Well-ordered Surface Research Articles

Concave Cubes as Experimental Models of Catalytic Active Sites for the Oxygen-Assisted Coupling of Alcohols by Dilute (Ag)Au Alloys

A major challenge in understanding structure–function relationships in heterogeneous catalysis is bridging the materials complexity gap between the well-ordered surfaces used in fundamental experimental and computational studies and the more complex and dynamic materials that exist under catalytic operating conditions. In this work, we utilized (Ag)Au concave cube nanoparticles as experimental models to test a prediction made by theory regarding a potential bimetallic active site for the dissociation of molecular oxygen, which is a key initiating step in the selective oxygen-assisted coupling of alcohols. As a consequence of their method of synthesis, the concave cubes have surfaces that are rich in Ag-stabilized Au step edges, which is the active site proposed by theory, and thus we predicted that they would have high activity for the methanol coupling reaction. Indeed, in addition to 99% selectivity toward the desired coupling product, methyl formate, the concave cubes show a major increase in activity compared to ozone-activated nanoporous gold, a comparable dilute (Ag)Au alloy catalyst for the same reaction, even without an activating ozone pretreament. Further, the well-defined surfaces of these concave cubes open up opportunities for in-situ microscopy and spectroscopy experiments that can provide a better understanding of (Ag)Au active sites. More broadly, this work highlights how nanoparticles with controlled shapes and well-defined surfaces can be rationally tailored to experimentally validate predictions from theory.

Effects of Surfactants on the Reactivity and Durability of Shape-Controlled Pt Nanoparticles for the ORR

In the last 10 years, a broad tool of synthetic routes has been developed to prepare shape-controlled metal nanoparticles for the electrocatalytic application, e.g. oxygen reduction reaction (ORR).[1-2] They have the great potential to reduce or to close the knowledge gap between extended and well-ordered surfaces and industrially used metal nanoparticles. However, surfactants and capping agents are still required to control the growth, orientation and size of the seeds to form nano-scaled single crystals with high monodispersity. Hence, the critical challenge is to remove the adsorbed surfactant from the surface of the shape-controlled nanoparticles without any structural loss. In this work, we prepared Pt nanocubes with an edge length of 6 nm for the ORR by using different surfactants/capping agents like polyvinylpyrrolidone (PVP), oleylamine etc.. The electronic and structural interactions between the adsorbed surfactant/capping agent and the metallic surface were studied by using high resolution (scanning) transmission electron microscopy (HR-(S)TEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), thermogravimetric analysis (TGA) and fourier-transform infrared spectroscopy (FTIR). Afterwards, several conditioning strategies like electrochemical cycling, thermal annealing and chemical treatment were applied to increase the number of exposed surface Pt atoms for the ORR and to investigate their effect on the structural stability of the Pt nanocubes. The effectiveness of the conditioning processes was compared with each other. Based on these results, a matrix was developed to correlate the electrochemical parameters (scan rate, potential range, cycle number, temperature, pH value, electrolyte, etc.) with the changes of the shape structure and the catalytic properties for the ORR. In case of PVP-adsorbed Pt nanocubes, the electrochemical cycling up to 0.8 V in acidic media increases the number of exposed surface Pt atoms, while the electrochemical treatment in alkaline media produces some residuals of oxidized PVP that can stronger block the surface of the nanocubes by re-adsorption.[3] After successful cleaning process, the catalytic properties and the structural durability of the Pt nanocubes were identified during an accelerated degradation protocol. According to the thermodynamic aspect, a structural transformation of the nanocubes to spherical nanoparticles was observed. The non-stabilized corner and edge surface atoms exhibit higher surface mobility and lead to the smoothing of the particle shape. This transformation process critically depends on the upper potential, cycle number and scan rate. Our goal is to better understand the interactions between surfactant and metallic surface for the development of cleaning protocols and to fill the knowledge gap between single crystal surfaces and nano-scaled polycrystalline nanoparticles for the ORR. Reference [1] S. Guo, E. Wang, Nano Today 2011, 6, 240-264. [2] Z. Peng, H. Yang, Nano Today 2009, 4, 143-164. [3] I. A. Safo, M. Oezaslan, Electrochimica Acta 2017, just accepted.

