Highly Effective and Efficient Self-Assembled Multilayer-Based Electrode Passivation for Operationally Stable and Reproducible Electrolyte-Gated Transistor Biosensors.

To ensure the operational stability of transistor-based biosensors in aqueous electrolytes during multiple measurements, effective electrode passivation is crucially important for reliable and reproducible device performances. This paper presents a highly effective and efficient electrode passivation method using a facile solution-processed self-assembled multilayer (SAML) with excellent insulation property to achieve operational stability and reproducibility of electrolyte-gated transistor (EGT) biosensors. The SAML is created by the consecutive self-assembly of three different molecular layers of 1,10-decanedithiol, vinyl-polyhedral oligomeric silsesquioxane, and 1-octadecanethiol. This passivation enables EGT to operate stably in phosphate-buffered saline (PBS) during repeated measurements over multiple cycles without short-circuiting. The SAML-passivated EGT biosensor is fabricated with a solution-processed In2O3 thin film as an amorphous oxide semiconductor working both as a semiconducting channel in the transistor and as a functionalizable biological interface for a bioreceptor. The SAML-passivated EGT including In2O3 thin film is demonstrated for the detection of Tau protein as a biomarker of Alzheimer's disease while employing a Tau-specific DNA aptamer as a bioreceptor and a PBS solution with a low ionic strength to diminish the charge-screening (Debye length) effect. The SAML-passivated EGT biosensor functionalized with the Tau-specific DNA aptamer exhibits ultrasensitive, quantitative, and reliable detection of Tau protein from 1 × 10-15 to 1 × 10-10 M, covering a much larger range than clinical needs, via changes in different transistor parameters. Therefore, the SAML-based passivation method can be effectively and efficiently utilized for operationally stable and reproducible transistor-based biosensors. Furthermore, this presented strategy can be extensively adapted for advanced biomedical devices and bioelectronics in aqueous or physiological environments.

Fabrication of Self-Healable, Robust Superhydrophobic Surfaces Using UV-Crosslinked Nanocomposite Films.

Studies on fabricating robust superhydrophobic surfaces by a low-cost method have been rare, despite the recent demand for nature-inspired superhydrophobic surfaces including self-healing ability in various industrial applications. Herein, we propose a fabrication method for self-healable, robust superhydrophobic nanocomposite films by facile solution-processed spray coating and UV curing. The components of the coating solution include functionalized hydrophobic silica nanoparticles for producing high roughness hierarchical textured structures with low surface energy, and UV-crosslinkable v-POSS and bi-thiol hydrocarbon molecules to improve the film stability. As a result of the synergetic effect of the hydrophobic nanoparticles and UV-crosslinked polymeric compounds, the spray-coated and UV-cured nanocomposite films possess excellent superhydrophobicity (water contact angles > 150º) and high stability, in addition to self-healing abilities.

Self-Assembled Hybrid Gate Dielectrics for Ultralow Voltage of Organic Thin-Film Transistors.

We developed self-assembled hybrid dielectric materials via a facile and low-temperature solution process. These dielectrics are used to facilitate ultralow operational voltage of organic thinfilm transistors. Self-assembly of bifunctional phosphonic acid and ultrathin hafnium oxide layers results in the self-assembled hybrid dielectrics. Additionally, the surface property of the top layer of hafnium oxide can be tuned by phosphonic acid-based self-assembled molecules to improve the function of the organic semiconductors. These novel hybrid dielectrics demonstrate great dielectric properties as low-level leakage current densities of <1.45×10-6 A/cm², large capacitances (up to 800 nF/cm²), thermal stability (up to 300 °C), and featureless morphology (root-mean-square roughness ˜0.3 nm). As a result, self-assembled gate dielectrics can be incorporated into thin-film transistors with p-type organic semiconductors functioning at ultralow voltages (<-2 V) to achieve enhanced performance (hole mobility: 0.88 cm²/V·s, and Ion/Ioff: > 105, threshold voltage: 0.5 V).

Cross-Linked Organic-Inorganic Hybrid Composite Films for One-Step Fabrication of Robust Superhydrophobic Surfaces.

