Nanoscale Surface Structures Research Articles

The Design and Analysis of the Fabrication of Micro- and Nanoscale Surface Structures and Their Performance Applications from a Bionic Perspective.

This paper comprehensively discusses the fabrication of bionic-based ultrafast laser micro-nano-multiscale surface structures and their performance analysis. It explores the functionality of biological surface structures and the high adaptability achieved through optimized self-organized biomaterials with multilayered structures. This study details the applications of ultrafast laser technology in biomimetic designs, particularly in preparing high-precision, wear-resistant, hydrophobic, and antireflective micro- and nanostructures on metal surfaces. Advances in the fabrications of laser surface structures are analyzed, comparing top-down and bottom-up processing methods and femtosecond laser direct writing. This research investigates selective absorption properties of surface structures at different scales for various light wavelengths, achieving coloring or stealth effects. Applications in dirt-resistant, self-cleaning, biomimetic optical, friction-resistant, and biocompatible surfaces are presented, demonstrating potential in biomedical care, water-vapor harvesting, and droplet manipulation. This paper concludes by highlighting research frontiers, theoretical and technological challenges, and the high-precision capabilities of femtosecond laser technology in related fields.

A Rapidly Self-Healing Superhydrophobic Coating Made of Polydimethylsiloxane and N-nonadecane: Stability and Self-Healing Capabilities

Superhydrophobic surfaces have garnered significant attention in various industrial applications, such as photovoltaic power generation, anti-icing, and corrosion resistance, due to their exceptional water-repellent properties. However, the poor durability of conventional superhydrophobic coatings has severely impeded their practical implementation. To achieve the dual self-recovery of microscale and nanoscale surface structures and maintain low surface energy after damage to superhydrophobic coatings, thereby enhancing their durability, a rapidly self-healing superhydrophobic coating was developed using polydimethylsiloxane (PDMS) and n-nonadecane in this study. The coating surface demonstrated exceptional hydrophobic characteristics, as evidenced by a water contact angle (WCA) of 157.5° and a sliding angle (SA) of 4.2° achieved at optimized proportions. Through scanning electron microscopy, it was observed that the coating surface exhibited a rough structure at both the microscale and nanoscale. The stability test results showed that the WCA only decreases by 5.7° and the SA only increases by 3.6° after 100 instances of external friction. The stability test results demonstrated that the superhydrophobic coating maintains excellent hydrophobicity under mechanical external forces and in acidic and alkaline environments. The results of the self-healing capability test showed that the WCA rebounded to 151.5° and 149.5° after we subjected the samples to 20 MPa of vertical pressure damage and chloroform exposure for 4 h, respectively. The coating regained a robust hydrophobic state even after experiencing repeated mechanical and chemical damage. The above results indicate that the resulting coating demonstrates outstanding durability, including high resistance to friction, stability against acids and alkalis, and the ability to self-recover hydrophobicity after repeated damage.

Bio-Inspired Micro- and Nano-Scale Surface Features Produced by Femtosecond Laser-Texturing Enhance TiZr-Implant Osseointegration.

Surface design plays a critical role in determining the integration of dental implants with bone tissue. Femtosecond laser-texturing has emerged as a breakthrough technology offering excellent uniformity and reproducibility in implant surface features. However, when compared to state-of-the-art sandblasted and acid-etched surfaces, laser-textured surface designs typically underperform in terms of osseointegration. This study investigates the capacity of a bio-inspired femtosecond laser-textured surface design to enhance osseointegration compared to state-of-the-art sandblasted & acid-etched surfaces. Laser-texturing facilitates the production of an organized trabeculae-like microarchitecture with superimposed nano-scale laser-induced periodic surface structures on both 2D and 3D samples of titanium-zirconium-alloy. Following a boiling treatment to modify the surface chemistry, improving wettability to a contact angle of 10°, laser-textured surfaces enhance fibrin network formation when in contact with human whole blood, comparable to state-of-the-art surfaces. In vitro experiments demonstrate that laser-textured surfaces significantly outperform state-of-the-art surfaces with a 2.5-fold higher level of mineralization by bone progenitor cells after 28 days of culture. Furthermore, in vivo evaluations reveal superior biomechanical integration of laser-textured surfaces after 28 days of implantation. Notably, during abiological pull-out tests, laser-textured surfaces exhibit comparable performance, suggesting that the observed enhanced osseointegration is primarily driven by the biological response to the surface.

