Laser Interference Patterning Research Articles

Advanced Laser Techniques for the Development of Nature-Inspired Biomimetic Surfaces Applied in the Medical Field

This review focuses on the innovative use of laser techniques in developing and functionalizing biomimetic surfaces, emphasizing their potential applications in the medical and biological fields. Drawing inspiration from the remarkable properties of various natural systems, such as the water-repellent lotus leaf, the adhesive gecko foot, the strong yet lightweight spider silk, and the unique optical structures of insect wings, we explore the potential for replicating these features through advanced laser surface modifications. Depending on the nature and architecture of the surface, particular techniques have been designed and developed. We present an in-depth analysis of various methodologies, including laser ablation/evaporation techniques, such as Pulsed Laser Deposition and Matrix-Assisted Pulsed Laser Evaporation, and approaches for laser surface structuring, including two-photon lithography, direct laser interference patterning, laser-induced periodic surface structures, direct laser writing, laser-induced forward transfer, and femtosecond laser ablation of metals in organic solvents. Additionally, specific applications are highlighted with the aim of synthesizing this knowledge and outlining future directions for research that further explore the intersection of laser techniques and biomimetic surfaces, paving the way for advancements in biomedical applications.

Fabrication of Multiscale and Periodically Structured Zirconia Surfaces Using Direct Laser Interference Patterning

AbstractThe functionalization of zirconia surfaces by accurate and fast printing of periodical patterns embedding sub‐micrometric features is of great interest to many engineering fields and is yet to be explored. This study aims to assess the influence of the Direct Laser Interference Patterning processing parameters on the morphology and microstructure of zirconia surfaces using a 532 nm 10 ps‐pulsed laser source. Well‐defined linear structures with a period of 3 µm are successfully produced. Depending on the laser parameters, the structures are developed at or below the surface level, with higher depths (≈1 µm) being seen for increasing values of laser fluence and pulse overlap. Line‐like hierarchical structures with smaller interference spatial structures (3 µm period) and higher secondary structures with different periods (18, 15, and 12 µm) and heights (7, 5, and 3 µm, respectively) are also obtained on zirconia surface. Ablated regions presented few traces of molten material, nano‐droplets, and sub‐micrometric (<1 µm) pores, while no (sub) micrometric cracks are detected. A slight amount of tetragonal to monoclinic phase transformation (≈5%) is detected by X‐ray diffractometry. A processability map for ps‐laser processing of zirconia is proposed based on the experimental data.

Microstructure versus topography: the impact of crystallographic substrate modification during ultrashort pulsed direct laser interference patterning on the antibacterial properties of Cu

Introduction: Topographic surface patterning in the micro- and nanometer scale has evolved into a well applied approach in surface functionalization following biomimetic blueprints from nature. Depending on the production process an additional impact of process-related substrate modification has to be considered in functional surface optimization. This is especially true in case of antimicrobial applications of Cu surfaces where a modification of the substrate properties might impact bactericidal efficiency.Methods: In this regard, the effect of ultrashort pulsed direct laser interference patterning on the microstructure of pure Cu and resulting antimicrobial properties was investigated alongside line-like patterning in the scale of single bacterial cells.Results and Discussion: The process-induced microstructure modification was shown to play an important role in corrosion processes on Cu surfaces in saline environment, whereas the superficial microstructure impacts both corrosive interaction and ion emission. Surprisingly, antimicrobial efficiency is not predominantly following deviating trends in Cu ion release rates but rather depends on surface topography and wettability, which was shown to be impacted by the substrate microstructure state, as well. This highlights the need of an in-depth understanding on how different surface properties are simultaneously modulated during laser processing and how their interaction has to be designed to acquire an effective surface optimization e.g., to agitate active antimicrobial surface functionalization.

