Direct Printing of Ultrathin Block Copolymer Film with Nano-in-Micro Pattern Structures

Nanotransfer printing (nTP) is one of the most promising nanopatterning methods given that it can be used to produce nano-to-micro patterns effectively with functionalities for electronic device applications. However, the nTP process is hindered by several critical obstacles, such as sub-20 nm mold technology, reliable large-area replication, and uniform transfer-printing of functional materials. Here, for the first time, a dual nanopatterning process is demonstrated that creates periodic sub-20 nm structures on the eight-inch wafer by the transfer-printing of patterned ultra-thin (<50 nm) block copolymer (BCP) film onto desired substrates. This study shows how to transfer self-assembled BCP patterns from the Si mold onto rigid and/or flexible substrates through a nanopatterning method of thermally assisted nTP (T-nTP) and directed self-assembly (DSA) of Si-containing BCPs. In particular, the successful microscale patternization of well-ordered sub-20 nm SiOx patterns is systematically presented by controlling the self-assembly conditions of BCP and printing temperature. In addition, various complex pattern geometries of nano-in-micro structures are displayed over a large patterning area by T-nTP, such as angular line, wave line, ring, dot-in-hole, and dot-in-honeycomb structures. This advanced BCP-replicated nanopatterning technology is expected to be widely applicable to nanofabrication of nano-to-micro electronic devices with complex circuits.

Layer-Controlled Perovskite 2D Nanosheet Interlayer for the Energy Storage Performance of Nanocomposites

Polymer-based nanocomposites are desirable materials for next-generation dielectric capacitors. 2D dielectric nanosheets have received significant attention as a filler. However, randomly spreading the 2D filler causes residual stresses and agglomerated defect sites in the polymer matrix, which leads to the growth of an electric tree, resulting in a more premature breakdown than expected. Therefore, realizing a well-aligned 2D nanosheet layer with a small amount is a key challenge; it can inhibit the growth of conduction paths without degrading the performance of the material. Here, an ultrathin Sr_1.8 Bi_0.2 Nb₃ O₁₀ (SBNO) nanosheet filler is added as a layer into poly(vinylidene fluoride) (PVDF) films via the Langmuir-Blodgett method. The structural properties, breakdown strength, and energy storage capacity of a PVDF and multilayer PVDF/SBNO/PVDF composites as a function of the thickness-controlled SBNO layer are examined. The seven-layered (only 14 nm) SBNO nanosheets thin film can sufficiently prevent the electrical path in the PVDF/SBNO/PVDF composite and shows a high energy density of 12.8 J cm^-3 at 508 MV m^-1 , which is significantly higher than that of the bare PVDF film (9.2 J cm^-3 at 439 MV m^-1 ). At present, this composite has the highest energy density among the polymer-based nanocomposites under the filler of thin thickness.

Highly Reliable Threshold Switching Characteristics of Surface-Modulated Diffusive Memristors Immune to Atmospheric Changes

Active cation-based diffusive memristors featuring essentially volatile threshold switching have been proposed for novel applications, such as a selector in a one-selector-and-one-resistor structure and signal generators in neuromorphic computing. However, the high variability of the switching behavior, which results from the high electroforming voltage, external environmental conditions, and transition to the non-volatile switching mode in a high-current range, is considered a major impediment to such applications. Herein, for the first time, we developed a highly reliable threshold switching device immune to atmospheric changes based on an ultraviolet-ozone (UVO)-treated diffusive memristor consisting of Ag and SiO₂ nanorods (NRs). UVO treatment forms a stable water reservoir on the surface of SiO₂ NRs, facilitating the redox reaction and ion migration of Ag. Consequently, diffusive memristors possess reliable switching characteristics, including electroforming-free, repeatable, and consistent switching with resistance to changes in ambient conditions and compliance levels during operation. We demonstrated that our approach is suitable for various metal oxides and can be used in numerous applications.

Correlating multimode strain and electrode configurations for high-performance gradient-index phononic crystal-based piezoelectric energy harvesting

A gradient-index phononic crystal (GRIN PnC) capable of manipulating wave propagation can serve as an excellent input wave energy focusing platform for amplifying energy harvesting power generation. However, despite its remarkable focusing capability, the finite wavelength of the propagating elastic waves in the focal area causes voltage cancellation inside a piezoelectric element under multimode strains having opposite directions; this limits the capacity of the GRIN PnC-based energy harvesting system. This study demonstrates a rational electrode configuration for a piezoelectric energy harvesting (PEH) device that can maximize the performance of a given GRIN PnC platform. The multimode strain analysis experimentally performed on the PEHs distributed over the focusing area confirms that the patterned electrode PEH configuration is the most effective in alleviating strain and voltage cancellation while efficiently transferring the focused elastic wave energy. Furthermore, a proper combination of electrical connections between the patterned electrodes substantially increases the piezoelectric potential across the ceramic by maximizing the strain difference. The simultaneous tailoring of the piezoelectric ceramic composition and the electrode configuration leads to a maximum power generation of 7.06 mW even under off-resonance conditions, the largest ever reported in elastic wave energy harvesting.

