Showing papers on "Substrate (electronics) published in 2021"

Degradation mechanism of hybrid tin-based perovskite solar cells and the critical role of tin (IV) iodide.

Abstract: Tin perovskites have emerged as promising alternatives to toxic lead perovskites in next-generation photovoltaics, but their poor environmental stability remains an obstacle towards more competitive performances. Therefore, a full understanding of their decomposition processes is needed to address these stability issues. Herein, we elucidate the degradation mechanism of 2D/3D tin perovskite films based on (PEA)0.2(FA)0.8SnI3 (where PEA is phenylethylammonium and FA is formamidinium). We show that SnI4, a product of the oxygen-induced degradation of tin perovskite, quickly evolves into iodine via the combined action of moisture and oxygen. We identify iodine as a highly aggressive species that can further oxidise the perovskite to more SnI4, establishing a cyclic degradation mechanism. Perovskite stability is then observed to strongly depend on the hole transport layer chosen as the substrate, which is exploited to tackle film degradation. These key insights will enable the future design and optimisation of stable tin-based perovskite optoelectronics.

Laser soliton microcombs heterogeneously integrated on silicon

Abstract: Silicon photonics enables wafer-scale integration of optical functionalities on chip. Silicon-based laser frequency combs can provide integrated sources of mutually coherent laser lines for terabit-per-second transceivers, parallel coherent light detection and ranging, or photonics-assisted signal processing. We report heterogeneously integrated laser soliton microcombs combining both indium phospide/silicon (InP/Si) semiconductor lasers and ultralow-loss silicon nitride (Si3N4) microresonators on a monolithic silicon substrate. Thousands of devices can be produced from a single wafer by using complementary metal-oxide-semiconductor-compatible techniques. With on-chip electrical control of the laser-microresonator relative optical phase, these devices can output single-soliton microcombs with a 100-gigahertz repetition rate. Furthermore, we observe laser frequency noise reduction due to self-injection locking of the InP/Si laser to the Si3N4 microresonator. Our approach provides a route for large-volume, low-cost manufacturing of narrow-linewidth, chip-based frequency combs for next-generation high-capacity transceivers, data centers, space and mobile platforms.

High-order superlattices by rolling up van der Waals heterostructures.

Abstract: Two-dimensional (2D) materials1,2 and the associated van der Waals (vdW) heterostructures3-7 have provided great flexibility for integrating distinct atomic layers beyond the traditional limits of lattice-matching requirements, through layer-by-layer mechanical restacking or sequential synthesis. However, the 2D vdW heterostructures explored so far have been usually limited to relatively simple heterostructures with a small number of blocks8-18. The preparation of high-order vdW superlattices with larger number of alternating units is exponentially more difficult, owing to the limited yield and material damage associated with each sequential restacking or synthesis step8-29. Here we report a straightforward approach to realizing high-order vdW superlattices by rolling up vdW heterostructures. We show that a capillary-force-driven rolling-up process can be used to delaminate synthetic SnS2/WSe2 vdW heterostructures from the growth substrate and produce SnS2/WSe2 roll-ups with alternating monolayers of WSe2 and SnS2, thus forming high-order SnS2/WSe2 vdW superlattices. The formation of these superlattices modulates the electronic band structure and the dimensionality, resulting in a transition of the transport characteristics from semiconducting to metallic, from 2D to one-dimensional (1D), with an angle-dependent linear magnetoresistance. This strategy can be extended to create diverse 2D/2D vdW superlattices, more complex 2D/2D/2D vdW superlattices, and beyond-2D materials, including three-dimensional (3D) thin-film materials and 1D nanowires, to generate mixed-dimensional vdW superlattices, such as 3D/2D, 3D/2D/2D, 1D/2D and 1D/3D/2D vdW superlattices. This study demonstrates a general approach to producing high-order vdW superlattices with widely variable material compositions, dimensions, chirality and topology, and defines a rich material platform for both fundamental studies and technological applications.

