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Atomic step structures on porous ZnO nanobelts provide coordinatively unsaturated sites that allow an outstanding sensitivity with a limit of detection (LOD) as low as 72 ppt.

ZnO nano-bullets were synthesized using solution plasma from only Zn electrode in water without any chemical agents. In this sustainable synthesis system, the rapid quenching reaction at the interface between the plasma/liquid phases facilitates the fast formation of nano-sized materials. The coil-to-pin type electrode geometry, which overcomes the discharge interruption owing to the electrode gap broadening of the typical pin-to-pin type enables the synthesis of numerous nanomaterials through a stable discharge for 1 h. The as-prepared samples exhibited a high crystalline ZnO structure without post calcination, and the length and width were 71.8 and 29.1 nm, respectively. The main exposed facet of ZnO nano-bullets was the (100) crystal facet, but interestingly, the (101) facet was confirmed at the inclined surfaces in the edges. The (101) crystal facet has an asymmetric Zn and O atom arrangement, and it could result in a focused electron density area with relatively high reactivity. Therefore, ZnO nano-bullets are promising materials for applications in advanced technologies.

NiO nanosheets are synthesized in situ on gas sensor chips using a facile solvothermal method. These NiO nanosheets are then used as gas sensors to analyze allyl mercaptan (AM) gas, an exhaled biomarker of psychological stress. Additionally, MnO

The development of a facile gas sensor for the ppb-level detection of acetone is required for realizing health diagnosis systems that utilize human breath. Controlling the crystal facet of a nanomaterial is an effective strategy to fabricate a high-response gas sensor without a novel metal catalyst. Herein, we successfully synthesized a SnO2 nanosheet structure, with mainly exposed (101) crystal facets, using a SnF2 aqueous solution at 90 °C. The SnO2 nanosheets obtained after various synthesis durations (2, 6, and 24 h) were investigated. The sample synthesized for 6 h (NS-6) exhibited a 10-fold higher response (Ra/Rg = 10.4) for 1 ppm of acetone compared to the other samples, where Ra and Rg are the electrical resistances under air and the target gas. Furthermore, NS-6 detected up to 200 ppb of acetone (response = 3). In this study, we attributed the high response (of low concentrations of acetone) to the (101) crystal facet, which is the main reaction surface. The (101) crystal facet allows the facile formation of a depletion layer due to the highly reactive Sn2+. Additionally, the acetone adsorption energy of the (101) crystal facet is relatively lower than that of other crystal facets. Owing to these factors, our pristine SnO2 nanosheet gas sensor exhibited significantly high sensitivity to ppb levels of acetone.

Herein, an enhanced electroluminescence (EL) performance of solution-processed silicon quantum dot light-emitting diodes (Si-QLEDs) is demonstrated. We prepared colloidal inks of silicon quantum do...

A zeolitic imidazolate framework-8 (ZIF-8) layer was introduced as a surface molecular separator to grant the selective gas-sensing ability to thin-film sensor material composed of SnO2 nanosheets. ZIF-8 possesses a molecular sieving ability, which is in the range of approximately 4.0–4.2 A. Compared to a SnO2 nanosheet gas sensor, a ZIF-8/SnO2 nanosheet gas sensor exhibited a decreased sensor signal response when the gas molecular sizes were large, e.g., C3H6 (4.120 A), 1-C4H8 (5.430 A), and C9H18O (12.011 A). However, the ZIF-8/SnO2 nanosheet sensor signal response to smaller-sized gas molecules, such as C2H4 (3.058 A), was slightly increased due to electron transfer at the ZIF-8 and SnO2 interface. Therefore, the control of gas selectivity based on molecular size was realized by introducing ZIF-8 as a surface molecular separator. These results pave the way for selective gas sensing in various types of applications that depend on gas selectivity.

Crystal growth-controlled Co3O4 nanoparticles were prepared to examine gas sensing properties. A cube-like, an irregular shaped, and three kinds of raspberry-type structures were observed by morphology analysis. The raspberry-type structures have an expanded lattice volume with a large oxygen deficiency area, and the cube-like structure has a contracted lattice volume as compared to the irregular shaped structure. The raspberry-type structures exhibited a higher sensor signal response than the others. A relationship between sensor properties and crystal defect was investigated, and it was revealed that the gas selectivity to a high dipole moment value of a reducing gas molecule increased with increasing oxygen deficiency area of the Co3O4 nanoparticle. It was considered that the oxygen deficiency area acted as an important reaction site, which can be attributed to the selective reaction of the Co3O4 nanoparticle with gas molecules.

