-polarized two-dimensional electron gas, which traces back to the Ti 3dxy orbitals, is achieved under compressive uniaxial strain.
 
Article
Mesoporous 3D architectures of silicon dioxide, nickel silicate, and cobalt silicate are for the first time prepared by using reed leafs as a sustainable silica source. Due to the 3D mesoporous architecture, nickel and cobalt silicate allow efficient charge transfer and mass transport, while at the same time buffering the volume changes during ion lithiation/delithiation processes. Especially, the nickel silicate electrode with the mesoporous 3D architecture shows a high specific capacitance, a good rate capability, and cycling stability for electrochemical capacitors.
 
Article
A novel 3D solid-state wire-shaped dye-sensitized solar cell (DSSC) with a hybrid photovoltaic (PV) structure is demonstrated. Carbon nanotube yarn provides excellent interfacial and electrocatalytic properties. The quantum dots (QDs) have been applied due to their high photon absorption coefficient. Finally, the cell shows an outstanding operational flexibility with an efficient photovoltaic efficiency (7.39%).
 
Article
Molten salts facilitate the reaction of CO2 with MgO by providing an alternate pathway to traditional gas-solid reactions. Molten salts partially dissolve bulk MgO and provide activated species accessible to CO2 at gas-solid-liquid triple phase boundaries. This methodology is also applicable to other basic metal oxides and molten salts, inspiring the design of new absorbent systems.
 
SPR sensorgrams for fi brinogen adsorption on uncoated silica and on a silica surface coated with DOPA-PCB-100 polymer (A), on C10 hydrophobic SAM reference and on a C10 hydrophobic SAM coated with DOPA-PCB-100 polymer (B). Fouling levels of fi brinogen (ng/cm 2 ) to an uncoated C10 SAM reference and to DOPA-PCB-100 coated on a C10 hydrophobic SAM calculated from Figure 1 B (C). A 1 nm shift in the resonant wavelength corresponds to a change in protein surface coverage of ∼ 17.0 ng/cm 2 .
Effect of water miscible solvents, methanol (M) and THF (T) on DOPA-PCB-300/dopamine mixed coatings on PP and PDMS.
SEM characterization of DOPA-PCB coatings on PP and PDMS. PP uncoated control (A), PP coating using TRIS buffer (B), PP coating using 20% methanol in TRIS (C), PDMS uncoated control (D), PDMS coating using TRIS buffer (E) and PDMS coating using 20% methanol in TRIS (F). 
Scheme 1. Synthesis of DOPA-PCB from DOPA-Br initiator via ATRP.
Article
It is highly desirable to develop a universal nonfouling coating via a simple one-step dip-coating method. Developing such a universal coating method for a hydrophilic polymer onto a variety of surfaces with hydrophobic and hydrophilic properties is very challenging. This work demonstrates a versatile and simple method to attach zwitterionic poly(carboxybetaine methacrylate) (PCB), one of the most hydrophilic polymers, onto both hydrophobic and hydrophilic surfaces to render them nonfouling. This is achieved by the coating of a catechol chain end carboxybetaine methacrylate polymer (DOPA-PCB) assisted by dopamine. The coating process was carried out in water. Water miscible solvents such as methanol and tetrahydrofuran (THF) are added to the coatings if surface wettability is an issue, as for certain hydrophobic surfaces. This versatile coating method was applied to several types of surfaces such as polypropylene (PP), polydimethyl siloxane (PDMS), Teflon, polystyrene (PS), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC) and also on metal oxides such as silicon dioxide.
 
Article
A new and highly versatile domain patterning method—ultraviolet direct write metal enhanced redox (UV direct write MER)—achieves deep domains with practically no thermally-induced damage on the surface of lithium niobate crystals. In UV direct write MER, after coating with a thin layer of chromium, the domain inversion is generated by a redox process induced in the crystal by illumination with high intensity UV in an ambient dry nitrogen atmosphere. This new technique enables the fabrication of practical piezoelectric acoustic superlattice structures on 128° YX-cut LiNbO3, the most widely used crystal cut for surface acoustic wave applications. For example, UV direct write MER was used to form an acoustic superlattice 128° YX structure that in turn enabled the generation of surface acoustic waves of sufficient strength to develop fluid flow within a droplet of water, demonstrating its potential in practical microfluidic manipulation. This is the first demonstration of a UV direct write surface acoustic wave transducer reported to date, made possible only due to the unique qualities of the MER domain engineering process.
 
