Dissertations / Theses on the topic 'Nanopatterned substrates'

2010/2011
The objective of this project was to develop new nanotechnology-based strategies to increase embryonic stem cells (ESCs) differentiation into neuronal lineage. In particular it was chosen to investigate a nanostructured physical support for in vitro stem cell culture in which both the nanometrical topography and mechanical properties are well controlled and characterized. Nanopatterned substrates were designed to have physical properties as close as possible to the in vivo microenvironment where stem cells normally grow and differentiate based on the assumption that mimicking the natural niche equilibrium is of fundamental importance for stem cell fate. First, an original nanotechnological approach to fabricate the substrates for in vitro neuronal precursors culture was developed. Secondly the substrate geometrical and mechanical parameters were optimized in order to achieve the maximum differentiation yield of ESCs-derived neuronal precursors (NPs). It was reached a neuronal yield of 74±7% at 48 hours after NPs differentiation induction, which represents the highest yield ever published using nanopatterned substrates with controlled and highthroughput reproducible nanometrical features for cell culture. Moreover it was demonstrated that the mechanical properties of the substrate play a major role with respect to other parameters, such as substrate composition and geometry. A time-dependent analysis showed that the first hours after cell seeding are crucial in the determination of the final differentiation yield. A further control of ESCs differentiation by manipulating the substrates physical parameters, required a deep understanding of the cell-substrate interaction, therefore it was studied the behavior of neuronal precursors when placed and grown on different artificial substrates using atomic force microscope, scanning electron microscope, and single cell force spectroscopy measurements. The latter lead to a quantification of the forces that develop between neuronal precursors and substrate and provided a clear relationship between adhesion forces and differentiation. My results suggested the importance of the physical parameter involved in the regulation of the neuronal differentiation and to new guidelines for future applications in regenerative medicine.
XXIV Ciclo
1984

The growth of barrier-type anodic alumina films formed by anodizing relatively rough substrates has been shown to proceed by high field ionic conduction. As a result of the ionic transport and the induced plasticity, smoothing of the oxide surfaces and the metal/oxide interfaces arises. However, such a smoothing model was deduced from topographical observations and, therefore little insight was gained about the transport mechanism leading to the flattening of the anodized specimens. Recently, the development of porous anodic alumina has been demonstrated to proceed by coupled ionic migration and material flow resulting from the field-induced mechanical stress. For rough metal surfaces, the electric field distribution is non-uniform across the specimen surface. Considering the square-dependence of the electrostrictive stress on the electric field and the distribution of the electric field across surface, a significant gradient of mechanical stress may arise across the anodic oxide layer during anodizing. As a result, stress-driven transport may participate, in addition to high field ionic conduction, to the smoothing of the specimen surface. Transport mechanisms were investigated during anodizing of patterned superpure aluminium specimens, by examination of the distributions of incorporated species, used as markers and tracers. The nature of the migration processes have been determined in correlation with the changes in the concentration of the tracer profiles as well as the variations in the anodic oxide film compositions.

L'intérêt pour les propriétés magnétiques des nanostructures de métaux de transition et de lanthanides de faible dimensionnalité n’a cessé de croitre au cours des deux dernières décennies, tant pour leur intérêt en recherche fondamentale que pour la perspective d’applications technologiques. De manière remarquable, les propriétés magnétiques des nanostructures peuvent être ajustées en contrôlant leur géométrie, leur structure atomique et leur environnement chimique. Dans cette thèse, un gabarit 1D composé de nanorubans de Si auto-organisés est utilisé pour guider la croissance de nanolignes de métaux de transition dans le but d’étudier leurs propriétés magnétiques. La géométrie et la structure atomique des nanorubans de Si et des nanolignes de métaux ont été étudiées in situ par microscopie par effet tunnel. Concernant le silicium, notre étude montre qu’une température de 490 K est nécessaire pour obtenir un gabarit 1D hautement ordonné. Les résultats obtenus sur les métaux de transition ont permis de déterminer la géométrie et la structure des nanolignes. Pour accéder aux propriétés magnétiques des nanolignes de Co, des mesures par XMCD ont été effectuées en température, en utilisant différentes orientations du champ magnétique. Les résultats montrent que les deux premières couches de Co adsorbées sur les nanorubans présentent une réponse magnétique faible, tandis que les couches supérieures présentent une aimantation exaltée. Deux axes d’anisotropie dans le plan ont été mis en évidence. Les moments magnétiques et l'énergie d’anisotropie magnétique ont été déterminés quantitativement. Les études en température suggèrent un comportement superparamagnétique
Interest in the magnetic properties of low dimensional transition metal and lanthanide nanostructures has seen an unprecedented rise in the last two decades due to both their fundamental interest and perspectives of technological applications. Remarkably, the magnetic properties of nanostructures can be tuned by controlling their geometry, atomic structure and chemical environments. In this thesis, a one-dimensional template composed of self-organized Si nanoribbons is used to grow transition metal nanolines, prior to the characterization of their magnetic properties. The geometries and the atomic structure of both the Si nanoribbons and the metal nanolines were investigated in situ by scanning tunneling microscopy. The growth mechanisms were investigated by exploring a large set of growth conditions. Regarding the Si growth, our study shows that a temperature of 490 K is necessary to obtain a long-range ordered one-dimensional template. Concerning the transition metal study, the results resolved the nanoline geometries and atomic structures.To access the magnetic properties of the Co nanolines on Si, XMCD measurements were performed using different magnetic field orientations and temperatures.The results show that the first two Co layers directly adsorbed onto the Si nanoribbons present a weak magnetic response while the upper Co layers exhibit an enhanced magnetization. Remarkably, two in-plane easy axes of magnetization were evidenced.The magnetic moments and the magnetic anisotropic energy are determined quantitatively.Temperature-dependent investigations strongly suggest a superparamagnetic behavior

