In situ electron holography of the dynamic magnetic field emanating from a hard-disk drive writer

The proliferation of mobile devices in society accessing data via the ‘cloud’ is imposing a dramatic increase in the amount of information to be stored on hard disk drives (HDD) used in servers. Forecasts are that areal densities will need to increase by as much as 35% compound per annum and by 2020 cloud storage capacity will be around 7 zettabytes corresponding to areal densities of 2 Tb/in2. This requires increased performance from the magnetic pole of the electromagnetic writer in the read/write head in the HDD. Current state-of-art writing is undertaken by morphologically complex magnetic pole of sub 100 nm dimensions, in an environment of engineered magnetic shields and it needs to deliver strong directional magnetic field to areas on the recording media around 50 nm x 13 nm. This points to the need for a method to perform direct quantitative measurements of the magnetic field generated by the write pole at the nanometer scale. Here we report on the complete in situ quantitative mapping of the magnetic field generated by a functioning write pole in operation using electron holography. Opportunistically, it points the way towards a new nanoscale magnetic field source to further develop in situ Transmission Electron Microscopy.

Classical and quantum aspects of multimode parametric interactions

Parametric interactions in nonlinear crystals represent a powerful tool in the optical manipulation of information, both in the classical and the quantum regime. Here, we analyze in detail classical and quantum aspects of three-and five-mode parametric interactions in chi(2) nonlinear crystals. The equations of motion are explicitly derived and then solved within the parametric approximation. We describe several applications, including holography, all-optical gates, generation of entanglement, and telecloning. Experimental results on the photon distributions and correlations of the generated beams are also reported and discussed.

A DIRECT INVERSION METHOD FOR SURFACE-STRUCTURE DETERMINATION FROM LEED INTENSITIES

LOW-ENERGY electron diffraction (LEED) has become the most successful technique in surface crystallography1, but because of the complexity of the surface-electron scattering interactions, analyses of LEED data are still conducted on a trial-and-error basis: a direct-inversion method for treating LEED intensity data remains an attractive goal2. Building on recent theoretical and experimental developments in electron holography from surface structures3-16, we show here that three-dimensional images with atomic resolution can be obtained by a direct transform of conventional LEED intensity spectra.

MULTIPLE-SCATTERING EFFECTS IN ELECTRON HOLOGRAPHIC IMAGES

An exact multiple-scattering formalism is used to simulate a wave multiply scattered from a cluster, and this is used to provide a direct quantitative analysis of the influence of multiple scattering on holographic imaging. Although multiple scattering may help in identifying atomic positions in real space, we show that it does cause a loss of resolution. We also show that a filter function can considerably reduce the multiple-scattering contribution to holographic images.

A STUDY ON THE HOLOGRAPHIC TRANSFORM FOR ELECTRON-DIFFRACTION FROM SURFACES

We break down photoelectron diffraction intensities into four terms in analogy to optical holography and discuss the effect of each term on reconstructed images. The second term involving products of scattered waves SIGMA-SIGMA-O(i)O(j)*, is in this case not structure-less. Theoretical analysis and simulations demonstrate that this term may lead to spurious features in real space images in holographic transforms of medium energy electron diffraction patterns. If it is small enough the problem may be overcome by an iterative correction process.