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This study was to evaluate the acid-buffering capacity and antibacterial properties of orthodontic adhesives containing bioactive glasses (BAGs) (45S5, 45S5F, S53P4), Hydroxyapatite, beta-tricalcium phosphate, and Canasite. Fillers comprising 15 wt% bioactive glasses, HAp, β-TCP, and Canasite incorporated with 55 wt% silanated glass were added to a mixture of UDMA/TEGDMA. Acid-buffering capacity was tested by exposing disc-shaped samples of each adhesive to medium of bacteria-produced acids, and pH changes were recorded at 24 and 48 h. Antibacterial properties were assessed by indirect testing by exposing polymerized adhesive samples to a medium and direct testing by immersing the specimens in solutions containing S. mutans and S. sanguinis. A significant buffering capacity was shown by the 45S5, 45S5F and S53P4 BAG adhesives. The antibacterial properties were not significant in all experimental adhesives. Therefore, the experimental orthodontic adhesives containing BAGs demonstrated a significant buffering capacity but did not show significant antibacterial properties against S. mutans and S. sanguinis.

Copper ferrite (CuFe2O4) has been well known because of its interesting physical properties, and it has been used as a candidate for many applications such as Li-ion storage, gas sensors, catalysts, and magnetic devices. Copper ferrite (CuFe2O4) structure is of significant importance in the context of engineered materials and their structure development due to the natural superlattice structure. In this work, copper ferrite (CuFe2O4) nanostructures with cobalt doped were prepared in the form on glass substrates by a spin-coating technique. The different doped amounts of cobalt (Co) doped copper ferrite thin films were used to prepare thin film at room temperature and then post-annealed at 500◦C in the air up to 5 hours. The nanostructures of fabricated thin films are characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS). The chemical composition of nanostructure in thin film form can be extracted XPS due to their surface sensitivities. The property modification by cobalt doping in copper ferrite (CuFe2O4) thin film was systematically investigated for various mixing ratios and post-anneal temperatures. It was found that the XPS spectra of copper 2p peak exhibited the significant change for the modified atomic arrangement of nanostructure thin film after etching.

Fused deposition modelling (3D) printing is used extensively in modern fabrication processes. Although the technique was designed for polymer printing, it can now be applied in advanced ceramic research. An alumina/aluminum (Al2O3/Al) composite refractory can be fabricated by mixing metallic aluminum in a polymer to form an Al/polymer composite filament. The filament can be printed via a regular thermoplastic material extrusion printer with no machine modification. In this study, Al/polymer composite samples were printed in a crucible shape and sintered at different temperatures to form Al2O3/Al composite refractory specimens. The sintered samples were examined via several analytical techniques such as scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, compressive testing, hardness testing, XPS, and Hall measurement. Unlike other ceramic printing techniques that require expensive 3D printing machines and a very high temperature furnace (above 1500 °C) for post processing, this study demonstrates the viability of fabricating refractory items using a cost-effective fused deposition modelling 3D printer and a low temperature furnace (900 °C). The samples did not disintegrate at 1400 °C and were still sufficiently electrically conductive for advanced refractory applications.

The objective of this study was to evaluate the antibacterial properties and pH changes of bioactive glasses and zinc oxide nanowire in different concentrations. Bioactive glasses (45S5 and 45S5F) were prepared in three concentrations of 10, 20, and 50 mg/ml and zinc oxide nanowire was prepared in 1 and 5 mg/ml concentrations. The materials were exposed to 500 ml brain heart infusion broth (BHI) with 1.5 x 107 of S.mutans and S.sanguinis separately. Antibacterial properties were tested indirectly by collecting 100 ml of each sample and transferred into a 96 well-plate. The optical density (OD) was evaluated using spectrophotometry at 630 nm at 24h and 48h. The pH changes were recorded. The data were statistically analyzed by Kruskal-Wallis tests. The result showed that the pH changes were significantly different in the Bioactive glass samples, while zinc oxide nanowire showed stable pH. Antibacterial activity against S.mutans was significant lower for 45S5 at 50 mg/ml, 45S5F and zinc oxide nanowire in all concentrations at 24 h. While in 48 h, 45S5, 45S5F and zinc oxide nanowire showed significant antibacterial activity in all concentration except 45S5F at 10 mg/ml. Antibacterial activity against S.sanguinis was significant for 45S5 and 45S5F at 20 and 50 mg/ml and zinc oxide nanowire in all concentration at 48h. It can be concluded that Bioactive glasses (45S5 and 45S5F) exhibited antibacterial properties and pH changes depending on its concentration, while zinc oxide nanowire exhibited antibacterial properties at low concentrations with a constant pH value.

