Nanotechnology | EPFL Graph Search

Nanotechnology, often shortened to nanotech, is the use of matter on atomic, molecular, and supramolecular scales for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabrication of macroscale products, also now referred to as molecular nanotechnology. A more generalized description of nanotechnology was subsequently established by the National Nanotechnology Initiative, which defined nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). This definition reflects the fact that quantum mechanical effects are important at this quantum-realm scale, and so the definition shifted from a particular technological goal to a research category inclusive of all types of research and technologies that deal with the special properties of matter which occur below the given size threshold. It is therefore common to see the

Supramolecular structures of polypeptides

Daniela Silvano

The formation of supramolecular structures is a central issue in bio- and nanotechnology and therein plays an important role for many novel developments such as biocompatible materials for integrating living cells or coating for implantable sensing devices as well as for designing smart molecular sensor surfaces for miniaturized bioanalytical techniques. The main focus of this thesis is the investigation of polypeptide layers on surfaces, in particular the formation of self-assembled monolayers (SAMs). SAMs made of long hydrocarbon chains or aromatic molecules comprising surface active and other functional groups have been deeply characterized over decades. Surprisingly, peptide SAMs did not meet the same strong interest despite their great potential in several areas. Natural (20) and artificial amino acids with different physical and chemical properties offer a plethora of novel possibilities to design coating of solid surfaces. In fact their combination in simple oligopeptide sequences provides a huge number of molecular components for the formation of SAMs. Control of SAM features such as density, flexibility, adaptability, interface properties, by tailoring the amino acid sequence opens a new route to manifold applications ranging from fundamental research to nano- and biotechnology. In this thesis different and complementary techniques have been used to investigate the self-assembling ability of polypeptides on surfaces with different physical and chemical properties. Infrared spectroscopy and circular dichroism allowed the determination of the peptide secondary structure on surfaces and in solution. Surface plasmon resonance provided the optical thicknesses of peptide SAMs on gold whereas contact angle measurements have been used to characterize their interfacial properties. In the first part of the thesis, a series of hydrophobic peptides (Ac-Cys-Alax-CONH2, x=3-6) have been self assembled on gold via the thiol group present in the cysteine. The main interest was whether these peptides formed densely packed SAMs with a defined secondary structure within the layer and how the properties of such SAMs depended on the length of the polypeptide backbone. The second part concerns the study of the interactions of an amphipathic helical peptide with various functionalized substrates. The aim was to investigate whether a proper design of the peptide could be used to predetermine its secondary structure on the substrate and whether the orientation of the peptide on the surface could be directly controlled via certain parameters of the surrounding medium. Since the hydrophilic residues of the peptide are histidines, a particular effort was spent in characterizing the peptide adsorption on substrates exposing nitrilotriacetic acid (NTA) moieties. Once established that the adsorption process did not alter its helical structure, the peptide was adsorbed on a substrate exposing two different functional groups: NTA, that could interact with the histidine residues, and methyl groups, that could interact with the hydrophobic ones. The goal was to bind the peptide in different orientation to the same substrate, exploiting the particular spatial distribution of its residues. The third part of this thesis concern the formation of nano- and micro-sized fibrils through molecular self-assembly of simple oligopeptides and protected amino acids. Such systems were chosen as models to investigate the role of the different driving forces in the formation of fibrillar structures. The aromatic protecting group being fixed, it could be shown that the protected amino acids formed fibrils with different sizes and morphologies, or did not form fibrils at all, depending on how strongly their side chains interact. The possibility of forming fibrils by using protected amino acids is of major importance not only in bio-related field but also in organic nanotechnology.

EPFL2008

In-situ Laue Diffraction During Compression of Directionally Solidified Mo Micropillars

