Nanotextured Surfaces Research Articles

Controllable dewetting transition on graphene-based nanotextured surfaces

Controllable wetting state on nanotextured surfaces is of fundamental importance in diverse applications, including self-cleaning, droplet manipulation, and lubrication. The Cassie–Baxter (CB) state, which has attracted broad interests due to the dramatic reduction of solid/liquid contact, can easily break down and the inverse transition (dewetting) is highly challenging. Herein, via molecular dynamics simulation, we show that the regulation of geometrical parameters characterizing the graphene-based surfaces enables one to control the wetting states. Our results demonstrate that decoration of carbon nanopillars on graphene could favor dewetting transition as solid surface fraction increases to a critical value. Furthermore, the ability repelling water for solid surface is highly sensitive to the local density distribution of water droplet along the direction perpendicular to nanopillared graphene. Importantly, the mechanistic pathway of self-recovery of CB state is illustrated in details. Dewetting initiates with the vapor cavity nucleation at the basal surface associated with the bottom water-graphene adhesion force, then the ascend of droplet exhibits strong dependence on the subsequent spontaneous expand of vapor cavity which is necessary to achieve the dewetting transition. Our results provide a rational way to achieve dewetting process, which could guide further design of engineering devices with controllable wetting-related applications.

Enhanced hydroxylation and carbon dioxide uptake on nanotextured silver oxide

Nanotexturing of silver substrates with silver (I) oxide, Ag2O, is demonstrated using a one-step laser micro-machining process. Where ablation of the silver substrate took place, a highly textured nanoscale topography is generated. In contrast, a film-like oxide is formed next to the machined areas. Interestingly, it was observed that Ag2O formed within the laser tool path was significantly more reactive towards atmospheric H2O and CO2 compared to the film-like oxide, leading to the formation of silver carbonate, Ag2CO3, only in this region. The ability to generate a periodic topography, in the form of a bulls-eye grating, combined with periodic surface chemistry, consisting of alternating regions of Ag2O and Ag2CO3 is also shown. Depending on the machining parameters and tool path used, the surfaces can become quite optically active. When combined with the propensity of a nanotextured Ag2O surface to react with carbon dioxide and water, an attractive system for applications involving photocatalytic CO2 reduction, CO2 capture and storage, and artificial photosynthesis is realized.

Bitumen surface microstructure evolution in subzero environments.

Bitumen is a widely used material employed as a binder in pavement engineering and as a surface sealant in construction. Its surface microstructure and microscale properties have been shown to be temperature-dependent, with effects manifesting themselves on surface composition and texture, including the formation of the visually striking catana 'bee'-like structures. Despite the importance of a good performance of bitumen in subzero environments (<0°C), the behaviour of bitumen surface texture and composition at cold temperatures, affecting cracking, degradation and road icing, has received practically no attention. In particular, such knowledge is relevant to world regions experiencing long periods of subzero temperatures during the year. Employing advanced atomic force microscopy combined with infrared spectroscopy (AFM-IR) and an environmental chamber, we demonstrate the ability to characterise surface structure and composition with nanoscale precision for a broad range of temperatures. We show that cooling bitumen to subzero temperatures can have several interesting effects on its surface microtexture, nanotexture and composition, especially on its three surface domains, catana, peri and para. We found that the para domain coarsens and extends to form an interfacial transition domain (characterised by increasing surface roughness with peri domain composition) between the para and peri domains. We show that the catana and peri domains have a similar composition, but have different mechanical and chemical properties compared to the para domain. The essential findings of this work improve our understanding of the behaviour of bitumen in subzero environments, aiding us in our quest towards attaining better road and sealant performance.

