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Strong light localization inside the nanoscale gaps provides remarkable opportunities for creation of various medical and biosensing platforms stimulating an active search for inexpensive and easily scalable fabrication at a sub-100 nm resolution. In this paper, self-organized laser-induced periodic surface structures (LIPSSs) with the shortest ever reported periodicity of 70 ± 10 nm were directly imprinted on the crystalline Si wafer upon its direct femtosecond-laser ablation in isopropanol. Appearance of such a nanoscale morphology was explained by the formation of a periodic topography on the surface of photoexcited Si driven by interference phenomena as well as subsequent down-scaling of the imprinted grating period via Rayleigh-Taylor hydrodynamic instability. The produced deep subwavelength LIPSSs demonstrate strong anisotropic anti-reflection performance, ensuring efficient delivery of the incident far-field radiation to the electromagnetic "hot spots" localized in the Si nanogaps. This allows realization of various optical biosensing platforms operating via strong interactions of quantum emitters with nanoscale light fields. The demonstrated 80-fold enhancement of spontaneous emission from the attached nanolayer of organic dye molecules and in situ optical tracing of catalytic molecular transformations substantiate bare and metal-capped deep subwavelength Si LIPSSs as a promising inexpensive multifunctional biosensing platform.

This paper reports on a facile bottom-up method for the direct integration of a silicon (Si)-magnesium silicide (Mg2Si) heterojunction solar cell (HSC) with a textured rear reflector made of stainless steel (SS). Modified wet chemical etching and post processing of SS substrates resulted in the formation of both a rough surface texture and diffusion barrier layer, consisting of magnetite (Fe3O4) with reduced optical reflection. Then, Si, Mg2Si and CaSi2 layers were stepwise thermally evaporated onto the textured SS surface. No traces of Fe and Cr silicide phases were detected by Raman spectroscopy, confirming effective suppression of impurity diffusion from the SS to the upper layers at least at temperatures required for Si deposition, as well as Mg2Si and CaSi2 formation. The obtained black-SS/Fe3O4/Si/Mg2Si/CaSi2 sample preserved, to some extent, its underlying textured morphology and demonstrated an averaged reflection of 15% over the spectral range of 200–1800 nm, while its prototype HSC possessed a wideband photoresponse with a photoelectric conversion efficiency of 7.5% under AM1.5 illumination. Moreover, Si layers deposited alone onto a black-SS substrate demonstrated competitive antireflection properties compared with black Si (b-Si) obtained by traditional top-down etching approaches, and hybrid b-Si/textured-SS structures with a glue-bonded interlayer.

n-Mg2Si/p-Si heterojunction solar cell with a 1.4 µm thick unintentionally doped (n = 3 × 1017 cm−3) silicide epitaxial layer on p-Si(1 1 1) (p = 5 × 1014 cm−3) was grown by low temperature (250 °C) molecular beam epitaxy. Heterojunction demonstrated clear rectification and zero bias photoresponse in the (400–1400) nm wavelength range at room temperature. Under AM 1.5 illumination, an open-circuit voltage of 0.21 V, a short-circuit current density of 3.3 mA/cm2, fill factor of 0.36 were obtained while the conversion efficiency reached 0.24%, which is the pioneering demonstration of Mg2Si-based solar cell operation. Combined minority-carrier lifetime, Raman and AFM mapping together with TEM and XRD data revealed that carrier dynamics and photovoltaic performance are limited by the presence of non-epitaxial Mg2Si grains in the upper silicide film layer. However, minority-carrier lifetime up to 7.3 µs for Mg2Si demonstrates its great potential as absorbing material for Si-based solar cells.

The detonation of mixtures of highly dispersed PETN with sodium bicarbonate with a mass fraction of the latter up to 90% is investigated using radio interferometric method and electron-optical method NANOGATE-22 along with a method using a polyvinylidene fluoride pressure sensor. The experimental results obtained indicate the possibility of the existence of various detonation regimes in mixtures. If the mass fraction of NaHCO3 is $$\le$$ 85%, the detonation wave propagation is mainly due to shock compression. At a higher NaHCO3 content (90%), the jets of explosion products predominantly serve as propagation agents.