Article
We identify a first-order, isosymmetric transition between a ferrielectric (FiE) and ferroelectric (FE) state in A-site ordered LaScO3/BiScO3 and LaInO3/BiInO3 superlattices. Such a previously unreported ferroic transition is driven by the easy switching of cation displacements without changing the overall polarization direction or crystallographic symmetry. Epitaxial strains less than 2% are predicted to be sufficient to traverse the phase boundary, across which we capture a ≈5× increase in electric polarization. Unlike conventional Pb-based perovskite ceramics with a morphotropic phase boundary (MPB) that show polarization rotation, we predict an electromechanical response up to 102 pC/N in the vicinity of the FiE-FE phase boundary due to polarization switching without any change in symmetry. We propose this transition as an alternative ferroic transition to obtain a piezoelectric response, with the additional advantage of occurring in benign chemistries without chemical disorder.
 
Article
Reversible switching of water-droplet adhesion between sliding and pinned states on a highly porous superhydrophobic polythiophene film is realized by adjusting electric potential. This large-area superhydrophobic polythiophene film is prepared readily by using a versatile electrodeposition method. Electrochromism along with reversible water-droplet adhesion switching of the film is also demonstrated.
 
Article
NEXAFS spectroscopy is used to precisely quantify the interfacial composition and P3HT chain orientation at the weak P3HT:PCBM/PEDOT:PSS interface. An increase of P3HT:PCBM and PEDOT:PSS interdiffusion with post electrode deposition annealing time and temperature is found to be the underlying mechanism for effectively improving the interlayer adhesion, which is essential for the commercial realization of organic photovoltaic devices.
 
Article
The group of silanes is one of the most abundant classes of molecules used for surface modification. In most studies, silanization is made from the vapor phase or solution. Here, an easy, robust, and fast way not only to modify, but also to map, control, and predict the wetting profiles on silicon surfaces after silanization and the final characteristics of a brush layer polymerized from this silane template profile are presented. The initiator molecule, 2-bromo-2-methyl-N-3-(triethoxysilyl) propyl propanamide (BTPAm), is spin-casted on a silicon substrate and a thermal gradient is applied using a combinatorial approach for studying the influence of temperature on the spin-casted silanes. Subsequently, polyacrylamide (PAAm) brushes are grown from the initiating end group of the BTPAm molecules through atom transfer radical polymerization (ATRP). Simulations of the heat distribution inside the silicon wafer allow both confirming the mapping of surface properties and designing desired profiles by predicting thermal distributions. An analytical expression for quantification is also provided. Thus, the wetting properties, surface roughness, and morphology of the brush layer after polymerization are mapped and correlated with the initial BTPAm gradient profile. The studies presented are envisioned to be of interest for designing surface profiles with different wetting properties, facilitating polymer brush growth, and to be used as predictive tools.
 
Article
Microgel particles display an interesting duality with properties attributed typically both to polymeric and colloidal systems. When adsorbed at a liquid-liquid interface, this duality becomes particularly apparent as the various phenomena at play are governed by different aspects of these soft and responsive particles. The introduction of a solid, fluorescently labeled, polystyrene core into the microgels allows direct and accurate visualization without the necessity of potential perturbing sample preparation techniques. By combining in-situ imaging and tensiometry, we determine that composite microgels at a wide variety of oil-water interfaces anchor strongly, with adsorption energies of approximately 106 kBT, typical for particle adsorption, yet accumulate at the interface spontaneously without any energy barrier, which is more typical for polymers. The high adsorption energies allow the particle to spontaneously form very dense crystalline packings at the liquid interface in which the microgels are significantly compressed with respect to their swollen state in bulk solutions. Finally, we demonstrate the unique nature of these particles by producing highly stable and monodisperse microgel-stabilized droplets using microfluidics.
 
Article
While metal-organic frameworks (MOFs) show great potential for gas adsorption and storage, their powder form limits deployment opportunities. Integration of MOFs on polymeric fibrous scaffolds will enable new applications in gas adsorption, membrane separation, catalysis, and toxic gas sensing. Here, we demonstrate a new synthesis route for growing MOFs on fibrous materials that achieves high MOF loadings, large surface areas and high adsorptive capacities. We find that a nanoscale coating of Al2O3 formed by atomic layer deposition (ALD) on the surface of nonwoven fiber mats facilitates nucleation of MOFs on the fibers throughout the mat. Functionality of MOFs is fully maintained after integration, and MOF crystals are well attached to the fibers. Breakthrough tests for HKUST-1 MOFs [Cu3(BTC)2] on ALD-coated polypropylene fibers reveal NH3 dynamic loadings up to 5.93 ± 0.20 mol/kg(MOF+fiber). Most importantly, this synthetic approach is generally applicable to a wide range of polymer fibers (e.g., PP, PET, cotton) and MOFs (e.g., HKUST-1, MOF-74, and UiO-66).
 
