Thermal Chemical Vapor Deposition Process Research Articles

Morphology-Controlled ZnO@ZnWO4 Hetero-Nanostructures for Efficient Photooxidation of Water in Near-Neutral pH.

One-dimensional ZnO nanorods (NRs) have been extensively studied as photoanodes because of their unique optical properties, high electron mobility, and suitable band positions for water oxidation. However, their practical efficiency is often compromised by chemical instability during water oxidation and high carrier recombination rates. To overcome this issue, precise morphological control of ZnO@ZnWO4 core-shell structured photoanodes, featuring a ZnO core and a ZnWO4 shell was used. This was accomplished by depositing WO3 onto hydrothermally grown ZnO NRs using the thermal chemical vapor deposition process. The photoelectrochemical performance of ZnO@ZnWO4 with an optimized morphology outperforms that of pristine ZnO NRs. Systematic optical and electrochemical analyses of ZnO@ZnWO4 demonstrated that the enhancement is attributed to the enhanced charge transfer efficiency facilitated by the optimized ZnWO4 shells.

Modified 3D Graphene for Sensing and Electrochemical Capacitor Applications.

Less defective, nitrogen-doped 3-dimensional graphene (N3DG) and defect-rich, nitrogen-doped 3-dimensional graphene (N3DG-D) were made by the thermal CVD (Chemical Vapor Deposition) process via varying the carbon precursors and synthesis temperature. These modified 3D graphene materials were compared with pristine 3-dimensional graphene (P3DG), which has fewer defects and no nitrogen in its structure. The different types of graphene obtained were characterized for morphological, structural, and compositional assessment through Scanning Electron Microscopy (SEM), Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) techniques. Electrodes were fabricated, and electrochemical characterizations were conducted to evaluate the suitability of the three types of graphene for heavy metal sensing (lead) and Electric Double-Layer Capacitor (EDLC) applications. Initially, the various electrodes were treated with a mixture of 2.5 mM Ruhex (Ru (NH3)6Cl3 and 25 mM KCl to confirm that all the electrodes underwent a reversible and diffusion-controlled electrochemical process. Defect-rich graphene (N3DG-D) revealed the highest current density, followed by pristine (P3DG) and less-defect graphene (N3DG). Further, the three types of graphene were subjected to a sensing test by square wave anodic stripping voltammetry (SWASV) for lead detection. The obtained preliminary results showed that the N3DG material provided a great lead-sensing capability, detecting as little as 1 µM of lead in a water solution. The suitability of the electrodes to be employed in an Electric Double-Layer Capacitor (EDLC) was also comparatively assessed. Electrochemical characterization using 1 M sodium sulfate electrolyte was conducted through cyclic voltammetry and galvanostatic charge-discharge studies. The voltammogram and the galvanostatic charge-discharge (GCD) curves of the three types of graphene confirmed their suitability to be used as EDLC. The N3DG electrode proved superior with a gravimetric capacitance of 6.1 mF/g, followed by P3DG and N3DG, exhibiting 1.74 mF/g and 0.32 mF/g, respectively, at a current density of 2 A/g.

Post-CMOS processing challenges and design developments of CMOS-MEMS microheaters for local CNT synthesis

