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Among two-dimensional (2D) materials, such as graphene, a new family of 2D anisotropic carbides and nitrides of early transition metals (MXenes) is very interesting because of the potential applications in electronics, medicine, and photocatalysis. In this paper, preparation, morphostructural characterization, band gaps determination, and salicylic acid photodegradation ability of Ti2C MXene and six nanocomposites consisting of the MXene modified by TiO2, Ag2O, Ag, PdO, Pd, and Au are reported. It was confirmed using electron diffraction studies, energy dispersive X-ray spectroscopy, and high-resolution transmission microscopy that metals and metal oxides occur on the MXene flakes as nanoparticles in a shape of spots. The band gaps determined experimentally using Tauc's method are placed in the region of 0.90-1.31 eV. In recent years, the method of photocatalytic decomposition of pollutants using semiconductor photocatalysts and UV-vis energy has become increasingly important. The MXene based nanocomposites revealed high activity in the salicylic acid (SA) photodegradation reaction (86.1-97.1% of degraded SA after 3 h, concentration of SA initial solution 100 μM, the circulation rate of the SA solution 0.875 cm3/min). The interfacial charge transfer mechanism and the role of the metallic and metal oxide nanoparticles in the photocatalytic activity of the MXene based nanocomposites are presented and discussed.

New synthesis of solution processable kesterite and kesterite-phenoxazine nanopowders were presented. The direct band-gap semiconductor Cu2ZnSnS4 has attracted the attention of many due to its large absorption coefficient (α > 104 cm-1) and (optical) band-gap energy close to the optimal value for solar light conversion (1.4-1.6 eV). The presence of a kesterite nanocrystal structure has been investigated and confirmed by (HR)TEM, X-ray powder diffraction, EDX and EXAFS measurements. Low-temperature photoluminescence (PL) measurements indicate the absence of PL in the Cu2ZnSnS4 nanocrystals. Electrochemical studies helped to prove that an inorganic-organic heterojunction of nanokesterite-phenoxazine was obtained. Device studies showed a two fold improvement in efficiency upon addition of a kesterite or phenoxazines-kesterite layer.

In today’s battle for the environment, renewable energy sources, including solar energy, plays a significant role. Therefore, it is necessary to develop new materials for solar cells. Ag2ZnSnS4 (AZTS) is a material that makes it possible to increase the efficiency of photovoltaic modules, compared to cells based on Cu2ZnSnS4. AZTS was obtained by several methods, but in these research it was synthesized by Chemical Vapor Transport method (CVT), using zinc chloride as transporting agent, for the first time. X-ray powder diffraction was used in the structural tests, which showed that through the CVT method it is possible to obtain a pure Ag2ZnSnS4 phase with a stannite crystal structure. Raman measurements were conducted to determine the crystal quality of samples and to check their phase homogeneity. Raman spectra were calculated from DFT analysis applying the LDA and GGA approximations. The measured Raman peaks were assigned to calculated ones for AZTS structure.

Gallium sulfide is a semiconducting material with a layered structure and a characteristic low interlayer interaction. Because of weak van der Waals forces, GaS crystals are relatively easy to exfoliate to very thin layers. In this work nanometric-GaS layers were obtained by a micro-mechanical exfoliation process and were transferred to Si/SiO2 substrate. The thickness of these layers was estimated from AFM measurements. Raman spectra were collected for different layer thicknesses ranging from one layer to bulk crystal. An analytical function fitted to experimental data is proposed to determine layer thickness from Raman measurements. For the first time, the Raman position and the FWHM of the main Raman peaks were measured on very thin GaS layers as a function of temperature in the range from 80 to 470 K. The first order temperature coefficients of the A 1g Raman peaks were determined. Phonon decay due to anharmonic processes at temperatures above 300 K in layers of thickness below 4 nm was observed. Contribution of optical phonon scattering processes to thermal properties of very thin GaS layers is discussed.

A simple chemical transport method was used to obtain Ga-core / SiO2-shell microstructures. The cone-shaped silica needles assembled in a highly ordered pattern on a gallium droplet. Morphology of those regularly arranged microstructures was present in scanning electron microscopy images. The chemical composition and structure were confirmed using energy dispersive X-ray and Raman spectroscopy. Such core-shell, gallium-silicon dioxide regular microstructures are reported for the first time.

Ammonium hexachlorostannate single crystals were obtained from gas phase of decomposition products of SnCl4·5NH3 formed in reaction of liquid tin(IV) chloride with gaseous ammonia. The crystals of both cubic (NH4)2SnCl6, obtained hitherto only by crystallization from solution, and of the formerly unknown orthorhombic polymorph were deposited on inner walls of the quartz reactor used. The values of the structure refinement factor R obtained is 0.01. Unit cell parameters of the new orthorhombic form of ammonium hexachlorostannate were determined and are reported.