Atomically resolved scanning force studies of vicinal Si(111)

Well-ordered stepped semiconductor surfaces attract intense attention owing to the regular arrangements of their atomic steps that makes them perfect templates for the growth of one- dimensional systems, e.g. nanowires. Here, we report on the atomic structure of the vicinal Si(111) surface with 10 degree miscut investigated by a joint frequency-modulation scanning force microscopy (FM-SFM) and ab initio approach. This popular stepped surface contains 7 x 7-reconstructed terraces oriented along the Si(111) direction, separated by a stepped region. Recently, the atomic structure of this triple step based on scanning tunneling microscopy (STM) images has been subject of debate. Unlike STM, SFM atomic resolution capability arises from chemical bonding of the tip apex with the surface atoms. Thus, for surfaces with a corrugated density of states such as semiconductors, SFM provides complementary information to STM and partially removes the dependency of the topography on the electronic structure. Our FM-SFM images with unprecedented spatial resolution on steps confirm the model based on a (7 7 10) orientation of the surface and reveal structural details of this surface. Two different FM-SFM contrasts together with density functional theory calculations explain the presence of defects, buckling and filling asymmetries on the surface. Our results evidence the important role of charge transfers between adatoms, restatoms, and dimers in the stabilisation of the structure of the vicinal surface.

Ge(001) surface cleaning methods for device integration

In recent years, research on Ge nanodevices has experienced a renaissance, as Ge is being considered a possible high mobility channel material replacement for Si MOSFET devices. However, for reliable high performance devices, an atomically flat and perfectly clean Ge surface is of utmost importance. In this review, the existing methods for cleaning the Ge(001) surface are reviewed and compared for the first time. The review discusses three broad categories of cleaning techniques that have been successfully demonstrated to obtain a clean Ge surface. First, the use of ultraviolet light and/or oxygen plasma is discussed. Both techniques remove carbon contamination from the Ge surface and simultaneously form an oxide passivation layer. Second, in situ ion sputtering in combination with germanium regrowth, which can lead to extremely clean and well-ordered Ge surfaces, is discussed. Finally, various wet-etching recipes are summarized, with focus on hydrofluoric acid (HF), NH4OH, and HCl. Despite the success of HF for Si surface preparation, it is demonstrated that in the case of Ge, HF is outperformed by other chemicals with respect to surface roughness, carbon and oxide removal efficiency. It is shown that several cleaning methods can lead to a perfectly clean Ge surface, but only a few methods can be considered for actual device integration due to their effectiveness, simplicity, and scaling ability.

Design and Development of Instrumentations for the Preparation of Platinum Single Crystals for Electrochemistry and Electrocatalysis Research. Part 2: Orientation, Cutting, and Annealing

In this contribution, which is the second paper in a series, we report on the design and development of several pieces of equipment, which facilitate the preparation of a hemispherical single crystal with a desired crystallographic surface structure starting with a spherical Pt single crystal. The pieces of equipment include a dual, high-resolution charge-coupled device (CCD)-based camera for acquiring Laue X-ray back-scattering patterns to orient spherical single crystals, a precision custom-designed jig for cutting and polishing pre-oriented single crystals, and an induction annealing system with controlled gaseous atmosphere for obtaining well-ordered and defect-free single crystal surfaces. Firstly, the paper describes the dual CCD camera setup, which allows acquiring, processing, and analyzing Laue back-scattering patterns in a digital format. The single crystal holder comprising a goniometer, the CCD-based detection system, and an optomechanical system together allow simple, adaptable, quick, and accurate single crystal orientation. Secondly, the paper presents details of a high-precision jig used in the cutting and polishing of single crystals. The jig setup includes a goniometer supporting a holder in which a single crystal is mounted and two micrometers. It maintains the desired single crystal surface parallel to the polishing disk on which abrasive materials are dispersed and polishing cloths are mounted. The micrometers allow monitoring the polishing rate and maintaining the desired single crystal surface exactly parallel to the polishing disk. Thirdly, the paper describes details of the annealing system. It consists of an induction-annealing furnace with a custom-made coil, a custom-designed quartz cell that facilitates single crystal annealing under controlled atmosphere conditions. Optimization of the induction annealing parameters and conditions, which determine the final quality of single crystal surfaces, is described in detail. Finally, the paper explains the unique aspects of this setup and methodically describes the operating procedures required to obtain a hemispherical single crystal with an atomically flat surface.