Improved Tribological Performance of ta-C/MoSx Coatings Deposited on Laser Micro-Structured Steel Substrates in Both Vacuum and Air

Vacuum and air atmospheres impose very different requirements on tribological-loaded contacts, which usually require different surface materials. While hard tetrahedral amorphous carbon (ta-C) coatings provide good tribological properties in air, soft coatings such as molybdenum disulfide (MoS2) work well in a vacuum. Tribological performance in the respective other environment, however, is poor. In this work, the combination of laser microstructured (direct laser interference patterning) steel substrates and the deposition of ta-C and MoSx coatings with vacuum arc evaporation (LaserArc™) was studied, resulting in steel/DLIP, steel/DLIP/ta-C, steel/DLIP/MoSx, steel/DLIP/ta-C/MoSx, and steel/MoSx surface combinations. The tribological properties were studied using a ball-on-disk tribometer with a steel ball counter body in air and in a vacuum (p < 5 × 10−7 mbar). The type of the topmost coating governed their tribological properties in the respective atmosphere, and no general beneficial influence of the microstructure was found. However, steel/DLIP/ta-C/MoSx performed best in both conditions and endured the highest contact pressure, which is attributed to the mechanical support of the ta-C coating and MoSx reservoir in the remaining structure, as evidenced by Raman spectroscopy. The findings suggest that such combination allows for surfaces bearing a high load capacity that can be applied in both a vacuum and in air, for example, in multi-use space applications.

Fabrication of Gradient Periodic Surface Structures on Stainless Steel Using Direct Laser Interference Patterning

In this work, the fabrication of gradient periodic line‐like structures with continuously changing spatial period on stainless steel by means of two‐beam direct laser interference patterning (DLIP) is studied. A 70 ps (picosecond [ps]) pulsed laser operating at 532 nm wavelength and 0.64 J cm−2 laser fluence is used to produce the gradient microstructures. By continuously changing the overlapping angle between the sub‐beams, the spatial period of gradient structures smoothly increases from 2.01 ± 0.09 to 3.99 ± 0.12 μm within a 500 μm long processed area. Different pulse‐to‐pulse overlaps are applied to study the influence of cumulated fluence on the topography of gradient structures. The surface topography is analyzed by optical confocal microscopy and is characterized by the roughness parameters Ra and Rz. Fourier transformations of the confocal images allows the verification of the variations of the spatial periods. In the experiments performed in this work, design rules are provided for fabricating complex microstructures in the future using DLIP‐based technology to achieve advanced surface function like anisotropic wetting or cell growth.

Influence of chemistry and topography on the wettability of copper

To understand the complex interplay of topography and surface chemistry in wetting, fundamental studies investigating both parameters are needed. Due to the sensitivity of wetting to miniscule changes in one of the parameters it is imperative to precisely control the experimental approach. A profound understanding of their influence on wetting facilitates a tailored design of surfaces with unique functionality.We present a multi-step study: The influence of surface chemistry is analyzed by determining the adsorption of volatile carbonous species (A) and by sputter deposition of metallic copper and copper oxides on flat copper substrates (B). A precise surface topography is created by laser processing. Isotropic topography is created by ps laser processing (C), and hierarchical anisotropic line patterns are produced by direct laser interference patterning (DLIP) with different pulse durations (D).Our results reveal that the long-term wetting response of polished copper surfaces stabilizes with time despite ongoing accumulation of hydrocarbons and is dominated by this adsorption layer over the oxide state of the substrate (Cu, CuO, Cu2O). The surfaces’ wetting response can be precisely tuned by tailoring the topography via laser processing. The sub-pattern morphology of primary line-like patterns showed great impact on the static contact angle, wetting anisotropy, and water adhesion. An increased roughness inside the pattern valleys combined with a minor roughness on pattern peaks favors air-inclusions, isotropic hydrophobicity, and low water adhesion. Increasing depth of the primary topography can also induce air-inclusions despite increasing peak roughness while time dependent wetting transitions were observed.

Antibacterial property alterations induced by low zinc content in laser-structured brass

Brass, along with other copper-based alloys, exhibits advantageous antibacterial properties that can be further enhanced by altering the surface topography to increase bacterial adhesion. This enhancement is achievable through a higher contact area created by precise periodic structures, each approximately the size of a single bacterial cell. One method for generating these structures is ultrashort pulsed direct laser interference patterning (USP-DLIP). However, this process may induce chemical alterations in addition to topographical changes, depending on the substrate’s composition. To mitigate unfavorable chemical alterations, brass with a 15% zinc content was selected for this study. The antibacterial effectiveness of the modified surfaces was tested against Escherichia coli, providing initial insights into the interaction between bacteria and the substrate. The results indicate that modified brass with a 15% zinc content shows improved antibacterial activity. Overall, this research demonstrates that by modifying a surface with the appropriate chemical composition, effective bacterial elimination through contact can be achieved.

