1,720,973 research outputs found
Three-dimensional Nanostructures Fabricated by Ion-Beam-Induced Deposition
No full textThe direct writing technology known as ion-beam-induced deposition (IBID) has been attracting attention mainly because of its high degree of flexibility of locally prototyping three-dimensional (3D) nanostructures. These high-resolution nanostructures have various research applications. However, no systematic study of the capability of IBID to fabricate 3D nanostructures has been published to date. This is partly caused by the lack of suitable methods to monitor and to access the numerous time-varying process parameters and our lacking overview of the interplay between the relevant parameters. This thesis partially aims to fill this gap. This thesis mainly includes three parts: (1) Exploration of the limits of IBID to fabricate nanopillars. Firstly to fabricate IBID pillars in a controllable and reproducible manner, we have studied the optimization of the pillar growth conditions. With the conventional Ga+ FIB and the novel He+ FIB approaches, the influence of precursor surface density and of the ion beam interaction have been investigated, respectively. Moreover, relevant simulation work is discussed to explain the interplay between vertical and lateral growth and their dependence on precursor depletion and replenishment. Combining these results, a comparison between Ga+ and He+ IBID pillar growth is made. Secondly, to improve the quality of IBID pillars, we have studied the formation of the irregular sidewall surface and the halo viz. the deposits around the bases of a typical Ga+ IBID pillar by comparing pillars grown on either an insulating Si3 N4 membrane or on a semiconducting Si wafer. Thirdly, by changing the substrate properties and the distance between neighboring pillars, we have studied the proximity effect in IBID pillar growth. This proximity effect is important when fabricating dense pillar arrays. The proximity effect of He+ IBID is similar to that of Ga+ IBID, though the trend is much less pronounced. (2) Exploration of the limits of IBID to fabricate nanopores in thin membranes. We have demonstrated that sub-10-nm-diameter nanopores in a Si3 N4 membrane can be fabricated in a single Ga+ IBID step by carefully adjusting the ion beam and gas exposure conditions. This is accomplished by exploiting the competition between sputtering and deposition processes during IBID. Apart from the simplicity and the speed, another advantage is a broad choice of material for the deposit and the membrane. At various stages of pore formation we have studied the chemical composition and the shape of the pore, which are the factors that determine the functionalization of the nanopores. For this purpose, energy dispersive x-ray (EDX), electron energy loss spectroscopy (EELS) analysis have been used for determining the chemical composition, and 3D electron tomography for determining the shape of the pore. It is found that the chemical structure in the rim of the pore depends on the properties of the precursor gas. Furthermore, simulation shows that the forward and the backward sputtering depend differently on membrane thickness. This difference can also play a role in the pore formation and shrinkage. (3) Study of the IBID process mechanisms. We have done a series of experiments to distinguish the roles of different mechanisms involved in IBID. Firstly we have found a significant contribution of secondary particles to Ga+ IBID. This result was obtained by comparing the volume of a deposited box with that of the material deposited onto a nearby sidewall. Subsequently we have investigated two models that describe IBID in terms of the impact of secondary electrons and of sputtered atoms, respectively. For this purpose, the yields of deposition, sputtering, and secondary electron emission as well as the energy spectra of the secondary electrons were measured in situ during Ga+ IBID as functions of ion incident angle and energy. The results indicate that the sputtered atom model describes Ga+ IBID better than the secondary electron model. I also briefly discuss the contribution of primary ions. Based on these results, we review the studies on the mechanisms of IBID with Ga+ or He+ ion beams and EBID mechanisms reported in the literature. I conclude that IBID has to be described by multiple mechanisms. The dominating mechanism is in Ga+ IBID related to sputtering, while in He+ IBID and EBID to secondary electron emission. In this thesis work, we have studied the capability of IBID to grow 3D nanostructures. Future efforts, for instance improvement of the purity of the deposits, will be necessary to functionalize IBID nanostructures.Kavli Institute of NanoscienceApplied Science
Stealth fiducial markers: Enhancing re-detection efficacy of defects on blank wafers
No full textIn this thesis a stealth fiducial marker system for blank wafers is designed, fabricated and validated. The goal of this marker system it to map the coordinates of TNO’s Rapid Nano (a fast optical inspection tool) to the coordinates of scanning electron microscopes and atomic force microscopes. This way defects, that have been detected in the Rapid Nano, can be re-detected with a higher efficacy in the scanning electron microscope or atomic force microscope for further study.Applied PhysicsKavli Nanolab/TNOApplied Science
Electronic Transport in Helium Beam Modified Graphene and Ballistic Josephson Junctions
