Chemical Vapor Deposition Reactor Research Articles

Solar-thermal cold-wall chemical vapor deposition reactor design and characterization for graphene synthesis

Manufacturing processes are often highly energy-intensive, even when the energy is primarily used for direct heating processes. The required energy tends to derive from local utilities, which currently employ a blend of sources ranging from fossil fuels to renewable wind and solar photovoltaics, among others, when the end manufacturing need is thermal energy. Direct solar-thermal capture provides a compelling alternative that utilizes renewable energy to reduce greenhouse gas emissions from industrial processes, but one that has rarely been employed to date. In this study, a 10 kWe custom-built high flux solar simulator (HFSS) that closely approximates the solar spectrum produces a heat flux distribution with an adjustable peak between 1.5 and 4.5 MW/m2. The HFSS system is coupled to a cold-wall chemical vapor deposition (CVD) system that is equipped to automate graphene synthesis while providing safe operation, precise control, and real-time monitoring of process parameters. A numerical heat transfer model of a thin copper substrate is derived and validated to compute the substrate’s temperature profile prior to the synthesis process. The peak substrate temperature is correlated to the HFSS supply current and vacuum pressure, as it serves as a critical design parameter during graphene synthesis. We report the synthesis of high-quality graphene films on copper substrates with an average Raman peak intensity ratio ID/IG of 0.17. Backscattered electron microscopy reveals a characteristic grain size of 120 μm, with an area ratio of 16 when compared to that of low-quality graphene on copper. The reported solar-thermal CVD system demonstrates the ability to produce a high-value product, namely, graphene on copper, directly from a renewable energy resource with process control and automation that enables synthesis under a variety of conditions.

Pressure Dependence of Rate Coefficients of Unimolecular and Chemical Activation Reactions Connected to the Potential Energy Wells of Si2H2Cl4, Si2Cl6, and Si2Cl4 via Rice-Ramsperger-Kassel-Marcus Calculations.

Rate coefficients for elementary reactions connected to the potential energy wells of Si2H2Cl4, Si2Cl6, and Si2Cl4, which are important Si2 species in chemical vapor deposition (CVD) processes that use chlorosilanes as silicon source gases, were determined through the Rice-Ramsperger-Kassel-Marcus theory under various conditions of temperature and pressure. The optimized structures and vibrational frequencies of the reactants, products, and transition state were obtained using (U)B3LYP/6-31+G(d,p), and the single-point energies of the optimized structures were recalculated using the coupled cluster method with single and double excitations plus triple perturbation (U)CCSD(T) with complete basis set extrapolation. Many of the unimolecular decomposition channels and chemical activation reactions investigated in this work were found to be in the fall-off regime under subatmospheric to moderately high-pressure conditions so that it is expected that accurate modeling of the gas phase in the chlorosilane CVD reactor requires careful determination of the rate coefficients as functions of temperature and pressure for the conditions of interest, instead of using high-pressure limit rate coefficients. The rate coefficients determined here were expressed through Chebyshev coefficients and also modified Arrhenius parameters to be used in simulations of systems under a wide range of temperature and pressure conditions.

Combining density functional theory and CFD-PBM model to predict TiO2 nanoparticle evolution during chemical vapor deposition

Preparation of TiO2 nanoparticles by TiCl4 hydrolysis during chemical vapor deposition (CVD) is one of the effective techniques for producing TiO2 nanoparticles, while the mechanisms of TiO2 nanoparticle evolution are not well understood. This paper uses computational fluid dynamics (CFD) population balance model (PBM) to predict particle size distribution during CVD, and density functional theory (DFT) calculations to explore reaction mechanisms. DFT calculations reveal that the gas phase hydrolysis reaction can be simplified into two processes, the hydrolysis of TiCl4 to form TiO(OH)2 and the decomposition of TiO(OH)2 to TiO2. During the surface reactions, the energy barriers of TiO(OH)2 decomposition reactions on the surfaces of (TiO2)n nanoclusters (n = 1–8) are generally lower than those in the gas phase reactions, and the largest energy barrier of the surface reaction occurs on the surface of (TiO2)6 nanoclusters. Simulations using a perfect stirred reaction model indicate that Ti(OH)4 is the dominant hydrolysis products when the temperature is lower than 548 K, while TiO2 production starts at ∼610 K, indicating reaction temperature is a crucial factor that governs the products of TiCl4 hydrolysis. CFD-PBM model predict the evolution of Particle Size Distribution (PSD) of nanoparticles in a CVD reactor, which is agreed with experimental measurements in the literature. Increasing the reaction temperature results in an increase of the peak of the PSD of nanoparticles in the reactor. This study provides atomic insights into the nanoparticle evolution and a practical model to predict the nanoparticle evolution during the CVD process.

