Ion Beam Nanomachining Research Articles

All Oxide-Based Magnetic Tunnel Junctions Fabricated by Focused Ion Beam Nanomachining Technique

This study offers a comprehensive investigation into the fabrication of all-oxide-based magnetic tunnel junctions (MTJs) utilizing the focused ion beam (FIB) nanomachining method. The oxide thin films of SrTiO3 (STO), La[Formula: see text]CaxMnO3 (LCMO) and La[Formula: see text]SrxMnO3 (LSMO) were grown using pulsed laser deposition (PLD). Magnetization measurements at 5K revealed a notable difference in coercivity between LCMO and LSMO films, highlighting their suitability as electrodes in MTJ device fabrication. The deposited trilayer structure of LCMO/STO/LSMO exhibited heteroepitaxial growth, enabling the independent magnetic switching of electrode layers in the MTJ with the STO barrier layer. Conventional photolithography and ion milling were used to create a series of 4[Formula: see text][Formula: see text]m Hall bar tracks in the deposited films. Nanopillar devices, sized 250[Formula: see text]nm[Formula: see text]×[Formula: see text]250[Formula: see text]nm, were successfully fabricated on these 4[Formula: see text][Formula: see text]m tracks by optimizing the FIB nanomachining technique. The fabricated MTJs demonstrated a high tunnel magnetoresistance (TMR) response, leading to the conclusion that the FIB nanomachining technique holds significant promise for the development of high-performance oxide-based spintronic devices.

Biomimetic Signal Propagation in a Two-Pore Solid-State System

A key characteristic of excitable ion channels is the ability to interact with neighboring pores so that localized environmental stimuli can initiate complex large-scale responses, such as an action potential propagating along a neuron. In the case of a nerve signal, this is accomplished through local changes in the membrane voltage and ion concentration inducing nearby pores to change conductance states. The replication of this behavior in synthetic nanopore platforms has the potential to enable new responsive materials useful for biomimetic componentry, drug delivery and filtration technologies. While gating has been demonstrated in synthetic nanopores, previous fabrication methods make it difficult to incorporate such pores into more complex systems due to lack of control over key attributes such as pore location. Here, we fabricate two neighboring nanochannels with controlled spacing such that the transport through one pore can induce a change in conductance of a neighboring pore which has been chemically modified to be ion concentration responsive. The two-pore system is made using focused ion beam nanomachining followed by ion-beam-controlled deposition of SiOx around one pore entrance. Chemistry selective for SiOx is then used to graft single stranded DNA only to the regions where the local deposition was performed providing a final platform that enables local control over the location, size, shape and surface chemistry of each pore in the system. The pore-pore interaction is measured through a step-like increase of the total current passing through the SiNx membrane vs time following a change in applied voltage. We explore the effects of voltage and bulk ionic concentration on the way the inter-pore signal behaves. This successful demonstration of a signal passed from one man-made pore to another is an important step towards the integration of nanopore technology into more complex multi-component systems.

Focused ion beam nanomachining of tapered optical fibers for patterned light delivery

With the advent of optogenetic techniques, a major need for precise and versatile light-delivery techniques has arisen from the neuroscience community. Driven by this demand, research on innovative illuminating devices has opened previously inaccessible experimental paths. However, tailoring light delivery to functionally and anatomically diverse brain structures still remains a challenging task. We progressed in this endeavor by micro-structuring metal-coated tapered optical fibers and exploiting the resulting mode-division multiplexing/de-multiplexing properties. To do this, a non-conventional Focused Ion Beam (FIB) milling method was developed in order to pattern the non-planar surface of the taper around the full 360°, by equipping the FIB chamber with a micromanipulation system. This led us to develop three novel typologies of micro-structured illuminating tools: (a) a tapered fiber that emits light from a narrow slot of adjustable length; (b) a tapered fiber that emits light from four independently addressable optical windows; (c) a tapered fiber that emits light from an annular aperture with 360° symmetry. The result is a versatile technology enabling reconfigurable light-delivery that can be tailored to specific experimental needs.

3C-SiC microdisk mechanical resonators with multimode resonances at radio frequencies

We report on the design, modeling, fabrication and measurement of single-crystal 3C-silicon carbide (SiC) microdisk mechanical resonators with multimode resonances operating at radio frequencies (RF). These microdisk resonators (center-clamped on a vertical stem pedestal) offer multiple flexural-mode resonances with frequencies dependent on both disk and anchor dimensions. The resonators are made using a novel fabrication method comprised of focused ion beam nanomachining and hydroflouic : nitric : acetic (HNA) acid etching. Resonance peaks (in the frequency spectrum) are detected through laser-interferometry measurements. Resonators with different dimensions are tested, and multimode resonances, mode splitting, energy dissipation (in the form of quality factor measurement) are investigated. Further, we demonstrate a feedback oscillator based on a passive 3C-SiC resonator. This investigation provides important guidelines for microdisk resonator development, ranging from an analytical prediction of frequency scaling law to fabrication, suggesting RF microdisk resonators can be good candidates for future sensing applications in harsh environments.

