Band Gap Measurements Research Articles

Semiconducting cobalt oxide nanocatalyst obtained through an eco-friendly thermal decomposition

The combination of an intense absorption of visible light and p-type semiconducting nature makes spinel cobalt oxide (Co3O4) a very attractive material for various optoelectronic applications. However, the traditional methods for its synthesis have been either time- and energy-consuming or relying on toxic chemicals. To solve this issue, a simple, facile, and eco-friendly method of synthesis was successfully developed to obtain spinel Co3O4 nanoparticles. The novel method for obtaining pure and monophasic Co3O4 reported here is based on the thermal decomposition of hexaaquacobalt(II) D-camphor10-sulfonate at 900 °C. This fast solid-state synthesis route overcomes the disadvantages of many combustion methods, most critically by avoiding the use of toxic organic solvents. The synthesized material was subjected to a detailed characterization to assess its potential for use as a nanocatalyst. The band gap measurements indicated the presence of two band gaps, one at 2.10 eV and another at 1.22 eV, confirming the purity and semiconducting properties of the sample. The electrochemical studies demonstrated a significant enhancement in the electron transfer kinetics with the addition of the synthesized Co3O4 to the carbon-paste electrode, leading to an enhanced electrocatalytic performance. These prominent functional properties, suitable for a wide range of technological applications, pave way for the implementation of the reported method for the synthesis of Co3O4 on a larger industrial scale.

Synthesis and characterization of dip-coated ZnO‒CuO composite thin film for room-temperature CO2 gas sensing

In this work, ZnO‒CuO composite thin film is prepared to achieve CO2 gas sensing at room-temperature. To achieve this purpose, a sol-gel dip-coating method was used to prepare the composite ZnO‒CuO thin films on a glass substrate by varying the precursor solution Zn/Cu molar ratio of 0.3, 0.5, and 0.7. The crystal structure of the films was determined by X-ray diffraction, indicating that the films were polycrystalline in nature with the presence of monoclinic CuO and hexagonal wurtzite ZnO phase, which was further confirmed by Raman spectroscopy. The homogeneous and porous surface morphology of the composite films obtained were observed by scanning electron microscopy. Optical properties and band gap measurements were explored by ultra-violet/visible spectroscopy and the direct band gap of synthesized ZnO‒CuO composite film was found to decrease from 1.54 to 1.45 eV, depending on the precursor solution Zn/Cu molar ratio. Various effective parameters on the performance of CO2 gas sensing, including the molar ratio of Zn/Cu, porous surface, water contact angle, film thickness, grain size, optical and electrical properties were investigated. Results demonstrated that the higher molar ratio (0.7) and thicker film (318 ± 5 nm) with the porous surface of ZnO‒CuO composite films exhibited the highest sensing (∼ 48%) response to 10,000 ppm CO2 at room-temperature. The obtained results suggest a direction for room-temperature ZnO–CuO composite-based sensor as efficient, fast as well as sensitive for CO2 detection.

Structural and Optical Properties of Tungsten Disulfide Nanoscale Films Grown by Sulfurization from W and WO3.

Tungsten disulfide (WS2) was prepared from W metal and WO3 by ion beam sputtering and sulfurization in a different number of layers, including monolayer, bilayer, six-layer, and nine-layer. To obtain better crystallinity, the nine-layer of WS2 was also prepared from W metal and sulfurized in a furnace at different temperatures (800, 850, 900, and 950 °C). X-ray diffraction revealed that WS2 has a 2-H crystal structure and the crystallinity improved with increasing sulfurization temperature, while the crystallinity of WS2 sulfurized from WO3 (WS2-WO3) is better than that sulfurized from W-metal (WS2-W). Raman spectra show that the full-width at half maximum (FWHM) of WS2-WO3 is narrower than that of WS2-W. We demonstrate that high-quality monocrystalline WS2 thin films can be prepared at wafer scale by sulfurization of WO3. The photoluminescence of the WS2 monolayer is strongly enhanced and centered at 1.98 eV. The transmittance of the WS2 monolayer exceeds 80%, and the measured band gap is 1.9 eV, as shown by ultraviolet-visible-infrared spectroscopy.

