Search

Bi12GeO20 ceramics sintered at 800°C had dense microstructures, with an average grain size of 1.5 μm, a relative permittivity (er) of 36.97, temperature coefficient of resonance frequency (τf) of −32.803 ppm/°C, and quality factor (Q × f) of 3137 GHz. The Bi12-xGeO20-1.5x ceramics were well sintered at both 800°C and 825°C, with average grain sizes exceeding 100 μm for x ≤ 1.0. However, the grain size decreased for x > 1.0 because of the Bi4Ge3O12 secondary phase that formed at the grain boundaries. Bi12-xGeO20-1.5x (x ≤ 1.0) ceramics showed increased Q × f values of >10 000 GHz, although the er and τf values were similar to those of Bi12GeO20 ceramics. The increased Q × f value resulted from the increased grain size. In particular, the Bi11.6GeO19.4 ceramic sintered at 825°C for 3 h showed good microwave dielectric properties of er = 37.81, τf = −33.839 ppm/°C, and Q × f = 14 455 GHz.

Flexible piezoelectric generators have attracted considerable attention in recent years on account of their potential applications in mechanical energy scavenging devices using portable, wearable, and implantable electronics. Key issues for realizing a flexible piezoelectric generator include insufficient output power generation and poor efficiency at low frequency. We therefore propose structural approaches to enhancing the output power of the flexible piezoelectric generator using polyvinylidene fluoride. Specifically, we propose the use of a substrate and curved structure, and optimization of the aspect ratio of the generator for maximizing output power density. Through these approaches, induced stress and output voltage of the generator are analyzed by finite element modeling and validated through experiments. Considering these results for generator optimization, we fabricate a multilayered flexible curved generator, which produces ~200 V of the peak output voltage and ~2.7 mA of the peak output current. The output power density of the generator reaches ~17 mW/cm 2 , which is sufficient to drive various commercial electronics as a power source. Furthermore, it is demonstrated that this power source can illuminate 952 LED bulbs. This conceptual technology can provide the groundwork to enhancing the output power of conventional piezoelectric generators, thereby enabling novel approaches to realizing self-powered systems.

Here we report comprehensive study of 2DEG at a-LAO/STO interfaces in comparison with 2DEG at crystalline LaAlO3 (c-LAO)/STO interfaces. We observe that the oxygen deficient environment during the deposition of LAO overlayer is essentially required to create 2DEG at LAO/STO interface regardless of growth temperature from 25°C to 700°C, indicating that the oxygen-poor condition in the system is more important than the crystallinity of LAO layer. The critical thickness (2.6 nm) of 2DEG formation at a-LAO/STO heterostructure is thicker than (1.6 nm) that at c-LAO/STO. Upon ex-situ annealing at 300°C under 300 mTorr of oxygen pressure, 2DEG at a-LAO/STO interface is annihilated, while that in c-LAO/STO interface is still maintained. With combing these findings and scanning transmission electron microscope (STEM) analysis, we suggest that oxygen vacancies at the LAO surface is attributed to the origin of 2DEG formation at the LAO/STO and the crystallinity of the LAO overlayer plays a critical role in the annihilation of 2DEG at a-LAO/STO interface rather than in the formation of 2DEG. This work provides a framework to understand the importance of prohibiting the LAO surface from being oxidized for achieving thermally stable 2DEG at a-LAO/STO interface.

We report on the effect of the excimer laser annealing on the electronic properties of indium tin oxide (ITO) sol–gel films by using spectroscopic ellipsometric technique. We found that the excimer laser annealing effectively induces the crystallization as well as condensation of the sol–gel film. As the laser power increased, the carrier concentration and the relaxation time of photo-annealed films increased, with the bandgap shifting to higher energies. Simultaneously, the extinction coefficient values in the visible region were reduced significantly. We suggest that the excimer laser annealing should be a promising method for low temperature preparation of the ITO film on heat-sensitive substrates via the sol–gel process.

Piezoelectric energy harvesters typically exhibit sharp peak in output power around resonance frequency (small bandwidth), which presents complexity in harvesting ambient vibrations that normally comprise of multiple frequencies. Prior attempts in designing energy harvesters with broadband response have met with practical challenges in terms of low output power, large mass and weight, and small improvements in bandwidth. Here, we report a breakthrough in demonstrating ultra-wide bandwidth piezoelectric energy harvesters through the automatic resonance tuning (ART) phenomenon. ART provides energy harvester ability to adjust its natural frequency in conjunction with ambient vibration without human intervention or additional tuning energy. The ART energy harvester utilizes the motion of the mobile proof mass in a doubly clamped oscillating beam structure to modulate the natural frequency of the beam. Detailed investigations are conducted in providing a fundamental understanding of the operation mechanism of the ART harvester by invoking beam dynamics over a wide range of vibration conditions. It is shown that bandwidth of the ART harvester (36 Hz) is 1400% larger compared to the fixed resonance energy harvester. The practical feasibility of the ART mechanism is demonstrated by evaluating the performance of the harvester mounted on a rotary pump. The results demonstrate that ART mechanism can provide the much-needed breakthrough in the deployment of mechanical energy harvesters for naturally occurring vibrations.

