Periodic Surface Microstructures Research Articles

A Review on Measurement of Spectral Directional Emissivity of Microstructured Surfaces in Infrared Wavelength Range

A survey of researches in the field of spectral directional emissivity measurements of microstructured surfaces by using direct and indirect radiometric methods in infrared wavelength range is presented. Nowadays, new concepts of periodic surface microstructures with geometrical dimensions of the same order of magnitude as the thermal radiation wavelengths are becoming one of the attractive methods for controlling spectral radiative properties of a surface like emissivity and reflectivity. Since the resonance effect between the periodic microstructures and the electromagnetic field has become one of the most promising ways to vary optical or radiative properties of the radiating surfaces artificially, in this review paper emphasis is given to the measurement of directional spectral emissivity of microstructured surfaces. A review of many systems is presented that are capable of measuring the spectral directional emissivities of solid surfaces at moderate temperatures. An overview of experimental setups is provided including the reference sources of radiation, the sample clamping and heating, detection systems, methods for the determination of surface temperature and procedures for emissivity evaluation. The paper is focused on methods of finding the emissivity of microstructures. Selected experimental data in the form of graph are presented for various microstructured surfaces.

Zirconia substrate with periodic surface microstructures enhances osteogenic differentiation of rat adipose-derived stem cells

Zirconia substrates with periodic surface microstructures formed by irradiation with a femtosecond laser previously enhanced osteogenic differentiation of rat bone marrow mesenchymal stem cells (BMSCs), associated with a reduction in the cell attachment area. Adipose-derived mesenchymal stem cells (ADSCs) are clinically less difficult in harvesting the cells than BMSCs. In this study, we investigated the effects of zirconia substrates with the periodic surface microstructures on osteogenic differentiation of rat ADSCs. Zirconia substrates with the periodic surface microstructures enhanced not adipogenic differentiation but osteogenic differentiation of rat ADSCs, associated with a reduction in the cell attachment area. Therefore, zirconia substrates with surface periodic microstructures formed by irradiation with a femtosecond laser could be useful in bone tissue engineering using ADSCs when BMSCs are unavailable.

Wrinkled surface microstructure for enhancing the infrared spectral performance of radiative cooling.

Radiative cooling is a passive cooling method that does not consume additional energy and has broad application prospects. In recent studies, the surface microstructure was found to have a significant influence on improving the emissivity in infrared spectra for radiative cooling. Accordingly, in this paper, an innovative wrinkled surface microstructure without any periodicity is proposed for enhancing the infrared spectral performance of radiative cooling. The effects of the height and number of wrinkles as well as the radius and volume fraction of particles on the infrared spectral performance of radiative cooling are investigated. The radiative cooling performances of the plane, pyramid, moth-eye, and wrinkled microstructures are comparatively investigated using the finite-difference time-domain (FDTD) method. The results show that the mean emissivity of innovative radiative cooling films with the wrinkled surface microstructure reaches 99.58% in the "atmospheric window" wavelength range. The mean emissivity of the wrinkled microstructure is improved by 19%, 22.16%, and 8.41% over those of the plane, pyramid, and moth-eye microstructures, respectively. This indicates that the wrinkled microstructure exhibits a better performance for radiative cooling than single periodic surface microstructures. Furthermore, the wrinkled microstructure has no periodicity so it has low production cost, which makes it possible to replace other periodic surface microstructures.

Surface buckling with deterministic peaks/valleys regulated by bio-inspired micro-structures periodically distributed on elastic bilayers

Surface buckling for film/substrate systems has an extensive application in flexible electronics, microfluidics, and adhesives. The location of the peaks and valleys, however, is still unpredictable due to its strong dependency upon external perturbations and the inevitable edge effects. Inspired by the sharp spines on ribbed stems of an echinopsis cactus, periodic surface micro-structures, including pyramidal intaglios and pyramidal reliefs, are adopted to tune the buckling experimentally and numerically. Although the instability patterns in our research are similar to those regulated by the stiff film pattern geometry, the wavelengths are nearly uniform in the whole area without obvious edge effects in the position of the surface micro-structures. The number of the wrinkle-like patterns between two micro-structures is equal to n when the width of the normalized center to center distance d¯ is in a range of about n−0.4 to n+0.6. More importantly, the pyramidal intaglios and pyramidal reliefs have well-regulated but opposite locations in different instability patterns, which means that the peaks and valleys are predictable upon the surface buckling. The deterministic peaks/valleys of the surface instability regulated by micro-structures provides a worthy guidance on the topography design, such as the distribution of the functional components in stretchable electronics based on structural designs.