Reusable Au/Pd-coated chestnut-like copper oxide SERS substrates with ultra-fast self-recovery

Reliable and reusable plasmonic substrates are crucial for the development of biosensing applications using surface-enhanced Raman scattering (SERS), as they can provide unique advantages for ultrafast and accurate single-molecule recognition of different species. These properties are unrevealed in this paper, where thermally annealed cupric CuO and cuprous oxide Cu2O heterostructures were used as templates for highly stable nanotextured surfaces and design of robust 3D plasmonic biochips. Differently tailored nano/micro-roughness provided outstanding light trapping abilities that lead to significant SERS performance improvement. It was found that Cu2O chestnut-like substrate activated with 80 nm Au/Pd alloy film reveals impressive 3.7-fold Raman signal increment in respect to grainy-like structure and about twice larger amplification than that of nanowires enriched platform decorated in the same manner. Large enhancement factor AEF ~5 × 105 of a chestnut-like Au/Pd@/Cu2O chip allows adding it up to the list of the most effective oxide-based plasmonic substrates. Moreover, the substrate shows unprecedented durability during repetitive plasma-cleaning, demonstrating a remarkable 100% self-recovery in less than 1 min, accompanied by virtually no thickness degradation of the plasmonic layer.

Improved emitter performance of RIE black silicon through the application of in-situ oxidation during POCl3 diffusion

Nano-texture has the potential to reduce the optical losses of crystalline silicon solar cells. RIE fabricated black silicon enables near zero reflectance across a broad range of wavelengths and the angular dependence has been shown to be superior to existing technologies. However, in front-contact cells which are the current industrial mainstream architecture, the emitter is located on the front textured side and is typically realized by POCl3 diffusion. The interaction of this process with the nano-texture is complex, which makes it challenging to optimise the electrical performance of the phosphorus emitter. This paper studies the impact of in-situ oxidation during emitter formation to the electrical performance of a POCl3 diffused RIE nanotextured emitter surface. Additional corona charge was applied on the ALD SiO2/Al2O3 stack to avoid the limitation on the emitter performance due to non-ideal surface passivation conditions. After saturation with surface charge, the results demonstrate in-situ oxidation to be an effective technique to improve the electrical performance. An emitter recombination factor of 147 fA/cm2 was achieved for a 127 Ω/□ emitter formed on reactive-ion etched sample with surface area enhancement factor and effective slope index of 4.19 and 1.63, respectively. Further paths for improvement are identified, particularly relating to the collection of carriers generated by short wavelength light and how that relates to the shape of the texture used.

Controlling porous titanium/soft tissue interactions with an innovative surface chemical treatment: Responses of macrophages and fibroblasts.

In order to create a stable interface with the host tissue, porous implants are widely used to ensure the in-growth of the cells and the colonization of the implant. An ideal porous implant should have a 3D architecture that enables fast migration of incoming cells while not inducing a significant pro-inflammatory response by the immune cells. Moreover, in patients where the healing is impeded (patients with co-morbidities and metabolic diseases), porosity by itself is not enough for fast colonization, and the surface properties of the implant should also be controlled. In this study, we present a controlled oxidation-based surface treatment of microbead-based porous titanium implants which not only increases the colonization by connective tissue cells but also decreases the macrophage attachment. The treatment created a nanotextured surface on the implants with an acidic shift of isoelectric point (from 4.09 to 3.09) without endangering implant's mechanical integrity. The attachment and metabolic activity of activated macrophages were significantly lower on treated surfaces with an increase in the secretion of anti-inflammatory IL-1RA and a decrease in pro-fibrotic CCL-18. Human fibroblasts proliferated faster on the treated surfaces over 14days with near complete colonization of the whole thickness of the implant with an accompanying an increase in the secretion of TGF-beta. The surface treated samples demonstrated partial filling of the entire pores. We demonstrated that the use of nanoscale surface treatments that can be applied to the whole internal surface of porous titanium implants can significantly alter both the immune response and the colonization of the implants and can be used to fine-tune and personalize implant interfaces according to patient needs.

Shape-Programmed Fabrication and Actuation of Magnetically Active Micropost Arrays.

Micro- and nanotextured surfaces with reconfigurable textures can enable advancements in the control of wetting and heat transfer, directed assembly of complex materials, and reconfigurable optics, among many applications. However, reliable and programmable directional shape in large scale is significant for prescribed applications. Herein, we demonstrate the self-directed fabrication and actuation of large-area elastomer micropillar arrays, using magnetic fields to both program a shape-directed actuation response and rapidly and reversibly actuate the arrays. Specifically, alignment of magnetic microparticles during casting of micropost arrays with hemicylindrical shapes imparts a deterministic anisotropy that can be exploited to achieve the prescribed, large-deformation bending or twisting of the pillars. The actuation coincides with the finite element method, and we demonstrate reversible, noncontact magnetic actuation of arrays of tens of thousands of pillars over hundreds of cycles, with the bending and twisting angles of up to 72 and 61°, respectively. Moreover, we demonstrate the use of the surfaces to control anisotropic liquid spreading and show that the capillary self-assembly of actuated micropost arrays enables highly complex architectures to be fabricated. The present technique could be scaled to indefinite areas using cost-effective materials and casting techniques, and the principle of shape-directed pillar actuation can be applied to other active material systems.

