A Top Coat with Solvent Annealing Enables Perpendicular Orientation of Sub‐10 nm Microdomains in Si‐Containing Block Copolymer Thin Films

Achieving sub‐10 nm high‐aspect‐ratio patterns from diblock copolymer self‐assembly requires both a high interaction parameter (χ, which is determined by the incompatibility between the two blocks) and a perpendicular orientation of microdomains. However, these two conditions are extremely difficult to achieve simultaneously because the blocks in a high‐χ copolymer typically have very different surface energies, favoring in‐plane microdomain orientations. A fully perpendicular orientation of a high‐χ block copolymer, poly(styrene‐block‐dimethylsiloxane) (PS‐b‐PDMS) is realized here using partially hydrolyzed polyvinyl alcohol (PVA) top coats with a solvent annealing process, despite the large surface energy differences between PS and PDMS. The PVA top coat on the block copolymer films under a solvent vapor atmosphere significantly reduces the interfacial energy difference between two blocks at the top surface and provides sufficient solvent concentration gradient in the through‐thickness direction and appropriate solvent evaporation rates within the film to promote a perpendicular microdomain orientation. The effects of interfacial energy differences and the swellability of PVA top coats controlled by the degree of hydrolysis on the orientation of micro­domains are examined. The thickness of the BCP film and top coats also affects the orientation of the BCP film.     

Interfacial Strain‐Induced Oxygen Disorder as the Cause of Enhanced Critical Current Density in Superconducting Thin Films

To understand the origin of the increase in critical current density of rare earth barium cuprate superconductor thin films with decreasing thickness, a series of sub‐300‐nm EuBa₂Cu₃O_7?δ thin films deposited on SrTiO₃ substrates are studied by X‐ray diffraction and electrical transport measurements. The out‐of‐plane crystallographic mosaic tilt and the out‐of‐plane microstrain both increase with decreasing film thickness. The calculated density of c‐axis threading dislocations matches the extent of the observed low‐field enhancement in critical current density for fields applied parallel to c. The in‐plane mosaic twist and in‐plane microstrain are both around twice the magnitude of the out‐of‐plane values, and both increase with decreasing film thickness. The results are consistent with the observed stronger field enhancement in critical current density for fields applied parallel to ab. The lattice parameter variation with thickness is not as expected from consideration of the biaxial strain with the substrate, indicative of in‐plane microstrain accommodation by oxygen disorder. Collectively, the results point to an enhancement of critical current by interfacial strain induced oxygen disorder which is greatest closest to the film‐substrate interface. The findings of this study have important implications for other thin functional oxide perovskite films and nanostructures where surface and interfacial strains dominate the properties.     

Mobile‐to‐mobile MIMO transmit–receive diversity systems: analysis and performance in three‐dimensional double‐correlated channels

Mobile‐to‐mobile (M‐to‐M) communications are expected to play a crucial role in future wireless systems and networks. In this paper, we consider M‐to‐M multiple‐input multiple‐output (MIMO) maximal ratio combining system and assess its performance in spatially correlated channels. The analysis assumes double‐correlated Rayleigh‐and‐Lognormal fading channels and is performed in terms of average symbol error probability, outage probability, and ergodic capacity. To obtain the receive and transmit spatial correlation functions needed for the performance analysis, we used a three‐dimensional (3D) M‐to‐M MIMO channel model, which takes into account the effects of fast fading and shadowing. The expressions for the considered metrics are derived as a function of the average signal‐to‐noise ratio per receive antenna in closed‐form and are further approximated using the recursive adaptive Simpson quadrature method. Numerical results are provided to show the effects of system parameters, such as distance between antenna elements, maximum elevation angle of scatterers, orientation angle of antenna array in the x–y plane, angle between the x–y plane and the antenna array orientation, and degree of scattering in the x–y plane, on the system performance. Copyright © 2011 John Wiley & Sons, Ltd.     