Nanoarchitectonics of metal oxide nanocrystal electrodes were developed for lithium-ion batteries. The electrodes included copper nanoparticles and doped fluorine. For the acicular nanocrystals, charge–discharge reactions progressed at 1.8 V over 100 cycles at 100 and 10 μA. A 15-mmdiameter battery containing acicular nanocrystals showed capacity, coulomb efficiency, and specific capacity, respectively of 20 μAh, 98%, and ~242 mAh/g at 100 μA and 40 μAh, 99%, and 484 mAh/g at 10 μA. The TiO2/SnO2 electrode consisted of a SnO2 sheet-assembled structure with surface layers of anatase TiO2. The TiO2/SnO2 battery operated at 1.3 (100 cycles) and 1.2 (50 cycles) V at 100 and 10 μA, respectively; its capacity, coulomb efficiency, and specific capacity, respectively were 50 μAh, 98%, and 161 mAh/g at 100 μA and 200 μAh, 97–98%, and 643 mAh/g at 10 μA. The characteristic microstructure, chemical composition, and crystal faces of both materials contributed to battery performance.

Driven by the emergence of colloidal semiconductor quantum dots (QDs) of tunable emission wavelengths, characteristic of exciton absorption peaks, outstanding photostability and solution processability in device fabrication have become a key tool in the development of nanomedicine and optoelectronics. Diamond cubic crystalline silicon (Si) QDs, with a diameter larger than 2 nm, terminated with hydrogen atoms are known to exhibit bulk-inherited spin and valley properties. Herein, we demonstrate a newly discovered size region of Si QDs, in which a fast radiative recombination on the order of hundreds of picoseconds is responsible for photoluminescence (PL). Despite retaining a crystallographic structure like the bulk, controlling their diameters in the 1.1-1.7 nm range realizes the strong PL with continuous spectral tunability in the 530-580 nm window, the narrow spectral line widths without emission tails, and the fast relaxation of photogenerated carriers. In contrast, QDs with diameters greater than 1.8 nm display the decay times on the microsecond order as well as the previous Si QDs. In addition to the five-orders-of-magnitude variation in the PL decay time, a systematic study on the temperature dependence of PL properties suggests that the energy structure of the smaller QDs does not retain an indirect band gap character. It is discussed that a 1.7 nm diameter is critical to undergo changes in energy structure from bulky to molecular configurations.

This study analyzed temporal variation of the composition of volatile organic compounds (VOCs) at different diffusion time of gaseous phase of aroma compounds of four essential oils, lavender, tea tree, eucalyptus, and melissa. GC/MS methodology with the trace gas sampling by a thermal desorption tube is used to quantitatively determine the concentration of the corresponding 14 kinds of major and original VOCs in four essential oils. This study revealed for the first time that the concentration level of gaseous phase composition is varied, with a diffusion time from that of the liquid phase at equilibrium with it and the VOCs in the essential oils are classified into two groups, depending on whether their concentration with the time. It is verified that the total concentration of VOCs of these essential oils in the room air diffused by the ultrasonic diffuser is as low as 0.6 ppb and decreased soon below 0.1 ppb.

Through the improvement of nanomaterial technologies, a gas sensor was developed for detecting ppm or ppb levels of gas. Our SnO

A family of mixed LiNixCo(1-x)VO4 (x = 0.2, 0.8) cathode materials has been synthesized using the sol–gel method. The thermal behavior of the materials has been examined by thermogravimetric (TG) analysis. The Rietveld refinement of powder X-ray diffraction showed the structure with $$ Fd\overline{3}m $$ (227) space group. Surface analysis was performed using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Analysis of Raman spectra reveals the local environment model including VO4 tetrahedra, (Ni,Co)O6, and LiO6 octahedra as vibrational local units. X-ray photoelectron spectroscopy (XPS) studies on synthesized powder indicate that the oxidation states of nickel, cobalt, and vanadium are + 2, + 3 and + 5, respectively. Charge–discharge cycling tests were carried out to study the performance of the cathode materials.

