Electron microscope study of aluminium films evaporated on air-cleaved sodium chloride

The article deals with the structure of thin aluminium films evaporated on air-cleaved NaCl substrates. The effect of the substrate temperature and the film thickness on the structure, the orientation and the grain size of the films was studied at a deposition rate of 10 Å/see (ev. 50 Å/see) in a vacuum of about 7. 10^–5 torr. The optimum temperature for epitaxial growth was found to be about 420°C. An almost regular arrangement of grains was found in the thickness region of 90–150 Å.     

Nickel-iron-gold magnetic films

Ni-Fe-Au films can be made by vacuum evaporation from a single melt since Au has an evaporation rate comparable to that of Ni and Fe. In films 400 Å thick the addition of Au does not changeH _c , butH _k increases 0·1 Oe per 1% Au until 10% Au is reached and then remains constant for Au percentages up to 26%. The change ofH _k with substrate deposition temperature is about the same as for Ni-Fe films (–0·01 Oe/°C). Films with 8% Au have the same skew as Ni-Fe films when made at a substrate temperature of 300 °C, but for Ni-Fe-Au films the change of skew with substrate temperature is about one fourth that of Ni-Fe films. The small area dispersion is reduced by a factor of 2 to 3 for Au additions of 4 to 26 percent.     

Rapid growth of ultra thin SiO2 films by a large-area electron beam

Rapid growth of ultra thin oxide films (40–180Å) of silicon using a low-energy large-area electron beam has been performed with a pressure ratio of 31 (O₂/He) and a total pressure of 0.5–0.7 Torr. A higher oxidation rate of about 625Ų/s is found for shorter irradiation time of the e-beam in the e-beam dose range 0.75–3 Coulomb/cm² and at lower substrate temperature 540–740°C. AES and XPS demonstrated a rapid electron-stimulated oxidation process of the Si surface. For the grown ultra thin oxide films, C-V characteristics, dielectric strength, uniformity of the film over the entire Si wafer and its thickness as a function of the processing time of the e-beam are also presented.     

Calculation of the electron-transfer parameters of thin polycrystalline films of metals

Electron transfer parametrs (scattering coefficient R, crystal-boundary transmission coefficient r, film-surface reflection coefficient) are calculated at temperatues t_msm=120, 293, and 573 K using Sc and Re films as an example. The conditions L d and L < d are satisfied, respectively, for these films (L is the mean diameter of the crystals and d is the thickness of the specimens). The films were obtained in a vacuum of 10^–6-5·10^–7 Pa. In the thickness ranges d200–500 Å (Re) and 300–800 Å (Sc), the films had a mean crystallite size of 250 and 600 Å, respectively. Experimental data on the dimensional effect of the temperature coefficient of resistance was analyzed within the framework of the Mayadas-Shatzkes (MS) theory, the model of isotropic carrier scattering, and the three-dimensional Tellier-Tosser-Pichard (TTP) model. It was concluded that the electrophysical properties of Sc films are satisfactorily described by the TTP model, while the MS theory yields exaggerated values of the coefficients r and p. In the case of films of Re, use was made of the isotropic scattering model and an approximation of the three-dimensional model for polycrystalline films. It was found that the coefficients r and R are independent of temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 42–47, June, 1988.We thank V. B. Lobode and L. G. Kulemzina for their assistance in conducting the investigation.     

Exchange-coupling across SiO

Strongly temperature-dependent ferromagnetic exchange coupling is observed between Fe films separated by an amorphous SiO barrier. Heating reversibly enhances the coupling strength which monotonically decreases with increasing SiO thickness. AtT=40K the coupling disappears for d_SiO20Å whereas at room temperature it persists up to a barrier thickness of 60 Å. The coupling strengthJ is determined by externally compensating the exchange field of samples grown on an antiferromagnetically biased Fe/Cr/Fe structure. It amounts toJ2·10^–6 J/m² for a sample with d_SiO=25 Å atT=300K. As a tentative explanation we propose that impurity or defect states within the large mobility gap of SiO carry the magnetic interaction across the insulating barrier.     