Temperature dependence of the band gap of Si28 :P at very low temperatures measured via time-resolved optical spectroscopy

We measure the temperature dependence of the indirect band gap of isotopically purified $^{28}\mathrm{Si}$:P in the regime from 0.1 K to 3 K by high-resolution absorption spectroscopy of the donor bound exciton transition. The measurements increase the up-to-date precision of the temperature-dependent band gap change by more than one order of magnitude and reveal a ${\mathrm{T}}^{4}$ dependence which is about a factor of two less than observed in previous measurements. Such a ${\mathrm{T}}^{4}$ dependence is predicted by theory, but the absolute values differ between our experiment and the most up-to-date calculations by a factor of 30, corroborating that the electron-phonon interaction at low temperatures is still not correctly included into theory. What is more, the ability of such very high-precision band-gap measurements facilitates the use of time- and spatially resolved $^{28}\mathrm{Si}$:P absorption as a contactless, local thermometer and electric field sensor with a demonstrated time resolution of milliseconds.

Modulating the Combinatorial Target Power of MgSnN2 via RF Magnetron Sputtering for Enhanced Optoelectronic Performance: Mechanistic Insights from DFT Studies.

The unique structural features of many ternary nitride materials with strong chemical bonding and band gaps above 2.0 eV are limited and are experimentally unexplored. It is important to identify candidate materials for optoelectronic devices, particularly for light-emitting diodes (LEDs) and absorbers in tandem photovoltaics. Here, we fabricated MgSnN2 thin films, as promising II-IV-N2 semiconductors, on stainless-steel, glass, and silicon substrates via combinatorial radio-frequency magnetron sputtering. The structural defects of the MgSnN2 films were studied as a function of the Sn power density, while the Mg and Sn atomic ratios remained constant. Polycrystalline orthorhombic MgSnN2 was grown on the (120) orientation within a wide optical band gap range of ∼2.20-2.17 eV. The carrier densities of 2.18× 1020 to 1.02 × 1021 cm-3, mobilities between 3.75 and 2.24 cm2/Vs, and a decrease in resistivity from 7.64 to 2.73 × 10-3 Ω cm were confirmed by Hall-effect measurements. These high carrier concentrations suggested that the optical band gap measurements were affected by a Burstein-Moss shift. Furthermore, the electrochemical capacitance properties of the optimal MgSnN2 film exhibited an areal capacitance of 152.5 mF/cm2 at 10 mV/s with high retention stability. The experimental and theoretical results showed that MgSnN2 films were effective semiconductor nitrides toward the progression of solar absorbers and LEDs.

Photoactivities of thiophene monomer/polymer transition in gel–based photoelectrochemical assembly: A theoretical/experimental approach

Photoactivities of bithiophene and/or terthiophene monomers and their mixtures were studied before and after being subjected to in situ oxidative electropolymerization in gel electrolyte (GE). Measured band gaps and density functional theory calculations supported the presence of oligomers in conjunction with the expected polymers. More oligomers formed during polymerization of the mixed monomers than with pure monomers. The generated photocurrent from the polymer/oligomer was always greater than that of the monomer. These results support the assumption that increasing π-bond conjugation leads to better e/h formation, and charge separation. The study also shows that the increase of the TerTh percentage in the monomer’s mix increased the generated photocurrent by the existing polymer/oligomer mix in a linear monotonic relationship

Adsorption and Desorption Study of Reusable Magnetic Iron Oxide Nanoparticles Modified with Justicia adhatoda Leaf Extract for the Removal of Textile Dye and Antibiotic.

The release of tetracycline hydrochloride (TCH) and methylene blue (MB) dye into the aquatic system uncontrollably caused major environmental and health problems; hence, their prevention required serious attention. Adsorption process is now being researched in order to increase adsorption efficiency and reprocess to alleviate environmental issues. The use of magnetic nanoparticle as an adsorbent for wastewater treatment has a lot of prospective. A magnetic iron oxide nanoparticle surface modified by Vasaka (Justicia adhatoda) leaf extract (JA-MIONs) is used to give a fast removal approach for MB dye and TCH antibiotics. Dynamic light scattering, UV–Vis and band gap measurement, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and transmission electron microscopy were operated to analyse the formation and size of these magnetic nanoparticles. The impacts of different factors such as contact time (30–150 min), adsorbate concentration (10–50 mg/L), pH (4–10), and adsorbent dose (2–10 mg) were explored. Adsorption kinetics and isotherms show that it follows the pseudo-first-order kinetic and the Freundlich isotherm, with maximum adsorption capacities of 76.92 mg/g for MB and 200 mg/g for TCH at 298 K. The reusability of the JA-MIONs eventually exhibited a decline in the adsorption percentage of MB and TCH after five and four times respectively. After the desorption-adsorption cycles, this adsorbent continued to exhibit significant adsorption capacity. This investigation furnished the significant reference data for the synthesis of JA-MIONs as a novel and auspicious adsorbent for the industrial clean-up of toxic dyes and heavily used antibiotics from water.