Autonomous Resonance-Tuning Mechanism for Environmental Adaptive Energy Harvesting

An innovative autonomous resonance-tuning (ART) energy harvester is reported that utilizes adaptive clamping systems driven by intrinsic mechanical mechanisms without outsourcing additional energy. The adaptive clamping system modulates the natural frequency of the harvester's main beam (MB) by adjusting the clamping position of the MB. The pulling force induced by the resonance vibration of the tuning beam (TB) provides the driving force for operating the adaptive clamp. The ART mechanism is possible by matching the natural frequencies of the TB and clamped MB. Detailed evaluations are conducted on the optimization of the adaptive clamp tolerance and TB design to increase the pulling force. The energy harvester exhibits an ultrawide resonance bandwidth of over 30 Hz in the commonly accessible low vibration frequency range (<100 Hz) owing to the ART function. The practical feasibility is demonstrated by evaluating the ART performance under both frequency and acceleration-variant conditions and powering a location tracking sensor.

Antibiotic use reduces efficacy of tyrosine kinase inhibitors in patients with advanced melanoma and non-small-cell lung cancer

Background

Antibiotic (ABX) use can reduce the efficacy of immune checkpoint inhibitors and chemotherapeutics. The effect for patients treated with targeted therapies, namely, small-molecule tyrosine kinase inhibitors (TKIs), is less known.

Patients and methods

Retrospective data were analysed for TKI-treated patients with advanced melanoma and non-small-cell lung cancer (NSCLC) between January 2015 and April 2017 at The Christie NHS Foundation Trust. Data on demographics, disease burden, lactate dehydrogenase (LDH) level, presence of brain metastases, ECOG performance status (PS) and ABX use were collected. Progression-free survival (PFS) and overall survival (OS) were compared between the ABX+ group (ABX within 2 weeks of TKI initiation-6 weeks after) and the ABX– group (no ABX during the same period).

Results

A total of 168 patients were included; 89 (53%) with NSCLC and 79 (47%) with melanoma. 55- (33%) patients received ABX. On univariable analysis, ABX+ patients demonstrated shorter PFS (208 versus 357 days; P = 0.008) and OS (294 versus 438 days; P = 0.024). Increased age, poorer PS and higher LDH were associated with shorter PFS and OS. On multivariable analysis, ABX use was independently associated with shorter PFS [hazard ratio (HR) 1.57, 95% confidence interval (CI) 1.05-2.34, P = 0.028] and OS (HR 2.19, 95% CI 1.44-3.32, P = 0.0002). The negative impact of ABX on OS was particularly pronounced for patients with PS of ≥2 (HR 3.82, 95% CI 1.18-12.36, P = 0.025).

Conclusion

For patients treated with TKIs, ABX use is independently associated with reduced PFS and OS and judicious use is warranted, particularly in patients with poorer PS.

Antibiotic use can reduce the efficacy of some systemic anticancer therapies.

The effect for patients treated with TKIs is less known.

This is a retrospective review of 168 patients with advanced melanoma and NSCLC treated with TKIs.

Patients on ABXs showed shorter progression-free (208 versus 357 days) and overall survival (294 versus 438 days).

ABX use was independently associated with shorter PFS (HR 1.57, P = 0.028) and OS (HR 2.19, P = 0.0002).

Heterointerface Effect on Two-Step Nucleation Mechanism of Bi Particles

The nucleation and crystallization of Bi particles on two matrices, crystalline bismuth sulfide (c-Bi₂S₃) and amorphized bismuth titanium oxide (a-Bi₁₂TiO₂₀), were studied by using in situ transmission electron microscopy (TEM) analysis. The atomic structures of the Bi particles were monitored by acquiring high-resolution TEM images in real time. The Bi particles were grown on c-Bi₂S₃ and a-Bi₁₂TiO₂₀ via a two-step nucleation mechanism; dense liquid clusters were clearly observed at the initial stage of nucleation, and the coalescence of clusters was frequently observed during the growth. However, the nucleation and crystallization behaviors of Bi particles were governed by the matrix; in particular, the evolution of their morphology and atomic structure was confined on c-Bi₂S₃ but free from matrix effects on a-Bi₁₂TiO₂₀. The matrix effect on the two-step nucleation mechanism was demonstrated from a thermodynamic point of view.