ABSTRACT INTERACTION BETWEEN MICRO AND NANO PATTERNED POLYMERIC SURFACES AND DIFFERENT CELL TYPES Ö
zç
elik, Hayriye Ph.D., Department of Biology Supervisor: Prof. Dr. Vasif Hasirci Co-Supervisor: Dr. Celestino Padeste August 2012, 139 pages Micro and nanopatterned surfaces are powerful experimental platforms for investigating the mechanisms of cell adhesion, cell orientation, differentiation and they enable significant contributions to the fields of basic cell and stem cell biology, and tissue engineering. In this study, interaction between micro and nanopatterned polymeric surfaces and different cell types was investigated. Three types of micropillars were produced by photolithography (Type 1-3), while nanometer sized pillars were produced in the form of an array by electron beam lithography (EBL). Replica of silicon masters were made of polydimethylsiloxane (PDMS). Polymeric [P(L-D,L)LA and a P(L-D,L)LA:PLGA blend] replica were prepared by solvent casting of these on the PDMS template and used in in vitro studies. The final substrates were characterized by various microscopic methods such as light microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). In order to investigate deformation of the nucleus in response to the physical restrictions imposed by micropillars, Type 1 and Type 2 pillars were used. These substrates were covered with pillars with different interpillar distances. While Type 1 is covered with symmetrically (in X-Y directions) distributed pillars, Type 2 pillars were distributed asymmetrically and the inter-pillar distances were increased. Nuclei deformation of five cell v types, two cancer cell lines (MCF7 and Saos-2), one healthy bone cell (hFOB1.19), one stem cell (bone marrow origined mesemchymal stem cells, BMSCs) and one standard biomaterial test cell type, (L929) fibroblasts was examined by using fluorescence microscopy and SEM. The nuclei of Saos-2 and MCF7 cells were found to be deformed most drastically. Nucleus deformation and intactness of nuclear membrane was examined by Anti- Lamin A staining. The interaction of the cells with micropillars was visualized by labelling focal adhesion complexes (FAC). Wettabilities of patterned and smooth surfaces were determined. As the patterns become denser (closer micropillars, Type 1) the hydrophobicity increased. Similar to water droplets, the cells were mostly spread at the top of the Type 1 pillars. The number of cells spread on the substrate surface was much higher on Type 2 patterned films. In order to support these qualitative findings, nucleus deformation was quantified by image analysis. Frequency of nucleus deformation was determined as the ratio of deformed to the total number of nuclei (%). In order to quantify the intensity of nuclei deformation, their circularity was evaluated. In addition to nucleus deformation, alterations in the ratio of cell area-to-nucleus area in response to micropillars were determined by image analysis. The results indicated that cancerous cells were more deformable. The qualitative microscopic evaluation and the data obtained by quantification of the nucleus and cellular deformation were in good agreement. In addition, the findings were consistent with expectations which suggest that cancerous cells are &ldquo
softer&rdquo
. In the second part of the research the force applied by the cells on arrays of micropillars with high aspect ratios (Type 3 substrates) during tugging at the pillars was investigated. Micropillars were produced using P(L-D,L)LA as well as a 60:40 blend of P(L-D,L)LA with PLGA. The blend is a material with lower stiffness than P(L-D,L)LA. The mechanical properties of the two materials were determined by tensile testing of solvent cast films. Deformation of Type 3 micropillars by the cellular tugging force of Saos-2 and L929 was studied by fluorescence and SEM microscopy, both on stiff and softer substrates. Displacements of the centers nodes of the pillars were evaluated from SEM micrographs. On the stiff surface, the two cell types bent the pillars to the same extent. On the other softer substrate (blends), however, the maximum displacements observed with Saos-2 cells were higher than the ones caused on the stiffer substrate or the ones caused by L929 cells. It is reported that stiffness of the substrate can determine stem cell lineage commitment. In order to examine the effects of change of substrate stiffness on osteogenic differentiation of BMSCs, osteopontin (OPN) expression was determined microscopically. It was found that osteogenic differentiation is enhanced when BMSCs are cultured on P(L-D,L)LA Type 3 pillars. vi In the last part of research, arrays of nanopillars whose interpillar distances systematically varied to form different fields were examined in terms of adhesion and alignment in order to determine the differential adhesion of BMSCs and Saos-2 cells. The difference in their adhesion preference on nanopillar arrays was quantified by image analysis. It was observed that BMSCs and Saos-2 cells behaved in an opposite manner with respect to each other on the fields with the highest density of nanopillars. The BMSCs avoided the most densely nanopillar covered fields and occupied the pattern free regions. The Saos-2, on the other hand, occupied the most densely nanopillar covered fields and left the pattern free regions almost unpopulated. It was also found that both BMSCs and Saos-2 cells aligned in the direction of the shorter distance between the pillars. Both BMSCs and Saos-2 cells started to align on the pillars if the distance in any direction was >
1.5 &mu
m. To better understand the effects of chemical and physical cues, protein coating and material stiffness were tested as two additional parameters. After fibronectin coating, the surfaces of P(L-D,L)LA films with the highly dense pillar covered fields, which were avoided when uncoated, were highly populated by the BMSC. Similarly, decreasing the stiffness of a surface which was normally avoided by the BMSCs made it more acceptable for the cells to attach.

