Microrelief Structures Research Articles

Formation of submicron relief structures on the surface of sapphire substrates

An analysis of technologies that allow creating microrelief structures on the surface of sapphire substrates has been carried out. It is shown that the most effective method of forming relief structures with submicron dimensions is ion beam etching through a protective mask formed by photolithography. The main problems in creating a microrelief on the surface of sapphire substrates are the removal of static electric charge in the process of ion beam etching of the substrates, as well as obtaining a protective mask with windows of specified sizes, through which etching of the sapphire substrate is performed.

Origination of free-form micro-optical elements using one- and two-photon grayscale laser lithography.

We discuss and describe the development of an origination process for planar free-form micro-optical elements from a given optical design. The targeted masters serve as origination structures for a roll-to-roll mass fabrication process. Specifically targeted are complex, optically smooth, surface relief structures with variable structure heights in the range of 1-20 µm, with typical lateral sizes of more than 5 µm. The area of the targeted masters is in the range of 1cm2. The main part of the paper is devoted to the description of a self-developed grayscale laser direct-write platform enabling one- and two-photon absorption lithography, also in combination on one and the same sample. In the following, we describe both methods and show that both lead to excellent structural quality of surface micro-relief structures. As a showcase of what the system can do in principle, we designed and fabricated free-form micro-optical elements to project light from an LED as a defined light pattern onto a wall. The proper optical functionality of the fabricated element was shown within a demonstrator setup.

Survival of polymeric microstructures subjected to interrogatory touch.

Polymeric arrays of microrelief structures have a range of potential applications. For example, to influence wettability, to act as biologically inspired adhesives, to resist biofouling, and to play a role in the "feel" of an object during tactile interaction. Here, we investigate the damage to micropillar arrays comprising pillars of different modulus, spacing, diameter, and aspect ratio due to the sliding of a silicone cast of a human finger. The goal is to determine the effect of these parameters on the types of damage observed, including adhesive failure and ploughing of material from the finger onto the array. Our experiments point to four principal conclusions [1]. Aspect ratio is the dominant parameter in determining survivability through its effect on the bending stiffness of micropillars [2]. All else equal, micropillars with larger diameter are less susceptible to breakage and collapse [3]. The spacing of pillars in the array largely determines which type of adhesive failure occurs in non-surviving arrays [4]. Elastic modulus plays an important role in survivability. Clear evidence of elastic recovery was seen in the more flexible polymer and this recovery led to more instances of pristine survivability where the stiffer polymer tended to ablate PDMS. We developed a simple model to describe the observed bending of micropillars, based on the quasi-static mechanics of beam-columns, that indicated they experience forces ranging from 10-4-10-7 N to deflect into adhesive contact. Taken together, results obtained using our framework should inform design considerations for microstructures intended to be handled by human users.

Двохелементні мікропризмові лінзи

Розглянуто оптичні параметри кругових мікропризмових заломлюючих пристроїв, які створені з двох ідентичних концентраторів світлових потоків із заданими граничними кутами заломлення променів. Виконано моделювання індикатриси променів для двохелементних рефракційних елементів. Розраховано параметри зменшення світлопропускання лінійних двохелементних пристроїв, які використовуються в офтальмології для визначення кута рефракції променів.

Моделювання та дослідження параметрів концентраторів світлових променів

Now, in many fields of applied optics, the focusing Fresnel lenses are used. Mostly, such devices are created for tracking different objects; they are used also for forming the precise visual images, even with a changing focal distance, for solar concentrators, and for many other applications. Different methods have been proposed for designing such optics. The flat focusing Fresnel structures were manufactured by the photolithography methods or by the adjustable direct laser recording with photoresists. Such methods allow the formation of known stepped structures [10–15] but the optical quality of images obtained with such aspherical surfaces is not very good. The high-quality images are not practically realized due to the defects of created aspherical surfacesHowever, for some light signal processing systems it is necessary to convert a parallel circular light beam into a uniformly illuminated light circle instead of focusing. Such transforming Fresnel lenses are often used in the optical sensor systems for imaging and optoelectronic integration or in the monitoring devices for automatically adjusting the output signal from the four-quadrant photodetectors. These structures can be easily made by a diamond cutting method [16–17]. This method provides a manufacture of Fresnel optics with refractive surfaces having minimum of optical defects due to the almost mirror-like quality of the working surfaces of the diamond cutting tools. The quality of formed images, in turn, is also very high.However, the refractive angles for sequential microprisms in the lens made but a diamond cutting can be changed only discretely, and only the discrete images can be formed. The value of above discreteness is determined by the width of the circular focusing zones, so the size of such zones should not be too large. It is proposed the method for simulating microrelief structures with the flat conical working faces for creating transforming Fresnel devices that form an almost uniformly illuminated light circle in the focal plane. The geometrical parameters of the relief for circular light beam concentrators are calculated. Some samples of such focusing microprismatic devices having been manufactured according to our simulation results were investigated experimentally. Fig.: 13. Refs: 8 titles.