Surface roughening and hemi-wicking: Synergistic impact on flow boiling

This study advances thermal management in flow boiling by investigating the synergy between nanoscale surface structures, hemi-wicking, and bubble dynamics during phase changes, with a particular focus on innovative surface morphology. Nanowires, known for enhancing heat transfer through surface roughening and interfacial wicking, play a crucial role. We highlight the importance of morphological roughening and its synergy with hemi-wicking in enhancing critical heat flux (CHF) in flow boiling. We demonstrate that surfaces functionalized with vertical silicon nanowires show a significant increase in CHF compared to smooth surfaces. This enhancement is attributed to improved liquid supply and prevention of bubble pinning, thus maximizing heat dissipation. However, the absence of hemi-wicking on nano-inspired surfaces unexpectedly leads to a substantial CHF reduction compared to smooth counterparts. By visualizing bubble dynamics under forced convection, we reveal the critical role of hemi-wicking in sustaining continuous liquid supply and postponing the onset of film boiling by ensuring an anti-pinning effect of bubbles. These findings offer valuable insights into interface functionalization and surface morphology design for efficient heat dissipation, emphasizing the often-overlooked role of hemi-wicking in preventing bubble pinning. This knowledge is pivotal for developing compact and high-efficiency cooling technologies.

Enabling Pd Catalytic Selectivity via Engineering Intermetallic Core@Shell Structure.

Core@shell nanoparticles (NPs) have been widely explored to enhance catalysis due to the synergistic effects introduced by their nanoscale interface and surface structures. However, creating a catalytically functional core@shell structure is often a synthetic challenge due to the need to control the shell thickness. Here, we report a one-step synthetic approach to core-shell CuPd@Pd NPs with an intermetallic B2-CuPd core and a thin (∼0.6 nm) Pd shell. This core@shell structure shows enhanced activity toward selective hydrogenation of Ar-NO2 and allows one-pot tandem hydrogenation of Ar-NO2 to Ar-NH2 and its condensation with Ar-CHO to form Ar-N═CH-Ar. DFT calculations indicate that the B2-CuPd core promotes the Pd shell binding to Ar-NO2 more strongly than to Ar-CHO, thereby selectively activating Ar-NO2. The chemoselective catalysis demonstrated by B2-CuPd@Pd can be extended to a broader scope of substrates, allowing green chemistry synthesis of a wide range of functional chemicals and materials.

Escherichia coli Adhesion and Biofilm Formation on Polymeric Nanostructured Surfaces.

Biofilm formation is a multistep process that requires initial contact between a bacterial cell and a surface substrate. Recent work has shown that nanoscale topologies impact bacterial cell viability; however, less is understood about how nanoscale surface properties impact other aspects of bacterial behavior. In this study, we examine the adhesive, viability, morphology, and colonization behavior of the bacterium Escherichia coli on 21 plasma-etched polymeric surfaces. Although we predicted that specific nanoscale surface structures of the surface would control specific aspects of bacterial behavior, we observed no correlation between any bacterial response or surface structures/properties. Instead, it appears that the surface composition of the polymer plays the most significant role in controlling and determining a bacterial response to a substrate, although changes to a polymeric surface via plasma etching alter initial bacteria colonization and morphology.

Surface characterization of CaF2 crystals irradiated with MeV ions below charge state equilibrium

Single crystals of CaF2, cleaved along the (111) plane, were irradiated by 35Cl, 39K, 52Cr, 58Ni, 79Br and 197Au ions with energies from 2 to 48 MeV, charge states from 1+ to 11+ and ion fluences from 2 × 1010 to 1 × 1013 ions/cm2. The surface properties of the irradiated samples were studied using Atomic Force Microscopy in contact mode. Nanoscale surface structures were observed for some surfaces irradiated by Cl, K, Cr, Ni, Br and Au ions. Thresholds for nanostructure formation were found in terms of projectile ion velocity and electronic stopping power (Se). Clear surface modification was observed for projectiles with specific energies above approximately 0.04 MeV/u. The threshold in Se for the generation of distinct triangular structures was observed to be velocity-dependent. The average formation efficiency, referring to the ratio of the number of distinct nanostructures observed on the surface to the number of incident ions, as well as the average height of nanostructures increases with Se.