Glass‐Like Through‐Plane Thermal Conductivity Induced by Oxygen Vacancies in Nanoscale Epitaxial La0.5Sr0.5CoO3−δ

Ultrafast time‐domain thermoreflectance (TDTR) is utilized to extract the through‐plane thermal conductivity (Λ _LSCO) of epitaxial La_0.5Sr_0.5CoO_3?δ (LSCO) of varying thickness (<20 nm) on LaAlO₃ and SrTiO₃ substrates. These LSCO films possess ordered oxygen vacancies as the primary means of lattice mismatch accommodation with the substrate, which induces compressive/tensile strain and thus controls the orientation of the oxygen vacancy ordering (OVO). TDTR results demonstrate that the room‐temperature Λ _LSCO of LSCO on both substrates (1.7 W m^?1 K^?1) are nearly a factor of four lower than that of bulk single‐crystal LSCO (6.2 W m^?1 K^?1). Remarkably, this approaches the lower limit of amorphous oxides (e.g., 1.3 W m^?1 K^?1 for glass), with no dependence on the OVO orientation. Through theoretical simulations, origins of the glass‐like thermal conductivity of LSCO are revealed as a combined effect resulting from oxygen vacancies (the dominant factor), Sr substitution, size effects, and the weak electron/phonon coupling within the LSCO film. The absence of OVO dependence in the measured Λ _LSCO is rationalized by two main effects: (1) the nearly isotropic phononic thermal conductivity resulting from the imperfect OVO planes when δ is small; (2) the missing electronic contribution to Λ _LSCO along the through‐plane direction for these ultrathin LSCO films on insulating substrates.     

Vertical Orientation of Nanodomains on Versatile Substrates through Self‐Neutralization Induced by Star‐Shaped Block Copolymers

Vertical orientation of lamellar and cylindrical nanodomains of block copolymers on substrates is one of the most promising means for developing nanopatterns of next‐generation microelectronics and storage media. However, parallel orientation of lamellar and cylindrical nanodomains is generally preferred due to different affinity between two block segments in a block copolymer toward the substrate and/or air. Thus, vertical orientation of the nanodomains is only obtained under various pre‐ or post‐treatments such as surface neutralization by random copolymers, solvent annealing, and electric or magnetic field. Here, a novel self‐neutralization concept is introduced by designing molecular architecture of a block copolymer. Star‐shaped 18 arm poly(methyl methacrylate)‐block‐polystyrene copolymers ((PMMA‐b‐PS)₁₈) exhibiting lamellar and PMMA cylindrical nanodomains are synthesized. When a thin film of (PMMA‐b‐PS)₁₈ is spin‐coated on a substrate, vertically aligned lamellar and cylindrical nanodomains are obtained without any pre‐ or post‐treatment, although thermal annealing for a short time (less than 30 min) is required to improve the spatial array of vertically aligned nanodomains. This result is attributed to the star‐shaped molecular architecture that overcomes the difference in the surface affinity between PS and PMMA chains. Moreover, vertical orientations are observed on versatile substrates, for instance, semiconductor (Si, SiO_x), metal (Au), PS or PMMA‐brushed substrate, and a flexible polymer sheet of polyethylene naphthalate.     

Symmetry Modulation and Enhanced Multiferroic Characteristics in Bi1‐xNdxFeO3 Ceramics

BiFeO₃ is recognized as the most important room temperature single phase multiferroic material. However, the weak magnetoelectric (ME) coupling remains as a key issue, which obstructs its applications. Since the magnetoelectric coupling in BiFeO₃ is essentially hindered by the cycloidal spin structure, here efforts to improve the magnetoelectric coupling by destroying the cycloidal state and switching to the weak ferromagnetic state through symmetry modulation are reported. The structure is tuned from polar R3c to polar Pna2₁, and finally to nonpolar Pbnm by forming Bi_1‐xNd_xFeO₃ solid solutions, where two morphotropic phase boundaries (MPBs) are detected. Greatly enhanced ferroelectric polarization is obtained together with the desired weak ferromagnetic characteristics in Bi_1‐xNd_xFeO₃ ceramics at the compositions near MPBs. The change of magnetic state from antiferromagnetic (cycloidal state) to ferromagnetic (canted antiferromagnetic) is confirmed by the observation of magnetic domains using magnetic force microscopy. More interestingly, combining experiments and first‐principles‐based simulations, an electric field‐induced structural and magnetic transition from Pna2₁ back to R3c is demonstrated, providing a great opportunity for electric field‐controlled magnetism, and this transition is shown to be reversible with additional thermal treatment.     