碩士
國立交通大學
光電系統研究所
101
In this paper we discuss the simulation of a nano-patterned sapphire substrates (NPSS) light emitting diode (LED) with two kind of optics software: wave optics software, Finite-Difference Time-Domain (FDTD) simulations, and the ray optics software, Light Tools (LTs) simulation. First, we find the trends and an optimal solution for the Light Extraction Efficiency (LEE) enhancement when the 2D-FDTD simulations are used to save on simulation time and computational memory. The rigorous coupled wave analysis (RCWA) method is utilized to evaluate the designs. The optimal solution is then applied in 3D-FDTD and LTs simulations. The results are similar and the difference in the LEE enhancement between the two simulations does not exceed 8.5% in the small LED chip area. More than 104 times computational memory is saved during the LTs simulation in comparison to the 3D-FDTD simulation. Moreover, the LEE enhancement from the side of the LED can be obtained in the LTs simulation. An actual size NPSS LED is simulated using the LTs. The results show a more than 307% improvement in the total LEE enhancement of the NPSS LED with the optimal solution compared to the conventional LED.

碩士
國立中央大學
機械工程學系
105
In this study, we applied nanopattened fluorine doped tin oxide (FTO) glass substrates to perovskite solar cells. In order to improve current density of cells by increasing of the surface area of cathode and the light harvesting by active layer. We used Rsoft optical simulation software to simulate our cells with nanopatterened FTO substrates. As the results, the light absorption of the cells using nanopatterned FTO substrates are higher than the cells using planar FTO substrates in the most range of wavelength. The method of fabricating nanopattened FTO substrates, first, was coating the FTO electrodes with photoresist, then arrayed monolayer SiO2 nano-spheres on the photoresist. After that, nanopatterns were created on photoresist by photolithography. In the end, transferring the nanopattern from photoresist to FTO by inductively coupled plasma (ICP) etching. We calculated the increasing of surface area when using nanopattened FTO substrates. The deeper etching depth are, the more increasing are. A 93.74% increasing of surface area was obtained by using 200nm-etching-depthed FTO substrate. The cell with planar FTO substrates as reference had Jsc of 19.27 mA/cm2 and PCE of 14.21%. The cell with 200nm-etching-depthed FTO substrate raised its Jsc to 21.72 mA/cm2. We further optimize the thickness of the meso layer on the patterned FTO substrates and the result showed the highest Jsc of 23.81 mA/cm2 and PCE of 17.85%, a 25.62% improvement of PCE was obtained.