Mapping of the microrelief structures using multitemporal very high resolution Space imagery

Mapping of the microrelief structures using multitemporal very high resolution Space imagery

Application of phyto-indication and radiocesium indicative methods for microrelief mapping

Remote sensing technologies are widely used for production of Digital Elevation Models (DEMs), and geomorphometry techniques are valuable tools for DEM analysis. One of the broadly used applications of these technologies and techniques is relief mapping. In the simplest case, we can identify relief structures using DEM analysis, and produce a map or map series to show the relief condition. However, traditional techniques might fail when used for mapping microrelief structures (structures below ten meters in size). In this case high microrelief dynamics lead to technological and conceptual difficulties. Moreover, erosion of microrelief structures cannot be detected at the initial evolution stage using DEM modelling and analysis only.In our study, we investigate the possibilities and specific techniques for allocation of erosion microrelief structures, and mapping techniques for the microrelief derivatives (e.g. quantitative parameters of microrelief). Our toolset includes the analysis of spatial redistribution of the soil pollutants and phyto-indication analysis, which complement the common DEM modelling and geomorphometric analysis. We use field surveys produced at the test area, which is arable territory with high erosion risks. Our main conclusion at the current stage is that the indicative methods (i.e. radiocesium and phyto-indication methods) are effective for allocation of the erosion microrelief structures. Also, these methods need to be formalized for convenient use.

Fate of cohorts in Melocactus (Cactaceae) species is affected by rainfall uncertainty and microrelief structures

Associations between plants and substrate in drylands enhance the ability of nutrient pools buildup and seedling establishment. However, this relationship has not been extensively demonstrated in populations of lithophytic plants. We report the effects of microrelief and neighboring plants on the population structure of Melocactus species in the semi-arid region of northeastern Brazil. The size classes of five populations and the seedling fate in two populations were examined through point pattern analysis. Association patterns between size classes were positive between seedlings and adults in all the populations. Cohorts were positively related to rainfall (>60 %). Recruitment events were microhabitat-dependent and showed high mortality levels (>70 %). The spatio-temporal decoupling between seedling fate and adults may favor population dynamic changes under rainfall uncertainty. Based on our analyses, we suggest that the relationship among size classes, microhabitat, and rainfall in lithophytic populations of Melocactus is crucial to buffer negative effects of environmental severity in seedling recruitment and survival.

Diffractive optical elements for optical identification

We present the design and fabrication of diffractive optical elements for optical identification purposes. Two methods for optical identification are discussed. In this feasibility study, approaches using one and two binary reflective diffraction gratings are demonstrated. The diffraction orders of the grating/gratings are used as a binary code for optical identification. The gratings are designed using the iterative Fourier transform algorithm for an incoming coherent monochromatic laser beam (633 nm, He–Ne laser). The microrelief structures are fabricated by a combination of atomic layer deposition and electron beam lithography. The scanning electron microscope images show good quality of diffraction gratings. Optical characterization and measurement results demonstrate the feasibility of the proposed identification methods.

Can infrared thermography be used to estimate soil surface microrelief and rill morphology?

This study presents a new technique to estimate soil surface microrelief and rill morphology using infrared thermography. This technique can be specifically useful to characterise soil surface microrelief to identify preferential flow paths in mulching conditions and to estimate soil surface elevation where other microrelief measurement techniques cannot be successfully applied. Laboratory tests were carried out using two soil flumes where different conditions were tested: with artificial rills created at the soil surface and with a surface eroded by flowing water. The technique was tested both in bare soil conditions and in the presence of different mulching surface cover densities. Heated water was used to create a temperature gradient on the soil surface and high resolution soil surface thermal imaging was obtained using a portable infrared video camera.The proposed technique allows us to identify different microrelief structures at the soil surface and to visualize preferential flow paths in mulching densities up to 4ton/ha. Where other microrelief measurement techniques cannot be used, the thermography allows to obtain 3D models of the soil surface elevation, with satisfactory accuracy. Higher mulch cover densities (above 4ton/ha) strongly affected the performance of the technique.

Microrelief structures for anti-counterfeiting applications

Microrelief surfaces including grating structures, greytone/micrographic features and microramps have been fabricated with depth features of up to 30 μm. Grey scale lithography has been used to produce the microstructures by a single UV exposure into a layer of thick resist. Arrays of the pixelated microstructures have formed the security features on the surface of optically variable devices. Each of the microstructures was designed to provide an intended optical effect in features such as portraits, symbols and lettering which comprised a larger image (typically 2.5×3 cm). An essential part of the process has been the determination of the optimum conditions for coating of the thick resist (AZ P4620) as a function of spin speed and exposure.

