We present experiments and micromagnetic simulations on Hall micromagnetometry of magnetic vortices. The magnetization reversal in a 2×2 μm2 Permalloy square of 20 nm thickness is investigated at liquid helium temperatures. Nucleation, displacement, and annihilation of the vortex state in an external magnetic field are observed by detecting its stray field. The findings are corroborated by images taken with a magnetic-force microscope at room temperature. The experimental data are compared to micromagnetic simulations.
Simple two-step wet-chemical cleans composed of an oxidizing step with in water dissolved ozone followed by an etching step have been studied for high-efficient hetero-junction silicon solar cell applications. For this purpose flat Si (111) samples passivated with amorphous silicon have been investigated. The effect of nanoroughness of the crystalline silicon surface on the minority carrier lifetime is shown. An influence of the storage time between cleaning and a-Si:H deposition was found and can partly be attributed to changes in surface roughness and native oxide growth.
As a high-efficiency silicon solar cell concept amorphous silicon/crystalline silicon (a-Si:H(n,p)/c-Si (p,n)) hetero-junction solar cells are of great scientific interest [1, . The a-Si:H emitter is deposited by plasma-enhanced chemical vapor deposition (PECVD). The biggest challenge is to avoid recombination at the a-Si:H(i)/c-Si interface where the p-n junction is located. A clean, smooth, hydrogen terminated c-Si surface is supposed to be mandatory for a high passivation quality of the deposited layer [3, 4]. It is well established that treatment in dilute hydrofluoric acid (dHF) solution (1-10%) produces a hydrogen-terminated, clean Si surface [e.g. 5, 6, 7]. H-termination is supposed to rise with increasing etch time [8]. Whereas prolonged rinsing after the etch step leads to a formation of OH-groups at the surface [8]. Because of the high sensitivity of the a-Si:H(i)/c-Si interface the influence of prolonged etching in dHF (1%) as well as prolonged rinsing in deionized water (DI water) on the passivation quality of the deposited a-Si:H(i) layer has to be carefully studied. Also the possibility of decreased hydrophobicity and a possible iron recontamination from the HF has been taken into account.
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