Despite the recent demands of bioinspired superhydrophobic surfaces with self-cleaning properties in various industrial applications, a low-cost fabrication method for superhydrophobic films with excellent stability has rarely been studied. Herein, we report a robust superhydrophobic organic- inorganic hybrid composites film produced via a facile one-step solution-process. As coating materials for the facile one-step fabrication of the robust superhydrophobic films, we included Al2O3 nanoparticles for micro/nano hierarchical dual-scale structures, alkylsilane for low surface energy, and organic cross-linkers for increasing the stability of the hybrid composite films. Based on the hydrophobicity and stability tests of the hybrid composite films, the optimized composition of the robust superhydrophobic hybrid composite films showed high water contact angles (>150°) and low sliding angles (<5°) as well as excellent mechanical and thermal stability (up to 350 °C).

UV-Cured Hafnium Oxide-Based Gate Dielectrics for Low-Voltage Organic and Amorphous Oxide Thin-Film Transistors.

In this study, we have fabricated hafnium oxide dielectrics for low-voltage organic and amorphous oxide thin-film transistors (TFTs) via a facile low-temperature solution method and investigated the electrical properties of these dielectrics. Hafnium oxide dielectric films can be easily fabricated by a sol-gel solution method and ultraviolet (UV) curing at room temperature. In addition, the surface energy of hafnium oxide films can be easily modified by using phosphonic-acid-based self-assembled monolayers. This modification makes these films compatible with organic semiconductors fabrication methods. These novel dielectrics exhibit excellent insulating properties (leakage current densities of <10-6 A/cm² at 2 V), high capacitances (up to 690 nF/cm²), and smooth surfaces (root-mean-square roughness <0.5 nm). Consequently, hafnium oxide-based dielectrics can be integrated into both pentacene-based and indium oxide-based TFTs, functioning at relatively low voltages (<±3 V) to achieve good performance (hole mobility: 0.31 cm²/V · s, electron mobility: 1.54 cm²/V · s, and on/off current ratios: >105).

Rationally Designed, Multifunctional Self-Assembled Nanoparticles for Covalently Networked, Flexible and Self-Healable Superhydrophobic Composite Films.

For constructing bioinspired functional films with various superhydrophobic functions, including self-cleaning, anticorrosion, antibioadhesion, and oil-water separation, hydrophobic nanomaterials have been widely used as crucial structural components. In general, hydrophobic nanomaterials, however, cannot form strong chemical bond networks in organic-inorganic hybrid composite films because of the absence of chemically compatible binding components. Herein, we report the rationally designed, multifunctional self-assembled nanoparticles with tunable functionalities of covalent cross-linking and hydrophobicity for constructing three-dimensionally interconnected superhydrophobic composite films via a facile solution-based fabrication at room temperature. The multifunctional self-assembled nanoparticles allow the systematic control of functionalities of composite films, as well as the stable formation of covalently linked superhydrophobic composite films with excellent flexibility (bending radii of 6.5 and 3.0 mm, 1000 cycles) and self-healing ability (water contact angle > 150°, ≥10 cycles). The presented strategy can be a versatile and effective route to generating other advanced functional films with covalently interconnected composite networks.

Multifunctional Hybrid Multilayer Gate Dielectrics with Tunable Surface Energy for Ultralow-Power Organic and Amorphous Oxide Thin-Film Transistors.

For large-area, printable, and flexible electronic applications using advanced semiconductors, novel dielectric materials with excellent capacitance, insulating property, thermal stability, and mechanical flexibility need to be developed to achieve high-performance, ultralow-voltage operation of thin-film transistors (TFTs). In this work, we first report on the facile fabrication of multifunctional hybrid multilayer gate dielectrics with tunable surface energy via a low-temperature solution-process to produce ultralow-voltage organic and amorphous oxide TFTs. The hybrid multilayer dielectric materials are constructed by iteratively stacking bifunctional phosphonic acid-based self-assembled monolayers combined with ultrathin high-k oxide layers. The nanoscopic thickness-controllable hybrid dielectrics exhibit the superior capacitance (up to 970 nF/cm2), insulating property (leakage current densities <10-7 A/cm2), and thermal stability (up to 300 °C) as well as smooth surfaces (root-mean-square roughness <0.35 nm). In addition, the surface energy of the hybrid multilayer dielectrics are easily changed by switching between mono- and bifunctional phosphonic acid-based self-assembled monolayers for compatible fabrication with both organic and amorphous oxide semiconductors. Consequently, the hybrid multilayer dielectrics integrated into TFTs reveal their excellent dielectric functions to achieve high-performance, ultralow-voltage operation (< ± 2 V) for both organic and amorphous oxide TFTs. Because of the easily tunable surface energy, the multifunctional hybrid multilayer dielectrics can also be adapted for various organic and inorganic semiconductors, and metal gates in other device configurations, thus allowing diverse advanced electronic applications including ultralow-power and large-area electronic devices.

