Nanoscale Texture Research Articles

Ultra-high brightness Micro-LEDs with wafer-scale uniform GaN-on-silicon epilayers

Owing to high pixel density and brightness, gallium nitride (GaN) based micro-light-emitting diodes (Micro-LEDs) are considered revolutionary display technology and have important application prospects in the fields of micro-display and virtual display. However, Micro-LEDs with pixel sizes smaller than 10 μm still encounter technical challenges such as sidewall damage and limited light extraction efficiency, resulting in reduced luminous efficiency and severe brightness non-uniformity. Here, we reported high-brightness green Micro-displays with a 5 μm pixel utilizing high-quality GaN-on-Si epilayers. Four-inch wafer-scale uniform green GaN epilayer is first grown on silicon substrate, which possesses a low dislocation density of 5.25 × 108 cm−2, small wafer bowing of 16.7 μm, and high wavelength uniformity (standard deviation STDEV < 1 nm), scalable to 6-inch sizes. Based on the high-quality GaN epilayers, green Micro-LEDs with 5 μm pixel sizes are designed with vertical non-alignment bonding technology. An atomic sidewall passivation method combined with wet treatment successfully addressed the Micro-LED sidewall damages and steadily produced nano-scale surface textures on the pixel top, which unlocked the internal quantum efficiency of the high-quality green GaN-on-Si epi-wafer. Ultra-high brightness exceeding 107 cd/m2 (nits) is thus achieved in the green Micro-LEDs, marking the highest reported results. Furthermore, integration of Micro-LEDs with Si-based CMOS circuits enables the realization of green Micro-LED displays with resolution up to 1080 × 780, realizing high-definition playback of movies and images. This work lays the foundation for the mass production of high-brightness Micro-LED displays on large-size GaN-on-Si epi-wafers.

Observation of Néel-type magnetic skyrmion in a layered non-centrosymmetric itinerant ferromagnet CrTe1.38

Magnetic skyrmions are nanoscale vortex-like magnetization textures that hold great promise for next-generation memory and spintronic devices. While extensive research has focused on discovering such localized spin textures in bulk magnets and multilayers with heavy metals, there is a growing interest in finding them in two-dimensional (2D) magnetic materials. In this research work, we report two distinct phases of the 2D CrxTey family: non-centrosymmetric CrTe1.38 and centrosymmetric CrTe0.96, with a Curie temperature of around 200 and 300 K, respectively. Detailed magnetic study indicates a prominent out-of-plane magnetic anisotropy in CrTe1.38. In contrast, CrTe0.96 exhibits a weak uniaxial magnetic anisotropy. Lorentz transmission electron microscopy shows that the spontaneous ferromagnetic ground state of CrTe1.38 consists of Néel skyrmions, whereas CrTe0.96 exhibits Bloch domain walls, consistent with their crystalline symmetries. This research expands the quasi-2D CrxTey family and opens up new avenues for exploring non-trivial spin structures and their potential applications in spintronic devices.

Anisotropic Stick-Slip Frictional Surfaces via Titania Nanorod Patterning.

Nanoscale or microscale surface texturing is an effective technique to tailor the tribological properties between two surfaces that are rubbed against each other. In order to achieve the desired frictional properties by a patterned surface, one needs an in-depth understanding of the underlying mechanisms. Here, we demonstrate anisotropic stick-slip friction achieved via a nanotextured surface of tilted titania nanorods (TiNRs). The surface was developed by using the glancing angle deposition (GLAD) technique, and exhibited load-dependent variations in stick-slip friction as well as frictional anisotropy in different sliding directions. For studying the frictional properties of the newly developed surface, lateral force microscopy (LFM) was performed in three different reciprocal orientations (0° rotated, 45° rotated, 90° rotated) using a custom-made colloidal alumina atomic force microscopy (AFM) probe. The frictional behavior was found to vary significantly with the orientation. At 0° rotated position) a prominent "stick-slip" was observed when scanning opposite to the tilt direction, whereas the phenomenon reduced significantly when the nanotextured surface was scanned along the tilt direction or rotated to different angles (45 and 90°) with respect to the sliding direction of the AFM cantilever supporting the probe. The experimental findings were interpreted based on the classical solution for large deflections of tilted elastic rods. Overall, the textured surface, LFM-based frictional measurement, and the quantitative analysis presented here provide a fundamental understanding of how friction can be significantly varied on a surface patterned with tilted TiNRs at a length scale of about 1 μm, which can be comprehensively applied to nanorod patterns of other materials on different substrates.

