Chemical Vapor Deposition Method Research Articles

INITIATED CHEMICAL VAPOR DEPOSITION (iCVD) OF POLY(ACRYLIC ACID): A COMPARISON BETWEEN CONTINUOUS AND CLOSED-BATCH iCVD APPROACHES

In this study, poly(acrylic acid) (PAA) thin films were deposited on silicon wafer and glass surfaces by initiated chemical vapor deposition (iCVD) method using di-tert-butyl peroxide (TBPO) as the initiator and acrylic acid (AA) as the monomer. During iCVD, two different precursor feeding approaches, namely continuous and closed-batch, were employed. The effects of substrate temperature and the precursor feeding approaches on the deposition rates and surface morphology of the films were investigated. The highest deposition rates for the continuous and closed-batch iCVD approaches were found as 26.1 nm/min and 18.6 nm/min, respectively, at a substrate temperature of 15 °C. FTIR analysis of the films deposited by both approaches indicated high structural retention of the monomer during the polymerization. AFM results indicated that, PAA thin films possessed low RMS roughness values of 2.76 nm and 1.84 nm using continuous and closed-batch iCVD, respectively. Due to the slightly higher surface roughness of the film deposited under continuous iCVD, that film exhibited a lower water contact angle of 16.1° than the film deposited in closed-batch iCVD. In terms of monomer utilization ratio, closed-batch system was found to be more effective, which may help to minimize the carbon footprint of iCVD process.

SYNTHESIS of P(N-ISOPROPYL ACRYLAMIDE - HYDROXYPROPYL METHACRYLATE) THERMO RESPONSIVE COPOLYMER FILMs BY INITIATED CHEMICAL VAPOR DEPOSITION METHOD

This study illustrates the deposition of thermo responsive p(N-isopropyl acrylamide-hydroxypropyl methacrylate) p(NIPAAm-HPMA) copolymer thin films by initiated chemical vapor deposition (iCVD) method using tert-butyl peroxide (TBPO) as the initiator. Copolymers were deposited at three different HPMA flow rates and the effects of NIPAAm/HPMA flow rate ratio on the deposition rate, structure and responsive properties of the as-deposited films were investigated. The highest deposition rate of 50 nm/min was observed for the copolymer deposited using lowest NIPAAm/HPMA monomer ratio studied. The deposition rate showed a significant increase with decreasing NIPAAm/HPMA flow ratio. Results of FTIR and XPS spectroscopy analyses revealed a significant preservation of structural retention in iCVD p(NIPAAm-HPMA) thermo-responsive films. Lower critical solution temperatures (LCST) of p(NIPAAm-HPMA) films were determined by carrying out a temperature-dependent contact angle analysis. Accordingly, it was shown that LCST was varied between 19 and 23 oC, which was observed to be dependent on the NIPAAm/HPMA monomer ratio. That LCST range is considerably below the literature- reported values for pNIPAAM, which makes the as-deposited copolymer suitable for applications that require thermos-responsive properties at lower temperatures.

Research Progress on Modification of Aerogels by Chemical Vapor Deposition.

Aerogels are three-dimensional nanomaterials with low thermal conductivity, low density, high specific surface area, and high porosity. They have demonstrated remarkable performance advantages in thermal insulation, catalysis, and adsorption in recent years. However, their inherent brittleness and weak skeletal structure limit their applications. In order to improve the resilience and expand the capabilities of aerogels, it is essential to optimize their intrinsic properties. The chemical vapor deposition (CVD) method offers a number of advantages, including fine control, high selectivity, and the ability to modify the aerogel in both the outer surface and the inner layer. This approach allows for reinforcement of the gel skeleton while achieving functionalization. This paper reviews the research progress of aerogel modification by the CVD method with a focus on hydrophobic modification, structural improvement, antioxidant modification, catalytic modification, etc. In light of the current demand for aerogel applications and the difficulties encountered in modifying aerogels, this review proposes future research directions for aerogel modification by CVD.

Ultra-thin DLC diaphragm-based optical fiber sensor achieving a highly sensitive and broadband acoustic response.