Diffraction-based approach for real-time monitoring of nanosecond direct laser interference patterning structure formation on stainless steel

Direct Laser Interference Patterning (DLIP) stands out as a versatile and cost-effective method for functionalizing material surfaces at high throughputs. Monitoring the dynamics of the structure formation can lead to a deeper understanding of the interplay between the main factors governing the process and ultimately to optimize the final texture. Here, the formation of gratings on stainless steel by DLIP with ns-pulses is studied using a diffraction-based approach, which measures the time-resolved reflectivity (TRR) of the sample. Measurements are performed for single pulses across different laser fluences. The melting dynamics are analyzed and compared with numerical results. By correlating the recorded signals with the structure depths, growth rates of 11 nm/ns and 57 nm/ns were estimated for fluences of 1.9 J/cm2 and 5.3 J/cm2, respectively. Furthermore, two growth regimes are identified. In the fast growth phase, the melting time increased from 73 to 380 ns for fluences of 1.9 J/cm2 and 5.9 J/cm2, respectively, showing a good agreement with the performed thermal simulations.

Nano/Microstructuring of Nickel Electrodes by Combining Direct Laser Interference Patterning and Polygon Scanner Processing for Efficient Hydrogen Production

The present work utilizes direct laser interference patterning in conjunction with a polygon scanner system to fabricate micro‐ and nanostructures on the surface of nickel foils. A picosecond pulsed laser source with an average power of ≈470 W is used to pattern line‐like structures having spatial periods of 11.0 and 25.0 μm and a maximum structure depth of up to 15 μm. The scanning speed and the number of consecutive scans, ranging from 5 to 500, are varied in order to assess their influence on the structure formation process. Furthermore, the use of ultrashort pulses permits the production of hierarchical surface structures having up to four feature size levels because of incubation effects and growth of different types of laser‐induced periodic surface structures. 2D‐fast Fourier transforms are applied to scanning electron microscopy images for analyzing the evolution of features from the nano‐ to microscale. The method proposed here permits the reduction of 22% in the overpotential of the hydrogen evolution reaction, which linearly correlates to the drop in energy required to drive this chemical reaction.

The friction of surface textured cylinder liner segments modified by Direct Laser Writing and Direct Laser Interference Patterning processes

Direct Laser Writing (DLW) using ultrashort pulsed lasers and galvanometer scanning, has become an established process for surface texturing, allowing an extensive variety of feature geometries and texture designs to be produced. The minimum feature sizes that can be generated are however limited by factors such as the laser output power, beam diameter, beam wavelength and associated optics. To address the need to produce even smaller texture features, Direct Laser Interference Patterning (DLIP) has been developed, which utilises bespoke beam splitting and converging optics to produce periodic interference fringing and enabling surface textures in the micrometric size range to be produced.In this study, the texturing of cast iron cylinder liner segments using DLW and DLIP processes is explored, to assess their tribological performance in high efficiency internal combustion engines, such as for hybrid applications. To facilitate the designs of textures and to capture high resolution data on surface interactions at specific points in the combustion cycle, the segmentation of cylinder lines and piston rings is undertaken. The results of tribology tests covering combinations of high and low speeds and contact pressures, have shown that the mechanical honing of cylinder liners could potentially be replaced with the cleaner DLIP texturing as an alternative.Optimised texture designs using the DLW process achieved up to a 54 % reduction in kinematic friction between the piston ring and textured cylinder liner surfaces, compared with mechanically honed cylinder liner segments. These results have indicated that DLW texturing offers the best improvement in friction performance in the boundary and mixed lubrication regimes at higher contact pressures, at both lower and higher sliding speeds. The results also provide useful comparative data on the performance of meso and micrometric scale textures and how they can be best applied to cylinder liners.

