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Dynamical systems based on the interplay of nonlinear feed- back mechanisms are ubiquitous in nature1–5. Well-understood examples from photonics include mode locking6 and a broad class of fractal optics7, including self-similarity8. In addition to the fundamental interest in such systems, fascinating techni- cal functionalities that are difficult or even impossible to achieve with linear systems can emerge naturally from them7 if the right control tools can be applied. Here, we demonstrate a method that exploits positive nonlocal feedback to initiate, and negative local feedback to regulate, the growth of ultrafast laser-induced metal–oxide nanostructures with unprecedented uniformity, at high speed, lowcost and on non-planar or flexible surfaces. The nonlocal nature of the feedback allows us to stitch the nanostructures seamlessly, enabling coverage of indefi- nitely large areas with subnanometre uniformity in periodicity. We demonstrate our approach through the fabrication of tita- nium dioxide and tungsten oxide nanostructures, but it can also be extended to a large variety of other materials.

Fabrication of Si (nc-Si), Ge (nc-Ge), and Si1-xGex (nc-Si1-xGex) nanocrystals embedded in SiO2 matrix is achieved by thermal annealing of magnetron-sputtered thin films. Effects of annealing conditions, namely duration and temperature, as well as Ge content on the photoluminescence properties are investigated. Origin and evolution of the photoluminescence signal in the weak quantum confinement regime are discussed. It is found that photoluminescence signals can be decomposed into four Gaussian peaks originating from Ge-related radiative defects located at the sub-oxide (GeOx), either inside the matrix or at the interface region (peak M), nc-Si1-xGex/SiO2 interface-related localized states (peak I), localized states in the amorphous Si1-xGex bandgap (peak A) and quantum confinement of excitons in small nanocrystals (peak Q). The role of small and large nanocrystals in the photoluminescence mechanism is investigated by varying the mean nanocrystal size from 3 nm to 23 nm (from strong to weak quantum confined regime). Our results demonstrate that the quantum confinement effect in Ge nanocrystals manifests though spectral blueshift due to increase in Ge content. We also propose that the decreasing photoluminescence signal intensity with an increase in Ge content may originate from Ge-related nonradiative P-b centers. (C) 2014 Elsevier B.V. All rights reserved.

Nano ölçekteki malzemeleri ve süreçleri makro dünya ile etkili bir biçimde bağlayabilmek hususundaki zorluk büyük ihtimalle nanoteknolojinin devrimsel etkisini sınırlayan en önemli problemdir. Malzeme özellikleri ve topolojisi birbirleri ile karmaşık bir ilişkide olup, atomik, mikro ve makro ölçek gereklilikleri genellikle aynı anda sağlanamamaktadır. Bu tez atomik ölçekten mikro ölçeğe kendini oluşturan ve nano ölçek özelliklerini bozmadan makro dünya ile iletişim kurabilen gelişmiş bir nanoyapı sunmaktadır. Üç boyutlu eşyönsüz rastgele silisyum kuvantum nokta ağı atomik ölçekte büyük oranda eşyönlü olup mikro ölçeğe doğru büyürken eşyönsüz hale gelmektedir. Bu çalışma ile bu yapılarda kuvantum hapsolma olgusunun geçerli olduğunu ve elektrik akımının ağ içerisinden verimsiz tünelleme mekanizmasına gerek duymadan aktığını gösterdik. Önceki atomik ölçeğe ait olan ve sonraki mikro ölçekte kendini gösteren bu iki özellik bu tezden önce aynı anda var olamaz olarak bilinirdi. Bu yapı silisyum-zengin silisyum oksit ince filmden kendiliğinden oluşmuştur. Mikro ölçekte kendiliğinden oluşma magnetron saçtırıcı tarafından sunulan dengede olmayan koşullarda kinetik olarak güdülmüş olup, yüzeyde oluşturulan sıcaklık farkı tarafından yüzey difüzyonunun kontrol edilmesi esasına dayanmaktadır. Atomik ölçekte kendiliğinden oluşma ise hızlı, rastgele çökertme süreci tarafından sağlanan bölgesel dengede olmayan koşullarda kimyasal olarak güdülmüş olup göreceli kararsız oksitlerin karalı hale getirilerek faz ayrışmasının önlemesi esasına dayanmaktadır. Bu tezde üretim yöntemimizin kendi özünde modüler, malzemeden ve başlangıç koşullarından bağımsız olduğunu gösterdik. Şöyle ki; dengede ve doğrusal olmayan koşullar altında kendiliğinden oluşma, ince film büyümesi hususundaki detayları etkileyen birçok faktörün önüne geçerek deneysel koşullarda gerçekleştirilebilecek birkaç basit 'kural' yardımı ile sonuç morfolojisini etkileyebilir. The most important problem limiting the impact of nanotechnology is probably the difficulty in effectively linking nanoscale materials and processes to the macroscopic world. Topology and material properties are intricately coupled and conditions that pertain to atomic, microscopic and macroscopic scales are often seemingly mutually exclusive. This thesis introduces a state-of-the-art nanostructure that hierarchically builds itself from the atomic to the microscopic scales, which can connect to the macroscopic world without detracting from its nanoscale properties. The three-dimensional anisotropic random network of silicon quantum dots is largely isotropic in the atomic scale but it grows to become anisotropic in the microscopic scale. We show that quantum confinement is preserved and the current flows through the network without relying on inefficient tunnelling currents. Former pertains to the atomic scale and latter manifesting at the microscale; these two scale-dependent features were thought to be mutually exclusive prior to this thesis. The structure is self-assembled from a silicon-rich silicon oxide thin film. Microscale self-assembly is kinetically driven under nonequilibrium conditions established by magnetron sputter deposition and relies on control of surface diffusion through a surface temperature gradient. Atomic scale self-assembly is chemically driven under local nonequilibrium conditions provided by fast stochastic deposition and relies on control of phase separation by stabilizing nominally unstable suboxides. We show that our fabrication methodology is inherently modular, material-independent, and is not affected substantially by the initial conditions, as self-assembly under nonequilibrium conditions and nonlinear dynamics sweeps aside a large number of factors that influence the details of thin-film growth, but provides simple a couple of `rules` with clearly identifiable corresponding experimental conditions to determine the final morphology. 191