The buckling behavior of single-layer MoS2 sheets on silica substrates

The buckling of a single-layer molybdenum disulfide (SLMoS2) sheet can strongly influence its stability and reliability of MoS2-based nanodevices. In the study, the buckling behavior of SLMoS2 sheets on the silica substrate is investigated by theoretical modeling and molecular dynamics simulation. The difference between the suspended and substrate-supported SLMoS2 sheets is compared. The effect of substrate surface morphology, including the groove and periodic surface microstructure substrate, on the buckling behavior is mainly focused. It is found that the critical strain increases significantly compared with the suspended SLMoS2 sheets due to the introduction of the underlying substrate. The evolution of SLMoS2 sheets on substrates with grooves contains two different paths depending on the groove height and the width. Additionally, both the period and effective contact area of the surface microstructure have direct impacts on the critical strain. The finding of buckling behavior of SLMoS2 sheets on substrates should be helpful for the design of MoS2-based flexible electronic devices.

Formation of periodic superhydrophilic microstructures by infrared nanosecond laser processing of single-crystal silicon

The evolution of the morphology and composition of the single-crystal silicon surface irradiated by infrared and visible nanosecond laser pulses is investigated as a function of processing parameters (laser fluence, irradiation spot size, the number of pulses, background gas pressure and composition). Two types of periodic surface microstructures are obtained with IR (1064 nm) laser pulses in a narrow fluence range of 3–6 J/cm2. At a relatively low number of laser pulses applied, a grid of cleavage cracks is produced within the irradiation spot along the crystal orientation. With further Si irradiation, periodic microhillocks are formed in the nodes of the crack grid. Silicon surface with such microhillocks exhibits superhydrophilic properties which are retained during prolonged storage in air. The cracks are produced in any environment (including vacuum) but the microhillocks are observed only in the presence of oxygen. No periodic structures were observed with visible (532 nm) laser pulses. Mechanisms of nanosecond laser-induced periodic microstructure formation on silicon are discussed.

基于激光诱导表面条纹微结构的着色机理

基于激光诱导表面条纹微结构的着色机理

Diffraction grating on chalcogenide glass (GeSe5)80B20 fabricated by mask ion implantation

An approach for creating of a diffraction chalcogenide semiconductor glass grating on the surface of (GeSe5)80B20 layer by low-energy high-dose mask ion implantation is presented. During Ag+-ion implantation, Ag nanoparticles were synthesized in unprotected areas of irradiated glass. The formation of periodic surface microstructures during local ion sputtering of semiconductor glass was observed by scanning electron and atomic force microscopy. With probed a He-Ne laser the efficiency of optical diffraction grating was demonstrated.

Influence of processing parameters on surface texture homogeneity using Direct Laser Interference Patterning

Surface functionalities in the field of tribology, wettability, biocompatibility and holographic marking introduced by well-defined surface structures strongly depend on the surface texture homogeneity and quality. This work presents strategies for the fabrication of homogeneous periodic surface microstructures employing the Direct Laser Interference Patterning (DLIP) technology with the fundamental transverse mode (TEM00) emitted from a nanosecond laser source. Ti6Al4V substrates are structured using line-like patterns with spatial periods of 7.20 µm, 5.82 µm and 4.31 µm. The impact of various DLIP process parameters such as laser fluence, pulse overlap, hatch distance and spatial period on the produced surface microstructures is introduced and the consequences on the surface texture homogeneity are discussed. Large-area analysis of micro structures is carried out through white light interferometry and scanning electron microscopy. A quantitative measurement scheme of the pattern homogeneity, based on topographical properties such as kurtosis, standard deviation and mean structure height was introduced. Furthermore, the influence of a second modulation arising from the employed hatch distance has been identified. A quantitative parameter, the surface error percentage, has been introduced and employed for the characterization of pattern homogeneity. It was found that specially for larger spatial periods and surfaces treated at high laser fluence, pulse-to-pulse overlaps and a short hatch distance, the overall surface texture homogeneity could be improved up to ∼80–90%.

