surface texturing by rapid scanning of pulsed laser beam
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This document discusses using rapid laser scanning to texture surfaces for applications such as solar cells and military equipment. It demonstrates that laser scanning allows for high flexibility and precision compared to other texturing methods. The document investigates different laser parameters and their effects on texturing mechanisms and performance. Optimal parameters were identified that enhanced light trapping for solar cells through crystalline structures and enabled stealth and thermal functions for military applications.
surface texturing by rapid scanning of pulsed laser beam
- 1. Surface Texturing by rapid scanning of pulsed laser beam Di Liu, Matthew Quigley Advisor: Dr. David Hwang Annual Student Research Poster Symposium, May 10, 2013 Department of Mechanical Engineering College of Engineering and Applied Sciences (CEAS) Surface texturing in micro/nanoscale plays an important role in many application fields including enhanced light trapping in solar cell, surface anti-icing by super hydrophobicity in wind turbine and airplane wings, and enhanced convective and radiative heat transfer from surface. In this study, we demonstrate high flexibility and control precision offered by the pulsed laser scanning method. Compared with conventional laser-based approach, nanosecond laser scanning method we tested corresponds to a highly cost-effective and uniform means for the texturing of arbitrary sample area and shape. Relevant texturing mechanisms are explained based on advanced characterization by scanning electron microscope and Raman spectroscopy. Acknowledgement Summary • Rapid laser scanning enabled superior textured surfaces for solar & military applications. • Detailed texturing mechanisms were investigated in relation to target device performance. • For solar cell, light trapping was greatly enhanced with optimal crystalline structures. • For military applications, desired stealth and thermo-fluidic functions were enabled. *. The research is supported by Yuco optics corp. (Bohemia, NY) through SPIR program, and Advanced Energy Research and Technology Center (Stony Brook, NY). *. SEM characterization was performed at the Center for Functional Nanomaterials, Brookhaven National Laboratory supported by US Department of Energy. New Approach : Rapid scanning of pulsed laser beam Conventional surface texturing techniques By D. Neuhaus et al. (2007)By D. Yong Wu et al. (2007) By L. Dobrzaǹski et al. (2008) By SiOnyx Ti c-Si c-Si c-Si Chemical Wet Etching • Limited flexibility as crystalline plane dictates Laser Ablative Texturing • Loose structural: issues on carrier transport and limit in current extraction Ultrafast Laser Texturing • High laser cost, lack of arbitrary scale uniformity Mechanical Roughing • Quality limited due to friction with abrasive particles Experimental setup Effect of laser parameters : 3 representative regimes Ablation dominant • Excellent light trapping • Structural issues Melting dominant • Excellent light trapping • Favorable structures Mild melting • Insufficient light trapping • Low textures Spectral reflectance data show Performance of Black Si depending on laser parameters Silicon surface texturing for enhanced light trapping Si surface morphology results comparison *Different optical properties are achieved by different surface texture structures *Brown Silicon is formed and dominated by ablative phase change *Shorter wavelength gives smaller scale of spikes and shallower affected depth Brown Si Black Si λ=355nm Super black metal surface texturing by laser scanning Black Cu SEM image http://en.wikipedia.org/wiki/F-117_Nighthawk http://thegundeck.blogspot.com/2011/01/how- much-for-pentagon.html Black Silicon for advanced Si solar cells • Laser-based texturing • High flexibility and control precision Light trapping enhancement Stealth function : minimal reflection of UV, visible and IR illumination Enforcing Pool boiling for improved heat transfer by phase change http://www.81.net/hangkongdongtai/04262301 92013_3.html http://isnps.unm.edu/research/facilities/ IR image Cu Blackbody-like Thermal Emission Key Advantages • Size independent uniformity • Precision texture control： active control of unit features dictated by local melting and thermo-capillary effect • Simultaneous annealing for improved carrier diffusion • Cost-effective laser solution Photograph image SEM image • Ablation dominant regime is superior in light trapping but with low crystalline quality • Melting dominant regime show good light trapping and excellent crystalline quality Improved heat transfer and control of phase change (cooling, anti-freezing) Transient behavior during laser process Necessary ablation for spikes formation Secondary annealing for efficient current extraction On Laser focus Off Laser focus Laser focal position effects on secondary annealing Extended laser beam for annealing Cross section Raman spectroscopy Anti icing texturing Non-textured Textured http://www.gao.pitt.edu/antiicing.html 522cm-1 (Single crystal Si peak) Black Si λ=532nm Raman shift /cm-1 Efficient Current Extraction *Good Crystallinity *Minimal stress Focused on military and defense applications Black Cu Colorized Steel Reflect specific wavelength