Julien René André Zimmermann

With recent developments in micro and nano-technologies, mechanical components such as those used in medicine or electronics tend to be miniaturized, requiring a new set of testing techniques to study their reliability and performance. One of the new methods is micro-pillar compression testing, which allows the study of mechanical properties of confined volumes precisely shaped by focused ion beam (FIB) milling from sometimes complex microstructures. This technique has garnered a great deal of interest in recent years; on one hand because of its apparent simplicity, on the other hand because it revealed an unexpected size dependence in the flow stress of single crystals when the pillar diameter was reduced below a few tenths of a micrometre. The flow stress of FIB milled face centred cubic (fcc) micro-pillars appears to follow a power law as a function of their size. In contrast, non-FIB milled, body centred cubic (bcc) eutectic Molybdenum (Mo) alloy pillars prepared by directional growth exhibit, in their pristine state, whisker-like behaviour without a size effect. Furthermore, after FIB milling or moderate pre-deformation, the whisker character is lost and the typical scatter of the flow stress usually observed for FIB milled pillars is reproduced. After large pre-deformation the scatter vanishes and the pillars exhibit no size effect. These findings show that 1) the deterministic parameter in the size effect can be correlated with the initial microstructure of the pillar, and 2) FIB milling influences this microstructure. This study aims to link the deformation modes occurring in small-scale pillars with their initial microstructure by studying directionally solidified eutectic Mo-alloy pillars with a diameter of 1 micrometre. In-situ Laue diffraction experiments during the compression of such defect-free pillars show that with readily-available dislocation sources from a concave pillar top, the {112}[111] slip system with the highest Schmid factor is initially activated and not the allegedly assumed {110}[111] slip system that is typical for bcc metals. Post-mortem slip trace analysis and TEM observations confirm this finding. Moreover, 3D atom probe measurements and TEM images show that this behaviour can be linked to the presence of both alloying elements and fcc nano-precipitates found in the bcc Mo-alloy. Both can lead to a decrease of the critical temperature and the observation of an fcc-like deformation. Additionally, it is shown that both FIB milling and pre-deformation introduce defects in the initially dislocation-free pillars. In addition to this, pillars prepared under similar conditions yield quite different microstructures. The angle between the focused ion beam and the crystal orientation is found to play an important role in the creation of defects. It can also be shown that pillars with high initial dislocation density deform bulk-like and exhibit strain hardening, while pillars with low initial dislocation content demonstrate a large scatter in the flow and yield stress and exhibit large strain burst at later deformation stages. Furthermore several slip systems are activated before the flow stress is reached for pillars containing initially low dislocation content. Interestingly the first activated slip system can be linked to the initial streaking direction; slip is observed on the {112} plane that contains excess dislocations. For both the as-prepared pillars and the pillars with low initial dislocation content, the yield seems to be source limited, which is not the case for pillars with high initial dislocation content.

EPFL2011

Scalable fabrication of functional nanostructures on stretchable substrates by capillary-assisted particle assembly and adhesion lithography

Shao-Chi Yu

The fabrication of metallic nanostructures on stretchable substrates enables specific applications that exploit the combination of the nano-scale phenomena and the mechanical tunability of the physical dimensions of the nanostructures. Due to the large difference in the thermal expansion coefficient between metals and polymer-based soft materials, patterning metallic nanostructures directly on a stretchable substrate is a known challenging task. In this thesis, scalable fabrications of metallic nanostructures on stretchable substrates by top-down and bottom-up methods are studied. Metallic nanostructures are first fabricated on Si substrates and subsequently transferred to stretchable substrates.In the first part of this thesis, fabrication of nanogap electrodes (NGEs) on a polydimethylsiloxane (PDMS) substrate using adhesion lithography is reported. With wafer-level processes, the nanogap is created on an Al sacrificial layer by separating two Au electrodes with an Al2O3 nanolayer. By etching the Al sacrificial layer, the NGEs are transferred to the PDMS substrate. Tunneling currents across the nanogap on PDMS are measured under various mechanical deformation statuses of the PDMS substrate. The electrical measurement results show that the nanogap distance is mechanically tunable in the quantum tunneling regime. The NGEs on PDMS might be eventually integrated with micro piezo-electric actuators to become miniaturized tunable NGEs, which could pave the way towards the application of an on-chip single-molecule detector. Apart from developing the fabrication process of the NGEs on PDMS, a yield study of the essential step of the adhesion lithography, e.g., the tape peeling process, is also conducted to understand the design principles of the NGEs. The yield of the wafer-level tape peeling process is larger than 80%.In the second part of this thesis, chip-level (~ 2 x 2 cm2) fabrication of ordered gold nanoparticles (AuNPs) on a PDMS substrate using capillary-assisted particle assembly (CAPA) technique is reported. AuNPs are first assembled on reusable Si templates with pre-defined topographical traps, and then transferred to the PDMS substrate by etching the Al sacrificial layer. The reusable assembly trap has the shape of the funnel which is designed for high assembly yield (> 90%) and precise particle placement (offset ~ 10 nm). The assembly yield, the particle position offset, the yield of the transfer process, and the reusability of the assembly template are systematically studied. Two functional AuNP structures are demonstrated using the reported fabrication process. The first structure is the plasmonic surface lattice resonance (SLR) arrays of 150 and 200 nm AuNP. The optical spectra of the AuNP arrays on PDMS are measured showing pitch-related SLR peaks that agree with the finite element method (FEM) simulation results. The second structure is the dimer of 200 nm AuNPs which has a nanogap between two AuNPs. By assembling two AuNPs in the same funnel-shaped trap, a nanogap is formed between two AuNPs. Combining Au electrodes fabricated using electron beam lithography and the lift-off process, NGEs are fabricated and successfully transferred to a PDMS substrate.

EPFL2022