The structure and the magnetic anisotropy of the films obtained by simultaneous deposition of iron and silicon on n-Si(111) 7×7 at 130°C are investigated. It is found the uniaxial magnetic anisotropy ...field for the Fe1−xSix films with x=0.25 (Fe3Si stoichiometric ratio) deposited on Si(111) 7×7 depends on both the surface miscut angle and the oblique sputtering direction and changes from 0.82Oe up to 117.26Oe.
•The structure and the magnetic anisotropy of the Fe-Si films are investigated.•Magnetic anisotropy depends on both the surface miscut and the oblique sputtering.•Uniaxial magnetic anisotropy field for Fe-Si films changes from 0.82 to 117.26Oe.
Three-layer iron-rich Fe3+xSi1−x/Ge/Fe3+xSi1−x (0.2 < x < 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of ...the structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe3+xSi1−x heterosystem due to the incorporation of Ge atoms into the Fe3+xSi1−x bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe3+xSi1−x. The average lattice distortion and residual stress of the upper Fe3+xSi1−x were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of −0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe3+xSi1−x layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe3+xSi1−x films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe3+xSi1−x, which implies the epitaxial orientation relationship of Fe3+xSi1−x (111)0−11 || Ge(111)1−10 || Fe3+xSi1−x (111)0−11 || Si(111)1−10. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms.
We fabricated Cu-doped TiNxOy thin film resistors by using atomic layer deposition, optical lithography, dry etching, Ti/Cu/Ti/Au e-beam evaporation and lift-off processes. The results of the ...measurements of the resistance temperature dependence, non-linearity, S-parameters at 0.01–26 GHz and details of the breakdown mechanism under high-voltage stress are reported. The devices’ sheet resistance is 220 ± 8 Ω/□ (480 ± 20 µΩ*cm); intrinsic resistance temperature coefficient (TCR) is ~400 ppm/°C in the T-range of 10–300 K; and S-parameters versus frequency are flat up to 2 GHz with maximum variation of 10% at 26 GHz. The resistors can sustain power and current densities up to ~5 kW*cm−2 and ~2 MA*cm−2, above which they switch to high-resistance state with the sheet resistance equal to ~200 kΩ/□ (~0.4 Ω*cm) caused by nitrogen and copper desorption from TiNxOy film. The Cu/Ti/TiNxOy contact is prone to ageing due to gradual titanium oxidation while the TiNxOy resistor body is stable. The resistors have strong potential for applications in high-frequency integrated and hybrid circuits that require small-footprint, medium-range resistors of 0.05–10 kΩ, with small TCR and high-power handling capability.
The growth of α-FeSi
2
nanocrystal ensembles on gold-activated and gold-free Si(001) surfaces at different Si/Fe flux ratios
via
molecular beam epitaxy is reported. The study reveals that the ...utilisation of gold as a catalyst regulates the preferable orientation relationship (OR) of the nanocrystals to silicon and their morphology at a given Si/Fe flux ratio. α-FeSi
2
free-standing crystals with continuously tuned sizes from 30 nm up to several micrometres can be grown with an α(001)//Si(001) basic OR under gold-assisted conditions and an α(111)//Si(001) OR under gold-free growth conditions on a Si(001) surface. The preferred morphology of nanocrystals with a particular OR can be altered through changes to the Si/Fe flux ratio. Herein, the microstructure and basic OR between the silicide nanocrystals and the silicon substrate, and the formation of nanocrystal facets were analysed in detail with the help of microscopic techniques and simulation methods based on the analysis of near coincidence site (NCS) distributions at silicide/silicon interfaces. On the basis of the simulations used, we managed to reveal the nature of the interfaces observed for the main types of α-FeSi
2
nanocrystals grown. Three types of interfaces typical for nanoplates with an α(001)//Si(001) basic OR, which are (i) stepped, (ii) stressed, and (iii) flat, are explained based on the tendency for the NCS density to increase at the interface. The results presented reveal the potential for the bottom-up fabrication of α-FeSi
2
nanocrystals with tuned physical properties as potentially important contact materials and as building blocks for future nanoelectronic devices.
An approach for tuning the preferable orientation relationships and shapes of free-standing α-FeSi
2
nanocrystals was demonstrated on a Si(001) surface.
Copper-doped titanium oxynitride (TiN x O y ) thin films were grown by atomic layer deposition (ALD) using the TiCl4 precursor, NH3, and O2 at 420 °C. Forming gas was used to reduce the background ...oxygen concentration and to transfer the copper atoms in an ALD chamber prior to the growth initiation of Cu-doped TiN x O y . Such forming gas-mediated Cu-doping of TiN x O y films had a pronounced effect on their resistivity, which dropped from 484 ± 8 to 202 ± 4 μΩ cm, and also on the resistance temperature coefficient (TCR), which decreased from 1000 to 150 ppm °C–1. We explored physical mechanisms causing this reduction by performing comparative analysis of atomic force microscopy, X-ray photoemission spectroscopy, X-ray diffraction, optical spectra, low-temperature transport, and Hall measurement data for the samples grown with and without forming gas doping. The difference in the oxygen concentration between the films did not exceed 6%. Copper segregated to the TiN x O y surface where its concentration reached 0.72%, but its penetration depth was less than 10 nm. Pronounced effects of the copper doping by forming gas included the TiN x O y film crystallite average size decrease from 57–59 to 32–34 nm, considerably finer surface granularity, electron concentration increase from 2.2(3) × 1022 to 3.5(1) × 1022 cm–3, and the electron mobility improvement from 0.56(4) to 0.92(2) cm2 V–1 s–1. The DC resistivity versus temperature R(T) measurements from 4.2 to 300 K showed a Cu-induced phase transition from a disordered to semimetallic state. The resistivity of Cu-doped TiN x O y films decreased with the temperature increase at low temperatures and reached the minimum near T = 50 K revealing signatures of the quantum interference effects similar to 2D Cu thin films, and then, semimetallic behavior was observed at higher temperatures. In TiN x O y films grown without forming gas, the resistivity decreased with the temperature increase as R(T) = – 1.88T 0.6 + 604 μΩ cm with no semimetallic behavior observed. The medium range resistivity and low TCR of Cu-doped TiN x O y make this material an attractive choice for improved matching resistors in RF analog circuits and Si complementary metal–oxide–semiconductor integrated circuits.
