Substrate Topography Research Articles

Effect of soft substrate topography on tribological behavior of multifunctional DLC coatings

In this study, the influence of soft substrate surface finishing (5 distinct conditions) on tribological properties of hydrogenated amorphous carbon (a-C:H) films is investigated. Low carbon steel substrates were plasma-nitrided and DLC-coated in a single PECVD batch. Topographical evolution was investigated through white light interferometry (WLI) and scanning electron microscopy (SEM). The substrate topography leads to a negligible impact on bonding structure and mechanical properties of a-C:H films, which were analyzed by Raman spectroscopy (RS) and nano-indentation. The nitriding and deposition process resulted in two groups of samples regarding the topographic features: (A) Rough—Sq coated ≈ 0.17–0.23 µm; (B) Smooth—Sq coated ≈ 0.08–0.11 µm. Tribological performance of multifunctional coatings under incremental normal load reciprocating dry sliding tests in ambient air revealed friction coefficients of 0.09 (Rough) and 0.05 (Smooth). Wear scars were analyzed by WLI, SEM and RS. The results suggest that rougher substrates inhibit tribolayer formation and stability, leading to higher friction coefficients.

The Role of Liquid Ink Transport in the Direct Placement of Quantum Dot Emitters onto Sub-Micrometer Antennas by Dip-Pen Nanolithography.

Dip-pen nanolithography (DPN) is used to precisely position core/thick-shell ("giant") quantum dots (gQDs; ≥10 nm in diameter) exclusively on top of silicon nanodisk antennas (≈500 nm diameter pillars with a height of ≈200 nm), resulting in periodic arrays of hybrid nanostructures and demonstrating a facile integration strategy toward next-generation quantum light sources. A three-step reading-inking-writing approach is employed, where atomic force microscopy (AFM) images of the pre-patterned substrate topography are used as maps to direct accurate placement of nanocrystals. The DPN "ink" comprises gQDs suspended in a non-aqueous carrier solvent, o-dichlorobenzene. Systematic analyses of factors influencing deposition rate for this non-conventional DPN ink are described for flat substrates and used to establish the conditions required to achieve small (sub-500 nm) feature sizes, namely: dwell time, ink-substrate contact angle and ink volume. Finally, it is shown that the rate of solvent transport controls the feature size in which gQDs are found on the substrate, but also that the number and consistency of nanocrystals deposited depends on the stability of the gQD suspension. Overall, the results lay the groundwork for expanded use of nanocrystal liquid inks and DPN for fabrication of multi-component nanostructures that are challenging to create using traditional lithographic techniques.

Substrate Topography Modulates Cell Aging on a Progeria Cell Model.

Aging is characterized by a progressive accumulation of cellular damage, which leads to impaired function. Little is known whether substrates can influence cell aging. This is of utmost importance in the development of medical devices that are in contact with human tissue for long periods of time. To address this question, we have used an accelerated aging cell model derived from Hutchinson-Gilford Progeria Syndrome (HGPS) induced pluripotent stem cells (iPSCs). Our results show that HGPS-iPSC smooth muscle cells (SMCs) have an increased aging profile in substrates with specific micropatterns than in flat ones. This is characterized by an up-regulation in the expression of progerin, β-galactosidase, annexin 3 and 5, and caspase 9. Signs of cell aging are also observed in SMCs without HGPS cultured in substrates with specific microtopographies. It is further showed that specific micropatterned substrates induce cell aging by triggering a DNA damage program likely by the disruption between cyto- and nucleoskeleton.