Metal-organic framework derived crystalline nanocarbon for Fenton-like reaction

Nanoporous carbons with tailorable nanoscale texture and long-range ordered structure are promising candidates for energy, environmental and catalytic applications, while the current synthetic methods do not allow elaborate control of local structure. Here we report a salt-assisted strategy to obtain crystalline nanocarbon from direct carbonization of metal-organic frameworks (MOFs). The crystalline product maintains a highly ordered two-dimensional (2D) stacking mode and substantially differs from the traditional weakly ordered patterns of nanoporous carbons upon high-temperature pyrolysis. The MOF-derived crystalline nanocarbon (MCC) comes with a high level of nitrogen and oxygen terminating the 2D layers and shows an impressive performance as a carbocatalyst in Fenton-like reaction for water purification. The successful preparation of MCC illustrates the possibility to discover other crystalline heteroatom-doped carbon phases starting from correctly designed organic precursors and appropriate templating reactions.

Investigating the Effects of Lubricant Infusion Methods on Polymer SLIPS.

Slippery lubricant infused porous surfaces (SLIPSs) are promising bioinspired surfaces with self-healing and droplet wetting properties, among many others, that are desirable due to their range of applications. Recently, there have been many developments in the SLIPS field regarding the creation of textured surfaces and lubricant selection. However, there is a lack of knowledge regarding the method of lubricant infusion. In this study, we aim to fill this void by investigating different infusion methods that impose external forces on the lubricant. We developed our SLIPS by hot embossing nanostructures onto polypropylene by using molds that were laser micromachined. These textured surfaces were then infused with silicone oil using three different infusion methods: ultrasonication, vacuum, and hydrostatic pressure. We analyzed the wettability and slipperiness of the SLIPS by evaluating the critical tilt angle and comparing the sliding velocities of water droplets on each sample at a tilt angle of 20°. Additionally, the durability of the SLIPS was tested by dropping 50 successive water drops onto the samples and evaluating the droplet-surface interactions throughout. The sonicated infusion method yielded SLIPS that performed the best with a contact angle hysteresis of 13°, a critical tilt angle of 18.3°, a sliding velocity of 1.66 mm/s, and the least accumulation of droplets over time with use. These values are greatly improved when compared to the control sample where lubricant was simply dripped on, which resulted in a contact angle hysteresis of 20°, a critical tilt angle of 26.3°, and a sliding velocity of 0.23 mm/s. The sonicated and drip infusion methods were also compared with different materials (stainless steel) and different textures (microstructures). It was found that the improvement in slipperiness using the sonicated infusion method is prominent for nanoscale textures on both stainless steel and polypropylene. In this study, we discuss the challenges with oil depletion in SLIPS (cloaking and wetting ridges) and with the selection of contact angle measurement methods. While further investigation as to why certain applied forces during infusion yield better SLIPS is warranted, these forces greatly affect the outcome. This work suggests that researchers should consider using sonication or other methods of lubricant infusion that apply external forces as infusion techniques to yield better SLIPS on the nanoscale.

Asymmetric energy barrier induced magnetic skyrmion diodes in synthetic antiferromagnetic nanotracks

Magnetic skyrmions are nanoscale spin textures with topological protection properties, which are regarded as promising information carriers. When skyrmions move along nanotracks, their trajectories will shift if affected by skyrmion Hall effect and pinning effect. In this work, the influence of trapezoidal notches in synthetic antiferromagnetic nanotracks on the dynamics of skyrmions is investigated through micromagnetic simulation. The results exhibit that the asymmetric energy barrier induced by the asymmetric geometric structure can hinder reverse motion of skyrmions to realize the unidirectional conduction function of the diodes. Adjusting the height and inclination angle of the trapezoidal notch can effectively expand the current operating windows of the diodes, and the larger the height or inclination angle, the higher the threshold current density to overcome the pinning effect of the geometric energy barrier. Furthermore, the failure mode has a crucial impact on the implementation of skyrmion diodes. By utilizing the asymmetric structure, the forward conduction and reverse cutoff of skyrmion-based diodes can be achieved within 4 ns, with lower energy consumption than traditional diodes, resulting in high efficiency and low energy consumption of diodes. This work proposes a method for realizing the diode functionality by simply altering the geometric structure of the nanotracks, which may play an important role in the design and application of skyrmion-based diodes.