Baking impact on photoelectrochemical cells performance of electrodeposited CdSe films

Cadmium selenide (CdSe) nanocrystalline thin films in the form of upright nanocones, perpendicular to substrate surface, are grown electrochemically onto a conducting and transparent indium-tin-oxide substrate at room temperature and impact of baking under oxygen flow on their structure, morphology, optical absorbance and dark-light photoelectrochemical cell performance is explored. Crystallinity improvement followed by enhancement in the surface roughness 11-19 nm and reduction in water contact angle from 60° to 22° (±0.2)° due to baking impact showed increase in crystallite size from 25 to 100 Å. Increase in current density from 0.07 to 5.61 mA/cm² after baking under oxygen flow has promoted the conversion efficiency to 0.5% from 0.007%.     

Electrical properties and structure of thin chromium films

The temperature dependence of the electrical resistance of thin chromium films produced by vacuum condensation at 1· 10^–4 mm Hg on mica, optical glass, and rock salt substrates is considered. The electrical resistance of chromium films condensed on substrates heated to temperatures below 450 °C increases irreversibly on subsequent heating and cooling. Chromium films condensed on substrates heated to 500–600 °C, however, retain stable electrical properties on repeatedly heating and cooling.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 9, pp. 56–60, September, 1971.     

Thermoelectric properties of Ag2Se

To obtain information on the temperature and concentration dependence of thermoelectric quality factor Z and to clarify the nature of scattering in Ag₂Se a study was made of electrical conductivity , thermo-emf , and thermal conductivity in silver selenide over the temperature range T=80–450°K at concentration levels of 2–43·10²⁴ m^–3. It is shown that in Ag₂Se the Lorentz number L, determined experimentally from the electronic fraction of the thermal conductivity, is less than the Sommerfeld number L_o. Calculation of L/L_o(n) performed with a theory considering inelastic scattering of carriers, shows that the inelasticity is produced by electron interaction. Comparison of experimental data on the temperature dependence of lattice thermal conductivity with theory permits the conclusion that in Ag₂Se in range 80–300°K the basic role in phonon scattering is played by three-phonon Umklapp processes. It is shown that with increase in T and decrease in n the thermoelectric quality factor of silver selenide increases. The highest value of Z was achieved in a specimen with electron concentration n=2·10²⁴ m^–3 at T=320°K. The rapid decrease in Z upon phase transition is related to discontinuous decrease in and at this point.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 27–31, October, 1981.     

Crystal structure and Mössbauer spectroscopic study of FeSnF6·6H2O

Large single crystals of FeSnF₆·6H₂O were grown when aqueous hydrofluoric solutions of SnF₂ and FeF₂ were allowed to evaporate in air. Tin-119 Mössbauer spectroscopy at ambient temperature shows a single line at slightly negative isomer shift relative to CaSnO₃ at room temperature (=–0.380(6) mm/s, =0). This is characteristic of tetravalent tin octahedrally coordinated by fluorine. The X-ray crystal structure shows that tin(IV) is coordinated by 6 fluorine atoms, and Fe(II) by 6 water molecules. Both sites show a slight distortion from octahedral symmetry: the six distances are equal (Sn-Fe=1.941(3) Å and Fe-O=2.112(3) Å), whereas there are two values of angles (Fe-Sn-F=90.4(1)° and 89.6(1)°; O-Fe-O=91.1(1)° and 88.9(1)°). The material is an ionic compound [SnF₆]^2–[Fe(H₂O)₆]²⁺.     

Electroluminescence at p-n junctions in ZnSe

Electroluminescent radiation at p-n junctions and the photovoltaic effect in ZnSe monocrystals were investigated. The p-n junctions were prepared by melting dots of indium on p-type ZnSe (ZnSe contained Cu impurities).The measurements were made at room temperature and at –150°C. The acceptor level depths estimated from a maximum emission are in accordance with the data in the literature.The decay time of electroluminescence measured at –150°C is 2·1×10^–6 sec. In sunlight a photovoltage of about 1·1 V was observed.I wish to thank Prof. Dr A. Jablonski for his interest in this problem.     

Tantalum and cobalt suicides: Temperature sensor applications

Ion bombardment induced mixing of Ta-Si films has been studied using 400 keV argon ions. Doses varied from 7×10¹⁴ to 1×10¹⁷ Ar⁺ cm^–2 with post-bombardment anneals of 180–900 s at temperatures in the range 600–860 °C using radiant heating. Silicide uniformity and stoichiometry were determined using alpha backscattering spectrometry. Optimum fabrication parameters were determined with regard to subsequent material sheet resistivity, temperature coefficient of resistance and application as a temperature sensing material. Similar measurements were made on CoSi₂ layers prepared by annealing ion bombarded samples and comparison with silicide films arising from purely thermal annealing was made.CoSi₂ was found to be the more suitable material for temperature-sensor applications, showing a positive linear variation in sheet resistivity in the range 0–400 °C for samples which could be prepared simply and reproducibly.     