A facile synthesis of reduced graphene oxide (rGO) and methionine film modified screen printed carbon electrode (rGO-methionine/SPCE) was proposed as a disposable sensor for determination of food colorants including amaranth, tartrazine, sunset yellow, and carminic acid. The fabrication process can be achieved in only 2 steps including drop-casting of rGO and electropolymerization of poly(L-methionine) film on SPCE. Surface morphology of modified electrode was studied by scanning electron microscopy (SEM). This work showed a successfully developed novel disposable sensor for detection of all 4 dyes as food colorants. The electrochemical behavior of all 4 food colorants were investigated on modified electrodes. The rGO-methionine/SPCE significantly enhanced catalytic activity of all 4 dyes. The pH value and accumulation time were optimized to obtain optimal condition of each colorant. Differential pulse voltammetry (DPV) was used for determination, and two linear detection ranges were observed for each dye. Linear detection ranges were found from 1 to 10 and 10 to 100 µM for amaranth, 1 to 10 and 10 to 85 µM for tartrazine, 1 to 10 and 10 to 50 µM for sunset yellow, and 1 to 20 and 20 to 60 µM for carminic acid. The limit of detection (LOD) was calculated at 57, 41, 48, and 36 nM for amaranth, tartrazine, sunset yellow, and carminic acid, respectively. In addition, the modified sensor also demonstrated high tolerance to interference substances, good repeatability, and high performance for real sample analysis.

Fused deposition modelling (3D) printing is used extensively in modern fabrication processes. Although the technique was designed for polymer printing, it can now be applied in advanced ceramic research. An alumina/aluminum (Al

A thick anodic aluminium oxide (AAO) was used as a laminated hard coating film on high-density polyethylene (HDPE) without a binder. This thick alumina surface has a large number of polymeric nanofibers rooting inside which makes it a composite between polymer fibre and alumina. The AAO-coated film was crystalline gamma-Al2O3 and its Vickers hardness was higher than super alloy and martensitic stainless steel which has a durable and wear resistance surface despite the substrate is still a lightweight polymer. The film surface was firmly adhered to the polymer substrate. Therefore, it can be applied in many applications which require an extreme hard coating such as a transparent hard film or a special made polymer knife in which the sharpness is hardly worn out.

Nickel doped CuFeO2were synthesized by using sol-gel method and two steps heat annealing. The first annealing was executed at 500°C in air to transform the dried gels into spinel oxide phases and the second one was done at 800°C in argon to transform the spinel oxide phase into the delafossite oxide phase. The crystal orientation and the morphology of nanostructure of annealed samples were investigated. Result revealed that CuFe1-xNixO2 samples are hexagonal delafossite structure and the average grain size is 0.258 – 0.760 µm. The CuFeO2 sample exhibited the paramagnetic behavior. The CuFe1-xNixO2 (x = 0.01–0.05) samples exhibited a weak ferromagnetic behavior and a linear paramagnetic behavior upon hysteresis was observed. The maximum of coercivity, remanence and area of hysteresis loop were 26.06 mT, 1.84x10-4 a.u. and 39.63x10-3, respectively. In addition, the valence states of delafossite oxide were also characterized. The results suggest that Cu oxidation state of mixture between Cu+ and Cu2+ ions, Fe oxidation state of Fe3+ as majority ions and Ni oxidation state of Ni2+ ions.