Wafer-Scale Epitaxial Growth of Unidirectional WS2 Monolayers on Sapphire.

Abstract: Realization of wafer-scale single-crystal films of transition metal dichalcogenides (TMDs) such as WS2 requires epitaxial growth and coalescence of oriented domains to form a continuous monolayer. The domains must be oriented in the same crystallographic direction on the substrate to inhibit the formation of inversion domain boundaries (IDBs), which are a common feature of layered chalcogenides. Here we demonstrate fully coalesced unidirectional WS2 monolayers on 2 in. diameter c-plane sapphire by metalorganic chemical vapor deposition using a multistep growth process to achieve epitaxial WS2 monolayers with low in-plane rotational twist (0.09°). Transmission electron microscopy analysis reveals that the WS2 monolayers are largely free of IDBs but instead have translational boundaries that arise when WS2 domains with slightly offset lattices merge together. By regulating the monolayer growth rate, the density of translational boundaries and bilayer coverage were significantly reduced. The unidirectional orientation of domains is attributed to the presence of steps on the sapphire surface coupled with growth conditions that promote surface diffusion, lateral domain growth, and coalescence while preserving the aligned domain structure. The transferred WS2 monolayers show neutral and charged exciton emission at 80 K with negligible defect-related luminescence. Back-gated WS2 field effect transistors exhibited an ION/OFF of ∼107 and mobility of 16 cm2/(V s). The results demonstrate the potential of achieving wafer-scale TMD monolayers free of inversion domains with properties approaching those of exfoliated flakes.

Seeded 2D epitaxy of large-area single-crystal films of the van der Waals semiconductor 2H MoTe 2

Abstract: The integration of two-dimensional (2D) van der Waals semiconductors into silicon electronics technology will require the production of large-scale, uniform, and highly crystalline films We report a route for synthesizing wafer-scale single-crystalline 2H molybdenum ditelluride (MoTe2) semiconductors on an amorphous insulating substrate In-plane 2D-epitaxy growth by tellurizing was triggered from a deliberately implanted single seed crystal The resulting single-crystalline film completely covered a 25-centimeter wafer with excellent uniformity The 2H MoTe2 2D single-crystalline film can use itself as a template for further rapid epitaxy in a vertical manner Transistor arrays fabricated with the as-prepared 2H MoTe2 single crystals exhibited high electrical performance, with excellent uniformity and 100% device yield

Gallium nitride-based complementary logic integrated circuits

Abstract: Owing to its energy efficiency, silicon complementary metal–oxide–semiconductor (CMOS) technology is the current driving force of the integrated circuit industry. Silicon’s narrow bandgap has led to the advancement of wide-bandgap semiconductor materials, such as gallium nitride (GaN), being favoured in power electronics, radiofrequency power amplifiers and harsh environment applications. However, the development of GaN CMOS logic circuits has proved challenging because of the lack of a suitable strategy for integrating n-channel and p-channel field-effect transistors on a single substrate. Here we report the monolithic integration of enhancement-mode n-channel and p-channel GaN field-effect transistors and the fabrication of GaN-based complementary logic integrated circuits. We construct a family of elementary logic gates—including NOT, NAND, NOR and transmission gates—and show that the inverters exhibit rail-to-rail operation, suppressed static power dissipation, high thermal stability and large noise margins. We also demonstrate latch cells and ring oscillators comprising cascading logic inverters. Through the monolithic integration of enhancement-mode n-type and p-type gallium nitride field-effect transistors, complementary integrated circuits including latch circuits and ring oscillators can be created for use in high-power and high-frequency applications.

Ultrathin Two-Dimensional Nanostructures: Surface Defects for Morphology-Driven Enhanced Semiconductor SERS.

