Substrate Temperature Profile Research Articles

Identifying Variables Influencing Traditional Food Solid-State Fermentation by Statistical Modeling.

Solid-state fermentation is widely used in traditional food production, but most of the complex processes involved were designed and are carried out without a scientific basis. Often, mathematical models can be established to describe mass and heat transfer with the assistance of chemical engineering tools. However, due to the complex nature of solid-state fermentation, mathematical models alone cannot explain the many dynamic changes that occur during these processes. For example, it is hard to identify the most important variables influencing product yield and quality fluctuations. Here, using solid-state fermentation of Chinese liquor as a case study, we established statistical models to correlate the final liquor yield with available industrial data, including the starting content of starch, water and acid; starting temperature; and substrate temperature profiles throughout the process. Models based on starting concentrations and temperature profiles gave unsatisfactory yield predictions. Although the most obvious factor is the starting month, ambient temperature is unlikely to be the direct driver of differences. A lactic-acid-inhibition model indicates that lactic acid from lactic acid bacteria is likely the reason for the reduction in yield between April and December. Further integrated study strategies are necessary to confirm the most crucial variables from both microbiological and engineering perspectives. Our findings can facilitate better understanding and improvement of complex solid-state fermentations.

Bioconversion of fresh chicken excreta by housefly larvae (Musca domestica L.) in relation to excreta sterilisation and carbohydrate addition

Housefly larvae can be reared on manure and used as animal feed. Larvae can utilise proteins and easily digestible carbohydrates and have a largely unknown relation with microorganisms. The hypothesis addressed in this study was that larvae compete with microorganisms for easily digestible carbohydrates such as starch. This was tested by adding starch or (non-digestible) fructo-oligosaccharides (FOS) to unsterilised or heat-sterilised fresh chicken excreta. Experimental substrates were unsterilised excreta (E), sterilised excreta (sE) with either starch (E + star, sE + star) or FOS (E + FOS, sE + FOS). The highest wet yield (9.7 g) and heaviest larvae (13.2 mg) were on sE + star, followed by E (7.2 g and 8.1 mg). Both E + FOS and sE + FOS had minimal yields and larval weights (0.3 and 0.2 g, 2.9 and 1.7 mg) with E + star intermediate (3.3 g and 7.5 mg). Survival differed between diets, sE and E averaged 70%, sE + star 57%, E + star 33% with 9% for E + FOS and sE + FOS. DM bioconversion decreased from E (3.5%), sE + star (3.1%), sE (2.6%), E + star (1%) to E + FOS and sE + FOS (0.1%). Nitrogen bioconversion was highest on sE + star (9.9%) and E (9.3%), lower on sE (6.6%), E + star (4%) and the lowest on E + FOS and sE + FOS (0.5%). Different substrate temperature profiles during the larval growth period and different larval size distributions were found for the different substrates. The results support the hypothesis that larvae compete with microorganisms for an easily digestible carbohydrate (starch).

Enhanced PVD process control by online substrate temperature measurement

In physical vapor deposition (PVD) processes pressure and temperature are of outstanding importance for process control and coating performance. The pressure measurement and its integration into the process control are state of the art in industrial coating units. In contrast, the precise determination of the substrate temperature Tsub presents an unequally greater challenge. In PVD processes the temperature control has a great importance in two respects. On the one hand, the morphology of the coating as well as the adhesion between the coating and substrate directly depend on Tsub. On the other hand, the process temperature is limited by the maximum permissible temperature Tmax as for example of heat-treated steel. Exceeding can easily lead to a critical loss of hardness and size accuracy of the substrate and production reject. The online measurement of Tsub using currently applicable systems such as drag pointer or pyrometer is either extremely complicated or simply not possible. This is particularly the case for large-volume industrial coating units with a rotating substrate table. Therefore, in coating processes, the influence of the different process parameters on Tsub is usually not quantified. Hence, Tsub is often several tens centigrades below Tmax. Within the scope of this paper, a temperature measuring system developed at the Surface Engineering Institute (IOT) of the RWTH Aachen University is used in an industrial coating unit with rotating substrate table. With this, the online temperature measurement of rotating substrates is possible throughout the entire coating process, from the heating to the etching over the coating to the cooling process phase. In the heating, etching and coating process phases, the influence of the heating power on Tsub was analyzed and described by characteristic trend lines. The results were used to improve the substrate temperature profile of an industrial-like coating process with regard to Tmax. Here the temperature difference between Tmax of the heat-treated steel and the realized Tsub was reduced to a feasible minimum over the entire process time. Investigations on the compound properties show an improved adhesion between coating and substrate.