Optimization of Hybrid Ink Formulation and IPL Sintering Process for Ink-Jet 3D Printing

Ink-jet 3D printing technology facilitates the use of various materials of ink on each ink-jet head and simultaneous printing of multiple materials. It is suitable for manufacturing to process a complex multifunctional structure such as sensors and printed circuit boards. In this study, a complex structure of a SiO₂ insulation layer and a conductive Cu layer was fabricated with photo-curable nano SiO₂ ink and Intense Pulsed Light (IPL)-sinterable Cu nano ink using multi-material ink-jet 3D printing technology. A precise photo-cured SiO₂ insulation layer was designed by optimizing the operating conditions and the ink rheological properties, and the resistance of the insulation layer was 2.43 × 10¹³ Ω·cm. On the photo-cured SiO₂ insulation layer, a Cu conductive layer was printed by controlling droplet distance. The sintering of the IPL-sinterable nano Cu ink was performed using an IPL sintering process, and electrical and mechanical properties were confirmed according to the annealing temperature and applied voltage. Then, Cu conductive layer was annealed at 100 °C to remove the solvent, and IPL sintered at 700 V. The Cu conductive layer of the complex structure had an electrical property of 29 µΩ·cm and an adhesive property with SiO₂ insulation layer of 5B.

Piezoelectric Energy Harvesting Design Principles for Materials and Structures: Material Figure-of-Merit and Self-Resonance Tuning

Piezoelectric energy harvesters (PEHs) aim to generate sufficient power to operate targeting device from the limited ambient energy. PEH includes mechanical-to-mechanical, mechanical-to-electrical, and electrical-to-electrical energy conversions, which are related to PEH structures, materials, and circuits, respectively; these should be efficient for increasing the total power. This critical review focuses on PEH structures and materials associated with the two major energy conversions to improve PEH performance. First, the resonance tuning mechanisms for PEH structures maintaining continuous resonance, regardless of a change in the vibration frequency, are presented. Based on the manual tuning technique, the electrically- and mechanically-driven self-resonance tuning (SRT) techniques are introduced in detail. The representative SRT harvesters are summarized in terms of tunability, power consumption, and net power. Second, the figure-of-merits of the piezoelectric materials for output power are summarized based on the operating conditions, and optimal piezoelectric materials are suggested. Piezoelectric materials with large k_ij , d_ij , and g_ij values are suitable for most PEHs, whereas those with large k_ij and Q_m values should be used for on-resonance conditions, wherein the mechanical energy is directly supplied to the piezoelectric material. This comprehensive review provides insights for designing efficient structures and selection of proper piezoelectric materials for PEHs.

Subwavelength Hollow-Nanopillared Glass with Gradient Refractive Index for Ultralow Diffuse Reflectance and Antifogging

Nanostructured glass with subwavelength hollow nanopillars of diameters of sub-65 nm was fabricated, showing high optical transmittance and ultralow diffuse reflectance. A simple process involving single-step plasma etching was used on a glass slide coated with a SiO₂ sacrificial film. First, SiO₂ nanodot structures were formed using plasma-induced anisotropic etching with CF₄ plasma. The SiO₂ nanodot array then became a secondary etching mask to form hollow nanopillars on the glass. The hollow structures formed at the upper part reaching up to the apex of the nanopillar had a lower solid fraction, while the lower part had a higher fraction. The refractive index (RI) gradually increased from 1.09 (near the value for air) to 1.42 (near the value for glass). Geometry-induced RI gradient enhanced light transmi, while it significantly reduced diffuse reflectance, particularly in the shorter wavelengths, thus suppressing the haziness or milky appearance of the nanostructured glass. Superhydrophilic and antifogging properties of nanostructured glasses and dental mirrored glasses were also demonstrated with water spraying and exhaled breath tests. Results showed that the wettability was enhanced in hydrophilicity and antifogging property by both the hydrophilic nature of the glass and the newly formed nanostructures. The nanostructured, superhydrophilic glass was also found to have easy cleaning nature against fine sand dust adhesion by simply blowing air or spraying water. Results of this study showed that such a hollow-pillared glass surface with gradient RI and special wettability could be applied in a variety of optical and optoelectronic applications requiring superwetting, such as optical windows for solar cell panels, display panels, light-emitting diodes, and medical devices even with curved surfaces.