Soft Ionic Diode Fabricated Using Asymmetric Ion Distribution in Li+-Zn(II)/Cu(II) Metallohydrogels.

The development of metal ions-incorporated soft materials is of great importance in the present scenario due to their essential requirement in the fabrication of the components such as ionic diodes and electrochemical transistors for soft electronic devices. In the current work, to fabricate a soft ionic diode, two distinct Li+-driven conductive metallohydrogels, namely, MG-Zn and MG-Cu, have been obtained by individually treating a LiOH deprotonated pregelator (H5APL) with Zn(OAc)2 or Cu(OAc)2. The pregelator and metallohydrogels have been well characterized by using various instrumental techniques, which supports their proposed formulations. Field emission scanning electron microscopic images of metallohydrogels reveal the presence of a fibrous network, which helps to create a gel matrix, whereas the rheological experimental results ascertain the true gel phase nature of the synthesized metallohydrogels. The obtained MG-Zn and MG-Cu metallohydrogels were subjected to electrochemical impedance spectroscopic and band gap measurements. The MG-Zn and MG-Cu showed ionic conductivities of 1.02 × 10-3 and 1.14 × 10-3 S/cm, along with band gaps of 2.82 and 2.85 eV, respectively, thus claiming their suitability for device fabrication. Further, the fabricated metallohydrogel-based ionic diode shows appreciable ability to rectify the ionic current with the forward and reverse bias currents of 19 and 1.9 mA at +/-4 V bias potential. Based on all the experimental results, the mechanism has been well established for the rectification behavior in the fabricated metallohydrogel ionic diode.

NaGaSe2: A Water-Loving Multifunctional Non-van der Waals Layered Selenogallate.

A missing member of well-known ternary chalcometallates, a sodium selenogallate, NaGaSe2, has been synthesized by employing a polyselenide flux and stoichiometric reaction. Crystal structure analysis using X-ray diffraction techniques reveals that it contains supertetrahedral adamantane-type Ga4Se10 secondary building units. These Ga4Se10 secondary building units are further connected via corners to form two-dimensional (2D) [GaSe2]∞- layers stacked along the c-axis of the unit cell, and the Na ions reside in the interlayer space. The compound has an unusual ability to absorb water molecules from the atmosphere or a nonanhydrous solvent to form distinct hydrated phases, NaGaSe2·xH2O (where x can be 1 and 2), with an expanded interlayer space, as verified by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), desorption, and Fourier transform infrared spectroscopy (FT-IR) studies. The in situ thermodiffractogram indicates the emergence of an anhydrous phase before 300 °C with the decrease of interlayer spacings and reverting to the hydrated phase within a minute of re-exposure to the environment, supporting the reversibility of such a process. Structural transformation induced through water absorption results in an increase of Na ionic conductivity by 2 orders of magnitude compared to that of the pristine anhydrous phase, as verified by impedance spectroscopy. Na ions from NaGaSe2 can be exchanged in the solid-state route with other alkali and alkaline earth metals in a topotactic or nontopotactic way, leading to 2D isostructural and three-dimensional networks, respectively. Optical band gap measurements show a band gap of ∼3 eV for the hydrated phase, NaGaSe2·xH2O, which is in good agreement with the calculated band gap using a density functional theory (DFT)-based method. Sorption studies further confirm the selective absorption of water over MeOH, EtOH, and CH3CN with a maximum water uptake of 6 molecules/formula unit at a relative pressure, P/P0, of 0.9.