Self-Assembly of Ionic Superdiscs in Nanopores.

Discotic ionic liquid crystals (DILCs) consist of self-assembled superdiscs of cations and anions that spontaneously stack in linear columns with high one-dimensional ionic and electronic charge mobility, making them prominent model systems for functional soft matter. Compared to classical nonionic discotic liquid crystals, many liquid crystalline structures with a combination of electronic and ionic conductivity have been reported, which are of interest for separation membranes, artificial ion/proton conducting membranes, and optoelectronics. Unfortunately, a homogeneous alignment of the DILCs on the macroscale is often not achievable, which significantly limits the applicability of DILCs. Infiltration into nanoporous solid scaffolds can, in principle, overcome this drawback. However, due to the experimental challenges to scrutinize liquid crystalline order in extreme spatial confinement, little is known about the structures of DILCs in nanopores. Here, we present temperature-dependent high-resolution optical birefringence measurement and 3D reciprocal space mapping based on synchrotron X-ray scattering to investigate the thermotropic phase behavior of dopamine-based ionic liquid crystals confined in cylindrical channels of 180 nm diameter in macroscopic anodic aluminum oxide membranes. As a function of the membranes' hydrophilicity and thus the molecular anchoring to the pore walls (edge-on or face-on) and the variation of the hydrophilic-hydrophobic balance between the aromatic cores and the alkyl side chain motifs of the superdiscs by tailored chemical synthesis, we find a particularly rich phase behavior, which is not present in the bulk state. It is governed by a complex interplay of liquid crystalline elastic energies (bending and splay deformations), polar interactions, and pure geometric confinement and includes textural transitions between radial and axial alignment of the columns with respect to the long nanochannel axis. Furthermore, confinement-induced continuous order formation is observed in contrast to discontinuous first-order phase transitions, which can be quantitatively described by Landau-de Gennes free energy models for liquid crystalline order transitions in confinement. Our observations suggest that the infiltration of DILCs into nanoporous solids allows tailoring their nanoscale texture and ion channel formation and thus their electrical and optical functionalities over an even wider range than in the bulk state in a homogeneous manner on the centimeter scale as controlled by the monolithic nanoporous scaffolds.

Release and re-enrichment of invisible gold in arsenian pyrite promoted by coupled dissolution-reprecipitation reactions

The mechanisms responsible for invisible gold enrichment driven by coupled dissolution-reprecipitation reaction (CDR) are debated. Here we report the micro- to nano-scale textures of arsenian pyrite in a high-grade (>10 g/t) gold ore from the Chang’an deposit to trace the gold enrichment process. Our study records a CDR-driven evolution of mineral growth from an As-rich, Au-poor pyrite core, with numerous fine arsenopyrite inclusions, to an inclusion-free, As-Au-rich oscillatory pyrite rim. The reaction occurred at ~260 °C under 4.7 to 5.8 pH and –36.6 to –32.9 logfO2 conditions. The elevated As but depleted S contents in the pyrite core indicate a combined elevation of S fugacity and solubility of Au. The coprecipitation of arsenopyrite inclusions in the core caused a depletion of S fugacity to –13.8 ~ –11.7, triggering Au enrichment in the rim. This non-unique process has the potential to explain the upgrade of invisible Au in arsenian sulfides, worldwide.