Interpenetrating networks (IPNs) of titania, having high cycling stability and rate capability, and carbon, having high electrical conductivity and capacity, ultrafine fibers were fabricated by a co-electrospinning technique in opposite directions. The IPN structure promoted a contact between titania and carbon fibers, minimized strain during ion de-insertion, and prevented agglomeration that shortened the cycling stability. Images from scanning electron microscopy with backscattering electron detector and X-ray diffraction spectra confirm the existence of the IPN structure of both types of fibers. Thermogravimetric analysis and Raman spectroscopy of the composite fibers reveal their 37 wt% of titania content and 1.2 ratio between disorder and graphitic carbon (I D /I G ). A galvanostatic curve displays stable reversible capacities of 202 and 247 mA h g −1 for charge and discharge after the fifth cycle at a current density of 25 mA g −1 . The material had a superior discharge capacity of 151 and 123 mA h g −1 at 125 and 250 mA g −1 , respectively. Moreover, the discharge capacity could be maintained at 134 mA h g −1 after 100 cycles at 125 mA g −1 with a Coulombic efficiency of more than 98%, presenting a long life cycle of batteries. Therefore, the prepared IPN composite fibers can be an efficient anode for sodium-ion batteries.

X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique that measures the elemental composition, empirical formula, chemical state and electronic state of the elements. Moreover, XPS is also widely used in semiconductor applications as the main characterization technique. In this work, chromium and magnesium doped copper ferrite thin films were prepared on the glass substrates by spin-coating technique at room temperature. The stoichiometry 1:2 ratio was used for copper (II) acetate monohydrate and iron (III) nitrate nonahydrate with different doping percentages from 5%, 10%, 15% to 20% of chromium and magnesium. After spin-coated, the films were annealed at 120°C, 200°C, 300°C and 400°C in air. The surface properties of the post-annealed thin films can be characterized by XPS technique due to their surface sensitivities. Therefore, the surface properties of different doped amounts of chromium and magnesium thin films were systematically investigated for different annealing temperatures. For varying anneal temperatures, the oxidation numbers of copper and iron ions were different. At low temperature, the oxidation number of copper was Cu+ and iron was a mixture of Fe2+ and Fe3+ while at high-temperature, the copper and iron ions showed Cu2+ and iron Fe3+ characteristics, respectively. After etching, the oxidation number of copper and iron ions at the surface shifted to lower oxidation state.

Highly cross-linked zinc oxide (ZnO) with the nanorod morphology of tetra-pods was successfully prepared using a microwave irradiation (MWI) technique. In comparison with the available conventional techniques, the MWI technique has the advantage of producing different morphological structures with high purity and in a shorter reaction time. These tetra-pods consist of a ZnO core in the zinc blende from which four ZnO arms emerge in the wurtzite structure. In this investigation, the effects of irradiation times and the growth mechanism of ZnO nanotetra-pods were discussed. The structural, morphological and optical properties of ZnO nanorods were investigated by field emission scanning electron microscopy, X-ray diffraction, an ultra violet visible spectrometry and energy-dispersive spectroscopy. The electrochemical corrosion behaviours of an AZ91-grade Mg alloy and a ZnO/PN nanotetra-pod-coated Mg alloy were investigated. The Tafel plot revealed that the corrosion of Mg drastically decreased on coating with a thin layer of ZnO nanotetra-pods and PN (Mg/PN/ZnO) compared to Mg in a KOH electrolyte.

In this work, a new room-temperature ammonia gas sensor based on n-type copper oxide (CuO) semiconductor was fabricated by 3D printing with fused deposition modeling (FDM) technique and sintering method. The polylactic acid (PLA) was blended together with Cu particles and extruded into the filament form for FDM printing. The PLA/Cu composite was printed and calcined in a furnace to obtain semiconducting CuO. The structural characterization results of 3D printed sensor showed monoclinic CuO phase and scaffold structures, which provided active porous sites for enhanced gas adsorption and room-temperature gas-sensing performances. According to gas-sensing data, the 3D printed CuO gas sensor exhibited good repeatability, high stability (>3 months), low humidity dependency (25–65 %RH), high sensitivity and selectivity towards ammonia at room temperature. The sensor response increased linearly with increasing NH3 concentration from 25 to 200 ppm. The sensing mechanism of the 3D printed CuO sensor was proposed based on the resistance change via reaction on adsorbed surface oxygen species or direct electron transfer between ammonia molecules and CuO. This approach could open up new ways to fabricate semiconductor gas sensors with controllable sizes and shapes for future gas-sensing applications.

