Narrow Results

Exploring the morphogical and structural properties along with gas sensing applications both pure and Ti-doped SnO₂ ultra-thin films, were meticulously crafted on micromachined silicon substrate heater devices using a combination of classical soft chemical processes and hydrothermal techniques (SCPHTP). The fabrication process involved a two-step approach: initially, a 20nm layer of tin oxide was hydrothermally deposited onto the substrates, followed by annealing in wet air at 600^∘C for 5h using a standardized temperature variation protocol. Subsequently, secondary layers with thicknesses of 20, 40 and 60nm were sequentially deposited onto the tin dioxide devices and oxidized in wet air at 550^∘C and 600^∘C for 20h each, using the same temperature modulation scheme. Throughout this process, the hydrothermal deposition temperature remained constant at 180^∘C for both the initial and secondary layers of tin dioxide deposition. Additionally, Ti layers with thicknesses of 4 and 8nm were deposited onto the 20nm + 40nm system, subjected to annealing at 550^∘C for 20h, followed by 1-min annealing in dry O₂ at 700^∘C and 800^∘C, respectively, using a Rapid Thermal Annealing (RTA) system. Characterization of the crystalline and surface structures of the devices revealed a transformation of the soft chemical tin dioxide solution into the cassiterite structure of SnO₂, resulting in uniform large surface areas for the sensor devices. Moreover, Ti metal layers of 4 and 8nm thicknesses were fully converted into TiO₂ on the surface of the devices. Subsequent testing showcased higher current values in sandwich systems of 20nm + 60nm and 20nm + 40nm compared to the 20nm + 20nm configuration. Sensitivity and stability assessments for various volatile organic compounds (VOCs) and CO gases at a constant DC temperature of 400^∘C indicated excellent performance, with sensitivity to CO gas being contingent on relative humidity (RH). Notably, RTA-annealed and Ti-8 nm-doped sensor devices exhibited superior sensitivity and reproducibility, particularly when treated at 800^∘C in dry O₂ for 1min. This heightened performance can be attributed to the occupation of chloride ions in the oxygen sites of the as-synthesized SnO₂, resulting in enhanced sensing capabilities for VOC gases.

A well-aligned single-crystalline barium titanate (BaTiO₃) nanostructured layer was prepared by the growth and conversion of vertically aligned TiO₂ nanorods. This was achieved through a two-step hydrothermal method on fluorine-doped tin oxide (FTO)-coated glass substrates via the dissolution-nucleation-recrystallization mechanism. The morphology, crystal structure and optical properties were investigated using field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL) and Z-scan techniques. The X-ray and selected area diffraction patterns (SAED) confirmed the formation of the aligned single-crystalline tetragonal BaTiO₃ layer. The room temperature Raman spectrum showed the tetragonal TiO₂-related vibrational modes in BaTiO₃. The PL spectra indicated the coalescence of band edge emissions of BaTiO₃ and TiO₂ in the blue and visible regions of the investigated spectra. The Z-scan experiments performed using the CW Nd:YAG laser revealed a positive nonlinear refractive index on the order of 10${}^{-7}$ cm²W${}^{-1}$, indicating the self-focusing type of cation in the BaTiO₃ sample. The nonlinear absorption coefficient of the BaTiO₃ nanostructures in the order of 10${}^{-7}$ cm W${}^{-1}$ was also calculated. As expected, the BaTiO₃ nanostructure synthesized in this study is a good candidate for use in nonlinear optics.

Anatase Ti_1-xCo_xO₂ nanoparticles were prepared by a hydrothermal process at 180 °C. Ferromagnetic hysteresis loops of the as-prepared samples were measured at room temperature. The Ti_1-xCo_xO₂ (x = 0.0376) powder shows coercivity up to 700 Oe, which is the highest value reported for anatase Ti_1-xCo_xO₂. X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetic measurement results provided evidence that Co was incorporated into TiO₂ lattice. Combined with the fact that the preparation was carried out in an oxidized environment starting from cobalt (II) in the oxidized state, it is suggested that the homogeneous doping of Co into the lattice of anatase should be responsible for the improvement of coercivity in anatase Ti_1-xCo_xO₂ nanoparticles.

Boron nitride nanocrystals have been prepared in a hydrothermal route. The crystalline phases have been identified as cubic boron nitride (cBN) and orthorhombic (oBN) by XRD and FTIR. Further evidences for the formation of cBN have been obtained from microanalysis and composition identification by HRTEM, SAED and EDS.