碩士
國立中央大學
機械工程學系
105
We fabricated standard Perovskite Solar Cells as structure FTO/TiO2 compact layer/TiO2 mesoporous layer/CH3NH3PbI3 active layer/Spiro-OMeTAD hole transfer layer/Silver in both anode and cathode. This cell has Jsc=20.78mA/cm2, Voc=1.02V, FF=70.66%, PCE=14.92%. Based on this standard perovskite solar cells, the experiment of this thesis are divided into three sections. The first section of the experiments. We used eggshells to react with titanium dioxide and synthesized mesoporous Ca/Ti compounds. In comparison with the control group, the cells used Ca/Ti compounds as mesoporous layer can improve the Jsc from 20.78 to 23.41 mA/cm2 and enhance the PCE from 14.92% to 18.02% (enhaced 20.78%). The second section of the experiments. We spinned coating photoresist on FTO surface and then arrayed single-layered SiO2 nanoparticles on top. After that, patterned periodic arrays nanoholes were created on FTO using photolithography technology and inductively coupled plasma dry etching. In comparison with the control group, the nanopatterned cells can improve the Jsc from 20.78 to 23.27 mA/cm2 and enhance the PCE from 14.92% to 16.93% (enhaced 13.47%). The final section of the experiments. We further optimize the thickness of the Ca/Ti compounds mesoporous layer on the patterned FTO substrates. As the result, the cells (PFS-mesoCa/Ti x2) shows the highest Jsc of 24.40 mA/cm2 and the PCE of 18.79% (enhanced 25.94%)

碩士
國立成功大學
光電科學與工程學系
100
We demonstrated a nanopatterning approach by direct nanoimprinting on flexible polycarbonate (PC) sheets with flexible nanopatterned molds. This method has advantages of low cost, large area fabrication, and high resolution. Different mold materials, including SiO2/Si rigid mold, polydimethylsiloxane (PDMS) flexible mold, and perfluoropolyether (PFPE) flexible mold, were employed to investigate their pattern transfer ability on PC sheets. For a SiO2/Si rigid mold, good pattern transfer ability was obtained by applying a temperature of 170°C and a pressure of 5 bar. PDMS flexible mold was found to have poor pattern transfer ability in all imprinting conditions. For a PFPE flexible mold, great pattern transfer ability was demonstrated at a temperature of only 150°C, which is lower than the applying temperature for a SiO2/Si rigid mold. No anti-sticking treatment was necessary for the PFPE flexible mold. The approach of direct nanoimprinting on flexible PC sheets was further applied to the fabrications of wire-grid polarizers (WGP) and surface plasmon resonance (SPR) sensors. Simple two-step processes were used to fabricate both optical devices. Nanostructures were obtained by direct imprinting onto PC sheets. No additional imprinted polymer was required in the imprinting step. For WGPs, aluminum (Al) nanowire structures were obtained by an oblique Al sputtering on PC one-dimensional (1D) gratings. The fabricated WGPs had high polarization extinction ratio (PER) in the infrared region. For SPR sensors, gold (Au) nanowire structures were achieved by an Au evaporation in a normal direction on PC 1D gratings. The SPR wavelength was red-shifted with an increment of environmental refractive index. The SPR sensor with a grating pitch of 1000 nm had a high sensitivity of approximately 920 nm/RIU.

博士
國立成功大學
微電子工程研究所碩博士班
101
GaAs and InAs are grown on geometric nanopatterned and nanoscale stripe patterned Si substrates with SiO2 as a mask by metal–organic vapor–phase epitaxy. Theoretical models suggest the possibility of strain relief and dislocation reduction via a decrease in the initial epitaxial areas to the nanoscale regime. Threading dislocations, which are stacked on the lowest–energy facet plane, are trapped by the SiO2 patterns, reducing the number of dislocations. For GaAs on a 55–nm round–hole patterned Si substrate with SiO2 as a mask, the etching pit density of the GaAs surface is about 3.3 × 10^5 cm^-2. Compared with the full width at half maximum measurement (FWHM) from X–ray diffraction (XRD) ω/2θ scans patterns and photoluminescence spectra of GaAs on a planar Si (001) substrate, those of GaAs on the 55–nm round–hole patterned Si substrate are reduced by 39.6 % and 31.4 %, respectively. The use of 70–nm–wide SiO2 convex–top patterns can suppress the coalescence dislocations of the epi–layer and lead to a further decrease the FWHM values of the XRD ω/2θ scan patterns by 11.5 % compared to those obtained with 70–nm–wide rectangular–top SiO2 patterns. Compared with the conventional planar Si substrate, depositing the epi–layers onto nanoscale stripe patterned Si substrates decreases the dislocation density from about 109 cm-2 to almost zero. With the aspect ratio increased from 0.44 to 2.04, the etching defect pit density can be significantly decreased. Almost etching–pit–free surfaces of GaAs and InAs nanofins are achieved using nanoscale stripe patterned Si (001). The lattice constants measured from the GaAs and InAs nanofins are 5.63 Å and 6.04 Å, respectively, which are similar to those of natural GaAs and InAs. An ultraviolet metal–semiconductor–metal photodetector was prepared on an almost crack–free epi–layer surface. With a 5–V applied bias, the UV–to–visible rejection ratio was estimated to be 1479 and the measured leakage current was 1.5×10^-11 A.