Tungsten Based Spectrally Selective Absorbers with Anisotropic Rough Surface Texture

Spectrally selective absorbers have received considerable interest due to their applications in thermophotovoltaic devices and as solar absorbers. Due to extreme operating conditions in these applications, such as high temperatures, thermo-mechanically stable and broadband spectrally selective absorbers are of interest. This paper demonstrates anisotropic random rough surfaces that provide broadband spectrally selective absorption for the thermo-mechanically stable Tungsten surfaces. Anisotropic random rough surface has different correlation lengths in the x- and y-directions, which means their topography parameters have directional dependence. In particular, we demonstrate that spectral absorptance of Tungsten random rough surfaces at visible (VIS) and near-infrared (NIR) spectral regions are sensitive to correlation length and RMS height variations. Our results indicate that by optimizing random rough surface parameters, absorption values exceeding 95% can be obtained. Moreover, our results indicate that anisotropic random rough surfaces broaden the bandwidth of the high absorption region. It is shown that in VIS and NIR regions, the absorption enhancements of up to 47% and 52% are achieved for the isotropic and anisotropic rough surfaces, respectively.

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Stress, Strain, and Energy at Fracture of Degraded Surfaces: Study of Replicates of Rough Surfaces

Volume 6: Beyond Design Basis Events; Student Paper Competition ◽

10.1115/icone21-16907 ◽

2013 ◽

Author(s):

Hector E. Medina ◽

Brian Hinderliter

Keyword(s):

Early Stage ◽

Rough Surfaces ◽

Local Maximum ◽

Stress Strain ◽

Element Analysis ◽

Correlation Lengths ◽

Random Roughness ◽

Random Rough Surfaces ◽

Load Carrying ◽

Service Conditions

Due to the aging of structures, the issues of plant life management and license extension are receiving increasing emphasis in many countries. Understanding failure of structures due to random roughness on surfaces at early stages of degradation is therefore crucial. It has been shown that even slightly sinusoidal roughness can increase stress concentration by a factor of 2 or 3, which can be critical for a brittle component due to the significant reduction of its load-carrying capacity, even with slight roughness. A more in-depth fracture analysis of surfaces possessing random roughness is needed in order to more profoundly understand, and hence develop models that will predict more accurately, failure of structural materials exposed to degrading, in-service conditions. Using a technique previously developed and successfully applied, replicates of random rough surfaces, imprinted with various levels of degradation, and at three distinct auto correlation lengths, were realized and mechanical testing was performed on them. The stress, strain and energy at fracture are reported. Finite element analysis was carried out to elucidate experimental results. Besides the expected reduction of energy at fracture with degradation, a relaxation region was observed where the energy slightly increases. This phenomenon implies that even after degradation has progressed there is a local maximum of energy at fracture due to the competing effect of tendons and growth of pits. The results find applications on the early stage of maintenance of surfaces of structures in service.

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Effect of Surface Roughness on Fouling of Calcium Carbonate: An Experimental Investigation

Volume 7: Fluid Flow, Heat Transfer and Thermal Systems, Parts A and B ◽

10.1115/imece2010-40623 ◽

2010 ◽

Author(s):

M. Izadi ◽

D. K. Aidun ◽

P. Marzocca ◽

H. Lee

Keyword(s):

Surface Roughness ◽

Calcium Carbonate ◽

Rough Surface ◽

Smooth Surface ◽

Rough Surfaces ◽

Operating Conditions ◽

Tubular Heat Exchanger ◽

Analytical Microscopy ◽

Deposit Layer ◽

Effect Of Surface

The effect of surface roughness on the fouling behavior of calcium carbonate is experimentally investigated. The real operating conditions of a tubular heat exchanger are simulated by performing prolonged experiments with duration of 3 to 7 days. The solution used is a mixture of sodium bicarbonate and calcium chloride in de-ionized water with the concentration of 0.4 g/l of each. An on-line fouling evaluation system was developed such that the fouling resistance for a selected solution could be measured in real time. The experiments are repeated with the same procedure for 90/10 Cu/Ni tubes with different internal surface roughness. After the experiment the surface is analyzed by analytical microscopy to investigate the morphology of the deposit layer. Comparison of the experimental results of smooth and rough surfaces shows that a combination of aragonite and calcite polymorphs are formed on rough surface while only dendritic porous aragonite crystals are formed on smooth surface. Accordingly, the deposit layer formed on rough surface is denser and has a higher thermal resistance comparing to that formed on smooth surface. The fouling factor-time curves of smooth and rough surfaces obtained by the current experimental study agree with the results found by the analytical microscopy of the surface and show higher fouling resistances for rough surface. Experimental data is significantly important for the design, and formulating operating, and cleaning schedules of the equipment.