Selective Adsorption and Photocatalytic Clean‐Up of Oil by TiO2 Thin Film Decorated with p‐V3D3 Modified Flowerlike Ag Nanoplates

AbstractVarious methods are developed and used to treat oil‐contaminated water, including mechanical separation, chemical treatment, biological treatment, membrane filtration, and sorption. Oil clean‐up via selective sorption of the oil by an engineered surface is the most accepted technique due to its high removal efficiency and low cost. Here, a multifunctional surface providing highly selective oil sorption and clean‐up capability via the photocatalytic decomposition is proposed. This novel surface is named as the “three‐in‐one (3‐in‐1) surface” since it is composed of 1) a highly photocatalytic layer, 2) micro‐ and nanostructures, and 3) a low surface energy layer. First, the TiO2 photocatalytic layer is prepared by magnetron sputtering. Then flowerlike Ag nanoplates are photocatalytically deposited on the sputtered TiO2 layer. Afterward, a low surface energy layer, poly‐1,3,5‐trivinyl‐1,3,5‐trimethylcyclotrisiloxane (p‐V3D3), is over‐coated on Ag/TiO2 surface by initiated chemical vapor deposition (iCVD) while retaining the topographical features of the surface (micro‐ and nanoscale surface structures). The p‐V3D3/Ag/TiO2 surface demonstrates a high selective adsorption to oil whereas simultaneously it shows extreme repellency to water. The p‐V3D3/Ag/TiO2 surface can also be photocatalytically cleaned up and this may find applications in various technology fields including water treatment, microfluidics, self‐cleaning, and water harvesting.

Engineered nanoscale schwertmannites as Fenton–like catalysts for highly efficient degradation of nitrophenols

The Fenton process has been considered as one of the most promising advanced oxidation processes (AOPs) for the treatment of persistent organic pollutants (POPs). Herein, engineered nanoscale schwertmannite (nano–SCH) were fabricated from a PVP (polyvinylpyrrolidone) assisted room–temperature synthesis. The as–prepared well–dispersed nano–SCH materials were further studied as Fenton–like catalysts for 4–nitrophenol (4–NP) degradation in the presence of H2O2. Results showed that the optimized nano–SCH–0.125 was able to degrade 91.0% of 4–NP in 60 min at 298 K, thanks to the nanoscale and hierarchical surface structures that provided abundant reactive sites at solid/solution interfaces. Moreover, mechanism study indicated that •OH radicals were the main reactive species responsible for the excellent 4–NP degradation performances during the Fenton–like processes. This work thus provides a viable pathway to engineer nanoscale materials with enhanced catalytic properties in oxidative degradation of environmental pollutants.

Modelling of Dynamics of Formation and Growth of Nanoscale Surface Structures in ‘Plasma–Condensate’ Systems

Modelling of Dynamics of Formation and Growth of Nanoscale Surface Structures in ‘Plasma–Condensate’ Systems

Large-Beam Picosecond Interference Patterning of Metallic Substrates

In this paper, we introduce a method to efficiently use a high-energy pulsed 1.7 ps HiLASE Perla laser system for two beam interference patterning. The newly developed method of large-beam interference patterning permits the production of micro and sub-micron sized features on a treated surface with increased processing throughputs by enlarging the interference area. The limits for beam enlarging are explained and calculated for the used laser source. The formation of a variety of surface micro and nanostructures and their combinations are reported on stainless steel, invar, and tungsten with the maximum fabrication speed of 206 cm2/min. The wettability of selected hierarchical structures combining interference patterns with 2.6 µm periodicity and the nanoscale surface structures on top were analyzed showing superhydrophobic behavior with contact angles of 164°, 156°, and 150° in the case of stainless steel, invar, and tungsten, respectively.

Novel multifunctional solid slippery surfaces with self-assembled fluorine-free small molecules

Functional slippery surfaces have broad applications in engineering and bioengineering processes, such as water harvesting, photocatalysis, wastewater treatment and food industry. In this work, for the first time, we report the fabrication of a novel type of functional slippery solid surfaces via the self-assembly of a non-fluorine small molecule, γ-mercaptopropyldi(trimethylsiloxy)methylsilane (MD(SH)M), which possess liquid-like slippery features. This new strategy avoids the requirement and fabrication of complex micro-/nano-scale surface structures and infused lubricant oils in conventional slippery surfaces. The as-prepared functional MD(SH)M surfaces allow facile transport of bubbles in aqueous media and water drops in oil, as well as facilitate the self-assembly of nanoparticles from their aqueous suspensions. The transport of air bubbles and water drops is driven by the buoyancy force or gravity force, against the sliding resistance associated with the bubble-solid-water or drop-solid-oil three-phase contact line. The functional slippery surfaces with lower surface energy and contact angle hysteresis show higher velocity of transporting bubbles/drops under the same test conditions, demonstrating better slippery behavior. The as-prepared functional slippery solid surfaces allow the three-phase contact line to move more freely as compared to the conventional lubricant liquid-infused slippery surfaces. This research provides a new and facile strategy for the fabrication of novel slippery coatings without the need of complex micro-/nano-scale surface structures and infused lubricant oils, with great potential applications in many engineering and bioengineering processes wherever low friction forces are desired.