SnO2 nanosheets with the (101) crystal face mainly exposed were prepared to investigate their sensing properties. The SnO2 nanosheets were ∼150 nm in size and well-dispersed on the sensor chip. The gas sensing properties of the SnO2 nanosheets were investigated for CH4, C2H4, C2H6, C3H6, C3H8, 1-C4H8, cis-2-C4H8, trans-2-C4H8, iso-C4H8, and n-C4H10 gases. Additionally, the relationship between the sensor signal response of the SnO2 nanosheets and the orbital energy of the target gas molecules was investigated. It was found that the sensor exhibited remarkable selectivity to alkene gases which have high HOMO energies. The presence of partially unoccupied oxygen sites was confirmed from crystal structure analysis. In addition, defects on the surface of the SnO2 nanosheets were certainly identified from the surface analysis. On the basis of these results, it was determined that the gas selectivity for alkene gases of the SnO2 gas sensor was improved by the formation of oxygen vacancy defects. This effect is ...

Research and development in the field of material science is aiming for further advancements, and expectations in the joining of materials and composite technology are progressively increasing. In particular, a new concept proposed for the control of interface phenomena with the aim to combine materials that are difficult to bond and composite has been attracting increasing interest. This concept has been accelerating progress in the interdisciplinary research area of material development. In this study, joining and compositing of various materials are carried out by precisely controlling the crystal growth and the interface phenomenon in an aqueous solution. Although joining of certain materials has been difficult in the past, these materials are now held together in nano- or micro-sized regions in order to control the microstructure (Masuda et al, Bull Ceram Soc Jpn 49(5):356–360, 2014; Masuda, Bull Ceram Soc Jpn 47(12):929–934, 2012). In particular, a composite structure of a tin oxide (SnO2) nanosheet assembly and a polymer material is prepared. Oxide materials, such as tin oxide, have been synthesized by high-temperature firing on the order of several hundred degrees and faced many difficulties in bonding and compositing the tin oxide structure to the surface of the polymer material with low heat resistance. Using the proposed method, synthesis of tin oxide crystals can be realized at ordinary temperatures by determining a suitable condition for tin oxide crystallization in an aqueous solution, thereby facilitating bonding with the polymer. In the aqueous solution, nucleation of tin oxide and crystal growth is controlled on the substrate surface to form a nanostructure. Furthermore, crystal growth in SnO2 is precisely controlled to form a tin oxide nanosheet, and an integrated structure composed of tin oxide nanosheets is synthesized. Moreover, the principle of this method can be applied to control the crystal growth and nanostructure in other materials. The wide applications of this method contribute to the development of various composite materials, and further progress in research on the interface phenomena of different materials is expected. We aim to develop a method to join different materials, control their nano/microstructure, and achieve patterning (Masuda et al, Bull Ceram Soc Jpn 49(5):356–360, 2014; Masuda, Bull Ceram Soc Jpn 47(12):929–934, 2012). Particularly, a composite material consisting a SnO2 nanosheet assembly and a polymer film is developed via crystal growth in the aqueous solution.

The development of a facile gas sensor for the ppb-level detection of acetone is required for realizing health diagnosis systems that utilize human breath. Controlling the crystal facet of a nanomaterial is an effective strategy to fabricate a high-response gas sensor without a novel metal catalyst. Herein, we successfully synthesized a SnO

Nanostructured TiO2 coatings were successfully formed on polyethylene terephthalate (PET) films and fluorine-doped tin oxide (FTO) films in aqueous solutions. They contained an assembly of nanoneedles that grow perpendicular to the films. The surface area of the coatings on PET films reached around 284 times that of a bare PET film. Micro-, nano-, or subnanosized surface roughness and inside pores contributed to the high nitrogen adsorption. The coatings on FTO films showed an acetaldehyde removal rate of 2.80 μmol/h; this value is similar to those of commercial products certified by the Photocatalysis Industry Association of Japan. The rate increased greatly to 10.16 μmol/h upon annealing in air at 500 °C for 4 h; this value exceeded those of commercial products. Further, the coatings showed a NOx removal rate of 1.04 μmol/h; this value is similar to those of commercial products. The rate decreased to 0.42 μmol/h upon annealing. NOx removal was affected by the photocatalyst’s surface area rather than its crystallinity.

The Na0.5Co0.9Cu0.1O2 thick film with the same thermoelectric performance as a Na0.5CoO2 bulk was formed on an alumina substrate by the screen-printing process. The power factor exceeded 0.3 mW/K2m, with the resistivity of 3.8 mWcm and the thermopower of 108 &mu, V/K. The thick film without any cracks strongly adhered to the substrate. The high-quality thick film had been realized through the carefully designed and improved process, mixing NaCl to promote the anisotropic sintering of Na0.5Co0.9Cu0.1O2, inserting a CuO interlayer to adhere the film and substrate, and Co&ndash, Cu substituting Cu for Co to control the sintering temperature.