Laser Processing of Low Optical Reflection Micro/Nano-patterned Si Substrates for SERS

ABSTRACTLight collection efficiency and specific molecular detection are crucial factors for the performance of bio-chemical molecule sensors. In this paper, the low optical-reflection silicon (Si) substrates which combine reduced optical reflectivity by light trapping effect and high Raman enhancement ability of gold nanoparticles (Au-NPs) coated textured Si substrates are investigated for surface-enhanced Raman scattering (SERS). A fast, single-step and highly controllable nanosecond (ns) laser processing technique is employed to fabricate textured Si substrates under ambient conditions. Parallel arrays of micro-pyramids are fabricated on Si surface by direct laser writing two-dimensional structures. SEM micrographs clearly show well-ordered surface features in the form of micro-pyramid shape with well-defined sharp tips on the laser processed Si substrates. The aggregation of Si micro/nanoparticles on Si surface forms nanocavities and nanogaps and further enhances the surface roughness in order to minimize the optical reflection. The low optical reflection Si substrates exhibit optical reflection below 15% over a broad wavelength range from 300 nm to 1200 nm. The textured Si substrates with high signal reproducibility are successfully applied as SERS substrates to detect a very small concentration of Rhodamine B molecules with an average enhancement factor of the order of ∼107. The low optical reflection and SERS signal amplification are also altered by the variation of laser pulse energy resulting into low optical reflection and high SERS signal intensity over the entire laser-patterned area. The effect of surface roughness on water contact angle was studied after the modification with Polydimethylsiloxane (PDMS), the surfaces show perfect superhydrophobicity with almost no water adhesion. This approach provides a novel high-speed and cost-effective method for fabricating SERS substrate with micro/nano-scale surfaces roughness and low optical reflection for high Raman signal enhancement.

Preparation of clean surfaces and Se vacancy formation in Bi2Se3 by ion bombardment and annealing

Bismuth Selenide (Bi2Se3) is a topological insulator (TI) with a structure consisting of stacked quintuple layers. Single crystal surfaces are commonly prepared by mechanical cleaving. This work explores the use of low energy Ar+ ion bombardment and annealing (IBA) as an alternative method to produce reproducible and stable Bi2Se3 surfaces under ultra-high vacuum (UHV). It is found that a clean and well-ordered surface can be prepared by a single cycle of 1keV Ar+ ion bombardment and 30min of annealing. Low energy electron diffraction (LEED) and detailed low energy ion scattering (LEIS) measurements show no differences between IBA-prepared surfaces and those prepared by in situ cleaving in UHV. Analysis of the LEED patterns shows that the optimal annealing temperature is ~450°C. Angular LEIS scans reveal the formation of surface Se vacancies when the annealing temperature exceeds 520°C.

SWCNT Photocatalyst for Hydrogen Production from Water upon Photoexcitation of (8, 3) SWCNT at 680-nm Light

Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n, m). Their application for solar energy conversion is difficult because of the large binding energy (>100 meV) of electron-hole pairs, known as excitons, produced by optical absorption. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C60 is the key for high power conversion efficiency. In contrast to thin film devices, photocatalytic reactions in a dispersion/solution system triggered by the photoexcitation of SWCNTs have never been reported due to the difficulty of the construction of a well-ordered surface on SWCNTs. Here, we show a clear-cut example of a SWCNT photocatalyst producing H2 from water. Self-organization of a fullerodendron on the SWCNT core affords water-dispersible coaxial nanowires possessing SWCNT/C60 heterojunctions, of which a dendron shell can act as support of a co-catalyst for H2 evolution. Because the band offset between the LUMO levels of (8, 3)SWCNT and C60 satisfactorily exceeds the exciton binding energy to allow efficient exciton dissociation, the (8, 3)SWCNT/fullerodendron coaxial photocatalyst shows H2-evolving activity (QY = 0.015) upon 680-nm illumination, which is E22 absorption of (8, 3) SWCNT.

Oxygen Vacancy Structure Associated Photocatalytic Water Oxidation of BiOCl

A central issue in understanding photocatalytic water splitting on a stoichiometric or defective nanostructured oxide surface is its adsorption mode and related reactivity. More than just improving the adsorption of water on oxide surfaces, we demonstrate in this work that surface oxygen vacancies (OVs) also offer a possibility of activating water toward thermodynamically enhanced photocatalytic water oxidation, while the water activation state, as reflected by its capability to trap holes, strongly depends on the structures of OVs. Utilizing well-ordered BiOCl single-crystalline surfaces, we reveal that dissociatively adsorbed water on the OV of the (010) surface exhibits higher tendency to be oxidized than the molecularly adsorbed water on the OV of the (001) surface. Analysis of the geometric atom arrangement shows that the OV of the BiOCl (010) surface can facilitate barrierless O–H bond breaking in the first proton removal reaction, which is sterically hindered on the OV of the BiOCl (001) surface, a...

