AES investigation of the composition of polar {0001} surfaces of CdS

The composition of polar {0001} surfaces of CdS was investigated by Auger electron spectroscopy. Both the A (0001) or cadmium face and the B (000¯1) or sulphur face showed sulphur enrichment. This enrichment is attributed to the forward scattering of sulphur below the surface and the subsequent exposure of these atoms through continued sputtering. The effect of carbon contamination on the S/Cd ratio on both faces was investigated. The decrease of this ratio with increased carbon contamination is explained in terms of differences in the escape depths of the sulphur and cadmium Auger electrons.     

Interfacial reactions between palladium thin films and InP

Palladium appears to be an important component in ohmic contact metallizations to III–V semiconductors. Very little is known about its interaction with InP. Consequently, the reaction between a thin layer of Pd (100 nm) and an InP substrate has been studied at annealing temperatures ranging from 250–450 °C for up to 30 sec, i.e., typical annealing conditions encountered during contact fabrication. Palladium reacts readily with InP, initially forming an amorphous ternary phase, which transforms to crystalline Pd₂InP on annealing. Pd₂InP has an ordered cubic structure, with a lattice parameter of 0.830 nm, and grows epitaxially on InP. Microtwins, 2–3 atomic layers thick, have been identified in the ternary phase and these form along the (110) and ( 10) planes.     

Reflection properties of oriented thin CdS films formed by laser ablation

Oriented thin (≈2 μm) films, CdS, prepared by laser ablation were characterized by the dependence of external and internal reflection on both the angle of incidence and the polarization of laser light. The samples exhibit perpendicular and parallel orientation of the crystallographic axis with respect to the surface of the glass substrate. The experiments were performed at 300 K using low intensity (<1 W/cm²) cw emissions at 476.5, 514.5 and 632.8 nm of argon and He–Ne lasers respectively. For blue and green light, the results are very well described by the theoretical models based on Fresnel reflection. In contrast to the external features, the internal reflectance exhibits dichroism and birefringence of the samples at 514.5 nm, revealing the sensitivity of the internal reflection technique to the optical anisotropy of the films. Considering multiple-beam interference, the model of Fresnel also describes satisfactorily the results for red light. However, a rather sensitive dependence on the incoming He–Ne laser intensity was observed. In fact, by increasing the intensity of 64 mW/cm² by about one order of magnitude, only the external reflectance shows good agreement with the theory, whereas the internal reflection properties are obviously influenced by additional effects, such as non-linear change of the optical constants, which are not included in Fresnel reflection considerations.     

Chemical bath deposition of SnS thin films on ZnS and CdS substrates

We illustrate that Tin sulfide (SnS) thin films of 110–500 nm in thickness may be deposited on ZnS and CdS substrates to simulate the requirement in developing window-buffer/SnS solar cells in the superstrate configuration. In the chemical bath deposition reported here, tin chloride and thiosulfate are the major constituents and the deposition is made at 25 °C. In a single deposition, film thickness of 110–170 nm is achieved and in two more successive depositions, the film thickness is 450–500 nm. The thicker films are composed of vertically stacked flakes, 100 nm across and 10–20 nm in thickness. The Sn/S elemental ratio is ~1 for the films 110–170 nm in thickness, but it slightly increases for thicker films. The crystalline structure is orthorhombic, similar to the mineral herzenbergite, and with crystallite diameters 13 nm (110–170 films) and 16 nm (450–500 nm films). The Raman bands at 94, 172 and 218 cm^?1 further confirm the SnS composition of the films. The optical band gap of SnS is 1.4–1.5 eV for the thinner films, but is 1.28–1.39 eV for the thicker films, the decrease being ascribed to the increase in the crystallite diameter. Uniform pin-hole free SnS thin films were successfully grown on two different substrates and can be applied in solar cell structures.     

