Uniformity Of Layer Research Articles

Study of horizontal and vertical uniformity of B-doped layer on mosaic single crystal diamond wafers by using hot-filament chemical vapor deposition

Aiming at developing inch-sized processing of diamond, B-doped layer was grown on mosaic single-crystallin diamond wafers by using hot-filament chemical vapor deposition (CVD), which is expected to have an advantage in terms of the deposition area compared with microwave plasma (MWP) CVD. Uniformity in horizontal and vertical directions is studied. It is found that the junctions of the monocrystalline diamond domains in the mosaic wafer and the direction of the crystal off-angles against to these junctions are less effective to the uniformity of the impurity concentrations. On the other hand, it is suggested that excess incorporation of W from the filament suppresses the growth and incorporation of B. It is shown that millimeter scale or more precise control of the arrangement of the wafer and the filament enables to obtain more uniform and efficient doping.

Surface Uniformity of Wafer-Scale 4H-SiC Epitaxial Layers Grown under Various Epitaxial Conditions

Wide band gap semiconductor 4H-SiC is currently widely used in the manufacture of high-frequency and high-voltage power devices. The size of commercial 4H-SiC wafers is increasing, from 4 inches to 6 inches. Surface roughness, as one of the parameters reflecting the quality of epitaxial wafers, is closely related to the performance of power devices. Most studies on the uniformity of epitaxial layers did not focus on RMS; however, the uniformity of epitaxial surface roughness also affects the device yield. In this paper, the root mean square roughness (RMS) and uniformity (σ) of epitaxial wafers are investigated as a function of epitaxy conditions, including C/Si ratio, growth temperature, and Si/H ratio. It was found that the best values of RMS and σ were obtained with C/Si ratio = 1 in the experimental range. Growth temperature had opposite effects on RMS and σ, with better RMS uniformity obtained at lower growth temperatures. An insignificant effect on RMS and σ has been found with the Si/H ratio changes in the experimental range. We hope that our experiments can play a certain role in promoting the improvement of the surface roughness of wafer-scale 4H-SiC epitaxial layers.

Bias-stress instabilities in low-temperature thin-film transistors made of Al2O3 and ZnO films deposited by PEALD

Thin film transistors (TFT) were fabricated by plasma-enhanced atomic layer deposition (PE-ALD) of aluminum oxide (Al2O3) and zinc oxide (ZnO) on glass substrates at 70 °C. The thicknesses of the Al2O3 (gate dielectric) and ZnO (n-type semiconductor) were 25 and 60 nm, respectively. Prior to Al2O3 deposition Cr/Au gate contacts were patterned using photolithography. Photolithography was also used to define aluminum source and drain contacts with thickness of 200 nm. The W/L ratio of the fabricated transistors was varied between 1 and 8 by varying the channel length L (40, 20 10 and 5 μm), while the channel width W was kept constant to 40 μm. Capacitance-voltage measurements revealed good uniformity of the Al2O3 layer with a dielectric constant value of ~8. The sheet resistance of the ZnO layer was found to be ~2400 Ω/sq. The TFT electrical characterization showed that the saturation mobility does not depend substantially on W/L ratio and had values between 0.82 and 1.1 cm2/V-s, while the subthreshold slope varied between 190 and 207 mV/dec. Moreover, a high on/off current ratio of ⁓107 was determined. The threshold voltage (Vth) instability was also characterized by positive and negative bias stress leading to a Vth shift of about −0.3 V and − 0.8 V, respectively.

MORPHOLOGICAL BEHAVIOR OF FEB AND FE2B IN BORIDE LAYER OF 304 STAINLESS STEEL UNDER DIFFERENT MEDIUM

This study investigates the morphological behavior of FeB and Fe2B phase in boronized 304 stainless steel under two different mediums which is powder and paste. Surface attrition was implemented in order to initiate better boron diffusivity. The comparison of microstructure in term of grain size and boride layer thickness were also analyzed. Scanning electron microscopy, X-Ray diffraction analysis and energy dispersive X-Ray Analysis were conducted to prove the existence of FeB and Fe2B phases. The relationship between the phase and Vickers microhardness was also investigated. The results show formation of flat-toothed boride layer in both sample with different FeB and Fe2B layer uniformity. Paste boronized sample with120 µm boride layer thickness had outperformed the powder boronized sample that with 43 µm boride layer thickness, thus providing significant improvement in microhardness values from 1500 Hv to 1800 Hv. In conclusion, paste medium provide outstanding boride layer thickness with 300% enhancement and excellent microhardness with 20% improvement. The results of this findings could offer a new insight in pack boronizing of stainless steel that can be complicated to boronized due to its high alloying element content.

