Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Solid state amorphization transformation in the mechanically alloyed Fe27.9Nb2.2B69.9 powders

Mössbauer spectrometry and Rietveld analysis of X-ray diffraction patterns were used to follow the solid state amorphization transformation during the milling process of the Fe_27.9Nb_2.2B_69.9 powders. The reaction between elemental Fe, Nb and B powders leads to the formation of the Nb(B) and Fe(B) solid solutions after 1 and 10 h of milling, respectively. A mixture of α-Fe, Nb(B) and highly disordered Fe(Nb, B) solid solution is found after 25 h of milling. An amorphous structure is obtained on further milling time (100 h). From the Mössbauer spectrometry results, it is observed that the total mixing of the elemental powders, at the atomic level, is achieved after 50 h of milling and a stationary state corresponding to a full paramagnetic amorphous phase is reached after 100 h of milling. The amorphization process can be described by an Avrami parameter close to n = 1.     

High resolution X-ray diffraction studies of real structure of nearly perfect single crystals

Real structure together with composition and elemental purity of single crystals controls their properties. This paper reviews recent work carried out at the National Physical Laboratory on application of high resolution X-ray diffractometry, topography and diffuse X-ray scattering for direct observation and characterization of real structure of single crystals of silicon, gallium arsenide, diamond and LiNbO₃. A series of six multicrystal X-ray diffractometers have been designed, developed and fabricated indigenously. The most versatile of these systems is a five crystal X-ray diffractometer with state-of-the-art level resolution. These techniques and equipments have been applied in studying several interesting problems. Even in dislocation-free crystals of silicon, remarkable differences in the defect structure have been observed if the growth method was changed from float zone to Czochralski. Study of effect of externally applied electric fields and ion implantation on real structure of crystals has yielded interesting results. Images of ‘filaments’ which show nonhomogeneous distribution of electric current through semiconductors and insulators have been recorded for the first time in high resolution traverse topographs. Diffracted X-ray intensities could be modified by externally applied electric fields. It has been shown that implantation of BF ₂ ⁺ ions in silicon for producing shallow junctions does not produce homogeneous distribution of boron. The impurity is partially in clustered form. Biaxial stress introduced by thin depositions in substrate crystals are of considerable applied concern. The value and nature of stress have been determined in a number of systems. Typical results obtained on GaAs: multilayer metallizations are described. Also, degradation of perfection of substrates has been monitored. This work has shown that the stress is not homogeneously distributed and is quite anisotropic. A new high resolution X-ray diffraction technique has been developed for direct observation and study of forward diffracted X-ray beam and anomalous transmission of X-rays through ‘thin’ diamond crystals of varying degrees of perfection.     

Raman spectroscopy for quality control and process optimization of chalcopyrite thin films and devices

We will demonstrate in this paper that Raman scattering of visible light is a versatile tool both for research and industrial process monitoring of thin chalcopyrite films for solar cells. Thin films of Cu(In, Ga)(S,Se)₂ (CIGSSe) are produced by rapid thermal processing of stacked elemental Cu-In-Ga-Se layers. The Raman investigations are accompanied by grazing incidence X-ray diffraction (GI-XRD) and X-ray florescence (XRF) measurements. GI-XRD measurements confirm that the films show a two-fold elemental gradient: a sulfur gradient from the top and a Ga gradient from the CIGSSe/Mo interface. By Rietveld refinement of the GI-XRD spectra of the surface-near (∼ 100nm) ratio of sulfur to selenium can be obtained which corresponds well to the intensity ratio of the two Raman A1 modes of CuInS₂ and CuInSe₂. The asymmetric line shape of both XRD diffractograms and Raman spectra is attributed to the sulfur gradient. In addition we show that the intensity ratio of the satellite Raman B and E modes shows a correlation with the Cu to In + Ga ratio obtained by XRF.     

Crystal growth and characterization of CuI single crystals by solvent evaporation technique

Cuprous iodide (CuI) crystals are grown by slow evaporation technique in three different solvents. Large CuI single crystals with dimensions of 7.5 mm × 5 mm × 3 mm are obtained in pure acetonitrile solvent at 40 °C. The as-grown crystals are analyzed by X-ray diffraction, energy-dispersive X-ray analysis, differential scanning calorimetry, current-voltage characteristic and photoluminescence spectrum. The results show that the CuI crystal has the zinc-blende structure with no secondary phase. The elemental Cu/I ratio is 1.09:1. The melting point of the crystal is 875 K and two phase transitions occur from room temperature to its melting point. The electrical conductivity of CuI platelet crystal is in the range of 1.11-2.38 Ω⁻¹ cm⁻¹. Under ultraviolet excitation, the CuI crystals exhibit three emission bands with peak positions at 426, 529 and 671 nm. The nature of the luminescence is discussed.     