Interface reactions between titanium thin films and (1¯1 2) sapphire substrates

We have studied the reactivity of Ti with the R-plane (1ˉ1 2) of sapphire from room temperature to 1250 °C by X-ray photoemission spectroscopy (XPS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Rutherford backscattering spectroscopy (RBS). The combination of these techniques allowed the interface reactions to be studied from the monolayer regime up to the bulk regime. XPS showed that at room temperature, monolayer coverages of Ti reduced the sapphire surface to form Ti-O and Ti-Al bonds. TEM, XRD, and RBS showed that annealing of room-temperature deposited Ti resulted in an interfacial region consisting of two layers, a Ti₃Al[O] layer adjacent to the sapphire and a Ti_0.67 [O_0.33] layer at the free surface. The growth of the Ti₃Al[O] layer had an activation energy of 103.4±25 kJ deg-mole. The nature of the interfacial reaction between Ti and sapphire was similar for Ti coverages from the monolayer to the bulk regime.     

The adhesion of thin plasma-polymerized organic films to metal substrates

The direct pull method was used to study the adhesion of thin (<1 μm) plasma-polymerized films on metal substrates. Application of this method provides information on the cohesive, as well as the adhesive, properties of these films. After breakage of the films by the pull method, the interface was analyzed by scanning electron microscopy to determine the nature of the breakage at the interface. Electron spectroscopy for chemical analysis was used to determine whether any chemically adsorbed layers of organic films remained after the films had been pulled from the metal substrate. The adhesive or cohesive strengths of plasma-polymerized tetrafluoroethylene and chlorotrifluoroethylene films on 304 stainless steel, aluminum and silver were measured by the pull method. Adhesive strength was found to be higher than cohesive strength for plasma-polymerized tetrafluoroethylene films on the various substrates. The result for plasma-polymerized chlorotrifluoroethylene films was not as expected, indicating that considerable care is required in the interpretation of tensile tests of laminates such as those conducted in this study.     

$$\hbox {SiO}_{2}\hbox {/TiO}_{2}$$ multi-layered thin films with self-cleaning and enhanced optical properties

Self-cleaning, high transmittance glazing was obtained by cold spray deposition for glazings. The thin films contain \(\hbox {TiO}_{2}\), \(\hbox {SiO}_{2}\) and Au nanoparticles in different structures which allow for tailoring the optical, hydrophilic and photocatalytic properties. The crystallinity, morphology and surface energy were correlated with the optical transmittance and reflectance; the transmittance increased from 89.45 (for the glass substrate) to 91.76% when Au nanoparticles were used in the tandem layered structures. The samples containing alternating multi-layered \(\hbox {SiO}_{2}\) and \(\hbox {TiO}_{2}\) thin films without gold nanoparticles show hydrophilic surface; for these layers, the photocatalytic efficiency reaches 40% under simulated solar radiation. A conditioning effect based on adsorption was observed to increase the photocatalytic efficiency. These highly transparent coatings are well suited for glazings and fenestration, showing the self-cleaning effect based on combined superhydrophilicity and photocatalysis.     

Optical and structural properties of chemically deposited CdS thin films on polyethylene naphthalate substrates

CdS thin films were deposited on polyethylene naphthalate substrates by means of the chemical bath deposition technique in an ammonia-free cadmium-sodium citrate system. Three sets of CdS films were grown in precursor solutions with different contents of Cd and thiourea maintaining constant the concentration ratios [Cd]/[thiourea] and [Cd]/[sodium citrate] at 0.2 and 0.1 M/M, respectively. The concentrations of cadmium in the reaction solutions were 0.01, 7.5 × 10⁻³ and 6.8 × 10⁻³ M, respectively. The three sets of CdS films were homogeneous, hard, specularly reflecting, yellowish and adhered very well to the plastic substrates, quite similar to those deposited on glass substrates. The structural and optical properties of the CdS films were determined from X-ray diffraction, optical transmission and reflection spectroscopy and atomic force microscopy measurements. We found that the properties of the films depend on both the amount of Cd in the growth solutions and on the deposition time. The increasing of Cd concentration in the reaction solution yield to thicker CdS films with smaller grain size, shorter lattice constant, and higher energy band gap. The energy band gap of the CdS films varied in the range 2.42-2.54 eV depending on the precursor solution. The properties of the films were analyzed in terms of the growth mechanisms during the chemical deposition of CdS layers.     