Hybrid nanomaterials with chemical composition integrating light-emitting low-loss semiconductors with plasmon-active metals are highly demanded for optoelectronics, nanophotonics and sensors. However, there is a still lack for high-performing and inexpensive methods allowing facile integration of plasmonic and all-dielectric concepts within unified practically relevant nanostructures and ensuring their production at gram-per-hour yield. Here, we report one-step synthesis of hybrid Au@Si nanomaterial with unique composition and morphology via scalable and high-performing pulsed laser irradiation of isopropanol solution containing commercial Si micro-powder and AuCl4- ions. The resulting hybrid nanomaterial represents sub-micron nanocrystalline Si grains embedded into Au surrounding forming micro-spheres (MSs) additionally decorated with Au nanoparticles. Such unique structure and chemical composition of the Au@Si MSs permits to efficiently absorb and enhance incident radiation within rather broad spectral range spanning from visible to near-IR making the nanomaterial promising for plasmon-mediated amplification of linear and nonlinear optical effects. Efficient generation of broadband hot-carrier-induced photoluminescence of nanocrystalline Si grains upon IR femtosecond-laser sub-nJ pump proves the produced nanomaterial as advanced nanophotonic platform for nano-spectroscopy and sensing.

The growth, structure, optical, electrical and thermoelectric properties of calcium silicides of various compositions on silicon substrates with (100) and (111) orientations were experimentally studied. It was found that when the atoms of Ca and Si are co-deposited on atomically clean silicon, the basis phases in the composition of the formed films depends on the substrate temperature and the annealing temperature: Ca2Si (TSi = 20°C, Tann = 330°C), CaSi (TSi = 190-320°C, Tann = 330°C) and CaSi2 (TSi = 500°C). It was established that the Ca2Si phase is a direct-gap semiconductor with a band gap of 0.82±0.02 eV, large contribution of defect levels to the absorption coefficient at energies 0.25 - 0.50 eV and huge transmission up 90% in the far IR region. In CaSi-based films the high transmission (30-40%) up to 25 μm was observed, which corresponds to a semimetal with a constant density of states near the Fermi level. It was found that CaSi-based films have the maximum Seebeck coefficient and the power factor (up to 430 μV/K and up to 1.14 × 10-6 W/(K2m), respectively) at 330K. CaSi2 films with CaSi2 lattice stretching and epitaxial ordering relative to the Si (100) substrate exhibit semimetal properties, with very high conductivity and light transparency (up 12%) in the photon energy range 0.06 - 0.65 eV.

A double-layer heterostructure with embedded into single-crystal silicon matrix nanocrystals (NCs) of gallium antimonide (GaSb) was grown. The NCs were formed by solid phase epitaxy method using 1.6-nm-thick Ga-Sb stoichiometric mixture and annealing at a temperature range of 200–500 °C. The embedded NCs have a concentration of about 5.4 × 1010 cm− 2, a mean height of 8.6 nm and a mean lateral dimension of 19.2 nm. A stress induced inside the NCs owing to lattice mismatch between Si and GaSb was fully relaxed by edge dislocations at Si/GaSb interface. All the NCs have identical epitaxial relationship: GaSb(111)||Si(111), GaSb 1 1 − 0 ||Si 1 1 − 0 .

The formation of iron silicide nanocrystals (NCs) and their embedding into monocrystalline silicon was studied. Solid phase epitaxy of 0.4 nm Fe at 630 °C resulted in formation of NCs consisted of β-FeSi2 and e-FeSi phases. Annealing of NCs at 750 °C for 90 min led to transformation of β-FeSi2 and e-FeSi into α-FeSi2. On the other hand, silicon layer growth over as-formed NCs, at the same temperature, resulted in formation of single phase NCs consisted of β-FeSi2. Silicon deposition rate proved to be the crucial point for a full embedding of NCs. The rate of 1 nm/min resulted in emersion of NCs to the surface during silicon overgrowth irrespective of Si cap layer thickness, while the rate of 8 nm/min led to the full embedding of β-FeSi2 NCs. Both incompletely and fully embedded β-FeSi2 NCs have epitaxial relationship and stress favorable for an indirect to direct band-gap transition at Y point.