Passivation of Transition Metal Dichalcogenides Monolayers with a Surface‐Confined Atomically Thick Sulfur Layer

Surface passivation can eliminate the charge doping of monolayer transition metal dichalcogenides (TMDs) during the device fabrication, which is important for the large‐scale production of ultra‐stable materials and high‐performance devices. The uniformity and atomical thickness of the passivating layers with a low dielectric constant (κ) are essentials to preserving the intrinsic properties of monolayer TMDs in harsh environments. Herein, a surface‐confined mechanism is developed to encapsulate TMDs monolayers by atomically thin sulfur layers with high spatial homogeneity (named S–MX2). The bottom bilayer S atoms are strongly confined by the upper S monolayers when the low‐κ S reaches three layers on the surface of TMDs, which spontaneously renders the uniform distribution on a large scale. The intrinsic electrical and optical properties of monolayer S–MX2 are well maintained and show excellent long‐term stability under harsh environments. Herein this work, a way to eliminate surface doping of monolayer TMDs for their practical application in large‐area‐integrated circuits is provided.

Uniform lithiophilic layers in 3D current collectors enable ultrastable solid electrolyte interphase for high-performance lithium metal batteries

Uniform lithium plating/stripping during charging/discharging in 3D lithiophilic current collectors (3DLCC) is essential to suppress growth of lithium dendrites and to mitigate infinite volume variations of lithium metal for long-lived lithium metal batteries. This study reveals the decisive role played by uniformity of the lithiophilic layer of the 3DLCC in achieving uniform lithium plating/stripping. Herein, a series of metal oxide-based 3DLCCs are successfully fabricated with a simple and an ultrafast solution combustion method, from which formation of a uniform and stable lithium dendrite-free solid electrolyte interphase via a uniform lithiophilic layer is demonstrated. Taking Co3O4 as the lithiophilic material deposited on a nickel foam as the 3DLCC (Co@NF) for a proof of concept, the loading amount of Co3O4, closely correlated with the uniformity of the Co3O4 layer, is modulated to optimize its lithium ion hosting performances. With a uniform Co3O4 layer grown in the 3DLCC, an ultralow nucleation overpotential of 33.4 mV is achieved in half-cell tests at 1 mA cm−2 and 1 mAh cm−2, and a high Coulombic efficiency of 97.1% is maintained after 210 cycles under a severe cycling condition of 2 mA cm−2 and 1 mAh cm−2. A small polarization voltage of 13 mV together with an ultralong cycle life of 2400 h at 0.5 mA cm−2 and 1 mAh cm−2 in symmetric Li cells is achieved. Moreover, the composite Li anode delivers sensational rate capability and cyclability in full-cells. This work not only provides new and valuable insights into the interphasial chemistry of solid electrolyte interphase layers, but also sheds light on the development of ultrastable lithium metal batteries.

Using copper-based biocathodes to improve carbon dioxide conversion efficiency into methane in microbial methanogenesis cells

Copper can be used as a metal catalyst for abiotic CO2 conversion into methane and organic chemicals, but it has not been examined as a catalyst for enhancing biotic methane generation in microbial methanogenesis cells (MMCs). In this study, copper-based electrodes prepared using several different techniques were compared to the performance of MMCs containing graphite block cathodes. Gas production was examined under both abiotic and biotic conditions at a fixed cathode potential of –0.9 V vs. Ag/AgCl in two-chamber electrochemical cells. All copper-based cathodes showed better methane production than plain graphite blocks except for the cathode made from copper foil which lacked a biocompatible surface. The cathode prepared by an electroless Cu deposition (electroless-Cu) method had the highest current density production of 0.6 A/m2 and methane production rate of 201 nmol/cm3/d, and its performance was stable over time. Both the electroless-Cu and electro-deposited Cu electrodes produced more current than that obtained with copper powders with a Nafion binder (Nafion-Cu), likely due to different surface characteristics such as hydrophobicity and uniformity of the copper layer. The results of this study showed that copper-based biocathodes improved methane production relative to plain graphite materials and techniques for preparing copper electrodes impact bioelectrochemical performance with the highest performance in the electroless-Cu reactors.