Kendiliğinden birleşme, bütün bilim dallarından pek çok araştırmacının ilgi odağı olmuştur. Dinamik yapılar kendilerini sürdürmek için enerji akışı gerektirirken, kristal gibi statik yapıların kendiliğinden birleşmesi, genellikle enerjinin minimizasyonu ile gerçekleşir. Bu konu üzerindeki pek çok çalışma, statik kendiliğinden birleşmeyle sınırlı kalmıştır. Doğada yaygın olmasına rağmen, dinamik kendiliğinden birleşme hakkındaki çalışmalar oldukça yetersizdir, çünkü sistemi dinamik durumda tutabilen deneysel ortamlar kısıtlıdır. Bununla beraber, 2017'de, yeni bir dinamik kendiliğinden birleşme metodu S.Ilday tarafından tanıtıldı. (Nature Communication, 2017) Buçalışmada da, bu yöntemi kullanarak dengeden uzak, dinamik adaptif koloidal kristallerin formasyonunu çalıştık. Quasi-2d koloid sistemini termodinamik dengeden uzak tutmak için, femtosaniye lazeri enerji kaynağı olarak kullandık. Sadece birbiriyle çarpışan ve etraftaki sıvının etkisindeki yüzlerce polystyrene kürelerden oluşan bukoloid sisteminde, ilk defa bu kadar çeşitli kristal desenleri gözlemledik. Bu çalışmada, periyodik 2D Bravais desenleri, Moire desenleri, honeycomb desenleri ve periyodik olmayan quasikristalleri gördük. Bununla beraber, bu çalışmada, sıvı filmlerin kalınlığı, Brownian ortalama hız gibi fiziksel sınırları, bu koloidal kristallerinformasyonunu etkileyen temel deneysel parametreleri tanımlayıp aynı zamanda bu parametrelerin analizini yaptık. Bu çalışmanın, basit parçalardan desenlerin ortaya çıkışının ardındaki fiziksel ilkeleri ortaya çıkarmak için bir başlangıç noktası olduğunu düşünüyoruz Self-assembly has been the center of attention of many researchers from all branches of science. Self-assembly of static structures such as crystals often forms through energy minimization, while dynamic ones need constant energy flow to maintain their state. Most of the studies on self-assembly are limited to static self-assembly, anddespite its ubiquity in nature, our comprehensions of dynamic self-assembly are still in its infancy due to lack of experimental settings that can keep the system in its dynamical state. In 2017 a state-of-the-art dissipative (dynamic) self-assembly method was introduced by S. Ilday, and co-workers (Nature Commun., 2017). Here, using thismethod, we studied the formation of dynamic adaptive colloidal crystals far from equilibrium. We use a femtosecond laser as an energy source to drive a quasi-2D confined colloidal system far from thermodynamic equilibrium, and for the first time, we observed the formation of a rich set of dynamic adaptive colloidal crystals of tens to hundreds of units of polystyrene spheres, which interact through hydrodynamic and hard-sphere interactions. We report formation of periodic 2D Bravais lattices, Moiré patterns, honeycomb lattices and aperiodic quasicrystals. Furthermore, we identify, analyze, and verify some of the key experimental parameters, e.g., physical boundaries, thickness of the liquid film, and the average velocity of Brownian motion, affecting the formation of such a variety of colloidal crystals. We anticipate this study to be a starting point to uncover the physical principles behind the emergence of patterns from simple parts. 115