A wide-angle X-ray scattering laboratory setup for tracking phase changes of thin films in a chemical vapor deposition chamber.

The few-layer transition metal dichalcogenides (TMD) are an attractive class of materials due to their unique and tunable electronic, optical, and chemical properties, controlled by the layer number, crystal orientation, grain size, and morphology. One of the most commonly used methods for synthesizing the few-layer TMD materials is the chemical vapor deposition (CVD) technique. Therefore, it is crucial to develop in situ inspection techniques to observe the growth of the few-layer TMD materials directly in the CVD chamber environment. We demonstrate such an in situ observation on the growth of the vertically aligned few-layer MoS2 in a one-zone CVD chamber using a laboratory table-top grazing-incidence wide-angle X-ray scattering (GIWAXS) setup. The advantages of using a microfocus X-ray source with focusing Montel optics and a single-photon counting 2D X-ray detector are discussed. Due to the position-sensitive 2D X-ray detector, the orientation of MoS2 layers can be easily distinguished. The performance of the GIWAXS setup is further improved by suppressing the background scattering using a guarding slit, an appropriately placed beamstop, and He gas in the CVD reactor. The layer growth can be monitored by tracking the width of the MoS2 diffraction peak in real time. The temporal evolution of the crystallization kinetics can be satisfactorily described by the Avrami model, employing the normalized diffraction peak area. In this way, the activation energy of the particular chemical reaction occurring in the CVD chamber can be determined.

Pressure Sensor Devices Featuring a Chemical Passivation Made of a Locally Synthesized Diamond Layer

The rear side of a pressure sensor diaphragm is prepared with an additional diamond layer as protective coating against harsh media. The preparation sequence for the diamond coating is developed as a simple backend process, combining only two additional steps in the standard process. These are the local seeding of nanodiamond layer and the low‐temperature diamond growth at <300 °C in a linear antenna microwave plasma‐enhanced chemical vapor deposition reactor, where only at the nanodiamond seeded sites, a high‐quality diamond film was synthesized. The seeding resolution in the setup used was limited to ≈80 μm, but can be further reduced. In an industry‐typical assembly sequence the diamond coated pressure sensor devices are further equipped with a support wafer and mounted to a TO‐8 socket. Tests of such sensor systems indicate that the diamond layer does not hamper the stability of the device. This proofed method of postprocessing an only‐local and low‐temperature synthesis of a diamond layer on the wafer‐level opens‐ up possibilities for many other applications, since this approach is scalable and in general cost effective.

Large Area Growth and Phase Selectivity of MoTe2 Nanosheets through Simulation‐Guided CVD Tellurization

AbstractAmong transition metal dichalcogenides, molybdenum ditelluride (MoTe2) holds significant attention due to its polymorphic nature including semiconducting, metallic, and topological semimetal phases. Considerable efforts are devoted to synthesizing MoTe2 nanosheets to make them suitable for device integration in nanotechnologies and for fundamental investigations. In this respect, chemical vapor deposition (CVD) via tellurization of a pre‐deposited Mo thin film is an easy and flexible way for synthesizing large scale MoTe2 nanosheets. Here, the study report on the CVD of large‐area (up to 4 cm × 1 cm) MoTe2 nanosheets with pure 1T’ and 2H phase selection by design. Within the tellurization scheme, the vapor‐solid reaction between the pre‐deposited molybdenum film and tellurium vapor is studied thus optimizing the scalability and quality of the MoTe2 nanosheets grown on SiO2/Si substrates. It is demonstrated that the MoTe2 structure and morphology are kinetically dictated by the tellurium concentration gradient on the reaction site with varying geometric configurations inside the CVD reactor. This study provides a pivot scheme for enabling scalable 1T’ and 2H‐MoTe2 integration in applications for novel micro‐ and nano‐electronics, spintronics, photonics, and thermoelectric devices.