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Growth dynamics of a nano-sized organic conductor typically synthesized by the electrochemical method are investigated in a nanoliter growth cell with a systematically varied mechanical agitation. Irreversibility of the new and conventional polymorph observed here indicates a metastability of this new polymorph. A theoretical model of microscopic ionic motion and fluid dynamics is developed to explain this behavior and its connection to exploring new phases through agitated electrochemical growth in nanoscale.
 
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Thermal responsive biocompatible textile pads are prepared via in situ polymerisation of pyrrole on nonwoven viscose rayon (NWVR) fabric. Molecular motions at the interface of PPy and NWVR are responsible for the thermal actuation behaviour. The thermal actuation behaviour of the PPy-NWVR composite and its practical applications in electronic circuits and robotic engineering are successfully demonstrated for the first time.
 
Article
Thumbnail image of graphical abstract The degradation mechanism of Al2O3 passivation on nanostructured Si is resolved by separate considerations of interface state density and fixed charge density at the interface of Al2O3/Si. Using the analysis of surface potentials, it is reported for the first time that the positive interface charges seriously deteriorate the field-effect passivation of Al2O3 on a nanostructured surface.
 
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Aligned Carbon nanotubes (A-CNT) based electrodes have emerged as high-performance elements in electric energy storage and conversion devices. Morphological tailoring of conformal coatings of poly(ethylenedioxythiophene) (PEDOT) conductive polymer (CP) on the A-CNT scaffold is demonstrated by controlling CP thickness at the nm scale. Results show that the CP nano-films dominate the electrode capacitance in a supercapacitor application, contributing as much as 10x (pseudo)capacitance over the electric double layer of pristine A-CNT due to volumetric vs. surface charge storage. Comparison to theoretical ion mobilities shows that the conformal CP films have active sites at ∼30% doping, indicating the CP quality is similar to thin films on flat substrates and that all these sites are accessed at all CP thickness values (up to 10 nm PEDOT thickness) and do not limit the rate of ion transport in and out of the CP film volume. Supercapacitor electrodes fabricated from these novel morphology-controlled nanostructured composites provide a new route towards high-performance next generation energy storage devices.
 
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The dependence of the energy level alignment (ELA) on structural defects at an organic/organic heterojunction (OOH) of perfluoropentacene (PFP)-on-diindenoperylene (DIP) was investigated using X-ray scattering and ultraviolet photoelectron spectroscopy. The density of structural defects near the interface between the PFP and DIP layers was varied by changing the growth temperature of the DIP film. A direct relationship was found between the defect density and the ELA at the OOH; the ELA together with the change in the electrostatic potential (quasi-interface dipole layer) at the OOH varies systematically with the defect density near the interface. This indicates that a key factor affecting the ELA is the electrostatic potential change across the OOH interface, which is produced by electron transfer from DIP occupied gap states to PFP unoccupied gap states. These gap states originate from the defects and are effectively controlled by adjusting the growth conditions of the organic films. As a result, the ELA at OOH interfaces can be controlled by the density of structural defect, which is important for organic devices employing OOHs, such as organic photovoltaic cells.
 
Article
Work function modification by polyelectrolytes and tertiary aliphatic amines is found to be due to the formation of a net dipole at the electrode interface, induced by interaction with its own image dipole in the electrode. In polyelectrolytes differences in size and side groups between the moving ions lead to differences in approach distance towards the surface. These differences determine magnitude and direction of the resulting dipole. In tertiary aliphatic amines the lone pairs of electrons are anticipated to shift towards their image when close to the interface rather than the nitrogen nuclei, which are sterically hindered by the alkyl side chains. Data supporting this model is from scanning Kelvin probe microscopy, used to determine the work function modification by thin layers of such materials on different substrates. Both reductions and increases in work function by different materials are found to follow a general mechanism. Work function modification is found to only take place when the work function modification layer (WML) is deposited on conductors or semiconductors. On insulators no effect is observed. Additionally, the work function modification is independent of the WML thickness or the substrate work function in the range of 3 to 5 eV. Based on these results charge transfer, doping, and spontaneous dipole orientation are excluded as possible mechanisms. This understanding of the work function modification by polyelectrolytes and amines facilitates design of new air-stable and solution-processable WMLs for organic electronics.
 
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A plant-inspired, amine-containing small phenol molecule, 5-pyrogallol 2-aminoethane (PAE), can perform surface functionalization in a material-independent manner. The co-existence of primary amine and pyrogallol moieties are essential for the material-independent coating ability of PAE. The multi-functionality of the PAE-mediated surface chemistry will be useful in many areas including biomedical applications, drug delivery, and the development of energy storage devices.
 
