Vapor Phase Growth Research Articles

High energy density supercapattery empowered by efficient binder-free three-dimensional carbon coated NiCo2O4/Ni battery and Fe3S4@NiCo pseudocapacitive electrodes

Through the progress of science and technology, the findings of supercharged electrodes are provoked to design the electrode material. Herein, a novel electrode made up of binary metallic oxide surrounded by a carbon matrix is designed as the positive electrode material that is substantially more active and efficient than the most reported electrode materials. The as-synthesized 3D-C-NiCo2O4 electrode revealed a specific capacity of 558.3C g−1 at 1 A g−1. Likewise, the 3D-Fe3S4@NiCo/SS electrode is effectively synthesized via the vapour phase growth method that worked as a negative pseudocapacitive material. It provides a gravimetric capacitance of 808.05 F g−1 at 1 A g−1. Moreover, the assembled 3D-C-NiCo2O4//3D-Fe3S4@NiCo/SS reveals a higher gravimetric capacitance of 150 F g−1 at 1 A g−1 with 70 % stability over 10,000 cycles. It offers a maximum energy and power density of 49.8 Wh kg−1 and 8100 W kg−1, respectively. These exceptional outcomes highlight that the as-fabricated 3D-C-NiCo2O4//3D-Fe3S4@NiCo/SS device can be an ultimatum source for high-performance energy findings. The present result demonstrates the combined approach of prepared electrodes, merits of battery type 3D-C-NiCo2O4 electrode, and the faradaic capacitance of 3D-Fe3S4@NiCo electrode.

3D-C-Fe4N@NiCu/Metallic macroporous frameworks for binder-free compact hybrid supercapacitors with high areal capacities

In the present research work, binder-free three-dimensional nickel-copper (3D-NiCu) over various substrates copper (Cu), stainless steel (SS) and titanium (Ti) were synthesized via dynamic hydrogen bubble template (DHBT) method and further deposited by carbon-doped iron nitride (C@Fe4N) electroactive material via vapor phase growth method to form 3D-C-Fe4N@NiCu/Cu, 3D-C-Fe4N@NiCu/SS, and 3D-C-Fe4N@NiCu/Ti electrodes, respectively. Unveiling the maximum performance among the three electrodes, 3D-C-Fe4N@NiCu/Cu delivered a high areal capacity value of 2118 mC/cm2 at 3 mA/cm2 current density along with 92% capacity retention. Further, the assembled hybrid supercapacitor(HSC) based on 3D-Co3O4/Ni‖3D-C-Fe4N@NiCu/Cu HSC delivered the best electrochemical performance including wide potential window (1.5 V), specific capacity and cycling stability (89%) among the three HSCs. The results conclude that the novel synthesis strategy of vapor phase growth over 3D bi-metallic templates, opens up a new avenue, towards the formation of reliable and competitive HSC negative electrodes over a range of metal substrates, divergent from conventional carbon-based negative electrodes, which is extendable to other metals and applications.

Spatially Templated Nanolines of Ru and RuO2 by Sequential Infiltration Synthesis

Nanoscale patterning of inorganics is crucial for the fabrication of advanced electronic, photonic, and energy devices. The emerging sequential infiltration synthesis (SIS) method fabricates nanofeatures by block-selective vapor-phase growth in block copolymer templates with tunable patterns. Yet, SIS has been demonstrated mainly for Al2O3 and a few other metal oxides, while deriving metal nanostructures from a single SIS process is a challenge. Here, we present SIS of the Ru metal in polystyrene-block-polymethyl methacrylate (PS-b-PMMA) templates without any pretreatment, using alternating infiltration of RuO4 and H2. RuO4 interacts selectively and strongly with the aromatic C═C and C–H groups in PS, leaving the PMMA domains inert. Density functional theory calculations corroborate that the PS–RuO4 interaction is energetically favorable, with a calculated interaction energy of −1.65 eV, whereas for PMMA–RuO4, the calculated energy of −0.05 eV indicates an unfavorable interaction. Morphological analysis on the di-BCP after the RuO4-H2 process indicates an increase in contrast as a function of SIS cycles and templated Ru incorporation. The crystalline nature of the Ru deposits is confirmed using grazing incidence wide-angle X-ray scattering. Plasma-aided removal of the organic components yields Ru nanolines with lateral dimensions of ca 20 nm. We further highlight the broad potential of RuO4 as a reactant for SIS by generating RuO2 nanopatterns via alternating RuO4 and methanol infiltration.

