Magnetic Resonance Lithography with Nanometer Resolution

We propose an approach for super-resolution optical lithography which is based on the inverse of magnetic resonance imaging (MRI). The technique uses atomic coherence in an ensemble of spin systems whose final state population can be optically detected. In principle, our method is capable of producing arbitrary one and two dimensional high-resolution patterns with high contrast

Metasurface Holographic Optical Traps for Ultracold Atoms

We propose metasurface holograms as a novel platform to generate optical trap arrays for cold atoms with high fidelity, efficiency, and thermal stability. We developed design and fabrication methodologies to create dielectric, phase-only metasurface holograms based on titanium dioxide. We experimentally demonstrated optical trap arrays of various geometries, including periodic and aperiodic configurations with dimensions ranging from 1D to 3D and the number of trap sites up to a few hundred. We characterized the performance of the holographic metasurfaces in terms of the positioning accuracy, size and intensity uniformity of the generated traps, and power handling capability of the dielectric metasurfaces. Our proposed platform has great potential for enabling fundamental studies of quantum many-body physics, and quantum simulation and computation tasks. The compact form factor, passive nature, good power handling capability, and scalability of generating high-quality, large-scale arrays also make the metasurface platform uniquely suitable for realizing field-deployable devices and systems based on cold atoms

From Materials to Devices: (I) Ultrathin Flexible Implantable Bio-probes with Biodegradable Sacrificial Layers (II) Carrier Spin Injection and Transport in Diamond

abstract: My research has been focusing on the innovations of material and structure designs, and the development of fabrication processes of novel nanoelectronics devices. My first project addresses the long-existing challenge of implantable neural probes, where high rigidity and high flexibility for the probe need to be satisfied at the same time. Two types of probes that can be used out of the box have been demonstrated, including (1) a compact probe that spontaneously forms three-dimensional bend-up devices only after implantation, and (2) an ultra-flexible probe as thin as 2 µm attached to a small silicon shaft that can be accurately delivered into the tissue and then get fully released in situ without altering its shape and position as the support is fully retracted. This work provides a general strategy to prepare ultra-small and flexible implantable probes that allow high insertion accuracy and minimal surgical damages with best biocompatibility. My second project focuses on the injection and characterization of carrier spins in single crystal diamond based nanoscale devices. The conventional diamond-based quantum information process that exploits nitrogen vacancy centers faces a major barrier of large scale communication. Electron/hole spin in diamond devices, on the other hand, could also be a good candidate for quantum computing due to the very small spin-orbit coupling and great coherent transport length of spin. To date, there has been no demonstration of carrier spin transport in diamond. In this work, I try to answer this fundamental question of how to inject and characterize electron spins in Boron doped diamond. Nanoscale diamond devices have been fabricated to investigate this question, including Hall bar device for material characterization, and lateral spin valve for injecting spin-polarized current into a mesoscopic diamond bar and detecting induced pure spin current. The preliminary results show signatures of spin transport in heavily doped diamond films. Looking into the future, the knowledge we obtained in these two projects, including the strategy to integrate thin-film nanoelectronics devices on a flexible bio-probe configuration, and how to build spintronic devices with diamond structures, could be unified in the exploration of spin-based sensors in biological systems.Dissertation/ThesisDoctoral Dissertation Materials Science and Engineering 201

A lithographic approach for quantum dot-photonic crystal nanocavity coupling in dilute nitrides

We report on a novel lithographic approach for the fabrication of integrated quantum dot (QD)-photonic crystal (PhC) nanocavity systems. We exploit unique hydrogen's ability to tailor the band gap energy of dilute nitride semiconductors to fabricate isolated site-controlled QDs via a spatially selective hydrogenation at the nanometer-scale. A deterministic integration of the realized site-controlled QDs with PhC nanocavities is provided by the inherent realignment precision (~ 20 nm) of the electron beam lithography system used for the fabrication of both QDs and PhC cavities. A detailed description of the fabrication steps leading to the realization of integrated QD-PhC cavity systems is provided, together with the experimental evidence of a weak coupling effect between the single-photon emitter and the PhC cavity