Article
Nanostructured materials and their interfaces have attracted recent interest for their functionality in a wide variety of different applications. However, the origins of these properties in several instances remain unknown. One promising aspect of nanomaterials is their role in materials design for mitigating radiation damage. In particular, engineered radiation tolerant materials would exploit the presence of internal interfaces to act as recombination centers and suppress damage accumulation. Realizing this promise, however, requires a fundamental understanding of how radiation-induced defects interact with interfaces. Thus, studying the interfacial atomic structure and chemistry before and after irradiation is critical. In this study, we have performed transmission electron microscopy on a series of pristine and ion-irradiated oxide interfaces to probe radiation-induced effects. The CeO2/SrTiO3 interface, chosen as a model system for these studies, is characterized by differences in SrTiO3 terminations or steps. Our salient result is that steps are centers for preferential amorphization in SrTiO3, which we attribute to defect flow across the interface induced by non-stoichiometry in CeO2. The study concludes the interfacial atomic ordering in the form of steps thereby modifies the response to ion irradiation and suggests interface patterning as another parameter to functionalize radiation tolerant materials.
 
Raman spectra of (a) rutile (R) on quartz; (b) amorphous Am layer as deposited on rutile (Am/R); (c) amorphous Am layer on plain glass (black line) and corresponding spectrum of the glass substrate (grey line); (d) typical A/R film; (e) pure anatase film on glass.
X-ray diffraction patterns of (a) as-deposited A/Am/R multilayer film and (b) control A/Am film (black lines). The grey lines show XRD patterns of the corresponding films (A/R and A, respectively) after heat treatment at 500 °C for 10 h.
Absorption spectra of anatase (A), rutile (R) and multilayer films before (A/Am/R) and after (A/R) heat treatment at 500 °C for 10 h. Inset: Tauc plots showing approximate bandgap energy values of the A,R crystalline phases.
IR spectra of stearic acid upon UVA illumination (1.2 mW cm−2) on a typical A/R film. (b) Integrated areas obtained during illumination of A/R (full triangles) and control A/Am (full circles) films. A blank test corresponding to stearic acid on plain glass is included for reference (empty symbols).
Article
Layered anatase-rutile titania thin-films were synthesized via atmospheric-pressure chemical vapor deposition and characterized using X-ray diffraction, Raman spectroscopy and electron microscopy. The interposition of an amorphous TiO2-based interlayer allowed direct vapor deposition of anatase on a rutile substrate, which is otherwise hindered by templating. This resourceful approach and the subsequent crystallization of the amorphous layer after annealing of the films allowed investigation on the impact of an efficient interface of the two anatase-rutile phases in the photodegradation of a model organic pollutant. Clear evidence is presented on the synergy between the two polymorphs and more importantly, on the charge flow across the interface, which, against much conventional understanding, it involves electron transfer from rutile to anatase and is in agreement with a recent theoretical model and electron paramagnetic resonance data. Here, an increasing density of trapped electrons on the anatase surface of the A/R film is confirmed by photoreduction of silver. This observation is attributed to a defect-free efficient contact between the two phases and the presence of small rutile particles that promote rapid electron transfer at the A-R interface of the films.
 
Article
Diamond-like carbon (DLC) film has emerged as a promising material for biomedical applications, but its low tribological properties in air could not be adapted in water and biological fluids. Herein, mussel-inspired catechol adhesive is presented to functionalize DLC film and then polymer brushes are grafted by surface initiated atom transfer radical polymerization (SI-ATRP) to mimic excellent biological lubrication of articular cartilage. Macroscopic tribological evaluation demonstrates low and stable friction coefficient of polymer brushe modified DLC film in water and biological fluids when sliding with a soft polydimethylsiloxane (PDMS) hemisphere, owing to viscous fluid-like boundary lubricant film being formed by high hydration of polymer chains. The strong adhesive capability of catechol anchors also prevents polymer chains being sheared off from the substrate during friction tests. The friction responsiveness of PSPMA brushes is observed in electrolyte solution due to the conformation change of polymer chains. The successful functionalization of DLC with polymer brushes affords DLC film excellent biological lubrication and thus will broaden the scope of its applications in biomedical field.
 
Top-cited authors
Yabing Qi
  • Okinawa Institute of Science and Technology
Luis K Ono
  • Okinawa Institute of Science and Technology
Shenghao Wang
  • Shanghai University
Xun Hou
  • Xi'an Jiaotong University
Feng Chen
  • Xi'an Jiaotong University