In the design of an extrinsic Fabry-Perot interferometer (EFPI) acoustic sensor, broadband response and high-sensitivity sensing are usually conflicting and need to be carefully balanced. Here, we present a novel, to the best of our knowledge, optical fiber acoustic sensor based on an ultra-thin diamond-like carbon (DLC) film, fabricated using the plasma-enhanced chemical vapor deposition method, and transferred by a surface-energy-assisted method. The sensor exhibits a broadband response ranging from 200 Hz to 100 kHz, maintains an average sensitivity of 457.3 mV/Pa within the range of 6 to 30 kHz, and can detect weak acoustic signals down to 3.23 µPa/Hz1/2@16.19 kHz. The combination of an ultra-thin DLC film with a relatively high Young's modulus and internal stresses results in a trade-off between high sensitivity and a broadband response. This performance demonstrates that our sensor is among the most advanced in the EFPI acoustic sensor family, with significant potential for applications such as photoacoustic spectroscopy, defect diagnosis, and bio-imaging.

Effect of gadolinia–stabilized zirconia nanoparticles manufactured from Mist CVD on the mechanical properties of ceramics sintered by SPS

Zirconia is an engineering ceramic material with excellent comprehensive properties. However, it suffers from the inherent disadvantage of low fracture toughness. To improve its fracture toughness, Gd2O3 is an effective stabilizer. In the present study, Gd2O3–ZrO2 composite powders were synthesized using the Mist CVD method. Following synthesis, these powders were pressed through spark plasma sintering. The crystallinity of the Gd2O3–ZrO2 powders improved as the deposition temperature increased from 600°C to 900°C. The tetragonality (c/2a) of the Gd–TZP composites increased from 0.99941 to 1.01571 as the Gd2O3 content increased from 2 mol% to 4 mol%, but it decreased when the content reached 5 mol%. The Gd2O3–ZrO2 nanoparticles produced via the Mist CVD approach presented a unique hollow spherical structure. Under moist chemical vapor deposition (CVD) conditions with 4 mol% Gd2O3 at 1400°C, the Gd–TZP composites exhibited fracture toughness and hardness values of approximately 12.03 ± 0.15 MPa·m1/2 and 12.16 ± 0.17 GPa, respectively.

Phosphorus doped hydrogenated silicon oxycarbide: Film formation, properties and its application on silicon heterojunction solar cell

An ultrathin phosphorus doped hydrogenated microcrystalline silicon oxycarbide (n-μc-SiCO:H) layer deposited by plasma enhanced chemical vapor deposition (PECVD) method can be used as a window layer for silicon heterojunction solar cells. The optical and electrical properties of n-μc-SiCO:H films were controlled by PECVD deposition conditions. The interplay effects of H2, CO2 and PH3 to SiH4 gas ratio on the chemical composition, material structure and properties of n-μc-SiCO:H film were systematically determined. O, H, C and P atoms were observed to incorporate into the silicon network of n-μc-SiCO:H layer, while most of the atoms bond directly to Si atoms. Incorporation of oxygen and carbon atoms into n-μc-SiCO:H film, confirmed by XPS as formation of Si-O and Si-C bonds, enlarged the optical absorption band gap (Eg) value. Both film crystallinity and phosphorus concentration in n-μc-SiCO:H layer were observed to be controlled by the H2, CO2 and PH3 to SiH4 gas ratio. The electric performance of HJT solar cell was depended on the optical and electrical properties of n-μc-SiCO:H layer. An average efficiency (across ∼ 120 cells) of 26.32 % was achieved in cells with optimized deposition parameters for the n-μc-SiCO:H layer. The reaction gas ratio was also the dominant factor in determining the number and size of nanoscale Si crystallites embedded in the n-μc-SiCO:H layer. The conductivity of n-μc-SiCO:H layer was determined by the activated phosphorus concentration but independent of the total phosphorus concentration. It was also found that large concentrations of small Si crystallites of size less than 3 nm improved film conductivity.