Vapor Phase Growth of Centimeter‐Sized Band Gap Engineered Cesium Lead Halide Perovskite Single‐Crystal Thin Films with Color‐tunable Stimulated Emission

AbstractSingle crystal metal halide perovskites thin films are considered to be a promising optical, optoelectronic materials with extraordinary performance due to their low defect densities. However, it is still difficult to achieve large‐scale perovskite single‐crystal thin films (SCTFs) with tunable bandgap by vapor‐phase deposition method. Herein, the synthesis of CsPbCl3(1–x)Br3x SCTFs with centimeter size (1 cm × 1 cm) via vapor‐phase deposition is reported. The Br composition of CsPbCl3(1–x)Br3x SCTFs can be gradually tuned from x = 0 to x = 1, leading the corresponding bandgap to change from 2.29 to 2.91 eV. Additionally, an low‐threshold (≈23.9 µJ cm−2) amplified spontaneous emission is achieved based on CsPbCl3(1–x)Br3x SCTFs at room temperature, and the wavelength is tuned from 432 to 547 nm by varying the Cl/Br ratio. Importantly, the high‐quality CsPbCl3(1–x)Br3x SCTFs are ideal optical gain medium with high gain up to 1369.8 ± 101.2 cm−1. This study not only provides a versatile method to fabricate high quality CsPbCl3(1–x)Br3x SCTFs with different Cl/Br ratio, but also paves the way for further research of color‐tunable perovskite lasing.

The morphology and magnetic properties of iron nanoclusters decorated multiwall carbon nanotubes

Vapor phase growth of magnetic nanoclusters on different substrates alters their physical, chemical, and magnetic properties. In this work, DC magnetron sputtering with inert gas condensation (IGC) technique was used to produce iron (Fe) based nanoclusters on multiwall carbon nanotubes (MWCNTs) and silicon (Si) substrates. For comparison, simple electron beam evaporation technique was used to deposit Fe on the same type of substrates. We observed that surface of the electron beam evaporation sample was oxidized from Fe to γ-Fe2O3 when exposed to air. IGC growth Fe/Si sample exhibited a magnetic negative exchange bias. Core level binding energy (BE) and the valance band maximum (VBM) shifts were affirmed the formation of a semi-metallic phase. There was substantial enhancement in the saturation magnetization in the IGC sample up to five times compared to the evaporated sample which can be applied to the magnetic applications.

Low Temperature Epitaxy of In Situ GaDoped Si1-XGex: Dopant Incorporation, Structural and Electrical Properties

