Emerging Applications of Liquid Crystals Based on Nanotechnology

Diverse functionalities of liquid crystals (LCs) offer enormous opportunities for their potential use in advanced mobile and smart displays, as well as novel non-display applications. Here, we present snapshots of the research carried out on emerging applications of LCs ranging from electronics to holography and self-powered systems. In addition, we will show our recent results focused on the development of new LC applications, such as programmable transistors, a transparent and active-type two-dimensional optical array and self-powered display systems based on LCs, and will briefly discuss their novel concepts and basic operating principles. Our research will give insights not only into comprehensively understanding technical and scientific applications of LCs, but also developing new discoveries of other LC-based devices.     

Low-Temperature-Processed High-Performance Pentacene OTFTs with Optimal Nd-Ti Oxynitride Mixture as Gate Dielectric

When processed at a low temperature of 200 °C, organic thin-film transistors (OTFTs) with pentacene channel adopting high-k Neodymium-Titanium oxynitride mixtures (NdTiON) with various Ti contents as gate dielectrics are fabricated. The Ti content in the NdTiON is varied by co-sputtering a Ti target at 0 W, 10 W, 20 W and 30 W, respectively, while fixing the sputtering power of an Nd target at 45 W. High-performance OTFT is obtained for the 20 W-sputtered Ti, including a small threshold voltage of −0.71 V and high carrier mobility of 1.70 cm²/V·s. The mobility improvement for the optimal Ti content can be attributed to smoother dielectric surface and resultant larger overlying pentacene grains as reflected by Atomic Force Microscopy measurements. Moreover, this sample with the optimal Ti content shows much higher mobility than its counterpart processed at a higher temperature of 400 °C (0.8 cm²/V·s) because it has a thinner gate-dielectric/gate-electrode interlayer for stronger screening on the remote phonon scattering by the gate electrode. In addition, a high dielectric constant of around 10 is obtained for the NdTiON gate dielectric that contributes to a threshold voltage smaller than 1 V for the pentacene OTFT, implying the high potential of the Nd-Ti oxynitride in future high-performance organic devices.     

新型金属氧化物半导体场效应晶体管探测器在放疗剂量监控中的应用

目的探索和评估自行开发研制的新型金属氧化物半导体场效应晶体管(MOSFET)探测器在体实时剂量测量中的应用特性。方法分别使用医科达加速器8、15MV光子线,以及6、8、12、18 MeV电子束刻度MOSFET探测器。根据探测器灵敏度随能量变化情况评估MOSFET探测器能量依赖性。使用8MV光子线在0～50 Gy范围内观察MOSFET探测器读数随累积剂量变化的线性情况,确定MOSFET探测器剂量测量的线性区间。将MOSFET探测器固定在圆柱形PMMA体模中央,顺时针每15°检测探测器信号响应,判断MOSFET探测器方向性。对1例乳腺癌放疗患者应用MOSFET探测器进行了全程剂量监测。在使用NE-2571指形电离室对该患者放疗计划剂量计算进行物理验证后,分别于首次治疗、每周1次治疗及最后1次治疗中应用MOSFET探测器测量患者体表吸收剂量,并将测量结果与该处计划剂量进行比较,确定乳腺癌三维放疗的总体剂量偏差。结果对8、15 MV光子线和6～18MeV电子束测量结果显示,MOSFET探测器灵敏度随能量变化的幅度＜2．5%。这表明MOSFET探测器对中高能射线具有较好的能量响应。在6 V门控电压状态下,MOSFET探测器在0～50 Gy的剂量范围内保持了较好的剂量线性,最大偏差＜3．0%。在每次测量前和测量后分别刻度MOSFET探测器并取其平均值可使其剂量线性误差控制在1%以内。该MOSFET探测器信号响应在270～90°之间呈现出各向同性,读数偏差＜1．5%。但在探测器背面(135～225°之间)的信号响应明显变小,背面与正面的读数偏差最大可达10．0%。应用于患者实时剂量监测的结果显示,实际测量剂量与计划剂量相比平均偏差2．8%,最大偏差＜5．0%,符合AAPM 13号报告对体外放疗剂量总不确定度的质量控制标准。结论该MOSFEYT探测器体积小,操作简单,对中高能辐射具有较好的能量响应和剂量线性,为治疗计划剂量验证和人体吸收剂量测量提供了一种较好的剂量工具。     

A decrease of intracellular ATP is compensated by increased respiration and acidification at sub-lethal parathion concentrations in murine embryonic neuronal cells: measurements in metabolic cell-culture chips