Effect of scanning velocity on femtosecond laser-induced periodic surface structures on HgCdTe crystal

In this paper, a femtosecond laser line-scanning irradiation was used to induce the periodic surface microstructure on HgCdTe crystal. Low spatial frequency laser induced periodic surface structures of 650–770nm and high spatial frequency laser induced periodic surface structures of 152–246nm were respectively found with different scanning speeds. The evolution process from low spatial frequency laser induced periodic surface structures to high spatial frequency laser induced periodic surface structures is characterized by scanning electron microscope. Their spatial periods deduced by using a two-dimensional Fourier transformation partly agree with the predictions of the Sipe-Drude theory. Confocal micro-Raman spectral show that the atomic arrangement of induced low spatial frequency laser-induced structures are basically consistent with the crystal in the central area of laser-scanning line, however a new peak at 164cm−1 for the CdTe-like mode becomes evident due to the Hg vaporization when strong laser ablation happens. The obtained surface periodic ripples may have applications in fabricating advanced infrared detector.

Formation of a periodic diffractive structure based on poly(methyl methacrylate) with ion-implanted silver nanoparticles

We propose to form optical diffractive elements on the surface of poly(methyl methacrylate) (PMMA) by implanting the polymer with silver ions (E = 30 keV; D = 5.0 × 1014 to 1.5 × 1017 ion/cm2; I = 2 μA/cm2) through a nickel grid (mask). Ion implantation leads to the nucleation and growth of silver nanoparticles in unmasked regions of the polymer. The formation of periodic surface microstructures during local sputtering of the polymer by incident ions was monitored using an optical microscope. The diffraction efficiency of obtained gratings is demonstrated under conditions of their probing with semiconductor laser radiation in the visible spectral range.

Anisotropic multi-step etching for large-area fabrication of surface microstructures on stainless steel to control thermal radiation

Controlling the thermal radiation spectra of materials is one of the promising ways to advance energy system efficiency. It is well known that the thermal radiation spectrum can be controlled through the introduction of periodic surface microstructures. Herein, a method for the large-area fabrication of periodic microstructures based on multi-step wet etching is described. The method consists of three main steps, i.e., resist mask fabrication via photolithography, electrochemical wet etching, and side wall protection. Using this method, high-aspect micro-holes (0.82 aspect ratio) arrayed with hexagonal symmetry were fabricated on a stainless steel substrate. The conventional wet etching process method typically provides an aspect ratio of 0.3. The optical absorption peak attributed to the fabricated micro-hole array appeared at 0.8 μm, and the peak absorbance exceeded 0.8 for the micro-holes with a 0.82 aspect ratio. While argon plasma etching in a vacuum chamber was used in the present study for the formation of the protective layer, atmospheric plasma etching should be possible and will expand the applicability of this new method for the large-area fabrication of high-aspect materials.

Prediction of the macroscopic fracture toughness of a composite/adhesive interface with periodic surface microstructures

We developed a formula for predicting the macroscopic fracture toughness of a composite/adhesive interface with periodic surface microstructures. The formula is an expression of the total energy consumption along the interface averaged by the macroscopic crack length. The formula takes the effect of the crack kinking energy into consideration to compensate for the difference between the otherwise predicted consumed energy and that determined by finite element (FE) analysis. The predictions of the developed formula indicate that the macroscopic fracture toughness increases with increasing aspect ratio and decreases with decreasing height of the microstructures, which is in agreement with the findings of our previous studies on crack growth analysis using a cohesive zone model. The validity of the formula was investigated using microstructures of various shapes and sizes, and good agreement was observed between its predictions and the results of FE analyses.

Ultrashort pulsed laser drilling and surface structuring of microholes in stainless steels

Microholes for the production of gasoline direct injection nozzles were obtained by ultrashort pulsed laser machining in martensitic stainless steels. The inner surface analysis was carried out by a specifically conceived Scanning Probe Microscopy instrument and revealed the presence of periodic surface microstructures whose formation was studied as a function of process parameters (pulse energy, repetition rate, rotational speed, drilling strategy). Experiments demonstrated that geometrical features of the microstructures can be varied by a proper parameter selection and open the perspective for an optimized process enabling a reduction of coking accumulation during service life and a more effective atomization of the fuel jet.

The formation of periodic diffractive plasmonic nanostructures with implanted copper nanoparticles by local ion etching of silica glass

Silica glass was subjected to a low-energy implantation with 40-keV Cu+ ions at a dose of 7.5 × 1016 ions/cm2 and an ion-beam current density of 5 μA/cm2 through a surface metal-wire mask with square holes of ∼40 μm. The formation of copper nanoparticles in the glass was determined from the occurrence of characteristic plasmon optical absorption and through the detection of particles using an atomic force micro- scope. The formation of periodic surface microstructures via the local etching of silica glass during implantation was observed using a scanning electron microscope. The operating efficiency of the diffractive optical plasmonic element based on silica glass microstructures with metallic copper nanoparticles was shown during its sounding by the emission of a helium-neon laser.