Reaction between permalloy and several thin metal films

To develop the electrode materials for thin permalloy film devices, the reactions between the permalloy Ni-19%Fe and several metal films were investigated. From the results of the annealing behaviour for thin bilayer films including the permalloy, it was clarified that aluminium, copper, chromium and gold films react with the permalloy below 250–350°C. However, molybdenum and tantalum do not react up to 400°C. Therefore it is considered that molybdenum and tantalum are good electrode materials for thin permalloy film devices.     

Interfacial reaction and adhesion between SiC and thin sputtered nickel films

Thin sputtered nickel films grown on SiC were annealed in an Ar/4 vol % H2 atmosphere at temperatures between 550 to 1450 °C for various times. The reactivity and the reaction-product morphology were characterized using optical microscopy, surface profilometry, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The reaction with the formation of silicides and carbon was observed to first occur above 650 °C. Above 750 °C, as the reaction proceeded, the initially formed Ni3Si2 layer was converted to Ni2Si and carbon precipitates were observed within this zone. The thin nickel film reacted completely with SiC after annealing at 950 °C for 2 h. The thermodynamically stable Ni2Si is the only observed silicide in the reaction zone up to 1050 °C. Above 1250 °C, carbon precipitated preferentially on the outer surface of the reaction zone and crystallized as graphite. The relative adhesive strength of the reaction layers was qualitatively compared using the scratch test method. At temperatures between 850 to 1050 °C the relatively higher critical load values of 20–33 N for SiC/Ni couples are formed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Interfacial reaction and adhesion between SiC and thin sputtered cobalt films

Thin sputtered cobalt films on SiC were annealed in an Ar/4 vol% H₂ atmosphere at temperatures between 500 and 1450 °C for various times. The reaction process and the reaction-product morphology were characterized using optical microscopy, surface profilometry, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The relative adhesive strength between the film and substrate was determined by the scratch test method. Below 850 °C sputtered cobalt with a thickness of 2 m on SiC showed no detectable reaction products. Cobalt initially reacted with SiC at 850 °C producing Co₂Si and unreacted cobalt in the reaction zone. At 1050 °C the first-formed Co₂Si layer reacted to CoSi, and carbon precipitates were formed in the reaction zones. Sputtered thin cobalt layers reacted completely with SiC after annealing at 1050 °C for 2 h. Above 1250°C only CoSi was observed with carbon precipitates having an oriented structure in the reaction zone. Above 1450°C, a significant amount of graphitic carbon in the reaction zone was detected.     

Ga doping induced structural and optical modification in $$\hbox {Ge}_{2}\hbox {Sb}_{2}\hbox {Te}_{5}$$ Ge 2 Sb 2 Te 5 thin films

\(\text {Ge}_2\text {Sb}_2\text {Te}_5\) (GST) is considered a promising candidate for next-generation data storage devices due to its unique property of non-volatility and low power consumption. In present work, the bulk alloys and thin films of (\(\text {Ge}_2\text {Sb}_2\text {Te}_5\))\(_{100-x}\text {Ga}_x\) (x = 0, 3, and 10) are prepared using melt quenching and thermal deposition method, respectively. The effect of Ga doping on host composition is investigated by analyzing X-ray diffraction patterns and field emission scanning electron microscope images. From obtained results, it is found that all doped thin films retained the amorphous nature and exhibited uniform and smooth morphology. In Raman spectra, the appearance of a new peak in 10% Ga-doped GST thin film indicated an alteration in the atomic arrangement of host lattice. Transmission spectra revealed the highly transparent nature of all deposited thin films in the near-infrared region. The optical band gap of Ga-doped GST thin film is lower than that of the pure GST thin film which can be correlated with an increase in band tailing, attributed to an increase in localized defect states in the band gap. Due to the pronounced electronegativity difference between the Ga and Te element, new Ga–Te bonds with a higher number of wrong bonds (Ge–Ge, Sb–Sb, and Ge–Sb) are expected to thermally stabilize the amorphous phase. Such results predict the better performance of Ga-doped GST composition for better performance of phase-change random access memory.