A Review on Flow Boiling Enhancement on Textured Surfaces

It is widely established that flow boiling, being a direct cooling technique also employing the latent heat of the fluid, has the potential to be more efficient than being useful in single-phase conventional cooling methods. This results in considerable potential for thermal management in many fields like microelectronics, space technology, thermal power plants, etc. The increasing demand for heat dissipation, consequent to component miniaturization, has pushed the development of new strategies for enhancing heat transfer efficiency, such as employment of functionalized surfaces. This review aims to describe in detail the current status of technology related to flow boiling heat transfer enhancement via micro/nanoscale surface functionalization. Key objectives are an increased nucleation site density and enhanced bubble dynamics. The vast majority of findings show favorable heat transfer performance, evidenced by an earlier onset of boiling (ONB), an improved flow boiling heat transfer coefficient (HTC), and an ameliorated critical heat flux (CHF). Increased pressure drop is a serious concern in certain application cases. Nanoscale textures mainly enhance capillary wicking to nucleation sites, thus being more effective in combination with microscale textures that define fixed nucleation sites. Degradation effects need to be more thoroughly and systematically characterized for application cases. Extra effects related to the manufacturing process can be easily overlooked, but one should be aware of their possible existence when drawing conclusions. Finally, the implementation of enhanced surfaces in mainstream applications is hindered by the absence of general predictive design tools for different channel configurations/materials, fluids, and operating conditions. A more universal understanding of the basic mechanisms involving texture geometry is needed in this aspect.

Study on the surface microtexture microscopic friction and wear characteristics of 304 stainless steel

In order to reveal the friction behaviour and wear mechanism of nanoscale textures on the friction pair of 304 stainless steel, molecular dynamics simulations were firstly used to investigate the effects of smooth and textured surfaces on the tribological properties of the stainless steel substrate, and then focus on the effects of sliding velocity and depth on the surface morphology, mechanical force, friction coefficient, anisotropy, stress, temperature and dislocations of the textured substrate. The results show that the temperature, friction, stress, and dislocation line length of the textured surface are relatively smaller than those of the non-textured surface, and the textured surface has a smaller and more stable friction factor, which ultimately leads to a reduction of the friction factor by about 0.090. When the sliding distance is 120 Å, the number of defective atoms in the textured substrate is reduced by 12.9%, and its anisotropy is more stable. At the same indentation depth, the average friction coefficient, temperature and anisotropy increase significantly with increasing sliding velocity. The average friction coefficient is maximum when the sliding velocity is increased to 400 m s−1, with a value of about 0.833. The sliding friction, friction coefficient, dislocation line length, number of defect atoms, number of stacked atoms, stress, temperature and anisotropy factor increase with increasing depth of abrasive indentation. The average friction coefficient is minimum at a sliding depth of 4 Å, with a value of about 0.556, and the number of defective atoms is reduced by 83.2%. This indicates that textured surface treatment of 304 stainless steel and selection of appropriate sliding parameters can effectively reduce the wear during the friction process and improve the wear resistance of the substrate.

Anti-corrosion and icephobic approach on rose leaf biomimetic surface

This study proposes a facile method for superhydrophobic and slippery-infused porous surfaces for water repellency and anti-icing purposes. Both adhesion force and time delaying were systematically investigated, showing their strong dependence on surface parameters and slipperiness. The uniform patterns of nanoscale textures inspired by rose leaf structure have been generated on silicon wafers using the plasma etching process. We believe the lower real contact area can play a dual role in the icing mechanism including reducing heat transfer and adhesion force attributed to the projected area. On the other hand, slipperiness plays an important role in reducing adhesion strength and preventing ice nucleation. The slippery superhydrophobic surface demonstrates outstanding in reducing the adhesion strength while documenting several times lower compared to bare Si, superhydrophobic Si, and slippery Si surfaces. In addition, the rational combination facilitates the efficient function after a number of test cycles, illustrating the mechanical anti-corrosion properties. The results lead to understanding the role of the icing process and designing the anti-icing structure.

Micro- to nanoscale textures of gold in arsenopyrite and scorodite from the As-Au-Bi assemblage of Drenjak locality (Serbia)

Arsenopyrite and pyrite are important carriers of Au that is present in the form of microscopic and “invisible” gold. Such gold can be expected to be released upon the process of oxidation of these sulfides. In studied gold mineralization at Drenjak, related to the granitoids of the Oligocene-Miocene Kopaonik Ore District, the main arsenopyrite-pyrite-(bismuthinite) sulfide assemblage was formed in the quartz bodies and partly replaced by scorodite (FeAsO4·2H2O) and Bi-arsenate. With only up to 5 ppm of gold recorded by LA-ICP-MS, aforementioned sulfide minerals are here practically free from lattice-bound gold. Native gold is present in the mineralization, generally ranging in grain size from 20 µm down to the nanoparticles, as revealed by TEM. It is mainly hosted by arsenopyrite and scorodite. In arsenopyrite, gold is polycrystalline and consists of nanocrystallites 20–30 nm in size. It was deposited after arsenopyrite, healing its cavities and microcracks, often associated with native bismuth and bismuthinite. The abundance of gold and Bi minerals correlates with the presence of scorodite. Two types of gold are present in scorodite and Bi arsenate: i) prevailing relict Au grains retained after arsenopyrite oxidation, ii) colloidal-like gold co-precipitated with the arsenates. Based on our observations, we additionally present and discuss indications of low-temperature hydrothermal origin of scorodite, formerly known only as a weathering product