Antibacterial Properties of Superhydrophilic Textured Copper in Contact with Bacterial Suspensions.

The method of pulsed laser processing with a nanosecond pulse duration was employed to obtain a nanotexture on the surface of copper alloys. The effect of the obtained micro- and nanotexture on the bactericidal properties of the surface upon its contact with suspensions containing of E. coli K12 C600 or K. pneumoniae 811 cells in a nutrient medium were studied. The evolution of cell morphology after on the nanotextured surface was analyzed using scanning electron microscopy, and changes in biological fluid during this contact were studied by mass spectrometry. It was shown that massive death of bacterial cells both in the suspension and on the nanotextured surface was determined by combined toxic effects of the hierarchically textured surface and high concentration of Cu2+ ions in the medium.

Mechanical behavior of core–shell nanostructures

Nanotexturing reduces the effective contact between surfaces in relative motion, which can result in a lower coefficient of friction. However, nanotextured surfaces lack structural integrity, resulting in permanent deformation even at moderate contact forces. Therefore, core–shell nanostructures (CSNs) have been developed to protect the structural integrity of nanotextured surfaces. These CSNs can withstand higher contact forces, might include some plastic deformation (dislocations), but during unloading there is no evidence of residual plastic deformation. Therefore, the CSN is deformation resistant. In the current study, molecular dynamics simulations are used to study the effect of core (aluminum) radius, shell (amorphous silicon) thickness, and the random atomic distribution in the amorphous shell, on mechanical properties of core–shell nanostructures. The results suggest that core radius does not have a significant influence on the initial plastic deformation of the CSN. The shell thickness should be chosen so that the core to shell ratio is less than two to have deformation resistant CSNs. Further we observe that with an increase in core radii or shell thickness, the ability of a CSN to fully recover decreases. These results will help in the design of deformation resistant surfaces for MEMS/NEMS applications.

Nature Inspired Antimicrobial Nanotextured Surfaces

The development of cross infections arising from bacteria transmission on frequently touched facilities has led to an urgent need to promptly disinfect these surfaces, such as hand railings, door handles and elevator buttons. Conventional antimicrobial disinfectants are not ideal as they contribute to the growing antimicrobial resistance crisis. In recent years, the discovery that the wings of insects such as the Clanger cicada (Psaltoda claripennis) possess naturally occurring antimicrobial properties has led to a growing interest to synthetically recreate these surfaces. The use of a physical contact killing mechanism on such nanotextured surfaces is a promising strategy for curbing the proliferation of bacteria, as it is unlikely to contribute to the formation of antimicrobial resistance. Here, I highlight the key advantages of using these antimicrobial nanotextured materials and how they could play a role in safeguarding public health security, especially during the current COVID-19 pandemic.

Development of a Monitoring Strategy for Laser-Textured Metallic Surfaces Using a Diffractive Approach.

The current status of research around the world concurs on the powerful influence of micro- and nano-textured surfaces in terms of surface functionalization. In order to characterize the manufactured topographical morphology with regard to the surface quality or homogeneity, major efforts are still required. In this work, an optical approach for the indirect evaluation of the quality and morphology of surface structures manufactured with Direct Laser Interference Patterning (DLIP) is presented. For testing the designed optical configuration, line-like surface patterns are fabricated at a 1064 nm wavelength on stainless steel with a repetitive distance of 4.9 µm, utilizing a two-beam DLIP configuration. Depending on the pulse to pulse overlap and hatch distance, different single and complex pattern geometries are produced, presenting non-homogenous and homogenous surface patterns. The developed optical system permitted the successfully classification of different pattern geometries, in particular, those showing single-scale morphology (high homogeneity). Additionally, the fabricated structures were measured using confocal microscopy method, and the obtained topographies were correlated with the recorded optical images.