Mg2Si films have been grown on Si(111) and Si(001) surfaces at ~ 387–477 °C by ultra-fast deposition in vacuum. The original pulse-type evaporator used allows Mg deposition rates of ~103–104 nm/s which provide effective accumulation of Mg on hot Si surfaces despite its fast re-evaporation. The silicide films at different stages of formation and growth have been obtained by varying the pulse duration, Mg deposit amounts and substrate temperatures. The local structure and crystal quality of the obtained Mg2Si films have been studied. The mechanism of the Mg2Si film formation and growth process is considered. The role of high temperatures in the formation of film texture is demonstrated. The existing to date experimental data on Mg–Si intermixing and Mg2Si formation are explained. Technologies of Si/Mg2Si solar cells can be based on these results.

An array of GaSb nanocrystallites (NCs) was formed on Si(001) substrate by solid-phase epitaxy at 500 °C. Owing to the embedded GaSb NCs, p+‑Si/NC‑GaSb/n‑Si mesa diode spectral sensitivity has extended up to 1.6 µm at room temperature, and its integral sensitivity has increased by 4–5% in the wavelength range of 1200–1600 nm, as compared to a conventional Si diode. This result was achieved by embedding only 10 nm of GaSb in the form of NCs inside a silicon matrix. In addition, we could obtain a significant electroluminescence (EL) signal at 120 K in a very wide wavelength range from 1.3 to 2.1 µm (0.95–0.59 eV). The EL spectrum has a broad maximum at 1700 nm (0.73 eV). The threshold pumping current density was as low as 0.75 A/cm2.

Formation of GaSb by means of solid phase epitaxy of amorphous Ga:Sb (1:1) layer on Si (001) substrate at 500 °C has been studied. At amorphous layer thickness of 16 nm, a continuous nanocrystalline layer of GaSb was formed. Decreasing of amorphous layer thickness up to 0.8 nm resulted in formation of separated GaSb nanocrystallites (NCs), which had a mean lateral size of 30–80 nm and mean height of 2–3 nm, while their concentration reached 3×109 cm-2. Atomic force microscopy and low energy electron diffraction data showed that GaSb NCs could be fully embedded into silicon lattice by deposition of 25-nm-thick silicon layer at 650 °C. Nevertheless, on a surface of the silicon layer, some holes have been formed because of NCs moving toward to the surface. The holes formation can be almost completely suppressed by deposition of additional 25-nm-thick silicon layer at 500 °C – so-called “stop-layer”.

The electroluminescence efficiency of silicon light-emitting diode structures with several layers of β-FeSi2 nanocrystallites embedded in the p-n junction is investigated. The nanocrystallites were formed by either solid-phase epitaxy or a combination of reactive and solid-phase epitaxy. For the structures in which the nanocrystallites were formed by the combined method, electroluminescence is observed only at low temperatures (below 70K). This is indicative of a high concentration of defects acting as nonradiative-recombination centers. For the structures with nanocrystallites formed by solid-phase epitaxy, intense electroluminescence is observed up to room temperature. The dependence of the electroluminescence intensity on the size of the nanocrystallites is studied.

Embedded in silicon β-FeSi2 nanocrystals (NCs) were grown on Si(111) by solid phase epitaxy of a thin iron film followed by Si molecular beam epitaxy. After solid phase epitaxy, a mixture of β-FeSi2 and e-FeSi nanocrystals is formed on the surface, sometimes β and e phases coexist inside one nanocrystal. During initial stage of Si molecular beam epitaxy all e-FeSi transforms into β-FeSi2. β-FeSi2 nanocrystals tend to move following Si growth front. By adjusting growth condition, we manage to prevent the nanocrystals from moving and to fabricate 7-layer n-Si(111)/β-FeSi2_NCs/p+-Si silicon heterostructure with embedded β-FeSi2 NCs. An epitaxial relationship and a stress induced in the nanocrystals by silicon matrix were found to be suitable for indirect to direct band gap transition in β-FeSi2. Of the heterostructure, a n-i-p avalanche photodetector and a light-emitting diode were formed. They have shown relatively good performance: ultrabroadband photoresponse from the visible (400 nm) to short-wavelength ...