Electric Field‐Directed Convective Assembly of Ellipsoidal Colloidal Particles to Create Optically and Mechanically Anisotropic Thin Films

A method of simultaneous field‐ and flow‐directed assembly of anisotropic titania (TiO₂) nanoparticle films from a colloidal suspension is presented. Titania particles are oriented by an alternating (ac) electric field as they simultaneously advect towards a drying front due to evaporation of the solvent. At high field frequencies (ν > ～25 kHz) and field strengths (E > 300 V cm^?1), the particles orient with their major axis along the field direction. As the front recedes, a uniform film with thicknesses of 1–10 µm is deposited on the substrate. The films exhibit a large birefringence (Δn ≈ 0.15) and high packing fraction (? = 0.75 ± 0.08), due to the orientation of the particles. When the frequency is lowered, the particle orientation undergoes a parallel–random–perpendicular transition with respect to the field direction. The orientation dependence on field frequency and strength is explained by the polarizability of ellipsoidal particles using an interfacial polarization model. Particle orientation in the films also leads to anisotropic mechanical properties, which are manifested in their cracking patterns. In all, it is demonstrated that the field‐directed assembly of anisotropic particles provides a powerful means for tailoring nanoparticle film properties in situ during the deposition process.     

Phase Transitions and Anisotropic Thermal Expansion in High Mobility Core‐expanded Naphthalene Diimide Thin Film Transistors

In situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) is used to study the in situ thermal behavior of solution‐processed, high mobility core‐expanded naphthalene diimide thin films. A series of three different molecules is studied where the side‐chain branching position is systematically varied through the use of 2‐, 3‐ and 4‐branched N‐alkyl chains. For all molecules, a number of different phases and their associated phase transitions are observed with heating up to 200 °C. In situ GIWAXS measurements allow following significant variations of packing in each phase including crystalline coherence length, orientation, d‐spacing, and paracrystallinity, as well as, for the first time, thin film thermal expansion coefficients in both the in‐plane and out‐of‐plane direction. Relating these parameters with device measurements of quenched films, a striking correlation is found between high field‐effect mobilities and low in‐plane thermal expansion coefficients. This relationship indicates that high in‐plane thermal expansion coefficients are detrimental to in‐plane charge transport due to the formation of nanoscale defects in the critical first few monolayers upon quenching.     

Influence of Cavity Thickness and Emitter Orientation on the Efficiency Roll‐Off of Phosphorescent Organic Light‐Emitting Diodes

This article describes the first systematic investigation of how the efficiency roll‐off in organic light‐emitting diodes (OLEDs) is influenced by the position and orientation of the emitter molecules within the OLED cavity. The efficiency roll‐off is investigated for two OLED stacks containing either the phosphorescent emitter Ir(MDQ)₂(acac) or Ir(ppy)₃ by varying the distance between emitter and metal cathode; a strong influence of emitter position and orientation on roll‐off is observed. The measurements are modeled by triplet‐triplet‐annihilation (TTA) theory yielding the critical current density and the TTA rate constant. It is found that Ir(MDQ)₂(acac) shows the lowest roll‐off when the emitter is located in the first optical maximum of the electromagnetic field, whereas the roll‐off of the Ir(ppy)₃ stack is lowest when the emitter is positioned closer to the metal cathode. Measurement and modeling of time‐resolved electroluminescence show that the different roll‐off behavior is due to the different orientation and the corresponding change of the decay rate of the emissive dipoles of Ir(MDQ)₂(acac) and Ir(ppy)₃. Finally, design principles are developed for optimal high‐brightness performance by modeling the roll‐off as a function of emitter‐cathode distance, emissive dipole orientation, and radiative efficiency.     