Termination of single-crystal Bi2Se3 surfaces prepared by various methods

Bismuth Selenide (Bi2Se3) is a topological insulator with a two-dimensional layered structure that enables clean and well-ordered surfaces to be prepared by cleaving. Although some studies have demonstrated that the cleaved surface is terminated with Se, as expected from the bulk crystal structure, other reports have indicated either a Bi- or mixed-termination. Low energy ion scattering (LEIS), low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) are used here to compare surfaces prepared by ex situ cleaving, in situ cleaving, and ion bombardment and annealing (IBA) in ultra-high vacuum (UHV). Surfaces prepared by in situ cleaving and IBA are well ordered and Se-terminated. Ex situ cleaved samples could be either Se-terminated or Bi-rich, are less well ordered and have adsorbed contaminants. This suggests that a chemical reaction involving atmospheric contaminants, which may preferentially adsorb at surface defects, could contribute to the non-reproducibility of the termination.

Growth of graphene monolayer by “internal solid-state carbon source”: Electronic structure, morphology and Au intercalation

Synthesis of a graphene monolayer atop Ni(111) film deposited on HOPG using method of “internal solid-state carbon source” due to low-temperature segregation of carbon atoms through Ni film from the Ni/HOPG interface was studied by core level and valence band photoelectron spectroscopy. The atomic structure and morphology were studied by STM. It was established that the synthesis of graphene occurs via a stage of transformation from the surface carbide phase (with stoichiometry Ni2C) as a result of the surface carbide decomposition. We consider that such transformation is a necessary stage of the graphene synthesis. We have shown that the method of “solid-state carbon source” indeed results in a graphene monolayer formation on top of Ni film. A graphene monolayer begins to form even under annealing at 180°C. Formation of practically full graphene covering with well-ordered structure takes place even at temperature of 260–270°C. The formed graphene is strongly coupled to the Ni substrate. STM images show formation of well-ordered atomic hexagonal surface structure characteristic for graphene monolayer. Intercalation of Au atoms leads to formation of the p(9×9) superstructure and blocks strong coupling. It testifies that the main part of the surface is covered by epitaxial graphene on Ni.

Disentangling Catalytic Activity at Terrace and Step Sites on Selectively Ru-Modified Well-Ordered Pt Surfaces Probed by CO Electro-oxidation

In heterogeneous (electro)catalysis, the overall catalytic output results from responses of surface sites with different catalytic activities, and their discrimination in terms of what specific site is responsible for a given activity is not an easy task. Here, we use the electro-oxidation of CO as a probe reaction to access the catalytic activity of different sites on high-Miller index stepped Pt surfaces with their {110} steps selectively modified by Ru at different coverages. Data from in situ Fourier transform infrared spectroscopy and cyclic voltammetry evidence that Ru deposited on {110} steps modifies the surface in a nontrivial way, favoring only the electrocatalytic oxidation of CO over {111} terraces. Moreover, these {111} terraces become catalytically active throughout a large potential window. On the other hand, after the deposition of Ru on {110} steps, the partial oxidation of a CO adlayer (by stripping voltammetry and in situ FTIR potential steps) shows that those {110} steps that remain fr...

Water dissociation on silica in the presence of atomic platinum

We have investigated the adsorption of water on well-defined silica and silica/Pt interfaces by synchrotron X-Ray Photoelectron Spectroscopy (SXPS). For that purpose silica surfaces grown on Si have been covered with atomic platinum in order to facilitate water dissociation. Water was adsorbed from the gas phase at cryogenic temperatures and its dissociation was observed on clean and platinum coated surfaces. After desorption the adsorbed hydroxides decompose on the blank surface, whereas the hydroxides remain stable if the surface was modified with platinum.The principal reversibility of the hydroxylation process implies the necessity of point defects in order to stabilize hydroxides on well-ordered silica surfaces. Deposited platinum atoms are able to stabilize hydroxides in their proximity and act as an acceptor state on the silica surface.

