This review presents MAX phases (M is a transition metal, A an A-group element, X is C or N), known for their unique combination of ceramic/metallic properties, as a recently uncovered family of ...novel magnetic nanolaminates. The first created magnetic MAX phases were predicted through evaluation of phase stability using density functional theory, and subsequently synthesized as heteroepitaxial thin films. All magnetic MAX phases reported to date, in bulk or thin film form, are based on Cr and/or Mn, and they include (Cr,Mn)2AlC, (Cr,Mn)2GeC, (Cr,Mn)2GaC, (Mo,Mn)2GaC, (V,Mn)3GaC2, Cr2AlC, Cr2GeC and Mn2GaC. A variety of magnetic properties have been found, such as ferromagnetic response well above room temperature and structural changes linked to magnetic anisotropy. In this paper, theoretical as well as experimental work performed on these materials to date is critically reviewed, in terms of methods used, results acquired, and conclusions drawn. Open questions concerning magnetic characteristics are discussed, and an outlook focused on new materials, superstructures, property tailoring and further synthesis and characterization is presented.
Thin TiO2 films were grown on Si(001) substrates by reactive dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) at temperatures ranging from 300 to 700°C. Optical and ...structural properties of films were compared both before and after post-annealing using scanning electron microscopy, low angle X-ray reflection (XRR), grazing incidence X-ray diffractometry and spectroscopic ellipsometry. Both dcMS- and HiPIMS-grown films reveal polycrystalline rutile TiO2, even prior to post-annealing. The HiPIMS-grown films exhibit significantly larger grains compared to that of dcMC-grown films, approaching 100% of the film thickness for films grown at 700°C. In addition, the XRR surface roughness of HiPIMS-grown films was significantly lower than that of dcMS-grown films over the whole temperature range 300–700°C. Dispersion curves could only be obtained for the HiPIMS-grown films, which were shown to have a refractive index in the range of 2.7–2.85 at 500nm. The results show that thin, rutile TiO2 films, with high refractive index, can be obtained by HiPIMS at relatively low growth temperatures, without post-annealing. Furthermore, these films are smoother and show better optical characteristics than their dcMS-grown counterparts.
•We demonstrate growth of rutile TiO2 on Si (111) by high power impulse magnetron sputtering.•The films exhibit significantly larger grains than dc magnetron sputtered films•TiO2 films with high refractive index are obtained without post-growth annealing
Thin TiN films were grown on SiO2 by reactive high power impulse magnetron sputtering (HiPIMS) at a range of temperatures from 45 to 600 degree C. The film properties were compared to films grown by ...conventional dc magnetron sputtering (dcMS) at similar conditions. Structural characterization was carried out using X-ray diffraction and reflection methods. The HiPIMS process produces denser films at lower growth temperature than does dcMS. Furthermore, the surface is much smoother for films grown by the HiPIMS process. The 200 grain size increases monotonically with increased growth temperature, whereas the size of the 111 oriented grains decreases to a minimum for a growth temperature of 400 degree C after which it starts to increase with growth temperature. The 200 crystallites are smaller than the 111 crystallites for all growth temperatures. The grain sizes of both orientations are smaller in HiPIMS grown films than in dcMS grown films.
The first experimental realization of a magnetic M(n+1)AX(n) (MAX) phase, (Cr(0.75)Mn(0.25))(2)GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent ...structural quality. This self-organized atomic laminate is based on the well-known Cr(2)GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.
We examine the properties of ultrathin TiN films grown by reactive dc magnetron sputtering on single-crystalline MgO(100) substrates at growth temperatures ranging from 30 to 650
°C. The resistance ...of the films is measured in-situ, during growth, to study the thickness at which the films coalesce and become structurally continuous. Both the in-situ resistance measurements and X-ray diffraction measurements show a clear transition from polycrystalline growth to epitaxial (100) growth well below typical TiN growth temperatures, or between 100 and 200
°C. The coalescence and continuity thicknesses are 1.09
±
0.06
nm and 5.5
±
0.5
nm, respectively, at room temperature but reach a minimum of 0.08
±
0.02
nm and 0.7
±
0.1
nm, respectively, at 600
°C. A large drop in resistivity is seen with increasing growth temperature and the resistivity reaches 16.6
μΩ
cm at 600
°C. Achieving epitaxy at such a low temperature and a low continuity thickness is important in a variety of applications such as device interconnects and metal–oxide–semiconductor devices.
We investigate the growth and structure properties of Mg:C thin films. The films are prepared using a dc magnetron sputtering discharge where the electrical resistance over the films is monitored ...during growth
in-situ with a four point probe setup. The structural properties of the films are investigated using X-ray diffraction measurements and the elemental composition and binding in the films is determined using elastic recoil detection analysis and X-ray photoelectron spectroscopy. The results show that during co-sputtering the carbon flux influences the initial stages of the film growth. The films are made of polycrystalline magnesium grains embedded in a carbon network, the size of which depends on the carbon content, but amorphous phases cannot be excluded. The XPS measurements show the presence of carbidic carbon whereas X-ray measurements find no Mg:C phases. The overall stability of the films is found to depend on the carbon content, where stable films capped with a 14
nm Pd layer cannot be obtained with carbon content above 18%.
Ultra thin platinum films were grown by dc magnetron sputtering on thermally oxidized Si (1 0 0) substrates. The electrical resistance of the films was monitored in situ during growth. The ...coalescence thickness was determined for various growth temperatures and found to increase from 1.1 nm for films grown at room temperature to 3.3 nm for films grown at 400 deg C. A continuous film was formed at a thickness of 2.9 nm at room temperature and 7.5 nm at 400 deg C. The room temperature electrical resistivity decreases with increased growth temperature, while the in-plain grain size and the surface roughness, measured with a scanning tunneling microscope (STM), increase. Furthermore, the temperature dependence of the film electrical resistance was explored at various stages during growth.
We present synthesis and characterization of a new magnetic atomic laminate: (Mo0.5Mn0.5)2GaC. High quality crystalline films were synthesized on MgO(111) substrates at a temperature of ∼530 °C. The ...films display a magnetic response, evaluated by vibrating sample magnetometry, in a temperature range 3-300 K and in a field up to 5 T. The response ranges from ferromagnetic to paramagnetic with change in temperature, with an acquired 5T-moment and remanent moment at 3 K of 0.66 and 0.35 μB per metal atom (Mo and Mn), respectively. The remanent moment and the coercive field (0.06 T) exceed all values reported to date for the family of magnetic laminates based on so called MAX phases.
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