Characterization of Fe-N nanocrystals and nitrogen–containing inclusions in (Ga,Fe)N thin films using transmission electron microscopy

Nanometric inclusions filled with nitrogen, located adjacent to FenN (n¼3 or 4) nanocrystals within (Ga,Fe)N layers, are identified and characterized using scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). High-resolution STEM images reveal a truncation of the Fe-N nanocrystals at their boundaries with the nitrogen-containing inclusions. A controlled electron beam hole drilling experiment is used to release nitrogen gas from an inclusion in situ in the electron microscope. The density of nitrogen in an individual inclusion is measured to be 1.460.3 g/cm3. These observations provide an explanation for the location of surplus nitrogen in the (Ga,Fe)N layers, which is liberated by the nucleation of FenN (n>1) nanocrystals during growth

Electron energy-loss spectroscopy of boron-doped layers in amorphous thin film silicon solar cells

Electron energy-loss spectroscopy (EELS) is used to study p-doped layers in n-i-p amorphous thin film Si solar cells grown on steel foil substrates. For a solar cell in which an intrinsic amorphous hydrogenated Si (a-Si-H) layer is sandwiched between 10-nm-thick n-doped and p-doped a-Si:H layers, we assess whether core-loss EELS can be used to quantify the B concentration. We compare the shape of the measured B K edge with real space ab initio multiple scattering calculations and show that it is possible to separate the weak B K edge peak from the much stronger Si L edge fine structure by using log-normal fitting functions. The measured B concentration is compared with values obtained from secondary ion mass spectrometry, as well as with EELS results obtained from test samples that contain ∼200-nm-thick a-Si:H layers co-doped with B and C. We also assess whether changes in volume plasmon energy can be related to the B concentration and/or to the density of the material and whether variations of the volume plasmon line-width can be correlated with differences in the scattering of valence electrons in differently doped a-Si:H layers.Fil: Duchamp, M.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Boothroyd, C.B.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Moreno, Mario Sergio Jesus. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Van Aken, B.B.. No especifíca;Fil: Soppe, W.J.. No especifíca;Fil: Dunin-Borkowski, R.E.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; Alemani

Lorentz near-field electron ptychography

Over the past few years, electron ptychography has drawn considerable attention for its ability to recover high contrast and ultra-high resolution images without the need for high quality electron optics. In this Letter, we focus on electron ptychography's other potential benefits: quantitatively mapping phase variations resulting from magnetic and electric fields over extended fields of view. To this end, we propose an implementation of near-field ptychography that employs an amplitude mask located in the electron microscope's condenser aperture plane. We demonstrate the capabilities of our method by imaging a magnetic Permalloy sample and compare our results with those of off-axis electron holography

Langevin Simulation of Thermally Activated Magnetization Reversal in Nanoscale Pillars

Numerical solutions of the Landau-Lifshitz-Gilbert micromagnetic model incorporating thermal fluctuations and dipole-dipole interactions (calculated by the Fast Multipole Method) are presented for systems composed of nanoscale iron pillars of dimension 9 nm x 9 nm x 150 nm. Hysteresis loops generated under sinusoidally varying fields are obtained, while the coercive field is estimated to be 1979 $\pm$ 14 Oe using linear field sweeps at T=0 K. Thermal effects are essential to the relaxation of magnetization trapped in a metastable orientation, such as happens after a rapid reversal of an external magnetic field less than the coercive value. The distribution of switching times is compared to a simple analytic theory that describes reversal with nucleation at the ends of the nanomagnets. Results are also presented for arrays of nanomagnets oriented perpendicular to a flat substrate. Even at a separation of 300 nm, where the field from neighboring pillars is only $\sim$ 1 Oe, the interactions have a significant effect on the switching of the magnets.Comment: 19 pages RevTeX, including 12 figures, clarified discussion of numerical technique