Gallium nitride is studied at ambient and nonambient temperatures by powder X-ray diffraction followed by Rietveld refinement of the structure. The structure is reported for the ambient temperature on the basis of laboratory data. The diffraction data collected using a synchrotron beam serve for derivation of the lattice parameter and thermal expansion dependencies on temperature. The variation of unit-cell size on temperature was studied in detail in a broad range 11 K

A rapid development of solar cells has been observed within recent years. Semiconducting materials based on Cu2ZnSnS4 with the kesterite structure offer a promise of low-cost and environmentally friendly solar cells. The energy gap of Cu2ZnSnS4, which is about 1.5 eV, can be optimized with addition of organic ligands. We report a method of obtaining kesterite nanopowders with grain diameter of approximately 5 nm via solution synthesis using metal chlorides and sulfur in oleylamine at 230 °C. The ligand exchange for diphenylamine upshifted the value of the bandgap to 2.2 eV, which makes it a promising material for an upper layer in tandem photovoltaic devices.

Efficient and inexpensive method of chemical transport based on Ag2S catalyst was used to produce relatively large crystals of SnS2, up to 5 mm in linear size. Good quality of the obtained layered crystals of SnS2 was confirmed by X-ray, SEM, EDX and Raman measurements, however the layers appeared to be slightly twisted in relation to each other. Nanometric (down to c.a. 10 nm) layers of SnS2 on a Si substrate were obtained by mechanical exfoliation.

The formation of a previously unknown salt with the stoichiometry Li5GeNO3 was found during studies on the reactivity of lithium metagermanate with lithium nitride, germanium oxynitride, and LiGeNO and Li3GeNO2 with lithium oxide. The possibility of existence of anion GeNO35− with mixed oxygen-nitrogen coordination shell of germanium had been predicted on the basis of analogies occurring among known silicon and germanium compounds. The course of thermal decomposition of the new salt was determined.

A rapid development of photovoltaics has been observed recently. Permanent interest in new cheap and efficient photovoltaic devices stimulates a constant search for new semiconductor materials and structures. The success of materials based on CIGS (CuIn1–xGaxSe2) is limited by the prohibitive prices of the elements In and Ga. A family of quaternary semiconducting materials of the Cu2ZnSnS4 type, crystallizing mainly in the kesterite structure, offers a promise of new cheap photovoltaic materials. Kesterite is manufactured from nontoxic and naturally abundant materials. The energy gap of Cu2ZnSnS4 is about 1.5 eV, and the absorption coefficient of this direct-band-gap material is α > 104 cm–1 for photon energies higher than the energy gap. In this paper, we report a method of obtaining free-standing single crystals of kesterite (Cu2ZnSnS4).

The structural properties of GaN and Ga1–xMnx N layers are reported. The GaN and Ga1–xMnx N layers were obtained by the sublimation sandwich method (SSM). Electron microprobe measurements detected high Mn concentration of up to 4.0 at% in Ga1–xMnx N materials. Raman investigations demonstrated that the prepared layers had a well-ordered structure. The densities of dislocations in the template MOCVD layer, SSM GaN layers and SSM Ga1–xMnx N layers were 3.9 × 108 cm–2, 1.4 × 108 cm–2 and 3.0 × 109 cm–2, respectively. The AFM studies demonstrated that the GaN RMS roughness increased with the increase in thickness. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The synthesis and characterization of Ga 1-x Mn x N thick layers are reported. The layers were prepared by the modified sublimation sandwich method (SSM) from GaN powder and powdered Mn sources and reacted with ammonia. Ga 1-x Mn x N layers having a current maximum size of 60 μm thickness and 10 mm x 10 mm area were obtained. The crystals of best crystalline quality were obtained with a growth rate of 25 μm/h. SIMS measurements showed the presence of layers containing up to 4 atom % Mn. Measurements involving X-ray diffraction (structure refinement), rocking curves, map of reflections, and EXAFS confirmed good structural properties without phase separation. The measurements carried out by a superconducting quantum interferometer showed that the material revealed typical paramagnetic properties.