Over the last few decades, MOSFET architectures have evolved from planar to 3D structures (FinFET and, more recently, gate-all-around and Forksheet devices) to improve the channel control at very scaled dimensions. In this framework, highly doped conformal Si1-xGex epitaxial films are used for source/drain (S/D) regions in pMOS devices to form ohmic metal-semiconductor contacts with low specific contact resistivities (ρc). Boron is the main p-type dopant in Si1-xGex thanks to its high active concentration (~ 1×1021 at./cm3) for Ge concentrations of ~ 50 at.% [1]. For higher Ge/Si ratios, gallium is considered a promising doping element due to its higher solid solubility in Ge compared with boron. However, a strong Ga surface segregation is reported to occur during the epitaxy of in situ doped Si1-xGex, leading to a Ga-rich second phase at the epilayer surface [2]. In films grown at temperatures ≥ 450°C, the Ga surface segregation limits the bulk Ga concentration ([Ga]chem) to 1×1018 at./cm3 [3]. This low doping level results in inferior electrical properties for current MOSFET applications. Models in the literature [4] indicate that, at sufficiently low temperature, dopant segregation is limited by surface kinetic mechanisms. Thus, the segregation ratio could be controlled by changing the process temperature. Based on this approach, low temperature, Si2H6 + Ge2H6 based processes with improved Ga incorporation were developed [5].In this contribution, we report on novel in situ Ga doped Si1-xGex epitaxial layers grown at temperatures ≤ 400°C. Using a HCl surface clean, necessary to avoid the SIMS Ga decay from the surface which can mask the real concentration profile [3], Ga box-shaped profiles with concentrations above 1×1020 at./cm3 are found (Fig. 1). Two growth temperatures are compared: 400°C and 350°C. For each temperature, variable Ga precursor (tri-tert-butyl gallium) flows (fTTBGa) were used. A reduction in the growth temperature enhances the Ga incorporation, as evidenced from the two SEM morphology inspections displayed in Fig. 1. Here, two samples with a similar bulk [Ga]chem of ~ 6 ×1019 at./cm3, as measured by SIMS, exhibit either a clustered or smooth surface depending on the deposition temperature applied.This improved Ga incorporation allows for systematic studies of in situ Ga doping on the structural and electrical properties of Si1-xGex. In both series of samples, the layer resistivities (ρ) follow a similar trend, characterized by a steep decrease at smaller fTTBGa and a plateau for higher flows (Fig. 2). The lowest ρ values are found for the layers grown at 350°C. This denotes that different saturation levels in the active Ga concentration ([Ga]act) exist for the process conditions used here. In a similar way to what is typically observed for B doping, an increase in the Ga doping level causes a boost in epilayer growth rate. This growth rate trend saturates simultaneously with ρ, suggesting that the phenomenon is linked to the level of incorporated substitutional Ga atoms. In addition, the resulting Ge concentrations of the Si1-xGex layers are found to increase with Ga concentration. From HR-XRD analysis, strain-relaxation is also found to progressively increase with the TTBGa flow and so the incorporated Ga may not be fully active. For this reason, X-ray absorption fine structure spectra (XAFS) were acquired at the Ga K-edge on Si0.4Ge0.6:Ga and Ge:Ga epilayers with the results obtained reported in Fig.3. Based on comparative analysis of the first coordination Ga shell with DFT simulation results, Ga dopants appear to be placed in substitutional positions for both materials. Furthermore, a shorter nearest-neighbors distance is measured for Ga in Si0.4Ge0.6 compared to Ge, indicating a difference in the local strain associated to the dopant for the two considered matrixes.[1] R. Loo et al., “Processing Technologies for Advanced Ge Devices,” ECS J. Solid State Sci. Technol., vol. 6, no. 1, pp. P14–P20, 2017.[2] J. Margetis et al., “Epitaxial Growth of Ga-doped SiGe for Reduction of Contact Resistance in finFET Source/Drain Materials,” ECS Trans., vol. 93, no. 1, pp. 7–10, 2019.[3] G. Rengo et al., “B and Ga Co-Doped Si1−xGex for p-Type Source/Drain Contacts,” ECS J. Solid State Sci. Technol., vol. 11, no. 2, 024008, 2022.[4] C. B. Arnold and M. J. Aziz, “Unified kinetic model of dopant segregation during vapor-phase growth,” Phys. Rev. B - Condens. Matter Mater. Phys., vol. 72, no. 19, 195419, 2005.[5] A. Y. Hikavyy et al., “Cutting-Edge Epitaxial Processes for Sub 3 Nm Technology Nodes: Application to Nanosheet Stacks and Epitaxial Wrap-Around Contacts,” ECS Trans., vol. 104, no. 4, pp. 139–146, Oct. 2021. Figure 1

Facile and Efficient Preparation of High-Purity Black Phosphorus Based on a Vapor–Solid–Vapor Phase Growth Mechanism

Facile and Efficient Preparation of High-Purity Black Phosphorus Based on a Vapor–Solid–Vapor Phase Growth Mechanism