Non-selective adsorption of organic cations enables conformal surface capping of perovskite grains for stabilized photovoltaic operation

Chemical passivation of defective perovskite surface is a fundamental strategy to stabilize solar cell operation by impeding the defect-dominant surface ion migration. Here, we show that the configuration of organic cations plays a key role in determining their surface adsorption energetics at various perovskite facets, which will strongly impact the spatial uniformity of the low-dimensional perovskite passivation layer (LDPL). A weak-anisotropic adsorption behavior is demonstrated for tertiary ammonium that can enable a conformal LDPL on the perovskite grain surface. Benefiting from comprehensive surface passivation, the migration of ionic perovskite species was suppressed and the as-fabricated p-i-n solar cells yielded an optimized power conversion efficiency of 22.6% with an expected T 80 lifetime of about 4,000 h under continuous 1-sun illumination. Our findings give insight into the design and preparation of heterostructured perovskite films toward efficient and stable solar cells. • Surface adsorption enthalpy of organic cations is closely related to their configuration • Tertiary ammonium passivation results in conformally capped low-dimension perov. phase • Ion migration is suppressed in heterostructured perovskite film • The as-modified solar cells possess a stable efficiency under various stressors Taking advantage of the weak-anisotropic adsorption nature of tertiary ammonium on perovskite facets, Zhou et al. demonstrate a comprehensive protection of perovskite grain surface by constructing a conformal low-dimensional perovskite passivation layer. The inhibited ion migration enables stabilized solar cell operation.

Development of a novel silica-based microwave receptor for high temperature processes

A novel silica-based microwave receptor was developed via a fluidized bed chemical vapor deposition (FBCVD) technique. In this study, the silica sand particles were successfully coated in an induction heating-assisted reactor, with carbon produced from thermal degradation of methane (TDM) at various reaction temperatures and times. The effect of FBCVD reaction parameters, temperature and reaction time, on the amount of carbon deposition, and the composition, coherence and thickness of the carbon coating layer were investigated using thermogravimetric and morphological analysis, respectively. The microwave heating performance of such developed receptors was further investigated in an innovative single-mode microwave apparatus and was subsequently compared with the relevant performance of sand and graphite particle mixtures. The developed microwave receptor stipulates low level of carbon content and high layer uniformity, extreme microwave heating rate, high durability, and excellent potential for application in gas-solid fluidized bed reactors as heat generator and catalyst support/promoter simultaneously.

Low temperature epitaxy of tensile-strained Si:P

Our long-term aim was to explore the Low Temperature Cyclic Deposition/Etch (CDE) of tensile-Si:P, in order to engineer the Sources and Drains of n-type Field Effect Transistors. We wanted to have high amounts of tensile strain and low resistivities in tensile Si:P layers grown at 550 °C, with (i) mainstream Si2H6 + PH3 gases for the non-selective deposition of t-Si:P and (ii) HCl + GeH4 for the selective etches of amorphous-Si:P versus monocrystalline Si:P (to have selectivity on patterned wafers). In the current study, we have focused on the deposition in such processes, having shown beforehand that, indeed, t-Si:P could be etched at 550 °C with HCl + GeH4 if the process conditions were right (Hartmann J.M. and Veillerot M., 2020 Semicond. Sci. Technol. 35 015015). Thanks to (i) high F(PH3)/(2*F(Si2H6)) Mass-Flow Ratios (MFR), (ii) a reduction of the H2 carrier flow, from the reference value of a few tens of standard liters per minute down to 1/5th of it and (iii) a chamber pressure increase, from 20 Torr up to 90 Torr, we succeeded in dramatically increasing the “substitutional” P concentration. and reaching values as high as 7.9%. 40 Torr was the best pressure in order to simultaneously have (i) a high “substitutional” P concentration (6.3%), (ii) a reasonable t-Si:P growth rate (5.5 nm min−1) and (iii) a low electrical resistivity (0.41 mOhm·cm), without being hampered by a layer uniformity that would be too degraded to be of use in actual devices. Those t-Si:P layers, grown with a MFR of 0.46, were of superior crystalline quality (in X-Ray Diffraction) and smooth (from haze measurements).