Coupling between diffusion and orientation of pentacene molecules on an organic surface.

The realization of efficient organic electronic devices requires the controlled preparation of molecular thin films and heterostructures. As top-down structuring methods such as lithography cannot be applied to van der Waals bound materials, surface diffusion becomes a structure-determining factor that requires microscopic understanding. Scanning probe techniques provide atomic resolution, but are limited to observations of slow movements, and therefore constrained to low temperatures. In contrast, the helium-3 spin-echo (HeSE) technique achieves spatial and time resolution on the nm and ps scale, respectively, thus enabling measurements at elevated temperatures. Here we use HeSE to unveil the intricate motion of pentacene admolecules diffusing on a chemisorbed monolayer of pentacene on Cu(110) that serves as a stable, well-ordered organic model surface. We find that pentacene moves along rails parallel and perpendicular to the surface molecules. The experimental data are explained by admolecule rotation that enables a switching between diffusion directions, which extends our molecular level understanding of diffusion in complex organic systems.

Growth and termination of a rutile IrO2(100) layer on Ir(111)

We investigated the oxidation of Ir(111) by gas-phase oxygen atoms at temperatures between 500 and 625K using temperature programmed desorption (TPD), low energy electron diffraction (LEED), low energy ion scattering spectroscopy (LEISS) and density functional theory (DFT) calculations. We find that a well-ordered surface oxide with (√3×√3)R30° periodicity relative to Ir(111) develops prior to the formation of a rutile IrO2(100) layer. The IrO2(100) layer reaches a saturation thickness of about four oxide layers under the oxidation conditions employed, and decomposes during TPD to produce a single, sharp O2 desorption peak at ~770K. Favorable lattice matching at the oxide-metal interface is likely responsible for the preferential growth of the IrO2(100) facet during the initial oxidation of Ir(111), with the resulting coincidence lattice generating a clear (6×1) moiré pattern in LEED. Temperature programmed reaction spectroscopy (TPRS) experiments reveal that CO and H2O molecules bind only weakly on the IrO2(100) surface and LEISS measurements show that the oxide surface is highly enriched in O-atoms. These characteristics provide strong evidence that the rutile IrO2(100) layer is oxygen-terminated, and thus lacks reactive Ir atoms that can strongly bind molecular adsorbates. Oxygen binding energies predicted by DFT suggest that on-top O-atoms will remain adsorbed on IrO2(100) at temperatures up to ~625K, thus supporting the conclusion that the rutile IrO2 layer grown in our experiments is oxygen-terminated. As such, the appearance of only a single O2 TPD peak indicates that the singly coordinate, on-top O-atoms remain stable on the IrO2(100) surface up to temperatures at which the oxide layer begins to thermally decompose.

Atomic-Scale Imaging of the Surface Dipole Distribution of Stepped Surfaces.

Stepped well-ordered semiconductor surfaces are important as nanotemplates for the fabrication of 1D nanostructures. Therefore, a detailed understanding of the underlying stepped substrates is crucial for advances in this field. Although measurements of step edges are challenging for scanning force microscopy (SFM), here we present simultaneous atomically resolved SFM and Kelvin probe force microscopy (KPFM) images of a silicon vicinal surface. We find that the local contact potential difference is large at the bottom of the steps and at the restatoms on the terraces, whereas it drops at the upper part of the steps and at the adatoms on the terraces. For the interpretation of the data we performed density functional theory (DFT) calculations of the surface dipole distribution. The DFT images accurately reproduce the experiments even without including the tip in the calculations. This underlines that the high-resolution KPFM images are closely related to intrinsic properties of the surface and not only to tip-surface interactions.

Ordered Fe(II)Ti(IV)O3 Mixed Monolayer Oxide on Rutile TiO2(011).