No full textThis thesis describes the capabilities of the helium ion microscope (HIM) and that of graphene to explore fundamental physics and novel applications. While graphene offers superior electronic properties, the helium ion microscope allows us to combine imaging and modification of materials at the nanoscale. We used the capabilities of HIM to grow 3D-AFM probes, which can be used in the critical dimension semiconductor metrology. Moreover, we studied the ion-material interactions, needed to enable the fabrication of functional graphene nanoribbons. Similarly, we used the superior electronic properties of graphene to make ballistic Josephson junctions and studied the current-phase relation (CPR) of these junctions.The core of this thesis is focused on the fabrication and electronic characterization of He+ beam modified graphene, He+ beam etched graphene nanoribbons, and graphene-based Josephson junctions (JJs). The graphene devices were prepared by a new polymer-free transfer "van der Waals pick-up" technique. The fabricated devices comprise graphene encapsulated in hexagonal boron nitride (BN) and contacted along the edge by either a normalmetal (Cr/Au) or by a superconductor. The encapsulation in BN keeps the graphene clean and the edge contacting technique provides transparent interfaces. The thesis is divided into two main topics. In particular, the first three studies are dedicated to the research based on the helium ion microscope, and the next three are dedicated to the research based on boron nitride encapsulated graphene Josephson junctions
Helium-Ion Induced Deposition: Modelling Nanopillar Growth with a Moving Ion Beam
No full textHelium-ion induced deposition (He-IBID) is a small-scale manufacturing technique that uses a helium microscope to focus a helium-ion beam onto an adsorbed precursor gas, causing nanometer-scaled depositions onto a substrate. However, due to local depletion of the precursor gas, the amount of deposition can not be expected to be proportional to the beam current. The mechanisms of this growth need to be well investigated to understand the limitations and capabilities of this technique. Most studies look at simple pillar growth with a stationary beam, and most models exclude the surface diffusion of precursor molecules. We attempt to model the growth of horizontally grown pillars using a horizontally moving ion beam. According to experiments with this type of growth \cite{HammerheadAFMProbes}, precursor surface diffusion is a key mechanism, and thus past studies may not be sufficient. We use develop a continuum model based on solving differential equations. One benefit over the more common Monte Carlo methods is that the effect of the various mechanisms are more explicitly written in differential equation form. Another benefit is that the simulation is differentiable, lending itself to better application of new differentiable programming techniques. One difficulty, however, is in the accurate modelling of the energy-dependent interactions with a source that has varying electron energies. We derive a system of ordinary differential equations to model a simplified two-dimensional approach and an approximation for an effective secondary electron flux to use in decomposition rate calculations. We investigate the available literature to find realistic values for the physical and operational parameters required to calculate solutions. Through numerical integration we find solutions and show how the model estimates pillar width changes when these parameters are altered. We use numerical integration to solve the ODE system, and present the results. We find a nucleation boundary---dependent on the beam movement speed and current---below which pillars cannot be grown, consistent with experiment \cite{HammerheadAFMProbes}. We find that the assumptions made in the surface diffusion calculation are too extreme, and that likely solving a PDE system of the full surface in three-dimensional space will be required for accurate results.Applied Mathematics | Applied Physic
Proximity effect in ion-beam-induced deposition of nanopillars
No full textIon-beam-induced deposition (IBID) is a powerful technique for prototyping three-dimensional nanostructures. To study its capability for this purpose, the authors investigate the proximity effect in IBID of nanopillars. In particular, the changes in shape and dimension of pillars are studied when a second pillar is grown near an existing pillar. On a semiconducting bulk Si and on an insulating Si3N4 membrane the first pillar gets broader, whereas on Si it starts to bend. They attribute the broadening and bending to the additional deposition induced by the particles scattered from the growing second pillar. On Si the second pillar is taller than the first one, while on Si3N4 it is shorter and rougher. This difference points to an important role of the substrate conductivity in the proximity effect. In a conductive environment the changes in the second pillar are mainly caused by a precursor coverage enhancement in the pillar surface. This enhancement is caused by precursor molecules, which are reflected or desorbed from the first pillar. In the case of an insulating environment, the changes in the second pillar are mainly caused by the reduction in the substrate surface charging due to the presence of the first pillar.QN/Quantum NanoscienceApplied Science
Method and apparatus for the formation of nanometer-scale electrodes, and such electrodes
No full textA method for the formation of nanometer-scale electrodes, wherein strip of electrically conductive material, in particular metal, is provided with a longitudinal direction, a width direction and a thickness direction and then, with the aid of an electron beam, a groove is provided in a top surface of the strip, in the width direction of the strip, with a nanometer- scale width in the longitudinal direction of the stripApplied Science
Fast single-step fabrication of nanopores
No full textWe report a new method for the fabrication of sub-10 nm nanopores in a fast single process step. The pore formation is accomplished by exploiting the competition between sputtering and deposition in ion-beam-induced deposition (IBID) on a thin membrane. The pore diameter can be controlled by adjusting the ion beam and gas exposure conditions. The pore diameter is well below the limit that can be achieved by focused ion beam (FIB) milling alone. There is no need of preparation and successive treatments. Apart from simplicity and speed, this method offers an additional advantage of a broad choice of material and thickness of the deposit and the membrane.Kavli Institute of NanoscienceApplied Science
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