Carbon nanotubes (CNTs) can be locally grown on custom-designed CMOS microheaters by a thermal chemical vapour deposition (CVD) process to utilize the sensing capabilities of CNTs in emerging micro- and nanotechnology applications. For such a direct CMOS-CNT integration, a key requirement is the development of necessary post-processing steps on CMOS chips for fabricating CMOS-MEMS polysilicon heaters that can locally generate the required CNT synthesis temperatures (~650–900 °C). In our post-CMOS processing, a subtractive fabrication technique is used for micromachining the polysilicon heaters, where the passivation layers in CMOS are used as masks to protect the electronics. For dielectric etching, it is necessary to achieve high selectivity, uniform etching and a good etch rate to fully expose the polysilicon layers without causing damage. We achieved successful post-CMOS processing by developing two-step reactive ion etching (RIE) of the SiO2 dielectric layer and making design improvements to a second-generation CMOS chip. After the dry etching process, CMOS-MEMS microheaters are partially suspended by SiO2 wet etching with minimum damage to the exposed aluminium layers, to obtain high thermal isolation. The fabricated microheaters are then successfully utilized for synthesizing CNTs by a local thermal CVD process. The CMOS post-processing challenges and design aspects to fabricate CMOS-MEMS polysilicon microheaters for such high-temperature applications are detailed in this article. Our developed process for heterogeneous monolithic integration of CMOS-CNT shows promise for wafer-level manufacturing of CNT-based sensors by incorporating additional steps in an already existing foundry CMOS process.

Flexible and lightweight graphene grown by rapid thermal processing chemical vapor deposition for thermal management in consumer electronics

Flexible and lightweight graphene grown by rapid thermal processing chemical vapor deposition for thermal management in consumer electronics

Flexible and lightweight graphene grown by rapid thermal processing chemical vapor deposition for thermal management in consumer electronics

Next-generation consumer electronics require excellent thermal management. Graphene is a good choice because its thermal conductivity is 13 times that of copper. Single-, bi- and few-layer graphene (SLG, BLG, FLG) with large sp2 domains were grown by rapid thermal processing chemical vapor deposition (RTP-CVD) from CH4 and H2 using Ar as the diluting gas. The quality of graphene was investigated by Raman spectroscopy and TEM. To demonstrate the heat dissipation capability of RTP-CVD-grown graphene, a 2 TB solid state drive was used and the temperature was measured by a FLIR thermal camera. Results indicate that high thermal conductivity graphene was prepared by diluting the precursor gas with Ar. SLG was prepared at a growth temperature of 1 000 °C and a time of 25 min. A transition from FLG to high-quality BLG was observed at low H2 concentrations. Using SLG, there was a 5 °C lower temperature rise than using a commercial copper heat dissipator. The heat dissipation ability of SLG was approximately 200 times that of commercial copper heat dissipators.

The Advantages of Double Catalytic Layers for Carbon Nanotube Growth at Low Temperatures (<400 °C) in 3D Stacking and Power Applications

A double catalytic layer scheme is proposed and investigated for the low temperature growth of carbon nanotubes (CNTs) over Co (Cobalt), Al (Aluminum), and Ti (Titanium) catalysts on a silicon substrate. In this work, we demonstrate the growth of CNTs by a thermal chemical vapor deposition (TCVD) process at both 350 °C and 400 °C. Based on scanning electron microscopy (SEM) and Raman spectroscopy analyses, the good quality of the CNTs is demonstrated. This study contributes to the on-going research on integrating semiconductors into packaging and power-related applications, as demonstrated with the low resistance (~128 Ω) and high thermal conductivity (~29.8 Wm−1 K−1) of our developed CNTs.

The demonstration of low-temperature (350 °C) grown carbon nano-tubes for the applications of through silicon via in 3D stacking and power-via

Low temperature Carbon Nano-tubes (CNTs) growth technology is developed in this work with the insert of Al (Aluminum) between Ni (Nickel) and Ti (Titanium) as the reactant. The optimized Al thicknesses are also investigated. CNTs growth at the low temperature below 400 °C is the key factor for the back end of line compatible process integration. In this work, we grow the CNTs by thermal chemical vapor deposition process at 350 and 400 °C. The low ratio of peak ID/IG in Raman spectra and scanning electron microscope images proves the CNTs material quality. On the other hand, the high thermal conductivity (k) value of ∼50 W m − 1 K − 1 is also demonstrated. Both high material quality and k value on our low temperature grown CNTs show promising opportunities for the integration of semiconductor three dimensional packages and power-via related applications.