The synthesis and characterization of GaN thick layers are reported in this paper. The layers were prepared by sublimation sandwich method (SSM). Powder of GaN was used as the source of gallium and ammonia was used as the source of nitrogen. Sapphire with 3 μm GaN thin film grown by MOCVD was used as the substrate. The GaN layers having a current maximum size of 200 μm thickness and 10 mm×10 mm area were obtained. It is also shown that the crystals of best crystalline quality are obtained with a growth rate of 20 μm/h. Characterization of the layers was performed using rocking curve, maps of reflection, structure refinement and SIMS. Quality of the material is good.

A growing interest in devices based on spintronics demands a development of magnetic semiconductors. A promising material for such applications is kesterite doped with ferromagnetic elements. We present a method of obtaining Cu2MSnS4 (M = Zn, Fe, Mn, Ni) single crystals, using metals, elemental sulfur and minor amounts of iodine. The syntheses were carried out in quartz ampoules closed under vacuum and heated in a tube furnace at 650 °C for 7 to 90 days. A method of synthesis of comparatively good tetragonal single crystals of Cu2FeSnS4 and Cu2MnSnS4 was achieved. Raman spectra of purely Mn- and Ni-substituted kesterites have been measured for the first time.

The formation of a previously unknown salt with the stoichiometry Li5GeNO3 was found during studies on the reactivity of lithium metagermanate with lithium nitride, germanium oxynitride, and LiGeNO and Li3GeNO2 with lithium oxide. The possibility of existence of anion GeNO35− with mixed oxygen-nitrogen coordination shell of germanium had been predicted on the basis of analogies occurring among known silicon and germanium compounds. The course of thermal decomposition of the new salt was determined.

A growing interest in devices based on spintronics demands a development of magnetic semiconductors. A promising material for such applications is kesterite doped with ferromagnetic elements. We present a method of obtaining Cu2MSnS4 (M = Zn, Fe, Mn, Ni) single crystals, using metals, elemental sulfur and minor amounts of iodine. The syntheses were carried out in quartz ampoules closed under vacuum and heated in a tube furnace at 650 °C for 7 to 90 days. A method of synthesis of comparatively good tetragonal single crystals of Cu2FeSnS4 and Cu2MnSnS4 was achieved. Raman spectra of purely Mn- and Ni-substituted kesterites have been measured for the first time.

Mixtures of powders of manganese, silicon and metallic gallium were annealed in a stream of ammonia at 1000–1050 °C. The products obtained were bulk single crystals of gallium nitride, dimensions up to 4.8×1.0×0.1 mm. The concentrations of the dopants were: Mn 7.8±0.12 at% and Si 0.5±0.2 at%. The influence of the process parameters (temperature, ammonia flow rate and composition of the Mn and Si mixtures in the substrate material) on the doping level of the obtained Ga(Mn,Si)N bulk single crystals was studied. Measurements involving X-ray diffraction and Raman methods confirmed good structural properties of Ga(Mn,Si)N single crystals. To characterize the magnetic properties of our materials, their magnetization was measured as a function of magnetic field.

Hydrogen plays an important role in GaN and related alloys. It is often a part of the growth environment and can be incorporated in GaN during different processing steps. Its behaviour is rather complicated and poorly understood. GaN doped with Fe has currently gained an increasing interest as a suitable magnetic semiconductor for spintronic applications. Here, we report results of the study on GaN doped with Fe and codoped with Mg for deep acceptors, Si for shallow donors and isoelectronic Al. Samples were grown by the chemical transport process in the form of small (~ 0.3 mm) crystallites and subsequently pressed to form platelets. As-grown samples and after annealing in different atmospheres (successively with N2 and NH3) were studied. Hydrogen concentration were determined by NRA using the 15N profiling method. Hydrogen release due to the analysing beam was evaluated using the molecular recombination model. Effective H-release cross-section was found to be the same for all GaFeN samples, independently of codoping. The lowest concentration of hydrogen among as-grown materials was revealed in GaFeN samples. Codoped materials showed higher hydrogen concentration, increasing in the following sequence: Mg, Si and Al. Hydrogen concentration can be substantially reduced by annealing in N2 atmosphere, whereas subsequent annealing in NH3 produces hydrogenation, however, to concentrations below that for pristine samples. The model of these processes has been proposed.