Fabrication of Micro-Relief Structures in Thick Resist for Anti-Counterfeiting Applications

ABSTRACTMicro-relief surfaces including grating structures, greytone/micrographic features and microramps have been fabricated with depth features of up to 30 μm. Grey scale lithography has been used to produce the microstructures by a single UV exposure into a layer of thick resist. Arrays of the pixelated microstructures have formed the security features on the surface of optically variable devices. Each of the microstructures was designed to provide an intended optical effect in features such as portraits, symbols and lettering which comprised a larger image (typically 2.5 × 3 cm). An essential part of the process has been the determination of the optimum conditions for coating of the thick resist (AZ P4620) as a function of spin speed and exposure.

The fabrication of microrelief structures in evaporated Ag/a-Ge 30 S 70 layers

The photo-stimulated diffusion of Ag in a-germanium sulfide is studied to obtain low relief resist masks for the purposes of diffractive optics. The thickness of the photodoped layer is found to be proportional to the illumination energy. An average chemical composition of the photodoping product, reproducible and constant in all photodoped areas is observed. This indicates the occurrence of a stoichiometric reaction as well as a step-like mechanism for the diffusion of Ag into the chalcogenide.

Preparation, morphology and physical properties of microrelief InP surfaces

The morphology of microrelief InP surfaces, prepared by anisotropic chemical etching without masking and the kinetics of this etching were studied. A statistical analysis of surface profiles shows that the surface studied has a Gaussian roughness distribution and the ratio of root-mean-square surface roughness δ to autocorrelation length σ is small and amounts to (2–5) × 10 −2 . For such a surface a reduction in specular reflection and increase in photocurrent of barrier structures have been observed. Such microrelief structures may be used to increase the collection efficiency of solar cells and the sensitivity of photodetectors.

Fabrication of kinoform structures for optical computing

The fabrication of kinoform micro-optical elements for applications in optical computing is described. The elements are recorded as continuous microrelief structures by programmable laser beam writing in photoresist with a computer-controlled precision xy stage and a modulated, focused laser beam. Kinoform structures can be programmed to any desired profile that is required for reproducing complex, optimized structures that are found by computer design techniques.

The morphology of moth and butterfly wing scales which exhibit reflective diffraction phenomena

The butterfly and moth families illustrate how nature has used diffractive micro-relief structures to achieve unique optical effects. Whereas the majority of insects use pigments (absorption) or occasionally thin film multi-layer structures (interference) to create colour, the wings of many families of butterfly and moth have complex 2-D or 3-D arrangements of submicron grating structures which produce zero and higher order diffraction conditions.The special properties of a diffraction grating can be understood by light incident perpendicularly on a transmission grating. The light is diffracted into a number of grating orders at angles θn given by the grating equation sin θn = n λ/d where λ is the wavelength of the light, n = 0, ± 1, --- and d is the grating period. The same conditions are valid for reflective diffraction structures. If the grating period is finer than the wavelength ie. d < λ, no first order diffraction exists for normal illumination.

Plasma and gaseous etching of compounds of Groups III-V

Abstract

Structural analysis of soil microrelief in palaeosols of the Lower Jurassic “Laterite Derivative Facies” (Mishhor and Ardon formations) Makhtesh Ramon, Israel

A sequence of palaeosols developed on exposed overbank sediments of successive alluvial cycles of the Lower Jurassic “Laterite Derivative Facies” (LDF) at Makhtesh Ramon, contains well-developed, penecontemporaneous soil microrelief structures. The folded structures commonly show overthrusting, and vary in wave length and amplitude. They are characterized by slickensided surfaces, cuspate in cross section with the curviplanar deformed surfaces oriented concave up. The palaeosol stratigraphy is well established over the entire Makhtesh Ramon area and this afforded the opportunity of obtaining controlled structural measurements on the folded surfaces and their associated slickensided striae as a means of providing data for reconstruction of the fold geometry. Stereographic projection of the poles to the LDF fold surfaces, on two separate palaeosol horizons from several localities, together with the slickensided striae, were plotted on the lower hemisphere of a Schmidt equal-area net. The LDF folds were seen to be symmetrical and asymmetrical structures with a gently plunging fold axis of 4–10°. Maximum and minimum dip values of the cuspate curviplanar surface (SP 1) were well emphasized by the plots (20° and 30° for symmetrical structures) and data from the two horizons obtained from several localities showed remarkable uniformity. A second slickensided, curviplanar surface of deformation (SP 2) shows the same range of dip values as SP 1 and intersects the SP 1 surface normal to the SP 2 fold axis. The internal arrangement of symmetry elements within the LDF folds remains approximately constant regardless of the large variation between the gross morphological parameters such as amplitude and wavelength, and this appears to be a reflection of the response of a soil with inherent anisotropies, to stress. The geometry of the LDF structure resembles that of linear or wavy gilgai. The SP 1 surface therefore is most likely the result of upthrusting on the edges of drainage rills affected by differential wetting. The SP 2 surface bears a constant geometric relationship with SP 1 and is therefore considered to have formed penecontemporaneously during the upthrusting of the SP 1 blocks. A rectangular surface fracture pattern parallel to and normal to topographic slope, is considered to be an alternative means of initiating the upward growth of the soil microrelief features.