A CuO semiconductor was successfully prepared by fused deposition modeling (FDM) and sintering technique. A 1.75 mm high-loading Cu composite was extruded and printed into a desired size and shape. The sample was sintered and calcined to transform Cu powder to CuO semiconductor. The 3-dimensional (3D) printed CuO had a scaffold structure with a half density of bulk CuO. It had a mechanical characteristic like a scaffold ceramic although prepared by FDM machine. van der Pauw measurement and UV-visible absorption spectroscopy were used to determine the electrical and optical properties of the 3D printed CuO respectively. The 3D printed CuO was used as an example of a 3D semiconductor which has a response to light, pressure, and temperature. This technique has a potential to be applied in any FDM machine which might allow anyone to print semiconductor or other related materials.

The commercial heating oven usually consumes the power around 2500–3000 Watt and the temperature inside the oven is still below 350 °C. If we need to increase a temperature above 500 °C, a special heating setup with a higher power furnace is required. However, in this work, we propose a composite material that interacts with 2.45 GHz 500 Watt microwave and rapidly redeems the thermal energy with the temperature around 600–900 °C. The composite amorphous material easily forms liquid ceramics phase with a high temperature output and responds to the microwave radiation better than that of the solid phase. During the heating process, phase transformation occurs. This method is very effective and can be used to drastically reduce the power consumption of any heating process.

In this work, 3D printed electrodes fabricated by blending Polylactic acid (PLA) with carbon nanotube (CNT), CNT/copper (Cu), CNT/zinc oxide (ZnO) composites were applied as cyclic voltammetric sensors for electronic tongue analysis. Porous rectangular rod-shape electrodes were fabricated by fused-deposition-modelling 3D printing of the CNT-based composites produced by a solution blending method. The physical and chemical properties of 3D printed electrodes were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, four-point-probe electrical tests and thermoelectric measurements. The characterization results confirmed uniform distributions of CNTs, Cu particles and ZnO nanorods in the composites and high electrical conductivity of interconnected CNT networks. The additions of Cu and ZnO nanostructures slightly modified the electrical conductivity but significantly changed thermoelectric properties of the material. Cyclic voltammetric (CV) data demonstrated satisfactory stability of the composite materials under corrosive CV conditions. In addition, Cu and ZnO additives provided distinct electrochemical behaviors towards K4Fe(CN)6, H2O2 and nicotinamide adenine dinucleotide. Principal component analysis of CV features could effectively distinguish the three chemicals with various concentrations, illustrating the possibility to apply 3D printed CNT/PLA-based electrodes for electronic tongue applications.

Photoresponse characteristic from efficient exciton dissociated heterojunction based on copper phthalocyanine (CuPc) and fullerene (C60) layers was observed the different spectrum responses under positive and negative biases. The nanostructures of CuPc and C60 thin films were fabricated between transparent indium tin oxide (ITO) and aluminum (Al) electrodes. The 100 nm thick of CuPc and C60 layers were deposited on patterned ITO glass substrates by thermal evaporation with quartz thickness monitor. Photoresponses of the fabricated devices were investigated by current measuring as a function of wavelength in range of 400 to 700 nm. Measured current in Al/C60/CuPc/ITO structure when applied negative voltage to ITO electrode is higher than that of positive voltage case. Under monochromatic light, the photoresponse characteristic of Al/C60/CuPc/ITO structure under negative bias shows dominate response current peak at around 450 nm and double peaks in range of 500-700 nm originated from C60 and CuPc layers, respectively. These two response characteristics can be described by the combination of responses from Al/C60/ITO and Al/CuPc/ITO structures. The response current characteristics of Al/C60/ITO and Al/CuPc/ITO structures also agree with the optical absorptions of C60 and CuPc layers, respectively. By applying positive bias to Al/C60/CuPc/ITO structure, the photoresponse characteristic has only one peak at about 450 nm that is similar to the response in Al/C60/ITO structure only. This indicates that under positive bias, the photocurrent only from C60 layer can be observed.

A novel fabrication of microelectronic nose based on ZnO nanowires and ZnO surface modifications including ZnO–ZnAl2O4 core–shell nanowires and ZnO–Zn2TiO4 core–shell nanowires gas-sensing elements operated at room temperature is reported. By combining vapor-phase transport processes and atomic layer deposition techniques, highly homogeneous core–shell nanowires structures can be successfully obtained on large scale areas. Under ultraviolet illumination of the specific oxide surfaces, photo-stimulated oxygen species (O2−(ads)) respond to and dominate the gas sensing mechanism of the core–shell nanowires at room temperature. Principal component analysis results show the perfect discrimination of gases including toxic gases and non-toxic gases. This novel device can be used to identify both gas types with concentrations in the ppb level at room temperature.