Cu seed step coverage evolution with target lifetime for long-throw self ionized physical vapor deposition chambers

The major approach for the deposition of Cu seed layers in copper interconnects is physical vapor deposition (PVD), with a self-ionized plasma (SIP) approach. However, the cutting-edge technologies still lack a full characterization of their efficiency throughout the entire lifetime of a Cu target. Following a previous study on standard SIP technology, in this contribution the robustness of Cu processes obtained by more advanced SIP co-resputtering approaches are investigated as a function of the Cu target lifetime. The conformality and uniformity of the Cu seed layer were studied on nanostructured features adopted in 90-nm node technology, with an aspect ratio up to 8. Transmission electron microscopy was adopted to fully characterize the Cu growth on trench features, highlighting the optimal process windows to be adopted for different SIP technologies. Furthermore, the effect of the resputtering obtained by applying a substrate bias is analyzed as a function of the target lifetime, shedding a light on its contribution to the overall layer uniformity.

Magnetic-plasmonic Ni nanotubes covered with gold for improvement of SERS analysis

The paper describes the synthesis of substrate for surface enhanced Raman spectroscopy (SERS) based on magnetic nickel nanotubes (Ni NTs). For the success application of Ni NTs in quantitative SERS analysis of organic molecules by the example of Rhodamine 6G (R6G), electroless deposition of gold (I) on Ni NTs in alkali media was performed. The purity and uniformity of the gold layer has been proven by methods of XRD, SEM-EDX, XPS and FTIR analysis. The magnetic properties of the obtained magnetic Ni-Au NTs measured by VMS did not change compared to the initial Ni nanotubes. The efficiency of substrates with Ni-Au NTs is determined by the optical properties of the substrate (the position of the plasmon resonance peak). The substrates with scattered nanotubes having a plasmon resonance position at 530 nm are the most effective for use in SERS when using a laser with a wavelength of 532 nm, as exemplified by the spectra of Radomin 6G. SERS analysis of R6G using Ni-Au NTs in concentration range from 10−3 to 10−8 led to average enhancement factor of 8∙105.

Numerical Investigation on Optimizing the Performance of Heat Transfer in Vertical Packed Bed at the Particle Scale

Enhancing the heat transfer efficiency in the vertical packed bed is deemed as significant focus issue and strategy. Heat transfer process in the vertical packed bed, granular flow profiles have obviously positive effect on the dynamics of heat transport between gas and solid matter. It is quite important to know the mechanism of various granular flow pattern related to these performances of heat transfer phenomena. In this study, discrete element numerical models coupled with continuous fluid are developed and proposed to optimize the effect of uniformity of granular flow on performance of heat transfer process. The coefficient of variation is introduced as quantitative measure of the uniformity of granular flow layer. The relation between granular flow profiles and the performance of heat transfer is verified by a combined numerical approach. The increase of uniformity of granular layer has a positive effect on improving of the efficient inter-phase heat transfer. The study also quantitative unfolds the efficient inter-phase heat transfer greatly enhanced by structural modification. The quantitative analysis for contribution of structural and operational modification to improve the efficient heat transfer is also performed.

