Controlling the Oxidation of Magnetic and Electrically Conductive Solid-Solution Iron-Rhodium Nanoparticles Synthesized by Laser Ablation in Liquids.

This study focuses on the synthesis of FeRh nanoparticles via pulsed laser ablation in liquid and on controlling the oxidation of the synthesized nanoparticles. Formation of monomodal γ-FeRh nanoparticles was confirmed by transmission electron microscopy (TEM) and their composition confirmed by atom probe tomography (APT). For these particles, three major contributors to oxidation were analysed: (1) dissolved oxygen in the organic solvents, (2) the bound oxygen in the solvent and (3) oxygen in the atmosphere above the solvent. The decrease of oxidation for optimized ablation conditions was confirmed through energy-dispersive X-ray (EDX) and Mössbauer spectroscopy. Furthermore, the time dependence of oxidation was monitored for dried FeRh nanoparticles powders using ferromagnetic resonance spectroscopy (FMR). By magnetophoretic separation, B2-FeRh nanoparticles could be extracted from the solution and characteristic differences of nanostrand formation between γ-FeRh and B2-FeRh nanoparticles were observed.

Three dimensional tracing of a charged particle by electrostatic detection.

Using a configuration of electrodes connected to charge sensitive amplifiers, the position of a charged particle in free space can be determined in all three dimensions. In our experiment, spheres with a diameter of a millimeter and a charge of about 0.1 pC are traced while they are bouncing at a surface. A spatial resolution of about 0.5 mm combined with a temporal resolution better than 10 µs is achieved. Moreover, the transfer of electric charges when touching a surface can be evaluated.

Electrometer with sub-attoampere current load.

By cooling a conventional junction field-effect transistor below 150 K, a simple and versatile electrometer with extremely high impedance can be realized. At operating condition, the leakage current to the gate amounts to a few hundredths of an attoampere. The electrometer can be used from DC up to a frequency of 10 kHz. Without reduction of the bandwidth, a sensitivity of a few µV is obtained. Working at low frequencies, currents as low as a few attoamperes can be detected. If the input voltage is out of the operational range, the forward current or the Zener current of the gate junction protects the transistor against destructive charging.