Water assisted atmospheric CVD super growth of vertically aligned CNT forest for supercapacitor application

We report a high growth rate (37 μm/min) synthesis of vertically aligned carbon nanotube (VACNT) forest, achieving remarkable height exceeding a millimetre with good crystallinity. VACNTs with few numbers of walls have been grown over Fe–Co/Al2O3/SiO2 coated Si wafer using the water assisted atmospheric pressure chemical vapour deposition (WACVD) method. The key to this success lies in the synergistic combination of a bimetallic catalyst (Fe-Co) with buffer Al2O3 layer and the WACVD method. Notably, the VACNT forest, synthesised at optimized conditions can be directly used without the need for additional post-growth purification processes, eliminating the risk of potential damage to the CNTs. Finally, the VACNT forest exhibits excellent areal capacitance of 133.33 mF/cm2 at a current density of 1 mA/cm2 with outstanding cyclic stability of 130 % @ 3000 cycles.

Impact of Water-Water Correlation at Suspended Graphene/Water Interface Under Different Electro-Modulated

Graphene-based devices have extensive applications in aqueous environments. The molecular interactions across the graphene sheet significantly impact various devices, although few researches focused on elucidating the interface effects. In this study, we utilize trench structure to make graphene unilaterally and bilaterally suspended in water. The conduction status of both lateral and longitudinal currents (Id, Is, Ig) of graphene was monitored under two suspension scenarios to investigate the changes in interface evolution with the introduction of solvent-solvent interactions. For unilaterally suspended graphene, the current perpendicular to the graphene channel direction remains in the off state. For bilaterally suspended graphene, the current path is formed vertically between the graphene channel and the gate electrode, perpendicular to the direction of the graphene. This experimental setup illustrates the possibilities for exploring interfacial characteristics at the interface between 2D materials and solutions through practical experimentation.The detailed fabrication process of the graphene field-effect-transistor (GFET) device is depicted in Fig. 1. To fabricate the microchannel structure, a microfluidic pattern was generated through photolithography on the SiO2/Si substrate spun with a layer of photoresist. Then, the corresponding microchannel pattern with a thickness of 300 nm SiO2 and 30 μm Si layer was etched by reactive-ion etching (RIE) to form a trench capable of storing water. Afterward, Au electrodes were placed next to the microfluidic channel via evaporation utilizing a shadow mask. The second critical step involves the preparation of graphene. Graphene sheets were grown on a copper foil through the chemical vapor deposition (CVD) method. With the support of PMMA film, physically stacked graphene bilayer graphene was transferred to the target substrate. Ultimately, the suspended bilayer graphene was submerged in acetone for 24 hours to remove the PMMA layer and immersed in isopropanol (IPA) and DI water to clean the residues.According to this device structure, we successfully fabricate the suspension of graphene unilaterally or bilaterally in water. When introducing water through the trench, the bottom surface of the suspended graphene contacts with water molecules, while the upper surface of the suspended graphene is exposed to air. This configuration leads to a unilateral suspension in water (unilateral-suspension GFET). Conversely, when water is introduced through the trench and water is also added above the graphene channel, graphene comes into contact with water on both sides. This configuration results in its bilateral suspension in the water (bilateral-suspension GFET). The electronic transport characteristics of unilateral-suspension GFET and bilateral-suspension GFET were measured by Agilent semiconductor analysis B1500A. The gate voltage was applied to water through an Ag/AgCl electrode. Fig. 2 (a) displays the Raman spectroscopy of suspended graphene on GFET device. The most notable features of the Raman spectrum are the G peak around 1580 cm-1, and the 2D band around 2700 cm-1, which are typical characteristics of graphene. The ID/IG ratio of 0.19 indicates the good quality of the graphene layers. As shown in Fig. 2 (b), the scanning electron microscope (SEM) result of suspended graphene on the GFET device verifies the presence of large-area graphene. The diagram displays a clear demarcation line, facilitating the identification of graphene presence on the substrate. This can also imply the excellent quality of graphene with few defects.The transport behavior of unilateral-suspension GFET and bilateral-suspension GFET are measured individually, as shown in Fig. 3. The sum (ΔI) of The drain current behavior (Id) and source current behavior (Is), and gate current behavior (Ig) are recorded with changed gate voltages (from -1V to +1V) and constant VDS (VDS= 0.1V). For unilateral-suspension GFET, ΔI and Ig keep constant at zero, and there is no conduction path perpendicular to the graphene channel direction. For bilateral-suspension GFET, ΔI and Ig at positive gate voltage are opposite in direction and equal in absolute value, this indicates the formation of an obvious path between the channel and gate electrode. The apparent interfacial evolution is believed to change with the introduction of the other side of water.In conclusion, we compare the electrical characteristics shown by two different suspension situations of graphene-based field effect transistors. There are some interesting results of the conduction path relating to interfacial evolution. This result has potential for chemical sensing or battery application. Furthermore, it can contribute to fundamental research about the interface interaction between suspended graphene and water. Figure 1