Analysis of influence of spatial distribution error of directional infrared light on temperature field of cryogenic targets

For an inertial-confinement-fusion cryogenic target, the fusion ice layer inside the capsule should have a uniformity more than 99% and an inner surface roughness less than 1 μm (root mean square) to avoid Rayleigh-Taylor instabilities. And this highly smooth ice layer required for ignition is generated in the presence of volumetric heat and affected by the thermal environment around the capsule. For the D<sub>2</sub> fuel targets, the uniformity of the fusion ice layer inside the capsule is consistent with the uniformity of the surface temperature around the capsule, and the latter can be controlled by directional infrared illumination. A major challenge of directional infrared illumination is the precision of directional infrared spatial distribution. In this paper, a numerical model coupling the directional infrared tracking and temperature field calculation is proposed and validated by experimental results. A three-dimensional physical model of the cryogenic target is used to study the influences of different forms of directional infrared spatial distribution errors on the temperature uniformity of the capsule. The results show that the eccentricity of IR band axis has the worst effect on the temperature uniformity of the capsule, followed by the distance between both IR bands, and the width of the IR band has the least effect on the temperature uniformity of the capsule. Therefore, the eccentricity of IR band axis should be avoided in experiment to ensure the uniformity of the temperature of the capsule, further ensuring the uniformity of the fuel ice layer inside the capsule.

Terahertz time domain characterization method of the adhesive layer uniformity in multiple bonding structures

Terahertz time domain characterization method of the adhesive layer uniformity in multiple bonding structures

Sandwich‐like Nafion composite membrane with ultrathin ceria barriers for durable fuel cells

Improving the durability of the membrane electrode assembly (MEA) while obtaining high performance is required to further commercialize polymer electrolyte membrane fuel cells (PEMFCs). The durability of PEMFCs is improved by incorporating radical scavengers, such as CeO2 (ceria), into the MEA, especially the membrane. However, nanosized ceria particles are generally mixed with ionomers and are cast on substrates to fabricate composite membranes. In such a case, controlling their morphology and avoiding particle agglomeration is difficult. Herein, we report a novel method for constructing a robust membrane by incorporating ultrathin ceria barriers into the outermost sides of a commercial Nafion membrane to effectively alleviate radical attacks while ensuring the high uniformity and controllability of ceria layers. The improved durability of the composite membrane is confirmed via ex situ Fenton's test and in situ operation of a fuel cell. Moreover, we observe that the amount of fluoride ion emission and the loss of proton conductivity of the membranes decrease as the CeO2 density increases. The MEA comprises a modified membrane with CeO2 barriers that show proper areal density. It demonstrates excellent durability under accelerated environmental conditions (open circuit voltage test) and acceptable initial performance with an insignificant decrease in proton conductivity.

Low-Temperature Chemical Vapor Deposition Growth of MoS2 Nanodots and Their Raman and Photoluminescence Profiles

We report on the growth of an ordered array of MoS2 nanodots (lateral sizes in the range of ∼100–250 nm) by a thermal chemical vapor deposition (CVD) method directly onto SiO2 substrates at a relatively low substrate temperature (510–560°C). The temperature-dependent growth and evolution of MoS2 nanodots and the local environment of sulfur-induced structural defects and impurities were systematically investigated by field emission scanning electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. At the substrate temperature of 560°C, we observed mostly few-layer MoS2, and at 510°C, multilayer MoS2 growth, as confirmed from the Raman line shape analysis. With reduced substrate temperature, the density of MoS2 nanodots decreases, and layer thickness increases. Raman studies show characteristic Raman modes of the crystalline MoS2 layer, along with two new Raman modes centered at ∼346 and ∼361 cm−1, which are associated with MoO2 and MoO3 phases, respectively. Room temperature photoluminescence (PL) studies revealed strong visible PL from MoS2 layers, which is strongly blue-shifted from the bulk MoS2 flakes. The strong visible emission centered at ∼ 658 nm signifies a free excitonic transition in the direct gap of single-layer MoS2. Position-dependent PL profiles show excellent uniformity of the MoS2 layers for samples grown at 540 and 560°C. These results are significant for the low-temperature CVD growth of a few-layer MoS2 dots with direct bandgap photoluminescence on a flexible substrate.

Effect of the Zeta Potential on the Corrosion Resistance of Electroless Nickel and PVDF Composite Layers Using Surfactants.