Role of Scale Wettability on Rain-Harvesting Behavior in a Desert-Dwelling Rattlesnake.

During storms in the southwestern United States, several rattlesnake species have been observed drinking rain droplets collected on their dorsal scales. This process often includes coiling and flattening of the snake’s body, presumably to enhance water collection. Here, we explored this rain-harvesting behavior of the Western Diamond-backed Rattlesnake (Crotalus atrox) from the perspective of surface science. Specifically, we compared surface wettability and texture, as well as droplet impact and evaporation dynamics on the rattlesnake epidermis with those of two unrelated (control) sympatric snake species (Desert Kingsnake, Lampropeltis splendida, and Sonoran Gopher Snake, Pituophis catenifer). These two control species are not known to show rain-harvesting behavior. Our results show that the dorsal scales of the rattlesnake aid in water collection by providing a highly sticky, hydrophobic surface, which pins the impacting water droplets. We show that this high pinning characteristic stems from surface nanotexture made of shallow, labyrinth-like channels.

Low-pressure nitrogen and ammonia plasma treatment on carboxymethyl guar gum/PVA hydrogels: impact on drug delivery, biocompatibility and biodegradability

Smart hydrogels comprising carboxymethyl guar gum and polyvinyl alcohol (CMGG/PVA) were fabricated using tetraethyl orthosilicate as crosslinker. The hydrogels were subjected to nonthermal plasma (NTP) treatment using nitrogen and ammonia mixture. An improvement in surface wettability ensuing from NTP-treatment was evident. Topographical studies revealed surface nanotexturing while the bulk attributes remained undeterred. An insignificant ageing effect was observed upon exposure to air for 20 days which indicated the high stability of the NTP-modified hydrogels. The hydrogels displayed higher swellability in intestinal pH than gastric pH. Appreciable biofilm eradication features against E. coli were observed from the NTP-modified hydrogels. Hemolytic assessment confirmed their compatibility with human blood cells. Release profiles from the hydrogels validated the controlled delivery of anticancer drug chrysin to the intestine. Pristine hydrogels were found to be cytocompatible whereas chrysin-loaded hydrogels displayed a strong inhibitory effect on MCF-7 cells. Additionally, the hydrogels were found to be biodegradable. Thus, N2 and NH3 plasma modified CMGG/PVA hydrogels are potent towards diverse biomedical applications.

Supersonic Cold Spraying for Energy and Environmental Applications: One-Step Scalable Coating Technology for Advanced Micro- and Nanotextured Materials.

Supersonic cold spraying is an emerging technique for rapid deposition of films of materials including micrometer-size and sub-micrometer metal particles, nanoscale ceramic particles, clays, polymers, hybrid materials composed of polymers and particulates, reduced graphene oxide (rGO), and metal-organic frameworks. In this method, particles are accelerated to a high velocity and then impact a substrate at near ambient temperature, where dissipation of their kinetic energy produces strong adhesion. Here, recent progress in fundamentals and applications of cold spraying is reviewed. High-velocity impact with the substrate results in significant deformation, which not only produces adhesion, but can change the particles' internal structure. Cold-sprayed coatings can also exhibit micro- and nanotextured morphologies not achievable by other means. Suspending micro- or nanoparticles in a liquid and cold-spraying the suspension produces fine atomization and even deposition of materials that could not otherwise be processed. The scalability and low cost of this method and its compatibility with roll-to-roll processing make it promising for many applications, including ultrathin flexible materials, solar cells, touch-screen panels, nanotextured surfaces for enhanced heat transfer, thermal and electrical insulation films, transparent conductive films, materials for energy storage (e.g., Li-ion battery electrodes), heaters, sensors, photoelectrodes for water splitting, water purification membranes, and self-cleaning films.

Ultratrace Nitroaromatic Vapor Detection via Surface-Enhanced Fluorescence on Carbazole-Terminated Black Silicon.