Improvement of Conductance Modulation Linearity in a Cu2+-Doped KNbO3 Memristor through the Increase of the Number of Oxygen Vacancies

The Pt/KNbO₃/TiN/Si (KN) memristor exhibits various biological synaptic properties. However, it also displays nonlinear conductance modulation with the application of identical pulses, indicating that it should be improved for neuromorphic applications. The abrupt change of the conductance originates from the inhomogeneous growth/dissolution of oxygen vacancy filaments in the KN film. The change of the filaments in a KN film is controlled by two mechanisms with different growth/dissolution rates: a redox process with a fast rate and an oxygen vacancy diffusion process with a slow rate. Therefore, the conductance modulation linearity can be improved if the growth/dissolution of the filaments is controlled by only one mechanism. When the number of oxygen vacancies in the KN film was increased through doping of Cu²⁺ ions, the growth/dissolution of the filaments in the Cu²⁺-doped KN (CKN) film was mainly influenced by the redox process of oxygen vacancies. Therefore, the CKN film exhibited improved conductance modulation linearity, confirming that the linearity of conductance modulation can be improved by increasing the number of oxygen vacancies in the memristor. This method can be applied to other memristors to improve the linearity of conductance modulation. The CKN memristor also provides excellent biological synaptic characteristics for neuromorphic computing systems.

Improvement of Conductance Modulation Linearity in a Cu2+-Doped KNbO3 Memristor through the Increase of the Number of Oxygen Vacancies

The Pt/KNbO₃/TiN/Si (KN) memristor exhibits various biological synaptic properties. However, it also displays nonlinear conductance modulation with the application of identical pulses, indicating that it should be improved for neuromorphic applications. The abrupt change of the conductance originates from the inhomogeneous growth/dissolution of oxygen vacancy filaments in the KN film. The change of the filaments in a KN film is controlled by two mechanisms with different growth/dissolution rates: a redox process with a fast rate and an oxygen vacancy diffusion process with a slow rate. Therefore, the conductance modulation linearity can be improved if the growth/dissolution of the filaments is controlled by only one mechanism. When the number of oxygen vacancies in the KN film was increased through doping of Cu²⁺ ions, the growth/dissolution of the filaments in the Cu²⁺-doped KN (CKN) film was mainly influenced by the redox process of oxygen vacancies. Therefore, the CKN film exhibited improved conductance modulation linearity, confirming that the linearity of conductance modulation can be improved by increasing the number of oxygen vacancies in the memristor. This method can be applied to other memristors to improve the linearity of conductance modulation. The CKN memristor also provides excellent biological synaptic characteristics for neuromorphic computing systems.

Highly Sensitive and Selective PbTiO3 Gas Sensors with Negligible Humidity Interference in Ambient Atmosphere

Three PbTiO₃ nanostructures were synthesized using a one-step hydrothermal reaction with different TiO₂ powders as Ti sources, and their gas-sensing properties were investigated. The sensor comprising PbTiO₃ nanoplates (NPs) exhibited a high response (resistance ratio = 80.4) to 5 ppm ethanol at 300 °C and could detect trace concentrations of ethanol down to 100 ppb. Moreover, the sensor showed high ethanol selectivity and nearly the same sensing characteristics despite the wide range of humidity variation from 20 to 80% RH. The mechanism for humidity-independent gas sensing was elucidated using diffuse reflectance infrared Fourier transform spectra. PbTiO₃ NPs are new and promising sensing materials that can be used for detecting ethanol in a highly sensitive and selective manner with negligible interference from ambient humidity.

Physical Properties of (Na1- xK x)NbO3 Thin Film Grown at Low Temperature Using Two-Dimensional Ca2Nb3O10 Nanosheet Seed Layer

A monolayer Ca₂Nb₃O₁₀ (CNO) nanosheet was deposited on a Pt/Ti/SiO₂/Si substrate using the Langmuir-Blodgett method. This monolayer CNO nanosheet with a (001) surface termination was used as a seed layer to reduce the growth temperature of the crystalline (Na_{1- x}K _x)NbO₃ (NKN) film. The crystalline NKN film was preferentially grown along the [001] direction at 400 °C. The ferroelectric and piezoelectric properties of this NKN film were influenced by the postannealing atmosphere due to the variations in the amounts of oxygen vacancies in the NKN film. The crystalline NKN film annealed at 300 °C under 50 Torr O₂ atmosphere showed promising ferroelectric and piezoelectric properties; ε_r of 303 and tan δ of 2.0% at 100 kHz, P_s of 15.3 μC/cm², P_r of 11.7 μC/cm², and E_c of 78 kV/cm, and d₃₃ of 139 pm/V. This NKN film showed the lowest leakage current, which can be explained by the Schottky emission mechanism. The Schottky barrier heights of the Pt/NKN and NKN/CNO/Pt interfaces were calculated to be 0.97 and 0.28 eV, respectively. The results of this work suggest a new method to grow crystalline thin films at low temperatures by using metal-oxide nanosheets as the seed layer.