Abstract: Two-dimensional (2D) semiconductors have recently become attractive candidate substrates for surface-enhanced Raman spectroscopy, exhibiting good semiconductor-based SERS sensing for a wider variety of application scenarios. However, the underlying mechanism remains unclear. Herein, we propose that surface defects play a vital role in the magnification of the SERS performances of 2D semiconductors. As a prototype material, ultrathin WO3 nanosheets is used to demonstrate that surface defect sites and the resulting increased charge-carrier density can induce strong charge-transfer interactions at the substrate-molecule interface, thereby improving the sensitivity of the SERS substrate by 100 times with high reproducibility. Further work with other metal oxides suggests the reduced dimension of 2D materials can be advantageous in promoting SERS sensing for multiple probe molecules.

Study on on-Chip Antenna Design Based on Metamaterial-Inspired and Substrate-Integrated Waveguide Properties for Millimetre-Wave and THz Integrated-Circuit Applications

Abstract: This paper presents the results of a study on improving the performance parameters such as the impedance bandwidth, radiation gain and efficiency, as well as suppressing substrate loss of an innovative antenna for on-chip implementation for millimetre-wave and terahertz integrated-circuits. This was achieved by using the metamaterial and the substrate-integrated waveguide (SIW) technologies. The on-chip antenna structure comprises five alternating layers of metallization and silicon. An array of circular radiation patches with metamaterial-inspired crossed-shaped slots are etched on the top metallization layer below which is a silicon layer whose bottom surface is metalized to create a ground plane. Implemented in the silicon layer below is a cavity above which is no ground plane. Underneath this silicon layer is where an open-ended microstrip feedline is located which is used to excite the antenna. The feed mechanism is based on the coupling of the electromagnetic energy from the bottom silicon layer to the top circular patches through the cavity. To suppress surface waves and reduce substrate loss, the SIW concept is applied at the top silicon layer by implementing the metallic via holes at the periphery of the structure that connect the top layer to the ground plane. The proposed on-chip antenna has an average measured radiation gain and efficiency of 6.9 dBi and 53%, respectively, over its operational frequency range from 0.285–0.325 THz. The proposed on-chip antenna has dimensions of 1.35 × 1 × 0.06 mm3. The antenna is shown to be viable for applications in millimetre-waves and terahertz integrated-circuits.

High-performance flexible nanoscale transistors based on transition metal dichalcogenides

Abstract: Two-dimensional (2D) semiconducting transition metal dichalcogenides could be used to build high-performance flexible electronics. However, flexible field-effect transistors (FETs) based on such materials are typically fabricated with channel lengths on the micrometre scale, not benefitting from the short-channel advantages of 2D materials. Here, we report flexible nanoscale FETs based on 2D semiconductors; these are fabricated by transferring chemical-vapour-deposited transition metal dichalcogenides from rigid growth substrates together with nano-patterned metal contacts, using a polyimide film, which becomes the flexible substrate after release. Transistors based on monolayer molybdenum disulfide (MoS2) are created with channel lengths down to 60 nm and on-state currents up to 470 μA μm−1 at a drain–source voltage of 1 V, which is comparable to the performance of flexible graphene and crystalline silicon FETs. Despite the low thermal conductivity of the flexible substrate, we find that heat spreading through the metal gate and contacts is essential to reach such high current densities. We also show that the approach can be used to create flexible FETs based on molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). By transferring two-dimensional semiconductors from rigid growth substrates together with nano-patterned metal contacts, flexible field-effect transistors can be fabricated with channel lengths down to 60 nm.

Highly ordered arrays of hat-shaped hierarchical nanostructures with different curvatures for sensitive SERS and plasmon-driven catalysis

Abstract: Regulation of hot spots exhibits excellent potential in many applications including nanolasers, energy harvesting, sensing, and subwavelength imaging. Here, hat-shaped hierarchical nanostructures with different space curvatures have been proposed to enhance hot spots for facilitating surface-enhanced Raman scattering (SERS) and plasmon-driven catalysis applications. These novel nanostructures comprise two layers of metal nanoparticles separated by hat-shaped MoS 2 films. The fabrication of this hybrid structure is based on the thermal annealing and thermal evaporation of self-assembled polystyrene spheres, which are convenient to control the metal particle size and the curvature of hat-shaped nanostructures. Based on the narrow gaps produced by the MoS 2 films and the curvature of space, the constructed platform exhibits superior SERS capability and achieves ultrasensitive detection for toxic molecules. Furthermore, the surface catalytic conversion of p-nitrothiophenol (PNTP) to p, p′-dimercaptobenzene (DMAB) was in situ monitored by the SERS substrate. The mechanism governing this regulation of hot spots is also investigated via theoretical simulations.