Optimization of Growth Parameters of Thermal Chemical Vapor Deposition Method for 2D MoS2 Synthesis

Even after a decade of research on MoS2, it is still quite challenging to obtain high quality MoS2 films using a controlled synthesis technique. Out of all the available methods chemical vapor deposition (CVD) has proven to be a reliable technique to produce MoS2 thin films. The CVD growth process is sensitive to variety of parameters involved in the process. In the present work, we report the effect of pressure, temperature, gas flow, and position of substrate on the growth of MoS2 films. After several failures, the technique is optimized to synthesize high quality MoS2 films on quartz substrate. Further, the films are characterized using XRD, UV-Vis Spectroscopy, Photoluminescence Spectroscopy and Raman Spectroscopy. The main objective of this work is to formulate a method that produces MoS2 films using thermal CVD process by optimizing various parameters.

Screen-Printing of Functionalized MWCNT-PEDOT:PSS Based Solutions on Bendable Substrate for Ammonia Gas Sensing.

Multi-walled carbon nanotubes (MWCNTs) were grown on a stainless-steel foil by thermal chemical vapor deposition (CVD) process. The MWCNTs were functionalized with carboxylic groups (COOH) on their surfaces by using oxidation and acid (3:1 H2SO4/HNO3) treatments for improving the solubility property of them in the solvent. The functionalized MWCNTs (f-MWCNTs) were conducted to prepare the solution by continuous stir in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), dimethyl sulfoxide (DMSO), ethylene glycol (EG) and Triton X-100. The solution was deposited onto a bendable substrate such as polyethylene terephthalate (PET) with a fabricated silver interdigitated electrode for application in a room-temperature gas sensor. A homemade-doctor blade coater, an UNO R3 Arduino board and a L298N motor driver are presented as a suitable system for screen printing the solution onto the gas-sensing substrates. The different contents of f-MWCNTs embedded in PEDOT:PSS were compared in the gas response to ammonia (NH3), ethanol (C2H5OH), benzene (C6H6), and acetone (C3H6O) vapors. The results demonstrate that the 3.0% v/v of f-MWCNT solution dissolved in 87.8% v/v of PEDOT:PSS, 5.4% v/v of DMSO, 3.6% v/v of EG and 0.2% v/v of Triton X-100 shows the highest response to 80 ppm NH3. Finally, the reduction in the NH3 response under heavy substrate-bending is also discussed.

Combined synthesis of carbon nanospheres and carbon nanotubes using thermal chemical vapor deposition process

Carbon spheres (CNSs) and carbon nanotubes (CNTs) are attracting more attention from researchers due to their excellent potential applications as adsorbents, catalyst carriers, and drug delivery. The synthesizing of CNTs and CNSs is a challenging and tedious process. A researcher has to produce different catalyst materials and precursors to synthesize CNTs and CNSs. Hence, an attempt has been made to combined in-situ synthesize of CNSs and CNTs in a single experiment. NiO/CuO/Al2O3 catalyst was used as a substrate. The thermal chemical vapor deposition (CVD) process with acetylene as a precursor gas was used to synthesize the CNSs and CNTs. The influence of process parameters and the growth mechanism of carbon nanomaterials were investigated. The obtained carbon nanomaterials samples were characterized using FESEM, HRTEM with SAED pattern, XRD analysis, Raman spectroscopy, and FTIR analysis. Results indicated that the catalyst morphology has a greater influence on the growth of CNTs and CNSs. The CVD process parameters play a vital role in deciding the structure of carbon nanomaterials. A schematic representation was proposed to understand the formation of carbon nanomaterials on top of the catalyst particles.

Formation of Thermally Stable, High-Areal-Density, and Small-Diameter Catalyst Nanoparticles via Intermittent Sputtering Deposition for the High-Density Growth of Carbon Nanotubes.