Improved adaptive backstepping control of MPCVD reactor systems with non-parametric uncertainties

This paper presents an improved adaptive backstepping control strategy for a microwave plasma chemical vapor deposition (MPCVD) reactor system. To describe the dynamics of the reactor system, a non-parametric uncertain nonlinear system model with unknown control direction functions is built up. In order to deal with the non-parametric uncertainties of the system, direct adaptive laws are primarily proposed to estimate such uncertainties, which is superior to traditional adaptive backstepping that can only address parametric uncertainties. Moreover, an equivalence transformation of the system is given to address the system unknown control direction functions. By using Lyapunov stability criterion, it can be proved that the target signals (desired temperature, desired pressure, and desired gas flow rates) are tracked by the reactor system outputs with small errors. Finally, simulation results are given to demonstrate the effectiveness of the proposed control method.

(Digital Presentation) Properties of Selectively Grown Si:P Layers below 500°C for Use in Stacked Nanosheet Devices

With the introduction of novel stacked CMOS transistor integration schemes such as sequential 3D and CFETs [1,2], there is an increasing need for highly active source/drain layers with a low overall thermal budget. For some integration schemes, processing temperatures below ~ 525°C are desired [3] and in most cases, the contacts need to be formed on the {110} surfaces of exposed Si nanosheets. In this paper, we report on selectively grown Si:P layers below 500°C targeting application in stacked nanosheet-based devices. In contrast to conventional approaches where selectivity is obtained at low temperatures using Cyclic-Deposition and Etch (CDE) with HCl/GeH4 as an etchant [4,5], we rely for this work on Cl2-based etching in combination with Si3H8 as a high-order Si precursor [6]. The Si:P layers were grown in a 300 mm ASM Intrepid® ES reduced pressure chemical vapor deposition reactor on Si (001) substrates.Figure 1 shows some typical characteristics for the Si:P layers without etching (“Dep-only”) and CDE Si:P layers below 500°C. As the temperature is lowered, the growth rate and P incorporation for a given PH3 flow decreases substantially, while the active concentration increases. For both the “Dep-only” and CDE layers, a minimum develops in the resistivity which corresponds to a maximum in active concentration as derived from micro-Hall measurements. Due to the etching during CDE, a P-enrichment takes place and the P concentration in the layers is enhanced compared to the “Dep-only” case. A minimum resistivity of 0.28 mOhm.cm (Pact ~ 6e20/cm3) is obtained for CDE at 480°C which is slightly larger than the minimum resistivity of 0.24 mOhm.cm (Pact ~ 1e21/cm3) for the “Dep-only” case at the corresponding temperature.Figure 2 shows the application of the CDE process on wafers with fins. By lowering the deposition time at a constant etching time per cycle, a (wafer-scale) selective regime can be reached. For the “Dep-only” case, quite some defects and nuclei are present on the sidewalls of the Si-fins and the oxide dielectric, respectively, which are finally removed by sufficient Cl2 etching.Figure 3 compares the corresponding X-TEMs of the above fins after “Dep-only” and selective CDE conditions. For the “Dep-only” case we can only observe a mono-crystalline growth in the <100> direction. For other growth directions like <110>, epitaxial breakdown-down occurs resulting in a substantially reduced crystalline thickness. With the use of Cl2 based CDE, a selective growth can be reached as well as a clear structural improvement in the <110> growth direction, which is very important for the application in nanosheet devices. Finally, once a (111) facet is formed, twin defects occur as expected for low temperature Si:P and Si:C:P [7].The growth behavior of the CDE processes in relevant nanosheet geometries is currently under investigation.