Amorphous to crystalline transition in Dy-Fe thin films

The crystallization of vacuum-deposited amorphous Dy-Fe thin films was studied by transmission electron microscopy and electron diffraction. The effect of thickness, deposition rate and substrate temperature on the crystallization process have been investigated. The results show that the crystallization thicknessd _c decreases with increasing deposition rate and substrate temperature. The number density of Dy-Fe islands were found to be almost constant at (4–5)×10¹¹ cm^–2 in the thickness range 20 Å<d <50 Å. The number density decreases with increase ind _c .     

Surface structures formed upon oxidation of the (311) face of copper

The oxidation of the copper (311) surface at temperatures from 25 to 900° C, and at oxygen pressures from 1 atm to 10⁻⁴ torr has been investigated by reflection high energy electron diffraction (RHEED). At room temperature, a poorly organized three-demensional epitaxial layer of Cu²O initially covers the surface, but it disappears when heated in vacuum to 200 °C. Between 300 and 600 °C, two symmetry-equivalent versions of a (4 × 1) two-dimensional surface structure form. Above 500 °C, this structure transforms into another having a hexagonal primitive cell with one axis coinciding with the Cu [011&#x0304;] direction and an axial length of 5.212 Å. This is the same cell which has been observed previously with oxidation of copper (100), (111), and (110) faces above 600 °C. Upon oxidation above 600 °C, the surface decomposes into (111) and (100) facets having the copper [010&#x0304;] direction in common.     

Surface morphology of sputter deposited low melting point metallic thin films

This paper describes the development of surface morphology of thin InSn(90/10), In, Sn and Cr films, deposited on unheated glass substrates by d.c. magnetron sputtering, with the film thickness. The experiments show that the surface morphology of metallic films with low melting pointsT _m[InSn(90/10)–150°C, In–156.6°C, Sn–231.8°C] and that with high melting pointT _m [Cr–1875°C] strongly differ. InSn(90/10) and Sn films with thickness greater than about 30 nm and also In films with even lower thickness of about 20 nm have a rough surface, milky color and matt appearance. On the contrary, Cr films of the same thickness have a smooth and shiny surface. It is due to a large difference in normalized temperaturesT/T _m for low-T _m films [Sn–0.59, In–0.70, InSn(90/10) –0.71] and for high-T _m films [Cr–0.14] deposited at low temperatures close to room temperature (RT). High values of the ratioT/T _m>0.5 clearly indicate that just the low melting point materials can crystallize at low temperatures close to RT. A crystallization of lowT _m films results in rough surface, milky color and matt appearance of these films.This work was supported in part by the Grant Agency of Czech Republic under Grant No. 202/93/0508.     

Influence of heat treatment on the structure and magnetic properties of the Co/Zr and Co/Hf multilayer amorphous films

The influence of annealing on the structure and magnetic properties of amorphous Co/Zr and Co/Hf multilayer films was studied with particular attention to the dependence of the magnetic properties, thermal stability and crystallization process on layer composition and thickness. The temperature at which crystallization commences increases from 400 to 460 °C as the layer thickness d_Zr or d_Hf increases from 6 to 18 Å, and decreases from 450 to 400 °C as d_Co increases from 12 to 18 Å. Multilayers containing 19–60 at% Zr were studied. The specific magnetization was found to increase even below the temperature at which crystallization commences. Our data are compared with non-multilayer Co–Zr amorphous films and rapidly quenched metallic glasses.     

Growth, coalescence, and electrical resistivity of thin Pt films grown by dc magnetron sputtering on SiO2

Ultra thin platinum films were grown by dc magnetron sputtering on thermally oxidized Si (1 0 0) substrates. The electrical resistance of the films was monitored in situ during growth. The coalescence thickness was determined for various growth temperatures and found to increase from 1.1 nm for films grown at room temperature to 3.3 nm for films grown at 400 °C. A continuous film was formed at a thickness of 2.9 nm at room temperature and 7.5 nm at 400 °C. The room temperature electrical resistivity decreases with increased growth temperature, while the in-plain grain size and the surface roughness, measured with a scanning tunneling microscope (STM), increase. Furthermore, the temperature dependence of the film electrical resistance was explored at various stages during growth.     