Composite layers of Ni-P and PVDF were obtained using surfactants to enhance the corrosion resistance of the fluoride ion. The zeta potential of PVDF particles was changed with the surfactants (cationic, anionic, and nonionic). The effects of the zeta potential of PVDF particles on the particle distribution, morphology, composition, hydrophobicity, and corrosion resistance of the composite layers were studied using the different types of surfactants. The deposition behaviors of the Ni-P layer and PVDF particles strongly depended on the zeta potential of PVDF particles. Using anionic surfactants, especially C12H25SO4Na (SDS), the zeta potential of PVDF particles was −30.6 mV. The densification and uniformity of the composite layers with a higher amount of PVDF particles were achieved, which resulted in the superior resistance to fluoride ion corrosion. After heating at 180 °C, the PVDF particles were melted, spread, and filled into the pores of the composite layers, which led to the further enhanced corrosion resistance. It was demonstrated that the zeta potential of PVDF particles affected the dispersion, stability, and codeposition with electroless nickel, which resulted in the uniform and dense composite layers and enhanced the corrosion resistance of the fluoride ion.

The effect of dip-coating parameters on the thickness and uniformity of BCZYZ electrolyte layer on porous NiO-BCZYZ tubular supports

The effect of dip-coating parameters on the coating thickness and uniformity have been investigated for BaCe0.7Zr0.1Y0.16Zn0.04O3-δ (BCZYZ) electrolyte on porous NiO-BCZYZ tubular supports. The calculated thicknesses of electrolyte using both pre-fired and full fired tubes' dimensions and both wet and dry weight gains have been compared to the measured ones using Scanning Electron Microscopy (SEM) analysis after full firing. The calculated thicknesses using pre-fired tubes’ dimensions using both wet and dry weight gains are found in a good agreement with the measured thicknesses. The minimum coating thickness of 20.49 ± 3.36 μ with 16% standard deviation (StDev) is achieved using 1.91 mm s−1 (20 step.s-1) withdrawal speed and 30 s dwell time. The most uniform coating layer is obtained using that withdrawal speed and 60 s dwell time, leading 23.14 ± 1.69 μ coating thickness and the minimum StDev% of 7%. Using the polynomial fit between StDev% and dwell time, the minimum StDev% can be achieved at that withdrawal speed has been determined as 80 s. The coating parameters have been optimized as 1.91 mm s−1 withdrawal speed and 80 s dwell time for BCZYZ electrolyte on porous Ni/NiO-BCZY tubular supports.

Slot-die-coating operability windows for polymer electrolyte membrane fuel cell cathode catalyst layers

Roll-to-roll (R2R) slot-die coating of polymer electrolyte membrane fuel cell (PEMFC) catalyst layers represents a scalable deposition method for producing 10–20 m2·min−1 of catalyst-coated gas diffusion layers (GDLs). This high-throughput production technique will help lower the cost of PEMFC catalyst layers. The uniformity of the wet layer applied by slot die deposition is affected by process parameters such as substrate speed, vacuum pressure applied at the upstream meniscus, gap between the slot die lips and substrate, ink rheology, and other ink and substrate properties. The set of conditions for producing a defect-free coating with a dilute ink typically requires little to no upstream vacuum pressure, so suitable operating conditions can be found easily through trial and error and operator intuition. However, the higher viscosity of more concentrated inks dramatically shifts the range of settings that result in a homogeneous coating to higher vacuum levels, which are harder to find through hit or miss. A predictive model showing the range of operable conditions decreases material wastage inherent in experimentally searching for suitable parameters. In this study, the defect-free coating parameter window is explored experimentally and theoretically for two concentrations of PEFC cathode inks. Both a full capillary hydrodynamic model and a computationally cheaper viscocapillary model successfully predict the experimentally determined coating window within the experimental and model uncertainty limits for inks with 5.3 wt% and 12.0 wt% solids ink while maintaining the 0.1 mgPt·cm−2Pt areal loading target. This paper demonstrates a viable pathway for meeting the $30/kWnet ultimate cost target of the United States Department of Energy (U.S. DOE) Hydrogen Fuel Cells Technologies Office (HFTO). The concentrated ink lowers the thermal energy and capital expenditure (CapEx) budget of the coating process by decreasing the amount of time, energy, and floorspace required for drying the coating.