Ion beam analysis laboratory and laboratory for nanomaterials

Ion beam analysis laboratory

The 5-MV tandem accelerator TAMIA was running very reliably through the whole year 2015. About half of the beam time was devoted to routine AMS radiocarbon measurements on various graphite samples, as shown in the figure below. Tests with the gaseous CO2 samples demonstrated that the same level of accuracy as with the graphitized samples can be reached.

samples

The other half of the beam time was devoted almost exclusively to IBA measurements with heavy ions, but some experiments employed also proton beams. The latter included 10-MeV proton irradiations for positron-annihilation spectroscopy (PAS) and for irradiations of MgO glass samples, test production of positron emitter for PAS using the (p,n) reaction at 6 and 10 MeV, and calibration tests using the 992-keV resonance in the 27Al(p,γ)28Si reaction. The calibration tests demonstrated that a good stability of the terminal high-voltage can be achieved also below 500 kV, bridging the gap between the energies of the 500-kV implanter and the 5-MV tandem.

The great majority of the IBA experiments were performed using routine TOF-ERDA measurements, producing altogether 605 TOF-ERDA spectra for the analysis. Of these spectra, 245 were measured together with the heavy-ion-induced X-rays and 360 without. About 200 new ALD samples were analyzed, most of them were produced at the Laboratory of Inorganic Chemistry of Helsinki University, some at VTT, Aalto University, AMS Microchemistry, and Vaisala. The ion beams for the TOF-ERDA measurements were Cl, Br, and I at energies from 15 to 55 MeV, complemented with some O and Ti beam experiments.

The RBS method with 12-MeV 12C ions was employed in a few cases, producing altogether 16 RBS spectra. A group of undergraduate students was invited to participate in RBS experiments with 3 -MeV protons. Until September 2015, the ion beams for the IBA measurements were extracted from the MISS ion source, but after successful tests of the MCGSNICS ion source (for elements other than carbon), all negative ions were produced exclusively with the latter.

The 500-kV ion accelerator KIIA was employed in routine implantation tasks producing about 150 different samples on various substrates. The ion beams used for the implantations were atomic (H) and molecular hydrogen (H2) at 200 keV, molecular deuterium (D2) at 60 keV, helium (He) at 30 keV, carbon (C) at 200 and 300 keV, oxygen (O) at 250 keV, copper (Cu) at 500 keV, cobalt (Co) at 80 keV, manganese (Mn) at 80 keV, and Au at 500 keV. Nitrogen depth profiles were measured with the NRA method employing the 429-keV resonance in the 15N(p,αγ)12C reaction.

The computer control and automation system that enables the remote operation of KIIA was installed and taken into routine use. With the exception of the current supply of the analyzing magnet, new power supplies were installed at the HV platform of the mini-separator. A modified thermomechanical leak system for feeding the ion source gases was also tested and put into routine operation. The beam raster scanner system at the implantation beam line was renovated.

Laboratory of nanomaterials

Nanocomposite multiferroics: multifunctionality embedded at the material level

Activity in the field of nanocomposite multiferroics was aimed at the development of new material systems and understanding of basic physics underlying their non-trivial properties. The systems of interest were different perovskite ferrites produced by Atomic Layer Deposition and chemical methods. Bismuth Ferrite (BiFeO3) thin films were studied within the framework of the Center of Excellence project in Atomic Layer Deposition (CoE ALD) funded by the Academy of Finland. Chemical Solution Deposition method was employed for synthesis of complex Bismuth Ferrite – Barium Titanate (BiFeO3-BaTiO3) thin films. These bismuth ferrite based systems are probably the most advanced to date multiferroics exhibiting in one phase co-existing magnetic ferroelectric and structural orders not only at cryogenic temperatures but also at high temperature. The latter makes them in particular interesting for wide use in the next generation electronics applications. Electromagnetic properties were studied using the facilities existing in our lab as well as those offered by our collaborating partners.

Gold nanoclusters and nanocrystalline films: intrinsic ferromagnetism

Bulk gold is well known to be diamagnetic. However, there is a growing body of experimental evidence and theoretical predictions that when produced in one of the low-dimensional forms (nanoclusters 0D, nanowires 1D or nanometer thin films 2D) gold can exhibit

departure from the bulk diamagnetism and show ferromagnetic behavior. We employ the FAcility for NAnostructure DEposition FANADE developed in our lab to produce ultra-high purity nanoclusters and surface-rich nanocrystalline films of gold with high surface to volume atomic ratio. These systems were found to exhibit ferromagnetism up to the room temperature and unusual spin-glass like behavior associated with surface magnetism.

SIMS/SNMS - XPS spectrometer: unique combination of analytical techniques


Our recently acquired new SIMS/SNMS-XPS spectrometer combines, in fact, four different analytical techniques in one instrument, viz., Secondary Ion Mass-Spectrometry SIMS, Secondary Neutral Mass-Spectrometry SNMS, X-ray Photoelectron Spectroscopy XPS and Residual Gas Analysis Spectrometry RGA. The basic instrument was a SIMS/SNMS spectrometer that has been upgraded by the supplier with the XPS option on request. This combination of different techniques turned out to be a rather powerful analytical tool for materials analysis that has triggered unexpectedly high interest from internal and external users. Being a unique instrument of this kind in Finland, the spectrometer is in heavy use in different projects.

Silicon based primary Coulomb Blockade Thermometer CBT: absolute thermometry below 1K

A hybrid CBT thermometer was fabricated on a thin silicon-on-insulator (SOI) film. The thermometer was made in form of an array of intermittent aluminum and silicon islands connected in series via tunnel junctions. Tunnel barriers in the micrometer size junctions were formed by metal-semiconductor Schottky contacts between aluminum electrodes and heavily doped silicon. Differential conductance through the array vs. bias voltage was found to exhibit characteristic features of competing thermal and charging effects enabling absolute temperature measurements over the range of 65 to 500 mK. The CBT performance implying the primary nature of the thermometer demonstrated for rather trivial architecture attempted in this work paves a route for introduction of Coulomb blockade thermometry into well-developed contemporary SOI technology.