Synaptic Plasticity and Metaplasticity of Biological Synapse Realized in a KNbO3 Memristor for Application to Artificial Synapse

Amorphous KNbO₃ (KN) films were grown on a TiN/SiO₂/Si substrate to synthesize a KN memristor as a potential artificial synapse. The Pt/KN/TiN memristor exhibited typical and reliable bipolar switching behavior with multiple resistance levels. It also showed the transmission properties of a biological synapse, with a good conductance modulation linearity. Moreover, the KN memristor can emulate various biological synaptic plasticity characteristics including short-term plasticity, long-term plasticity, spike-rate dependent plasticity, paired-pulse facilitation, and post-tetanic potentiation by controlling the number and rate of the potentiation spike. Spike-timing-dependent plasticity (STDP), which is an essential property of biological synapses, is also realized in the KN memristor. The synaptic plasticity of the KN memristor can be explained by oxygen vacancy movement and oxygen vacancy filaments. The metaplasticity of biological synapses was also implemented in the KN memristor, including the metaplasticity of long-term potentiation and depression, and of STDP. Therefore, the KN memristor could be used as an artificial synapse in neuromorphic computing systems.

Low-Temperature-Grown KNbO3 Thin Films and Their Application to Piezoelectric Nanogenerators and Self-Powered ReRAM Device

Amorphous KNbO₃ (KN) film containing KN nanocrystals was grown on TiN/SiO₂/Si substrate at 350 °C. This KN film showed a dielectric constant (ε_r) and a piezoelectric strain constant (d₃₃) of 43 and 80 pm/V at 10 V, respectively, owing to the existence of KN nanocrystals. Piezoelectric nanogenerators (PNGs) were fabricated using KN films grown on the TiN/polyimide/poly(ethylene terephthalate) substrates. The PNG fabricated with the KN film grown at 350 °C showed an open-circuit output voltage of 2.5 V and a short-circuit current of 70 nA. The KN film grown at 350 °C exhibited a bipolar resistive switching behavior with good reliability characteristics that can be explained by the formation and rupture of the oxygen vacancy filaments. The KN resistive random access memory device powered by the KN PNG also showed promising resistive switching behavior. Moreover, the KN film shows good biocompatibility. Therefore, the KN film can be used for self-powered biomedical devices.

Flexible Indium-Tin Oxide Crystal on Plastic Substrates Supported by Graphene Monolayer

Flexible and crystallized indium–tin oxide (ITO) thin films were successfully obtained on plastic polyethylene terephthalate (PET) films with monolayered graphene as a platform. The highly crystalline ITO (c-ITO) was first fabricated on a rigid substrate of graphene on copper foil and it was subsequently transferred onto a PET substrate by a well-established technique. Despite the plasma damage during ITO deposition, the graphene layer effectively acted as a Cu-diffusion barrier. The c-ITO/graphene/PET electrode with the 60-nm-thick ITO exhibited a reasonable sheet resistance of ~45 Ω sq⁻¹ and a transmittance of ~92% at a wavelength of 550 nm. The c-ITO on the monolayered graphene support showed significant enhancement in flexibility compared with the ITO/PET film without graphene because the atomically controlled monolayered graphene acted as a mechanically robust support. The prepared flexible transparent c-ITO/graphene/PET electrode was applied as the anode in a bulk heterojunction polymer solar cell (PSC) to evaluate its performance, which was comparable with that of the commonly used c-ITO/glass electrode. These results represent important progress in the fabrication of flexible transparent electrodes for future optoelectronics applications.

Sintering and Microstructure of BaTiO3 Nano Particles Synthesized by Molten Salt Method

In order to establish thinner dielectric layers in thick film electronic components such as MLCC (Multilayer ceramic capacitor), BaTiO3 nanoparticles have been utilized. However, studies on the synthesis of nanoparticles smaller than 20 nm, the characteristics of the BaTiO3 powder, and the powder's sintering are lacking. Therefore, this paper aims to synthesize BaTiO3 particles smaller than 20 nm by using the molten salt method and evaluate the microstructure and dielectric properties by varying the sintering temperature from 750 degrees C to 1200 degrees C. Through the molten salt method and by using KOH-KCl mixed salt, 20 nm BaTiO3 powder was synthesized at a low temperature of 150 degrees C. Sintering the pellets formed from the synthesized 20 nm BaTiO3 nano powder led to the observation of an unusual phenomenon where the particles grew to approximate sizes below 850 degrees C where densification progressed. At sintering temperatures above 950 degrees C, particles that expanded into rod shapes were observed and these particles were identified to be unreacted TiO2 based on the results of the EDX (Energy Dispersive X-ray Spectroscopy) analysis and phase analysis results.