Rapid and reversible detection of trace amounts of H2S in air and packaged food using a biogenic bismuth oxide nanorod colorimetric sensor

A colorimetric reversible sensor has been developed for detection of trace amount of H2S gas in air and sealed meat packages. The active sensing area includes high surface area bismuth oxide (Bi2O3) nanorod prepared by green synthesis method. The as fabricated sensor demonstrates a rapid response in just 25 s for sensing 1 ppm H2S gas with distinct colour change in the active sensing area from white to brown. Sensing pellets were used to optimize the performance of the H2S sensor in terms of sensitivity and selectivity in air. Flexible nitrocellulose membrane filter papers coated with Bi2O3 were used to detect spoilage in packaged raw animal food products such as meat, poultry and fish. The sensor is reversible and can be recovered within a short cycle (3 min) of heat treatment at 300 °C. X-ray diffraction, Raman spectroscopy and band gap measurements confirmed partial conversion of Bi2O3 nanorods into Bi2S3 when exposed in the range of 1–100 ppm H2S gas.

Ultrasonically-assisted synthesis of CeO2 within WS2 interlayers forming type II heterojunction for a VOC photocatalytic oxidation.

Here, we investigate the band structure, density of states, photocatalytic activity, and heterojunction mechanism of WS2 with CeO2 (CeO2@WS2) as a photoactive heterostructure. In this heterostructure, CeO2's growth within WS2 layers is achieved through ultrasonicating WS2 and intercalating CeO2's precursor within the WS2 interlayers, followed by hydrothermal treatment. Through a set of density functional calculations, we demonstrate that CeO2 and WS2 form an interface through a covalent bonding that can be highly stable. The electrochemical impedance spectroscopy (EIS) found that the CeO2@WS2 heterostructure exhibits a remarkably higher conductivity (22.23 mS cm-2) compared to either WS2 and CeO2, assignable to the interface in CeO2@WS2. Furthermore, in a physically mixed CeO2-WS2 where the interaction between particles is noncovalent, the resistance was significantly higher (0.67 mS cm-2), confirming that the heterostructure in the interface is covalently bonded. In addition, Mott-Schottky and the bandgap measurements through Tauc plots demonstrate that the heterojunction in CeO2 and WS2 is type II. Eventually, the CeO2@WS2 heterostructure indicated 446.7µmolg -1 CO2 generation from photocatalytic oxidation of a volatile organic compound (VOC), formic acid, compared to WS2 and CeO2 alone.

Understanding the structural and optical characteristics in Sr2xLa2-2xLi2xTe2-2xO6 perovskites

Perovskites of the type Sr2xLa2-2xLi2xTe2-2xO6; x = 0.25, 0.4, 0.5, 0.6, 0.75 were analyzed for the first time for their structural and optical characteristics. All the compounds were found to be monoclinic with the P21/n structure thereby indicating a double perovskite structure formation. The x = 0.5 composition with Li+ and Te6+ was found to represent an ordered double perovskite having the least B-site disorder while x = 0.4 and x = 0.6 were found to have the highest disorder based on the refined occupancies. The tolerance factor calculations indicated that the symmetry is lowered on account of the octahedral tilting and Li-O-Te bending in making room for any divergence in symmetry that may arise due to a change to monoclinic from cubic structure. A greater tilting of the octahedral were observed in all compositions except x = 0.5 in terms of the tilting angle resulting in a drop in the bond angle of Li-O-Te. FTIR measurements indicate the existence of symmetric and antisymmetric stretching vibrations of the Li(Te)O6 octahedra. Energy band gap measurements indicated a depletion in the conduction band width and an increase in the energy gap. The ability for conducting is found to be the best in x = 0.25 and x = 0.6 as these compositions have the least value of energy band gap. This behavior can be accounted for by the possible presence of polarons in these compositions. Also, an increase in the energy band gap is observed when going from x = 0.25 to x = 0.5 due to an increase in cell volume for these compositions. SEM and EDX measurements carried out for x = 0.25, 0.5 and 0.75 indicate rough and agglomerated particles with a near uniform distribution in terms of their shape and the presence of elements as per the stoichiometric formula.