Nanocrystal MnO₂ was successful synthesized by hydrothermal method under pulsed magnetic field. The effect of pulsed magnetic field on the nucleation and growth of MnO₂ was studied by XRD and SEM analysis. It was found that the morphology of MnO₂ has been changed comparing without magnetic field. However, there were no different phases presented when pulsed magnetic field was applied.

Single crystalline hydroxyapatite nanorods (HAp-NRs) were synthesized using a simple hydrothermal method. The synthesized HApNRs have an aspect ratio of about 8-10. A closer inspection of the nanostructure of a single nanorod revealed a highly regular and defect-free lattice with unique crystallographic plane orientations. X-ray Diffraction (XRD) pattern shows the highly crystalline nature of the product. The Field Emission Scanning Electron Microscopic (FESEM) image shows the uniform size distributed rod like morphology of length 100-150nm and diameter of about 15-20nm. Transmission Electron Microscopic analysis (TEM) and High-Resolution TEM (HRTEM) images provide further insight into the microstructure and morphology of the product. The selected area electron diffraction (SAED) pattern confirms that the nanorods are single crystal in nature. The mechanical strength of hydroxyapatite was studied by reinforcing hydroxyapatite with High Molecular Weight Polyethylene (HMWPE). It clearly shows that the mechanical properties of the nanorods are high when compared to that of bulk HAp. Finally the composites were characterized by means of thermal analysis including thermogravimetry analysis and differential thermal analysis (TGA-DTA) in order to study the thermal stability of the composite and the effect of filler in HMWPE.

In this paper, a newly designed composite of magnetic nano-Co₃O₄ fiber coated on carbon fiber (Cf) is prepared and characterized for the electromagnetic interference (EMI) shielding properties. XRD, SEM and TEM are used to investigate the micromorphology and microstructure evolution during the preparation. By hydrothermal method, the flowerlike clusters of single crystal flake-Co(OH)₂ are first obtained on Cf. The firstly prepared Co(OH)₂ sheets then turn into Co₃O₄ fibers during the next calcination step. The continuous and loose coating of magnetic Co₃O₄ nanofibers is finally obtained on the Cf. The loose coating is in proportion to the weight loss, and the wirelike Co₃O₄ is good for the interface strength for the Cf composite preparation. Based on the above work, the loose magnetic fibers coating on the Cf could be a feasible composite structure for the EMI composite materials integrated with absorbing and reflecting.

In this study, the preparation of ternary photocatalyst using a simple hydrothermal method is shown with high performance. A ternary composite consisting of tungsten sulfide (WS${}_2)$ nanosheets, titanium oxide (TiO${}_2)$ and gold (Au) nanoparticles is used to the extend the visible-light absorption region of TiO₂. The morphological and spectroscopic natures of the prepared sample were analyzed using scanning electron microscopy (SEM), Raman spectroscopy and ultraviolet–visible (UV–vis) photospectroscopy. The photocatalysis measurement for photodegradation of methylene blue dye was performed under the visible light. The photocatalytic studies suggest that in the ternary composite, consisting of three materials with different energy levels, the electrons excited form a cycle to lower the probability for the recombination of electron–hole pairs enhancing the property of photocatalytic activity of TiO₂.

CaWO₄ crystals were prepared by hydrothermal method assisting with phenol-formaldehyde polymer. The morphology can be controlled by polymer, and X-ray diffraction patterns results present a scheelite-type tetragonal structure, characteristic infrared active modes for O–W–O in the range from 500 cm${}^{-1}$ to 4000 cm${}^{-1}$ by Fourier transform infrared spectroscopic techniques. Raman results indicate that the crystals possess seven Raman active modes in the range from 100 cm${}^{-1}$ to 1000 cm${}^{-1}$. A scanning electron microscopy study reveals that the particles exhibit uniform morphology. Luminescent properties were investigated by photoluminescence measurements, multicolor phosphors were obtained when Ca${}^{2+}$ was substituted partly by lanthanide ions.

In this research, rod-like undoped and Zn doped h-MoO₃ thin films were grown on top of MoO₃ seed layers, using hydrothermal technique without adding any surfactant. Seed layers of MoO₃ were coated on top of glass substrates using spray pyrolysis technique. Structural, morphological and optical properties of thin films were examined. XRD pattern analysis showed that the seed layer has orthorhombic crystal structure. Also, it confirms the formation of hexagonal structure for thin films grown by hydrothermal. FESEM images show the formation of long, well-shaped hexagonal rod-likes. UV-Vis spectroscopy reveals band gap increasing from 3.2 eV to 3.54 eV, by increasing Zn.