Cataloged from PDF version of article. Thesis (Master's): Bilkent University, Department of Materials Science and Nanotechnology, İhsan Doğramacı Bilkent University, 2022. Includes bibliographical references (pages 111-118). Zeolites are microporous (pore sizes < 2 nm) inorganic aluminosilicate materials with well-defined molecular pores and high surface areas used widely for various chemical processes, primarily as catalysts, sorbents, and ion exchangers. Aside from 40 types of natural zeolite, 253 different synthetic zeolitic framework types are synthesized and recognized by the International Zeolite Association (IZA). Zeolite synthesis requires moderate temperatures between 50°C - 270°C and high pressures (up to 120 bar). A fundamental challenge in zeolite synthesis is to elucidate and control the nucleation and growth of the zeolite crystals. The main reason for this is the fast kinetics of zeolite synthesis and rapid conformational transitions between quasi-equilibrium phases. Zeolite synthesis is a complex process because more than 40 different types of silica polymerization and depolymerization reactions occur simultaneously in a reaction mixture (i.e., precursor suspension). Reaction time scales of the silica polymerization are within the range of picoseconds and femtoseconds. Using the traditional hydrothermal synthesis method, which is occurring near thermal equilibrium, it is impossible to control the system at the time scale of these simultaneous polymerization reactions due to the slow energy deposition, which can be from 24 hours to several days. Other types of zeolite synthesis methods such as microwave synthesis are capable of depositing high energies in short time scales. However, the synthesis method is lacking the control of the excess heating of the full volume of the precursor suspension. During microwave heating, several hot spots form inside the precursor suspension, causing the boiling of the liquid. Growth by inhomogeneous heating leads to the formation of fused (i.e., interconnect) crystals instead of the discrete ones that dominate the end product in microwave-assisted synthesis method of zeolites. Here, we introduce a novel femtosecond laser-assisted synthesis method for the synthesis of Silicalite-1 zeolites. Femtosecond laser pulses ensure the delivery of a precise amount of energy per area within a given time interval, and therefore the spatiotemporal control over the energy delivered to the precursor suspension could be done on the time scale of the polymerization reactions of the zeolite synthesis. Thanks to the femtosecond laser pulses, the appropriate environment for zeolite synthesis, such as local high temperature and local high pressure (shock waves), has been created. In the laser-assisted synthesis method, the time required for zeolite synthesis decreased drastically compared to the hydrothermal method, overall control and product quality increased compared to the microwave synthesis method of zeolites. Unlike other rapid synthesis methods such as microwave synthesis, the uncontrollable temperature rise over the full volume of precursor suspension was not observed, resulting in 'discrete' crystals in the final product. Energy intake of the transparent precursor suspension was achieved through multiphoton absorption of the femtosecond laser pulses inducing steep spatiotemporal thermal gradients. Since surface tension of fluid is a function of temperature, surface tension gradients form as well, causing Marangoni flow. The ‘stirring effect’ of these flows leads to the distribution of the formed clusters evenly to the system, which is not attained by static hydrothermal synthesis of zeolites. It is proposed that vigorous flow induced in the laser-assisted synthesis assembles nuclei/polymerized clusters much faster than the other synthesis methods, which may be the reason for the drastically reduced reaction times compared to hydrothermal synthesis (i.e., 30 - 48h for hydrothermal vs. 3h - 5h for laser-assisted syntheses). Growth kinetics of the Silicalite-1 zeolite was examined in detail. In addition, templatefree nanosized microporous Zeolite Y, and mesoporogen-free hierarchical ZSM-5 zeolites with micro and meso-porosity were synthesized with reduced reaction times through laser-assisted synthesis method (i.e., 24 - 45h for hydrothermal vs. 1 - 5h for laser-assisted syntheses), which is important in terms of green synthesis approaches drawing attention in recent years. by Mehdi Hagverdiyev M.S.

Hyperuniformity is evolving to become a unifying concept that can help classify and characterize equilibrium and nonequilibrium states of matter. Therefore, understanding the extent of hyperuniformity in dissipative systems is critical. Here, we study the dynamic evolution of hyperuniformity in a driven dissipative colloidal system. We experimentally show and numerically verify that the hyperuniformity of a colloidal crystal is robust against various lattice imperfections and environmental perturbations. This robustness even manifests during crystal disassembly as the system switches between strong (class I), logarithmic (class II), weak (class III), and non-hyperuniform states. To aid analyses, we developed a comprehensive computational toolbox, enabling real-time characterization of hyperuniformity in real- and reciprocal-spaces together with the evolution of several order metric features, and measurements showing the effect of external perturbations on the spatiotemporal distribution of the particles. Our findings provide a new framework to understand the basic principles that drive a dissipative system to a hyperuniform state.