Microbial forensics, exploiting bacteria, archaea, and eukaryotes, has been considered as one of the primary fields to trace the postmortem interval from the decaying cadavers. On the other hand, there remain several challenges of laboratory-based analysis for prediction of postmortem interval, including long-time measurement, complicated measuring procedure, and bacterial growth while carrying samples from the scene. Herein, we introduce the Smart Forensic Kit, which consists of a highly sensitive colorimetric gas sensor, a quality control algorithm, and a smartphone-based analysis method, to quantify the bacterial-derived ammonia gas in real-time. As a result, the estimation system of the postmortem interval has a superior selectivity to the ammonia gas with a detection limit of 38.7 ppb, response linearity to the target bacteria (Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas putida), and short measuring time (10 min) with the maximum predicted postmortem interval from the mouse carcass (168 h). Furthermore, thanks to measuring the postmortem interval within 10 min, the negligible increase rate of bacterial concentration was observed. Consequently, the results reflected a high correlation between the ammonia gas emitted from bacteria and the postmortem interval so that we believe the Smart Forensic Kit will be applied for tracing down the decomposition of the cadavers in the near future.

Despite the many studies reporting mW-level power output from various hybridized energy harvesters, few succeeded in demonstrating real-life applications such as the commercial Internet of Things (IoT) sensor modules. This owes in large part to the limited time-averaged power output, especially under the requirement for the power-consuming circuitry such as rectifiers and AC to DC converters. At the heart of the limited power lies the lack of detailed analyses and optimization strategies to hybridizing two or more distinct energy harvesters. Here, we first develop design guidelines and optimization strategies based on a parametric model for hybridized energy harvesters coupling two or more distinct mechanisms. The model treats electric current-generating energy harvesters as electric dampers in the spring-mass-damper system and seeks to minimize the total damping consisting of electrical and mechanical damping. We then demonstrate the design guidelines to an oval-shaped hybrid energy harvester consisting of piezoelectric and electromagnetic generators, achieving the time-averaged power output of 25.45 mW at 60 Hz and 0.5 G input vibration. Also, the detailed analyses reveal that the two coupled generators operate in a complementary manner, maintaining a reasonable power output even when one generator suddenly degrades or fails. We finally demonstrate powering a commercial IoT sensor module with the hybrid energy harvester, receiving the sensed information to a smartphone via Bluetooth connectivity.

Introduction The diagnosis and differentiation of IBD (Inflammatory Bowel Disease) lacks a single gold standard. IBD commonly suffers from a delay in time from first occurrence of symptoms to diagnosis, especially in young patients with ileal disease, which hinders our ability to alter the progression of disease. Also, once the diagnosis of IBD is made its sub categorization into CD (Crohn’s Disease) or UC (ulcerative colitis) is critical for determining the optimal treatment strategy. It is important to identify at risk population that could benefit from a therapeutic approach [1]. Metabolomics studies have recently enter the field of IBD. A variety of studies have been conducted to be significantly different between CD, UC and heathy controls [2]. Limitation for use of metabolomics markers would be too time-consuming and expensive for assessment of IBD or invasive testing in cases. An ideal approach regarding IBD assessment is that breath metabolome offers great potential with simply, easy to use, non-invasive, cheap, rapid and reproducible [3]. An electronic nose system, which is an instrument comprises an array of chemical sensors with partial specificity and an appropriate pattern recognition system capable of recognition simple or complex odors [4], has been suggested a potential alternative as a novel approach for breath analytic technique. In this presentation, we introduce exhaled breath analysis for assessment of IBD from controls and CD from UC using an electronic nose system incorporating a solid-phase micro extraction (SPME) technique. Method We have been developed an electronic nose system composed one chip type array of chemical sensors, chamber, data acquisition system with microprocessor, and sampling system for SPME fiber operation for non-invasive heath care monitoring. The 2x4 sensor array in the system consisted of three oxides of SnO2, NiO2, and In2O3 using Au, Pt, and Pd as catalyst and fabricated on one chip by glancing angle deposition method [5]. A chamber was used to maintain the stable operating temperature of sensor array, and SPME fiber used transferring of exhaled breath samples for measurement. Figure 1 is shown electronic nose system which has been used for experimental work in the hospital. The collection of exhaled breath for IBD patients (23 CD, 32 UC) and 15 controls was carried out using tedlar bag in connection with mouthpiece having a saliva trap to prevent humidity. The SPME fiber coated 85μm Polyacrylate was inserted into the tedlar bag and exposed to the collected breath at an ambient temperature. The system exposed the fiber to the heated sensor array desorbing the volatile off the fiber directly onto the sensors in the chamber. The collection and measurement of expiration were conducted in a hospital after approval of the IRB (Institutional Review Board) at Dongsan Medical Center, Deagu, Korea. Results and Conclusions The primary result for collected data from electronic nose system is shown at Figure 2 using Linear Discriminant Analysis (LDA) algorithm. As shown in Figure 2, IBD patients and controls are distinguished, especially IBD subgroup between CD and UC is well separated each other. However, some samples from UC subgroup are mixed with controls. In this study, we implemented an electric nose system by fabricating a one chip sensors array incorporating SPME sampling technique. Throughout the experimental result, we investigate the possibility of classification between IBD including 2 subgroup discrimination and controls. However, we need more research to improve discrimination regarding UC and controls following by optimal VOCs markers between UC and control including instrument control. References [1] S. Kurada, N. Alkhouri, C. Fiocchi, R. Dweik, F. Rieder Review Article: Breath Analysis in Inflammatory Bowel Disease, Aliment Pharmacol Ther 41 (2015) 329 - 341. [2] R. P. Arasaradnam, N. Ouaret, M. G. Thomas, N.Quraish, E. Heatherington, C. U. Nwokolo, K. D. Bardhan, J. A. Covington A Novel Tools for Noninvasive Diagnosis and Tracking of Patients with Inflammatory Bowel Disease, Inflamm Bowel Dis 19 (2013) 999 – 1003. [3] A. D. Wilson, M. Baietto, Applications and Advances in Electronic-Nose Technologies, Sensors 9 (2009) 5099 – 5148. doi:10.3390/s90705099. [4] J. Gardner, P. Bartlett, Electronic Noses Principles and Applications, Meas Sci Technol 11 (2000) 20-25. [5] Y. Song, Y. Shim, S. Kim, S. Han, H. Moon, M. Noh, K. Lee, H. Lee, J. Kim, B. Ju, C. Kang, Downsizing gas sensors based on semiconducting metal oxide: Effect electrodes on gas sensing properties, Sensors and Actuators B. 248 (2017) 949-956 Acknowledgement This work was supported by Institute for Information & Communications Technology Promotion (IITP) grant funded by the Korea government (MISP) (No.2019-0-00725, Development of Non-Contact Dementia Screening and Cognitive Enhancer Content Technology) Figure 1