In this study, transition metal dichalcogenide (TMD) material WS₂ and Au nanoparticles were combined with TiO₂ to enhance the photocatalytic performance under visible light. The WS₂ nanosheets were synthesized from bulk WS₂ via ultrasonic process, and the Au nanoparticles were prepared through the reduction reaction from HAuCl₄. The composite photocatalysts of WS₂/TiO₂/Au, TiO₂/Au, and WS₂/TiO₂ were synthesized by a one-step hydrothermal process. The light absorption property of the composites was determined by ultraviolet-visible (UV-vis) photospectroscopy. Surface analysis of WS₂ nanosheet, TiO₂ nanoparticles, and Au nanoparticles was performed by scanning electron microscopy (SEM). The chemical structure of composites and thickness of WS₂ nanosheets were analyzed by Raman spectra. The photocatalytic activity was measured by methylene blue degradation reaction under visible light. These results revealed the photocatalytic behavior of WS₂/TiO₂/Au, TiO₂/Au, and WS₂/TiO₂ composites, as well as WS₂ nanosheets. The WS₂/TiO₂/Au composite showed improved photocatalytic behavior among all samples. It is believed that the WS₂ nanosheet and Au nanoparticle extend the light absorption range from UV region to the visible region, as well as the WS₂/TiO₂/Au composite reduces the recombination of electrons. This study shows that the enhanced photocatalytic behavior of WS₂/TiO₂/Au composite can be used as photocatalytic applications in the future.

Thin film technology is significant in technological progress and modern research because it allows for the production of optoelectronic devices with improved characteristics. Because of its superior chromatic efficiency, tungsten oxide (WO₃) is one of the best candidates for energy-saving applications. In this study, undoped and tin (Sn)-doped WO₃ films were grown on top of WO₃ seed layers directly by a facile hydrothermal route at a temperature as low as 110^∘C for 24h. The seed layers were also deposited on top of glass substrates using spray pyrolysis. The results of tin doping on the structural, optical, and morphological characteristics of the WO₃:Sn films were studied. X-ray diffraction patterns show that peak intensities increase significantly by adding Sn and the films’ crystallinity was improved by rising Sn content. In the visible region, the average optical transmittance is around 13% and the optical bandgap changes from 2.61eV to 2.81eV, by increasing the dopant amount. Finally, the room temperature photoluminescence of samples shows intense green light emissions. The results of this research can be beneficial for the fabrication and performance optimization of electrical and optical devices such as gas sensors, electrochromic devices, and photosensors.

Well-defined CdS branched nanorod arrays on ITO glass were fabricated via a facile one-step hydrothermal approach in large scale employing cadmium sulfide and thiourea as starting agents. Structural and morphological evolutions of CdS branched nanorod arrays were studied by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A formation mechanism of the hierarchical structure via this one-step synthesis was tentatively studied by investigating the reaction time. Tree-like nanostructures can also be obtained at relative higher reaction temperatures. As CdS can directly grow on transparent conductive substrate, the product obtained here should have potential applications in optoelectric devices such as solar cells and light sources.

In this study, surface-enhanced Raman spectroscopic (SERS) substrates with reusability were carefully fabricated and investigated. Based on a simple and cost-effective hydrothermal process, zinc sheets were used as a base for growing zinc oxide nanorods (ZnO NRs) with hexagonal structures as templates for the SERS substrates. In the experimentation, the authors explored a variation of the physical NR structures based on precursors of zinc nitrate (Zn(NO${}_3{)}_2)$: hexamethylenetetramine (HMTA) at 1:1 ratio, in aqueous solution with DI water at a concentration of 2.5–20mM. The prepared zinc oxide templates were finally decorated with gold nanoparticles (Au NPs) with the sputtering deposition for 90s in order to promote the SERS-active surface. From physical observations, the scanning electron microscopic (SEM) results showed that the ZnO NRs exhibited an increase in size from 56.4nm to 244.06nm as the solution concentration was increased. Further investigations also demonstrated that the Au-decorated SERS-active samples had the gold nanoparticles covering the top of the ZnO NRs. The prepared SERS substrates were finally measured for the Raman enhancement with methylene blue (MB) as the test molecules. The results showed that the SERS substrates could detect the Raman peaks of the MB at the limit of detection of $1\times 10^{-6}$M. In addition, the SERS substrates were tested for reusability with the UV exposure, up to at least nine cycles. This work therefore reported the progress of the fabrications of the SERS-active materials with the reusable potentials in several SERS applications.