Synthesis, Characterization, and Electronic Properties of ZnO/ZnS Core/Shell Nanostructures Investigated Using a Multidisciplinary Approach

ZnO/ZnS core/shell nanostructures, which are studied for diverse possible applications, ranging from semiconductors, photovoltaics, and light-emitting diodes (LED), to solar cells, infrared detectors, and thermoelectrics, were synthesized and characterized by XRD, HR-(S)TEM, and analytical TEM (EDX and EELS). Moreover, band-gap measurements of the ZnO/ZnS core/shell nanostructures have been performed using UV/Vis DRS. The experimental results were combined with theoretical modeling of ZnO/ZnS (hetero)structures and band structure calculations for ZnO/ZnS systems, yielding more insights into the properties of the nanoparticles. The ab initio calculations were performed using hybrid PBE0 and HSE06 functionals. The synthesized and characterized ZnO/ZnS core/shell materials show a unique three-phase composition, where the ZnO phase is dominant in the core region and, interestingly, the auxiliary ZnS compound occurs in two phases as wurtzite and sphalerite in the shell region. Moreover, theoretical ab initio calculations show advanced semiconducting properties and possible band-gap tuning in such ZnO/ZnS structures.

Structural, Optical and Morphological Properties of Ag Doped CuO Thin Films Produced by Spin Coating Method

Son yıllarda, bakır (II) oksit (CuO) ince filmler benzersiz fiziksel ve kimyasal özelliklerinden dolayı araştırmacılardan büyük ilgi görmektedir. Bu çalışmada, gümüş (Ag) katkılı bakır oksit ince filmleri, çeşitli katkı oranlarında dönel kaplama tekniği uygulanarak cam alttaş üzerinde üretildi. Farklı gümüş katkısına bağlı olarak hazırlanan ince filmlerin yapısal, morfolojik ve optik özellikleri sırasıyla X-ışını kırınımmetresi (XRD), taramalı elektron mikroskobu (SEM) ve UV-VİS spektrofotometrisi kullanılarak incelenmiştir. Ag katkılı CuO filmlerinin XRD desenleri, tüm ince filmlerin polikristal doğaya sahip tenorite yapılı olduğunu göstermiştir. En belirgin yönelimler için stres, düzlemler arası mesafe, kristal büyüklüğü ve dislokasyon yoğunluğu X-ışını kırınımı analizi kullanılarak hesaplandı. En fazla kristal büyüklüğü değeri (111) tercihli yönelimi için katkısız CuO filmine ait olup yüksek kalitede kristalliğe sahip olduğu söylenilebilir. SEM ölçümü, film yüzeylerinde çok küçük bir topaklama ile beraber, ince film yüzeylerinde homojen olarak dağılmış nanoyapı parçacıkların varlığını göstermektedir. SEM görüntülerinin sonucu atomik kuvvet mikroskopu (AFM) ile benzer yapıdadır. EDX bağlantılı FEI Quanta 250 FEG taramalı elektron mikroskopu ile filmlerin tabaka kalınlığı yaklaşık olarak 460 nm civarındadır. Ayrıca, elde edilen örneklerin optik özellikleri, UV-VİS spektrofotometrisi kullanılarak bant aralığı ölçümleri, soğurma ve geçirgenlik değerleri türünden analiz edildi. İnce filmlerin ultraviyole-görünür ölçümleri, oda sıcaklığında CuO ince filminin geçirgenlik ve soğurma değerlerinin Ag katkılanma sonucu değiştiği görülmektedir. Aynı şekilde enerji bant aralığı, artan Ag katkı oranına bağlı olarak değişti.

Preparation and Characterization of Nanostructured Inorganic Copper Zinc Tin Sulfide-Delafossite Nano/Micro Composite as a Novel Photodetector with High Efficiency

A novel photodetector, based on Cu2ZnSnS4, CZTS, is deposited on Cu/CuFeO2 for wavelength and light power intensity detection. The preparation of CuFeO2 is carried out by the direct combustion of Cu foil wetted with Fe(NO3)2 solution. The preparation of CZTS is carried out using the hydrothermal method, then it is dropped on CuFeO2 using the drop casting method at 70 °C. Various analyses are used to look at the chemical, morphological, and optical aspects of the Cu/CuFeO2/CZTS, such as UV–vis, SEM, TEM, selected-area electron diffraction, and XRD, in which all characteristic peaks are confirmed for the prepared materials. The Cu/CuFeO2/CZTS thin film’s SEM image has a homogeneous morphology, with particles that are around 350 nm in size, demonstrating a significant improvement in morphology over Cu/CuFeO2/CZTS thin film. The TEM analysis verified the nanostructured morphology of Cu/CuFeO2/CZTS. From XRD analysis of Cu/CuFeO2/CZTS, the high intensity of the generated peaks indexed to hexagonal (2H) CuFeO2 and kesterite CZTS crystal structures revealed a compact highly crystal material. From optical analysis, CZTS, Cu/CuFeO2, and Cu/CuFeO2/CZTS thin films recoded band gaps of 1.49, 1.75, and 1.23 eV, respectively. According to the band gap measurements, the optical absorption of the Cu/CuFeO2/CZTS photodetector has clearly increased. The Cu/CuFeO2/CZTS as photodetector has a detectivity (D) and responsivity (R) of 1.7 × 1010 Jones and 127 mAW−1, respectively. Moreover, the external quantum efficiency (EQE) is 41.5% at 25 mW·cm−2 and 390 nm. Hence, the prepared Cu/CuFeO2/CZTS photodetector has a very high photoelectrical response, making it very promising as a broadband photodetector.