Mapping of Domain Orientation and Molecular Order in Polycrystalline Semiconducting Polymer Films with Soft X‐Ray Microscopy

We utilize scanning transmission X‐ray microscopy (STXM) to study the domain structure of polycrystalline films of the semiconducting polymer poly(9,9’‐dioctylfluorene‐co‐benzothiadiazole) (F8BT). By taking several images at different orientations of the film with respect to the polarization of the X‐ray beam, we are able to compute quantitative maps of molecular alignment/order and molecular orientation, including both the backbone direction and phenyl ring plane orientation, as well as the in‐plane and out‐of‐plane components. We show that polycrystalline F8BT films consist of well‐ordered micron‐sized domains with the transition from one domain orientation to another characterized either by a smooth transition of orientation or by ～ 200 nm wide disordered domain boundaries. The morphology of the disordered domain boundaries resemble the electroluminescence patterns observed previously in F8BT light‐emitting field‐effect transistors suggesting that charge trapping at these disordered domain boundaries facilitates charge recombination in ambipolar operation. A relatively narrow distribution of local average tilt angles is observed that correlates with film structure, with the ordered domains in general showing a higher tilt angle than the disordered domain boundaries. We also use secondary electron detection to image the surface domain structure of polycrystalline F8BT films and demonstrate that the polycrystalline structure extends to the film/air interface. Finally, we calculate ideal NEXAFS spectra corresponding to a perfect F8BT crystal oriented with the 1s – π^* transition dipole moment parallel and perpendicular to the electric field vector of a perfectly linearly polarized X‐ray beam.     

Long‐Range Nonvolatile Electric Field Effect in Epitaxial Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 Heterostructures

One of the ideal candidates of using electric field to manipulate magnetism is the recently developed multiferroics with emergent coupling of magnetism and electricity, particularly in synthesizing artificial nanoscale ferroelectric and ferromagnetic materials. Here, a long‐range nonvolatile electric field effect is investigated in Fe/Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ heterostructure using the dependence of the magnon‐driven magnetoelectric coupling on the epitaxial Fe thin film (4–30 nm) thickness at room temperature using measurements based on the ferromagnetic resonance. The magnon‐driven magnetoelectric coupling tuning of the ferromagnetic resonance field shows a linear response to the electric field, with a resonance field shift that occurs under both positive and negative remanent polarizations, and demonstrates nonvolatile behavior. Moreover, the spin diffusion length of the epitaxial Fe thin film of ≈9 nm is obtained from the results that the change of the cubic magnetocrystalline anisotropy field under different electric fields varies with Fe thickness. These results are promising for the design of future multiferroic devices.     

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

For applications to semi‐transparent and/or bifacial solar cells in building‐integrated photovoltaics and building‐applied photovoltaics, studies are underway to reduce the processing cost and time by decreasing the thickness of Cu(In_1?x,Ga_x)Se₂ (CIGSe) absorber to the ultra‐thin scale (≤500 nm). To dynamically and affordably meet the growing demand for electric power, daylighting, and architectural aesthetics of buildings in urban area, flexible semi‐transparent ultra‐thin (F‐STUT) CIGSe solar cells are proposed on flexible ultra‐thin glass (UTG) and compared with rigid semi‐transparent ultra‐thin (STUT) CIGSe solar cells fabricated on soda‐lime glass (SLG). At all the tested deposition temperatures of CIGSe, the F‐STUT CIGSe solar cells exhibit superior performance compared to the rigid STUT CIGSe solar cells. Furthermore, through realistic measurement under ≈1.3‐sun illumination, maximum bifacial power conversion efficiency of 11.90% and 13.23% are obtained for SLG and UTG, respectively. The major advantages of using UTG instead of SLG are not only the intrinsic characteristics of UTG, such as flexibility and high transmittance, but also collateral benefits such as the larger CIGSe grain size at the deposition temperature, better CIGSe crystalline quality, more precise controllability of the alkali element, and reduced thickness of the interfacial GaO_x layer, which enhance the photovoltaic parameters.     

Molecular Orientation Unified Nonfullerene Acceptor Enabling 14% Efficiency As‐Cast Organic Solar Cells

Molecular orientation and π–π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk‐heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2‐b:2?,3?‐d]pyrrol) core with meta‐ or para‐alkoxyphenyl sidechains are designed and denoted as m‐INPOIC or p‐INPOIC , respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart ( INPIC‐4F ) bearing para‐alkylphenyl sidechains. With inward constriction toward the conjugated backbone, m‐INPOIC presents predominant face‐on orientation to promote charge transport. The as‐cast organic solar cells (OSCs) by blending m‐INPOIC and PBDB‐T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC₇₁BM as the solid processing‐aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as‐cast single‐junction OSCs reported in literature to date. More attractively, PBDB‐T: m‐INPOIC :PC₇₁BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as‐cast devices make m‐INPOIC a promising candidate NFA for large‐scale solution‐processable OSCs.     

