We report here a simple hydrothermal synthesis of 100-200 nm flakes of tochilinite (Fe
1−
x
S)·
n
(Mg,Fe)(OH)
2
constructed by interchanging atomic sulfide and hydroxide sheets as a representative of ...a new platform of multifunctional two-dimensional materials. The reliable formation of tochilinites was ensured by an excess of sodium sulfide, with the assembly of the metal sulfide and hydroxide sheets driven by their opposite electric charges. X-ray photoelectron spectroscopy found that the hydroxide layers involved Fe
3+
cations from 10 to 40% of total iron tuned by addition of Al and Li entering the layers; the Fe
1−
x
S sheets comprised comparable amounts of high-spin Fe
3+
and Fe
2+
centers, and minor S-S bonding. The room-temperature Mössbauer spectra fitted with several doublets (chemical shift of 0.35-0.4 mm s
−1
and varying quadrupole splitting) transformed to three six-line patterns (hyperfine fields of ∼290, 350 and 480 kOe) due to magnetic ordering at 4.2 K, albeit the paramagnetic behavior observed in SQUID experiments. A series of UV-vis absorption maxima were explained in terms of both the high-index all-dielectric Mie resonance, in line with the permittivity measurement data, and the ligand-metal charge transfer resembling that in Fe-S clusters in proteins. Prospective properties and applications of the materials are discussed.
We report the reliable synthesis of 2D iron sulfide-magnesium hydroxide nanoflakes. The sulfide and hydroxide sheets assemble
via
opposite electric charges. Comparable amounts of high-spin Fe
3+
and Fe
2+
centers occur in the sulfide layers.
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.
A top-down nanofabrication approach involving molecular beam epitaxy and electron beam lithography was used to obtain silicon nanowire-based back gate field-effect transistors with Schottky contacts ...on silicon-on-insulator (SOI) wafers. The resulting device is applied in biomolecular detection based on the changes in the drain-source current (IDS). In this context, we have explained the physical mechanisms of charge carrier transport in the nanowire using energy band diagrams and numerical 2D simulations in TCAD. The results of the experiment and numerical modeling matched well and may be used to develop novel types of nanowire-based biosensors.
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•A simple approach for fabrication of a silicon nanowire field-effect transistor for protein detection.•An evaluation of the biosensor performance with model molecules.•An explanation of electrical detection mechanism.•A demonstration of the energy bands shifting.•2D simulation considering the biosensor surface charge concentration.
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.
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.
The utilization of graphene on silicon carbide (SiC) substrates holds substantial promise for advancements in spintronics and nanoelectronics. Furthermore, incorporating magnetic metals provides an ...optimal framework for probing fundamental physical phenomena. The approach to developing such systems is in situ intercalation of graphene with magnetic metals. Herein, the electronic structure is analyzed and the magnetic properties of the system are synthesized by the thermal decomposition of 6H‐SiC(0001) surface and subsequent intercalation of graphene with cobalt (Co) and iron (Fe) atoms. X‐ray photoemission spectroscopy and low‐energy electron diffraction are employed to control the synthesis and metal intercalation processes. The morphological characteristics of the synthesized system are studied by means of atomic force microscopy. The findings derived from magneto‐optic Kerr effect measurements reveal a homogeneous ferromagnetic ordering at room temperature. Angle‐resolved photoemission spectroscopy is used to ascertain the impact of intercalation on graphene's electronic structure. The results of this study are essential for the development of graphene‐based spintronics and nanoelectronic devices as well as for fundamental studies in magnetic graphene systems.
This study investigates graphene's potential on silicon carbide (SiC) for spintronics and nanoelectronics by in situ intercalation with magnetic metals. The system was obtained by thermal decomposition of 6H‐SiC(0001) and subsequent intercalation with cobalt (Co) and iron (Fe) atoms. The findings reveal formation of the bilayer graphene and room temperature ferromagnetic order in the system.
The use of spintronic devices with a tunable magnetic order on small scales is highly important for novel applications. The MAX phases containing transition metals and/or magnetic ion-substituted ...lattices attract a lot of attention. In this study, the magnetic and electronic properties of (Cr4-xFex)0.5AC (A = Ge, Si, Al) compounds were predicted and investigated within the density functional theory. It was established that single-substituted (Cr3Fe1)0.5AC (A = Ge, Si, Al) lattices are favorable in terms of energy. An analysis of the magnetic states of the MAX phases demonstrated that their spin order changes upon substitution of iron atoms for chromium ones. It was found that mostly the (Cr4-xFex)0.5GeC and (Cr4-xFex)0.5AlC lattices acquire a ferrimagnetic state in contrast to (Cr4-xFex)0.5SiC for which the ferromagnetic spin order dominates. It was pointed out that the atomic substitution could be an efficient way to tune the magnetic properties of proposed (Cr4-xFex)0.5AC (A = Ge, Si, Al) MAX phases.
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.
We have prepared thin indium oxide films by the autowave oxidation reaction. Measurements of temperature dependence of resistivity, Hall carrier concentration and Hall mobility have been conducted in ...the temperature range 5-272 K. Before ultraviolet (UV) irradiation, the indium oxide film had a semiconductor-like temperature dependence of resistivity and the ratio of (5 K) (272 K) was very limited (∼1.2). It was found that after UV irradiation of the In2O3 film, the metal-semiconductor transition (MST) was observed at ∼100 K. To show that this MST is reversible and repeatable, two full cycles of 'absence of MST-presence of MST' have been done using UV irradiation (photoreduction) as the induced mechanism and exposure to an oxygen environment as the reversible mechanism, respectively. MST in transparent conducting oxide (TCO) is possibly associated with the undoped structure of metal oxide, which has some disorder of oxygen vacancies. It was suggested that reversible UV induced metal-semiconductor transition would occur in other TCOs.
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