Worst-case and Distributional Robustness Analysis of a Thin Film Deposition Process

This paper presents a comparison between worst-case and distributional uncertainty analysis in a thin film deposition process. The key idea is to evaluate the effect of model parameter uncertainties on thin film properties employing power series expansion (PSE). The worst-case deviation in the film properties is obtained under bounded parameter uncertainties while the probabilistic bounds are estimated under distributional uncertainties. To describe the growth process on the surface of a substrate, a multiscale approach that integrates kinetic Monte Carlo (KMC) simulations with continuum modelling is employed. The uncertainty analysis in this work is applied to estimate the optimal substrate temperature profile for robust optimization of the thin film end-point properties.

Uncertainty analysis and robust optimization of multiscale process systems with application to epitaxial thin film growth

Multiscale modeling of materials growth involves inherently coupled processes that span over a wide range of time and length scales. As a common practice, a multiscale model is adopted to simulate the thin film deposition process that augments Partial Differential Equations (PDEs), describing the macro-scale phenomena, with a high-order lattice-based kinetic Monte Carlo (KMC) simulator, which aims to capture thin film microstructure. Although such a model is a fair representation of the system, the evolution of thin film encompasses processes that are subject to model parameter uncertainty that can significantly affect the control and optimization objectives of this process, e.g. film׳s roughness and thickness. Thus, to provide a robust and more realistic strategy, it is crucial to perform an uncertainty analysis for this process. This work explores a systematic framework to analyze model parameter uncertainty for robust control and optimization of multiscale models. Such an analysis is extremely challenging due to (i) the lack of a closed formulation between the process optimization objective (i.e. film thickness) and the model parameters and (ii) the computational costs incurred to model the fine-scale events, typically performed using KMC simulation. To tackle these challenges, Power Series Expansion (PSE) is employed to analyze model uncertainty propagation. The PSE-based method for uncertainty analysis is more computationally efficient in comparison to the traditional Monte Carlo approach. The distributional uncertainty in rates of microscopic events is characterized by series expansions of the uncertain parameters. The fitted distributions to the rate of events at a given confidence level are employed to estimate upper and lower bounds on the desired outputs (e.g. film roughness). The computational efficiency of the approach is achieved by employing multiple reduced-order lattices in the KMC simulator. The potential application of the proposed method is illustrated through an optimization problem that aims to specify the robust optimal substrate temperature profile that maximizes the endpoint thin film thickness in the presence of uncertainty.

Thermal sensitivity analysis of on‐chip interconnects

A new method for time-domain sensitivity analysis of on-chip coupled interconnects with non-uniform substrate temperature profiles is presented. The parametric macromodelling is performed via multivariate rational approximation using magnitude vector fitting algorithms. The waveform relaxation algorithm with transverse partitioning is employed for efficient sensitivity analysis of coupled interconnects. With these techniques, the thermal sensitivity of on-chip global interconnects arising from typical substrate thermal profiles are investigated.

Enhancement of surface activity in CO oxidation on Pt(110) through spatiotemporal laser actuation

We explore the effect of spatiotemporally varying substrate temperature profiles on the dynamics and the resulting reaction rate enhancement of the catalytic oxidation of CO on Pt(110). The catalytic surface is "addressed" by a focused laser beam whose motion is computer controlled. The averaged reaction rate is observed to undergo a characteristic maximum as a function of the speed of this moving laser spot. Experiments as well as modeling are used to explore and rationalize the existence of such an optimal laser speed.

Transient modeling of micro-grooved heat pipe

One-dimensional transient model for fluid flow and heat transfer is presented for a micro-grooved heat pipe of any polygonal shape utilizing a macroscopic approach. The coupled non-linear governing equations for the fluid flow, heat and mass transfer are developed based on first principles and are solved simultaneously. The transient behavior for various parameters, e.g. substrate temperature, radius of curvature, liquid velocity, etc. are studied. The effects of the groove dimensions, heat input and Q-profiles on the studied parameters have been evaluated. The steady state profiles for substrate temperature, radius of curvature, liquid velocity etc. have also been generated. The model predicted steady state substrate temperature profile is successfully compared with the experimental results from the previous study. The general nature of the model and the associated parametric study ensure the wide applicability of the model.

LPCVD silicon nitride uniformity improvement using adaptive real-time temperature control

An effective approach to improve silicon nitride thickness uniformity has been demonstrated on a batch LPCVD furnace platform. Implementation of adaptive real-time temperature control provides accurate, real-time estimation of substrate temperature profiles that enables model-based optimization of process temperature. Optimization of a 200-nm silicon nitride deposition yielded long-term, overall nitride thickness uniformity of 0.79% 1/spl sigma/ over a seven-week period, compared to 1.24% for an equivalent PID-tuned process. Three sequential silicon nitride deposition iterations were implemented in the process recipe to enable increased temperature ramp rates for more efficient optimization of within-wafer uniformity. The optimized process requalified quickly after major and minor equipment maintenance, and is suitable for use in a manufacturing environment. The ART-optimized temperature ramp intervals used in this study are comparable to temperature deltas often used to offset dichlorosilane depletion effects encountered in some large-batch vertical furnace depositions. SIMS depth profiling of ART-optimized silicon nitride does reveal small oxygen and chlorine peaks, indicating slight interface formation between deposition steps.