Human mesenchymal stem cell basal membrane bending on gratings is dependent on both grating width and curvature

The topography of the extracellular substrate provides physical cues to elicit specific downstream biophysical and biochemical effects in cells. An example of such a topographical substrate is periodic gratings, where the dimensions of the periodic gratings influence cell morphology and directs cell differentiation. We first develop a novel sample preparation technique using Spurr’s resin to allow for cross-sectional transmission electron microscopy imaging of cells on grating grooves, and observed that the plasma membrane on the basal surface of these cells can deform and bend into grooves between the gratings. We postulate that such membrane bending is an important first step in eliciting downstream effects. Thus, we use a combination of image analysis and mathematical modeling to explain the extent of bending of basal membrane into grooves. We show that the extent to which the basal membrane bends into grooves depends on both groove width and angle of the grating ridge. Our model predicts that the basal membrane will bend into grooves when they are wider than 1.9 µm in width. The existence of such a threshold may provide an explanation for how the width of periodic gratings may bring about cellular downstream effects, such as cell proliferation or differentiation.

Graphene transport mediated by micropatterned substrates

Engineered substrates offer a promising avenue towards graphene devices having tunable properties. In particular, topographically patterned substrates can expose unique behavior due to their ability to induce local variations in strain and electrostatic doping. However, to explore the range of possible science and applications, it is important to create topographic substrates that both have tunable features and are suitable for transport measurements. In this letter, we describe the fabrication of tunable, topographically patterned substrates suitable for transport measurements. We report both optical and transport measurements of graphene devices fabricated on these substrates and demonstrate the characteristic strain and local doping behavior induced by the topographic features.

Effect of laser ablation treatment on corrosion resistance of adhesive-bonded Al alloy joints

Laser ablation treatment modifies the chemical property (i.e. increased surface oxide layer) and topography (i.e. rough surface microstructures) of Al alloy substrates, and both aspects are considered as contributing factors to the corrosion resistance of adhesive-bonded joints. To analyze the effects of modified chemical property and topography on corrosion resistance of adhesive-bonded Al alloy joints, the laser ablation treatments were applied to Al alloy with/without argon shielding gas and in different power levels. Results show that although the increased surface oxide layer resulting from laser ablation treatment greatly improves the corrosion resistance of Al alloy substrate, it has negligible effect on corrosion resistance of adhesive-bonded Al alloy joints. Nevertheless, the modified surface topography has a significant effect on corrosion resistance of adhesive-bonded Al alloy joints. The bonding interfaces of joints fabricated from Al alloy substrates with relatively smooth surface topography are continuously broken by salt solution with the extension of corrosion exposure time, which changes the failure mode from cohesive to adhesive failure. The rough surface topography prevents the diffusion of salt solution through the Al/adhesive bonding interface and consequently protects Al alloy from being corroded, which results in better corrosion resistance of adhesive-bonded Al alloy joints.

Tuning Material Properties of Oxides and Nitrides by Substrate Biasing during Plasma-Enhanced Atomic Layer Deposition on Planar and 3D Substrate Topographies.

Oxide and nitride thin-films of Ti, Hf, and Si serve numerous applications owing to the diverse range of their material properties. It is therefore imperative to have proper control over these properties during materials processing. Ion-surface interactions during plasma processing techniques can influence the properties of a growing film. In this work, we investigated the effects of controlling ion characteristics (energy, dose) on the properties of the aforementioned materials during plasma-enhanced atomic layer deposition (PEALD) on planar and 3D substrate topographies. We used a 200 mm remote PEALD system equipped with substrate biasing to control the energy and dose of ions by varying the magnitude and duration of the applied bias, respectively, during plasma exposure. Implementing substrate biasing in these forms enhanced PEALD process capability by providing two additional parameters for tuning a wide range of material properties. Below the regimes of ion-induced degradation, enhancing ion energies with substrate biasing during PEALD increased the refractive index and mass density of TiOx and HfOx and enabled control over their crystalline properties. PEALD of these oxides with substrate biasing at 150 °C led to the formation of crystalline material at the low temperature, which would otherwise yield amorphous films for deposition without biasing. Enhanced ion energies drastically reduced the resistivity of conductive TiNx and HfNx films. Furthermore, biasing during PEALD enabled the residual stress of these materials to be altered from tensile to compressive. The properties of SiOx were slightly improved whereas those of SiNx were degraded as a function of substrate biasing. PEALD on 3D trench nanostructures with biasing induced differing film properties at different regions of the 3D substrate. On the basis of the results presented herein, prospects afforded by the implementation of this technique during PEALD, such as enabling new routes for topographically selective deposition on 3D substrates, are discussed.