Enhanced piezoelectric properties of vertically aligned single-crystalline NKN nano-rod arrays

Piezoelectric materials capable of converting between mechanical and electrical energy have a great range of potential applications in micro- and nano-scale smart devices; however, their performance tends to be greatly degraded when reduced to a thin film due to the large clamping force by the substrate and surrounding materials. Herein, we report an effective method for synthesizing isolated piezoelectric nano-materials as means to relax the clamping force and recover original piezoelectric properties of the materials. Using this, environmentally friendly single-crystalline Na_xK_1-xNbO₃ (NKN) piezoelectric nano-rod arrays were successfully synthesized by conventional pulsed-laser deposition and demonstrated to have a remarkably enhanced piezoelectric performance. The shape of the nano-structure was also found to be easily manipulated by varying the energy conditions of the physical vapor. We anticipate that this work will provide a way to produce piezoelectric micro- and nano-devices suitable for practical application, and in doing so, open a new path for the development of complex metal-oxide nano-structures.

Enhanced electrochemical performance of a ZnO–MnO composite as an anode material for lithium ion batteries

A reduced ZnO–MnO composite electrode exhibits improved electrochemical performance as an anode material for lithium ion batteries.

Electrochemical properties of Sn-substituted LiMn2O4 thin films prepared by radio-frequency magnetron sputtering

The LiMn2O4 and LiSn0.0125Mn1975O4 thin films were grown on Pt/Ti/SiO2/Si (100) substrate by RF magnetron sputtering. To obtain the structural stability and good cycle performance, deposition parameters, namely working pressure, sputtering gas ratio of Ar and O2, post-annealing temperature were established. The structure and surface morphology of thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemical properties were estimated by two electrode half-cell test with WBCS 3000 (Wonatech, Korea) at constant current rate of 1 C-rate. The Sn substituted LiMn2O4 thin film deposited at 10 mtorr with mixture of argon and oxygen (Ar/O2 = 3/1) and then annealed at 500 degrees C in O2 atmosphere showed good cycle performance. The Sn substituted LiMn2O4 thin films showed larger capacity of -30 microAh/microm-cm2 and higher cyclability than LiMn2O4 thin films.

Resistance random access memory based on a thin film of CdS nanocrystals prepared via colloidal synthesis

We demonstrate that resistance random access memory (RRAM) can be fabricated based on CdS-nanocrystal thin films. A simple drop-drying of the CdS-nanocrystal solution leads to the formation of uniform thin films with controlled thickness. RRAMs with a Ag/Al(2) O(3) /CdS/Pt structure show bipolar switching behavior, with average values of the set voltage (V(Set) ) and reset voltage (V(Reset) ) of 0.15 V and -0.19 V, respectively. The RRAM characteristics are critically influenced by the thickness of the Al(2) O(3) barrier layer, which prevents significant migration of Ag into the CdS layer as revealed by Auger electron spectroscopy (AES). Interestingly, RRAM without an Al(2) O(3) layer (i.e., Ag/CdS/Pt structure) also shows bipolar switching behavior, but the polarity is opposite to that of RRAM with the Al(2) O(3) layer (i.e., Ag/Al(2) O(3) /CdS/Pt structure). The operation of both kinds of devices can be explained by the conventional conductive bridging mechanism. Additionally, we fabricated RRAM devices on Kapton film for potential applications in flexible electronics, and the performance of this RRAM device was comparable to that of RRAMs fabricated on hard silicon substrates. Our results show a new possibility of using chalcogenide nanocrystals for RRAM applications.

Synthesis of lead-free (K, Na)(Nb, Ta)O3 nanopowders using a sol-gel process

Lead-free (K0.5Na0.5)(Nb0.7Ta0.3)O3 piezoelectric material was successfully synthesized via a sol-gel process. Crystalline (K0.5Na0.5)(Nb0.7Ta0.3)O3 nanopowders were obtained after heat treatment at 700 degrees C. The particle size was estimated to be 87nm +/- 23 nm. The transmission electron microscopy images showed that individual nanoparticles were single crystalline and had a pseudo-cubic structure with a lattice parameter of -3.96 angstroms. Both X-ray diffraction and scanning electron microscopy studies consistently showed that the crystallization of the (K0.5Na0.5)(Nb0.7Ta0.3)O3 occurred slightly above 500 degrees C. The samples have an appropriate stoichiometry as found via energy dispersive X-ray spectroscopy. The demonstration of the synthesis of (K0.5Na0.5)(Nb0.7Ta0.3)O3 via a sol-gel process as presented in this paper can provide an important foundation for the development of a synthetic route towards (K0.5Na0.5)(Nb0.7Ta0.3)O3 doped with various other elements for high performance piezoelectric devices.