A slow and cold particle beam for nanotechnological purposes

In this thesis we report the production of a Cesium atomic beam by means of laser cooling techniques and its photoionization, in order to evaluate its applicative potential for specific technological purposes. A comprehensive analysis of the atomic beam is carried out, based on a variety of diagnostics, such as fluorescence imaging at different distances from the pyramidal-MOT, absorption spectroscopy, optical time-of-flight. The results demonstrate that the atomic beam owns peculiar dynamical properties, in particular in terms of longitudinal and transverse velocity distribution. The average value of the longitudinal velocity is on the order of ten m/s, with a spread on the order of m/s, accompanied by a few mrad divergence: such features motivate the names “slow” and “cold” we have attributed to our atomic beam. Thanks to them, the beam can find applications where sources of particles with controlled and rather homogeneous dynamical properties are required. The main motivation behind photoionization of the Cesium beam was to set the basis for exploring the capabilities of the slow and cold beam in producing an ion beam. This part of the research was carried out within the frame of a European industry-oriented collaboration (FP7-MC-IAPP Project ”COLDBEAMS”) aimed at exploiting laser manipulation tools for the realization of unconventional charged particle beams with superior dynamical properties. The technology presently used for instance in FIB columns is in fact based on beams with “thermal” velocity distribution, that leads to non-monochromatic samples severely suffering chromatic aberration in the focusing stage. To this aim, a two-colour photoionization scheme has been implemented, involving resonant excitation of Cesium 6P atoms and interaction with 405 nm photons. Photoionization was demonstrated and the rate estimated on the order of about 3 · 10^6 s^(−1). The corresponding ion current is on the order of 0.5 pA. A preliminary insight into the dynamical properties of the ion beam has been given by ion time-of-flight measurements upon pulsed laser ionization. Interpretation of the results required a careful description of the electric fields in the collection region, which, while not being optimized by design for this specific purpose, were numerically simulated. The results demonstrate that, owing to the peculiar features of the neutral atom beam, the ions exhibit a rather monochromatic longitudinal energy distribution, with a monochromaticity essentially limited by the size of the ionizing laser beam and by the weak collection field. Such properties are comparable to those of the ion sources used at present

Anomalous Properties of Sub-10-nm Magnetic Tunneling Junctions

Magnetic Logic Devices have the advantage of non-volatility, radiation hardness, scalability down to the sub-10nm range, and three-dimensional (3D) integration capability. Despite these advantages, magnetic applications for information processing remain limited. The main stumbling block is the high energy required to switch information states in spin-based devices. Recently, the spin transfer torque (STT) effect has been introduced as a promising solution. STT based magnetic tunneling junctions (MTJs), use a spin polarized electric current to switch magnetic states. They are theorized to bring the switching energy down substantially. However, the switching current density remains in the order of 1 MA/cm2 in current STT-MTJ devices, with the smallest device reported to date around 10nm. This current density remains inadequately high for enabling a wide range of information processing applications. For this technology to be competitive in the near future it is critical to show that it could be favorably scaled into the sub-10-nm range. This is an intriguing size range that currently remains unexplored. Nanomagnetic devices may display promising characteristics that can make them superior to their semiconductor counterparts. Below 10nm the spin physics from the vii surface become dominate versus those due to volume. The goal is to understand the size dependence versus the switching current

Design and fabrication of bifunctional metalenses

Regarding light beams, an interesting feature is the spatial distribution of their wavefront. In fact, the wavefront of light beams can be engineered to obtain a precise shape through the local modification of the phase of the electromagnetic wave. This process is known as light structuring and can be realized through the use of dedicated optics. The most popular light structuring feature is the generation of helicoidal wavefronts, with the presence of the so called vortex singularity, which provide light with orbital angular momentum (OAM). This task can be achieved through the use of metalenses, flat nanostructured devices. A particular type of metalens are called dual-function metalenses that can manage of two distinct spin states. This multiple functionality is possible due to the specific structure of the meta-units, each containing a nanofin with different shape and orientation. The aim of this thesis work is the design, fabrication and characterization of this spinmultiplexing metalens. The device is realized in silicon.The design process is carried out through the meta-units simulation with finite element method analysis. The fabrication is performed in nanofabrication facility. The device behaviour is then characterized by laser illumination and the quality of the intensity pattern was evaluated. Among its applications, this device has a potential for telecommunication purposes in quantum regime level and contrast phase microscopy.Regarding light beams, an interesting feature is the spatial distribution of their wavefront. In fact, the wavefront of light beams can be engineered to obtain a precise shape through the local modification of the phase of the electromagnetic wave. This process is known as light structuring and can be realized through the use of dedicated optics. The most popular light structuring feature is the generation of helicoidal wavefronts, with the presence of the so called vortex singularity, which provide light with orbital angular momentum (OAM). This task can be achieved through the use of metalenses, flat nanostructured devices. A particular type of metalens are called dual-function metalenses that can manage of two distinct spin states. This multiple functionality is possible due to the specific structure of the meta-units, each containing a nanofin with different shape and orientation. The aim of this thesis work is the design, fabrication and characterization of this spinmultiplexing metalens. The device is realized in silicon.The design process is carried out through the meta-units simulation with finite element method analysis. The fabrication is performed in nanofabrication facility. The device behaviour is then characterized by laser illumination and the quality of the intensity pattern was evaluated. Among its applications, this device has a potential for telecommunication purposes in quantum regime level and contrast phase microscopy

Projecting the nanoworld: Concepts, results and perspectives of molecular electronics

A bottom-up approach is a promising alternative to build nanodevices and/or nanomachines starting from molecular building blocks. The idea of molecular electronics comes from a farsighted paper by Aviram and Ratner, predicting that single molecules with a donor–spacer–acceptor structure would have rectifying properties when placed between two electrodes. Today, molecular electronics is emerging as an alternative to Si-nanoelectronics for building integrated devices. This review aims to give an overview of this emerging field, analysing the concepts, the key results and the perspectives