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Surface Roughness Characterization of al Films by Spectroscopic Ellipsometry

MRS Proceedings ◽

10.1557/proc-54-669 ◽

1985 ◽

Vol 54 ◽

Cited By ~ 1

Author(s):

J. R. Blanco ◽

K. Vedam ◽

P. J. McMarr ◽

J. M. Bennett

Keyword(s):

Surface Roughness ◽

Rough Surface ◽

Spectroscopic Ellipsometry ◽

Rough Surfaces ◽

Scalar Theory ◽

Nondestructive Technique ◽

Aluminum Films ◽

Random Rough Surfaces ◽

Scalar Theory Of Diffraction

ABSTRACTWell characterized rough surfaces of aluminum films have been studied by the nondestructive technique of Spectroscopie Ellipsometry (SE). The roughness of the aluminum specimens had been characterized earlier by Total Integrated Scattering and Stylus Profilometry techniques to obtain numerical estimates of ras roughness and autocovariance lengths. The present SE measurements on these specimens were carried out at a number of angles of incidence in the range 30–80° and at a number of discrete wavelengths in the spectral range 300–650nm. The SE results were then analyzed by the scalar theory of diffraction from random rough surfaces by treating the surface as a simple random rough surface. The results of such analyses of the SE measurements are compared with the results of the earlier characterization techniques.

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Analysis of Laminar Flow Over a Non-Conventional Random Rough Surface Based on Lattice Boltzmann Method

Journal of Tribology ◽

10.1115/1.4005517 ◽

2012 ◽

Vol 134 (1) ◽

Cited By ~ 1

Author(s):

Ping Zhou ◽

Dongming Guo ◽

Renke Kang ◽

Zhuji Jin

Keyword(s):

Laminar Flow ◽

Rough Surface ◽

Flow Model ◽

Rough Surfaces ◽

Average Flow ◽

Random Rough Surface ◽

Surface Slopes ◽

Boltzmann Method ◽

Polishing Pads ◽

Average Flow Model

The average flow model offers a great convenience for the analysis of laminar flow over rough surfaces and is widely used in simulation studies. Flow factors used in the average flow model are generally expressed as a function of statistical properties of a single level rough surface with gentle slopes. However, for a nonconventional surface with multilevel roughness or high local surface slopes, such as polishing pads used in chemical mechanical planarization (CMP), it has not been verified whether this model is still applicable as expected. Generally, computations based on the Reynolds equation are carried out repeatedly for the same problem regarding different but statistically identical rough surfaces, and the average flow model is applicable if stable flow factors (statistical average) are obtained. However, due to the complex topography and high local surface slopes of polishing pads used in CMP, the Reynolds equation is no longer valid, and thus a new method needs to be developed to estimate the applicability of the average flow model and to calculate the flow factors accurately. In this study, aiming to research the flow over a nonconventional random rough surface such as the slurry flow in CMP, a new strategy is developed to research the incompressible laminar flow through a narrow gap between various nonconventional rough surfaces by combining the lattice Boltzmann method (LBM) and numerical simulation of random rough surface. With this strategy, it is convenient to simulate the flow field in a narrow gap between various random rough surfaces and obtain the flow factors. In addition, an analytical formula for calculating the flow factors of a dual-level rough surface, i.e., surface composed of two different types of microstructure, is introduced and verified through a comparison with the results obtained using the presented numerical simulation strategy.