(Digital Presentation) Investigation of the Damage of Focus Ion Beam (FIB) on Nanocrystals Formed in Terbium-Doped Silicon Oxide Thin Films

Terbium-doped oxygen-rich silicon oxide (ORSO:Tb) thin films were fabricated using Integrated magnetron sputtering and electron cyclotron plasma-enhanced chemical vapor deposition (IMS ECR-PECVD) method. To investigate damage from focus ion beam (a comparison is made between mechanical and FIB methods measurements, which did not reveal crystal damage induced by FIB.Silicon-based thin films are fundamental materials in electronics and photonics, and doping is a common method to enhance silicon-based thin film’s luminescence. Terbium (Tb), characterized by well-defined emission lines, ranging from 400 to 620 nm (green emission), provides compelling reasons for using Tb as a dopant in silicon-based thin films (1).TEM is a method employed for studying. Preparation methods are required to make a TEM sample that is transparent to the electron beam (with a thickness of approximately 100 to 200 nm) (2). While conventional techniques, like electrolytic polishing and mechanical milling, are commonly used for preparing TEM samples, they fall short of achieving the precise preparation of a TEM sample in a specific area of interest with high spatial resolution.FIB has been used for preparing TEM specimens, which is fast and reliable. By scanning the beam across the cross-section, it becomes possible to reduce the thickness of the sample to prepare it for TEM (4)(5). The primary issue is due to the impact of ion beams accelerated to high energy therefore, examination effect of FIB on structure is important. Damages resulting from using FIB have mainly been studied on Silicon-based materials (6)(7)(8).In this paper, Tb-doped silicon oxide (oxygen-rich) thin film deposited by IMS ECR-PECVD offers a more uniform distribution and well-controlled rare-earth doping (9). To investigate the damages induced in the preparation process, ORSO:Tb annealed at 1200 °C was divided into two parts, and then a comparison between the mechanical and FIB preparations for TEM samples was made.ORSO:Tb were fabricated using an IMS ECR-PECVD system, employing 2 sccm SiH4 at 30% Ar and 28 sccm O2 at 10% as silicon (Si) and oxygen (O) precursors. These gas sources were delivered to the ECR chamber, pure Tb target with a sputtering power of 30 W and the substrate temperature was set at 350 °C. Following deposition, the thin film underwent annealing at 1200 °C for 1 hour.The TEM samples prepared by mechanical method and annealed at 1200 ⁰C, Fig. 1(a), showed a well-defined crystal structure. The dark points on the sample represent the nanocrystals of terbium disilicate. The average thickness of the sample is approximately 168.88 nm. Fig. 1(b) displays the ORSO:Tb annealed at 1200 ⁰C, showing the cross-sectional morphology of well-ordered nanostructures on the specimen with Tb doping, prepared by FIB. The cross-section of the thin film is well-ordered, and the FIB process did not disrupt the crystal structure of the sample annealed at high temperature, nor did it lead to the formation of a new structure. Furthermore, a comparative analysis between the TEM-prepared sample employing the mechanical method and the one prepared using FIB makes it evident that the FIB-prepared sample possesses superior resolution. The size distribution of particles is approximately the same, while due to the higher resolution of the TEM sample prepared through FIB, exhibits a particle distribution with a greater range with more details. In contrast, particle size determination in the mechanical method is more challenging due to its lower resolution, determining details and size characterization more difficult. Conclusion The ORSO:Tb sample was fabricated using the IMS ECR-PECVD system at 1200 degrees. Based on the findings presented in the paper, the effect of FIB, particularly at high annealing temperatures, does not induce significant damage to the crystal structure of ORSO:Tb thin film. The particle size distribution in the TEM sample prepared with FIB is broader and more detailed than in the mechanical due to its higher resolution. Particle size determination using the mechanical method is more challenging due to its lower resolution, making it more difficult to distinguish details and characterize sizes. Additionally, atomic composition analysis indicated the accurate abundance of oxygen in oxygen-rich silicon oxide. Figure 1