Solid–liquid phase transition induced electrocatalytic switching from hydrogen evolution to highly selective CO2 reduction

Abstract: Conventional strategies for modifying electrocatalysts for efficient CO2 reduction are mainly based on doping, defect/morphology engineering, substrate design and so on. In most cases, these methods can only tune their structures, electronic states and thereby catalytic properties in a gradual way. Here we report that the solid–liquid phase transition of Ga–Sn/Ga–In alloys can induce an instant and radical transformation of their atomic and electronic structures during electrocatalysis, which dramatically impacts their catalytic properties. The transition of Sn/In active components from phase-segregated clusters to dispersed single atoms during melting results in a unique electronic structure through further reduction of both metallic Sn/In and Ga. Such atomic/electronic structure transitions can correlate well with suppression of the hydrogen evolution reaction and an enhanced formate Faradaic efficiency from 95%. This two-state switching strategy may be extended to other catalytic reactions to determine correlations between their structures and catalytic properties. Common strategies for catalyst design explore ways of fine-tuning continuous structure–property relationships. Here, the abrupt solid–liquid transition of Ga–In and Ga–Sn alloys is shown to have a profound impact on the CO2 electroreduction performance, with the molten alloy achieving a Faradaic efficiency of 95% formate production.

Novel low-εr MGa2O4 (M = Ca, Sr) microwave dielectric ceramics for 5 G antenna applications at the Sub-6 GHz band

Abstract: Two novel low-er gallates MGa2O4 (M = Ca, Sr) have been synthesized via a standard solid-state reaction method. According to the X-ray diffraction results, CaGa2O4 crystallizes in space group Pna21 with an orthorhombic symmetry, while SrGa2O4 belongs to the monoclinic P21/c system. Both ceramics show ever-improving microstructures with the increasing sintering temperature. The optimal microwave dielectric properties (er = 9.2, Qf = 66,000 GHz, τf =–85 ppm/°C for SrGa2O4 and er = 10.6, Qf = 15,400 GHz, τf =–58 ppm/°C for CaGa2O4) are obtained when sintered at 1275 °C. A patch antenna is fabricated using SrGa2O4 ceramics as the substrate, which realizes a return loss of –19.94 dB and total efficiency of –1.38 dB (72.8 % in power ratio) at 4.84 GHz. The exceptional performances indicate that SrGa2O4 ceramics are promising candidates for antenna applications at the Sub-6 GHz band.

High-k erbium oxide film prepared by sol-gel method for low-voltage thin-film transistor.

Abstract: In this work, high-dielectric-constant (high-k) erbium oxide（Er2O3）thin film with good dielectricity was fabricated on P-Si substrate by spin coating and annealed at a series of temperatures (from 400 ℃ to 700 ℃) The effect of annealing temperature on the microstructural and electrical properties of Er2O3 thin film was investigated by means of techniques To demonstrate the applicability of the Er2O3 film, the indium oxide (In2O3) thin film transistor (TFT) based amorphous Er2O3 dielectric film at different temperatures was fabricated The TFT based EO-600 showed a low-operating voltage and good electrical properties, and was connected with a resistor to construct an inverter The results demonstrate that the Er2O3 thin film synthesized by sol-gel method could be a promising candidate for using as dielectric layer in a low-power electronic device