Nanopatterning via Self-Assembly of a Lamellar-Forming Polystyrene-block-Poly(dimethylsiloxane) Diblock Copolymer on Topographical Substrates Fabricated by Nanoimprint Lithography.

The self-assembly of a lamellar-forming polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) diblock copolymer (DBCP) was studied herein for surface nanopatterning. The DBCP was synthesized by sequential living anionic polymerization of styrene and hexamethylcyclotrisiloxane (D3). The number average molecular weight (Mn), polydispersity index (Mw/Mn) and PS volume fraction (φps) of the DBCP were MnPS = 23.0 kg mol−1, MnPDMS = 15.0 kg mol−1, Mw/Mn = 1.06 and φps = 0.6. Thin films of the DBCP were cast and solvent annealed on topographically patterned polyhedral oligomeric silsesquioxane (POSS) substrates. The lamellae repeat distance or pitch (λL) and the width of the PDMS features (dL) are ~35 nm and ~17 nm, respectively, as determined by SEM. The chemistry of the POSS substrates was tuned, and the effects on the self-assembly of the DBCP noted. The PDMS nanopatterns were used as etching mask in order to transfer the DBCP pattern to underlying silicon substrate by a complex plasma etch process yielding sub-15 nm silicon features.

Sol-gel TiO2 colloidal suspensions and nanostructured thin films: structural and biological assessments

The role of substrate topography in phenotype expression of in vitro cultured cells has been widely assessed. However, the production of the nanostructured interface via the deposition of sol-gel synthesized nanoparticles (NPs) has not yet been fully exploited. This is also evidenced by the limited number of studies correlating the morphological, structural and chemical properties of the grown thin films with those of the sol-gel ‘brick’ within the framework of the bottom-up approach. Our work intends to go beyond this drawback presenting an accurate investigation of sol-gel TiO2 NPs shaped as spheres and rods. They have been fully characterized by complementary analytical techniques both suspended in apolar solvents, by dynamic light scattering (DLS) and nuclear magnetic resonance (NMR) and after deposition on substrates (solid state configuration) by transmission electron microscopy (TEM) and powder x-ray diffraction (PXRD). In the case of suspended anisotropic rods, the experimental DLS data, analyzed by the Tirado-Garcia de la Torre model, present the following ranges of dimensions: 4–5 nm diameter (∅) and 11–15 nm length (L). These results are in good agreement with that obtained by the two solid state techniques, namely 3.8(9) nm ∅ and 13.8(2.5) nm L from TEM and 5.6(1) ∅ and 13.3(1) nm L from PXRD data. To prove the suitability of the supported sol-gel NPs for biological issues, spheres and rods have been separately deposited on coverslips. The cell response has been ascertained by evaluating the adhesion of the epithelial cell line Madin–Darby canine kidney. The cellular analysis showed that titania films promote cell adhesion as well clustering organization, which is a distinguishing feature of this type of cell line. Thus, the use of nanostructured substrates via sol-gel could be considered a good candidate for cell culture with the further advantages of likely scalability and interfaceability with many different materials usable as supports.

Microenvironmental Regulation of Stem Cell Behavior Through Biochemical and Biophysical Stimulation.

Stem cells proliferate by undergoing self-renewal and differentiate into multiple cell lineages in response to biochemical and biophysical stimuli. Various biochemical cues such as growth factors, nucleic acids, chemical reagents, and small molecules have been used to induce stem cell differentiation or reprogramming or to maintain their pluripotency. Moreover, biophysical cues such as matrix stiffness, substrate topography, and external stress and strain play a major role in modulating stem cell behavior. In this chapter, we have summarized microenvironmental regulation of stem cell behavior through biochemical and biophysical stimulation.