Multilayer poly (3-hexylthiophene)-CNT/C60 thin films on ITO glass substrate was fabricated regarding to the function of each layer. Poly (3-hexylthiophene) (P3HT) is used as a donor layer and fullerene (C60) is used as an acceptor layer of the device. The carbon-nanotube (CNT) is homogeneously mixed in the donor layer to increase charge transportability. The structures of poly (3-hexylthiophene), poly (3-hexylthiophene)-CNT were fabricated in comparison of poly (3-hexylthiophene)-CNT/C60 thin films. The P3HT-CNT bulk heterojunction was deposited on ITO glass substrate by spin coating technique and then the C60 thin film was deposited on the P3HT by thermal evaporating technique. The I-V characteristic of ITO/P3HT-CNT/Al and ITO/P3HT-CNT/C60/Al were investigated in the monochromatic light. The result showed that the ITO/P3HT-CNT/Al structures respond with red and green light, and the ITO/P3HT-CNT/C60/Al structure responds with blue light. The UV absorption was measured and the result was consistence with the I-V characterization.

A general schematic is developed for the main parameters leading to the formation of vapor–solid and catalyst-assisted-grown ZnO nanowires. We developed a schematic representation of the different parameters influencing the growth and discuss them in detail. Selected shape diagrams are presented that correlate the various changes in parameters (carrier and reaction gas flow, powder and substrate temperature) to the observed nanostructures. With the help of the here-presented shape diagrams, we are able to identify unique parameter ranges for film formation, vapor–solid growth, and the switching to the catalyst-assisted VLS-growth mechanism. The systematic experiments demonstrate the controlled growth of VS and catalyst-assisted-grown ZnO nanowires in a CVD reactor by the carbothermal reduction method based on either upstream or downstream deposition techniques.

Defi ning the position of an object on a planar substrate by force sensors is a common technology nowadays. Many products are commercialized worldwide, which make use of force sensors, especially, for instance, touchpads. Here advanced lithography processes together with piezoelectric materials are demonstrated to fabricate an extremely high resolution force sensor. The approach combines a large array of nanoscale piezoelectric lines fabricated on Si wafer by phase-shift lithography and atomic-layer-deposition-based spacer lithography techniques. These key lithography methods are utilized to fabricate ultralong (cm range) nanolines on the wafer scale. ZnO and P(VDF-TrFE) are selected here as materials for piezoelectric signal generators. The detection mechanisms are explained and simulations combined with experimental data are demonstrated to prove the concept. The signal generated when an object approaches one single line is in the nanoampere range. The result enables a new and simple path for a device fabrication, which defi nes the position with micro- and nanometer resolution and can be used, for example, as micro- and nanoparticle trackers.

A variety of nanowires can be grown in a tube furnace via the transport of evaporated species by a carrier gas toward substrates. The insufficient understanding and the resulting limited control typical for this research area motivated us to systematically study the distribution of the growth species in such processes and evaluate its effect on the nanowire growth. Calculations based on simple considerations as well as more sophisticated numerical (COMSOL) simulations were utilized to follow the time evolution of the species distribution at different carrier gas pressures and flow rates. We demonstrate that the balance between diffusion and convection must be appropriately tuned to ensure steady growth conditions (not achieved in many of the previously reported experiments). Experimental data of Si and ZnO nanowires growth is presented and supports the simulations. Insight into the appropriate design of nanowires growth experiments and a universal basis to compare between the results of different laborato...

A simple fabrication of ZnO-nanowire-based device and their implementation as a pH sensor, temperature sensor, and photo detector is reported. The presented multifunctional ZnO multiple-nanowire sensor platform contains a Au finger structure, which is realized by conventional photolithography on a SiO2 substrate. The nanowires are grown using thermal chemical vapor deposition. In order to detect the physical signals, changes in electrical signals were measured (conductance and current). For temperature sensing, the current behavior from 90 to 380 K under vacuum conditions exhibit a tunneling behavior between spaced nanowires. For photo sensing, the current response between the “on” and “off” states of light was measured when exposed to different wavelengths ranging from UV to visible light. Finally, for pH sensing the conductance was measured between a pH of 5 and 8.5. The ZnO nanowires were protected from chemical attacks by a thin layer of C4F8-plasma-based coating.