Modeling of a biosensor using Tamm resonance excited by graphene

Abstract: In this paper, nanoscale pores in silicon layers are exploited to model and optimize a one-dimensional hybrid graphene-porous silicon photonic crystal biosensor. The physical nature of the proposed sensor is based on Tamm resonance. The transfer matrix method is applied to detect the change of the index of refraction in an aqueous solution. The proposed model is (PSi1/PSi2)N/G/Substrate, in which PSi1 and PSi2 are porous silicon layers with different porosities, N is the number of periods, and G is the number of graphene layers. The numerical simulations show that the proposed sensor has good performance. The variation of the number of periods, number of graphene layers, porosities, thicknesses of silicon layers, incident angles, and the sample layer thickness affect the performance of the sensor. By varying these parameters, the sensitivity and figure of merit of the sensor can be controlled. The study shows that the sensitivity and figure of merit of the proposed sensor reach 4.75 THz/RIU and 475RIU−1, respectively. The proposed sensor has a good capability in biological detection within terahertz. It is the first time, to our knowledge, that graphene has been used to excite the Tamm resonance using the photonic crystal of porous silicon and using it in biosensing applications.

High quality factor cold sintered LiF ceramics for microstrip patch antenna applications

Abstract: Cold sintering is adopted to pre-densify LiF ceramics, where the relative density increases significantly from 72.1 % at 125 MPa to 88.9 % at 500 MPa. The following post-annealings at 800 °C lead to further optimizations of densification, and near-full densifications with relative densities of 95.6 % and 97.6 % are achieved at 375 and 500 MPa, respectively. Qf value increased with increasing uniaxial pressure until it reaches the maximum value of 134,050 GHz at 375 MPa, which is 1.82 times higher than that via conventional sintering (73,800 GHz). er and τf are mainly determined by the relative density, and the optimum microwave dielectric properties are obtained as follows: er = 8.45, Qf = 134,050 GHz, τf =–135 ppm/°C. A microstrip patch antenna is designed and fabricated using the LiF ceramic as the substrate, which gives an S11 of –20.3 dB, a simulated high efficiency of 90.5 %, and a gain of 4.25 dB at the resonant frequency of 6.81 GHz.

Ferroelectrics everywhere: Ferroelectricity in magnesium substituted zinc oxide thin films

Abstract: We demonstrate ferroelectricity in Mg-substituted ZnO thin films with the wurtzite structure. Zn1−xMgxO films are grown by dual-cathode reactive magnetron sputtering on (111)-Pt // (0001)-Al2O3 substrates at temperatures ranging from 26 to 200 °C for compositions spanning from x = 0 to x = 0.37. X-ray diffraction indicates a decrease in the c-lattice parameter and an increase in the a-lattice parameter with increasing Mg content, resulting in a nearly constant c/a axial ratio of 1.595 over this composition range. Transmission electron microscopy studies show abrupt interfaces between Zn1−xMgxO films and the Pt electrode. When prepared at pO2 = 0.025, film surfaces are populated by abnormally oriented grains as measured by atomic force microscopy for Mg concentrations >29%. Raising pO2 to 0.25 eliminates the misoriented grains. Optical measurements show increasing bandgap values with increasing Mg content. When prepared on a 200 °C substrate, films display ferroelectric switching with remanent polarizations exceeding 100 μC cm−2 and coercive fields below 3 MV cm−1 when the Mg content is between ∼30% and ∼37%. Substrate temperature can be lowered to ambient conditions, and when doing so, capacitor stacks show only minor sacrifices to crystal orientation and nearly identical remanent polarization values; however, coercive fields drop below 2 MV/cm. Using ambient temperature deposition, we demonstrate ferroelectric capacitor stacks integrated directly with polymer substrate surfaces.

Deposition of Atomically Thin Pt Shells on Amorphous Palladium Phosphide Cores for Enhancing the Electrocatalytic Durability.