Low-Temperature Synthesis of Linear Carbon Chain inside Single-Walled Carbon Nanotubes

Linear carbon chain (LCC) has attracted much interest concerning its structure and applications. It has been reported that LCC possesses higher strength, elastic modulus, and stiffness than any known material, which provides a possibility for LCC as a new composite material, yet its chemical stability remains an issue [1]. Therefore, finding a method to efficiently synthesize LCC has become a meaningful research topic in recent years. A landmark study on LCC synthesis was given by using double-walled carbon nanotubes (DWCNTs) as the template combined with a high-temperature annealing treatment at 1460°C to acquire long chains composed of more than 6,000 carbon atoms [2]. Except for DWCNTs, LCC synthesis starting from single-walled carbon nanotubes (SWCNT) as templates was also reported. However, given the instability of SWCNTs at higher temperature [2] the synthesis efficiency is not as good as for DWCNTs. As far as we know, there is still no report on an efficient LCC synthesis inside SWCNTs. Herein, we report the low-temperature (400°C) efficient LCC synthesis starting from a SWCNT template.To this end, a SWCNT dispersion [3] underwent a surfactant exchange process and was fabricated into a SWCNT film by the filtration method. The SWCNT film was annealed under 400°C in an argon atmosphere to synthesize LCC. Raman spectroscopy (laser wavelength 532 nm) was used to characterize the efficiency of the LCC synthesis. A strong peak at 1863 cm-1 appeared after annealing, originating from the well-known C-mode of the linear carbon chain [4] thereby confirming its existence inside SWCNTs. SWCNTs synthesized by a low-pressure alcohol catalytic chemical vapor deposition (ACCVD) method [5] were also adopted for the LCC synthesis template, resulting in a similar LCC Raman peak at 1863 cm-1. We attribute this successful low-temperature LCC synthesis to the appropriate surfactant which could be encapsulated inside CNTs and converted to LCC during the annealing process.Keywords: Linear Carbon Chain, Single-walled Carbon Nanotubes, Surfactants

(Invited) Emerging Opto-Electronics and Quantum-Photonics Based on Ultra-Low Temperature Epitaxy of Group-IV Nanolayers

Germanium has already successfully entered Si technology through electronics and photonics applications [1,2]. However, due to the inherent lattice mismatch between Ge and Si, high-crystalline SiGe epitaxial layers of a sufficient thickness could only be grown for relatively low Ge concentration (<40%). At higher concentrations, the epitaxial SiGe layers relax the strain through either plastic or elastic relaxation. Thus, for about 2% (and 4%) strain between substrate and epilayer, only layer thicknesses of < 2nm (<0.5 nm) can be grown before elastic relaxation leads to quantum dot formation. In principle, such epitaxial Ge-rich QDs on Si(001) substrates can be successfully used to enhance the light emission properties of SiGe material [3-7]. However, planar Ge-rich two-dimensional layers would be preferred for efficient large-scale integration and reliable addressing of the nanostructures.Here, we demonstrate that ultra-low temperature (ULT) growth, carried out in a temperature window between 100°C and 350°C, is the key to extensive epilayer supersaturation, leading to layer thicknesses that are about one order of magnitude larger than what can be achieved by conventional epitaxy [8]. Thereby, we highlight that molecular beam epitaxy is the suitable choice for ULT growth since, using chemical vapor deposition methods for Si deposition, the ULT range cannot be reached due to the lack of precursor decomposition. However, we also stress that the chamber conditions during the growth need to be excellent in order to limit detrimental point defect formation during epitaxy.If these preconditions are met, ULT growth can lead to up to now unattainable layer structures. These, in turn, can be used, e.g., for the first available double heterostructure (DHS) light-emitting diodes in the group-IV system. We demonstrate that these LEDs, emitting in the telecom band, work efficiently up to room temperature and above. Light emission above room temperature is eventually limited by minority carrier injection.Additionally, novel electronic device concepts such as reconfigurable field effect transistors (RFETs) can be realized using several nanometer-thick Ge layers grown directly on silicon on insulator substrates. We argue that these devices have distinct advantages in performance and integration possibilities as compared to conventional nanoelectronics devices based on Ge-rich material, for which typically vertically grown nanowires are employed [9,10].