Scanning electron microscopic study of ZnO crystallites

Scanning electron microscopic study of ZnO crystallites. / A. Jishiashvili, Z. Shiolashvili, D. Jishiashvili, N. Makhatadze, A. Chirakadze, V. Gobronidze. / Nano Studies. – 2020. – # 20. – pp. 105-110. – eng. The wide band-gap semiconductor – zinc oxide finds broad applications due to its unique electrical, optical, and biomedical properties. This work deals with a new method of synthesis. Scanning electron microscopy was used to study the morphology and composition of a layer produced on the Si substrate after deposition of volatile species produced by pyrolytic decomposition of CuO, ZnO, and NH4Cl source powders. Heating of the source at 650°C caused the formation of hexagonal ZnO crystallites with maximum diameters and heights up to tens of micrometers. Energy dispersive spectroscopy and selected area electron diffraction confirmed the synthesis of wurtzite structured ZnO, which was growing along the c-axis. ZnO crystallites were growing only in the presence of CuO in the source powder. We proposed that ZnO was nucleated from the molten copper chloride salts after over-saturating with Zn and oxygen. The further growth of ZnO was performed by the vapor phase growth using precursors formed after pyrolysis of source powders. Fig. 5, Tab. 1, Ref. 17.

Preparation and optical properties of sulfur-doped silicon oxide microbelts and microrods

Amorphous S-doped and non-doped silicon oxide (SiO 2 ) one-dimensional structures with various morphologies are synthesized on Si substrates by vapor deposition with Ag 2 S as the precursor in a horizontal tube furnace. Curved microwires, grass-like microwires, S-doped microbelts, and straight S-doped microrods are obtained at the downstream of the furnace with different deposition temperatures in sequence. The microwires and microbelts are formed by the direct vapor-solid mechanism. The morphologies of microwires are largely determined by the inherent isotropy of their amorphous structure and the competitive growth in vapor phase. The microbelts are formed by the lateral growth of small microwires and the doped S played a critical role in their formation. However, the Ag–Si–S–O nanoparticles located at the growth ends suggests that the formation of S-doped SiO 2 microrods should be controlled by the vapor-liquid-solid mechanism. Both curved and grass-like microwires have similar photoluminescence behavior with strong blue/green/yellow bands and weak violent/red bands. However, S-doped microbelts exhibit strong violet/blue bands and relative strong a red band, and S-doped microrods exhibit low violet/blue bands and a strong red band. The obvious shifts in the intensities and wavelengths of the violet/blue/yellow bands are attributed to the morphology/size effects of microwires and microbelts, while the improved red-light emission is assigned to the doped S in microbelts and microrods. • S-doped SiO 2 nanobelts and nanorods are synthesized by vapor deposition. • S-doped SiO 2 nanobelts and nanorods are twist-free and straight. • Doped S determines the formation and morphology of the nanobelts. • Doped S can tune the optical properties of the nanobelts and nanorods.

Vapor phase growth and properties of mixed layered Pb1-xCdxI2 semiconductors

Pb1-xCdxI2 crystals (x = 0.1; 0.9) have been obtained by crystallization from a vapour phase in a closed system at over-stoichiometric iodine vapour pressure. An alloy of CdI2 and PbI2 was used as a source of evaporation. As a result of X-ray diffraction studies, it has been found that the obtained crystals belong to 4H-polytype, the space symmetry group is P63mc. The lattice parameters and the unit cell volume of crystals have been determined: for Pb0.9Cd0.1I2 a = 4,529 Å, c = 13,96 Å, V = 247,9 Å3; for Pb0.1Cd0.9I2 a = 4.258 Å, c = 13.70 Å, V = 215.0 Å3. The morphology of Pb1-xCdxI2 solid solutions crystals has been studied by scanning electron microscopy. Grown light orange Pb0.9Cd0.1I2 crystals have the shape of plates and ribbons, the surface of which is sculpted by growth figures. The transparent mixed Pb0.1Cd0.9I2 crystals have been grown from the vapour phase only in the form of plates. The spectral dependences of the optical absorption of Pb1-xCdxI2 crystals at room temperature have been studied. The optical widths of the band gaps of the grown crystals have been determined from the absorption spectra using the Tauc relation.