We report the formation of thermally stable catalyst nanoparticles via intermittent sputtering deposition to prevent the agglomeration of the nanoparticles during thermal chemical vapor deposition (CVD) and for the high-density growth of carbon nanotubes (CNTs). The preparation of high-areal-density and small-diameter catalyst nanoparticles on substrates for the high-density growth of CNTs is still a challenging issue because surface diffusion and Ostwald ripening of the nanoparticles induce agglomeration, which results in the low-density growth of large-diameter CNTs during high-temperature thermal CVD. Enhancing the adhesion of nanoparticles or suppressing their diffusion on the substrate to retain a small particle diameter is desirable for the preparation of thermally stable, high-areal-density, and small-diameter catalyst nanoparticles. The intermittent sputtering method was employed to deposit Ni and Fe metal nanoparticles on a substrate for the synthesis of high-areal-density CNTs for Fe nanoparticle catalyst films. The metal particles deposited via intermittent sputtering with an interval time of over 30 s maintained their areal densities and diameters during the thermal CVD process in a vacuum for CNT synthesis. An interval of over 30 s was expected to oxidize the metal particles, which resulted in thermal stability during the CVD process. The intermittent sputtering method is thus a candidate process for the preparation of thermally stable catalyst films for the growth of a high density of long CNTs, which can be combined with the present CNT production process.

Enhanced straylight suppression of short carbon nanotubes by using Platinum silicide catalyst enhancer in rapid thermal chemical vapor deposition process

This paper focuses on the role of Platinum as a catalyst enhancer in between Inconel catalyst and silicon for the growth of vertically aligned CNT (VACNT) in a rapid thermal chemical vapor deposition (RTCVD) process for optical applications. VACNT grown over Inconel/Pt/Si showed very low hemispherical reflectance over wide ranges of wavelengths with short CNT growth of 6 um height that can significantly reduce the shadowing effects in the optical devices, an important phenomenon often compromised due to adhesive layers or from much taller CNTs. A NASA flight qualification vibration and shock tests showed CNT stability during environmental testing. The origin of such enhancements is due to the formation of nano-structured Pt-Si alloys under the catalyst layer as evident by various structural and surface characterization techniques and utilization of RTCVD. Systematic studies of CNT growth were conducted by varying the catalyst thickness, gas flow rate, temperature, and pressure during RTCVD. After optimization, we achieved hemispherical reflectance of CNT below 0.8% at 250 nm and 0.2% from 1250 to 2500 nm. Presence of vertical multi-wall CNT growth was confirmed by XPS, SEM and Raman spectroscopy. Micron-scale control over CNT heights and uniformity were achieved and confirmed by laser imaging.

ANFIS-based Models for Coating Quality Prediction for Thin-Film Deposition Processes

Thin-film deposition processes have gained much popularity due to their unique capability to enhance the physical and chemical properties of various materials. Identification of the best parametric combination for a deposition process to achieve desired coating quality is often considered to be challenging due to the involvement of a large number of input process parameters and conflicting responses. This study discusses the development of adaptive neuro-fuzzy inference system-based models for the prediction of quality measures of two thin-film deposition processes, i.e., SiCN thin-film coating using thermal chemical vapor deposition (CVD) process and Ni–Cr alloy thin-film coating using direct current magnetron sputtering process. The predicted response values obtained from the developed models are validated and compared based on actual experimental results which exhibit a very close match between both the values. The corresponding surface plots obtained from the developed models illustrate the effect of each process parameter on the considered responses. These plots will help the operator in selecting the best parametric mix to achieve enhanced coating quality. Also, analysis of variance results identifies the importance of each process parameter in the determination of response values. The proposed approach can be applied to various deposition processes for modeling and prediction of observed response values. It will also assist as an operator in selecting the best parametric mix for achieving desired response values.