Orientation-dependent etching of silicon by fluorine molecules: A quantum chemistry computational study

Anisotropic etching is a widely used process in semiconductor manufacturing, in particular, for micro- and nanoscale texturing of silicon surfaces for black silicon production. The typical process of plasma-assisted etching uses energetic ions to remove materials in the vertical direction, creating anisotropic etch profiles. Plasmaless anisotropic etching, considered here, is a less common process that does not use ions and plasma. The anisotropy is caused by the unequal etching rates of different crystal planes; the etching process, thus, proceeds in a preferred direction. In this paper, we have performed quantum chemistry modeling of gas-surface reactions involved in the etching of silicon surfaces by molecular fluorine. The results confirm that orientation-dependent etch rates are the reason for anisotropy. The modeling of F2 dissociative chemisorption on F-terminated silicon surfaces shows that Si–Si bond breaking is slow for the Si(111) surface, while it is fast for Si(100) and Si(110) surfaces. Both Si(100) and Si(110) surfaces incorporate a larger number of fluorine atoms resulting in Si–Si bonds having a larger amount of positive charge, which lowers the reaction barrier of F2 dissociative chemisorption, yielding a higher etch rate for Si(100) and Si(110) surfaces compared to Si(111) surfaces. Molecular dynamics modeling of the same reactions has shown that the chosen reactive bond order potential does not accurately reproduce the lower reaction barriers for F2 dissociative chemisorption on Si(100) and Si(100) surfaces. Thus, reparameterization is necessary to model the anisotropic etching process that occurs at lower temperatures.

CP2 skyrmions and skyrmion crystals in realistic quantum magnets

Magnetic skyrmions are nanoscale topological textures that have been recently observed in different families of quantum magnets. These objects are called CP1 skyrmions because they are built from dipoles—the target manifold is the 1D complex projective space, CP1 ≅ S2. Here we report the emergence of magnetic CP2 skyrmions in a realistic spin-1 model, which includes both dipole and quadrupole moments. Unlike CP1 skyrmions, CP2 skyrmions can also arise as metastable textures of quantum paramagnets, opening a new road to discover emergent topological solitons in non-magnetic materials. The quantum phase diagram of the spin-1 model also includes magnetic field-induced CP2 skyrmion crystals that can be detected with regular momentum- (diffraction) and real-space (Lorentz transmission electron microscopy) experimental techniques.

Multi-scale hierarchical microstructure modulation towards high room temperature thermoelectric performance in n-type Bi2Te3-based alloys

Bi2Te3-based thermoelectric materials are widely used in near room temperature refrigeration filed. Although Bi2Te3-based polycrystals prepared by powder metallurgy method exhibit good mechanical properties, the low room temperature dimensionless figure of merit (zT) for n-type alloys restricts their further usage. In this work, the electrical and thermal transport properties are manipulated synergistically by multi-scale hierarchical microstructure modulations in n-type Ag2Te/Bi2Te3 composites, including atomic-scale extrinsic point defects, nano-scale low-angel grain boundaries, mesoscale precipitate, and texturing. The carrier concentration is optimized by extrinsic point defects and the carrier mobility is improved due to the strengthened texture, and thus the power factor reaches a high value of 3.6 × 10−3 Wm−1/K2, which is even higher than the hot deformed counterparts. Simultaneously, the phonon scattering is enhanced by the multi-scale defects and the lattice thermal conductivity is suppressed. A high room temperature zT of ∼1.0 and an average zT of 0.96 in the 300–500 K range with good mechanical properties are obtained without hot deformation. This work puts forward a paradigm of enhancing the thermoelectric properties via multi-scale hierarchical microstructure modulations and is significant to the industrialization of manufacturing Bi2Te3-based alloys and devices.