Enhanced highly bismuth‐doped multicomponent phosphate glass fibers for broadband amplifiers

AbstractBismuth (Bi)‐doped glass fibers are being developed into next‐generation broadband amplifiers and tunable lasers. Yet, the well‐developed Bi‐doped fiber devices only realize silica‐based optical fibers prepared by the modified chemical vapor deposition method, which faces challenges such as low doping concentration, high cost, intricate device structure, and high preparation difficulty. Here, a novel highly Bi‐doped multicomponent phosphate glass was developed. The high ion solubility of this phosphate glass facilitates achieving a Bi doping concentration of 8 mol%. The introduction of aluminum nitride (a new reducing agent) can create a local reducing environment, further increasing the concentration of low‐valence near‐infrared (NIR) active Bi ions. Furthermore, the resulting enhanced highly Bi‐doped multicomponent phosphate glass with efficient 900–1600 nm NIR emission can be drawn into corresponding optical fibers by a rod‐in‐tube method. Broadband NIR amplified spontaneous emission with a 3 dB bandwidth of 275 nm was achieved in this new fiber. As far as we know, this is the first successful preparation of Bi‐doped multicomponent phosphate glass fiber. Our results indicate that this fiber will be a powerful alternative to Bi‐doped silica‐based fibers for the preparation of related Bi‐doped fiber devices.

Atomic-Thin WS2 Kirigami for Bidirectional Polarization Detection.

The assembly and patterning engineering in two-dimensional (2D) materials hold importance for chip-level designs incorporating multifunctional detectors. At present, the patterning and stacking methods of 2D materials inevitably introduce impurity instability and functional limitations. Here, the space-confined chemical vapor deposition method is employed to achieve state-of-the-art kirigami structures of self-assembled WS2, featuring various layer combinations and stacking configurations. With this technique as a foundation, the WS2 nano-kirigami is integrated with metasurface design, achieving a photodetector with bidirectional polarization-sensitive detection capability in the infrared spectrum. Nano-kirigami can eliminate some of the uncontrollable factors in the processing of 2D material devices, providing a freely designed platform for chip-level multifunctional detection across multiple modules.

Catalytic particles formation from thin nickel films for the synthesis of multi-walled carbon nanotubes

We have investigated the formation of a catalyst for the synthesis of multi-walled carbon nanotubes (MWCNT) using nickel-on-titanium thin films. Nickel decomposes into nanoparticles in the synthesis setup prior to MWCNT growing through the plasma enhanced chemical vapor deposition method. Oxidation and reduction of the catalyst are conducted to control the morphology of the formed nanoparticles array. In this case, the redox treatments required preventing the formation of silicides and Ti–Ni alloys are combined with the well-known effect of low-temperature disintegration (dewetting) of thin films. Detailed studies using a combination of Auger, atomic force, scanning (SEM), and transmission electron microscopy (TEM) show the interaction of metals on a silicon substrate, the influence of treatments parameters on the catalyst's state. The features and morphology of MWCNT synthesized on the obtained catalysts were studied via Raman spectroscopy, SEM and TEM. Overall, showing a link between the catalyst formation process and MWCNT growth, we demonstrate a technological and versatile method for controlling of nanotube growth for various applications.