We report on the sensitive and selective sensing properties of SnO2 nanorods (NRs) based gas sensors coupled with a miniature gas chromatography (mini-GC) system for the detection of acetylene. The SnO2 NRs were fabricated by a glancing angle deposition (GLAD) method and their average height and diameter were ∼200 nm and ∼30 nm, respectively. In order to overcome a selectivity issue of metal oxide semiconductor gas sensors, we integrated our SnO2 NRs based sensors with a packed column. The device accurately and selectively detected acetylene within 2 min (∼120 s). We found that loading a thin layer (5 nm) of metal catalysts such as Au, Pt or Pd increases the sensing abilities of the SnO2 NRs sensors. Among the tested sensors, the Pd-coated SnO2 NRs sensor (Pd-SnO2 NRs) exhibited the best sensing performance for the detection of 10 ppm of acetylene and the lower detection limit of 0.01 ppm. The superior sensing properties of Pd-SnO2 NRs are due to the large amount of oxygen deficiencies on the surface of Pd-SnO2 NRs, which acts as reactive sites. More importantly, the mini-GC device can be used to selectively detect 10 ppm of acetylene from other gases such as H2. Our findings demonstrate that Pd-SnO2 NRs integrated with a mini-GC device can be utilized to monitor the dissolved acetylene gas in transformer oil in real time.

Ultralow power chemical sensing is essential toward realizing the Internet of Things. However, electrically driven sensors must consume power to generate an electrical readout. Here, a different class of self-powered chemical sensing platform based on unconventional photovoltaic heterojunctions consisting of a top graphene (Gr) layer in contact with underlying photoactive semiconductors including bulk silicon and layered transition metal dichalcogenides is proposed. Owing to the chemically tunable electrochemical potential of Gr, the built-in potential at the junction is effectively modulated by absorbed gas molecules in a predictable manner depending on their redox characteristics. Such ability distinctive from bulk photovoltaic counterparts enables photovoltaic-driven chemical sensing without electric power consumption. Furthermore, it is demonstrated that the hydrogen (H2 ) sensing properties are independent of the light intensity, but sensitive to the gas concentration down to the 1 ppm level at room temperature. These results present an innovative strategy to realize extremely energy-efficient sensors, providing an important advancement for future ubiquitous sensing.

Despite the wide applicability of oxynitrides from photocatalysis to refractory coatings, our understanding of the materials has been limited in terms of their thermodynamics. The configurational entropy via randomly mixed O/N or via cation vacancies are known to stabilize oxynitrides, despite the positive formation enthalpies. Here, using tin oxynitrides as a model system, we show by ab initio computations that oxynitrides in seemingly charge-unbalanced composition stabilize by forming pernitrides among metal-(O,N)6 octahedra. The nitrogen pernitride dimer, =(N-N)=, results in the effective charge of −4, facilitating the formation of nitrogen-rich oxynitrides. We report that the dimer forms only in structures with corner-sharing octahedra, since the N-N bond formation requires sufficient rotational degrees of freedom among the octahedra. X-ray photoemission spectra of the synthesized tin oxynitride films reveal two distinct nitrogen bonding environments, confirming the computation results. This work opens the search space for a novel kind of oxynitrides stabilized by N dimer formation, with specific structural selection rules.

The utilization of edge sites in two-dimensional materials including transition-metal dichalcogenides (TMDs) is an effective strategy to realize high-performance gas sensors because of their high catalytic activity. Herein, we demonstrate a facile strategy to synthesize the numerous edge sites of vertically aligned MoS

Hollow-structured nanomaterials are presented as an outstanding sensing platform because of their unique combination of high porosity in both the micro- and nanoscale, their biocompatibility, and flexible template applicability. Herein, we introduce a bacterial skeleton method allowing for cost-effective fabrication with nanoscale precision. As a proof-of-concept, we fabricated a hollow SnO

We present a heterosensor array that exploits the collective recognition ability of a set of different gas sensors to identify individual chemical vapors. In contrast to the conventional sensing approach based on the "lock-and-key" design, the heterosensor array rely on the response patterns produced over the collection of different sensors. Diverse sensors with different operating principles are employed to provide as much chemical diversity as possible. We demonstrate that this platform provides a highly discriminative tool with single element precision.