Mathematical model for the nonsteady decomposition of intumescent coatings

AbstractA 1‐D transient mathematical model was studied for a composite system consisting of a substrate (steel) and an intumescent coating exposed to radiative heating. By applying a simple heat conduction equation for the first material, a general model proposes the coating consisting of three components, which degrade according to independent finite‐rate reactions. Mass and heat transfer take place across a variable volume medium, including a simplified mechanism for bubble dynamics and material swelling. A parametric analysis clarifies the role of several parameters on the fire retardancy performance of the coating. Good agreement is obtained between predictions and measurements of the substrate temperature profiles.

High dose rate effects in silicon by plasma source ion implantation

An investigation of high dose rate effects in silicon subsurface morphology has been performed. The unique capability of plasma source ion implantation to operate in the high current/low energy regime, where the near-surface structure can be effectively controlled, has been studied. At an ion energy of ∼40 keV and an estimated dose of 1×1015 cm−2 Ar ions were implanted at various instantaneous dose rates (0.75–8.3 mA/cm2) and two different pulse widths (25–50 μs) into 2 in. diam silicon wafers at a constant repetition rate of 10 Hz. The irradiation damage to the wafers’ structures was characterized by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). A visual observation indicated amorphization of the silicon at 0.75 mA/cm2, but not at 8.3 mA/cm2. The transition from the crystalline-to-amorphous phase was confirmed by TEM electron diffraction studies. RBS data, however, indicated there was a large discrepancy in the total dose retained between the high dose rate (8.3 mA/cm2) and the low dose rate (0.75 mA/cm2). Two simulation methods for the substrate temperature profile have been compared to predict the profile. A comparison of the fraction of irradiation damage from the RBS data indicated that the substrate heating effects are more dominant then the dose rate effects. Improved methods of cooling the wafer are presently being investigated.

Effects of microstructures on microwave properties in Y-Ba-Cu-O microstrip-resonators

We examined the microwave properties of YBa/sub 2/Cu/sub 3/O/sub x/ films with different microstructures at 5.7 GHz using a microstrip resonator technique. The films were prepared with several types of substrate temperature profiles. Films with small grains (/spl sim/100 nm) and larger critical current density show fairly small rf magnetic field dependence of surface resistance and resonance frequency up to about 50 Oe. On the other hand, films with large grains (/spl sim/200 nm) and smaller critical current density show significant changes in these properties. These results suggest that the coupling strength at the grain boundaries mainly dominates the power handling capability, according to a qualitative explanation based on the coupled-grain model. >

Wavelength shift in vertical cavity laser arrayson a patternedsubstrate

The authors demonstrate a spatially chirped emission wavelength in vertical cavity surface emitting laser (VCSEL) arrays grown by molecular beam epitaxy. The wavelength shift is due to a lateral thickness variation in the Al0.2Ga0.8As cavity, which is induced by a substrate temperature profile during growth. A 20 nm shift in lasing wavelength is obtained in a VCSEL array.

The effect of substrate surface temperature on the morphology and quality of diamond films produced by the oxyacetylene combustion method

Diamond films were synthesized using an oxyacetylene flame on a molybdenum substrate mounted on a water-cooled copper block. The morphology and quality of the synthetic diamond films produced depend on several factors including the substrate temperature, gas flow rates and their ratio, and substrate position. The substrate temperature profile was shown to be influenced by the coolant flow rate, nozzle size, substrate position on the heat sink, substrate position in the combustion flame, and the total flow rate of mixed gas (acetylene and oxygen). In this paper, the effects of substrate temperature and nozzle size on the morphology and quality of diamond films are discussed. Fine-gage thermocouples were used to measure the temperature distribution in the substrate during the process. Scanning electron microscopy of the produced diamond films is used to show the variation of crystal morphology.

ZnO/CdS/CuInSe2 thin-film solar cells with improved performance

An important milestone in the development of photovoltaic thin-film solar cells is the achievement of 15% conversion efficiency. This letter describes the highest efficiency single junction thin-film cell reported to date. An active area efficiency of 14.8% is obtained with the cell structure n-ZnO/n-CdS/p-CuInSe2 deposited on a soda-lime glass substrate. The current achievements are due to improved properties of the CuInSe2 layer and the heterojunctions compared to previously reported results. The rate and substrate temperature profiles used during the coevaporation process yield a relatively large-grained material with very strong 〈112〉 orientation and low porosity. This results in reduced recombination rates, hence higher open circuit voltage and fill factor.