Modification of the titanium implants surface with TiO2 coatings obtained by sol-gel method via dip-coating

Within the framework of the study, TiO2 coatings were obtained by sol-gel method via dip-coating. For the films obtaining, manual drawing the substrate from the solution at a relatively high rate of 30 mm / min and automated drawing from the solution at low drawing rates (from 1 to 10 mm / min) were used. The morphology of coatings has been studied by scanning electron microscopy. The influence of the mode and the rate of drawing of the substrate from the solution on the films morphology was demonstrated. Analysis of the data showed, that the surface morphology of the coatings obtained at lower drawing rates by an automated method is much more homogeneous - the titanium dioxide films completely repeats the topography of the substrate surface, there are practically no fissures. Qualitative coatings of titanium dioxide, completely replicating the surface relief of the substrate, can be obtained by this method. Selection of the substrate drawing rate allows reducing the influence of the substrate topography and avoiding the appearance of crystallization centers, and as a consequence, the appearance of defects in the morphology of coatings, such as fissures or microparticles.

Anisotropic Growth of Otavite on Calcite: Implications for Heteroepitaxial Growth Mechanisms

Elucidating the molecular-scale mechanisms driving complex growth behaviors during heteroepitaxial growth in aqueous media has remained a challenging endeavor. Toward this goal, in situ atomic force microscopy was employed to image the heteroepitaxial growth of otavite (CdCO3) at the (1014) surface of calcite (CaCO3) single crystals in static aqueous conditions. Heteroepitaxial growth proceeded via spreading of three-dimensional (3D) islands and two-dimensional (2D) atomic layers at low and high initial saturation levels, respectively. Experiments were carried out as a function of applied force and imaging mode thus enabling determination of growth mechanisms unaltered by imaging artifacts. This approach revealed the significant anisotropic nature of heteroepitaxial growth on calcite in both growth modes and its dependence on supersaturation, film thickness, and substrate topography. The 3D islands not only grew preferentially along the [421] direction relative to the [010] direction, resulting in rod-l...

Tightly adhering diamond-like carbon films on copper substrates by oxygen pre-implantation

Copper is one of the substrates that are difficult to coat with a diamond-like carbon film because of the latter's poor adhesion. Two factors that can improve the adhesion in this case are the surface roughness and the oxidation of the surface. The dependence of the adhesive strength of the diamond-like carbon film on both factors was measured for samples that were prepared by a plasma process using a pulsed voltage. The main parameter was the ion energy of the oxygen ions. For pulse voltages higher than −16kV a drastically increased adhesion was found, correlated to a rough surface and the presence of Cu2O in the interface. The adhesive strength of the film surpasses the maximum amount that can be measured with a pull test. The same good adhesion can be realized at lower voltages by changing the plasma gas to a mixture of oxygen and argon. The additional argon changes the surface topography of a polycrystalline copper substrate.

Responsiveness of voltage-gated calcium channels in SH-SY5Y human neuroblastoma cells on micropillar substrates

In this study, poly-L-lactic acid micropillar substrates were fabricated to evaluate the influence of topographic substrates on cell morphological and functional characteristics, such as spreading area, voltage-gated calcium channels (VGCCs) and membrane potential. The proliferation, spreading area, perimeter and circularity of SH-SY5Y cells interfaced with different substrates were first investigated. In addition, the cytoskeleton and focal adhesion of a cell as important manifestations of cell morphology were analyzed by immunofluorescence. VGCC responsiveness was evaluated by measuring the dynamic changes in intracellular Ca2+ evoked by 50 mM extracellular K+. To determine study whether the differences in VGCC responsiveness were caused by the differences in VGCC gene expression, the expression of N/L- type VGCCs was determined by qPCR and fluorescence staining. Notably, improved measurement of the membrane potential with potentiometric fluorescent dye TMRM was applied to determine the membrane potential of SH-SY5Y cells. Results indicated that the SH-SY5Y cells were deformed significantly to adapt to the substrates; however, no distinct effect on the proliferative ability of SH-SY5Y cells was observed. The micropillar substrates markedly influenced VGCC responsiveness, which correlated strongly with cell spreading but not with VGCC expression. The resting membrane potential of SH-SY5Y cells cultured on different substrates also changed, but no effect on responsiveness of VGCC was observed. These results suggest that the effect of the micropillar substrates on cell VGCC responsiveness may be attributed to changes in the functionality of the ion channel itself. Thus, topographic substrates can be used to engineer cell functionality in cell-based drug screening.