Unlike bulk materials, many physical properties of thin-film materials depend on film thickness due to extrinsic effects such as residual stress and the dead layer. In this work, the effect of thickness on the electrocaloric properties of Pb0.9La0.1(Zr0.65Ti0.35)O3(10/65/35) (PLZT) films grown by the sol–gel method was studied experimentally. In the sol–gel synthesis, the annealing process results in residual stress and the metal–dielectric contact generates a dead layer. These extrinsic effects influence the dielectric and ferroelectric properties of the thin films, and their roles are film thickness dependent. For PLZT of nanometer thickness (from 420 nm to 1080 nm), the permittivity and polarization, and their temperature dependences, showed strong dependence on film thickness. In particular, in the temperature range from 70°C to 350°C, the electrocaloric temperature change showed threefold improvement (from 0.2°C to 0.6°C) as the thickness was increased from 420 nm to 840 nm. This work will aid development of polycrystalline thin films including PLZT for electrocaloric applications.

This study presents a piezoelectric composite generator using PDMS polymer, PZT nanorods, and Ag nanowires. To enhance output power of the generator, we inserted the Ag NWs into the PDMS-PZT composite, which play very important roles in our generator: First, it enables the PZT NRs well distributed in PDMS polymer. Second, it is to reinforce the applied stress of the device by enhancing its flexibility. Finally, conduction paths formed by the Ag networks can reduce the internal resistance of the device. To assess these effects, we have compared and evaluated output voltage and current of four different generators.

We grew Pt films on TiO2-terminated SrTiO3 (001) by atomic layer deposition, using trimethyl(methylcyclopentadienyl)-platinum(IV) as the Pt source and O2 and O3 as the oxidants. The orientation of the Pt films grown with O2 varied from (111) to (001) as the growth temperature was increased from 220 to 350 °C, while the Pt films grown with O3 have a strong preference for the (111) orientation even at a high growth temperature of 350 °C. The difference in the orientation of the Pt films on SrTiO3 (001) was attributed to changes in the degree of chemical bonding across the Pt/SrTiO3 interface with respect to the oxidant. We observed an increase in Pt–O bonding at the interface between the Pt grown with O3 and the SrTiO3 substrate. The interfacial energy of Pt (111)∥SrTiO3 (001) may have been significantly decreased by the increase in Pt–O bonding at the interface, which eventually led to the strong (111) preference of the Pt grown with O3. The findings provide the possibility of controlling the orientation o...

The 2-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 heterointerface was analyzed using frequency-dependent impedance spectroscopy. The electrical conduction of 2DEG significantly influences the high-frequency impedance and induces dielectric amplification at low frequency regimes. The impedance responses obtained from the LaAlO3/SrTiO3 oxide was modeled using an equivalent circuit model. The frequency-dependent characterization used here does not necessitate the formation of ohmic contacts between the 2DEG layer and the adjacent electrodes. Through thermal bias-stress tests, the 2DEG conduction mechanism is proposed to partially originate from the oxygen vacancy-controlled defect concepts, indicating the controllability of 2DEG transport.

As highly sensitive H2S gas sensors, Au- and Ag-catalyzed SnO2 thin films with morphology-controlled nanostructures were fabricated by using e-beam evaporation in combination with the glancing angle deposition (GAD) technique. After annealing at 500 °C for 40 h, the sensors showed a polycrystalline phase with a porous, tilted columnar nanostructure. The gas sensitivities (S = Rgas/Rair) of Au and Ag-catalyzed SnO2 sensors fabricated by the GAD process were 0.009 and 0.015, respectively, under 5 ppm H2S at 300 °C, and the 90% response time was approximately 5 s. These sensors showed excellent sensitivities compared with the SnO2 thin film sensors that were deposited normally (glancing angle = 0°, S = 0.48).

The crystal structure and piezoelectric properties of (1−x)Pb(Zr1−yTiy)O3-xPb(Zn0.4Ni0.6)1/3Nb2/3O3 [(1−x)PZ1−yTy-xPZNN] ceramics were investigated. The 0.665PZ0.45T0.55-0.335PZNN ceramic has the triple point composition, where the rhombohedral, pseudocubic, and tetragonal structures coexist. Maximum d33 and kp values of 770 pC/N and 0.69, respectively, were observed from this specimen; it also exhibited a large eT33/eo value of 3250. Although the maximum d33 value was obtained from the triple point composition specimen, its g33 and d33 × g33 values were relatively small because of its large eT33/eo value. However, the 0.665PZ0.46T0.54-0.335PZNN ceramic, which has a rhombohedral structure, exhibited a large g33 value of 43 × 10−3 Vm/N and a d33 × g33 value of 27 000 × 10−15 m2/N. Therefore, this ceramic is a good candidate for multilayer actuators and piezoelectric energy harvesters.