Combining Carbon Nanoparticle Coatings and Laser Surface Texturing for Enhanced Lubricity Under High Loads

Developing new lubrication concepts greatly contributes to improving the energy efficiency of mechanical systems. Nanoparticles such as those based on carbon allotropes or 2D materials have received widespread attention due to their outstanding mechanical and tribological performance. However, these systems are limited by a short wear life. Combining nanoparticle coatings with laser surface texturing has been demonstrated to substantially improve their durability due to the reservoir effect which prevents immediate particle removal from the contact. In this study, we investigate the high-load (20 N) tribological performance of AISI 304 austenitic stainless-steel substrates, which are line-patterned by laser interference patterning and subsequently coated with different carbon nanoparticle coatings (carbon nanotubes, carbon onions, carbon nanohorns) against alumina and 100Cr6 counter bodies. In addition to that, benchmark testing is performed with conventional solid lubricant coatings (graphite, MoS2, WS2). Electrophoretic deposition is used as the main coating technique along with air spraying (for WS2). All coatings substantially improve friction compared to the purely laser-patterned reference. Among all coating materials, carbon nanotubes demonstrate superior lubricity and the longest wear life against 100Cr6 and alumina counter bodies. Detailed characterization of the resulting wear tracks by energy-dispersive X-ray spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy provides insights into the friction mechanisms of the various solid lubricant particles. Further, material transfer is identified as an important aspect for effective and long-lasting lubrication.

Functionalization of Ti64 via Direct Laser Interference Patterning and Its Influence on Wettability and Oxygen Bubble Nucleation.

The nucleation of bubbles on solid surfaces is an important phenomenon in nature and technological processes like electrolysis. During proton-exchange membrane electrolysis, the nucleation and separation of the electrically nonconductive oxygen in the anodic cycle plays a crucial role to minimize the overpotential it causes in the system. This increases the efficiency of the process, making renewable energy sources and the "power-to-gas" strategy more viable. A promising approach is to optimize gas separation by surface functionalization in order to apply a more advantageous interface to industrial materials. In this work, the connection between the wettability and bubble nucleation of oxygen is investigated. For tailoring the wettability of Ti64 substrates, the direct laser interference patterning method is applied. A laser source with a wavelength of 1064 nm and a pulse duration of 12 ps is used to generate periodic pillar-like structures with different depths up to ∼5 μm. The resulting surface properties are characterized by water contact angle measurement, scanning electron microscopy, confocal microscopy, and X-ray photon spectroscopy. It was possible to generate structures with a water contact angle ranging from 20° up to nearly superhydrophobic conditions. The different wettabilities are validated based on X-ray photon spectroscopy and the different elemental composition of the samples. The results indicate that the surface character of the substrate adapts depending on the surrounding media and needs more time to reach a steady state for deeper structures. A custom setup is used to expose the functionalized surfaces to oxygen-oversaturated solutions. It is shown that a higher hydrophobicity of the structured surface yields a stronger interaction with the dissolved gas. This significantly enhances the oxygen nucleation up to nearly 350% by generating approximately 20 times more nucleation spots, but also smaller bubble sizes and a reduced detachment rate.

Pulsed laser interference patterning of transition‐metal carbides for stable alkaline water electrolysis kinetics

AbstractWe investigated the role of metal atomization and solvent decomposition into reductive species and carbon clusters in the phase formation of transition‐metal carbides (TMCs; namely, Co3C, Fe3C, TiC, and MoC) by pulsed laser ablation of Co, Fe, Ti, and Mo metals in acetone. The interaction between carbon s–p‐orbitals and metal d‐orbitals causes a redistribution of valence structure through charge transfer, leading to the formation of surface defects as observed by X‐ray photoelectron spectroscopy. These defects influence the evolved TMCs, making them effective for hydrogen and oxygen evolution reactions (HER and OER) in an alkaline medium. Co3C with more oxygen affinity promoted CoO(OH) intermediates, and the electrochemical surface oxidation to Co3O4 was captured via in situ/operando electrochemical Raman probes, increasing the number of active sites for OER activity. MoC with more d‐vacancies exhibits strong hydrogen binding, promoting HER kinetics, whereas Fe3C and TiC with more defect states to trap charge carriers may hinder both OER and HER activities. The results show that the assembled membrane‐less electrolyzer with Co3C∥Co3C and MoC∥MoC electrodes requires ~2.01 and 1.99 V, respectively, to deliver a 10 mA cm−2 with excellent electrochemical and structural stability. In addition, the ascertained pulsed laser synthesis mechanism and unit‐cell packing relations will open up sustainable pathways for obtaining highly stable electrocatalysts for electrolyzers.