The electronic structure, transport and optical properties of thin films of Mn
4
Si
7
and Mn
17
Si
30
higher manganese silicides (HMS) with the Nowotny “chimney-ladder” crystal structure are ...investigated using different experimental techniques and density functional theory calculations. Formation of new Mn
17
Si
30
compound through selective solid-state reaction synthesis proposed and its crystal structure is reported for the first time, the latter belonging to
I
-
42d
. Absorption measurements show that both materials demonstrate direct interband transitions around 0.9 eV, while the lowest indirect transitions are observed close to 0.4 eV. According to ab initio calculations, ideally structured Mn
17
Si
30
is a degenerate n-type semiconductor; however, the Hall measurements on the both investigated materials reveal their p-type conductivity and degenerate nature. Such a shift of the Fermi level is attributed to introduction of silicon vacancies in accordance with our DFT calculations and optical characteristics in low photon energy range (0.076–0.4 eV). The Hall mobility for Mn
17
Si
30
thin film was found to be 25 cm
2
/V s at
T
= 77 K, being the highest among all HMS known before. X-ray photoelectron spectroscopy discloses a presence of plasmon satellites in the Mn
4
Si
7
and Mn
17
Si
30
valence band spectra. Experimental permittivity spectra for the Mn
4
Si
7
and Mn
17
Si
30
compounds in a wide range (0.076–6.54 eV) also indicate degenerate nature of both materials and put more emphasis upon the intrinsic relationship between lattice defects and optical properties.
The growth of α-FeSi 2 nanocrystal ensembles on gold-activated and gold-free Si(001) surfaces at different Si/Fe flux ratios via molecular beam epitaxy is reported. The study reveals that the ...utilisation of gold as a catalyst regulates the preferable orientation relationship (OR) of the nanocrystals to silicon and their morphology at a given Si/Fe flux ratio. α-FeSi 2 free-standing crystals with continuously tuned sizes from 30 nm up to several micrometres can be grown with an α(001)//Si(001) basic OR under gold-assisted conditions and an α(111)//Si(001) OR under gold-free growth conditions on a Si(001) surface. The preferred morphology of nanocrystals with a particular OR can be altered through changes to the Si/Fe flux ratio. Herein, the microstructure and basic OR between the silicide nanocrystals and the silicon substrate, and the formation of nanocrystal facets were analysed in detail with the help of microscopic techniques and simulation methods based on the analysis of near coincidence site (NCS) distributions at silicide/silicon interfaces. On the basis of the simulations used, we managed to reveal the nature of the interfaces observed for the main types of α-FeSi 2 nanocrystals grown. Three types of interfaces typical for nanoplates with an α(001)//Si(001) basic OR, which are (i) stepped, (ii) stressed, and (iii) flat, are explained based on the tendency for the NCS density to increase at the interface. The results presented reveal the potential for the bottom-up fabrication of α-FeSi 2 nanocrystals with tuned physical properties as potentially important contact materials and as building blocks for future nanoelectronic devices.
This paper presents a new palynological record from a 146cm long finely laminated sediment core obtained in 2009 from the deep-water meromictic Lake Shira (54°30′38″N, 90°12″09′E; ca. 353ma.s.l.) ...situated in the Khakassian steppe region of southern Siberia between the rivers Ob' and Yenisei. The area is rich in lakes and represents an exceptionally well preserved sequence of Bronze and Iron Age archeological cultures. Little is known about the changes in vegetation and climate of the region during the Holocene. The palynological analysis of the core allows us to partly fill up this gap in current knowledge. The record of pollen and non-pollen palynomorphs presented here covers the past 2450year interval with an average resolution of 22years. The results obtained support the interpretation that the late Holocene vegetation changes around Lake Shira are mainly associated with large-scale atmospheric circulation processes controlling the regional water balance rather than with human activities. An attempt to trace human impact in the pollen assemblages provides no clear evidence for anthropogenic activity, except for the last few decades since ca. 1955, though the region has a long history of mobile pastoralists. For explanation of decadal-scale changes in the regional vegetation cover, the Artemisia/Chenopodiaceae (A/C) pollen ratio proved to be a reliable indicator of effective moisture availability. Using available fossil and published instrumental data our study suggests a link between the North Atlantic warmer/colder temperatures and higher/lower atmospheric precipitation (or moisture availability) in southern Siberia at multi-decadal to centennial scales.
•Meromictic Lake Shira discloses high-resolution climate archive from the Khakassian steppe.•Artemisia/Chenopodiaceae pollen ratio reflects regional moisture variability around Lake Shira.•The Atlantic Multidecadal Oscillation may affect moisture variability in southern Siberia.
Three-layer iron-rich Fe
Si
/Ge/Fe
Si
(0.2 <
< 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of the ...structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe
Si
heterosystem due to the incorporation of Ge atoms into the Fe
Si
bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe
Si
. The average lattice distortion and residual stress of the upper Fe
Si
were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of -0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe
Si
layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe
Si
films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe
Si
, which implies the epitaxial orientation relationship of Fe
Si
(111)0-11 || Ge(111)1-10 || Fe
Si
(111)0-11 || Si(111)1-10. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms.
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