Pore size dependence of diffuse light scattering from anodized aluminum solar cell backside reflectors

The development of backside reflectors (BSRs) is crucial for the efficiency of future low cost thin-film silicon solar cells. In this work, the scattering efficiency of bare aluminum BSRs with different pore sizes and ordering of surface microstructures are investigated. The BSRs were fabricated by utilizing the process of self-ordering anodic oxidation on aluminum foils resulting in regions with an approximately hexagonally periodic surface microstructure. It was found that the total and diffuse light scattering reflectance spectra showed opposite tendencies when increasing the pore size of the microstructures. When the pore size was increased to 700 nm, more than 68% of the incident light with wavelengths from 250 nm to 800 nm was reflected by scattering. For a similar geometry, except that it had less ordering, this number was increased to around 80%. This large fraction of reflected light observed in the form of scattering is promising for the use of the considered geometries as BSRs in thin-film silicon solar cells.

Applied validity of effortless method for design of sinusoidal surface microstructure

With the purpose of easily analyzing and designing the transmittance performance of a sinusoidal surface microstructure, the validity of effortless methods including scalar diffraction theory and effective medium theory has been evaluated quantitatively by the comparison of diffraction efficiencies predicted from scalar theory and effective indices theory, respectively, with exact results calculated with the rigorous vector method of Fourier modal method. Generally speaking, when the normalized period of surface microstructure is less than ten wavelengths of the incident light the scalar diffraction theory is believed to be inaccurate for designing and analyzing the diffraction efficiency of surface microstructure. But, in this paper, it is found that scalar diffraction theory can be used for predicting transmittance of the optical elements when the normalized period is more than three wavelengths of incident light within the error less than 5% at normal incidence. In addition, it is generally recognized that the effective medium theory is inaccurate for analyzing periodic surface microstructure when the normalized period is more than a tenth of the wavelength of incident light. However, the results in this study shows that effective medium theory is accurate as only zero-order waves are to propagate through the surface profiles, which the maximum difference between zero-order effective indices method and rigorous vector method reaches to 1%. Besides, the limitation of both simplified theories is dependent on not only the normalized period of a surface microstructure but also the normalized groove depth. Therefore, the range of applied validity of scalar theory and effective medium theory is expanded quantitatively compared to that of previous inaccuracy application for more easily designing and analyzing a sinusoidal surface microstructure.

Generation of surface electromagnetic waves in semiconductors under the action of femtosecond laser pulses

It is demonstrated that intense photoexcitation of the surface of a semiconductor with femtosecond laser pulses can induce fundamental changes in its optical response and ensure conditions for the generation of surface electromagnetic waves of various types. The connection between electronic processes initiated in the surface layer by photoexcitation and the formation of periodic surface microstructures observed in experiments on irradiation of Si targets is considered. The importance of photoemission in the processes taking place under ultrashort excitation is confirmed.

Periodic microstructuring of iron cylinder surface in nitric acid in a magnetic field

The periodic surface microstructure of an iron cylinder is revealed under its corrosion in a solution of nitric acid in a constant magnetic field. The temporary dependencies of the microstructure parameters have been obtained for the cylinders with different diameters and lengths. The effect of microstructuring is a new example of nonlinear self-organization in a magnetic field. The results of the paper can be used for controlled etching of metallic surfaces with the help of a magnetic field application.

Iridescent colors on seashells: an optical and structural investigation of Helcion pruinosus.

Many animal species display exceptionally bright iridescent coloration caused by interference or diffraction from a periodic surface microstructure. Although many mollusks are colored, only few utilize such a form of structural coloration. We are not referring to the well-known pearly appearance that is due to the nacreous layer found on the inner surfaces of most shells, but to small brightly colored spots on the outer surface. The Helcion pruinosus is one such example. We show by optical measurements and scanning electron microscopy (SEM) that coloration in this shell is indeed of a structural nature based on thin-film interference from a layered quarter-wave stack tilted by approximately 24 degrees with respect to the outer surface. The microstructure is embedded in the transparent top layer of the shell approximately 50 microm below the surface. By comparing the SEM and optical measurements, we were able to establish that the layered structure is made from a birefringent material (crystalline aragonite) giving slightly different spectral peaks for S- and P-type reflections.