Replicative Production of Multifunctional Microfluidic Polymer Films for Biomedical Disposables

Increasing demands on the reproducibility and accuracy of lab-on-a-chip systems in the life science sector require new tools for the molding of polymer films with spatially selectively functionalized surfaces. By applying local micro- and nanostructuring to the molding tools, the aim is to achieve multifunctionality of the polymer films, by setting certain wetting properties. This means that fluid-affecting properties (hydrophobic, hydrophilic) should be possible. To functionalize polymer films, the replication tools were specifically microstructured using laser-based surface functionalization. The periodic micro- and nanostructures were produced with the help of nanosecond pulsed and picosecond pulsed laser systems using Direct Laser Interference Patterning. For this purpose, complex functional microstructures in the range of 0.1 µm to 100 µm were developed based on a bionic approach. The functional properties were transferred in a one-step replicative process using UV-imprinting and were subsequently verified by determining the wetting behavior of the molded microfluidic films and the corresponding laser microstructured replication tools. This publication presents the successfully developed processes and the promising results of this series of experiments.

Tribo-Electric Analysis of Multi-Cycle Wear in Asymmetric Laser-Structured Cu-Sn Connectors

One of the key objectives of the connector industry for the past years has been to reduce the insertion friction forces of detachable electrical connections, where the majority of approaches combine a particular connector design with the usage of lubricants. The necessity for a solution that uses less contact force to maintain a lasting electrically conductive connection without sacrificing the mechanical robustness of the connection during use is a significant challenge in this situation. The approach in this work is to create surfaces supporting asymmetric friction, meaning lower insertion than removal forces. By Direct Laser Interference Patterning (DLIP), asymmetric saw-tooth structures with different structural inclinations and periodicities were generated on Sn-coated Cu plates. It is determined that topographical interlocking is the primary operating mechanism providing the required anisotropy. Multiple insertion/removal cycles were simulated on the tailored surfaces to tribologically characterize them and to determine the evolution of the electrical contact resistance at the end of each insertion motion. The vast majority of the generated structures showed an improvement compared to the reference state, with lower insertion and higher removal forces while the electrical behavior is not significantly impacted.

Single‐ and Multiscale Laser Patterning of 3D Printed Biomedical Titanium Alloy: Toward an Enhanced Adhesion and Early Differentiation of Human Bone Marrow Stromal Cells

AbstractThis study explores the enhancement of biocompatible titanium‐based implants through surface functionalization for improved bone healing. Specifically, a near‐beta type Ti‐13Nb‐13Zr alloy is 3D printed using laser powder bed fusion and subsequently textured using nanosecond (ns) and picosecond (ps) direct laser interference patterning (DLIP) to create single‐scale and multi‐scale surface textures. On these textures, the cell behavior, morphology, metabolic activity and osteogenic differentiation potential of human bone marrow stromal cells are assessed using fluorescence microscopy and MTS assays. Moreover, tissue non‐specific alkaline phosphatase activity served as an early osteoblast production marker. Compared to untextured specimens, both types of textures exhibited higher metabolic activity and cell proliferation. Single‐scale ns‐DLIP textures encouraged cell extensions anchored in groove regions, while ps‐DLIP textures with hierarchical structures promoted cell extensions attaching to nanostructures on sidewalls. The groove width and nanotopographies in groove areas facilitated cell spreading. Surface topography, roughness, and surface chemistry (surface energy, wettability) influenced cell adhesion, proliferation, and differentiation. A comprehensive evaluation of DLIP‐generated surface textures, including their topography and chemical states, complements the factors affecting in vitro cell behavior. Overall, this research demonstrates the potential of surface‐functionalized 3Dprinted titanium for a novel generation of biocompatible implants.

Large area structural color printing based on dot-matrix laser interference patterning.

Optically Variable Devices (OVDs) are widely used as security features in anti-counterfeiting efforts. OVDs enable the display of color dynamic effects that are easily interpreted by the user. However, obtaining these elements over large areas poses certain challenges in terms of efficiency. The paper presents a modified approach for manufacturing plasmonic type OVDs through dot-matrix technology, which is a standard origination step of security holograms. By adjusting the spatial filters in the optical scheme, it is possible to double the resolution of the recorded quasi-sinusoidal diffraction gratings. The experiments confirm the creation of diffraction gratings with frequencies from 1600 to 3500 lines per mm, which facilitates the production of plasmonic zero-order spectral filters. The paper shows how the transmission characteristics of the studied elements are affected by the geometric parameters of the diffraction grating, silver layer thickness, angle of incidence, and polarization of light. The results have shown that using the proposed method it is possible to obtain 1D or 2D structural color OVD-image on a large area - several square centimeters and more. High speed recording of such elements is provided: the exposure time was from 120 to 400 ms depending on the grating resolution for a 0.05 mm2 frame, the total printing time for the size of the 25×25 mm2 OVD was about 2.5 hours for a 1D element, and less than 3.5 hours for a 2D element. Thus, the proposed method and the OVD elements produced by it can be useful to designers of optical security elements as a simpler and faster alternative to electron-beam lithographic technologies.

