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We present the construction and performance of an ultra-low-temperature scanning tunneling microscope (STM), working in ultra-high vacuum (UHV) conditions and in high magnetic fields up to 9 T. The cryogenic environment of the STM is generated by a single-shot 3He magnet cryostat in combination with a 4He dewar system. At a base temperature (300 mK), the cryostat has an operation time of approximately 80 h. The special design of the microscope allows the transfer of the STM head from the cryostat to a UHV chamber system, where samples and STM tips can be easily exchanged. The UHV chambers are equipped with specific surface science treatment tools for the functionalization of samples and tips, including high-temperature treatments and thin film deposition. This, in particular, enables spin-resolved tunneling measurements. We present test measurements using well-known samples and tips based on superconductors and metallic materials such as LiFeAs, Nb, Fe, and W. The measurements demonstrate the outstanding performance of the STM with high spatial and energy resolution as well as the spin-resolved capability. [ABSTRACT FROM AUTHOR]

We present the design, setup, and operation of a new dip-stick scanning tunneling microscope. Its special design allows measurements in the temperature range from 4.7 K up to room temperature, where cryogenic vacuum conditions are maintained during the measurement. The system fits into every 4He vessel with a bore of 50 mm, e.g., a transport dewar or a magnet bath cryostat. The microscope is equipped with a cleaving mechanism for cleaving single crystals in the whole temperature range and under cryogenic vacuum conditions. For the tip approach, a capacitive automated coarse approach is implemented. We present test measurements on the charge density wave system 2H-NbSe2 and the superconductor LiFeAs which demonstrate scanning tunneling microscopy and spectroscopy data acquisition with high stability, high spatial resolution at variable temperatures and in high magnetic fields. [ABSTRACT FROM AUTHOR]

Tin oxide nanoparticles with sizes in the range 5-30 nm are generated within a low pressure flame reactor setup in the gas phase. We study the effect of preparation parameters such as precursor concentration, flame to substrate distance, and post-deposition annealing procedures on the morphology and crystal structure of the particles utilizing transmission electron microscopy and X-ray diffraction in order to characterize the particle formation process. The structural investigations indicate that monoxide particles form from SnO monomers within the flame. These primary particles need to be further oxidized and thermally annealed to transform into single phase rutile type SnO 2 nanoparticles. [ABSTRACT FROM AUTHOR]

Low pressure premixed H2/O2Ar flames (H2/O2 = 1.69, 1.04 ⩽ Ar/(H2 + O2) ⩽ 1.36) were doped with small amounts of SiH4 (131 ppm ⩽ SiH4/(H2 + O2 + Ar) ⩽ 524 ppm) and were stabilized on a flat, water-cooled sintered bronze plate at pressures 27.5 mbar ⩽ p ⩽ 30 mbar. Particles formed during the flame reaction process were extracted at different heights from the flame zone by a molecular beam sampling technique, which is part of a particle mass spectrometer. PMS. This instrument, which was developed earlier in this laboratory, generates a particle beam in a high vacuum containment. From direct measurements of both, the kinetic energy and the velocity of charged particles, their mass was directly determined. As the amount of naturally charged particles in the SiH4-doped H2/O2/ Ar flame was nearly zero. small amounts of C2H2 (about 5 ppm) was added to the flame, which changes the charging situation drastically. The PMS measurements indicate a strong formation rate of charged particles at flame co-ordinate x ⩾ 20 mm, which were in the mass range 3.7 10-20 g ⩽ mp, ⩽ 58.3 1O-20g. The equivalent particle size determined with a material density of ρ = 2.65 g cm- 3 was 3.0 nm ⩽ dp ⩽ 7.6 nm. The absolute particle mass depends on the amount of SiH4 on the dilution ratio, and is a function of the flame co-ordinate. J;. An increasing amount of C2H2 added to the H2/O2/Ar + SiH4 flame results in an increase in the amount of charged particles by more than one order of magnitude. The experimental results on SiO2 particle formation were verified by a theoretical model. It includes the futl homogeneous H2/O2 and SiH4/O2 kinetics as well as transport properties of burner stabilised flames. The particle formation was described based on homogeneous nucleation of SiO2-vapour and Brownian coagulation, simulated both by a monodisperse as well as by a sectional model. Considering the size dependent charging probability of neutral particles by chemo-ions, good agreement in particle size and size distribution between the experimental results and the computer simulations was obtained. [ABSTRACT FROM PUBLISHER]

Magnetic cooling prototypes based on the magnetocaloric effect require the magnetic refrigerant to be shaped into geometries that enable quick and efficient heat-transfer to the transfer fluid. Simple solutions include a stack of parallel-plates or a bed of packed-spheres. Here, we demonstrate how more sophisticated geometries can be made by using selective laser melting, a rapid prototyping technique to form three-dimensional shapes. Using excellent magnetocaloric La(Fe,Co,Si)13 as starting-powder we made two geometries: a wavy-channel block with a high surface-to-volume ratio and an array of fin-shaped rods which eliminate unwanted heat conduction along the magnetic part. After annealing treatment, the geometries are intact and can survive more than 106 cycles of applying a magnetic field while still maintaining good magnetocaloric properties. This fabrication approach shows promise for making near-net shaped magnetic refrigerants with superior heat transfer properties and performance. [ABSTRACT FROM AUTHOR]

For high-resolution powder diffraction in material science, high photon energies are necessary, especially for in situ and in operando experiments. For this purpose, a multi-analyser detector (MAD) was developed for the high-energy beamline P02.1 at PETRA III of the Deutsches Elektronen-Synchrotron (DESY). In order to be able to adjust the detector for the high photon energies of 60 keV, an individually adjustable analyser-crystal setup was designed. The adjustment is performed via piezo stepper motors for each of the ten channels. The detector shows a low and flat background as well as a high signal-to-noise ratio. A range of standard materials were measured for characterizing the performance. Two exemplary experiments were performed to demonstrate the potential for sophisticated structural analysis with the MAD: (i) the structure of a complex material based on strontium niobate titanate and strontium niobate zirconate was determined and (ii) an in situ stroboscopy experiment with an applied electric field on a highly absorbing piezoceramic was performed. These experiments demonstrate the capabilities of the new MAD, which advances the frontiers of the structural characterization of materials., (open access.)

Details of fast-resistive-heating setups, controlled heating ranging from ∼10 1 K s -1 to ∼10 3 K s -1 , to study in situ phase transformations (on heating and on cooling) in metallic glasses by high-energy synchrotron x-ray diffraction are discussed. Both setups were designed and custom built at the Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden) and have been implemented at the P02.1 Powder Diffraction and Total Scattering Beamline and the P21.1 Swedish Materials Science Beamline at PETRA III storage ring, DESY, Hamburg. The devices are interchangeable at both beamlines. Joule heating is triggered automatically and is timed with the incident beam and detector. The crystallization process can be controlled via a feedback circuit by monitoring the change in the time-dependent resistivity and temperature of glasses. Different ambient atmospheres, such as vacuum and inert gases (He and Ar), can be used to control oxidation and cooling. The main focus of these devices is on understanding the crystallization mechanism and kinetics in metallic glasses, which are brittle and for which fast heating gives defined glass-crystal composites with enhanced plasticity. As an example, phase-transformation sequence(s) in a prototyped Cu-Zr-based metallic glass is described on heating, and a crystalline phase beneficial to the plasticity is identified.