We present a label-free in vitro method for testing the toxic potentials of chemical substances using primary neuronal cells. The cells were prepared from 16-day-old NMRI mouse embryos and cultured on silicon chips (www.bionas.de) under the influence of different parathion concentrations with sensors for respiration (Clark-type oxygen electrodes), acidification (pH-ISFETs) and cell adhesion (interdigitated electrode structures, IDES). After 12 days in vitro, the sensor readouts were simultaneously recorded for 350 min in the presence of parathion applying a serial 1:3 dilution. The parathion-dependent data was fitted by logistic functions. IC₅₀ values of approximately 105 μM, 65 μM, and 54 μM were found for respiration, acidification, and adhesion, respectively. An IC₅₀ value of approximately 36 μM was determined from the intracellular ATP-levels of cells, which were detected by an ATP-luminescence assay using micro-well plates. While the intracellular ATP level and cell adhesion showed no deviation from a simple logistic decay, increases of approximately 29% in the respiration and 15% in the acidification rates above the control values were found at low parathion concentrations, indicating hormesis. These increases could be fitted by a modified logistic function. We believe that the label-free, continuous, multi-parametric monitoring of cell-metabolic processes may have applications in systems-biology and biomedical research, as well as in environmental monitoring. The parallel characterization of IC₅₀ values and hormetic effects may provide new insights into the metabolic mechanisms of toxic challenges to the cell.     

Neuronal field potential in acute hippocampus slice recorded with transistor and micropipette electrode

Arrays of planar electrodes are often applied to record spatial patterns of neuronal field potentials in acute brain slices. The approach is hampered by layers of inactive tissue caused by the cutting process and also by a film of bath electrolyte that may exist between the slice and the substrate. To address this issue, we used a micropipette electrode to measure the vertical profile of evoked field potentials across acute slices from mouse hippocampus. In this way, we found that the signal due to an excitatory postsynaptic potential (EPSP) at the bottom of the slice was about 40% of the maximum at its centre. The vertical profile was matched by a volume-conductor model with proper boundary conditions. Simultaneously, voltage transients caused by EPSPs were measured with a field-effect transistor in the substrate. The transistor signals were in agreement with the evoked field potentials at the bottom of the slice. The study demonstrates: (i) that the loss of signal amplitude from the centre of a slice to the bottom is modest, despite an inactive tissue layer; and (ii) that in principle, planar sensors are able to record the field potential at the bottom of a slice. The results raise questions about the small voltages that are often observed with planar metal electrodes and about the reconstruction of the neuronal activity from field potentials at the bottom of acute slices using current-source density analysis.     

A modality-specific somatosensory evoked potential test protocol for clinical evaluation: A feasibility study

ObjectiveWe aimed to establish an objective neurophysiological test protocol that can be used to assess the somatosensory nervous system.MethodsIn order to assess most fiber subtypes of the somatosensory nervous system, repetitive stimuli of seven different modalities (touch, vibration, pinprick, cold, contact heat, laser, and warmth) were synchronized with the electroencephalogram (EEG) and applied on the cheek and dorsum of the hand and dorsum of the foot in 21 healthy subjects and three polyneuropathy (PNP) patients. Latencies and amplitudes of the modalities were assessed and compared. Patients received quantitative sensory testing (QST) as reference.ResultsWe found reproducible evoked potentials recordings for touch, vibration, pinprick, contact-heat, and laser stimuli. The recording of warm-evoked potentials was challenging in young healthy subjects and not applicable in patients. Latencies were shortest within Aβ-fiber-mediated signals and longest within C-fibers. The test protocol detected function loss within the Aβ-fiber and Aδ-fiber-range in PNP patients. This function loss corresponded with QST findings.ConclusionIn this pilot study, we developed a neurophysiological test protocol that can specifically assess most of the somatosensory modalities. Despite technical challenges, initial patient data appear promising regarding a possible future clinical application.SignificanceEstablished and custom-made stimulators were combined to assess different fiber subtypes of the somatosensory nervous system using modality-specific evoked potentials.     