Hydrophilic modification of feed spacer and its impacts on antifouling performance of reverse osmosis membrane

AbstractFeed spacers improve mixing and mass transfer in membrane modules. However, they also lead to foulant deposition in the vicinity of the spacer surface. In this paper, two hydrophilic monomers, namely, acrylic acid (AA) and 2‐hydroxyethyl methacrylate (HEMA), are respectively coated on the surface of a commercial feed spacer via a plasma‐enhanced chemical vapor deposition (PECVD) method. The resulting modified spacers are then evaluated alongside with a reverse osmosis (RO) membrane for its solute rejection, water permeability, and antifouling properties. Results show that the surface hydrophilicity of feed spacers has been enhanced upon the AA and HEMA deposition. During filtration test, the HEMA‐modified spacer demonstrates higher flux recovery rate (94.17%) and salt rejection (95.78%) for the RO membrane. In contrast, the membrane with the unmodified spacer only shows 89.44% and 92.46%, respectively. Additionally, the membrane with the HEMA‐modified spacer has a thinner fouling layer (200 nm) compared to the unmodified spacer (700 nm). The HEMA‐coated spacer outperforms all the tested spacers, demonstrating that feed spacer modification with a hydrophilic monomer via the PECVD method can effectively reduce membrane fouling.

Development of Self-Doped Monolayered 2D MoS2 for Enhanced Photoresponsivity.

Transition metal dichalcogenides (TMDs) exist in two distinct phases: the thermodynamically stable trigonal prismatic (2H) and the metastable octahedral (1T) phase. Phase engineering has emerged as a potent technique for enhancing the performance of TMDs in optoelectronics applications. Nevertheless, understanding the mechanism of phase transition in TMDs and achieving large-area synthesis of phase-controlled TMDs continue to pose significant challenges. This study presents the synthesis of large-area monolayered 2H-MoS2 and mixed-phase 1T/2H-MoS2 by controlling the growth temperature in the chemical vapor deposition (CVD) method without use of a catalyst. The field-effect transistors (FETs) devices fabricated with 1T/2H-MoS2 mixed-phase show an on/off ratio of 107. Photo response devices fabricated with 1T/2H-MoS2 mixed-phase show ≈55 times enhancement in responsivity (from 0.32 to 17.4AW-1) and 102 times increase in the detectivity (from 4.1×1010 to 2.48×1012cmHzW-1) compare to 2H-MoS2. Introducing the metallic 1T phase within the 2H phase contributes additional carriers to the material, which prevents the electron-hole recombination and thereby increases the carrier density in the 1T/2H-MoS2 mixed-phase in comparison to 2H-MoS2. This work provides insights into the self-doping effects of 1T phase in 2H MoS2, enabling the tuning of 2D TMDs properties for optoelectronic applications.

High-temperature assisted barium molybdate incorporation into heteroatom-doped porous carbon sheets for selective detection of sulfonamide derivatives

Electrochemical sensors are inherently dependent upon novel electrocatalyst materials with excellent properties. A rapid analytical technique was developed to determine 5-aminosalicylic acid (5-ASA) without the need for time-consuming separation steps. In this study, the perovskite-type barium molybdate (BaMoO3) nanocubes and phosphorous-doped graphitic carbon nitride (P-gC3N5) were prepared by coprecipitation followed the chemical vapour deposition method. Various spectroscopic techniques were performed to analyse the morphology and structure of the proposed electrocatalyst (BaMoO3/P-gC3N5). BaMoO3/P-gC3N5 modified glassy carbon electrodes (GCE) exhibit superior electrocatalytic activity towards 5-ASA detection over unmodified electrodes. Difference Pulse Voltammetry (DPV) was used under optimal experimental conditions for determining 5-ASA accurately. Combining BaMoO3 and P-gC3N5 forms an electrocatalytic hybrid composite with a large specific surface area, rapid electron transfer, and high electrical conductivity. BaMoO3/P-gC3N5 modified electrodes possess a broad detection range (0.01–723 µM), low limit of detection (4.0 nM), excellent selectivity, sensitivity (1.046 µAµM-1cm−2), and good reproducibility toward the detection of 5-ASA. Human serum, urine, and river water samples were successfully tested for 5-ASA content with the electrochemical sensor fabricated.