A shape diagram of ZnO nanostructures grown by thermal evaporation of a ZnO:C powder (carbothermal method) was derived by varying the powder source temperature (Tp) and the substrate temperature (T...

Semiconductor nanowire devices have several properties which match future requirements of scaling down the size of electronics. In typical microelectronics production, a number of microstructures are aligned precisely on top of each other during the fabrication process. In the case of nanowires, this mandatory condition is still hard to achieve. A technological breakthrough is needed to accurately place nanowires at any specific position and then form devices in mass production. In this article, an upscalable process combining conventional micromachining with phase shift lithography will be demonstrated as a suitable tool for nanowire device technology. Vertical Si and ZnO nanowires are demonstrated on very large (several cm(2)) areas. We demonstrate how the nanowire positions can be controlled, and the resulting nanowires are used for device fabrication. As an example Si/ZnO heterojunction diode arrays are fabricated. The electrical characterization of the produced devices has also been performed to confirm the functionality of the fabricated diodes.

ZnO nanowires and related materials are in the focus of attention for electronic, optical or sensor applications. However, size, position and arrangement control are essential conditions for the development of future nanowire based devices. Various kinds of template methods including nanosphere lithography and UV laser interference lithography are powerful tools for the preparation of the starting metal catalyst arrays and will be demonstrated and discussed. However, only if the growth mechanism and its guiding parameters are understood in detail, the template will force a pattern arranged growth of nanowires. The paper gives an overview of the various kinds of growth modes for vertical arranged nanowires. Specific experimental conditions establishing the VS or the VLS growth are discussed. In addition, insight is given why the patterning is not all the time conserved and how to overcome these obstacles. In the second part different kinds of applications are summarized. Electronic properties are discussed based on metal-semiconductor-metal devices. The influence of a core-shell nanowire structure on the optical properties is demonstrated. In addition, a simple approach for ZnO nanowire based gas sensors is discussed and shown. As a last example, the transfer of Al 2 O 3 coated nanowires into spinel tubes is reported.

The controlled reversible switching between vapor−solid (VS) and vapor−liquid−solid (VLS) growth of ZnO nanowires (NWs) mediated by organic solvents, namely, ionic liquids (ILs), is demonstrated. S...

A binary flow of a Ar/Zn mixture has been used in simulations as well as in physical growth experiments for ZnO nanowire growth by vapor phase deposition. Systematic investigations of the gas transport and the chemical behavior under controlled vacuum and flow conditions revealed that the gases emerging from carbothermal reduction, namely, CO(g) and CO2(g), are not enough to stimulate a controlled ZnO nanowire growth. An optimum O-2 concentration is crucial to promote nanowire growth, while CO(g) and CO2(g) enhance the tendency to grow a film. importantly, the here presented simulations can be used to predict and tailor the region of nanowire growth under appropriate assumptions for any tube furnace.

In this work, the controlled fabrication of highly ordered ZnO nanowire (NW) arrays on silicon substrates is reported. Si NWs fabricated by a combination of phase shift lithography and etching are used as a template and are subsequently substituted by ZnO NWs with a dry-etching technique and atomic layer deposition. This fabrication technique allows the vertical ZnO NWs to be fabricated on 4 in Si wafers. Room temperature photoluminescence and micro-photoluminescence are used to observe the optical properties of the atomic layer deposition (ALD) based ZnO NWs. The sharp UV luminescence observed from the ALD ZnO NWs is unexpected for the polycrystalline nanostructure. Surprisingly, the defect related luminescence is much decreased compared to an ALD ZnO film deposited at the same time ona plane substrate. Electrical characterization was carried out by using nanomanipulators. With the p-type Si substrate and the n-type ZnO NWs the nanodevices represent p–n NW diodes.The nanowire diodes show a very high breakthrough potential which implies that the ALD ZnO NWs can be used for future electronic applications.