Development of omniphobic behavior in molecular self-assembled monolayer-coated nanowire forests.

The wetting characteristics of self-assembled monolayers (SAMs) on three different surface structures of thin film, microcone array, and nanowire forest topologies, which were chemically modified using phosphonic acid (HDF-PA and OD-PA) and trichlorosilane (HDF-S), were investigated. The molecular SAM-coated nanowire forest structures exhibited superhydrophobic properties with contact angles of 150.6°-155.4°, compared with the other structures combined with OD-PA, HDF-PA, and HDF-S SAMs, which displayed contact angles of 99.5°-116.8°. Moreover, the HDF-PA and HDF-S SAM-coated nanowire forest structures showed omniphobic properties for both flat and curved surfaces, irrespective of the substrate form. Four liquid droplets of different viscosities and composition (water, urea solution, oil, and photoresist) slid on the HDF-PA and HDF-S SAM-coated nanowire forest surfaces without leaving any traces. The omniphobic properties of the molecular SAM-coated nanowire forest structures developed in this study could be used for various applications in which their slippery effect is desirable, such as in medical tubes and the interior of pipes. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 204-210, 2017.

Transparent, self-cleaning and waterproof surfaces with tunable micro/nano dual-scale structures.

The rational design and facile fabrication of optically transparent, superhydrophobic surfaces can advance their versatile applications, including optoelectronic devices. For the easily accessible and scalable preparation of transparent, superhydrophobic surfaces, various coating methods using a solution-process have been developed. However, obtaining highly transparent, non-wetting surfaces with excellent properties is challenging due to the difficulty in controlling surface roughness. Here, we report on a novel approach to control the surface roughness by fabricating tailorable micro/nano dual-scale surface structures via solution-processed nanoparticle coating. The surface roughness was able to be controlled by micro/nano dual-scale structures that can be manipulated by varying the mixture ratio of two different sizes of Al2O3 nanoparticles. The controllable micro/nano dual-scale structures were optimized to achieve the superior surface properties in both hydrophobicity and transparency, exhibiting a high water contact angle (>160°), low sliding angle (<2°) and high transmittance (>90%). These characteristics allowed an excellent transparency and self-cleaning capability as well as a superior waterproof ability even under applied voltage. Furthermore, we demonstrated the versatile applicability of the developed surface-coating method to a wide range of substrates including glass, paper, fabrics, and even flexible plastics.

Low Temperature Solution-Processed Gate Dielectrics for Low-Voltage Organic Field-Effect Transistors.

We report on the design, preparation, and electrical properties of novel solution-processed organic-inorganic hybrid dielectric films for the low-voltage operation of organic field-effect transistors (OFETs). Hybrid dielectric thin films (-20 nm thick) are easily fabricated by spin-coating a zirconium chloride precursor/organic additive reagent mixture, followed by annealing at low temperatures (-150 degrees C). The smooth and transparent hybrid dielectrics exhibit great insulating properties (leakage current densities -10(-7) A/cm2 at 2 MV/cm), high capacitance (170 nF/cm2). OFETs fabricated with hybrid dielectric and pentacene semiconductor function great at relatively low voltage (mobility: 1 cm2/V x s, on/off current ratio: 10(5)).

Hybrid gate dielectric materials for unconventional electronic circuitry.

Recent advances in semiconductor performance made possible by organic π-electron molecules, carbon-based nanomaterials, and metal oxides have been a central scientific and technological research focus over the past decade in the quest for flexible and transparent electronic products. However, advances in semiconductor materials require corresponding advances in compatible gate dielectric materials, which must exhibit excellent electrical properties such as large capacitance, high breakdown strength, low leakage current density, and mechanical flexibility on arbitrary substrates. Historically, conventional silicon dioxide (SiO2) has dominated electronics as the preferred gate dielectric material in complementary metal oxide semiconductor (CMOS) integrated transistor circuitry. However, it does not satisfy many of the performance requirements for the aforementioned semiconductors due to its relatively low dielectric constant and intransigent processability. High-k inorganics such as hafnium dioxide (HfO2) or zirconium dioxide (ZrO2) offer some increases in performance, but scientists have great difficulty depositing these materials as smooth films at temperatures compatible with flexible plastic substrates. While various organic polymers are accessible via chemical synthesis and readily form films from solution, they typically exhibit low capacitances, and the corresponding transistors operate at unacceptably high voltages. More recently, researchers have combined the favorable properties of high-k metal oxides and π-electron organics to form processable, structurally well-defined, and robust self-assembled multilayer nanodielectrics, which enable high-performance transistors with a wide variety of unconventional semiconductors. In this Account, we review recent advances in organic-inorganic hybrid gate dielectrics, fabricated by multilayer self-assembly, and their remarkable synergy with unconventional semiconductors. We first discuss the principals and functional importance of gate dielectric materials in thin-film transistor (TFT) operation. Next, we describe the design, fabrication, properties, and applications of solution-deposited multilayer organic-inorganic hybrid gate dielectrics, using self-assembly techniques, which provide bonding between the organic and inorganic layers. Finally, we discuss approaches for preparing analogous hybrid multilayers by vapor-phase growth and discuss the properties of these materials.