Application of modified PROMETHEE method for coating quality enhancement in thin film deposition processes

ABSTRACT Thin film coatings are extensively used to enhance the physical and chemical properties of various materials by depositing a thin layer of coatings of different materials onto various substrates. Several deposition processes are available which are widely adopted by many manufacturing industries to meet such demands. To exploit the fullest potential of those deposition processes, it is often advised to operate them with the optimal combination of process parameters. In this research, a modified PROMETHEE (preference ranking organisation method for enrichment evaluation) method as an effective multi-objective optimisation tool is applied for identifying the optimal parametric combinations of two thin film deposition processes: silicon carbonitride thin film coating using a thermal chemical vapour deposition process and zirconium-containing diamond-like-carbon thin film coating using an unbalanced magnetron sputtering process. The derived optimal parametric combinations are validated based on developed regression equations, which exhibit that the proposed approach can attain better response values as compared to other popular optimisation techniques. The analysis of variance results and the developed surface plots further illustrate the influence of various deposition parameters on coating quality.

Highly Aligned Polymeric Nanowire Etch-Mask Lithography Enabling the Integration of Graphene Nanoribbon Transistors.

Graphene nanoribbons are a greatly intriguing form of nanomaterials owing to their unique properties that overcome the limitations associated with a zero bandgap of two-dimensional graphene at room temperature. Thus, the fabrication of graphene nanoribbons has garnered much attention for building high-performance field-effect transistors. Consequently, various methodologies reported previously have brought significant progress in the development of highly ordered graphene nanoribbons. Nonetheless, easy control in spatial arrangement and alignment of graphene nanoribbons on a large scale is still limited. In this study, we explored a facile, yet effective method for the fabrication of graphene nanoribbons by employing orientationally controlled electrospun polymeric nanowire etch-mask. We started with a thermal chemical vapor deposition process to prepare graphene monolayer, which was conveniently transferred onto a receiving substrate for electrospun polymer nanowires. The polymeric nanowires act as a robust etching barrier underlying graphene sheets to harvest arrays of the graphene nanoribbons. On varying the parametric control in the process, the size, morphology, and width of electrospun polymer nanowires were easily manipulated. Upon O2 plasma etching, highly aligned arrays of graphene nanoribbons were produced, and the sacrificial polymeric nanowires were completely removed. The graphene nanoribbons were used to implement field-effect transistors in a bottom-gated configuration. Such approaches could realistically yield a relatively improved current on–off ratio of ~30 higher than those associated with the usual micro-ribbon strategy, with the clear potential to realize reproducible high-performance devices.

Low-Temperature Chemical Vapor Deposition Growth of Graphene Layers on Copper Substrate Using Camphor Precursor.

A two-step, low-temperature thermal chemical vapor deposition (CVD) process, which uses camphor for synthesizing continuous graphene layer on Cu substrate is reported. The growth process was performed at lower temperature (800 °C) using camphor as the source of carbon. A threezone CVD system was used for controlled heating of precursor, in order to obtain uniform graphene layer. As-grown samples were characterized by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). The results show the presence of 4-5 layers of graphene. As-grown graphene transferred onto a glass substrate through a polymer-free wet-etching process, demonstrated transmittance ~91% in visible spectra. This process of synthesizing large area, 4-5 layer graphene at reduced temperature represents an energy-efficient method of producing graphene for possible applications in opto-electronic industry.

Morphological, Mechanical Property Analysis and Comparative Study over Structural Properties of CVD TiN Film Grown under Different Substrate Temperature in Nitrogen Gas Atmosphere

Titanium Nitride (TiN) thin films were deposited by thermal chemical vapor deposition process (CVD) over Si (100) substrate under different substrate temperatures. Morphological, mechanical, and structural properties were characterized by different techniques e.g. SEM, AFM, Nanoindentation and XRD. SEM images reveal the presence of agglomerated particles over the surface and AFM images reveal the enhancement of surface roughness with higher deposition temperature. The analysis of electrochemical polarization and electrochemical properties of TiN coatings reveals decrease in corrosion resistance with increase in process temperature. The nanoindentation analysis has confirmed that TiN coating possess maximum fracture toughness (KC), hardness (H), and Young’s modulus (Ef) when synthesized at the temperature of 1150 °C. For comparative study, an analysis over structural properties using different models e.g. UDM, UDEM, SSP etc. have been used in this study. The data analysis of TiN coatings are carried out by using Origin 9.0 software.