By method of in situ differential spectroscopy it was established that at the formation of monolayer Fe, Cr, Ca, Mg silicide and Mg stannide islands on the atomically clean silicon surface an appearance of loss peaks characteristic for these materials in the energy range of 1.1-2.6 eV is observed. An optimization of growth processes permit to grow monolithic double nanoheterostructures (DNHS) with embedded Fe, Cr and Ca nanocrystals, and also polycrystalline DNHS with NC of Mg silicide and Mg stannide and Ca disilicide. By methods of optical spectroscopy and Raman spectroscopy it was shown that embedded NC form intensive peaks in the reflectance spectra at energies up to 2.5 eV and Raman peaks. In DNS with β-FeSi2 NC a photoluminescence and electroluminescence at room temperature were firstly observed.

The [Formula: see text]–[Formula: see text]–[Formula: see text] diode structures with a variable number of [Formula: see text]-FeSi2 and CrSi2 nanocrystal (NC) bilayer were studied at room and liquid nitrogen temperatures. The high crystal quality of Si and embedded NCs was determined by HRTEM cross-sectional data. This diode demonstrated a photoresponse in the IR region (1.02–0.8[Formula: see text]eV) which was associated with a decrease in recombination losses with the main contribution coming from CrSi2 NCs. Calculations of photoyield and its extrapolation to zero resulted in band gap values of 0.35[Formula: see text]eV at 300[Formula: see text]K and 0.46[Formula: see text]eV at 90[Formula: see text]K. The spectral sensitivity of [Formula: see text][Formula: see text]A/W and specific detectivity of [Formula: see text][Formula: see text](cm Hz[Formula: see text]/W) were determined at [Formula: see text][Formula: see text][Formula: see text]m and T=300[Formula: see text]K.

Light-emitting silicon diode structures with embedded β -FeSi2 nanocrystallites have been fabricated using solid phase epitaxy and a combination of reactive deposition and solid phase epitaxy. Electroluminescence (EL) of the structures is studied over various temperatures and current densities under forward and reverse biases. We can state that β -FeSi2 NCs formed by the combined RDE+SPE method results in the formation of high density of dislocations and point defects. In contrast, defect-free structures with β -FeSi2 NCs formed by SPE demonstrate intense EL (η = 1.2×10-5%) in the wavelength range 1.4–1.6 µm even at room temperature. EL intensity dependence on the number of layers with embedded β -FeSi2 NCs is almost linear for the heterostructures formed on Si(100) and sublinear for the heterostructures formed on Si(111) substrate. The increase of the initial Fe layer thickness leads to the electroluminescence quenching. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We develop an approach and present results of the combined molecular dynamics and density functional theory calculations of the structural and optical properties of the nanometer-sized crystallites embedded in a bulk crystalline matrix. The method is designed and implemented for both compatible and incompatible lattices of the nanocrystallite (NC) and the host matrix, when determining the NC optimal orientation relative to the matrix constitutes a challenging problem. We suggest and substantiate an expression for the cost function of the search algorithm, which is the energy per supercell generalized for varying number of atoms in the latter. The epitaxial relationships at the Si/NC interfaces and the optical properties are obtained and found to be in a reasonable agreement with experimental data. Dielectric functions show significant sensitivity to the NC's orientation relative to the matrix at energies below 0.5 eV.

By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p+-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3–4 and 15–20 nm and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2% and a specific detectivity of 1.2 × 109 cm × Hz1/2/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2.

This article describes the development of an Si-based light-emitting diode with β-FeSi2 nanocrystals embedded in the active layer. Favorable epitaxial conditions allow us to obtain a direct band gap type-I band alignment Si/β-FeSi2 nanocrystals/Si heterostructure with optical transition at a wavelength range of 1500–1550 nm at room temperature. Transmission electron microscopy data reveal strained, defect-free β-FeSi2 nanocrystals of diameter 6 and 25 nm embedded in the Si matrix. Intense electroluminescence was observed at a pumping current density as low as 0.7 A/cm2. The device reached an optical emission power of up to 25 μW at 9 A/cm2 with an external quantum efficiency of 0.009%. Watt–Ampere characteristic linearity suggests that the optical power margin of the light-emitting diode has not been exhausted. Band structure calculations explain the luminescence as being mainly due to radiative recombination in the large β-FeSi2 nanocrystals resulting from the realization of an indirect-to-direct band ga...