Low Temperature Selective Epitaxy of Group-IV Semiconductors for Nanoelectronics

Continuous improvement of device performance is becoming very challenging as the transistor dimension approaches the physical limits of scalability. In particular, the source/drain (S/D) layer resistivity and contact resistance at the S/D region became major components for further parasitic resistance reduction [1]. Therefore, layers with high active doping concertation is required for future technology nodes. From another side, novel architectures such as 3D-stacked devices constraints the allowed thermal budget for epitaxy processes [2]. In this work, we will review our recent achievements on LT epitaxy for both Si:P and SiGe:B layers to enable (i) parasitic resistance reduction and (ii) novel integration schemes.All layers were grown in a 300 mm ASM reduced pressure chemical vapor deposition reactor on Si(001) substrates and patterned substrates.Firstly, we will discuss the benefits of SiP growth at low temperature leading to high active doping concentrations (~1.1×1021 cm-3), as reported in our previous work [3]. Figure 1 shows the omega-2theta scans around the symmetric (004) reflections of the Si:P/Si stacks. As expected, reducing the Si precursor flow leads to a higher substitutional P (~7.5%) incorporation in the layer. The good crystallinity of the SiP layer is attested by the well-defined thickness fringes. Figure 2a represents the XRR scans of non-selective SiP process and selective SiP process compared to 100 nm bare SiO2 on Si substrate. The presence of fringes (red curve) indicates that a 2D amorphous SiP layer is deposited on SiO2. To confirm the full selectivity of the process and the absence of nuclei on the SiO2 surface, top view SEM was performed (cf. Figure 2b).Afterwards, we will focus on the SiGe:B epitaxy at low temperature. Figure 3a shows omega-2theta scans around the symmetric (004) reflections of the SiGe:B/Si stacks for various B flows. The apparent Ge content drops from 52.1% to around 41.3% when B flow was multiplied by 16. The inset represents the reciprocal space map (RSM) around the asymmetric (224) peak of SiGe:B layers grown on Si(001) substrates with the highest B flow. The RSM clearly indicates high quality and fully strained SiGe:B layer. Figure 3b depicts the apparent Ge drop vs B flow. This reduction in Ge content is attributed to B strain compensation effect leading to artificially lower Ge content [4]. Figure 3c represents SiGe:B layer resistivity vs B flow. Resistivity drops until a critical B flow and then increases with increasing B flow. Figure 4 shows active doping concentration and Hall mobility as function of the B flow. The Hall measurements were performed on a cleaved wafer edge and assume a Hall scattering factor of 1. Active carrier concertation increases with increased B flow. As a side effect of the higher activation, the Hall mobility is lowered likely due to an increase in ionized impurity scattering which is the reason why the resistivity does not decrease substantially below a certain value for higher B flows at current growth conditions. Layers with similar physical properties have resulted in S/D metal contact resistivity of ~5×10-10 Ohm.cm2 [5]. Figure 5 depicts the selective process on advanced patterned nanosheet test structures. Figure 5a illustrates the selectivity towards several nanosheet structures, Figure 5b shows a zoomed in image indicating selective process towards inner SiN spacers and SiO2. Figure 5c is a FFT of the SiGe:B area indicated by red square and Figure 5d is an EDS map of the key elements (Si, Ge, O, C, Cl, F, N). Figure 6a and 6b show the selective process stability over 20 runs. The HR-XRD measurements at wafer center are represented in Figure 6a. Figure 6b represents the resistivity at the wafer center. Thickness uniformity across one of the wafer is illustrated in Figure 6c. The results indicate excellent wafer to wafer and within wafer uniformities despite low temperature processing.LT epitaxy offers several advantages to reach high active doping concentrations and enable novel integration schemes. Despite challenges associated to LT epitaxy, in this work we showed the possibility to grow selective layers while maintaining the excellent physical layer properties, within wafer uniformity and wafer to wafer reproducibility.[1] H. Wu et al. EEE International Electron Devices Meeting (IEDM), (2018), pp. 35.4.1.[2] A. Vandooren et al. IEEE Symposium on VLSI Technology, (2018), pp. 69-70.[3] R. Khazaka et al. ECS Meeting s, MA2020-02(24), (2020) 1734-1734.[4] J.M. Hartmann et al. ECS JSST, 3(11) (2014) 382.[5] H. Xu et al. IEEE Symposium on VLSI Technology, (2022), (to be published). Figure 1

(Si)GeSn Isothermal Multilayer Growth for Specific Applications Using GeH4 and Ge2H6