A van der Waals Heterostructure with an Electronically Textured Moiré Pattern: PtSe2/PtTe2

The interlayer interaction in Pt-dichalcogenides strongly affects their electronic structures. The modulations of the interlayer atom-coordination in vertical heterostructures based on these materials are expected to laterally modify these interlayer interactions and thus provide an opportunity to texture the electronic structure. To determine the effects of local variation of the interlayer atom coordination on the electronic structure of PtSe2, van der Waals heterostructures of PtSe2 and PtTe2 have been synthesized by molecular beam epitaxy. The heterostructure forms a coincidence lattice with 13 unit cells of PtSe2 matching 12 unit cells of PtTe2, forming a moiré superstructure. The interaction with PtTe2 reduces the band gap of PtSe2 monolayers from 1.8 eV to 0.5 eV. While the band gap is uniform across the moiré unit cell, scanning tunneling spectroscopy and dI/dV mapping identify gap states that are localized within certain regions of the moiré unit cell. Deep states associated with chalcogen pz-orbitals at binding energies of ∼ -2 eV also exhibit lateral variation within the moiré unit cell, indicative of varying interlayer chalcogen interactions. Density functional theory calculations indicate that local variations in atom coordination in the moiré unit cell cause variations in the charge transfer from PtTe2 to PtSe2, thus affecting the value of the interface dipole. Experimentally this is confirmed by measuring the local work function by field emission resonance spectroscopy, which reveals a large work function modulation of ∼0.5 eV within the moiré structure. These results show that the local coordination variation of the chalcogen atoms in the PtSe2/PtTe2 van der Waals heterostructure induces a nanoscale electronic structure texture in PtSe2.

Simulation of Anti-Reflective TiO2/SiO2 Coating for Silicon Photovoltaic Application by Ray Tracing

n solar systems, anti-reflective coatings are used to reduce reflection and increase efficiency. However, the front surface on the solar cells alone is not effective because most of the light from the sun is reflected and very less energy absorption into the solar cells occur. An anti-reflective coating (ARC) of a sufficient thickness can greatly reduce front surface reflectance. Nanoscale surface texturing, on the other hand, can efficiently capture a higher ratio of incident light to boost optical absorption. In this study, the light trapping scheme within the wavelength of 300 to 1200 nm was used to improve the overall efficiency of silicon solar cells. A thin layer of TiO2 and SiO2 anti-reflective coating with different thicknesses was stacked alternatingly due to their different refractive index with TiO2 having a high refractive index and SiO2 with a low refractive index. Solar irradiance spectrum AM1.5G at normal incidence was used in this present work. For the ray-tracing simulation, the front planar with multilayer ARC with different thicknesses were investigated to obtain the optimum value for optical properties and current density. All the four combination arrangements of SiO2 and TiO2 were evaluated and the maximum potential photocurrent density (Jmax) was calculated. The Jmax value of thin crystalline silicon, c-Si (without ARC) was 24.93 mA/cm2 and increased to 30.28 mA/cm2when ARC was used on the front surface. This represents an increasing of 21.46 % enhancement compared to the Jmax of the c-Si reference. Simulation of Anti-Reflective TiO2/SiO2 Coating for Silicon Photovoltaic Application by Ray TracingImran Al-Haqeem Bin Jaffar1, Siti Hajar Mohmad Salleh2*, Mohd Zaki Mohd Yusoff31,2Faculty of Applied Sciences, Universiti Teknologi MARA, Cawangan Perlis, Campus Arau, 02600 Perlis, Malaysia3Faculty of Applied Science, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia*Corresponding author’s E-mail: sitiha2902@uitm.edu.myReceived: 08 August 2022 Accepted: 17 February 2023Online First: 17 March 2023

Sputter yields of surfaces with nanoscale textures: Analytical results and Monte Carlo simulations