Nanotopographic Regulation of Human Mesenchymal Stem Cell Osteogenesis.

Mesenchymal stem cell (MSC) differentiation can be manipulated by nanotopographic interface providing a unique strategy to engineering stem cell therapy and circumventing complex cellular reprogramming. However, our understanding of the nanotopographic-mechanosensitive properties of MSCs and the underlying biophysical linkage of the nanotopography-engineered stem cell to directed commitment remains elusive. Here, we show that osteogenic differentiation of human MSCs (hMSCs) can be largely promoted using our nanoengineered topographic glass substrates in the absence of dexamethasone, a key exogenous factor for osteogenesis induction. We demonstrate that hMSCs sense and respond to surface nanotopography, through modulation of adhesion, cytoskeleton tension, and nuclear activation of TAZ (transcriptional coactivator with PDZ-binding motif), a transcriptional modulator of hMSCs. Our findings demonstrate the potential of nanotopographic surfaces as noninvasive tools to advance cell-based therapies for bone engineering and highlight the origin of biophysical response of hMSC to nanotopography.

Foraging Fish as Zoogeomorphic Agents: An Assessment of Fish Impacts at Patch, Barform, and Reach Scales

AbstractFlume studies have demonstrated that foraging by fish can modify the structure and topography of gravel substrates, thereby increasing particle entrainment probabilities and the amount of sediment mobilized during subsequent experimental high flows. However, the zoogeomorphic impact of benthic foraging has not previously been investigated in the field. This paper reports field experiments that examined the nature and extent of disturbance of riverbed gravels by foraging fish, predominately Cyprinids, at patch, riffle, and reach scales and complementary ex situ experiments of the impacts on bed stability. At patch scale, benthic feeding fish displaced particle sizes ≤90 mm in diameter, increased bed surface microtopography and grain protrusion, and loosened surface structures. Although enhanced mobility was expected from these structural changes, foraging also caused localized coarsening of sediments, and the ex situ experiments recorded significantly reduced grain entrainment, bedload flux, and total transported mass from foraged patches. Foraging disturbed bed materials at all 12 riffles in the study reach and, on average, disturbed 26.1% of riffle area per 24 h feeding period. These findings demonstrate for the first time that foraging fish, which are widespread and feed perennially, can act as zoogeomorphic agents in rivers, affecting grain‐size distributions and bed material structure, with potential implications for bed stability and bedload transport at reach and river scales. Whether fish increase or reduce bed mobility is probably dependent on a host of factors, including the net effects of both structural disturbance and biogenic particle sorting, as these affect entrainment stresses under subsequent competent flows.

Investigation of surface topography and stiffness on adhesion and neurites extension of PC12 cells on crosslinked silica aerogel substrates.

Fundamental understanding and characterization of neural response to substrate topography is essential in the development of next generation biomaterials for nerve repair. Aerogels are a new class of materials with great potential as a biomaterial. In this work, we examine the extension of neurites by PC12 cells plated on matrigel-coated and collagen-coated mesoporous aerogel surfaces. We have successfully established the methodology for adhesion and growth of PC12 cells on polyurea crosslinked silica aerogels. Additionally, we have quantified neurite behaviors and compared their response on aerogel substrates with their behavior on tissue culture (TC) plastic, and polydimethylsiloxane (PDMS). We found that, on average, PC12 cells extend longer neurites on crosslinked silica aerogels than on tissue culture plastic, and, that the average number of neurites per cluster is lower on aerogels than on tissue culture plastic. Aerogels are an attractive candidate for future development of smart neural implants and the work presented here creates a platform for future work with this class of materials as a substrate for bioelectronic interfacing.