Influence of NaBr on structural studies of PVA/TiO2 polymer composites

PVA-TiO2-NaBr (PVATN) polymer composites were synthesized using solution casting technique. XRD, optical absorption, FTIR, and Raman spectroscopy techniques were being used to evaluate the impact of TiO2/NaBr on PVATN polymer samples. XRD spectra have been used to examine the modification of semi-crystalline phase of PVATN polymers with regard to TiO2/NaBr weight % and TiO2 anatase phase. With the composition, the optical absorption spectra of PVATN polymer samples indicated a blue shift in the absorption edges. At the cost of TiO2, NaBr was employed to increase the indirect optical band gap measurements. Urbach energy and refractive index values were assessed and discussed in depth using optical data. The FTIR spectra of several functional groups of PVA/TiO2 were examined. The Raman spectra revealed the existence of C-C stretch, C-O stretch, O-H bend, and C-H bend vibrations, as well as O-Ti-O bend vibrations.

Redshift of the optical gap in ferrite doped Gd2O3

We report the measurement of the optical bandgap in ferrite doped Gd2O3. Doping of the nickel zinc ferrite (Ni0.5Zn0.5Fe2O4) nanoparticles to Gd2O3 powder was done through thermal decomposition of the mixture at 1000 °C. The average grain size of the thermally decomposed mixture was determined to be around 95 nm and contained phases of cubic Gd2O3, GdO, and orthorhombic prisms of GdFeO3. The imaginary part of the complex dielectric function was calculated from the absorbance measurements that showed an optical bandgap at 1.8 eV. The observed value of the fundamental energy gap is on average 4.0 eV smaller than suggested by early experiments. A model for the ferrite doped Gd2O3 was constructed to suggest that the Ni, Zn, and Fe atoms occupy Gd sites in the Gd2O3 lattice. A new band at Γ point is formed due to the hybridization of the atomic orbitals of dopant and Gd3+ that shifts the fundamental absorption edge to the red part of the photon energy spectrum. Despite having a high density of negatively charged carriers contributed by the dopant, the onset of the direct interband transitions is clearly resolved.

Thiophene-Appended Benzothiazole Compounds for Ratiometric Detection of Copper and Cadmium Ions with Comparative Density Functional Theory Studies and Their Application in Real-Time Samples.

A thirst for the development of a simple fluorescence probe for enhanced sensing application has been achieved by synthesizing a stupendous thiophene-appended benzothiazole-conjugated compound L2. The synthesized compound L2 was characterized using nuclear magnetic resonance and mass spectrometry techniques. Furthermore, a photophysical property of L1 and L2 reveals the enhanced emission spectrum of L2 because of a restricted spin-orbital coupling as a result of increased conjugation compared to the ligand L1. Therefore, comparative studies were undertaken for L1 and L2. Henceforth, L2 was deployed for the ratiometric detection of Cd2+ ions in THF:water and L1 for the detection of Cu2+ ions in THF medium. The chemosensor L2 shows an outstanding water tolerance up to 60% and is stable between pH 2 and 7. This level of water tolerance and stability make L2 a suitable probe for analyzing real-time and biological samples. While the cadmium ion was added to L2, there was a significant red shift in emission from 496 to 549 nm, which indicates the controlled ICT due to complex formation. The metal-ligand complexation was also confirmed by noticing a decreased band gap of metal complex compared to the ligand as calculated using Tauc's plot with solid-phase UV data. The stoichiometric ratio was obtained by Job's plot that exhibited a 1:1 ratio of L2 and Cd2+ ions, and the limit of detection (LOD) was found to be 2.25 nM by the photoluminescence spectroscopic technique. The fluorescence lifetime of both L2 and L2-Cd2+ was found to be 58.3 ps and 0.147 ns, respectively. Alongside, the colorimetric-assisted ratiometric detection of Cu2+ by L1 with 1:2 stoichiometric ratio having an LOD of 1.06 × 10-7 M was also performed. Furthermore, the practical applicability of the probe L2 in sensing cadmium was tested in sewage water and vegetable extract; the recovery was approximately 98 and 99%, respectively. The experimental data were supported by theoretical investigation of structures of L1, L2, L1-Cu2+ , and L2-Cd2+ , complex formation, charge transfer mechanism, and band gap measurements done by quantum chemical density functional theory calculations.