The experimental demonstration of Ge1-xSnx alloys lasers opened group-IV materials towards high-performance electronic and photonic devices that can be easily integrated with the current Si semiconductor technology. In recent years, GeSn-based optoelectronic devices including light-emitting and detectors, modulators, and CMOS have been proven.The major challenges for the Ge1-xSnx epitaxy arise from the low solid solubility of Sn in Ge, the large lattice mismatch, and the reduced thermal stability between Ge and Sn. All these are becoming extremely critical at higher Sn contents. Non-equilibrium conditions offered by molecular beam epitaxy (MBE), chemical vapor deposition (CVD), flash lamp, or laser annealing have been lately investigated. Between them, CVD is to date the preferred growth technique for its current development compatible with the industry offering micron-thick layers with the highest crystal quality.While Tin-tetrachloride (SnCl4) becomes the standard Sn precursor, for Ge different gasses, like germane (GeH4) and digermane (Ge2H6) are used attempting to archive high Sn incorporation and high material quality. While Ge1-xSnx films with the same high Sn content can be obtained regardless of the used precursor, the advantages and disadvantages of each precursor are discussed in this work. The use of Ge2H6 is accompanied by high growth rates, being favorable in applications where relatively thick films are needed, such as laser structures. On the other hand, with a relatively low growth rate, GeH4 provides a greater thickness control, achieving clear and sharp interfaces in heterostructures. For this reason, GeH4 is the appropriate precursor for quantum transport or spintronic.The biggest challenge in heterostructure designs is going up and down in Sn content. The growth of a Ge1-ySny on a Ge1-xSnx, y<x, or SiGeSn layer cannot be performed by increasing the growth temperature. Post-annealing processes lead to strong crystallinity degradation of the already grown layer by strong Sn diffusion or Sn segregation due to the limited thermal stability of Ge1-xSnx alloys.In this work, we address simple methodologies to enhance the gradient or step Sn content without changing the process temperature. Controlling only the carrier gas flow while keeping the standard growth parameters constant, high-quality Ge1-xSnx alloys with uniform Sn content up to 15 at.% are obtained. The proposed method acts as guidance to produce Ge1-xSnx heterostructures that can be extended to any CVD reactor, independently of the used precursor, GeH4 or Ge2H6. Different devices structures are presented proving the applicability of the isothermal multilayer growth. Figure 1

High Performance Planar Antimony-Based Superlattice Photodetectors Using Zinc Diffusion Grown by MBE

In this letter, we report a mid-wavelength infrared (MWIR) planar photodetector based on InAs/InAs1−xSbx type-II superlattices (T2SLs) that has a cut-off wavelength of 4.3 μm at 77 K. The superlattice for the device was grown by molecular beam epitaxy while the planar device structure was achieved by Zinc diffusion process in a metal–organic chemical vapor deposition reactor. At 77 K, the peak responsivity and the corresponding quantum efficiency had the value of 1.42 A/W and 48% respectively at 3.7 μm under −20 mV for the MWIR planar photodetector. At 77 K, the MWIR planar photodetector exhibits a dark current density of 2.0 × 10−5 A/cm2 and the R0A value of ~3.0 × 102 Ω∙cm2 under −20 mV, which yielded a specific detectivity of 4.0 × 1011 cm·Hz1/2/W at 3.7 μm. At 150 K, the planar device showed a dark current density of 6.4 × 10−5 A/cm2 and a quantum efficiency of 49% at ~3.7 μm under −20 mV, which yielded a specific detectivity of 2.0 × 1011 cm·Hz1/2/W.

Numerical simulation of carbon nanotube fibers motion in the chemical vapor deposition reactor

In order to explore the motion of carbon nanotube fibers prepared by the chemical vapor deposition reactor, the gas flow field in the reactor is simulated using the computational fluid dynamics software. The dynamics analysis of carbon nanotube fibers in the gas flow field is carried out based on the bead-rod fiber model. The fiber motion is simulated numerically by introducing the gas velocity into the fiber dynamics equation. Through iterative computation, the instantaneous motion state and trajectory of carbon nanotube fibers in the reactor are obtained. The simulation results are consistent with the motion diffraction photo of carbon nanotube fibers and explain the cause of ‘sock’ structure in the preparation process of carbon nanotube fibers preliminary. The results show the great potential of this research for understanding the forming mechanism of carbon nanotube fibers.

Remarkable enhancement in CNT fiber synthesis by reducing convection vortex in floating catalyst chemical vapour deposition

Synthesis of carbon nanotube fiber (CNT fiber) in a floating-catalyst chemical vapor deposition (FC-CVD) reactor suffers from very low carbon efficiency and yield. One of the major causes of poor conversion is the formation of internal convection vortex near the inlet, where catalyst particles undergo agglomeration and deactivation resulting in a significant reduction in the yield. It also lowers the average aspect ratio of the CNTs. In this work, a novel method of using an internal heating rod has been employed to reduce the convection vortex by altering the temperature gradient locally. The optimum position, temperature and size of the heating rod have been determined by computational fluid dynamics (CFD) for enhanced carbon conversion. The yield and the aspect ratio of CNT fiber, synthesized at the optimized condition have enhanced by 90% and 50%, respectively while the average ratio of D to G peak in Raman spectra (ID/IG) has reduced by 58%. For the first time, residence time distribution (RTD) analysis has been used to describe the effect of convection vortex on carbon conversion for the synthesis of CNT fiber. This work demonstrates simultaneous enhancement in yield, crystallinity and aspect ratio of the CNT fiber by reducing the convection vortex.