Impact of zinc salt counterion on poly(ethylene oxide) solution viscosity, conductivity, and ability to generate electrospun MOF/nanofiber composites

The effect of seeding poly(ethylene oxide), PEO, aqueous solutions with zinc acetate (ZA) and zinc chloride (ZC) on solution properties (e.g., viscosity and electrical conductivity) and the ability to electrospin nanofibers was investigated. The impacts of the type of Zn counterion and overall salt concentration on solution viscosity and electrical conductivity were correlated to the ability to electrospin nanofibers, as well as the resulting fiber morphology. In dilute PEO solutions, Zn salt addition reduced the PEO hydrodynamic radius ( R h ) and viscosity likely as a result of PEO chain envelopment of Zn cations, while in semi-dilute entangled regimes, Zn salt addition increased R h and viscosity likely due to interactions a single Zn cation with multiple polymer chains. The addition of Zn salts had limited effects on the overlap concentration ( c* ), but increased the entanglement concentration ( c e ), and the presence of either ZA or ZC enabled electrospinning of bead-free fibers at lower PEO concentrations (than without salt) because of the increased electrical conductivity of the solution. However, increasing the ZA concentration in solution had limited effect on fiber diameter and morphology, while raising the ZC concentration in solution resulted in the fusion of fibers into webs and films likely due to charge carryover. The resulting salt-doped PEO nanofibers were used as a template to synthesize a zeolitic imidazolate framework, ZIF-8, through a vapor-deposition approach exploiting the embedded Zn as nucleation sites for heterogeneous growth in a ‘Fiber-first’ strategy. • Aqueous poly(ethylene oxide) solutions were seeded with zinc salts. • Zinc salts, notably Zn acetate, reduced polymer concentration required to spin bead-free fibers. • Zinc chloride, especially at higher loadings, led to electrospun fused webs instead of fibers. • Zinc counterion type impacted solution conductivity and affected bead-free fiber development. • Zinc salt seeding enabled the vapor-phase growth of the zeolitic imidazolate framework ZIF-8.

Sawtooth Faceting in Rutile Nanowires.

Sawtooth faceting, with a diameter-dependent period, is pervasively observed in many Si, III–V, and II–VI nanowires during vapor-phase growth. This can be linked to an oscillation in surface energies, which are influenced by many factors such as crystal anisotropy, surface decoration, and twinning. Without the presence of surface decoration and planar defects, TiO2 rutile nanowires, axially oriented along a low-symmetry axis of ⟨110⟩, are promising to decouple the effect of crystal anisotropy from other factors. In this work, we synthesized ⟨110⟩ rutile nanowires, which exhibit complex periodic faceting consisting of {101} and {11̅0} facets. In addition to the expected linear width dependence, rutile nanowires, with the same width but different outward-inclined shapes, maintain the same period of their sawtooth faceting, as measured from TEM micrographs. In spite of different surface energy oscillations caused by different shapes, identical nucleation sites, which become energetically favorable during sawtooth growth, are predicted using thermodynamic models for nanowires with different shapes. This finding provides new insights into the morphological control of nanowires.

Engineering of Thermally Converted 3D-NiO[sbnd]Co3O4/Ni//3D-ϒ-Fe4N[sbnd]C@Ni/SS Porous Electrodes for High-performance Supercapatteries

The designing of higher dimensional multifunctional architecture is an attractive feature to boost the electrochemical performance of the electrodes. Herein, bimetallic 3D-NiOCo3O4/Ni positive electrode is prepared via a facile electrodeposition route followed by a post-annealingmethod. Likewise, the 3D porous ϒ-Fe4NC@Ni/SS negative electrode is successfully developed through vapour phase growth process. The as-prepared 3D-NiOCo3O4/Ni demonstrate a high specific capacity of 98.92 mC cm−2 than 30.92 and 22 mC cm−2 of NiO and Co3O4, respectively. Furthermore, the 3D-ϒ-Fe4NC@Ni/SS electrode is delivered an areal capacitance of 125 mF cm−2. Moreover, enhanced electrochemical performance is observed for the assembled 3D-NiOCo3O4/Ni//3D-ϒ-Fe4NC@Ni/SS supercapattery enactment of individual electrodes. It is demonstrated a maximum energy density of 100.47 mWh cm−3 at a power density of 14.69 W cm−3 and 87% capacitance retention combined with 100% coulombic efficiency after 20,000 operation cycles. The attained results are witnessed the successful fabrication of 3D porous template with bimetallic involvement as well as the 3D-ϒ-Fe4NC nanostructure, easy ion penetration, and shorter diffusion path length. Additionally, the present outcome reveal the binder-free growth of both the battery-type and capacitive electrodes for the next-generation energy storage devices.