Fabrication of a phase photon sieve on an optical fiber tip by focused ion beam nanomachining for improved fiber to silicon photonics waveguide light coupling.

PSS) as an alternative, more advantageous method to the metallization prior to FIB milling. The near field scans of the intensity profile along the optical axis under fiber illumination of a laser at λ = 1.55 μm are presented. We have analyzed the focusing properties and demonstrated the validity of our structure for light coupling into silicon photonics waveguides with improved efficiency and alignment tolerance.

Erosive-thermal transition in high-flux focused ion beam nanomachining of surfaces

Focused ion beams (FIB) are increasingly used for surface modification and fabrication with nanometer scale precision. In FIB, an energetic beam of ions strikes a surface and removes material, a process that is understood to depend upon the properties of the beam (e.g. beam flux, ion energy) and is thought to be due to ion induced sputter erosion. We show that the material removal rate is also strongly affected by the thermal properties of the material, sample temperature, and geometry. Furthermore, we deduce a dimensionless parameter, a ratio of incident power to thermally dissipated power (QFIB), which parameterizes a switch of the underlying mechanism of material removal. It predicts with remarkable accuracy a previously overlooked transition from slow erosive material removal to significantly accelerated thermal vaporization material removal. Its critical value explains an observed transition in data covering a range of beam fluxes, ion energies, spot sizes, film thicknesses, materials, ion species, and temperatures. Large-scale parallel molecular dynamics simulations support this transition.

Effects of current on early stages of focused ion beam nano-machining

In this report we investigate the effects of focused ion beam machining at low doses in the range of 1015–1016 ions cm−2 for currents below 300 pA on Si(100) substrates. The effects of similar doses with currents in the range 10–300 pA were compared. The topography of resulting structures has been characterized using atomic force microscope, while crystallinity of the Si was assessed by means of Raman spectroscopy. These machining parameters allow a controllable preparation of structures either protruding from, or recessed into, the surface with nanometre precision.

High-resolution direct-write patterning using focused ion beams

Abstract

The Effect of Crystallinity on Materials Removal Rate of Polyolefins During Ga+ Focused Ion Beam Nanomachining

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

The Sputtering Behavior of Polymeric Materials During Focused Ion Beam Nanomachining

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Cold atoms near surfaces: designing potentials by sculpturing wires

The magnetic trapping potentials for atoms on atom chips are determined by the current flow pattern in the chip wires. By modifying the wire shape using focused ion beam nano-machining we can design specialized current flow patterns and therefore micro-design the magnetic trapping potentials. We give designs for a barrier, a quantum dot, and a double well or double barrier and show preliminary experiments with ultra cold atoms in these designed potentials.

Limitations of focused ion beam nanomachining

In this article, some limitations of the processing of structures with dimensions in the nanometer range by focused ion beams will be discussed. In order to enable exact depth control of nanometer structures, the effective sputter yield of silicon was determined as function of the ion dose. At ion doses below 1016 cm−2, the effective sputter yield is not constant and the volume of the area processed increases due to the implantation of ions. Material removal can be measured for doses above 2×1016 cm−2 and it reaches equilibrium for doses of about 3×1017 cm−2. This dose dependence of the effective sputter yield becomes especially effective in beam tail regions with low ion intensity. The shape of nanostructures is further determined by combining the beam shape and the angle dependence of the sputter yield which was experimentally determined. Using this approach with a Gaussian beam shape, a comparison of simulated and measured sidewall angles has shown good agreement for trench structures. Only sidewall regions close to the surface and to the bottom of deep structures show slight deviations. At the surface, non-Gaussian beam tails lead to unintentional sputtering at the corners of the processed area. At the bottom, forward scattered ions lead to higher sputter erosion.

Fabrication of silicon aperture probes for scanning near-field optical microscopy by focused ion beam nano machining

Scanning near-field optical microscopy (SNOM) probes can be realized by aperture probes based on metal coated atomic force microscopy (AFM) sensors. The application of focused ion beam (FIB) nano machining for the fabrication of apertures with well defined geometry and dimensions down to 60 nm will be described. Problems related to the processing of laterally and vertically well defined structures will be discussed. Apertures with circular and rectangular shape with dimensions below 100 nm will be presented. TEM cross sections of apertures reaching through the metal into silicon will be shown. Optical near-field measurement (wavelength of light 1064 nm) was used to demonstrate the functionality of the SNOM probes. Resolution down to 60 nm (1/17 of wavelength) has been achieved.