Gallium nitride growth by Sandwich Sublimation Method has been studied. Experiments were carried out in a tubular quartz reactor with induction heating. The obtained GaN layers possessed irregular surface morphology with a thickness range up to 1 mm. Raman spectroscopy and X-ray studies were used to investigate the films. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The present study was undertaken to determine if boron phosphide (BP) crystals could be produced by a simple technique, close-spaced vapor transport (CVST). This technique has proven very successful in achieving very high growth rates for a wide variety of materials including ZnSe, AlN, and SiC. Both silicon (100) and sapphire substrates were used for the CSVT growth. The resulting films were characterized by Raman spectroscopy. Sublimation of BP powder from 1050 to 1450 °C in an argon atmosphere produced a range of deep orange colour, single and polycrystalline BP crystals. The crystal size increased and the crystal density decreased with increasing temperature. Well-faceted crystals were produced at an intermediate temperature of 1200 °C. At temperatures higher then 1450 °C no BP crystals were grown. Only a fibrous mass of fine whiskers, loosely attached to the substrate were produced. The peak position of the Raman LO mode of the BP crystals was shifted to higher wavenumbers than the BP powder source, suggesting that the crystals were compressively strained. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Powder diffraction data for fine AlN and GaN powders were collected at a Bragg–Brentano diffractometer equipped with a Johansson monochromator and a semiconductor strip detector. Rietveld-refinements were performed in order to determine the structural parameters of these wurtzite-type (space group, P 6 3 mc ) materials. The following crystallographic data were obtained: a = 3.11197(2) A, c = 4.98089(4) A, c / a =1.60056(2), u = 0.3869(5) for aluminium nitride and a = 3.28940(1) A, c = 5.18614(2) A, c / a = 1.62606(1), u = 0.3789(5) for gallium nitride. These structural data are discussed in the light of earlier experimental and theoretical results.

Magnetoresistance and Hall effect in (Ga,Mn)N, (Ga,Mn,Si)N, and (Ga,Fe)N bulk crystals has been studied in the temperature range from 4.2 K to 300 K. No anomalous Hall effect contribution to the Hall voltage vs. magnetic curve has been found. The negative magnetoresistance has been found only in samples with metallic type of conductivity and is interpreted as resulting from weak localization of current carriers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

X-ray absorption spectroscopy has been used to study the local structure of Mn atoms in Ga 0.952 Mn 0.048 N crystals. Mn K-edge absorption spectra have been analyzed in both X-ray near-edge structure and extended X-ray absorption fine structure ranges. Modelling of the spectra has been done using real-space multiple-scattering calculations (FEFF 8 code). The substitutional model with Mn on the Ga site best describes the data. The Mn–N distance is 0.12 A longer than the Ga–N distance in GaN, and the second-shell distance (Mn–Ga) is 0.02 A longer than Ga–Ga distance in GaN. Disorder in the second coordination shell is identified by Debye–Waller factor analysis.

Gallium nitride is a novel material for short wavelength (blue) optoelectronics. Our previous investigation showed that Mn doped GaN has paramagnetic or antiferromagnetic properties opening new possible applications. The high concentration of magnetic ions possibly allows for the use of such a material in magnetooptic and spintronic devices. GaMnN and GaMnMgN powders were prepared by heating mixtures of gallium and manganese powder or powders of gallium nitride and manganese in a stream of ammonia at the temperature up to 1250°C. The powders have a grain size about 1–10 μm and they contain more than 2% of manganese by weight. Powders of doped GaN were prepared in a series of technological processes at various temperatures, ammonia flow rates and concentration of dopants in initial mixtures. Since hydrogen largely attributes to the passivation of p-dopants it plays an essential role in determination of electrical properties of these materials. Hydrogen content analysis was performed by the NRA method using the 1 H( 15 N, αγ ) 12 C reaction. This reaction has a sharp resonance of the cross-section at 6.3385 MeV. Therefore it is possible by changing the incident 15 N beam energy to measure depth distribution of hydrogen. It was found out that hydrogen concentration in our materials was below 1.5 at%.

Wurtzite (Ga,Fe)N bulk crystals were, for the first time, successfully grown by AMMONO and chemical transport methods. The magnetization measurements of (Ga,Fe)N crystals revealed the coexistence of paramagnetic and ferromagnetic contributions. The paramagnetic component was shown to be growth condition dependent. The Brillouin-type behavior was observed in the samples obtained by both methods. Some (Ga,Fe)N samples (especially those codoped with Si) grown by the chemical transport method show a Van Vleck–type paramagnetic behavior.

Lattice parameters for hexagonal boron nitride (hBN) were determined using X-ray powder diffraction at a synchrotron-radiation source (beamline B2, Hasylab/DESY, Hamburg) in the previously uninvestigated temperature range from 10 K up to 297.5 K. The relative change of a and c with rise of temperature in the studied range is anisotropic and amounts to about -0.05% and +0.82%, respectively. The corresponding increase of the unit-cell volume is 0.73%. The evaluated values of thermal expansion coefficients derived from the lattice-parameter dependences on temperature are generally consistent with earlier data determined by interferometryfor T≥82 K.