Forecasting carbon nanotube diameter in floating catalyst chemical vapor deposition

Carbon nanotube (CNT) diameter control is essential for many conductive and structural applications; to date, a general diameter methodology applicable to all floating catalyst chemical vapor deposition (FC-CVD) reactors is not yet established. Single-walled CNT (SWCNT) diameter was robustly controlled by systematically exploring an extensive variety of fundamental FC-CVD reactor parameters (631 experiments) including: CO2, H2, and Ar flowrates; fuel flowrate; added H2O (up to an unprecedented 30% of fuel by mass); ferrocene concentration; reactor temperature (covering temperatures with solid and liquid floating catalyst); and quartz reactor tube age. As a function of these experimental input factors, across three Raman wavelengths, validated statistical models robustly predicted: 1) diameter of SWCNTs, via the weighted average of the radial breathing modes (RBMs); 2) the conditions which led to SWCNT growth, via the categorical appearance of viable RBMs. This is noteworthy because it illustrates a new paradigm of FC-CVD reactor control, accounting for interaction between reactor input factors, system noise, and other non-linear responses. Oxidative influences (including laboratory humidity) yield smaller CNT diameters, although H2O becomes important only at higher temperatures and CO2 is countered by H2 addition. Increasing reactor temperature increased diameters. Pyrolysis calculations showed species inside the reactor differ substantially from species injected. A kinetic-thermodynamic model of catalyst particle size and chemical state revealed that adding oxidative species kept the active catalyst particles small, explaining the resulting small CNT diameters. The powerful combination of our multivariate statistical approach with kinetic-thermodynamic modeling enables unprecedented insight and control over CNT synthesis.

Ti3SiC2-SiC multilayer thin films deposited by high temperature reactive chemical vapor deposition

Ti3SiC2-SiC multilayer film coatings synthesis was investigated with the high temperature reactive chemical vapor deposition technique. The method consists of a reaction between SiC (as the substrate and interlayers) and H2-TiClx gaseous mixture. Cross-section morphologies and phases were studies by scanning electron microscopy (SEM), X-ray diffraction (XRD) and automated crystal orientation mapping in transmission electron microscopy (ACOM-TEM). Thermodynamic calculations were carried out to select more appropriate gas composition for reactor conditions and understand the chemistries of reaction between layers in the different steps. Nano and Vickers micro-indentation mechanical tests determined hardness and elastic modulus of the Ti3SiC2 and Ti5Si3Cx surfaces samples. Oxidation tests and emissivity measurements allowed the evaluation of Ti3SiC2-SiC coatings as materials for high temperature applications. The multilayered systems kept their mechanical integrity and showed low degradation after 25 h of thermal cycles at 900 °C in air. The measurement of the optical properties also revealed an increase of the absorptivity after the oxidation of Ti3SiC2 surface sample.

In-situ synthesis of graphene encapsulated Fe/Fe2O3 nanoparticles for possible biomedical applications

This paper reports on the in-situ synthesis, optimization, characterization and cytotoxicity tests of multi-layer graphene (MLG) encapsulated Fe/Fe2O3 nanoparticles (Fe/Fe2O3@C core–shell nanostructures) by spray drying-assisted chemical vapor deposition (CVD) using iron-nitrate/silica-based precursors. The influences of CVD reaction temperature, holding time, CH4/H2 gas flows and pressure on the synthesis of MLG encapsulated Fe/Fe2O3 nanoparticles were investigated. CVD-synthesized powders were purified using acid leaching to remove residual silica and probable uncoated Fe/Fe-oxide phases. XRD analyses revealed the presence of FCC (Fe,C), BCC Fe, graphite/graphene and trace amount of Fe2O3 phases. Raman spectra confirmed the existence of MLG shells. TEM indicated that MLG (from at least 3 to maximum of 35 layers) wrapped around the metallic cores ranged between 4 and 85 nm. Purification of nanoparticles did not degrade, dissolve or create discontinuity on the MLG structure. VSM measurements showed that nanoparticles obtained from the optimized conditions (900 °C, 100 ml/min CH4/H2, 50 mbar) had a soft ferromagnetic behavior with low saturation magnetization (∼85 emu/g) and coercivity (∼552 Oe) values. Optimized MLG encapsulated Fe/Fe2O3 nanoparticles were successfully suspended in water using a poly(acrylic acid) coating. Aqueous MLG encapsulated Fe/Fe2O3 nanoparticles were cytocompatible below 100 μg/ml at short incubation times, and showed the potential to be used in biomedical applications.