Microstructure, mechanical properties and cutting performance of CVD Ti(B,N) coatings

TiB0.19N1.06, TiB0.70N0.66, and TiB1.23N0.19 coatings were deposited on cemented carbide via the chemical vapor deposition (CVD) method based on the calculated phase diagrams of the Ti–B–N system. The microstructures, mechanical properties and cutting performances of the Ti(B,N) coatings were systematically studied via X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), nanoindentation, etc. The coating compositions obtained via thermodynamic calculations show the same trend as the experimental values. The XRD and selected area electron diffraction (SAED) results of the coatings reveal that the phase assemblages transform from a dominant cubic structure of TiB0.19N1.06 to a hybrid of cubic and hexagonal structure of TiB0.70N0.66 and finally to a dominant hexagonal structure of TiB1.23N0.19. According to the XPS results, the TiB0.19N1.06 and TiB0.70N0.66 coatings consist of the crystalline phases TiN and TiB2 as well as amorphous BN and TiB, and the TiB1.23N0.19 coating mainly consists of the crystalline phases TiB2 and TiN. The hardness values of the TiB0.19N1.06, TiB0.70N0.66, and TiB1.23N0.19 coatings are 33.6, 35.1, and 39.1 GPa, respectively. The content of amorphous phase in the Ti(B,N) coatings decreases while the hardness increases as the B content increases and N content decreases. The TiB0.19N1.06 coating exhibits a composite structure of nanocrystallite embedded in amorphous matrix. The TiB1.23N0.19 coated tool prepared in this study demonstrates excellent performance in milling titanium alloy TC18 with a long cutting life up to 56.1 min, an increase of ∼9 % and ∼28 % compared to the TiB1.98 coated tool and commercial grade deposited with CVD TiB2 coating, respectively.

Spectroscopic analysis of pulsed-mode plasma with argon addition for diamond growth

The advancement of high-speed growth technology for large-scale single-crystal diamonds is desired. In the widely used microwave plasma chemical vapor deposition method, the gas temperature in the plasma atmosphere significantly contributes to the generation of reactive radicals and enhancement of crystal growth. However, the impact of electron-dominated reactions in the plasma on the crystal growth remains unclear. In this study, we actively controlled the plasma environment by adding argon gas and adopting microwave pulse modulation to generate the plasma. We estimated the gas temperature and electron density of the plasma using optical emission spectroscopy. Our results implied that an increase in gas temperature alone hardly explained the enhancement of the growth rate by the argon addition or pulse modulation. In addition to the increase in the electron density due to the argon addition and pulse modulation, gas-phase chemical reaction calculations showed that the radical production enhancement became remarkable under an electron density higher than a threshold (1017 m−3). Therefore, the enhancement of the growth rate mentioned above may be attributed to electron-dominated reactions in the discharge region. These findings suggest that increasing the electron density can further improve the growth rate and potentially enable diamond synthesis at lower temperatures than traditional methods.

5 MeV Si ion irradiation effects on structural and morphological properties of multiwalled carbon nanotubes

Carbon based nanomaterials (CBNs) such as multi walled carbon nanotubes (MWCNTs), graphene etc have attracted huge interest due to their widespread applications in contemporary nanotechnology. The ion bombardment is an important method which can be used for tuning of the structural and morphological properties of the CBNs. In the present work, we have carried out ion irradiation on MWCNTs (prepared by chemical vapour deposition method) with 5 MeV Si ions at different fluences ranging from 1 × 1014 to 5 × 1016 ions/cm2. The resulting structural and morphological modifications on the pristine MWCNTs have been characterized by using X-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy. Results observed after successful characterization are compared with pristine sample results and we observed that the irradiation creates defects in MWCNTs and causes amorphized carbon nanomaterials depending on the fluence and energy deposited by energetic ions inside the MWCNTs.