Quantitative statistical analysis of dielectric breakdown in zirconia-based self-assembled nanodielectrics.

Uniformity of the dielectric breakdown voltage distribution for several thicknesses of a zirconia-based self-assembled nanodielectric was characterized using the Weibull distribution. Two regimes of breakdown behavior are observed: self-assembled multilayers >5 nm thick are well described by a single two-parameter Weibull distribution, with ß ≈ 11. Multilayers ≤5 nm thick exhibit kinks on the Weibull plot of dielectric breakdown voltage, suggesting that multiple characteristic mechanisms for dielectric breakdown are present. Both the degree of uniformity and the effective dielectric breakdown field are observed to be greater for one layer than for two layers of Zr-SAND, suggesting that this multilayer is more promising for device applications.

Solution-deposited organic-inorganic hybrid multilayer gate dielectrics. Design, synthesis, microstructures, and electrical properties with thin-film transistors.

We report here on the rational synthesis, processing, and dielectric properties of novel layer-by-layer organic/inorganic hybrid multilayer dielectric films enabled by polarizable π-electron phosphonic acid building blocks and ultrathin ZrO(2) layers. These new zirconia-based self-assembled nanodielectric (Zr-SAND) films (5-12 nm thick) are readily fabricated via solution processes under ambient atmosphere. Attractive Zr-SAND properties include amenability to accurate control of film thickness, large-area uniformity, well-defined nanostructure, exceptionally large electrical capacitance (up to 750 nF/cm(2)), excellent insulating properties (leakage current densities as low as 10(-7) A/cm(2)), and excellent thermal stability. Thin-film transistors (TFTs) fabricated with pentacene and PDIF-CN(2) as representative organic semiconductors and zinc-tin-oxide (Zn-Sn-O) as a representative inorganic semiconductor function well at low voltages (<±4.0 V). Furthermore, the TFT performance parameters of representative organic semiconductors deposited on Zr-SAND films, functionalized on the surface with various alkylphosphonic acid self-assembled monolayers, are investigated and shown to correlate closely with the alkylphosphonic acid chain dimensions.

Flexible low-voltage organic thin-film transistors enabled by low-temperature, ambient solution-processable inorganic/organic hybrid gate dielectrics.

We report here on the design, synthesis, processing, and dielectric properties of novel cross-linked inorganic/organic hybrid blend (CHB) dielectric films which enable low-voltage organic thin-film transistor (OTFT) operation. CHB thin films (20-43 nm thick) are readily fabricated by spin-coating a zirconium chloride precursor plus an α,ω-disilylalkane cross-linker solution in ambient conditions, followed by curing at low temperatures (~150 °C). The very smooth CHB dielectrics exhibit excellent insulating properties (leakage current densities ~10(-7) A/cm(2)), tunable capacitance (95-365 nF/cm(2)), and high dielectric constants (5.0-10.2). OTFTs fabricated with pentacene as the organic semiconductor function well at low voltages (<-4.0 V). The morphologies and microstructures of representative semiconductor films grown on CHB dielectrics prepared with incrementally varied compositions and processing conditions are investigated and shown to correlate closely with the OTFT response.

How water meets a very hydrophobic surface.

Is there a low-density region ("gap") between water and a hydrophobic surface? Previous x-ray and neutron reflectivity results have been inconsistent because the effect (if any) is subresolution for the surfaces studied. We have used x-ray reflectivity to probe the interface between water and more hydrophobic smooth surfaces. The depleted region width increases with contact angle and becomes larger than the resolution, allowing definitive measurements. Large fluctuations are predicted at this interface; however, we find that their contribution to the interface roughness is too small to measure.