Vapor-Phase Living Assembly of π-Conjugated Organic Semiconductors.

In contrast to well-studied amphiphilic block copolymers (BCPs) and π-stacked dyes, living assembly of hydrophobic π-conjugated materials has not yet been explored to date. Using a microspacing physical vapor transport (PVT) technique, the prefabricated microrods of organic semiconductors involving 9,10-dicyanoanthracene (DCA, A) or its binary alloy (B) can act as seeds to initiate living homoepitaxial growth from their ends, giving elongated microrods with controlled length. Red-green-red tricolor fluorescent microrod heterostructures with low dispersity are further realized by living heteroepitaxial growth of B microrod blocks on A seed microrod tips. Upon varying the growth sequence of each block, reverse triblock microrods are also accessible. Such a seed-induced living growth is applicable to triblock microrod heterostructures of more binary combinations as well as even more complex penta- and hepta-block heterostructures comprising A and B. By virtue of a convenient vapor-phase growth method, the present work demonstrates the generality of living assembly of π-conjugated materials.

On-wire axial perovskite heterostructures for monolithic dual-wavelength laser

All-inorganic lead halide perovskites have attracted tremendous attention for their tunable bandgaps, excellent photoluminescence efficiency and robust stability. Here, we report on a direct vapor-phase growth of high-quality CsPbCl3/CsPbI3 axial perovskite heterostructure and multi-heterojunction nanowires using a newly developed magnetic-pulling chemical vapor deposition approach. Microstructural characterization and optical investigations reveal that these structures are crystalline with abrupt heterojunctions. Micro-photoluminescence spectra and mapping at the heterojunctions exhibit dual-wavelength emissions at 417 nm and 698 nm, from the adjacent two disparate perovskites, respectively, further demonstrating the formation of unique heterostructures. Additionally, under a focused laser illumination, asymmetrical waveguide behavior along a single CsPbCl3/CsPbI3 wire is clearly observed. Taking a step further, we fabricated a monolithic dual-wavelength laser using an on-wire axial perovskite heterostructure and successfully realized blue and red emissions (425.5 nm and 687.4 nm). The capability to synthesize on-wire heterostructures represents a major step toward high-integration optoelectronic circuits and nanophotonics.

Aldehyde Gas Detection using Nanostructured Zno-based Gas Sensor fabricated via Horizontal Vapor Phase Growth Technique

Detection of aldehydes such as pentanal, hexanal, octanal, and nonanal are studied with the use of nanostructured zinc oxide (ZnO) as sensing element. ZnO nanowires synthesized at optimized growth parameters using horizontal vapor phase growth (HVPG) technique was used due to its unique properties in gas sensing applications. Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray (EDX) were used to verify the growth of ZnO nanowire structures. Further characterization using Source Meter was used to measure its resistance and resistivity based on the I-V graph. The sensor substrate wire set-up is connected to the Source Meter for resistance measurements as exposed to the different gas concentration of aldehydes. Gas sensing measurements were done at the static headspace gas concentration of the identified aldehydes. The sensor response of nanostructured ZnO-based gas sensor towards different gas concentrations ranges from 5.84% to 38.08%. Response time varies but it was observed that octanal gas has the longest response while pentanal has the fastest response.

Controllable synthesis of the polymorphic porous carbon with N-doping/Ni magnetic nanohybrids for high performance supercapacitor and environment applications

Porous carbon with heteroatom-doping/metal nanohybrids are of specific interest for many promising applications such as supercapacitors and pollutants removal, while their controllable synthesis is still a considerable challenge. Herein, we report a kind of novel polymorphic porous carbon with N-doping/Ni magnetic nanohybrids (NC@Ni), which can be fabricated via a simple self-jet vapor-phase growth assisted strategy, and the microstructure of the NC@Ni nanohybrids can be facilely controlled through adjusting the stoichiometric ratio of the precursors nickel nitrate hexahydrate and lactose monohydrate. Characterization results show that the fabricated NC@Ni nanohybrids own large specific surface area, ultrahigh nitrogen and oxygen doping content, abundant pore structure and attractive saturation magnetization. When used as supercapacitor electrode material, the typical NC@Ni-1 electrode exhibited an attractive specific capacity of 590C g−1 at 1 A g−1, remarkable rate performance (74.5%, 1–20 A g−1), and excellent cycling stability. Meanwhile, the assembled asymmetric supercapacitor delivered an excellent energy density up to 75.1 Wh kg−1 at a power density of 1055 W kg−1. As an adsorbent, the typical product NC@Ni-0.75 displayed high capture capability towards MG dye (889 mg g−1) and phosphate (26.2 mg P g−1) at 25 OC.

