Simulating three dimensional self-assembly of shape modified particles using magnetic dipolar forces

The feasibility of 3D self-assembly of milli-magnetic particles that interact via magnetic dipolar forces is investigated. Typically magnetic particles, such as isotropic spheres, self-organize in stable 2D configurations. By modifying the shape of the particles, 3D self-assembly may be enabled. The design of the particles and the experimental setup are presented. The magnetic configurations of simple particle arrangements are obtained via energy minimization in simulations. The simulations show that a 3D configuration can become energetically favourable over 2D configurations, if the shape of the particle is modified

Determination of bit patterned media noise based on island perimeter fluctuations

We measured the fluctuation in shape of magnetic islands in bit patterned media fabricated by laser interference lithography. This fluctuation can be accurately described by a model based on a Fourier series expansion of the perimeter of the islands. The model can be easily linked to amplitude and jitter noise. We show that the amplitude and jitter noise are in principle correlated, and the jitter noise increases with increasing island area. The correlation is small for media prepared by laser interference lithography, but expected to gain importance for high density bit patterned media

Fully three-dimensional sound speed-corrected multi-wavelength photoacoustic breast tomography

Photoacoustic tomography is a contrast agent-free imaging technique capable of visualizing blood vessels and tumor-associated vascularization in breast tissue. While sophisticated breast imaging systems have been recently developed, there is yet much to be gained in imaging depth, image quality and tissue characterization capability before clinical translation is possible. In response, we have developed a hybrid photoacoustic and ultrasound-transmission tomographic system PAM3. The photoacoustic component has for the first time three-dimensional multi-wavelength imaging capability, and implements substantial technical advancements in critical hardware and software sub-systems. The ultrasound component enables for the first time, a three-dimensional sound speed map of the breast to be incorporated in photoacoustic reconstruction to correct for inhomogeneities, enabling accurate target recovery. The results demonstrate the deepest photoacoustic breast imaging to date namely 48 mm, with a more uniform field of view than hitherto, and an isotropic spatial resolution that rivals that of Magnetic Resonance Imaging. The in vivo performance achieved, and the diagnostic value of interrogating angiogenesis-driven optical contrast as well as tumor mass sound speed contrast, gives confidence in the system\'s clinical potential

Magnetic interactions in 2D and 3D arrays

Magnetostatic interactions manifest themselves via the fields and forces between and within magnetized bodies. This thesis topics magnetostatic interactions in arrays at the nano- and millimeter scale. These arrays may find application in magnetic data storage and in future 3D electronics fabricated by self-assembly. On the nanoscale, interactions are investigated that are involved in reading and writing 2D patterned arrays of magnetic ~100 nm Co/Pt multilayered islands with perpendicular anisotropy, by magnetic force microscopy (MFM), and by modeling and simulations. Such 2D arrays are prototypes for future hard disk drive media, i.e. bit patterned media. Concerning reading, a new model for media noise is presented. The model captures the fluctuation in the shapes of the islands by the power spectrum of their perimeter, and predicts correlated amplitude and position jitter in the read back pulses of the islands. Besides media noise, 2D inter symbol interference (ISI) inhibits the correct detection of bits. A simple 2D modulation code that avoids the worst case interference patterns at the cost of a 5/6 code rate can handles more jitter compared to a previously developed code. Using MFM, first an off-line correction for the topographic distortion due to the liftmode MFM operation is investigated. Next, in-field MFM is used to determine the remanent switching fields of individual islands in an array. Remarkably, the measurements reveal that the switching mechanism varies within the array. Lastly, the read back signal and write field of side-coated MFM tips are investigated by imaging patterned arrays and varying the coating thickness. Due to undesired tip-sample interactions, the coating thickness is limited to about 80 nm, which limits the field of the tip to about 200 kA/m, typically smaller than the switching field distribution of a bit patterned array. On the millimeter scale, interactions are investigated that bind and drive the self-assembly of 2D and 3D arrays. Simulations show that 3–4 spherical particles equipped with magnets prefer to assemble in 2D configurations. By indenting the particles, a 3D configuration is possible if the magnets can rotate freely. In addition, magnetic levitation is used to drive the self-assembly of 0.5 mm Si cubes into, desirably, 2D and 3D arrays. Higher quality arrays are obtained when the hydrophilicity of the particles is reduced or when the bottom of the liquid container is used as a template. In calculations, it is confirmed that the particles indeed minimize the magnetostatic energy in a self-assembly experiment

Determination of bit patterned media noise based on island perimeter fluctuations

This abstract topics a new media noise model for bit patterned media (BPM) that incorporates fluctuations in the shape of the magnetic islands

Remarkable difference in reversal mechanism between identically patterned thin film Co/Pt elements of 70 nm diameter in an array

We show that the switching fields of individual islands have different dependencies on the applied field angle. The switching fields of weak islands for perpendicular fields appear to be dominated by domain wall movement, whereas the strong islands show a mechanism closer to coherent-rotation. These angular dependent switching fields are well described by two parameters using a modified Kondorsky model

Using magnetic levitation for 2D and 3D self-assembly of cubic silicon macroparticles

Today's micro- and nano-fabrication is essentially two-dimensional, with very limited possibilities of accessing the third dimension. The most viable way to mass-fabricate functional structures at the nano-scale, such as electronics or MEMS, with equal feature sizes in all directions, is by three-dimensional self-assembly. Up to now, three-dimensional self-assembly has mainly been restricted to crystals of polymer spheres. We report on two- and three-dimensional self-assembly of silicon cubes, levitated in a paramagnetic fluid. We demonstrate the benefits of templating and study the effect of a change in hydrophilicity of the cubes. These experiments bring us one step closer to three-dimensional self-assembly of anisotropic, semiconducting units, which is a crucial milestone in overcoming the scaling limits imposed by contemporary 2D microfabrication

A novel decoding scheme for product codes in bit patterned media

We present a novel decoding scheme for product codes that combat 2D intersymbol interference in bit patterned media. The new scheme is up to 42% faster and allows for 22% more jitter compared to the traditional iterative decoding scheme