Recovery behaviour of shape memory polymer with laser-inscribed hierarchical micro/nanoscale features

This report studies the recovery behaviour of a shape memory polymer (SMP) with femtosecond laser-machined hierarchical micro- and nano-scale surface structures over the course of multiple deformation and recovery cycles. In an effort to identify the respective contributions of the nano and microscale texture, we investigate samples with a typical laser-induced porous network of nanostructures in comparison to microstructures such as pillars and holes of square and triangular shape covered in alike laser-induced nanostructures. Square microstructures recovered fully even after multiple cycles. In contrast, triangular shaped microstructures, which exhibited good recovery after one cycle, lost their structural integrity after multiple deformations. The difference in recovery between the different geometries is explained by the respective elongation of the geometrical features under deformation. The porous nanostructure showed poor recovery over the course of repeated deformations, which we attribute to surface energy minimization during the squeezed deformation stage. Contact angle measurements on all surfaces before and after deformations correlated well with the detailed topographical analysis. The observations of this SMP on these small scales shed some light on the limitations of these materials and of laser micromachining as an industrially versatile processing method.

Superhydrophilic Polyurethane/Polydopamine Nanofibrous Materials Enhancing Cell Adhesion for Application in Tissue Engineering.

The use of nanofibrous materials in the field of tissue engineering requires a fast, efficient, scalable production method and excellent wettability of the obtained materials, leading to enhanced cell adhesion. We proposed the production method of superhydrophilic nanofibrous materials in a two-step process. The process is designed to increase the wettability of resulting scaffolds and to enhance the rate of fibroblast cell adhesion. Polyurethane (PU) nanofibrous material was produced in the solution blow spinning process. Then the PU fibers surface was modified by dopamine polymerization in water solution. Two variants of the modification were examined: dopamine polymerization under atmospheric oxygen (V-I) and using sodium periodate as an oxidative agent (V-II). Hydrophobic PU materials after the treatment became highly hydrophilic, regardless of the modification variant. This effect originates from polydopamine (PDA) coating properties and nanoscale surface structures. The modification improved the mechanical properties of the materials. Materials obtained in the V-II process exhibit superior properties over those from the V-I, and require shorter modification time (less than 30 min). Modifications significantly improved fibroblasts adhesion. The cells spread after 2 h on both PDA-modified PU nanofibrous materials, which was not observed for unmodified PU. Proposed technology could be beneficial in applications like scaffolds for tissue engineering.

Multiscale Surface Patterning of Zirconia by Picosecond Pulsed Laser Irradiation

Abstract Irradiation of yttria-stabilized zirconia (YSZ) was performed by a picosecond pulsed laser to investigate the possibility for multiscale surface patterning. Nanoscale laser-induced periodic surface structures (LIPSS) were successfully generated inside microscale grooves over a large surface area under specific conditions. A thermally induced phase transformation of YSZ was identified after laser irradiation, and this phase transformation was restrained by reducing the laser power or the number of irradiations. Moreover, it was found that the generation of LIPSS greatly changed the surface wettability of YSZ. These results demonstrated the possibility of creating zirconia hybrid patterns with high functionality, which may expand the applications of YSZ in industry.

Decimating Spatial Frequency Components in Periodically Modulated Nanoscale Surface Structures for Sensing of Ambient Refractive Index Changes.

In our previous study, we developed an array of unique porous structures (an array of barnacle-like porous structures) to apply to biosensing chips. The porous structure was formed by an internal swelling phenomenon of a polystyrene colloidal particle monolayer, which was surrounded by a poly(vinyl alcohol) layer, for the duration of the monolayer’s immersion in a toluene bath. Barnacle-like porous structures were formed when polystyrene particles that had rapidly swelled broke the outer layer around the top of the particles. However, after the surface was coated with a thin Ag layer, the porous structure showed a relatively broad extinction spectrum that was undesirable for sensing chips based on both surface plasmon extinction and grating coupling. In this paper, we propose an approach to obtain relatively sharp extinction spectra based on the decimation of the spatial frequencies of the porous structures. This study also investigates formation properties in more detail to control the structural features of the resultant porous structures. A relatively sharp peak in the extinction spectrum was ultimately obtained.

Nanoscale surface structures of DNA bound to Deinococcus radiodurans HU unveiled by atomic force microscopy.