Piezoelectric composite nanofibers based on (Na 0.5 ,K 0.5 )NbO 3 (NKN) nanoparticles embedded in poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] polymer are investigated in terms of their performance as nanogenerators. Perovskite NKN nanoparticles with ∼30–105 nm were separately prepared by combustion synthesis using polyacrylic acid (PAA) as a fuel. Surface modification of nanoparticles by tetradecylphosphonic acid (TDPA) was essential to secure proper adhesion with the polymer in the nanofibers prepared by electrospinning. Location-dependent piezoelectricity measurements confirmed that the region of embedded NKN filler particles exhibited better piezoelectricity than the P(VDF–TrFE) matrix region. Energy harvesting performance of the flexible composite nanogenerator demonstrated ∼0.98 V output voltage and ∼78 nA output current, which were enhanced depending on the volume fraction of the NKN nanoparticles dispersed in the polymer.

With the widespread use of wearable electronics, the flexible piezoelectric energy harvesting devices have been extensively studied to efficiently convert the physical motion of the human body into electrical energy. The major obstacles for realizing a flexible piezoelectric generator include the insufficient output power generation and the poor efficiency at the low-frequency regime. Here, we demonstrate a curved piezoelectric generator favorable for wearable applications, generating a high output power. The curved structure plays a key role to improve the power generation, by effectively distributing the applied force across the piezoelectric layer, as well as to allow operation at the low frequency vibration range. Accordingly, this generator produces � 120 V of peak output voltage and � 700 mA of peak output current during a cycle. Furthermore, our generator can operate at low frequencies below 50 Hz, generating � 55 V of output voltage and 250 mA of output current at 35 Hz, and it even works at frequencies as low as 1 Hz. With this generator, we successfully lit up 476 commercial LED bulbs. In addition, we experimentally demonstrate the possibility that the generator can be used in shoes, watches, and clothes as a power source. Our results will provide a framework to enhance the output power of conventional piezoelectric generators, and open a new avenue for realization of self-powered systems, such as wearable electronic devices.

Vertically ordered SnO2 nanorods with Au nanoparticles deposited in multiple steps, namely, SnO2 nanobamboos are synthesized by a glancing-angle deposition technique. The highly ordered porous structures enable us to detect sub-ppb levels of volatile reducing gases with a fast response speed by maximizing the sensitization effects of the Au nanoparticles.

A facile and scalable synthesis of mesoporous films impregnated with Au nanoparticles (NPs) as effective dielectrics is demonstrated for enhancing the nanogenerator performance based on vertical contact-separation mode. This technique is so simple and scalable, providing a promising solution for developing large-scale and practical self-powered devices. The spatial distribution of Au NPs made it possible to fabricate an Au NP-embedded mesoporous triboelectric nanogenerator (AMTENG) with a high output power of 13 mW under cycled compressive force, giving over 5-fold power enhancement, compared with a flat film-based TENG under the same mechanical force. It is proposed that the presence of aligned dipoles produced due to the charges created by the contact between Au NPs and PDMS inside the pores can influence the surface potential energy of mesoporous films. With such an enhanced power output and unique device design, we demonstrate various applications such as self-powered shape mapping sensors, foot-step driven large-scale AMTENGs, and integrated circuits with capacitors for powering commercial cell phones for realizing self-powered systems from footsteps, wind power, and ocean waves.

Highly-stretchable piezoelectric hemispheres composed composite thin film nanogenerators are fabricated as a self-powered, exceptionally sensitive sensor for providing sensitive motion information from a human body. The composite films are based on the highly-ordered piezoelectric hemispheres embedded in a soft matrix, polydimethylsiloxane (PDMS) and generate large power output up to 6 V and 0.2 μA/cm2 under normal bending force. The electrical outputs increase by stacking such hemispheres layer-by-layer. The strain sensitivity of the films differs according to the bending direction, and the high sensitivity is achieved by convex bending for hemisphere composite due to the strong electric dipole alignment. The films are attached on the surface of a wrist and its output voltage/current density provides the information on the wrist motion.

The utilization of p–p isotype heterojunctions is an effective strategy to enhance the gas sensing properties of metal-oxide semiconductors, but most previous studies focused on p–n heterojunctions owing to their simple mechanism of formation of depletion layers. However, a proper choice of isotype semiconductors with appropriate energy bands can also contribute to the enhancement of the gas sensing performance. Herein, we report nickel oxide (NiO)-decorated cobalt oxide (Co3O4) nanorods (NRs) fabricated using the multiple-step glancing angle deposition method. The effective decoration of NiO on the entire surface of Co3O4 NRs enabled the formation of numerous p–p heterojunctions, and they exhibited a 16.78 times higher gas response to 50 ppm of C6H6 at 350 °C compared to that of bare Co3O4 NRs with the calculated detection limit of approximately 13.91 ppb. Apart from the p–p heterojunctions, increased active sites owing to the changes in the orientation of the exposed lattice surface and the catalytic ef...