Structural and luminescence properties of GaN nanowires grown on Si substrate by Au catalyst

The synthesis of hexagonal wurtzite one-dimensional GaN nanowires on Si (111) substrate was investigated using a thermal chemical vapor deposition process. The diameter of the GaN NWs was controlled by varying the growth time using a mixture of GaN powder and gallium metal with the ammonia gas reaction. The grown GaN nanowires exhibited a hexagonal perfect wurtzite structure which has been confirmed by high resolution X-ray diffraction analysis. The morphology and elemental analysis of grown GaN nanowires has been studied by scanning electron microscopy and energy dispersive X-ray analysis. Photoluminescence spectra under the excitation of 244 nm showed a strong near band-edge emission around ~ 372 nm and a broad emission at 450–650 nm related to deep-level defects.

Chemical vapor deposition of TiN on a CoCrFeNi multi-principal element alloy substrate

The reactivity of a quaternary multi-principal element alloy (MPEA), CoCrFeNi, as a substrate in thermal halide chemical vapor deposition (CVD) processes for titanium nitride (TiN) coatings was studied. The coatings were deposited at 850 °C–950 °C using TiCl4, H2 and N2 precursors. The coating microstructures were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM) with energy dispersive X-ray spectroscopy (EDS). Thermodynamic calculations of substrate and coating stability for a gas phase environment of N2 and H2 within a temperature range relevant for the experiments showed that Cr is expected to form hexagonal Cr2N and cubic (Ti1−ε1Crε1)N or (Cr1−ε2Tiε2)N phases. These phases could however not be discerned in the samples by XRD after the depositions. Cr was detected at the grain boundaries and the top surface by EDS for a sample synthesized at 950 °C. Grain boundary and surface diffusion, respectively, were the suggested mechanisms for Cr transport into the coating and onto the top surface. Although thermodynamic calculations indicated that Cr is the most easily etched component of the CoCrFeNi alloy to form gaseous chlorides in similar concentrations to that of the residual Ti-chlorides, no sign of etching were found according to the imaging of the sample cross-sections using SEM and TEM. Cross-section and top surface images further confirmed that the choice of substrate had no significant detrimental influence on the film growth or microstructure.

Ultrafast growth of large single crystals of monolayer WS2 and WSe2.

Monolayer transition metal dichalcogenides (TMDs) have attracted considerable attention as atomically thin semiconductors for the ultimate transistor scaling. For practical applications in integrated electronics, large monolayer single crystals are essential for ensuring consistent electronic properties and high device yield. The TMDs available today are generally obtained by mechanical exfoliation or chemical vapor deposition (CVD) growth, but are often of mixed layer thickness, limited single crystal domain size or have very slow growth rate. Scalable and rapid growth of large single crystals of monolayer TMDs requires maximization of lateral growth rate while completely suppressing the vertical growth, which represents a fundamental synthetic challenge and has motivated considerable efforts. Herein we report a modified CVD approach with controllable reverse flow for rapid growth of large domain single crystals of monolayer TMDs. With the use of reverse flow to precisely control the chemical vapor supply in the thermal CVD process, we can effectively prevent undesired nucleation before reaching optimum growth temperature and enable rapid nucleation and growth of monolayer TMD single crystals at a high temperature that is difficult to attain with use of a typical thermal CVD process. We show that monolayer single crystals of 450 μm lateral size can be prepared in 10 s, with the highest lateral growth rate up to 45 μm/s. Electronic characterization shows that the resulting monolayer WSe2 material exhibits excellent electronic properties with carrier mobility up to 90 cm2 V−1 s−1, comparable to that of the best exfoliated monolayers. Our study provides a robust pathway for rapid growth of high-quality TMD single crystals.