Oxide monolayers supported or intermixed with an oxide support are potential nanocatalysts whose properties are determined by the interplay with the support. For fundamental studies of monolayer oxides on metal oxide supports, well-defined systems are needed, but so far, the synthesis of monolayer oxides with long-range order on single-crystal oxide surfaces is rare. Here, we show by a combination of scanning tunneling microscopy, photoemission spectroscopy, and density functional theory (DFT)-based computational analysis that the rutile TiO2(011) surface supports the formation of an ordered mixed FeTiO3 monolayer. Deposition of iron in a slightly oxidizing atmosphere (10(-8) Torr O2) and annealing to 300 °C results in a well-ordered surface structure with Fe in a 2+ charge state and Ti in a 4+ charge states. Low-energy ion scattering suggests that the cation surface composition is close to half Fe and half Ti. This surface is stable in ultrahigh vacuum to annealing temperatures of 300 °C before the iron is reduced. DFT simulations confirm that a surface structure with coverage of 50% FeO units is stable and forms an ordered structure. Although distinct from known bulk phases of the iron-titanium oxide systems, the FeTiO3 monolayer exhibits some resemblance to the ilmenite structure, which may suggest that a variety of different mixed oxide phases (of systems that exist in a bulk ilmenite phase) may be synthesized in this way on the rutile TiO2(011) substrate.

Structure and morphology of epitaxially grown Fe3O4/NiO bilayers on MgO(001)

Crystalline Fe3O4/NiO bilayers were grown on MgO(001) substrates using reactive molecular beam epitaxy to investigate their structural properties and their morphology. The film thickness either of the Fe3O4 film or of the NiO film has been varied to shed light on the relaxation of the bilayer system. The surface properties as studied by X-ray photoelectron spectroscopy and low energy electron diffraction show clear evidence of stoichiometric well-ordered film surfaces. Based on the kinematic approach X-ray diffraction experiments were completely analyzed. As a result the NiO films grow pseudomorphic in the investigated thickness range (up to 34nm) while the Fe3O4 films relax continuously up to the thickness of 50nm. Although all diffraction data show well developed Laue fringes pointing to oxide films of very homogeneous thickness, the Fe3O4/NiO interface roughens continuously up to 1nm root-mean-square roughness with increasing NiO film thickness while the Fe3O4 surface is very smooth independent on the Fe3O4 film thickness. Finally, the Fe3O4/NiO interface spacing is similar to the interlayer spacing of the oxide films while the NiO/MgO interface is expanded.

Establishing a Link between Well-Ordered Pt(100) Surfaces and Real Systems: How Do Random Superficial Defects Influence the Electro-oxidation of Glycerol?

Glycerol (GlOH) accumulation and its very low price constitute a real problem for the biodiesel industry. To overcome these problems, it is imperative to find new GlOH applications. In this context, electrochemistry arises as an important alternative to the production of energy or fine chemicals using GlOH as a reactant. To make these opportunities a reality, it is fundamentally necessary to understand how the glycerol electro-oxidation reaction (GEOR) occurs on catalysts used in real systems. Thus, research using model surfaces has generated the first insight into the electrochemistry of extremely complex real catalysts. Accordingly, in this work, we generate Pt(100) disturbed surfaces in a reproducible manner, carefully controlling the surface defect density. Then, GEOR is studied on well-ordered Pt(100) and on the disturbed Pt(100) surfaces in 0.5 M H2SO4 using cyclic voltammetry (CV) and in situ Fourier transform infrared spectroscopy (FTIR). The CV profile of GEOR consists of a single peak in the positive scan. The onset reaction displays the influence of defects present on the surface. On a surface with a high degree of disorder, the main GlOH oxidation process begins at 0.8 V vs RHE, whereas for well-ordered Pt(100), it starts 0.1 V earlier. FTIR experiments show the presence of carbon monoxide and carbonyl absorption bands. The electrochemical and spectroelectrochemical results are supported by density functional theory calculations showing that both CO and GlOH bind more strongly on disturbed than on well-ordered surfaces. Thus, our experiments show that Pt–CO (or other GlOH residue) bond breaking may be the GEOR rate-determining step.

Surface Wrinkling Patterns of Film–Substrate Systems With a Structured Interface

Wrinkling of thin films resting on compliant substrates has emerged as a facile means to create well-ordered surface patterns. In this paper, both theoretical analysis and numerical simulations are presented to study the surface wrinkling of a film–substrate system with periodic interfacial structures. It is demonstrated that a variety of novel surface wrinkling patterns can be generated through the introduction of interfacial architectures. These surface patterns can be easily tuned by adjusting two geometric parameters: the lengths of the thin films in the thick and the thin regions. A phase diagram is established for the onset of different wrinkling morphologies with respect to the two geometric dimensions. This study offers a promising route for engineering the surfaces of materials endowed with tunable properties and functions.