     

Interaction between thin indium films and single-crystal ZnAs2 substrates

X-ray photoelectron and Auger electron spectroscopic studies of In/ZnAs₂ structures revealed a chemical reaction at the film-substrate interface at substrate temperatures between 400 and 650 K. Gibbs energy calculations showed that the more likely products of the interfacial reaction are InAs and Zn₃As₂.     

Synthesis and enhanced photocatalytic activity of g-$$\hbox {C}_{3}\mathrm{N}_{4}$$ hybridized CdS nanoparticles

The highly effective g-\(\hbox {C}_{3}\hbox {N}_{4}\) hybridized CdS photocatalysts were synthesized via a successive calcination and hydrothermal process. The as-prepared photocatalysts were characterized by X-ray powder diffraction, transmission electron microscopy and UV–Vis diffuse reflectance spectroscopy. The photocatalytic performance of the \(\hbox {C}_{3}\hbox {N}_{4}\)/CdS nanocomposites was evaluated by the photodegradation of RhB under visible light irradiation. The results showed that photocatalytic ability of the \(\hbox {C}_{3}\hbox {N}_{4}\)/CdS nanocomposites was higher than that of pure \(\hbox {C}_{3}\hbox {N}_{4}\) and CdS. The enhanced photocatalytic activity could be attributed to the high separation efficiency of the photo-excited electron-hole pairs. A possible mechanism of the photocatalytic degradation of RhB on \(\hbox {C}_{3}\hbox {N}_{4}/\)CdS nanocomposites was also proposed.     

Interfacial reactions between liquid Sn3.5Ag0.5Cu solders and Ag substrates

The morphology and growth kinetics of intermetallic compounds (IMCs) formed during the soldering reactions between Sn3.5Ag0.5Cu and Ag substrates at various temperatures ranging from 250 to 350 °C were investigated. The interfacial microstructure was quantified with scanning electron microscopy (SEM) for each processing condition. Experimental results show that the thickness of the scallop-shaped Ag₃Sn IMCs layer increased with increasing soldering time and temperature. Furthermore, Cu₆Sn₅ particle precipitates were observed in the Ag₃Sn IMCs layer around and thus suppressing the Ag₃Sn IMCs layer growth. Furthermore, the large Cu₆Sn₅ IMCs tend to appear in the vicinity of interfacial wicker-Ag₃Sn IMCs. Kinetics analyses showed that growth of the Ag₃Sn intermetallic compound was diffusion controlled. The activation energies for the growth of Ag₃Sn IMCs are calculated to be 66.7 kJ/mol.     

Laser damage of CdS and ZnS thin films

A method which has been used previously for three-dimensional space groups was applied to the determination of zero-slope points for all possible special wavevectors in the Brillouin zone for each of the plane groups. The results are tabulated for both non-magnetic and magnetic crystals and are relevant to electronic energy bands and to quasiparticle dispersion relations for surface states or thin film states. They enable one to identify the sources of peaks in density-of-states curves, and they also provide an aid to drawing energy bands or quasiparticle dispersion relations in the vicinity of wavevectors of special symmetry.     

Optical and electrical characterization of CdS thin films

Thin CdS films have been grown by chemical bath (CdCl₂, thiourea, ammonia) deposition (CBD) on SnO₂ (TO)-coated glass substrate for use as window materials in CdS/CdTe solar cells. High-resolution transmission electron microscopy revealed grains with an average size of 10 nm. The structure was predominantly hexagonal with a high density of stacking faults. The film crystallinity improved with annealing in air. Annealing in a CdCl₂ flux increased the grain size considerably and reduced the density of stacking faults. The optical transmission of the as-deposited films indicated a band gap energy of 2.41 eV. Annealing in air reduced the band gap by 0.1 eV. Annealing in CdCl₂ led to a sharper optical absorption edge that remained at 2.41 eV. Similar band gap values were obtained by photocurrent spectroscopy and electroabsorption spectroscopy (EEA) using an electrolyte contact. EEA spectra were broad for the as-deposited and air-annealed samples, but narrower for the CdCl₂-annealed films, reflecting the reduction in stacking fault density. Donor densities of ca. 10¹⁷ cm ^–3 were derived from the film/electrolyte junction capacitance.