High-performance solution-processed amorphous zinc-indium-tin oxide thin-film transistors.

Films of the high-performance solution-processed amorphous oxide semiconductor a-ZnIn(4)Sn(4)O(15), grown from 2-methoxyethanol/ethanolamine solutions, were used to fabricate thin-film transistors (TFTs) in combination with an organic self-assembled nanodielectric as the gate insulator. This structurally dense-packed semiconductor composition with minimal Zn(2+) incorporation strongly suppresses transistor off-currents without significant mobility degradation, and affords field-effect electron mobilities of approximately 90 cm(2) V(-1) s(-1) (104 cm(2) V(-1) s(-1) maximum obtained for patterned ZITO films), with I(on)/I(off) ratio approximately 10(5), a subthreshhold swing of approximately 0.2 V/dec, and operating voltage <2 V for patterned devices with W/L = 50. The microstructural and electronic properties of ZITO semiconductor film compositions in the range Zn(9-2x)In(x)Sn(x)O(9+1.5x) (x = 1-4) and ZnIn(8-x)Sn(x)O(13+0.5x) (x = 1-7) were systematically investigated to elucidate those factors which yield optimum mobility, I(on)/I(off), and threshold voltage parameters. It is shown that structural relaxation and densification by In(3+) and Sn(4+) mixing is effective in reducing carrier trap sites and in creating carrier-generating oxygen vacancies. In contrast to the above results for TFTs fabricated with the organic self-assembled nanodielectric, ZnIn(4)Sn(4)O(15) TFTs fabricated with SiO(2) gate insulators exhibit electron mobilities of only approximately 11 cm(2) V(-1) s(-1) with I(on)/I(off) ratios approximately 10(5), and a subthreshhold swing of approximately 9.5 V/dec.

High-performance single-crystalline arsenic-doped indium oxide nanowires for transparent thin-film transistors and active matrix organic light-emitting diode displays.

We report high-performance arsenic (As)-doped indium oxide (In(2)O(3)) nanowires for transparent electronics, including their implementation in transparent thin-film transistors (TTFTs) and transparent active-matrix organic light-emitting diode (AMOLED) displays. The As-doped In(2)O(3) nanowires were synthesized using a laser ablation process and then fabricated into TTFTs with indium-tin oxide (ITO) as the source, drain, and gate electrodes. The nanowire TTFTs on glass substrates exhibit very high device mobilities (approximately 1490 cm(2) V(-1) s(-1)), current on/off ratios (5.7 x 10(6)), steep subthreshold slopes (88 mV/dec), and a saturation current of 60 microA for a single nanowire. By using a self-assembled nanodielectric (SAND) as the gate dielectric, the device mobilities and saturation current can be further improved up to 2560 cm(2) V(-1) s(-1) and 160 microA, respectively. All devices exhibit good optical transparency (approximately 81% on average) in the visible spectral range. In addition, the nanowire TTFTs were utilized to control green OLEDs with varied intensities. Furthermore, a fully integrated seven-segment AMOLED display was fabricated with a good transparency of 40% and with each pixel controlled by two nanowire transistors. This work demonstrates that the performance enhancement possible by combining nanowire doping and self-assembled nanodielectrics enables silicon-free electronic circuitry for low power consumption, optically transparent, high-frequency devices assembled near room temperature.

Low-temperature solution-processed amorphous indium tin oxide field-effect transistors.

Amorphous indium tin oxide (ITO)-based thin-film transistors (TFTs) were fabricated on various dielectrics [SiO(2) and self-assembled nanodielectrics (SANDs)] by spin-coating an ITO film precursor solution consisting of InCl(3) and SnCl(4) as the sources of In(3+) and Sn(4+), respectively, methoxyethanol (solvent), and ethanolamine (base). These films can be annealed at temperatures T(a) < or = 250 degrees C and afford devices with excellent electrical characteristics. The optimized [In(3+)]/[In(3+) + Sn(4+)] molar ratio (0.7) and annealing temperature (T(a) = 250 degrees C) afford TFTs exhibiting electron mobilities of approximately 2 and approximately 10-20 cm(2) V(-1) s(-1) with SiO(2) and SAND, respectively, as the gate dielectric. Remarkably, ITO TFTs processed at 220 degrees C still exhibit electron mobilities of >0.2 cm(2) V(-1) s(-1), which is encouraging for processing on plastic substrates.