Temperature accelerated dielectric breakdown of PECVD low-k carbon doped silicon dioxide dielectric thin films

The dielectric breakdown strength of carbon doped silicon dioxide thin films with thickness d from 32 nm to 153 nm is determined at 25 °C, 50 °C, 100 °C, 150 °C and 200 °C, using I–V measurements with metal-insulator-semiconductor (MIS) structures. It is found that the dielectric breakdown strength, E_B, decreases with increasing temperature for a given film thickness. In addition, a film thickness dependence of breakdown is also observed, which is argued to show an inverse relation to thickness d in the form of E_B∝(d-d_c)^-n. The exponential parameter n and critical thickness limit d_c also exhibit temperature dependent behavior, suggesting a temperature accelerated electron trapping process. The activation energy for the temperature acceleration was shown to be thickness dependent, indicating a thickness dependent conduction mechanism. It is thereafter demonstrated that for relatively thick films (thickness >50 nm), the conduction mechanism is Schottky emission. For relatively thin films (thickness <50 nm), the Schottky conduction mechanism was obeyed at low field region while FN tunnelling was observed as a prevail one in the high field region. PACS 73.40.Qv     

Dielectric properties of SrZrO3 thin films prepared by pulsed laser deposition

SrZrO₃ (SZO) thin films have been prepared on Pt-coated silicon substrates and directly on Si substrates by pulsed laser deposition (PLD) using a ZrSrO target at a substrate temperature of 400 °C in 20 Pa oxygen ambient. X-ray –2 scans showed that the as-deposited films remain amorphous at a substrate temperature of 400 °C. The dielectric constant of SZO has been determined to be in the range 24–27 for the Pt/SZO/Pt structure. Capacitance–voltage (C–V) characteristics of a metal-oxide-semiconductor (MOS) structure for SZO films deposited in 20 Pa oxygen ambient and 20 Pa nitrogen ambient (SZON) indicated that incorporation of nitrogen during the substrate heating and film deposition can suppress the formation of an interfacial SiO₂ layer, and the SZON films have a lower equivalent oxide thickness (EOT) than that of the SZO films. However, the leakage current of the SZON films is larger than that of the SZO films. The EOT is about 1.2 nm for a 5-nm SZON film deposited at 400 °C. The leakage-current characteristics of as-deposited SZON films and SZON films post-annealed in oxygen ambient by rapid thermal annealing (RTA) have been studied comparatively. The films post-annealed with RTA have a lower leakage current than the as-deposited SZON films. Optical transmittance measurements showed that the band gap of the films is about 5.7 eV. It is proposed that SrZrO₃ films prepared at 400 °C are potential materials for alternative high-k gate-dielectric applications. PACS 77.84.Bw; 77.84.-s; 77.55.+f     

CEMS study of ultra-thin films of57Fe interfaced with nickel

Using conversion electron Mössbauer spectroscopy, we have studied the hyperfine field distributions of ultra-thin iron films interfaced on both sides with nickel. The configuration of the studied system was (Ni/⁵⁷Fe/Ni) _n =(20 nm/X nm/20 nm) _n , withn=3–7 andX=0.5–1.5 nm. The films were grown at room temperature in high vacuum on (111) buffer layers of nickel previously deposited on mica substrates at 300 °C. It has been found that the average hyperfine field is practically independent of the iron layer thickness, while this parameter strongly affects the distribution profiles and the orientation of iron atom spins.     

Temperature dependence of anisotropy in monocrystalline lithium ferrite films

A study of crystallographic and uniaxial anisotropy in monocrystalline Li-ferrite films in the temperature range 4.2–550°K is presented. The experimental results K₁(T) agree well with calculations based on the one ion model with crystalline field coefficients of a_A=–2.77 ·10^–2 cm^–1, a_B=3.34 · 10^–2 cm^–1. An experimental function K_u(T) is obtained which does not contradict the assumption that anisotropic stresses are responsible for the development of uniaxial anisotropy in Li-ferrite films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 113–116, August, 1973.