Well-oriented TiO₂ nanorod (NR) arrays were fabricated directly on conductive side of F/SnO₂ substrates via hydrothermal technique. The effect of growth time on the TiO₂ NR thin film was examined. Field emission scanning electron microscope revealed that NRs exhibited a tetragonal structure with square top facets. Thickness measurements indicated that the thicknesses of the samples increased from 0.234$\mu$m to 1.544$\mu$m as the growth time was extended. The investigation of XRD indicates that the TiO₂ films are single-crystalline type of rutile. The effect of growth time on optical and electrical properties has been studied. With optimum growth time, dye sensitized solar cell (DSSC) efficiency of 1.48% could be reached using 1.544$\mu$m long TiO₂ NR arrays as electrode.

A carbon precursor film was formed on a titanium plate by a hydrothermal method using glucose, and an amorphous film was obtained by carbonization at 400^∘C under an Ar atmosphere. The morphology and composition of the surface was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), and the interface contact resistance (ICR) under different pressures by simulating the working mode of the fuel cell. The corrosion resistance of amorphous carbon coatings was tested by simulating the proton exchange membrane fuel cells (PEMC). The amorphous coating showed excellent interfacial conductivity and great corrosion resistance, with high potential application in bipolar plates of PEMFCs

In this work, ZnO nanorods (ZnO NRs) were successfully synthesized on FTO-glass via hydrothermal technique. Two steps were followed to grow ZnO NRs. In the first step, the seed layer of ZnO nanocrystals was deposited by using a drop cast method. The second step was represented by the hydrothermal growth of ZnO NRs on a pre-coated FTO- glass with the seed layer. The hydrothermal growth was conducted at 90^∘C for 2h. The resulted structure, morphology and optical properties of the produced layers were analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) and UV-visible spectrophotometer, respectively. The analysis confirmed that the ZnO NRs grown by the hydrothermal method have a hexagonal crystal structure which was grown randomly on the FTO surface. The crystallite size was recorded 50nm and a slight microstrain (0.142%) was calculated. The bandgap was found to be in the range of 3.14–3.17eV. The ZnO NRs have a high density and large aspect ratio. A pH sensor with high sensitivity was fabricated using a two-electrode cell configuration. The ZnO NRs sensor showed the sensitivity of $-$59.03mV/pH, which is quite promising and close to the theoretical value ($-$59.12mV/pH).

Silver nanoparticles (Ag NPs) are prepared using two different techniques namely hydrothermal and laser ablation methods. The purpose of this study is to find a more suitable method to prepare Ag NPs through comparison that can give stable and size-controlled silver nanoparticles. Techniques used for observations are X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Comparison of results exhibited that hydrothermal process is a more suitable method to prepare silver nanoparticles with smaller uniform size and better yield as compared to laser ablation method. Also, at low temperature, NPs obtained using hydrothermal process provide better control on morphology, high purity and narrow size distribution.

In this work, morphological and physical properties of pyramid-like ZnO nanostructures fabricated on Sb-doped ZnO seeding films annealed under different atmospheres are extensively studied. The Sb-doped ZnO seeding films were first prepared by sol–gel spin coating technique onto glass substrate then annealed in nitrogen, air and argon followed by low-temperature hydrothermal process for ZnO nanostructures fabrication. The morphological results exhibit the growth of pyramid-like ZnO nanostructure with increasing density of the ZnO nanostructures. The crystal structure shows pyramid-like ZnO wurtzite hexagonal growth along the c-axis without any impurity phase. The growth of pyramid-like ZnO nanostructures is due to the high growth rate of (002) plane. Photoluminescence spectra exhibit the near-band-edge of all samples while the red emission appears in ZnO nanostructures after the hydrothermal process due to the imperfection in the crystal. The reflectance of ZnO nanostructures covers the visible region with the absorption edge of 375nm. The calculation shows the relevant energy band gaps in the range of 3.26–3.28eV. The difference in hydrothermally grown ZnO nanostructures is significantly affected by different annealing atmospheres.

The effect of iron content on the structure, morphology and magnetic properties of (Ni${}_{60}$Co${}_{40}$)${}_{100-}$${}_x$Fe${}_x$ powders synthesized by hydrothermal method has been studied. Several samples have been elaborated for different Fe content ($x$= 0, 3, 5, 7, 10 and 13.5). The as- prepared samples have been characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometry (VSM). From XRD spectra and for all Fe content, we have shown the presence of both face centered cubic (FCC) and Hexagonal (HCP) nanosized phases. The lattice parameter increases with increasing Fe content and the grains size varies with Fe content to reach a minimum value of 32 nm for (Co${}_{40}$Ni${}_{60}$)${}_{90}$Fe${}_{10}$. From hysteresis curves, we have extracted the saturation magnetization, Ms, and the coercivity, Hc. We noticed that Ms increases and then decreases as a function of Fe content. The values of Hc vary from 156 Oe to 186 Oe depending on the particles shape.