AFM tip-based cutting of grooves on permalloy nanowires for controlling the motion of magnetic domain walls

The research reported in this paper presents a new application of the AFM tip-based nanomachining process in the context of investigating the development of data storage devices. In particular, nanoscale grooves are machined with the tip of an AFM probe on the top surface of nanowires made of a ferromagnetic material. These grooves are cut with the purpose of creating artificial pinning sites for controlling the motion of magnetic domain walls within such nanowires. The experimental and computational results obtained when implementing this approach on permalloy nanowires 55 nm thick and 320 nm wide show that the strength of such artificial pinning sites increases with the increase in the depth of the machined grooves. It is anticipated that the application of AFM tip-based nanomachining in this context could contribute to the development of a variety of magnetic domain wall devices including those for logic function, data storage or sensor applications

Intelligent techniques for automatic feature recognition in CAD models

The solutions suggested in this research are implemented in a prototype AFR system and its performance verified on commonly used benchmarking parts that are composed of machining features.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Fabrication of periodic nanostructures using dynamic plowing lithography with the tip of an atomic force microscope

The fabrication of periodic nanostructures with a fine control of their dimensions is performed on poly(methyl methacrylate) (PMMA) thin films using an atomic force microscope technique called dynamic plowing lithography (DPL). Different scratching directions are investigated first when generating single grooves with DPL. In particular, the depth, the width and the periodicity of the machined grooves as well the height of the pile-up, formed on the side of the grooves, are assessed. It was found that these features are not significantly affected by the scratching direction, except when processing took place in a direction away from the cantilever probe and parallel to its main axis. For a given scratching direction, arrays of regular grooves are then obtained by controlling the feed, i.e. the distance between two machining lines. A scan-scratch tip trace is also used to reduce processing time and tip wear. However, irregular patterns are created when combining two layers oriented at different angles and where each layer defines an array of grooves. Thus, a “combination writing” method was implemented to fabricate arrays of grooves with a well-defined wavelength of 30 nm, which was twice the feed value utilized. Checkerboard, diamond-shaped, and hexagonal nanodots were also fabricated. These were obtained by using the combination writing method and by varying the orientation and the number of layers. The density of the nanodots achieved could be as high as 1.9 × 109 nanodots per mm2

Examining slit pore widths within plasma-exfoliated graphitic material utilising Barrett–Joyner–Halenda analysis

Plasma-exfoliated multilayer graphitic material (MLG) consists of orderly aligned stacks which contain many partially oxidised graphitic layers. Slit pores are present between successive stacks and their presence allows for improved friability, facile dispersion and accessibility for the intercalation of compounds. Whilst much research exists into the synthesis and application of MLG, there is a lack of quantitative data regarding their porous structures. This report outlines the structure of MLG as well as the application of Barrett–Joyner–Halenda (BJH) analysis to estimate the distance between adjacent stacks of orderly aligned graphitic layers within MLG. It was found that the distance between stacks can vary quite substantially between 2–131 nm within these plasma-derived materials, correlating with the width of meso- and macro-slit pores. Furthermore, t-plot data also suggests that micropores, likely to exist in the form of both slit pores and in-plane pores, are present within the material, hence stack separations may also exhibit distances of <2 nm. Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) were used to assist in this interpretation and to correlate with the BJH analysis. MLG was further analysed using Transmission Electron Microscopy (TEM), Brunauer–Emmett–Teller (BET) and t-plot analysis, X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy to gain a comprehensive understanding of the material investigated. The above techniques provided results which were consistent with the BJH porosity analysis, thus establishing it as a straightforward and highly effective method for understanding materials with broad pore distributions such as MLGs

Numerical investigation of size effects in tension and torsion of micro-scale copper wires using a strain gradient modified Johnson-Cook constitutive model

While material behaviour on the micro to nanoscale may be investigated using various experimental methods, it is of interest to develop complementary 3-dimensional (3D) numerical approaches to simulate material deformation at such small scales. In particular, these simulations provide a means to shed further light on key mechanisms at play, especially in the region of plastic strain. The size effect in tension and torsion of microscale copper wires is numerically investigated in this study using a strain gradient modified Johnson-Cook method. This 3D algorithm is implemented by self-compiled subroutines using the ABAQUS/Explicit solver. The simulated flow stress and yield stress in torsion of micro-scale copper wires were observed to increase with the decrease of the wire diameter, which correlates well with experimental findings reported in the literature. A similar size effect, although not as significant as that in torsion, was also observed in the simulated tension experiments, again in line with existing experimental reports. This work contributes to the efforts of the research community in the simulation material behaviour at the micro- to nanoscale, especially when considering the combined influence of both size effect and strain rate