Control of Competing Thermodynamics and Kinetics in Vapor Phase Thin-Film Growth of Nitrides and Borides.

Thin-film growth is a platform technique that allows the preparation of various undeveloped materials and enables the development of novel energy generation devices. Preferred phase formation, control of crystalline orientation and quality, defect concentration, and stoichiometry in thin films are important for obtaining thin films exhibiting desired physical and chemical properties. In particular, the control of crystalline phase formation by utilizing thin-film technology favors the preparation of undeveloped materials. In this study, thin-film growth of transition metal nitride and rare-earth metal boride was performed using remote plasma–assisted molecular beam epitaxy and hybrid physical–chemical vapor deposition techniques, and was successfully achieved by tuning the competition between thermodynamics and kinetics during vapor-phase thin-film growth. Growth conditions of high crystalline quality titanium nitride thin films and high phase purity ytterbium boride thin films were not thermodynamically favorable. Appropriate control of the contribution degree of thermodynamics and kinetics during vapor-phase thin-film growth is crucial for fabricating high phase purity and high crystalline quality thin films.

Novel Christmas Branched Like NiO/NiWO4/WO3 (p–p–n) Nanowire Heterostructures for Chemical Sensing

AbstractEstablishing a platform comprising different nanostructured oxides is an emerging idea to develop highly sensitive and selective sensing devices. Herein, novel 3D‐heterostructures (p–p–n) consisting of 1D nanowires of NiO and WO3 along with their intermediate reactive product, i.e., NiWO4 seed, are produced by a two‐steps vapor phase growth method. In‐depth morphological and structural investigations describing the growth mechanism of these heterostructures are presented. Finally, the p–p–n heterostructures are integrated into conductometric sensing devices and their performances are investigated toward different gases. It is observed that by modulating the charge‐carrier transport with temperature, the heterostructure sensors exhibit selective behavior toward different gas analytes. Indeed, at 300 °C, the heterostructure sensors show relatively selective behavior toward NO2, while at 400 °C, high selectivity toward VOCs is observed. The improvement in sensing performances is mainly based on charge carrier transport through the two interfaces (one at WO3/NiWO4 (n–p) and the other at NiWO4/NiO (p–p)) and the modulation of charge carriers in the electron depletion layer of WO3 and hole accumulation layer of NiO and NiWO4. The remarkable performance of these complex heterostructures with low ppb‐level detection limits makes them excellent candidates for chemical/ gas sensing applications in e‐noses.

Engineered Hierarchical CuO Nanoleaves Based Electrochemical Nonenzymatic Biosensor for Glucose Detection