Holography is the most promising route to true-to-life three-dimensional (3D) projections, but the incorporation of complex images with full depth control remains elusive. Digitally synthesized holograms1,2,3,4,5,6,7, which do not require real objects to create a hologram, offer the possibility of dynamic projection of 3D video8,9. Despite extensive efforts aimed at 3D holographic projection10,11,12,13,14,15,16,17, however, the available methods remain limited to creating images on a few planes10,11,12, over a narrow depth of field13,14 or with low resolution15,16,17. Truly 3D holography also requires full depth control and dynamic projection capabilities, which are hampered by high crosstalk9,18. The fundamental difficulty is in storing all the information necessary to depict a complex 3D image in the 2D form of a hologram without letting projections at different depths contaminate each other. Here, we solve this problem by pre-shaping the wavefronts to locally reduce Fresnel diffraction to Fourier holography, which allows the inclusion of random phase for each depth without altering the image projection at that particular depth, but eliminates crosstalk due to the near-orthogonality of large-dimensional random vectors. We demonstrate Fresnel holograms that form on-axis with full depth control without any crosstalk, producing large-volume, high-density, dynamic 3D projections with 1,000 image planes simultaneously, improving the state of the art12,17 for the number of simultaneously created planes by two orders of magnitude. Although our proof-of-principle experiments use spatial light modulators, our solution is applicable to all types of holographic media.

The dental implant drilling procedure is an essential step for implant surgery, and frictional heat in bone during drilling is a key factor affecting the success of an implant. The aim of this study was to increase the dental implant drill lifetime and performance by using heat- and wear-resistant protective coatings to decrease the alveolar bone temperature caused by the dental implant drilling procedure. Commercially obtained stainless steel drills were coated with titanium aluminum nitride, diamond-like carbon, titanium boron nitride, and boron nitride coatings via magnetron-sputter deposition. Drilling was performed on bovine femoral cortical bone under the conditions mimicking clinical practice. Tests were performed under water-assisted cooling and under the conditions when no cooling was applied. Coated drill performances and durabilities were compared with those of three commonly used commercial drills with surfaces made from zirconia, black diamond. and stainless steel. Protective coatings with boron nitride, titanium boron nitride, and diamond-like carbon have significantly improved drill performance and durability. In particular, boron nitride-coated drills have performed within safe bone temperature limits for 50 drillings even when no cooling is applied. Titanium aluminium nitride coated drills did not show any improvement over commercially obtained stainless steel drills. Surface modification using heat- and wear-resistant coatings is an easy and highly effective way to improve implant drill performance and durability, which can improve the surgical procedure and the postsurgical healing period. The noteworthy success of different types of coatings is novel and likely to be applicable to various other medical systems. This study was financially supported by TUBITAK, The Scientific and Technological Research Council of Turkey, Grand number 108S180 and Erciyes University Scientific Research Projects, Grand number B-785

Multiscale self-assembly is ubiquitous in nature but its deliberate use to synthesize multifunctional three-dimensional materials remains rare, partly due to the notoriously difficult problem of controlling topology from atomic to macroscopic scales to obtain intended material properties. Here, we propose a simple, modular, noncolloidal methodology that is based on exploiting universality in stochastic growth dynamics and driving the growth process under far-from-equilibrium conditions toward a preplanned structure. As proof of principle, we demonstrate a confined-but-connected solid structure, comprising an anisotropic random network of silicon quantum-dots that hierarchically self-assembles from the atomic to the microscopic scales. First, quantum-dots form to subsequently interconnect without inflating their diameters to form a random network, and this network then grows in a preferential direction to form undulated and branching nanowire-like structures. This specific topology simultaneously achieves two scale-dependent features, which were previously thought to be mutually exclusive: good electrical conduction on the microscale and a bandgap tunable over a range of energies on the nanoscale. © 2016 American Chemical Society.

Femtosecond laser-based Nonlinear Laser Lithography (NLL) was applied to AISI 316L stainless steel, which requires surface modification to achieve satisfactory tribological behaviour. NLL advances over the well-known Laser Induced Periodic Surface Structures (LIPSS) in terms of uniformity and long-range order of high speeds, over large areas. A galvanometric scanner head was used for an high production rate. Dry and lubricated sliding tests, considering different orientations of the nanotexture showed that COF values after NLL treatment are significantly lower. In lubricated tests, COF values of NLL-treated surfaces are nearly half the values of untreated surfaces, whereas the difference further increases when measured in dry conditions, where the orientation of the surface texturing influences the results.

Date of Conference: 21–25 June 2015 Conference name:2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference The production of nanostructures on different materials attracts much attention in different fields of manufacturing as a result of increased availability, affordability and technical capability of laser-based methods [1,2]. However, some shortcomings such as relatively low speed of processing, problems with material control, and lack of uniformity and/or repeatability over large areas continue to limit their practical adaptation.