A Si n-i-p avalanche photodetector with embedded β-FeSi2 nanocrystals was developed. The device showed an ultrabroadband photoresponse from the visible (400 nm) to short-wavelength infrared (1800 nm) ranges. Specific detectivity at zero bias conditions reaches 2 × 109 cmHz1/2/W at 1300 nm and 2 × 108 cmHz1/2/W above 1400 nm at room temperature. Observed quantum-confined Stark effect together with avalanche multiplication resulted in a simultaneous two orders of magnitude increase in the photoresponse and spectral sensitivity expanding to 1800 nm when the device is operated in avalanche mode. The application fields of the proposed photodetector potentially include integrated Si photonics and multicolor photodetection; the quantum-confined Stark effect gives grounds for the development of fast-operated electro-optical modulators.

Mg2Si thin film was embedded in amorphous silicon matrix by solid phase epitaxy. The structure and optical properties were investigated by electron energy loss, X-ray photoelectron, Raman, and photo thermal deflection spectroscopy measurements. It was found that in the photon energy range of 0.8–1.7 eV, the light absorption of the structure with magnesium silicide (Mg2Si) film embedded in a-Si(i) matrix is 1.5 times higher than that for the same structure without Mg2Si.

The cross-section for the double charmed baryon production at a $B$-factory is estimated on the basis of the perturbative QCD calculations for the $c c$-diquark production as well as of the quark-hadron duality., Comment: Prepint IHEP 94-56, 7 LATEX pages, figures are not avaleble

The cross-section for the production of\(b\bar bc\bar c\) quarks ine+e− annihilation, that proves to be at a level of\(\sigma (e^ + e^ - \to b\bar bc\bar c)/\sigma (e^ + e^ - \to b\bar b) \sim 10^{ - 2} \) for\(\sqrt s = M_Z \) is calculated within the frames of the QCD perturbation theory. The cross sections for the associated production of 1S-and 2S-wave states ofBc-meson in the reaction\(e^ + e^ - \to B_c b\bar c\) were calculated in the nonrelativistic model of a heavy quarkonium. The number ofΛbc-hyperons to be expected at LEP is estimated on the basis of the assumption on quark-hadron duality.

Thin (45–50 nm) non-doped and doped (by Sb and Al) polycrystalline Mg stannide films consisting mainly of Mg2Sn semiconductor phase and containing small quantity of Mg2Si phase have been grown by multiple layer deposition at room temperature and single step annealing at 150 °C of the (Sn–Mg) bi-layers on Si(111) n-type wafers with 7.5 Ωcm resistivity. Optical spectroscopy data have shown that the grown Mg stannide films is a semiconductor with direct band gap of 0.17 ± 0.03 eV, with second and third direct interband transitions at 0.34 ± 0.02 and 0.45 ± 0.04 eV. An undispersed refraction index: n0 = 3.78 ± 0.06 was calculated from phonon energy dependence of the refraction index of the grown films in the 0.12–0.20 eV energy range. Temperatures dependent Hall effect measurements have revealed about 0.28 eV electrical band gap value in the films.

Using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, p-Si/β-FeSi2 nanocrystallites/n-Si(001) diode structure was fabricated. The diode exhibited a current responsivity of 15 mA/W and external quantum efficiency of about 1% at a wavelength of 1300 nm at 120 K without bias and 200 mA/W and 10%, respectively, at −30 V. The device specific detectivity calculated at 120 K in zero bias conditions of 2.1 × 1011 cmHz1/2/W at a wavelength of 1.3 µm is the highest ever reported for Si/β-FeSi2 systems. The Franz–Keldysh effect gives grounds for applying such systems not only for the development of optrons but also for that of electro-optical modulators.

Light-emitting silicon diode structures with embedded β-FeSi2 nanocrystallites have been fabricated using solid phase epitaxy and a combination of reactive deposition and solid phase epitaxy. Electroluminescence (EL) of the structures was studied over various temperatures and current densities under forward and reverse biases. The structures with nanocrystallites formed by the combined method exhibited EL at temperatures below 70 K only, suggesting the presence of a high concentration of defects—non-radiative centers. High-quality defect-free structures with nanocrystallites formed by solid phase epitaxy revealed intensive room temperature EL in energy range 0.76–1.08 eV at current densities as low as 1 A/cm2.