Composition and crystallinity of silicon nanoparticles synthesised by hot wire thermal catalytic pyrolysis at different pressures

The effect of pressure on the structure and composition of silicon nanoparticles synthesized by hot wire thermal catalytic pyrolysis (HW-TCP) of pure silane has been investigated. Light brown powders were produced at silane pressures of 10 and 50 mbar, at a flow rate of 50 sccm, using a tungsten filament at temperatures of 1900 °C and 1800 °C respectively. As determined by transmission electron microscopy and X-ray diffraction, the particles produced at lower pressure have sizes around 10 nm, whereas those produced at higher pressure are typically 50 nm. High resolution transmission electron microscopy (HR-TEM) shows a surface layer of between 2 and 5 nm thickness, which was confirmed by X-ray photoemission spectroscopy to be an oxide shell. Both X-ray diffraction and HR-TEM confirm a high degree of crystallinity in both sets of particles, with Raman spectroscopy indicating an increase in crystalline fraction with synthesis pressure.     

Synthesis and characterization of thermally evaporated Cu2SnSe3 ternary semiconductor

Copper Tin Selenide (CuSnSe) powder was mechanically alloyed by high energy planetary ball milling, starting from elemental powders. Synthesis time and velocity have been optimized to produce Cu₂SnSe₃ materials. Thin films were prepared by thermal evaporation on Corning glass substrate at T_s = 300 °C. The structural, compositional, morphological and optical properties of the synthesized semiconductor have been analyzed by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM) and transmission electron microscopy. The analyzed powder exhibited a cubic crystal structure, with the presence of Cu₂Se as a secondary phase. On the other hand, the deposited films showed a cubic Cu₂SnSe₃ ternary phase and extra peaks belonging to some binary compounds. Furthermore, optical measurements showed that the deposited layers have a relatively high absorption coefficient of 10⁵ cm⁻¹ and present a band gap of 0.94 eV.     

Imaging X-ray fluorescence spectroscopy: laboratory measurements

Following on from the proof-of principle measurements of Martin et al. (X-ray Spectrom. 28 (1999) 64) we further describe the development of an imaging X-ray fluorescence (IXRF) spectrometer with no moving parts. Our laboratory system is based on a microchannel plate (MCP) “lens”, a CCD X-ray detector with good sub-keV quantum efficiency and a conventional electron bombardment X-ray source. We have used this equipment to form images of a standard XRF target, demonstrating that “elemental maps” (images of the target in the characteristic X-rays of one particular element) may be formed with sub-millimetre resolution. In addition to fluorescent X-rays, we detected X-rays which had been Bragg reflected from the polycrystalline aluminium substrate of the target. It is possible that the resulting “Bragg images” may be exploited to measure spatially varying strain, manifested as lattice distortion, introduced, for example, by thin films deposited on the surface of a sample.     

Synthesis of stable spherical platinum diphosphide, PtP2/carbon nanocomposite by reacting Pt(PPh3)4 at elevated temperature under autogenic pressure

The synthesis of microsized carbon spheres supporting the semiconductor platinum diphosphide, PtP₂, was conducted by the thermal decomposition of an organometallic precursor. This novel reaction was carried out using the reaction under autogenic pressure at elevated temperature (RAPET) method by dissociating Pt(PPh₃)₄ at 1000 °C. The product was characterized using methods of electron microscopy (scanning electron microscope (SEM), transmission electron microscope (TEM), selected area energy dispersive spectroscopy (SAEDS), elemental analyzer (EA) and energy dispersive X-ray analysis (EDX)) and powder-XRD. Transmission electron microscope images indicate that the particle size of the nanoparticles of PtP₂ coated on the carbon spheres is 50 nm.     

Structural variations in layered alkaline earth metal cyclohexyl phosphonates

Two series of alkaline earth metal cyclohexyl phosphonates, M(C₆H₁₁PO₃H)₂(H₂O) (M = Ca, Sr and Ba) (1–3) and M(C₆H₁₁PO₃)(H₂O) (M = Mg, Ca, Sr, and Ba) (4–7) have been synthesized under mild reaction conditions. All new compounds have been characterized using elemental analysis, IR, TGA and powder X-ray diffraction techniques. The molecular structure of compound 2 determined using single crystal X-ray diffraction technique reveals a layered polymeric structure.     