Detection of nitroaromatic compounds (NACs) is an important applied task for environmental monitoring, medical diagnostics, and forensic analysis. However, detection of NAC vapors is challenging owing to their low vapor pressure and relatively weak sensitivity of the existing detection techniques. Here, we propose a novel concept to design fluorescence (FL) detection platforms based on chemical functionalization of nanotextured dielectric surfaces exhibiting resonant light absorption, trapping, and localization effects. We demonstrate highly-efficient NAC vapor sensor with selective FL-quenching response from monolayers of carbazole moieties covalently bonded to a spiky silicon surface, "black" silicon, produced over the centimeter-scale area using simple reactive ion etching. The sensor is shown to provide unprecedented ppt (10-12) range limits of detection for several NAC vapors. Easy-to-implement scalable fabrication procedure combined with simple and versatile functionalization techniques applicable to all-dielectric surfaces make the suggested concept promising for realization of various gas sensing systems for social and environmental safety applications.

Study on axial wetting length and evaporating heat transfer in rectangular microgrooves with superhydrophilic nano-textured surfaces for two-phase heat transfer devices

Advanced thermal management solutions for various applications in energy systems have promoted the developments of novel hybrid wicks for two-phase heat transfer devices (TPHTD). In this study, a novel micro-nano hybrid wick combined rectangular microgrooves with superhydrophilic copper hydroxide nano-textured surfaces is developed. Comparative experiments on the axial wetting lengths, evaporating flow characteristics and evaporating heat transfer performance are systematically conducted for different microgrooves-based wick samples, i.e., the pristine rectangular microgrooves (RMs) and rectangular microgrooves with superhydrophilic nano-textured surfaces (RMSNSs). The distilled water and ethanol are both used as working fluids. The experimental results indicate that the RMSNSs wick produces remarkable increases in axial wetting lengths compared to the pristine RMs wick. Under the unheated condition, the total wetting length (Lt) of water in RMSNSs is more than 4 times of that in RMs. Under the same condition of heat flux, the Lt of RMSNSs is also distinctly larger. The improved axial wetting characteristics can be attributed to the effect of surface wettability enhancement, which have a critical influence on the evaporating heat transfer. The sample temperature of RMSNSs is much lower at each given heat flux and the decrement is more than 15 °C. The maximum incremental ratio of heat transfer coefficient can approach 100%. The enhanced evaporating heat transfer highly depends on the significantly increased thin liquid film area. Furthermore, a theoretical model is presented to facilitate the understanding on axial wetting and heat transfer enhancements effect of RMSNSs. The proposed model is applicable and satisfactorily accurate to predict the axial wetting lengths for microgrooves-based wick sample under the evaporating heat transfer condition. This study provides an in-depth insight into the enhanced axial flow and heat transfer characteristics of micro-nano hybrid wick incorporating microgrooves and nanostructures, and consequently can facilitate the further optimization design of microgrooves-based wick for advanced TPHTD. It is believed that this superior hybrid wick with advantages of facile and rapid fabrication is highly promising in the applications of heat energy transfer, conversion and management.

Evaporative Wicking Phenomena on Nanotextured Surfaces

AbstractAs modern electronics become miniaturized with high power, thermal management for electronics devices has become significant. This motivates the implementation of new cooling solutions to dissipate high-heat levels from high-performance electronics. Evaporative cooling is one of the most promising approaches for meeting these future thermal demands. Thin-film evaporation promotes heat dissipation through the phase change process with minimal conduction resistance. In this process, it is important to design surface structures and corresponding surface properties that can minimize meniscus thickness, increase liquid–vapor interfacial area, and enhance evaporation performances. In this study, we investigate thin-film evaporation by employing nanotextured copper substrates for varying thermal conditions. The liquid spreading on the nanotextured surfaces is visualized using a high-speed imaging technique to quantify evaporative heat transfer for various surfaces. The permeability is calculated using an enhanced wicking model to estimate the evaporation effect combined with the mass measurements. Then, infrared (IR) thermography is employed to examine two-dimensional temporal temperature profiles of the samples during the evaporative wicking with a given heat flux. The combination of optical time-lapse images, evaporation rate measurements, and temperature profiles will provide a comprehensive understanding of evaporation performances using textured surfaces.

Self-Cleaning Mechanism: Why Nanotexture and Hydrophobicity Matter.