Electrically Conductive Thin Films Prepared from Layer‐by‐Layer Assembly of Graphite Platelets

Layer‐by‐layer (LBL) assembly of carbon nanoparticles for low electrical contact resistance thin film applications is demonstrated. The nanoparticles consist of irregularly shaped graphite platelets, with acrylamide/ββ‐methacryl‐oxyethyl‐trimethyl‐ammonium copolymer as the cationic binder. Nanoparticle zeta (ζζ) potential and thereby electrostatic interactions are varied by altering the pH of graphite suspension as well as that of the binder suspension. Film thickness as a function of zeta potential, immersion time, and the number of layers deposited is obtained using Monte Carlo simulation of the energy dispersive spectroscopy measurements. Multilayer film surface morphology is visualized via field‐emission scanning electron microscopy and atomic‐force microscopy. Thin film electrical properties are characterized using electrical contact resistance measurements. Graphite nanoparticles are found to self‐assemble onto gold substrates through two distinct yet overlapping mechanisms. The first mechanism is characterized by logarithmic carbon uptake with respect to the number of deposition cycles and slow clustering of nanoparticles on the gold surface. The second mechanism results from more rapid LBL nanoparticle assembly and is characterized by linear weight uptake with respect to the number of deposition cycles and a constant bilayer thickness of 15 to 21 nm. Thin‐film electrical contact resistance is found to be proportional to the thickness after equilibration of the bilayer structure. Measured values range from 1.6 mΩ cm^?2 at 173 nm to 3.5 mΩ cm^?2 at 276 nm. Coating volume resistivity is reduced when electrostatic interactions are enhanced during LBL assembly.     

On the polarization caused by bulk charges and the ionic conductivity in TlInSe2 crystals

TlInSe₂ crystals are investigated in dc and ac electric fields in the temperature range of 100–400 K. A decrease in the electrical conductivity σ with time in a dc field is revealed. The complex-impedance spectra Z*(f) are measured in the frequency range of 10–10⁶ Hz. Diagrams in the (Z″-Z′) complex plane are analyzed using the method of equivalent circuits. It is shown that the electrical properties of TlInSe₂ crystals in the investigated ranges of temperatures and frequencies are determined by hopping conductivity and the accumulation of charge carriers near blocking platinum electrodes.     

New Roll‐to‐Roll Processable PEDOT‐Based Polymer with Colorless Bleached State for Flexible Electrochromic Devices

Conjugated electrochromic (EC) polymers for flexible EC devices (ECDs) generally lack a fully colorless bleached state. A strategy to overcome this drawback is the implementation of a new sidechain‐modified poly(3,4‐ethylene dioxythiophene) derivative that can be deposited in thin‐film form in a customized high‐throughput and large‐area roll‐to‐roll polymerization process. The sidechain modification provides enhanced EC properties in terms of visible light transmittance change, Δτ_v = 59% (ΔL* = 54.1), contrast ratio (CR = 15.8), coloration efficiency (η = 530 cm² C^?1), and color neutrality (L* = 83.8, a* = ?4.3, b* = ?4.1) in the bleached state. The intense blue‐colored polymer thin films exhibit high cycle stability (10 000 cycles) and fast response times. The design, synthesis, and polymerization of the modified 3,4‐ethylene dioxythiophene derivative are discussed along with a detailed optical, electrochemical, and spectroelectrochemical characterization of the resulting EC thin films. Finally, a flexible see‐through ECD with a visible light transmittance change of Δτ_v = 47% (ΔL* = 51.9) and a neutral‐colored bleached state is developed.     

A universal roll‐to‐roll slot‐die coating approach towards high‐efficiency organic photovoltaics

This work develops a combinational use of solvent additive and in‐line drying oven on the flexible organic photovoltaics to improve large‐area roll‐to‐roll (R2R) slot‐die coating process. Herein, addition of 1,8‐diiodooctane (DIO) in the photoactive layer is conducted to yield a performance of 3.05% based on the blending of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C₆₁‐butyric acid methyl ester (PC₆₁BM), and a very promising device performance of 7.32% based on the blending of poly[[4,8‐bis[(2‐ethylhexyl)oxy] benzo[1,2‐b:4,5‐b’] dithiophene‐2,6‐diyl] [3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7) and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM). Based on this R2R slot‐die coating approach for various polymers, we demonstrate the high‐performance result with respect to the up‐scaling from small high‐PCE cell to large‐area module. This present study provides a route for fabricating a low‐cost, large‐area, and environmental‐friendly flexible organic photovoltaics.     