Direct Laser Interference Patterning of Zirconia Using Infra‐Red Picosecond Pulsed Laser: Effect of Laser Processing Parameters on the Surface Topography and Microstructure

AbstractThis study investigates the influence of processing parameters when applying direct laser interference patterning (DLIP) on the morphology and microstructure of zirconia surfaces using a 10 ps‐pulsed laser source with 1064 nm wavelength. An experimental testing matrix is built with different values of laser fluence (5.7–18.2 J cm−2) and pulse overlap (66–98%). Surface morphology and microstructure are characterized by confocal microscopy and scanning electron microscopy. Homogeneous line‐like patterns with periodic spatial repetition of 5.0 µm, with varying depths, widths, and aspect ratio, are fabricated using proper processing parameters (5.7–7.6 J cm−2 and 92–96%). Structures with maximum depth of 1.5 µm and sharp edges are obtained (7.6 J cm−2 and 96% overlap). Ablated regions presented a morphology typical of photophysical ablation mechanism, with signs of molten material at the surface. Sub‐micrometric pores and nanodroplets are registered for all conditions, while sub‐micrometric cracks developed only for higher fluences. A processing window conducing to homogenous DLIP structures is set based on experimental data. Periodic structures with multiscale topographic features are successfully obtained on zirconia surfaces using DLIP technology in this study. These outcomes open new perspectives for fabrication of multifunctional zirconia surfaces for advanced biomedical and engineering applications.

On the Corrosion Properties of Aluminum 2024 Laser‐Textured Surfaces with Superhydrophilic and Superhydrophobic Wettability States

AbstractIn this work, the mechanism of the corrosion behavior of laser‐treated aluminum is studied. Two different laser techniques are used to fabricate the samples, direct laser interference patterning (DLIP) and direct laser writing (DLW), using nanosecond laser sources. The DLIP treatment uses a two‐beam optical configuration producing line‐like periodic structures. The DLW technique is employed to produce non‐periodic structures on the Al‐surface with the same cumulated fluences as in DLIP. The surface topography is analyzed by confocal microscopy, and the formation of oxide layers is investigated by scanning electron microscopy of cross‐sections produced using a focused ion beam. Wetting measurements performed on the laser‐treated samples exhibit a contrasting behavior, leading to either superhydrophobic or superhydrophilic states. In the case of the DLIP treatment, the static water contact angle is increased from 81° up to 158°, while for DLW, it decreases to 3°. Electrochemical tests demonstrate a decreased corrosion rate after laser treatment. Additionally, findings indicate no correlation between wettability and corrosion reduction. Therefore, the improvement in corrosion resistance is mainly attributed to the oxide layer formed by laser treatment. Although similar corrosion rates are achieved for both treatments, surfaces produced with DLIP can be beneficial when additional surface properties are required.

Increasing Heat Transfer from Metal Surfaces through Laser-Interference-Induced Microscopic Heat Sinks.

With the increasing processing power of micro-electronic components and increasing spatial limitations, ensuring sufficient heat dissipation has become a crucial task. This work presents a microscopic approach to increasing the surface area through periodic surface structures. Microstructures with a periodic distance of 8.5 µm are fabricated via Direct Laser Interference Patterning (DLIP) on stainless steel plates with a nanosecond-pulsed infrared laser and are characterized by their developed interfacial area ratio. The optimal structuring parameters for increasing the surface area were investigated, reaching peak-to-valley depths up to 12.8 µm and increasing surface area by up to 394%. Heat dissipation in a natural convection environment was estimated by measuring the output voltage of a Peltier element mounted between a hot plate and a textured sample. The resulting increase in output voltage compared to an unstructured sample was correlated to the structure depth and developed interfacial area ratio, finding a maximum increase of 51.4%. Moreover, it was shown that the output voltage correlated well with the structure depth and surface area.