Parametric Effects on the Substrate Temperature Profile in Oxy-Acetylene Flames

In the oxy-acetylene combustion method, the quality and morphology of the diamond film depends on a variety of factors, including the substrate surface temperature, gas flow rates and their ratio, and substrate position. Due to the nature of the oxy-acetylene flame, surface temperature of the substrate varies in the radial direction. The substrate temperature profile, in turn, is influenced by the coolant flow rate, nozzle size, substrate position on the heat sink, substrate position in the combustion flame, and the total flow rate of mixed gas (acetylene and oxygen). In this article, temperature measurements using fine-gauge thermocouples were made to characterize the influence of these parameters on the substrate temperature profile.

InP substrate temperature measurements in a horizontal, low-pressure metalorganic chemical vapor deposition reactor by infrared laser interferometric thermometry

Infrared laser interferometric thermometry was used to measure InP substrate temperatures in a horizontal, low pressure metalorganic chemical vapor deposition (MOCVD) reactor. These measurements were made by using a 1.53 μm distributed feedback laser, demonstrating the use of semiconductor lasers to diagnose an epitaxial crystal growth process. The laser beam was reflected off of 2 inch diameter (100) n-type InP substrates in a commercial low-pressure MOCVD reactor. Substrate temperature profiles were taken as a function of reactor pressure from 20–1000 mbar and as a function of substrate position on the susceptor. For a constant susceptor set-point temperature of 640°C, temperatures increase monotonically from 600 to 615°C at 20 mbar along the substrate in the gas flow direction, increasing to 621 to 655°C at 1000 mbar for a substrate positioned in the downstream location of a two-well susceptor used for normal epitaxial growth runs. The variation in temperature decreases when the substrate is placed in a center well susceptor. The data shows that improvements in temperature uniformity, and hence compositional uniformity can be achieved by judicious choice of substrate position and reactor pressure. In particular, uniform temperature profiles resulted in improved compositional uniformity obtained for 1.15 μm InGaAsP layers grown on a 2 inch diameter substrate placed in the center well susceptor.

Radiative heat transfer in hot-filament chemical vapor deposition diamond reactors

Hot-filament chemical vapor deposition is a common method employed for diamond deposition. Due to the filament-substrate proximity, large temperature variations across the substrate is often possible. Variations in substrate temperature need to be minimized in order to deposit polycrystalline diamond films of uniform thickness over large areas. Thus heat transfer calculations which consider radiation from the filament to the substrate, radiation from the substrate to the reactor walls, and finally conduction in the silicon wafer have been developed to predict substrate temperature profiles as a function of the filament shape and geometry. The calculated values are found to be in reasonable agreement with experimentally measured substrate temperatures. It was found that hydrogen atom recombination makes a significant contribution to the absolute substrate temperature, but that the normalized temperature profiles are determined primarily by the radiation flux distribution. The effects of the other deposition parameters are also discussed. Comparison with experimental results show an apparent correlation between growth rate profiles and radiation flux profiles from the filament as predicted by the calculations.

The role of heat transfer during reactive-ion etching of polymer films

A study of the kinetics of O2 and Ar reactive-ion etching (RIE) of organic polymer films and an analysis of substrate heat transfer was carried out. Radiative heat transfer played a significant role in determining the substrate temperature profile during RIE. At the relatively low pressure of 5 mTorr, where anisotropic etch profiles are typically achieved, radiative heat transfer accounted for nearly 85% of the total energy (heat) flux away from the substrate. RIE processing time (substrate temperature) drastically affected the RIE rate of chain-scissioning polymers, which included poly(methyl methacrylate) and poly(α-methylstyrene), while processing time had absolutely no effect on etch rates of cross-linking polymers. To confirm the role of radiative heat transfer during RIE, the underside of a silicon wafer was painted black, which increased the total radiative surface emittance and lowered the steady-state substrate temperature for a given set of RIE conditions. Ultimate etch rates of poly(methyl methacrylate) were measurably lower for films on the black-silicon substrates. Thermal bonding alleviated substrate heating and greatly improved etch rate control.

Optical absorption aspects of laser soldering for high density interconnects

In laser soldering, one has direct control over the incident laser pulse energy and duration but only indirect control over the temperature profile of the parts to be soldered. To understand the conversion of incident laser energy into a substrate temperature profile, two processes need to be understood: first, the optical absorption as a function of temperature and, second, the temperature distribution as a function of absorbed energy. The optical absorption aspect is addressed here. A set of total reflectivity measurements for real surfaces of interest is presented along with analytical calculations of the temperature dependence of the optical absorption for both specular and rough surfaces.