Abstract: As an excellent electrocatalyst, platinum (Pt) is often deposited as a thin layer on a nanoscale substrate to achieve high utilization efficiency. However, the practical application of the as-designed catalysts has been substantially restricted by the poor durability arising from the leaching of cores. Herein, by employing amorphous palladium phosphide (a-Pd-P) as substrates, we develop a class of leaching-free, ultrastable core-shell Pt catalysts with well-controlled shell thicknesses and surface structures for fuel cell electrocatalysis. When a submonolayer of Pt is deposited on the 6 nm nanocubes, the resulting Pd@a-Pd-P@PtSML core-shell catalyst can deliver a mass activity as high as 4.08 A/mgPt and 1.37 A/mgPd+Pt toward the oxygen reduction reaction at 0.9 V vs the reversible hydrogen electrode and undergoes 50 000 potential cycles with only ∼9% activity loss and negligible structural deformation. As elucidated by the DFT calculations, the superior durability of the catalysts originates from the high corrosion resistance of the disordered a-Pd-P substrates and the strong interfacial Pt-P interactions between the Pt shell and amorphous Pd-P layer.

Wafer-Scale Lateral Self-Assembly of Mosaic Ti3C2Tx MXene Monolayer Films.

Abstract: Bottom-up assembly of two-dimensional (2D) materials into macroscale morphologies with emergent properties requires control of the material surroundings, so that energetically favorable conditions direct the assembly process. MXenes, a class of recently developed 2D materials, have found new applications in areas such as electrochemical energy storage, nanoscale electronics, sensors, and biosensors. In this paper, we present a lateral self-assembly method for wafer-scale deposition of a mosaic-type 2D MXene flake monolayer that spontaneously orders at the interface between two immiscible solvents. ReaxFF molecular dynamics simulations elucidate the interactions of a MXene flake with the solvents and its stability at the liquid/liquid interface, the prerequisite for MXene flakes self-assembly at the interface. Moreover, facile transfer of this monolayer onto a flat substrate (Si, glass) results in high-coverage monolayer films with uniform thickness and homogeneous optical properties. Multiscale characterization of the resulting films reveals the mosaic structure and sheds light on the electronic properties of the films, which exhibit good electrical conductivity over cm-scale areas.

Epitaxial Growth of Two-Dimensional Insulator Monolayer Honeycomb BeO

Abstract: The emergence of two-dimensional (2D) materials launched a fascinating frontier of flatland electronics. Most crystalline atomic layer materials are based on layered van der Waals materials with weak interlayer bonding, which naturally leads to thermodynamically stable monolayers. We report the synthesis of a 2D insulator composed of a single atomic sheet of honeycomb structure BeO (h-BeO), although its bulk counterpart has a wurtzite structure. The h-BeO is grown by molecular beam epitaxy (MBE) on Ag(111) thin films that are also epitaxially grown on Si(111) wafers. Using scanning tunneling microscopy and spectroscopy (STM/S), the honeycomb BeO lattice constant is determined to be 2.65 A with an insulating band gap of 6 eV. Our low-energy electron diffraction measurements indicate that the h-BeO forms a continuous layer with good crystallinity at the millimeter scale. Moire pattern analysis shows the BeO honeycomb structure maintains long-range phase coherence in atomic registry even across Ag steps. We find that the interaction between the h-BeO layer and the Ag(111) substrate is weak by using STS and complementary density functional theory calculations. We not only demonstrate the feasibility of growing h-BeO monolayers by MBE, but also illustrate that the large-scale growth, weak substrate interactions, and long-range crystallinity make h-BeO an attractive candidate for future technological applications. More significantly, the ability to create a stable single-crystalline atomic sheet without a bulk layered counterpart is an intriguing approach to tailoring 2D electronic materials.