Optical and gas sensing properties of TiO2/RGO for methanol, ethanol and acetone vapors

• Preparation of TiO 2 /RGO nanocomposite by annealing method at 180 °C. • Employing TiO 2 /RGO nanocomposite toward sensing methanol, ethanol and acetone vapors with different ppm. • Observation an excellent response for ethanol detection even in low gas volume. Reduced graphene oxide and metal oxides derivatives are introduced as relatively benign materials for improving gas sensors' performance as exemplified by the synthesis of TiO 2 /GO nanocomposite via ultrasonication, and then the assembly of RGO adorning TiO 2 nanoparticles (NPs) (TiO 2 /RGO) is accomplished using the thermal annealing method. The characterization of the as-fabricated sample indicated that irregular shaped TiO 2 NPs with size of 26 nm covered the RGO nanosheets. The optical band gap measurement indicated the values of 3.19, 2.1 and 2.5 eV for TiO 2 , GO and TiO 2 /RGO samples, respectively. The ensued nanocomposites are then deployed for the gas sensing response of three common organic vapors of ethanol, methanol, and acetone with concentrations of 20, 40, 60, 80, 100 ppm, at ambient temperature. The TiO 2 /RGO sensor relatively exhibited an excellent response (3–4 times) for ethanol detection. These results indicated that the application of TiO 2 /RGO can help assist in the evolvement of portable gas sensing devices endowed with the capability to detect common place organic vapors.

Structure, Oxygen Content and Electric Properties of Titanium Nitride Electrodes in TiNx/La:HfO2/TiNx Stacks Grown by PEALD on SiO2/Si.

This work reports experimental results of the quantitative determination of oxygen and band gap measurement in the TiNx electrodes in planar TiNx top/La:HfO2/TiNx bottom MIM stacks obtained by plasma enhanced atomic layer deposition on SiO2. Methodological aspects of extracting structural and chemical information from (scanning) transmission electron microscopy imaging (bright field and high angular annular dark field), energy dispersive X-ray spectrometry and electron energy loss spectroscopy are thoroughly considered. The study shows that the oxygen concentration is higher in the TiNxOy bottom electrode (about 14.2 ± 0.1 at. %) compared to the TiNxOy top electrode (about 11.4 ± 0.5 at. %). The following average stoichiometric formulas are TiN0.52O0.20 top and TiN0.54O0.26 bottom for top and bottom electrodes, respectively. The amount of oxygen incorporated into TiNx during PEALD because of oxygen impurities in the plasma is minor compared to that because of diffusion from SiO2 and HfO2. This asymmetry, together with results on a sample grown on a Si substrate, shows that incorporating oxygen impurity from the plasma itself is a minor part compared to diffusion from the SiO2 substrate and HfO2 dielectric during the PEALD growth. We observe the presence of TiO2 at the interface between the Hf oxide layer and the Ti nitride electrodes as well as at the SiO2 interface. EELS analysis led to a band gap ranging from 2.2 to 2.5 eV for the bottom TiNxOy and 1.7–2.2 eV for the top TiNxOy, which is in fair agreement with results obtained on the top TiNx electrode (1.6 ± 01 eV) using optical absorption spectra. Measurement of sheet resistance, resistivity and temperature coefficient of resistance by a four-point probe on the top TiNxOy electrode from 20 to 100 °C corresponds to the typical values for semiconductors.