Coplanar Donor–Acceptor Semiconducting Copolymers to Achieve Better Conjugated Structures: Side‐Chain Engineering

It is reported on the allocation effects of branched alkyl chains, when used as solubility and ordering enhancers of the conjugated donor–accepter (D –A ) copolymer backbones, on the ordering and π–π overlapping of the copolymers, that drastically affect the electrical properties of organic field‐effect transistors (OFETs). Triisopropylsilylethynyl‐benzo[1,2‐b :4,5‐b ′]dithiophene (TIPSBDT) and diketopyrrolopyrrole (DPP)‐based copolymers, which have two linear alkyl spacers (methylene (C 1) or butylene (C 4)) between the DPP and side‐substituent (C₁₀H₂₁)CH(C₈H₁₇) , are synthesized by Suzuki cross‐coupling. These copolymer films are spun cast onto a polymer‐treated SiO₂ dielectric surface, and some are further thermally annealed. The longer spacer, C 4, is found to efficiently enhance the coplanarity and conjugation of the D –A backbone, while the C 1 does not. The resulting C 4‐bridged TIPSBDT‐DPP‐based copolymer readily develops a superior π‐extended layer on the dielectric surface; the edge‐on chains with randomly oriented side chains can be closely packed with a short π‐planar distance (d ₍₀₁₀₎) of 3.57 Å. Its properties are superior to those of the short spacer C 1 system with d ₍₀₁₀₎ ≈3.93 Å. The C 4‐bridged TIPSBDT‐DPP copolymer films yield a field‐effect mobility up to 1.2 cm² V⁻¹ s⁻¹ in OFETs, 12 times as higher than that of the C 1 spacer system.

     

From the Cover: Spray-combustion synthesis: Efficient solution route to high-performance oxide transistors

Metal-oxide (MO) semiconductors have emerged as enabling materials for next generation thin-film electronics owing to their high carrier mobilities, even in the amorphous state, large-area uniformity, low cost, and optical transparency, which are applicable to flat-panel displays, flexible circuitry, and photovoltaic cells. Impressive progress in solution-processed MO electronics has been achieved using methodologies such as sol gel, deep-UV irradiation, preformed nanostructures, and combustion synthesis. Nevertheless, because of incomplete lattice condensation and film densification, high-quality solution-processed MO films having technologically relevant thicknesses achievable in a single step have yet to be shown. Here, we report a low-temperature, thickness-controlled coating process to create high-performance, solution-processed MO electronics: spray-combustion synthesis (SCS). We also report for the first time, to our knowledge, indium-gallium-zinc-oxide (IGZO) transistors having densification, nanoporosity, electron mobility, trap densities, bias stability, and film transport approaching those of sputtered films and compatible with conventional fabrication (FAB) operations.Metal-oxide (MO) semiconductors, especially in amorphous phases, represent an appealing materials family for next generation electronics owing to their high carrier mobilities, good environmental/thermal stability, mechanical flexibility, and excellent optical transparency (1–3). MO films complement organic semiconductors (4, 5), carbon/oxide nanomaterials (6), and flexible silicon (7, 8) for enabling new technologies, such as flexible displays and printed sensors. For fabricating high-performance electronics with acceptable fidelity, conventional processes require capital-intensive physical/chemical vapor deposition techniques. Capitalizing on the solubility of MO precursors in common solvents, solution methods have been used to fabricate semiconducting MO layers for thin-film transistors (TFTs). However, the fabrication process and field-effect mobilities of these TFTs are not competitive with the corresponding vapor-deposited (e.g., sputtered) devices (9), and developing routes to solution-derived MO TFTs with technologically relevant thicknesses and performance comparable to state of the art vapor-deposited devices is a critical milestone for MO electronics evolution.Sol-gel techniques are used extensively for MO film growth, including films for high-performance TFTs (10–13). However, the required sol-gel condensation, densification, and impurity removal steps typically require >400–500 °C processing temperatures, which are incompatible with inexpensive glasses and typical flexible plastic substrates (14). Progress toward significantly reducing the processing temperatures of sol gel-derived MO films has afforded excellent TFT mobilities; however, achieving both reproducible high-performance and stable device operation remains an unsolved issue for Ga-containing materials (15). Sol-gel on-a-chip for indium-zinc-oxide (3) and deep-UV irradiation of spin-coated MO precursor films (1) represent significant advances; however, challenges remain. Recently, this laboratory reported a low-temperature solution method, spin-coating combustion synthesis (spin-CS), for fabricating MO TFTs (SI Appendix, Fig. S1) (2, 16). By incorporating an oxidizer and a fuel in the precursor solution, localized, highly exothermic chemical transformations occur within the spin-coated films, effecting rapid condensation and M-O-M lattice formation at temperatures as low as 200–300 °C, which was assessed by thermal and X-ray diffraction (XRD) analysis, and yielding high-performance TFTs. Additional work has subsequently broadened the spin-CS fuel/oxidizer options and accessible MO compositions (17).Note, however, that independent of the particular solution processing method, significant quantities of gaseous H₂O, N₂, NO_x, CO₂, etc. are evolved, compromising film continuity and densification in single-step, thick-film growth processes (17–21). These issues also apply to combustion synthesis, especially because the exotherm is of short duration. Therefore, films must be sufficiently thin (typically <10–20 nm for conventional sol gel and <5–10 nm for combustion) to yield high-quality films (2, 3, 15). For MO TFT implementation in, for example, active-matrix display backplanes, semiconductor thicknesses must be 50–100 nm to avoid back-channel effects, delayed turn-on, and bias stress shifting (22, 23). Thus, for current generation MO TFT structures, suitable film thicknesses from conventional solution processes require inefficient multiple deposition and anneal sequences, which are time-consuming, and invariably create bulk trap states at the semiconductor interfaces.In contrast to spin coating, spray processes are readily adapted to continuous large-area, high-throughput coating as in roll-to-roll processing. Simple spray coating has been used to fabricate organic solar cells (24), organic TFTs (25), and MO electronics (26) using heated substrates. In pioneering work, spray-coated sol-gel ZnO TFTs achieved mobilities of ∼0.1 cm² V⁻¹ s⁻¹ for 200 °C growth and ∼25 cm² V⁻¹ s⁻¹ for 500 °C growth (26). These results raise the intriguing question of whether combustion processing can be combined with spray coating to realize, at low temperatures, dense high-mobility MO films having significant, precisely controlled thicknesses in a single step and specifically, growing the most technologically relevant oxide film materials: semiconducting indium-gallium-tin oxide (IGZO) and conducting indium-tin-oxide (ITO).Here, we report a low-temperature, nanometer-thickness, controlled solution route to high-performance MO electronics through spray-combustion synthesis (SCS). Reduced gaseous byproduct trapping yields dense, high-quality, macroscopically continuous films of both crystalline and amorphous MOs. Single-layer (50-nm-thick) IGZO TFTs with carrier mobilities 10²–10⁴× greater (7–20 cm²/Vs) than those achieved with sol gel and conventional combustion synthesis are demonstrated and rival those of magnetron-sputtered IGZO TFTs. Film characterization includes the first positron annihilation spectroscopy (PAS) measurements on oxide thin films to our knowledge, X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), and capacitance-voltage (C-V) data, supporting the broad applicability of SCS.     