Low-voltage-driven pentacene thin-film transistors with cross-linked poly(4-vinylphenol)/high-k Bi55b3O15 hybrid dielectric for phototransistor

This paper describes the fabrication of pentacene thin-film transistors (TFTs) with an organic/inorganic hybrid gate dielectric, consisting of cross-linked poly(4-vinylphenol) (PVP) and Bi5Nb3O15. A 300-nm-thick Bi5Nb3O15 dielectric film, grown at room temperature, exhibits a high dielectric constant (high-k) value of 40 but has an undesirable interface with organic semiconductors (OSC). To form better interfaces with OSC, a cross-linked PVP dielectric was stacked on the Bi5Nb3O15 dielectric. It is shown that, with the introduction of a hybrid dielectric, our devices not only can be operated at a low voltage (- -5 V) but also have improved electrical characteristics and photoresponse, including a field-effect mobility of 0.72 cm2/V x s, current sub-threshold slopes of 0.29 V/decade, and a photoresponse of 4.84 at a gate bias V(G) = 0 V under 100 mW/cm2 AM 1.5 illumination.

Optical study of Mn-doped Bi4Ti3O,12 thin films by spectroscopic ellipsometry

Mn-doped Bi4Ti3O12(B4T3) thin films grown at 400 degrees C on a Pt/Ti/SiO2/Si substrate through pulsed laser deposition (PLD) were analyzed via spectroscopic ellipsometry (SE). The PLD targets were produced through the conventional solid-state sintering method, and the film samples were annealed at 600 degrees C. The SE spectra of B4T3 films were measured using a rotating analyzer type ellipsometer within the 1.12 to 6.52 eV energy range, with the various incidence angles. The optical properties of the B4T3 films with increasing Mn-mol concentration were extracted using a multilayer model for the whole structure and the Tauc-Lorentz (TL) dispersion relation for the B4T3 film layer. The analysis results clearly showed that the significant changes in optical properties of B4T3 films are caused by thermal annealing procedure and the Mn-mol concentrations. X-ray diffraction (XRD) measurement was also performed to confirm the results of SE analysis.

BaTiO3 doped Na0.5K0.5NbO3 thin films deposited by using eclipse shutter enhanced pulsed laser deposition method

We have investigated structural, electrical, and electro-mechanical properties of lead-free piezoelectric BaTiO3 doped Na0.5K0.5NbO3 (BTO-NKN) thin films deposited by pulsed laser deposition (PLD) methods. BTO-NKN thin films have been deposited on La0.5Sr0.5CoO3 (LSCO) bottom electrodes with LaAlO3 (LAO) substrates. X-ray diffraction data have shown that all the BTO-NKN and bottom electrodes are highly oriented with their c-axes normal to the substrates. In order to improve the morphology of BTO-NKN thin films, we have located an eclipse shutter between a target and a substrate. Root-mean-square roughness was changed from 91 nm to 21 nm with eclipse shutter enhanced PLD (E-PLD) method. Furthermore, the enhanced surface morphology leads to the improvement in electrical or electro-mechanical properties mainly due to increased density. Typical capacitance and d33 values of a BTO-NKN film deposited by E-PLD method are 1000 pF and 30 pmN, respectively.

Microstructure and piezoelectric properties of (Na0.5K0.5)NbO3 lead-free piezoelectric ceramics with V2O5 addition

Various amounts of Nb(2)O(5) in the (Na(0.5)K(0.5)) NbO(3) (NKN) ceramic were replaced by V(2)O(5) to decrease its sintering temperature to below 950 degrees C. A small V(2)O(5) content resulted in a dense microstructure with an increased grain size for the specimen sintered at 900 degrees C due to the presence of a liquid phase. When V(2)O(5) was added to the NKN ceramics, their orthorhombic-to-tetragonal transition temperature increased from 178 degrees C to around 200 degrees C. However, their Curie temperature decreased from 402 degrees C to around 330 degrees C. The k(p), epsilon(3) (T)/epsilon(0), and Q(m) values increased with V(2)O(5) addition, probably due to the increased density and poling state, which was identified by the phase angle. The specimen with x = 0.05, sintered at 900 degrees C for 8 h, exhibited the following piezoelectric properties: k(p) = 0.32, epsilon(3) (T)/epsilon(0) = 245, d(33) = 120 (pC/N), and Q(m) = 232.

A flexible amorphous Bi(5)Nb(3)O(15) film for the gate insulator of the low-voltage operating pentacene thin-film transistor fabricated at room temperature

The amorphous Bi(5)Nb(3)O(15) film grown at room temperature under an oxygen-plasma sputtering ambient (BNRT-O(2) film) has a hydrophobic surface with a surface energy of 35.6 mJ m(-2), which is close to that of the orthorhombic pentacene (38 mJ m(-2)), resulting in the formation of a good pentacene layer without the introduction of an additional polymer layer. This film was very flexible, maintaining a high capacitance of 145 nF cm(-2) during and after 10(5) bending cycles with a small curvature radius of 7.5 mm. This film was optically transparent. Furthermore, the flexible, pentacene-based, organic thin-film transistors (OTFTs) fabricated on the poly(ether sulfone) substrate at room temperature using a BNRT-O(2) film as a gate insulator exhibited a promising device performance with a high field effect mobility of 0.5 cm(2) V(-1) s(-1), an on/off current modulation of 10(5), and a small subthreshold slope of 0.2 V decade(-1) under a low operating voltage of -5 V. This device also maintained a high carrier mobility of 0.45 cm(2) V(-1 )s(-1) during the bending with a small curvature radius of 9 mm. Therefore, the BNRT-O(2) film is considered a promising material for the gate insulator of the flexible, pentacene-based OTFT.