An efficient chemistry-enhanced CFD model for the investigation of the rate-limiting mechanisms in industrial Chemical Vapor Deposition reactors

An efficient CFD model for the deposition of alumina from a gas mixture consisting of AlCl3, CO2, HCl, H2 and H2S in an industrial CVD reactor with multiple disks and a rotating feeding tube, is proposed. The goal is twofold: (i) to predict the thickness of the deposited material, (ii) to investigate whether the process rate is determined by the reaction rate or by diffusion. A reaction model that consists of a gas-phase homogeneous reaction and a heterogeneous reaction is implemented, with a proposed kinetics rate that includes the effect of the H2S concentration. The latter has a catalytic effect, but the mechanism is not entirely understood. The entire reactor geometry (consisting of 40–50 perforated disks) is divided into appropriately chosen 7-disk sections. The 2D, time-dependent CFD model is validated using production data for the deposition thickness. The proposed computational tool delivers accurate predictions (average relative error 5%) for different geometries corresponding to real reactor set-ups. Extending the functionality beyond prediction, a computational experiment is performed to illuminate the interplay between species diffusion and chemical reaction rates, which determines the rate-limiting mechanism. The results indicate that species diffusion is fast enough and therefore reaction kinetics determine the overall deposition rate.

Aerosol based synthesis of highly conducting carbon nanotube macro assemblies by novel mist assisted precursor purging system

Taking hardware complexity into consideration of traditional continuous precursor purging systems for synthesis of few wall carbon nanotubes (CNTs) is a big challenge. Therefore, a novel precursor purging system for aerosol formation is designed to achieve uniform diameter distribution of CNTs, with the aerosol flow rate controlled either by number of ultrasonic mist makers or flow rate of carrier gas. Large droplets are turned into aerosol via an as-customized mist-producing system without the use of temperature or any chemical reaction. A built-in atomized gas valve is used to introduce the aerosol into a floating catalyst chemical vapour deposition (FCCVD) reactor. After an influential comparison of as-customized purging systems to the mostly used complex and big-budget systems for uniform diameter distribution, the quality of these CNT assemblies, synthesized using two different carrier gases (argon and hydrogen) is examined. Herein, CNT sheets with mostly fewer walls CNTs (diameter 2–10 nm) have been synthesized using this approach, with the controlled size of catalyst nanoparticles, under H2 atmosphere exhibiting low sulphur impurities, as evidenced by Raman, EDS, and XPS spectra, and have a fourteen-fold greater electrical conductivity (5.78 × 104S/m) than those synthesized under Ar atmosphere. Moreover, these sheets are also twisted and wrapped by insulating heat shrink tubes. The maximum current density of these conducting CNT wires having 250 µm diameter is 8.15 × 106A/m2. Further, one of the domestic applications of LED bulb (3–45 W) lightning is also demonstrated which shows the suitability of these conducting wires in numerous hi-profile applications.

Lowest Concentration of Chlorine Trifluoride Gas for Cleaning Silicon Carbide Chemical Vapor Deposition Reactor

A dilute chlorine trifluoride gas at less than 1% was possible for the cleaning of a silicon carbide chemical vapor deposition (CVD) reactor. For 20 min, the chlorine trifluoride gas at the concentrations of 0.5%–1% in ambient nitrogen at atmospheric pressure could detach the 30 μm-thick particle-type polycrystalline silicon carbide CVD film from the susceptor which had a coating film made of a purified pyrolytic carbon (PPyC). While the PPyC film had some damage due to the shallow fluorine diffusion, it could be recovered without any pit formation by annealing in ambient nitrogen containing a trace amount of oxygen at atmospheric pressure for 10 min at the temperature of 845 °C.