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Rough-surface shadowing of self-affine random rough surfaces

Journal of Quantitative Spectroscopy and Radiative Transfer ◽

10.1016/j.jqsrt.2007.01.025 ◽

2007 ◽

Vol 106 (1-3) ◽

pp. 398-416 ◽

Cited By ~ 24

Author(s):

Hannu Parviainen ◽

Karri Muinonen

Keyword(s):

Rough Surface ◽

Rough Surfaces ◽

Random Rough Surfaces

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Stress, Strain, and Energy at Fracture of Degraded Surfaces: Study of Replicates of Rough Surfaces

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4025660 ◽

2013 ◽

Vol 136 (3) ◽

Cited By ~ 2

Author(s):

Hector E. Medina ◽

Brian Hinderliter

Keyword(s):

Early Stage ◽

Rough Surfaces ◽

Local Maximum ◽

Stress Strain ◽

Element Analysis ◽

Correlation Lengths ◽

Random Roughness ◽

Random Rough Surfaces ◽

Load Carrying ◽

Service Conditions

Due to the aging of structures, the issues of plant life management and license extension are receiving increasing emphasis in many countries. Understanding failure of structures due to random roughness on surfaces at early stages of degradation is therefore crucial. It has been shown that even slightly sinusoidal roughness can increase stress concentration by a factor of two or three, which can be critical for a brittle component due to the significant reduction of its load-carrying capacity, even with slight roughness. A more in-depth fracture analysis of surfaces possessing random roughness is needed in order to more profoundly understand, and, hence, develop models that will predict more accurately, failure of structural materials exposed to degrading, in-service conditions. Using a technique previously developed and successfully applied, replicates of random rough surfaces, imprinted with various levels of degradation, and at three distinct auto correlation lengths, were realized and mechanical testing was performed on them. The stress, strain, and energy at fracture are reported. Finite element analysis was carried out to elucidate experimental results. Besides the expected reduction of energy at fracture with degradation, a relaxation region was observed where the energy slightly increases. This phenomenon implies that even after degradation has progressed there is a local maximum of energy at fracture due to the competing effect of tendons and growth of pits. The results find applications on the early stage of maintenance of surfaces of structures in service.

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A Ray Tracing Approach to the Scattering of Electromagnetic Waves from Random Rough Surfaces at Terahertz Frequencies

2020 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) ◽

10.1109/irmmw-thz46771.2020.9370474 ◽

2020 ◽

Author(s):

Fawad Sheikh ◽

Yida Zhang ◽

Yamen Zanteh ◽

I. Mabrouk ◽

M. Hasan ◽

...

Keyword(s):

Ray Tracing ◽

Electromagnetic Waves ◽

Rough Surfaces ◽

Random Rough Surfaces ◽

Terahertz Frequencies

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Enhancing sub-bandgap external quantum efficiency by photomultiplication for narrowband organic near-infrared photodetectors

Nature Communications ◽

10.1038/s41467-021-24500-2 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jonas Kublitski ◽

Axel Fischer ◽

Shen Xing ◽

Lukasz Baisinger ◽

Eva Bittrich ◽

...

Keyword(s):

Charge Transfer ◽

Quantum Efficiency ◽

External Quantum Efficiency ◽

Near Infrared ◽

Optical Cavity ◽

Hole Injection ◽

Visible Range ◽

Absorption Region ◽

Electromagnetic Signals ◽

Organic Photodetectors

AbstractDetection of electromagnetic signals for applications such as health, product quality monitoring or astronomy requires highly responsive and wavelength selective devices. Photomultiplication-type organic photodetectors have been shown to achieve high quantum efficiencies mainly in the visible range. Much less research has been focused on realizing near-infrared narrowband devices. Here, we demonstrate fully vacuum-processed narrow- and broadband photomultiplication-type organic photodetectors. Devices are based on enhanced hole injection leading to a maximum external quantum efficiency of almost 2000% at −10 V for the broadband device. The photomultiplicative effect is also observed in the charge-transfer state absorption region. By making use of an optical cavity device architecture, we enhance the charge-transfer response and demonstrate a wavelength tunable narrowband photomultiplication-type organic photodetector with external quantum efficiencies superior to those of pin-devices. The presented concept can further improve the performance of photodetectors based on the absorption of charge-transfer states, which were so far limited by the low external quantum efficiency provided by these devices.

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