Giant persistent photoconductivity in monolayer MoS2 field-effect transistors

Abstract: Monolayer transition metal dichalcogenides (TMD) have numerous potential applications in ultrathin electronics and photonics The exposure of TMD-based devices to light generates photo-carriers resulting in an enhanced conductivity, which can be effectively used, eg, in photodetectors If the photo-enhanced conductivity persists after removal of the irradiation, the effect is known as persistent photoconductivity (PPC) Here we show that ultraviolet light (λ = 365 nm) exposure induces an extremely long-living giant PPC (GPPC) in monolayer MoS2 (ML-MoS2) field-effect transistors (FET) with a time constant of ~30 days Furthermore, this effect leads to a large enhancement of the conductivity up to a factor of 107 In contrast to previous studies in which the origin of the PPC was attributed to extrinsic reasons such as trapped charges in the substrate or adsorbates, we show that the GPPC arises mainly from the intrinsic properties of ML-MoS2 such as lattice defects that induce a large number of localized states in the forbidden gap This finding is supported by a detailed experimental and theoretical study of the electric transport in TMD based FETs as well as by characterization of ML-MoS2 with scanning tunneling spectroscopy, high-resolution transmission electron microscopy, and photoluminescence measurements The obtained results provide a basis for the defect-based engineering of the electronic and optical properties of TMDs for device applications

Influence of buffer layer on surface and tribomechanical properties of laser cladded Stellite 6

Abstract: Wear resistance coatings of Stellite 6 were deposited on SS316 substrate by blending a buffer layer of Inconel 625 with varying Linear Heat Inputs (LHI). The mechanical and microstructural properties of Stellite 6 coatings are investigated to evaluate the effect of buffer layer. The surface flaws, microstructure, micro-hardness and wear resistance of Stellite 6 clads with buffer layer are studied and compared with direct deposited Stellite 6. The results show an increment in clad height by 30% and 9% at lower and higher LHIs, respectively as compared to pre-deposited Stellite 6 clads. The deposition pattern (with and without buffer) are free from surface and internal cracks. The dilution is reduced by 25% and 10% whereas the microhardness shown an improvement by 12% and 5% with addition of buffer layer. Further, a fine-grain microstructure is observed in buffer layer clads at the interface zone. Moreover, the studies on wear rate have shown improvement of 14% and 3%, respectively with low coefficient of friction (COF) in buffer layer deposition because of high microhardness and fine grain microstructure. Thus, laser cladding of Stellite 6 at lower LHI with buffer layer has shown excellent mechanical and microstructural properties.

Boosting of NO2 gas sensing performances using GO-PEDOT:PSS nanocomposite chemical interface coated on langasite-based surface acoustic wave sensor

Abstract: Although the physicochemical properties of graphene oxide-Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (GO-PEDOT:PSS) nanocomposite has widely reported, the urgency of this nanocomposite in the surface acoustic wave (SAW) technology still remains at the infancy stage. In this work, a high response SAW NO2 gas sensor was developed by depositing the GO-PEDOT:PSS nanocomposite on piezoelectric LGS substrate. The pristine LGS SAW sensor has showed a resonant center frequency of 136.10 MHz and it was shifted to 135.78 MHz for the GO-PEDOT:PSS coated LGS SAW sensor. The observed shift in resonance frequency likely due to the mass loading effect of GO-PEDOT:PSS nanocomposite interface. However, under the gas ambient the GO-PEDOT:PSS/LGS SAW sensor exhibited a significant negative differential frequency shift (Δf) of 5.89 kHz to100 ppm of NO2 gas with a good cycling stability, excellent sensitivity and a low detection limit (∼175 ppb) at room temperature (RT), while the pristine GO/LGS and PEDOT:PSS/LGS SAW sensors showed the Δf of about 0.9 kHz and 2.1 kHz, respectively. In addition, under the various relative humidity conditions at RT for 100 ppm of NO2, the GO-PEDOT:PSS/LGS SAW device showed a dominant Δf. Our experimental results divulged that the effect of mass loading is the responsible underlying mechanism for the superior NO2 gas sensing performances. In turn, the predominant mechanism between the chemical interface and NO2 gas molecules on GO-PEDOT:PSS/LGS SAW device has been deliberately discussed in detailed by comparing with chemo-resistive type gas sensing properties These intriguing results indicate that the significance of GO-PEDOT:PSS has a synergetic effect in SAW sensor applications.