The Deinococcus radiodurans protein HU (DrHU) was shown to be critical for nucleoid activities, yet its functional and structural properties remain largely unexplored. We have applied atomic force microscopy (AFM) imaging to study DrHU binding to pUC19-DNA in vitro and analyzed the topographic structures formed at the nanoscale. At the single-molecule level, AFM imaging allows visualization of super-helical turns on naked DNA surfaces and characterization of free DrHU molecules observed as homodimers. When enhancing the molecular surface structures of AFM images by the Laplacian weight filter, the distribution of bound DrHUs was visibly varied as a function of the DrHU/DNA molar ratio. At a low molar ratio, DrHU binding was found to reduce the volume of condensed DNA configuration by about 50%. We also show that DrHU is capable of bridging distinct DNA segments. Moreover, at a low molar ratio, the binding orientation of individual DrHU dimers could be perceived on partially "open" DNA configuration. At a high molar ratio, DrHU stiffened the DNA molecule and enlarged the spread of the open DNA configuration. Furthermore, a lattice-like pattern could be seen on the surface of DrHU-DNA complex, indicating that DrHU multimerization had occurred leading to the formation of a higher order architecture. Together, our results show that the functional plasticity of DrHU in mediating DNA organization is subject to both the conformational dynamics of DNA molecules and protein abundance.

4D electron microscopy of T cell activation

T cells can be controllably stimulated through antigen-specific or nonspecific protocols. Accompanying functional hallmarks of T cell activation can include cytoskeletal reorganization, cell size increase, and cytokine secretion. Photon-induced near-field electron microscopy (PINEM) is used to image and quantify evanescent electric fields at the surface of T cells as a function of various stimulation conditions. While PINEM signal strength scales with multiple of the biophysical changes associated with T cell functional activation, it mostly strongly correlates with antigen-engagement of the T cell receptors, even under conditions that do not lead to functional T cell activation. PINEM image analysis suggests that a stimulation-induced reorganization of T cell surface structure, especially over length scales of a few hundred nanometers, is the dominant contributor to these PINEM signal changes. These experiments reveal that PINEM can provide a sensitive label-free probe of nanoscale cellular surface structures.

Nanoscale Surface Compositions and Structures Influence Boron Adsorption Properties of Anion Exchange Resins.

Boron adsorption properties of poly(styrene-co-divinylbenzene) (PSDVB)-based anion-exchange resins with surface-grafted N-methyl-d-glucamine (NMDG) depend strongly on their local surface compositions, structures, and interfacial interactions. Distinct boron adsorption sites have been identified and quantified, and interactions between borate anions and hydroxyl groups of NMDG surface moieties have been established. A combination of X-ray photoelectron spectroscopy (XPS), solid-state nuclear magnetic resonance (NMR), and Fourier-transform infrared (FT-IR) spectroscopy were used to characterize the atomic-level compositions and structures that directly influence the adsorption of borate anions on the NMDG-functionalized resin surface. Surface-enhanced dynamic-nuclear-polarization (DNP)-NMR enabled dilute (3 atom % N) tertiary alkyl amines and quaternary ammonium ions of the NMDG groups to be detected and distinguished with unprecedented sensitivity and resolution at natural abundance 15N (0.4%). Two-dimensional (2D) solid-state 11B{1H}, 13C{1H}, and 11B{11B} NMR analyses provide direct atomic-scale evidence for interactions of borate anions with the NMDG moieties on the resin surfaces, which form stable mono- and bischelate complexes. FT-IR spectra reveal displacements in the stretching vibrational frequencies associated with the O-H and N-H bonds of NMDG groups that corroborate the formation of chelate complexes on the resin surfaces. The atomic-level compositions and structures are related to boron adsorption properties of resin materials synthesized under different conditions, which have important remediation applications.

Non-fluorinated superhydrophobic Al7075 aerospace alloy by ps laser processing

The metallic surfaces with low affinity or high repellence towards water molecules are extremely desirable. The present investigation reports the development of non-fluorinated super or ultrahydrophobic aerospace aluminum alloy (Al7075) surface by laser patterning and high vacuum process for 4 h. Lamellar and lotus leaf papillae like structures covered with nanoscale protrusions are found to be formed depends on the laser fluence and spatial shifts of laser scans. The fresh laser processed hydrophilic surface was vacuum processed to create layer of hydrocarbon to reduce the surface free energy for the wetting property transformation. The analysis of the results shows the synergistic effect of hierarchical structures and dominant presence of non-polar elements is critical for superhydrophobic property. The surface geometry is primarily responsible for the wetting property transformation by entrapping μ-volume of air to generate a composite interface of solid-gas-liquid. Micro and nanoscale (dual scale) surface structures are essential for the durable and consistent superhydrophobic property with high degree of water repellence for bigger volume of water droplets. Further, sole presence of nanoscale structures on inherent hydrophilic aluminum alloy surface with predominant presence of non-polar elements can yield only near superhydrophobic surface due to random spacing of nanoscale protrusions.