Amorphous KNbO

Crystalline (Zr,Ti) 0.85 (Ca,Sr) 0.15 O 1.85 (ZTCS) films were grown on a Pt/Ti/SiO 2 /Si substrate at various temperatures by using rf-magnetron sputtering. The ZTCS films had a cubic stabilized zirconia structure. The dielectric constant ( k ) of the ZTCS film grown at 300 °C was approximately 30.5 with a low tan δ value of 0.007 at 100 kHz. Further, this film exhibited a similar k value of 30.4 and a high quality factor of 225 at 1.0 GHz. Moreover, it showed a high capacitance density of 290 nF/cm 2 with a small TCC of −60.7 ppm/°C at 100 kHz. A low leakage current (1.4×10 −8 A/cm 2 at 1.5 MV/cm) with a high breakdown electric field (1.85 MV/cm) was also observed in this film; the leakage current of this film was explained by Schottky emission. Therefore, it can be concluded that ZTCS films grown at low temperatures (≤300 °C) are good candidates for use as embedded capacitor in printed circuit boards.

SnO 2 thin films were grown by atomic layer deposition (ALD) with dimethylamino-2-methyl-2-propoxy-tin(II) (Sn(dmamp) 2 ) and O 3 in a temperature range of 100–230 °C. The ALD window was found to be in the range of 100–200 °C. The growth per cycle of the films in the ALD window increased with temperature in the range from 0.018 to 0.042 nm/cycle. Above 230 °C, the self-limiting behavior which is a unique characteristic of ALD, was not observed in the growth because of the thermal decomposition of the Sn(dmamp) 2 precursor. The SnO 2 films were amorphous in the ALD window and exhibited quite a smooth surface. Sn ions in all films had a single binding state corresponding to Sn 4+ in SnO 2 . The concentration of carbon and nitrogen in the all SnO 2 films was below the detection limit of the auger electron spectroscopy technique and a very small amount of carbon, nitrogen, and hydrogen was detected by secondary ions mass spectroscopy only. The impurity contents decreased with increasing the growth temperature. This is consistent with the increase in the density of the SnO 2 films with respect to the growth temperature. The ALD process with Sn(dmamp) 2 and O 3 shows excellent conformality on a hole structure with an aspect ratio of ∼9. This demonstrates that the ALD process with Sn(dmamp) 2 and O 3 is promising for growth of robust and highly pure SnO 2 films.

Two-dimensional electron gas (2DEG) at the complex oxide interfaces have brought about considerable interest for the application of the next-generation multifunctional oxide electronics due to the exotic properties that do not exist in the bulk. In this study, we report the integration of 2DEG into the nonvolatile resistance switching cell as a bottom electrode, where the metal-insulator transition of 2DEG by an external field serves to significantly reduce the OFF-state leakage current while enhancing the on/off ratio. Using the Pt/Ta2O5-y/Ta2O5-x/SrTiO3 heterostructure as a model system, we demonstrate the nonvolatile resistance switching memory cell with a large on/off ratio (10(6)) and a low leakage current at the OFF state (∼10(-13) A). Beyond exploring nonvolatile memory, our work also provides an excellent framework for exploring the fundamental understanding of novel physics in which electronic and ionic processes are coupled in the complex heterostructures.

For various additives doped- critical temperature sensors using the nature of semiconductor to metal transition, the crystallinity, microstructure, and temperature vs. resistance characteristics were systematically investigated. As a starting material of sensor, vanadium pentoxide () powders were used, and CaO, SrO, , , and PbO dopants were used, respectively. The powders with dopants were mixed with a vehicle to form paste. This paste was silk screen-printed on substrates and then -based thick films were heat-treated at for 2 hours in gas atmosphere for the reduction to . From X-ray diffraction analysis, phases for pure , and CaO and SrO-doped thick films were confirmed and their grain sizes were 0.57 to . The on/off resistance ratio of the sensor in phase transition temperature range was and that of the 0.5 wt.% CaO-doped sensor was . The presented critical temperature sensors could be commercialized for fire-protection and control systems.

The pseudocubic structure of a (Na0.5K0.5)NbO3 (NKN) film grown on a Pt/Ti/SiO2/Si substrate changed to an orthorhombic structure when the film was transferred onto a polyimide substrate. Piezoelectric constant for the transferred NKN film increased considerably from 74 ± 11 to 120 ± 18 pm/V because the crystal structure of the film had changed from pseudocubic to orthorhombic. A gold interdigitated electrode was deposited onto the transferred NKN film to synthesize a NKN piezoelectric energy harvester. The NKN piezoelectric energy harvester was poled before bending under a 100 kV/cm DC electric field across the electrodes. When a strain of 0.85% and a strain rate of 4.05%/s were applied to the NKN piezoelectric energy harvester, it produced a maximum output voltage of 1.9 V and a current of 38 nA, corresponding to a power density of 2.89 μW/cm3.

The electrocaloric effect of 9/65/35 PLZT thin film fabricated by the sol-gel method, which has not been studied yet, was investigatedfor its structural, electrical properties as well as temperature change property. The relaxor ferroelectric property of 9/65/35 PLZT thinfilm was confirmed by examining its dielectric and electrical properties. The relaxor property can cause a more pronounced elec-trocaloric effect (ECE) in a wider temperature range than normal ferroelectric film. To avoid errors caused by using an indirect mea-surement method, the leakage current generated by increasing temperatures was minimized by using the optimal maximum electric field(350 kVcm -1 ) in the thin film. The largest temperature change ΔT (0.23 K) and the electrocaloric strength ξ (0.68 mkcm/kV), calculatedby equations were obtained. The maximum field change ΔE (191 kVcm -1 ) was in the vicinity of the curie temperature (200 o C).Keywords: Electrocaloric effect, Cooling device, PLZT, Ferroelectric material