Chemical Vapor Deposition of Wide-Bandgap p-Type Semiconductor Cuprous Iodide for Optoelectronic Device Applications

Continuous, pinhole-free thin films of transparent conductive materials (TCMs) with p- and n-type conductivity are critical components of optoelectronic devices including photovoltaics (PV), transparent electronics, and LEDs [1]. TCMs with n-type conductivity are widely available in the form of semiconducting oxides [2]; however, p-type TCMs (hole transport materials, HTMs) with suitable conductivity are comparatively rare [1]. Particularly in the rapidly growing field of thin film perovskite PV, device-quality thin films of HTMs with high stability and conductivity are urgently needed to replace the organic HTMs typically employed in perovskite PV research [3]. As such, techniques to deposit inorganic HTM thin films are desired.With a focus on applying HTMs in optoelectronic devices at the commercial scale, these materials must be deposited by a scalable technique yielding thin, continuous, pinhole-free films. Chemical vapor deposition (CVD) is a highly scalable thin film deposition technique widely used in industry, with a proven ability to yield high-quality thin films on large-area substrates [4]. A variety of n-type TCMs are accessible by CVD techniques, but few CVD methods exist for p-type TCMs; examples include atomic layer deposition of NiOx and VOx [5].The cuprous halides (CuX, X = Cl, Br, I), which are optically transparent p-type semiconductors with bandgaps ~3 eV, are promising inorganic HTM candidates. Cuprous iodide is of particular interest due to its low resistivity (~10-2 Ohm·cm), high hole concentration and mobility (~1019 cm-3 and ~1-10 cm2V-1s-1, respectively), and its valence band maximum position (ionization potential: 5.0-5.4 eV), which is well-aligned with common perovskite absorber materials [6]. While CuI crystallite arrays have been obtained by metal-organic CVD [7], CVD of continuous CuI thin films has only been achieved by a two-step vapor conversion process, requiring initial deposition of a copper chalcogen followed by vapor-phase conversion to the halide [6].Our group has recently published a CVD technique enabling direct deposition of continuous CuBr thin films via CVD reaction between hydrogen bromide and vinyltrimethylsilane(hexafluoroacetylacetonato)copper(I) [Cu(hfac)(vtms)] [8], and this technique has been extended to deposition of CuI. X-ray photoelectron spectroscopy indicates pure CuI films with an atomic ratio of approximately 1:1 Cu:I, and x-ray diffraction confirms deposition of γ-CuI. Similar to our observations for CuBr films, substrate identity has significant effects on CuI film continuity. Progress towards CVD of continuous CuI films on substrates of interest for practical application in optoelectronic devices will be discussed, with a particular focus on perovskite PV.[1] A. N. Fioretti and M. Morales-Masis, "Bridging the p-type transparent conductive materials gap: synthesis approaches for disperse valence band materials," J. Photon. Energy, 10, 042002 (2020).[2] M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, and C. Ballif, "Transparent Electrodes for Efficient Optoelectronics," Adv. Electron. Mater., 3, 1600529 (2017).[3] B. Gil, A. J. Yun, Y. Lee, J. Kim, B. Lee, and B. Park, "Recent Progress in Inorganic Hole Transport Materials for Efficient and Stable Perovskite Solar Cells," Electron. Mater. Lett., 15, 505 (2019).[4] R. Gordon, "Chemical Vapor Deposition of Coatings on Glass," J. Non-Cryst. Solids, 218, 81 (1997).[5] J. A. Raiford, S. T. Oyakhire, and S. F. Bent, "Applications of atomic layer deposition and chemical vapor deposition for perovskite solar cells," Energy Environ. Sci., 13, 1997 (2020).[6] R. Heasley, L. M. Davis, D. Chua, C. M. Chang, and R. G. Gordon, "Vapor Deposition of Transparent, p-Type Cuprous Iodide Via a Two-Step Conversion Process," ACS Appl. Energy Mater., 1, 6953 (2018).[7] V. Gottschalch, S. Blaurock, G. Benndorf, J. Lenzner, M. Grundmann, and H. Krautscheid, "Copper iodide synthesized by iodization of Cu-films and deposited using MOCVD," J. Cryst. Growth, 471, 21 (2017).[8] C. M. Chang, L. M. Davis, E. K. Spear, and R. G. Gordon, "Chemical Vapor Deposition of Transparent, p-Type Cuprous Bromide Thin Films," Chem. Mater., 33, 1426 (2021).