We find the spatially averaged sputter yield Y¯ analytically for non-planar surfaces that have slowly varying surface heights h=h(x,y). To begin, nonlocal effects like redeposition of sputtered material and secondary sputtering are neglected. We show that the leading order corrections to Y¯ are proportional to the spatial averages of (∂h/∂x)2 and (∂h/∂y)2. The constants of proportionality can be written in terms of the first and second derivatives of the sputter yield of a flat surface with respect to the ion incidence angle θ. For a range of θ values, Y¯ is a decreasing function of the amplitude of the surface texture. We also determine how the contribution of redeposition to Y¯ depends on the amplitude and characteristic lateral length scale of the surface morphology. As a test of our theory and to quantify the roles of redeposition and secondary sputtering, we performed Monte Carlo simulations of sputtering from Si targets with sinusoidal surfaces by 1 keV Ar+ ions. The theory agrees remarkably well with our Monte Carlo simulations. Our simulations also lead to the notable result that atoms that are sputtered and then strike the surface can themselves cause significant sputtering.

Alchemy of color

Alchemy of Color: Enlightening Nanoworlds is a research/creation project designed to challenge the certitudes of our perception, by presenting gold and silver objects sculpted at a nanoscale, invisible to all optical processes. The result is two complementary installations: A Thousand Shades of Green, an Attempt – nanolithographies, a nanoengraving on a glass disk, and Alchimie de la lumière – nanosculptures. Coloring is an artistic gesture, a sensitive use of light associated with human visual perception. But coloring is also a physicochemical process associated with the interaction between photons and the molecular matter of pigments and inks. The colors of nanoparticles are a consequence of another light and matter interaction. Smaller than the photons that strike them, the metal nanosculptures are electrified and deflect the rainbow’s path. Here, color is no longer a molecular property of light absorption by pigments or dyes but a resonance that makes form tangible. This photonic resonance of light with nanoscale textures belongs to the family of structural coloration. It differs from the latter through interferences that occurs when the object is larger, a fraction of a micron in size, about half the photon’s wavelength. Classical pigments absorb light, as do plants: they appear green since the chlorophyl absorbs the blue and the red of the visible spectrum. One of alchemy’s ancient goals was to transmute matter, lead into gold, copper into silver. In the present project, the nanoscale sculptures that interfere with light are made of gold and silver and the alchemy refers here to the transmutation of the photons into plasmon. In an inversion of roles, invisible gold and silver objects are performing, in front of the spectator, the alchemical transformation of light, producing new colors, as if light and colors were matter. A Thousand Shades of Green, an Attempt, is a nano engraving test using electronic lithography employing millions of gold cylinders, whose diameters increase from 50 to 100 nanometers, on a 2-square-centimeter glass disk. During the process, some parts of the metal layer deposited through the lithographic mask—too large for current technologies (limited to 1 square millimeter)—are torn away when the mask is peeled off. The damaged areas then reveal a world of iridescence, in green, orange, and blue. The two installations, Alchimie de la lumière – nanosculptures, resemble cabinets of curiosity cabinet; they were created for the exhibition OU\/ERT in Bourges (2019) and Bourges contemporain in 2021. The glass forms, isolated or creating a landscape, change color according to the transformations of the light scene. The blown forms contain metallic nanoparticles, produced by chemical assembly, which emit a thousand new shades of green, depending on the angle that we look at it from. The aqueous nanoparticle solution thus appears green when seen in direct light and orange or blue in transparency. Thus, the two installations constitute a modern form of vanities. In classical painting, earthly goods, money, scientific instruments, or symbols of knowledge were represented scattered or broken on the ground, alluding to their all being in vain with respect to a higher, inaccessible reality, a transcendence. Here, the nano engraving on the disk is broken and the perfect silver and gold nano spheres are invisible and only reveal their presence in the transformation of light into the multiple shades produced, the sensible dimension taking over the sensitive control.

Reaction-Diffusion Pathways for a Programmable Nanoscale Texture of the Diamond-SiC Composite.

The diamond-SiC composite has a low density and the highest possible speed of sound among existing materials except for diamond. The composite is synthesized by a complex exothermic chemical reaction between diamond powder and liquid Si. This makes it an ideal material for protection against impact loading. Experiments show that a system of patterns is formed at the diamond-SiC interface. Modeling of reaction-diffusion processes of composite synthesis proves a formation of ceramic materials with a regular (periodic) interconnected microstructure in a given system. The composite material with interconnected structures at the interface has very high mechanical properties and resistance to impact since its fractioning is intercrystallite.