Luminescence properties of Ca(Y(0.915-x)Gd(x)Al0.025Eu0.06)BO4 phosphors under VUV irradiation

The major phase of post-treated Ca(Y(0.915-x)Gd(x)A10.025Eu0.06)BO4 (0 < or = x < or = 0.3) phosphors was solid solutions of the constituent oxides, which had an orthorhombic warwickite-like structure. The calculated crystallite size of the Ca(Y(0.915-x)Gd(x)Al0.025Eu0.06)BO4 phosphors was approximately 36 nm. The Gd additive significantly enhanced both the charge transfer (CT) transition of O2(-) -Eu3+ and the absorption of the host materials, thereby resulting in an increase in emission intensity. The Ca(Y(0.715)Gd0.2Al0.025Eu0.06)BO4 phosphor showed the highest emission intensity at 593 nm, which was over five times as strong as that of a Gd-free Ca(Y0.915Al0.025Eu0.06)BO4 phosphor. The addition of Gd was desirable for improving the photoluminescent properties of red-emitting Ca(Y0.915Al0.025Eu0.06)BO4 phosphors.

Photoluminescent properties of (la(1-x)Y(x))(0.94)Tb(0.06)PO4 phosphor powders prepared by ultrasonic spray pyrolysis

The calculated crystallite sizes of (La(1-x)Y(x))(0.94)Tb(0.06)PO4 (0 < or = x < or = 1.0) phosphors ranged from 37-39 nm. Annealed (La(1-x)Y(x))(0.94)Tb(0.06)PO4 (0 < or = x < or = 1.0) phosphors showed a smooth, regular, and spherical morphology. Strong excitation peaks were appeared at 226 and 270 nm for all the phosphors. These were caused by the crystal splitting of 7D and 9D of 4f75d1 configuration in Tb3+, respectively. The characteristic emission peaks were observed at 489, 543, 585, and 621 nm, which were caused by the 5D4-7F(j) (j = 6-3) transitions of Tb3+, respectively. The emission intensity at 543 nm increased with an increase in Y content up to 0.5 and then decreased for a higher Y content.

Synthesis of carbon-nitrogen nanostructures by hot isostatic pressure apparatus and their field emission properties

Carbon-nitrogen (CN) nanofibers were synthesized in argon-nitrogen gas mixture at 75 MPa by high isostatic pressure (HIP) apparatus using a graphite resistive heater. The CN nanofibers were grown in random with the diameter of about 200 nm and the length over 5 microm. The structures obtained can be divided bamboo-like, spring-like, and bead necklace-like CN nanofibers. The nitrogen content of up to 8.4% was found in CN nanofibers by EELS analysis. Field emission results showed that the density of field emitters and the field enhancement factors changed by surface treatments and that CN nanofibers contained glass frit. The screen-printed CN nanofiber had a turn-on field of 2 V/microm.

Synthesis of Double-Walled Carbon Nanotubes by Catalytic Chemical Vapor Deposition and Their Field Emission Properties

Double-walled carbon nanotubes (DWCNTs) were synthesized by catalytic chemical vapor deposition using Fe-Mo/MgO as a catalyst at 1000 degrees C under the mixture of methane and hydrogen gas. The nanotubes were purified by acid but were not damaged. Thermogravimetric analysis revealed the purity of the tubes to be about 90%. The high-resolution transmission electron microscopy image showed that DWCNTs have inner tube diameters of 1.4-2.6 nm and outer tube diameters of 2.3-3.4 nm. We observed radial breathing modes in Raman spectra, which are related to the diameter of inner nanotubes. The purified DWCNTs were mixed with organic vehicles and glass frit, and then they were screen-printed on glass substrate coated with indium tin oxide. The field emission properties of the screen-printed DWCNT films were examined by varying the amount of glass frit ingredient within the DWCNT paste. The results showed that DWCNT emitters had good emission properties such as turn-on field of 1.33-1.78 V/microm and high brightness. When the applied anode voltage was gradually increased, current density and brightness became saturated. We also observed DWCNTs adsorbed on the anode plate; they were DWCNTs peeled off from the cathode plate for field emission measurement.