Cr(VI) adsorption on functionalized amorphous and mesoporous silica from aqueous and non-aqueous media

A mesoporous silica (SBA-15) and amorphous silica (SG) have been chemically modified with 2-mercaptopyridine using the homogeneous route. This synthetic route involved the reaction of 2-mercaptopyridine with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry and elemental analysis. The solid was employed as a Cr(VI) adsorbent from aqueous and non-aqueous solutions at room temperature. The effect of several variables (stirring time, pH, metal concentration and solvent polarity) has been studied using the batch technique. The results indicate that under the optimum conditions, the maximum adsorption value for Cr(VI) was 1.83 ± 0.03 mmol/g for MP-SBA-15, whereas the adsorption capacity of the MP-SG was 0.86 ± 0.02 mmol/g. On the basis of these results, it can be concluded that it is possible to modify chemically SBA-15 and SG with 2-mercaptopyridine and to use the resulting modified silicas as effective adsorbents for Cr(VI).     

Band offset of the In2S3/indium tin oxide interface measured by X-ray photoelectron spectroscopy

In₂S₃ thin films have been grown on Indium Tin Oxide (ITO) by Chemical Spray Pyrolysis. The structural and physical-chemical properties of the films have been investigated by means of X-ray Diffraction and X-ray Photoelectron spectroscopy (XPS). The valence band discontinuity at the In₂S₃/ITO interface has been determined by XPS resulting in a value of 1.9 ± 0.2 eV. Consequently, the conduction band offset has been estimated to be 1.0 ± 0.4 eV.     

A new approach to joining of bulk copper using microwave energy

Metallurgical joining of high thermal conductivity materials like copper has been technically challenging. This paper illustrates a novel method for joining of bulk metallic materials through microwave heating. Joining of copper in bulk form has been carried out using microwave energy in a multimode applicator at 2.45 GHz and 900 W. Charcoal was used as susceptor material to facilitate microwave hybrid heating (MHH). Copper in coin and plate forms have been successfully joined through microwave heating within 900 s of exposure time. A sandwich layer of copper powder with approximately 0.5 mm thickness was introduced between the two candidate surfaces. Near complete melting of the powder particles in the sandwich layer does take place during the microwave exposure leading to metallurgical bonding of the bulk surfaces. Characterisation of the joints has been carried out through microstructure study, elemental analysis, phase analysis, microhardness survey, porosity measurement and tensile strength testing. X-ray diffraction (XRD) pattern indicates that some copper powder particles got transformed into copper oxides. XRD analysis also reveals that the dominant orientation (3 1 1) in starting copper powder got transformed into a preferential orientation (1 1 1) in the joint. A dense uniform microstructure with good metallurgical bonds between the sandwich layer and the interface was obtained. The hardness of the joint area was observed to be 78 ± 7 Hv, while the porosity in the joint was observed to be 1.92%. Strength character of the copper joints shows approximately 29.21% elongation with an average ultimate tensile strength of 164.4 MPa.     

Interfacial reactions in Mo-Zr multilayer structure: an X-ray reflectivity study

The effect of elevated temperature on the structural stability and alloy formation in Mo-Zr multilayers is investigated. Mo-Zr multilayers deposited by the electron beam evaporation technique under ultra-high vacuum conditions are annealed up to 650 °C. The changes induced due to thermal treatment are observed using X-ray reflectivity (both specular and off-specular) and X-ray diffraction techniques. The Mo-Zr multilayers remained as an insoluble layered structure even after annealing as revealed from X-ray reflectivity measurements. The interfacial roughness is found to be very similar at all interfaces and decreases on annealing. The multilayer structure remains intact on annealing with expansion of the multilayer period and a marginal increase in X-ray reflectivity.     