Optical pH Sensor with Rapid Response Based on a Fluorescein‐Intercalated Layered Double Hydroxide

The preparation of a highly oriented photoluminescent film of fluorescein (FLU) and 1‐heptanesulfonic acid sodium (HES) co‐intercalated in a layered double hydroxide (LDH) matrix by electrophoretic deposition (EPD) is reported, and its application as an optical pH sensor is demonstrated. The FLU‐HES/LDH films with thickness ranging from nanometer to micrometer on indium tin oxide substrates exhibite good c‐orientation of LDH platelets (the ab‐plane of the LDH platelets parallel to the substrate), as confirmed by X‐ray diffraction and scanning electron microscopy. Polarized luminescence of the film is observed with anisotropy value r = 0.29, resulting from the highly oriented FLU in the LDH gallery. Furthermore, the optical pH sensor with film thickness of 300 nm exhibits a broad linear dynamic range for solution pH (5.02–8.54), good repeatability (relative standard deviation (RSD) less than 1.5% in 20 consecutive cycles) and reversibility (RSD less than 1.5% in 20 cycles), high photostability and storage stability (ca. 95.2% of its initial fluorescence intensity remains after one month) as well as fast response time (2 s). Therefore, this work creates new opportunities for the preparation and application of LDH‐based chromophores in the field of optical sensors.     

On the Relation between Morphology and FET Mobility of Poly(3‐alkylthiophene)s at the Polymer/SiO2 and Polymer/Air Interface

The influence of the interface of the dielectric SiO₂ on the performance of bottom‐contact, bottom‐gate poly(3‐alkylthiophene) (P3AT) field‐effect transistors (FETs) is investigated. In particular, the operation of transistors where the active polythiophene layer is directly spin‐coated from chlorobenzene (CB) onto the bare SiO₂ dielectric is compared to those where the active layer is first spin‐coated then laminated via a wet transfer process such that the film/air interface of this film contacts the SiO₂ surface. While an apparent alkyl side‐chain length dependent mobility is observed for films directly spin‐coated onto the SiO₂ dielectric (with mobilities of ≈10^?3 cm² V^?1 s^?1 or less) for laminated films mobilities of 0.14 ± 0.03 cm² V^?1 s^?1 independent of alkyl chain length are recorded. Surface‐sensitive near edge X‐ray absorption fine structure (NEXAFS) spectroscopy measurements indicate a strong out‐of‐plane orientation of the polymer backbone at the original air/film interface while much lower average tilt angles of the polymer backbone are observed at the SiO₂/film interface. A comparison with NEXAFS on crystalline P3AT nanofibers, as well as molecular mechanics and electronic structure calculations on ideal P3AT crystals suggest a close to crystalline polymer organization at the P3AT/air interface of films from CB. These results emphasize the negative influence of wrongly oriented polymer on charge carrier mobility and highlight the potential of the polymer/air interface in achieving excellent “out‐of‐plane” orientation and high FET mobilities.     

Single‐Crystalline Films of the Homologous Series InGaO3(ZnO)m Grown by Reactive Solid‐Phase Epitaxy

Single‐crystalline thin films of the homologous series InGaO₃(ZnO)_m (where m is an integer) are fabricated by the reactive solid‐phase epitaxy (R‐SPE) method. Specifically, the role of ZnO as epitaxial initiator layer for the growth mechanism is clarified. High‐temperature annealing of bilayer films consisting of an amorphous InGaO₃(ZnO)₅ layer deposited at room temperature and an epitaxial ZnO layer on yttria‐stabilized zirconia (YSZ) substrate allows for the growth of single‐crystalline film with controlled chemical composition. The epitaxial ZnO thin layer plays an essential role in determining the crystallographic orientation, while the ratio of the thickness of both layers controls the film composition.