Role of microtopography in the expression of soil propagule banks on reclamation sites

The legacy propagule banks of salvaged topsoils are excellent sources of plant propagules for reclamation of mine sites; however, earlier studies show that less than 50% of the species found in original propagule banks actually establish. We hypothesize that the expression of this legacy propagule bank is limited by a lack of diversity of microsites and appropriate growing conditions. In an operational‐scale field experiment we manipulated topographical characteristics and substrate materials and explored early vegetation establishment on an east‐ and south‐facing slope. Three different site treatments with different microtopographic characteristics: (1) leveled surface, (2) parallel ridges, and (3) large loose piles were created using salvaged upland and lowland forest floor soil materials. Placing materials in loose hills and providing heterogeneity in substrates more than doubled plant abundance, species richness, and increased the proportion of species that require higher soil moisture. Lower micro‐elevations and northern microaspects of the microtopographic treatments had up to three times higher soil water content and double the species richness. However, the overall slope aspect had a modulating effect on microtopographic positions. The greatest treatment effect of micro‐elevation and microaspect on species richness and plant abundance occurred on the east‐facing slope, while the greatest effect of treatment on the proportion of species requiring higher soil moisture conditions was observed on the south‐facing slope. Variability in microtopography and substrate can create favorable growing conditions at an operational scale and help express a wider range of species from the legacy propagule bank.

Theory of Finite-Length Grain Boundaries of Controlled Misfit Angle in Two-Dimensional Materials.

Grain boundaries in two-dimensional crystals are usually thought to separate distinct crystallites and as such they must either form closed loops or terminate at the boundary of a sample. However, when an atomically thin two-dimensional crystal grows on a substrate of nonzero Gaussian curvature, it can develop finite-length grain boundaries that terminate abruptly within a monocrystalline domain. We show that by properly designing the substrate topography, these grain boundaries can be placed at desired locations and at specified misfit angles, as the thermodynamic ground state of a two-dimensional (2D) system bound to a substrate. Compared against the hypothetical competition of growing defectless 2D materials on a Gaussian-curved substrate with consequential fold development or detachment from the substrate, the nucleation and formation of finite-length grain boundaries can be made energetically favorably given sufficient substrate adhesion on the order of tens of meV/Å2 for typical 2D materials. New properties specific to certain grain boundary geometries, including magnetism and metallicity, can thus be engineered into 2D crystals through topographic design of their substrates.

Experimental Analysis on the Molten-Phase Dewetting Characteristics of AuPd Alloy Films on Topographically-Structured Substrates

AuPd nanoparticles are formed on fluorine-doped tin oxide (FTO) by a nanosecond laser irradiation-induced dewetting process of deposited AuPd films. In particular, we analyze the effect of the surface topography of the substrate on the dewetting process and, so, on the final mean size of the formed nanoparticles. In fact, we used two supporting FTO substrates differing in the surface topography: we used a FTO layer which is un-intentionally patterned since it is formed by FTO pyramids randomly distributed on the glass slide as result of the deposition process of the same FTO layer, namely substrate A. We used, also, a further FTO substrate, namely substrate B, presenting, as a result of a chemical etching process, a higher roughness and higher mean distance between nearest-neighbor pyramids with respect to substrate A. The results concerning the size of the obtained AuPd NPs by the laser irradiations with the laser fluence fixed shows that the substrate topography impacts on the dewetting process. In particular, we found that below a critical thickness of the deposited AuPd film, the NPs formed on substrates A and B have similar size and a similar trend for the evolution of their size versus the film thickness (i.e., the dewetting process is not influenced by the substrate topography since the film does not interact with the substrate topography). On the other hand, however, above a critical thickness of the deposited AuPd film, the AuPd NPs show a higher mean size (versus the film thickness) on substrate B than on substrate A, indicating that the AuPd film interacts with the substrate topography during the dewetting process. These results are quantified and discussed by the description of the substrate topography effect on the excess of chemical potential driving the dewetting process.