Microstructural and piezoelectric properties of 0.72Pb(Zr1−xTix)–0.28Pb(Zn0.4Ni0.6)1/3Nb2/3O3 (PZ1−xTx-PZNN) ceramics with 0.50 ≤ x ≤ 0.55 were investigated for evaluating the possibility of their use in multilayer actuators and energy harvesters, which demand a large piezoelectric strain constant (d33) and a small dielectric constant (eT33/eo). The PZ0.47T0.53-PZNN ceramic with a morphotropic phase boundary (MPB) composition showed large d33 and eT33/eo values, making it unsuitable for use in multilayer actuators and energy harvesters. However, the PZ0.48T0.52-PZNN ceramic with a rhombohedral structure showed a small eT33/eo value of 1605, yet maintained a large d33 of 550 pC/N. Thermal stimulation did not have any significant effect on the piezoelectric properties of this specimen, except for a slight increase in the eT33/eo value upon heating the specimen at 150°C for 4 h. In an effort to reduce the sintering temperature, CuO was used as an additive for the ceramic. As a result, the CuO-added PZ0.48T0.52-PZNN ceramic was well sintered at 900°C. In particular, the 1.0 mol% CuO-added PZ0.48T0.52-PZNN ceramic exhibited a large d33 value of 554 pC/N and a small eT33/eo value of 1620, making it highly suitable for use in multilayer actuators and energy harvesters.

WO3 nanoigloos decorated with Ag-, Pd-, and Au nanoparticles are fabricated by soft-template method and self-agglomeration of metal films. The responses of WO3 nanoigloos decorated with metal nanoparticles to various gases such as NO2, CH3COCH3, C2H5OH, and H2 are much higher than those of bare WO3 nanoigloos. According to the surface decoration, WO3 nanoigloos show significantly different behaviors in the response enhancement, revealing that Pd-decorated WO3 nanoigloos exhibit the highest response to H2 together with fast response time to H2, C2H5OH, and CH3COCH3 (below 10 s), Au-decorated WO3 nanoigloos exhibit the highest response to NO2. The catalytic effect of Ag is relatively weaker than Pd and Au nanoparticles, however, it exhibit the fastest response time to NO2. These are attributed to not only the varied catalytic activities of the metal nanoparticles, but also the different work function energies of them. Our results show that highly sensitive and selective WO3 nanoigloos decorated with metal nanoparticles can be an effective platform to fabricate an electronic nose for the further application of semiconducting metal oxide gas sensors.

Cobalt oxide-based Ca3Co4O9 ceramics are known for their good thermoelectric (TE) performance and chemical stability at high temperatures (

An amorphous phase was formed in a 0.95(Na0.5K0.5)NbO3–0.05CaTiO3 (NKN-CT) film grown at 300°C, and a low-temperature transient Ca2Nb2O7 phase was formed in the film grown at 500°C. In films grown at high temperatures (≥600°C), secondary phases such as K5.75Nb10.85O30 and K4Ti10Nb2O27 were developed without the formation of a NKN-CT phase, probably because of Na2O evaporation. The same secondary phases were formed in the film grown at 300°C and subsequently annealed at 850°C under an air atmosphere. However, a homogeneous NKN-CT phase was formed in films grown at 300°C and subsequently annealed at 830°C–880°C under the K2O and Na2O atmospheres. Moreover, the film annealed at 830°C in particular exhibited good electric and piezoelectric properties, including a high dielectric constant of 747 with a low dissipation factor of 0.93% at 100 kHz, low leakage current density of 2.0 × 10−7 A/cm2 at 0.1 MV/cm, and high Pr and d33 values of 15.4 μC/cm2 and 124 pm/V at 100 kV/cm, respectively.

The effects of vanadium substitution on the dielectric properties of amorphous SrBi2Ta2O9 (SBT) thin films have been investigated. Vanadium substitution at the Ta site exists in the V3+ valence state and acts as an acceptor, reducing the number of intrinsic oxygen vacancies and the leakage current of the amorphous SBT thin films. Furthermore, the dielectric properties are also improved. The leakage current values of the 92 and 31 nm thick SBTV thin-film capacitors were 8.8 nA cm−2 and 0.62 μA cm−2 at 1 V, respectively.

We present gas sensing performance based on 22 sensor array with four different elements (TiO2, SnO2, WO3 and In2O3 thin films) fabricated by rf sputter. Each thin film was deposited onto the selected SiO2/Si substrate with Pt interdigitated electrodes (IDEs) of 5 m spacing which were fabricated on a SiO2/Si substrate using photolithography and dry etching. For 5 ppm NO2 and 50 ppm CO, each thin film sensor has a different response to offers the distinguishable response pattern for different gas molecules. Compared with the conventional micro-fabrication technology, 22 sensor array with such remarkable response pattern will be open a new foundation for monolithic integration of high-performance chemoresistive sensors with simplicity in fabrication, low cost, high reliablity, and multi- functional smart sensors for environmental monitoring.

A particle-based photocatalyst with a permanent internal field prepared by a corona poling method is presented as a novel approach to enhance the hydrogen evolution reaction in a particulate-suspension system. Photocatalytic activity of K0.5Na0.5NbO3 was significantly improved by 7.4 times after the polarization.