Fluorine-Terminated Polycrystalline Diamond Solution-Gate Field-Effect Transistor Sensor with Smaller Amount of Unexpectedly Generated Fluorocarbon Film Fabricated by Fluorine Gas Treatment

In this study, a partially fluorine-terminated solution-gate field-effect transistor sensor with a smaller amount of unexpectedly generated fluorohydrocarbon film on a polycrystalline diamond channel is described. A conventional method utilizing inductively coupled plasma with fluorocarbon gas leads the hydrogen-terminated diamond to transfer to a partially fluorine-terminated diamond (C–F diamond); an unexpected fluorohydrocarbon film is formed on the surface of the diamond. To overcome this issue, we newly applied fluorine gas for the fluoridation of the diamond. Analytical results of X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry suggest that the fluorocarbon film does not exist or only a smaller amount of fluorocarbon film exists on the diamond surface. Conversely, the C–F diamond fabricated by the conventional method of inductively coupled plasma with a perfluoropropane gas (C₃F₈ gas) source possesses a certain amount of fluorocarbon film on its surface. The C–F diamond with a smaller amount of unexpectedly generated fluorohydrocarbon film possesses nearly ideal drain–source–voltage vs. gate–source–current characteristics, corresponding to metal–oxide–silicon semiconductor field-effect transistor theory. The results indicate that the fluorine gas (F₂ gas) treatment proposed in this study effectively fabricates a C–F diamond sensor without unexpected semiconductor damage.     

阿托品敏感场效应传感器的研制和应用

本研究以阿托品-四苯硼酸缔合物为电活性物制成离子敏感膜,涂层于金属氧化物半导体场效应晶体管的栅极引出线(铂丝)上,制成涂丝阿托品敏感场效应传感器。该器件斜率为55mV,线性范围在2.0×10~(-2)～6.3×10~(-5)mol/L,检测下限为1.6×10~(-5)mol/L,pH范围在3.2～8.2。测定了阿托品片剂和注射剂的含量,经t检验,其结果与药典法基本一致。