Dust particles can adhere to surfaces, thereby decreasing the efficiency of diverse processes, such as light absorption by solar panels. It is well known that superhydrophobicity reduces the friction between water droplets and the surface, thus allowing water drops to slide/roll and detach (clean) particles from surfaces. However, the forces that attach and detach particles from surfaces during the self-cleaning mechanism and the effect of nanotextures on these forces are not fully understood. To shed light on these forces and the effect of nanotexture on them, we prepared four Si-based samples (relevant to solar panels): (1) smooth or (2) nanotextured hydrophilic surfaces and (3) smooth or (4) nanotextured hydrophobic surfaces. In agreement with previous publications, it is shown that the efficiency of particle removal increases with hydrophobicity. Furthermore, nanotexture enhances the hydrophobicity, whereby particle removal is further increased. Specifically, hydrophilic particle removal increased from ∼41%, from hydrophilic smooth Si wafers to 98% from superhydrophobic Si-based nanotextured surfaces. However, the reason for the increased particle removal is not low friction between the droplets and the superhydrophobic surfaces; it is the reduction of the adhesion force between the particle and the surface and the altered geometry of the water-particle-air line tension acting on the particles on superhydrophobic surfaces, which increases the force that can detach particles from the surfaces. The experimental methods we used and the criterion for particle removal we derived can be implemented to engineer self-cleaning surfaces using other surfaces and dust particles, exhibiting different chemistries and/or textures.

Influence of laser surface nanotexturing on the friction behaviour of the silicon/sapphire system

The aim of the present work was to investigate the influence of textures consisting of Laser-Induced Periodic Surface Structures (LIPSS) on the friction coefficient of silicon under unlubricated conditions, using nanoscale friction tests. The tests were performed on 〈111〉 single crystal wafers of p-doped silicon. Surface texturing was performed by a direct writing technique, using 560 fs pulses of 1030 nm wavelength radiation and parameters allowing large areas with a uniform LIPSS texture to be obtained. The tribological tests were performed in air using a ball-on-flat nanotribometer with 3 mm diameter sapphire balls as counterbodies. The wear scars were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The friction coefficient of polished Si remains approximately constant during the tests and is independent of the applied load, with values in the range 0.12–0.14. The morphology of the wear scars indicated that the predominant material removal mechanism is mild oxidative wear, independently of the testing conditions used, which explains the low values of the friction coefficient measured. The LIPSS texture leads to an increase of the friction coefficient, in particular in the perpendicular sliding direction. The friction coefficient increases with the applied load and is larger for the perpendicular sliding direction than for the parallel sliding direction, the difference increasing with increasing load. The morphology of the wear scars showed that the predominant wear regime remains oxidative wear, but significant contributions of plastic deformation and ploughing appear. This plastic deformation in Si, which is brittle at room temperature, shows that significant surface heating is being caused by the interaction of the asperities in motion and under load. This temperature increase also accelerates surface oxidation and increases the wear rate. Surface temperature calculations showed that the temperature increase is larger for the perpendicular sliding direction than for the parallel one, which explains the difference of friction coefficient observed in the two directions.

A graphene based–biomimetic molecularly imprinted polyaniline sensor for ultrasensitive detection of human cardiac troponin T (cTnT)

Abstract In the present work, a biomimetic nano-molecularly imprinted polymer (N-MIP) electrode based on a graphene screen-printed electrode was developed for the ultrasensitive detection of cardiac troponin T (cTnT). The biomimetic cavities for targeted sensing for analyte were fabricated by the electropolymerization of conductive co-polymer matrix of aniline and carboxylated aniline on the graphene oxide (GO) electrode, in the presence template protein (cTnT for cardiac troponin T probe) by cyclic voltammetry. The surface characterization of the sensor was performed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and scanning electron microscopy (SEM). The best biomimetic surface nanotexture was obtained at aniline/carboxylatedaniline ratio of 1:4. The linear range of cTnT probe was in the range of 0.02 to 0.09 ng/mL, with the detection limit of 0.008 ng/mL. The reliability of the N-MIP cTnT sensor was examined by comparing the results with those obtained from HPLC method, and it was observed that the results from N-MIP sensors and HPLC have a great correlation.