The piezoelectric energy generation properties of transparent flexible devices (TFD) based on PbZr 0.52 Ti 0.48 O 3 (PZT) films, which were fabricated by laser lift-off (LLO) process, were studied for a piezoelectric energy harvester. Through the introduction of indium-tin-oxide (ITO) and polyethylene terephthalate (PET) substrates, TFDs were implemented, respectively. The TFDs based on PZT films generated an AC-type output signal and output power of 8.4 nW/cm 2 , at periodically bending and releasing motion. In addition, inverted output signals were observed when the manufactured TFDs were connected to the measuring equipment in reverse and were bended to the reverse direction, demonstrating that the generating signals originated from the piezoelectric effect of TFDs. The experimental results clearly showed that the TFDs based PZT film have potential for use in next generation of electronic devices applications such as flexible devices, transparent electronics, and energy harvester.

Binary system of 0.05Pb(Al 0.5 Nb 0.5 )O 3 −0.95Pb(Zr 0.52 Ti 0.48 )O 3 (PAN–PZT) thin films were deposited on alumina substrates by a pulsed laser deposition method and we investigated effects of oxygen pressure on ferroelectric domain structure and the piezoelectric characteristics of the films by piezoelectric force microscope (PFM). The films in optimum oxygen pressure exhibited the remnant polarization of 58.4 and 24.4 μC/cm 2 , and 180° and 90° domain switching behavior were observed from PFM analysis. We obtained a large effective piezoelectric constant ( d 33 ) value (∼110 pm/V) in the films. As a result, we can determine the ferroelectric domain structure and improve the piezoelectric properties of the PAN–PZT films using an oxygen pressure control during the process and it helps to obtain suitable piezoelectric thin films for sensors and actuators applications.

Lead zirconate titanate (PZT) nanotubes fabricated by template-assisted method using sol–gel solution infiltration are applied for energy harvester. To fabricate PZT nanotubes, an anodic aluminum oxide is used for the template, and as-prepared PZT solution dropped on the surface of the AAO is infiltrated by vacuum pump into the pores in the AAO. The template including PZT solution is dried at 80 °C for 1 min and dried again at 300 °C for 10 min, and then it treated at 650 °C for 30 min to anneal PZT and form the expected perovskite phase. The fabricated nanotubes were mixed with PDMS polymer composite and polyimide films coated Pt/Ti were used for electrodes. Finally, it demonstrated that the energy harvester could generate the output power of 37 nW/cm2.

The functionalization of two-dimensional electron gas (2DEG) at oxide interfaces can be realized integrating 2DEG with multifunctional oxide overlayers by epitaxial growth. Using a ferroelectric Pb(Zr0.2 Ti0.8 )O3 overlayer on 2DEG (LaAlO3 /SrTiO3 ), we demonstrate a model system of the functionalized 2DEG, where electrical conductivity of 2DEG can be reversibly controlled with a large on/off ratio (>1000) in a non-volatile way by ferroelectric polarization switching.

Amorphous BaTi4O9 (BT4) films for use as capacitors embedded in PCB substrates were grown on Cu electrodes at low temperatures (≤ 200°C). The dielectric constant (k) of the amorphous BT4 film grown at room temperature (RT) was 38, and its dissipation factor was 3.2% at 100 kHz. A similar k value was obtained at radio-frequency ranges, with a quality factor of 143 at 1.0 GHz. The films showed a capacitance density of 200 nF/cm2, a temperature coefficient of capacitance of 296 ppm/°C at 75 kHz, and a breakdown voltage of 42.5 V. This film therefore satisfies the requirements of the International Technology Roadmap for Semiconductors for 2016 for capacitors grown on organic substrates. In addition, the leakage current mechanism of the amorphous BT4 films was found to be Schottky emission, and the Schottky barrier height was calculated as 2.26 eV.

Mg2SiO4 (forsterite) thin films grown by rf magnetron sputtering from a ceramic target have been investigated particularly for thin film hybrids requiring a low loss dielectric layer. Understanding of the processing parameters and their correlations to dielectric properties is the main concern of this work. Fundamental parameters, such as working pressure and post-deposition annealing temperature, were found to influence phase evolution, morphology and dielectric properties. For example, polycrystalline α-Mg2SiO4 could be obtained above the annealing temperature of 500 °C regardless of working pressure. The dielectric constant increased gradually while the dielectric loss showed a reverse trend of decrease with raising annealing temperature to 700 °C. Dielectric constant of ~ 6.8 and dielectric loss of ~ 2.8 × 10− 3 were obtained at 1 MHz from the sample annealed at 700 °C. A promising planarized thin film structure for fine line multilevel packaging was demonstrated without any significant inter-diffusion and damages between Mg2SiO4 and Pt layers.

A record-high, near-theoretical intrinsic magnetoelectric (ME) coupling of 7 V cm-1 Oe-1 is achieved in a heterostructure of piezoelectric Pb(Zr,Ti)O3 (PZT) film deposited on magnetostrictive Metglas (FeBSi). The anchor-like, nanostructured interface between PZT and Metglas, improved crystallinity of PZT by laser annealing, and optimum volume of crystalline PZT are found to be the key factors in realizing such a giant strain-mediated ME coupling.