The blood glucose concentration is the basis of diabetes mellitus “chronic and metabolic disease” diagnosis. The elevated levels of blood sugar “glucose” lead to many health problems, such as chronic kidney failure, stroke, cardiovascular disease, eyes retina damage, and foot ulcers. Hence, early diagnosis is crucial to prevent and avoid life-threatening complications caused at abnormal glucose levels. In recent, different methods (such as electrochemical, colorimetric, piezoelectric, and thermoelectric based biosensors) have been utilized for glucose concentration detection. Among these methods, the electrochemical based biosensors were extensively employed; however, most of the biosensors were enzyme-based. The enzyme-modified electrodes suffered from some drawbacks, for instance, complicated immobilization procedures, high cost, instability, and low sensitivity. Therefore, it becomes crucial to develop novel electrode nanomaterials that work as electrocatalyst for glucose oxidation and also result in high sensitivity and stability. The performance of nonenzymatic glucose biosensors depends on the morphology of the electrode material. Hence, a variety of nanostructured nanomaterials are utilized to fabricate nonenzymatic biosensors with a high working electrode surface area.To fabricate nonenzymatic biosensors for glucose detection, significant efforts have been made to synthesize nanomaterials and use them as an electrocatalyst, for example, metals, metal oxides, and their hybrid nanostructures16-18. Among different catalysts, nanostructures of copper oxide (CuO) have received considerable interest19, 20. CuO is the best candidate to fabricate electrochemical based nonenzymatic glucose biosensors, as CuO based biosensors directly oxidizes glucose on the working electrode surface. Moreover, CuO nanostructures possess advanced properties, which are beneficial for designing biosensors.Research has been concentrated on the shape/dimensions controlling during synthesis of (nano)materials, which have better structural properties that results in enhanced electrochemical performance due to high specific surface area. Previously, a variety of morphologies of CuO nanomaterials have been produced (i.e. nanoparticles, nanowires, nanowhiskers, nanoneedles, nanorods, nanoshuttles, nanoribbons, and nanotubes) using solution-based approach, sonochemical deposition, vapor phase growth, high temperature synthesis, double-jet precipitation, micro-emulsion synthesis, etc. Among these synthesis methods, hydrothermal method presents an environmentally friendly, simple, cost-effective, high-yield, and low-temperature method to synthesize various CuO nanostructures.Herein, we report hierarchical CuO nanoleaves synthesis in large-quantity by a low-temperature hydrothermal method. Hierarchical CuO nanoleaves were synthesized using a low-temperature (95 °C) hydrothermal method (Fig. 1a). For synthesis, 0.25g Cu(CO2CH3)2·H2O and 0.77g CTAB were added in 40 mL deionized (DI) water. Next, 4 mL of 50 mM NaOH was added in the above solution while stirring. Then, the above solution was poured into a refluxing pot on a heating mantle and refluxed at 95 °C for 5h. Finally, black colored precipitates were washed using methanol and DI water to remove impurities and dried at room temperature. FESEM images and EDS analysis of CuO nanoleaves are shown in Fig. 1b-d. The low- and high-magnification images confirm that the CuO nanostructures prepared bear nanoleaves like morphology, and the nanoleaves are uniformly grown in large quantity. EDS analysis of CuO nanoleaves shows that nanoleaves are made of copper (Cu) and oxide (O) elements only (Fig. 1d, inset). EDS spectra shows an additional peak of Si, which is originating from Si substrate used to spread CuO nanoleaves sample for FESEM and EDS analysis. To fabricate hierarchical CuO nanoleaves based nonenzymatic glucose biosensor; first, the slurry of engineered CuO nanoleaves was prepared after mixing with conducting butyl carbitol acetate binder (8:2 v/v ratio) (Fig. 1a). The prepared slurry (2-6 μL) was cast on cleaned glassy carbon electrode (GCE, 0.071 cm2) and kept for drying. Finally, Nafion (5 μL) was coated on the electrode (CuO nanoleaves/GCE) surface and kept for overnight at 4 °C.The electrochemical behavior of fabricated biosensor towards glucose was analzed with cyclic voltammetry (CV) and amperometry (i-t) techniques. Owing to the high electroactive surface area, hierarchical CuO nanoleaves based nonenzymatic biosensor electrode shows enhanced electrochemical catalytic behavior for glucose electro-oxidation in 100 mM sodium hydroxide (NaOH) electrolyte. The nonenzymatic biosensor displays a high sensitivity (1467.32 mA/(mM cm2)), linear range (0.005-5.89 mM), and detection limit of 12 nM (S/N = 3). Moreover, biosensor displayed good selectivity, reproducibility, repeatability, and stability at room temperature over three-week storage period. Further, as-fabricated nonenzymatic glucose biosensors were employed for practical applications in human serum sample measurements. The obtained data were compared to the commercial biosensor, which demonstrates the practical usability of nonenzymatic glucose biosensors in real sample analysis. Therefore, we believe our engineered CuO nanoleaves based nonenzymatic biosensor can pave the way to detect glucose in low glucose level samples (i.e., saliva, tear, sweat).