Effect of the substrate on the electrodeposition of Bi2Te3−ySey thin films

The potentiostatic electrodeposition of n-type Bi₂Te_3−ySe_y thermoelectric films onto stainless steel and gold substrates from nitric acid aqueous solutions has been carried out at room temperature. The cathodic process during the electrodeposition of Bi₂Te_3−ySe_y films was investigated by cyclic voltammetric experiments. The structure and surface morphology of Bi₂Te_3−ySe_y films deposited on both substrates were characterized by X-ray diffraction (XRD) and environment scanning electron microscopy (ESEM) coupled with energy dispersive spectroscopy (EDS). Electrical and thermoelectric properties of as-deposited films were also measured at room temperature. The results show that the reduction process under the same depositing conditions on gold and stainless steel substrates is very different. On gold substrates, H₂SeO₃ in the electrolyte is firstly reduced to elemental Se, and then the deposited Se reacts with HTeO₂⁺ and Bi³⁺ to form Bi₂Te_3−ySe_y alloy. On stainless steel substrates, HTeO₂⁺ in the electrolyte is firstly replaced by elemental Fe to produce elemental Te, and subsequently the generated Te reacts with H₂SeO₃ and Bi³⁺ to form Bi₂Te_3−ySe_y alloy. Analysis of ESEM show that the surface morphology of the films electrodeposited on gold substrates is more compact than that on stainless steel substrates. The XRD patterns indicate that the films electrodeposited on both substrates exhibit preferential orientation along (1 1 0) plane, but the relative peak intensity of (0 1 5) and (2 0 5) planes on stainless steel substrates is stronger than that on gold substrates. The Seebeck coefficient and electrical resistivity of the films deposited on stainless steel substrates are higher than that on gold substrates.     

Advances in silicon carbide X-ray detectors

The latest advances in SiC X-ray detectors are presented: a pixel detector coupled to a custom ultra low noise CMOS preamplifier has been characterized at room and high temperature. An equivalent noise energy (ENE) of 113 eV FWHM, corresponding to 6.1 electrons r.m.s., has been achieved with the detector/front-end system operating at +30 °C. A Fano factor of F=0.10 has been estimated from the ⁵⁵Fe spectrum. When the system is heated up to +100 °C, the measured ENE is 163 eV FWHM (8.9 electrons r.m.s.). It is determined that both at room and at high temperature the performance are fully limited by the noise of the front-end electronics. It is also presented the capability of SiC detectors to operate in environments under unstable temperature conditions without any apparatus for temperature stabilization; it has been proved that a SiC detector can acquire high resolution X-ray spectra without spectral line degradation while the system temperature changes between +30 and +75 °C.     

A novel nanostructure of cadmium oxide synthesized by mechanochemical method

Cauliflower-like cadmium oxide (CdO) nanostructure was synthesized by mechanochemical reaction followed calcination procedure. Cadmium acetate dihydrate and acetamide were used as reagents and the resulting precursor was calcinated at 450 °C for 2 h in air. The structures of the precursor and resultant product of the heating treatment were characterized using Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and elemental analysis, X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy analysis (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction pattern (ED). SEM and TEM images revealed the cauliflower-like morphology of the sample. This structure includes the bundles of rods and tubes in nanoscale, which combine with each other and form the resulting morphology with the average diameter, 68 nm of the components. ED pattern indicated the single crystal nature of the formed bundles.     

High textured AlN thin films grown by RF magnetron sputtering; composition, structure, morphology and hardness

High quality thin aluminum nitride (AlN) films have been deposited onto a silicon (1 0 0) substrate by radio frequency magnetron sputtering of a pure Al target using different gas (Ar, N₂) mixtures. The depositions were carried out at substrate temperatures varying from room temperature (plasma heating) up to 400°C. The crystalline structures were investigated by X-ray diffractometry (XRD) revealing a pronounced texture of the deposited films. Some of the compounds investigated were deposited onto a thin buffer layer of pure Al. The film surface morphology was investigated by Atom Force Microscopy (AFM) (SPM-9500J3 from Shimadzu Co), and was found to depend distinctively upon the different deposition conditions. Generally, two kinds of structures were found—a columnar one, which was densely packed or organized in planar parallel sheets, and a flat structure, (typical for mono-crystals), with rms roughness below 0.2 nm. In this paper, the influence of argon added to the sputtering gas environment on the film properties is investigated and discussed. The depth elemental distributions were calculated using 2.4 MeV ⁴He⁺ Rutherford Backscattering Spectrometry (RBS). Finally, the mechanical characteristics were described using hardness tests.     

Phase formation, chemical composition and electrical studies of Ti/Si bilayer system

The annealing effects over a range of temperatures of the titanium film (90 nm) grown on Si(111) by electron gun evaporation technique were investigated using physical and electrical measurements. Grazing Incidence X-ray Diffraction experiment shows a stable titanium disilicides formation at higher annealing temperature. The depth profiling data using X-ray Photoelectron Spectroscopy show that the properties are closely related to the change of the interfacial layer and chemical state under the high-temperature annealing. The Schottky Barrier Height, as estimated by the current-voltage measurement is 0.75, 0.695, 0.662 and 0.60 eV for pristine and annealed samples at 450, 550 and 700 °C respectively.