Silicon nitride powders were obtained in a reaction of SiO 2 powders with NH 3 . The influence of the following parameters on the quality of Si 3 N 4 was determined: silica particle size, temperature and furnace heating programme, sample heating time, ammonia flow rate and application of the selected mineralising agents. The powders of silica were characterised by: optical microscopy, SEM, X-ray phase analysis and thermal analysis. The products of the syntheses were tested by: optical microscopy, SEM, X-ray phase analysis, IR spectroscopy and classic quantitative analysis. The investigations resulted in elaboration of a method of preparation of crystalline silicon nitride powders containing more than 96% Si 3 N 4 . The discussion on the influence of magnesium nitride additive on the Si 3 N 4 synthesis process has also been carried out.

Mixtures of powders of gallium nitride and manganese were annealed in a stream of ammonia at temperatures from the range of 1200–1250°C. The procedure resulted in preparation of bulk single crystals of gallium nitride of dimensions up to 2.7×1.5×0.5 mm and containing up to 2% of Mn by weight. The influence of temperature, ammonia flow rate and manganese concentration in the substrate material on the doping level of the obtained bulk crystals was studied. The concentration of manganese was determined by means of an electron microprobe method. Raman investigations supported the conclusion on the well ordered structure of the prepared crystals. The measurements done by a superconducting quantum interferometer showed that the crystals doped with manganese ions manifested paramagnetic properties.

Lattice parameter and thermal-expansion coefficient for magnesium nitride, Mg 3 N 2 , were determined using X-ray powder diffraction at the B2 beamline in Hasylab (DESY) in the temperature range from 11 K up to 304.5 K. The relative change of lattice parameter on raising the temperature in the studied range is about 0.14%. At 300 K, its value is 9.9644(1) A and the linear thermal expansion coefficient derived from a polynomial approximation is a =1.1×10 −5 K −1 .

Gallium nitride powder was prepared from gallium and ammonia at temperatures of 1000–1200°C. Parameters of the crystallographic lattice as well as photoluminescence and Raman spectra were determined for the obtained powder. As a result of GaN powder sublimation, GaN single crystals of 3×2×0.2 mm were received, at temperatures 1200–1250°C. Single crystals of gallium nitride were also synthesised in a reaction of gallium vapours with ammonia. Crystals up to 1.5×1×0.1 mm were obtained at the temperature range of 850–1150°C. The obtained single crystals were studied by X-ray methods resulting in structure refining, mapping of reflexes and rocking curves. In addition, Raman spectroscopy studies and conductivity measurements were carried out. It was also demonstrated that the crystallographic structure of the crystals and powders was well pronounced. Homoepitaxial GaN films of several tens of micrometers were deposited onto selected GaN single crystals. The influence of grain size on the GaN sublimation process was studied. The 50–500 μm GaN crystalline powder sublimation resulted in the growth of single crystals whose quality was significantly better in comparison to effects of the sublimation of a few micrometer crystalline powder.

Ga1-xMnxN, heavily p-type doped, should reveal ferromagnetic ordering at ambient temperatures. Here we report a method of obtaining free-standing single crystals of Ga1-xMnxN. The method of co-doping with Mn and Si was also used. The dimensions of the crystals obtained were up to 4.8 × 2.5 × 0.4 mm.

Ferromagnetic behavior of GaN doped with Mn (Ga1−zMnzN) grown by the ammonothermal and chemical transport methods is discussed in terms of a second phase (ferromagnetic one) produced during the growth process. The reference manganese nitride samples grown by the same method as (Ga,Mn)N reveal room-temperature ferromagnetic behavior, depending on the growth details. Different MnxNy phases are suggested to be responsible for ferromagnetic behavior of (Ga,Mn)N.

Small MnxGa1−xN crystals grown by the resublimation method have been characterised by Raman scattering technique. It has been shown, that for small concentration of manganese the concentration of free electrons in the material is high as in typical free standing GaN crystals, but for higher contents of manganese the concentration of free carriers in the alloy has been substantially reduced. The measured Raman spectra have been compared with the calculated phonon density of states, and it has been shown that the Raman peaks correspond to the peaks of the phonon density of states. In consequence the new Raman peaks found in the material are ascribed to disorder activated phonon modes.

Ga1-xMnxN, heavily p-type doped, should reveal ferromagnetic ordering at ambient temperatures. Here we report a method of obtaining free-standing single crystals of Ga1-xMnxN. The method of co-doping with Mn and Si was also used. The dimensions of the crystals obtained were up to 4.8 × 2.5 × 0.4 mm.