A simple and generic CAD/CAM approach for AFM probe-based machining

Atomic Force Microscopy (AFM) probe-based machining allows surface structuring at the nano-scale via the mechanical modification of material. This results from the direct contact between the tip of an AFM probe and the surface of a sample. Given that AFM instruments are primarily developed for obtaining high-resolution topography information of inspected specimen, raster scanning typically defines the trajectory followed by the tip of an AFM probe. Although most AFM manufacturers provide software modules to perform user-defined tip displacement operations, such additional solutions can be limited with respect to 1) the range of tip motions that can be designed, 2) the level of automation when defining tip displacement strategies and 3) the portability for easily transferring trajectories data between different AFM instruments. In this context, this research presents a feasibility study, which aims to demonstrate the applicability of a simple and generic CAD/CAM approach when implementing AFM probe-based nano-machining for producing two-dimensional (2D) features with a commercial AFM instrument

Effect of machining parameters and cutting tool coating on hole quality in dry drilling of fibre metal laminates

Fibre metal laminates (FMLs) are a special type of hybrid materials, which consist of sheets of metallic alloys and prepregs of composite layers stacked together in an alternating sequence and bonded together either mechanically using micro hooks or thermally using adhesive epoxies. The present paper contributes to the current literature by studying the effects of three types of cutting tool coatings namely TiAlN, AlTiN/TiAlN and TiN on the surface roughness and burr formation of holes drilled in an FML commercially known as GLARE®. While the cutting tool geometry is fixed, the study is also conducted for a range of drilling conditions by varying the spindle speed and the feed rate. The obtained results indicate that the spindle speed and the type of cutting tool coating had the most significant influence on the achieved surface roughness metrics, while tool coating had the most significant effect on burr height and burr root thickness. The most important outcome for practitioners is that the best results in terms of minimum roughness and burr formation were obtained for the TiN coated drills. However, such drills outperform the other two types of tools, i.e. with TiAlN and AlTiN/TiAlN coatings, only when used for short series of hole drilling due to rapid tool deterioratio

A simple and generic CAD/CAM approach for AFM probe-based machining

Atomic Force Microscopy (AFM) probe-based machining allows surface structuring at the nano-scale via the mechanical modification of material. This results from the direct contact between the tip of an AFM probe and the surface of a sample. Given that AFM instruments are primarily developed for obtaining high-resolution topography information of inspected specimen, raster scanning typically defines the trajectory followed by the tip of an AFM probe. Although most AFM manufacturers provide software modules to perform user-defined tip displacement operations, such additional solutions can be limited with respect to 1) the range of tip motions that can be designed, 2) the level of automation when defining tip displacement strategies and 3) the portability for easily transferring trajectories data between different AFM instruments. In this context, this research presents a feasibility study, which aims to demonstrate the applicability of a simple and generic CAD/CAM approach when implementing AFM probe-based nano-machining for producing two-dimensional (2D) features with a commercial AFM instrument

Fabrication of Aluminium Nanowires by Differential Pressure Injection

The reported study aims to demonstrate the application of a simple technique, which is referred to as pressure differential injection, to prepare metallic nanowires. This technique relies on the difference in pressure between the inside of sealed nanochannels of an anodic aluminium oxide (AAO) substrate and the ambient atmosphere to inject a molten metal, which is previously deposited on the substrate, into the AAO pores. The application of this technique enabled the fabrication of nanowires in aluminium with diameters comprised between 55 nm and 65 nm

Modelling of a shear-type piezoelectric actuator for AFM-based vibration-assisted nanomachining

Recent research investigations have reported the benefit of enhancing conventional AFM-based nanoscale machining operations by the introduction of high frequency vibrations between the AFM tip and the processed material. The technique relies on piezoelectric actuation and is relatively straight forward to implement in practice. However, the non-linearity of piezoelectric actuators when operated under high electric field and frequency conditions can affect the dimensional accuracy of the fabricated nanostructures. To address these issues, the paper reports a method based on coupled mechanical-electrical Finite Element (FE) modelling to predict the relative motion between an AFM tip and a workpiece for vibration-assisted AFM-based nanomachining applications. In particular, the novelty of the proposed method is that it combines two classical approaches for modelling the nonlinear behaviour of piezoelectric materials. More specifically, two sources of non-linearity are considered simultaneously by combining the field-dependant model from Muller and Zhang with the frequency-dependant model from Damjanovic. The resulting combined model is employed to establish the piezoelectric constitutive equations implemented in the developed coupled field FE model. A further distinguishing characteristic of the work is that the proposed approach was subsequently validated by comparing the predicted widths of nanoscale grooves against those machined with a custom AFM-based vibration-assisted nanomachining configuration