A new technique is reported for the transformation of smooth nonpolar ZnO nanowire surfaces to zigzagged high-index polar surfaces using polycrystalline ZnO thin films deposited by atomic layer deposition (ALD). The c-axis-oriented ZnO nanowires with smooth nonpolar surfaces are fabricated using vapor deposition method and subsequently coated by ALD with a ZnO particulate thin film. The synthesized ZnO-ZnO core-shell nanostructures are annealed at 800 °C to transform the smooth ZnO nanowires to zigzagged nanowires with high-index polar surfaces. Ozone sensing response is compared for all three types of fabricated nanowire morphologies, namely nanowires with smooth surfaces, ZnO-ZnO core-shell nanowires, and zigzagged ZnO nanowires to determine the role of crystallographic surface planes on gas response. While the smooth and core-shell nanowires are largely non-responsive to varying O(3) concentrations in the experiments, zigzagged nanowires show a significantly higher sensitivity (ppb level) owing to inherent defect-rich high-index polar surfaces.

Two novel approaches for patterned growth of ZnO nanowires (NWs) based on the selective deposition of zinc acetate (ZA) solution precursors are presented and compared. The first is using the topographical confinement within a photoresist pattern on Si/SiO2 substrates (type I), and the second is using preferential chemisorption on self-assembled monolayer modified Au electrodes on Si/SiO2 substrates (type H). In both approaches, the ZnO seeds from the ZA solution form crystallites without severe defects over a large area via annealing at 350 degrees C. These seed layers were used to grow ZnO NWs via a catalyst-free vapor-phase deposition method using temperatures of up to 900 degrees C. The presented method is effective for realizing NW growth on both Si and Au electrodes by preserving the electrode configuration even at such high temperatures used for NW growth, which is a novelty and crucial for future sensor applications. As a result NWs connected through metal contact pads or electrodes have been realized in very simple and effective way. As a test of principle the resulting configurations were used to demonstrate a highly sensitive room temperature CO sensor. A CO concentration as low as 120 ppb was detected using both types of sensors. The type II sensor exhibited enhanced sensing properties compared to that of type I.

One-step device fabrication through the integration of nanowires (NWs) into silicon microchips is still under intensive scientific study as it has proved difficult to obtain a reliable and controllable fabrication technique. So far, the techniques are either costly or suffer from small throughput. Recently, a cost-effective method based on thin-film fracture that can be used as a template for NW fabrication was suggested. Here, a way to integrate NWs between microcontacts is demonstrated. Different geometries of microstructured photoresist formed by using standard photolithography are analyzed. Surprisingly, a very simple ‘‘stripe’’ geometry is found to yield highly reproducible fracture patterns, which are convenient templates for fault-tolerantNWfabrication. Microchips containing integrated Au, Pd, Ni, and Ti NWs and their suitability for studies of conductivity and oxidation behavior are reported, and their suitability as a hydrogen sensor is investigated. Details of the fabrication process are also discussed.

In this work, the ionic liquid assisted technique was used to control the growth characteristic of ZnO nanowires (NWs). The major change after adding ionic liquid into the growth system was the change in NW growth orientation, which was shifted from polar c- to non-polar a-orientation. Room temperature photoluminescence demonstrates a big reduction of the green luminescence which implies an annihilation of deep level emission. We propose two possible mechanisms responsible for the reduction of the green emission: The first mechanism is the passivation of ZnO NWs surface by fractions of ionic liquid employed for the growth, which further reduces the green emission. The second mechanism is the reduction of the defect density by changing the growth orientation. By using a semi-empirical Austin Model 1 method, the formation energy of oxygen vacancies in c- and a-oriented ZnO NWs has been simulated and compared. Accordingly, the gas-sensor constructed from ionic liquid assisted ZnO nanowires does not response when exposed to CO. This inert sensitivity is caused by the suppressed adsorption of CO molecules due to the presence of the passivation layer. The study presented here provides a new insight of how the recombination appears at the surface of ZnO NWs.

We report the electrical properties of individual as-grown ZnO nanowires (NWs) on SiO2∕Si and GaN/sapphire substrates. Carrier transport in metal-semiconductor-metal junction is interpreted in terms of thermionic emission and tunneling current which was assumed to dominate independently on reverse and forward contacts. Current flow in ZnO NWs grown on SiO2∕Si was dominated by thermionic emission. In contrast, both thermionic emission and tunneling current contributed to the transport in ZnO NWs epitaxially grown on GaN/sapphire. Carrier concentrations of ZnO NWs were estimated to be around 8.88×1017cm−3 if grown on SiO2∕Si and 1.18×1018cm−3 if grown on GaN/sapphire, respectively.