On the role of ion bombardment parameters in AES sputter depth profiling of Ta2O5/Ta with Ar+ and Xe+

Summary In order to study the influence of the ion bombardment parameters on the achievable depth resolution of AES sputter depth profiles, 500 Å thick Ta₂O₅-layers produced by anodic oxidation of polished polycrystalline Ta-substrates were sputter depth profiled with Ar⁺- and Xe⁺-ions in a Scanning Auger Microprobe. The 90%–10% interface widthsz were measured for bombarding ion energies from 0.5 to 5 keV and angles of incidence of 15°, 33° and 56°, respectively.z reduces from 48 Å for Ar⁺-bombardment at = 15° andE = 5 keV to 20 Å when bombarding at = 56° andE = 1 keV. The corresponding values for Xe⁺-bombardment are 31 Å and 18 Å. The influence of the ion bombarding energy and angle on the interface broadening is discussed by means of a simple model. From corresponding evaluations the maximum transportation length of layer species into the substrate is found to be proportional toE ^0.5.

---

Zum Einfluß der Ionenbeschußparameter auf die Tiefenauflösung bei der AES-Sputtertiefenprofil-analyse von Ta₂O₅/Ta mit Ar⁺ und Xe⁺

     

Synthetic diamond electrodes: Photoelectrochemical behavior of vacuum-annealed undoped polycrystalline diamond films

The photocurrent and photopotential for undoped polycrystalline diamond film electrodes prepared by chemical vapor deposition and annealed in vacuum at 1500–1640°C are measured. The metal-like samples (annealed at 1630°C) have a negligible photosensitivity. Judging from the positive sign of the photopotential and the cathodic direction of the photocurrent, the material under study formally behaves as a p-type semiconductor. The photoeffects are presumably caused by structure defects, in particular, the dislocations in diamond crystallites formed close to intercrystalline boundaries during the high-temperature annealing.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 343–349.Original Russian Text Copyright © 2005 by Pleskov, Krotova, Ralchenko, Khomich, Khmelnitskii.     

Investigation of gettering effects in CZ-type silicon with SIMS

Ion implantation is a well-known standard procedure in electronic device technology for precise and controlled introduction of dopants into silicon. However, damage caused by implantation acts as effective gettering zones, collecting unwanted metal impurities. This effect can be applied for proximity gettering reducing the concentration of impurities in the active device region. In this study the consequences of high-energy ion implantation into silicon and of subsequent annealing were analysed by means of secondary ion mass spectrometry (SIMS). Depth profiles were recorded of such impurities as copper, oxygen and carbon to obtain information about their gettering behaviour. The differences in impurities gettering behaviour were studied as a function of the implanted ions, P and Si, of the implantation dose and annealing time at T=900°C. Besides impurities gettering at the mean projected range (Rp) of implanted ions, Rp-effect, defects at around half of the projected ion range, Rp/2-effect, and even in some cases beyond Rp, trans-Rp-effect, have also been found to be effective in gettering of material impurities.     

Comparison of the annealing behavior of thin Ta films deposited onto Si and SiO<Subscript>2</Subscript> substrates

Structural changes at annealing temperatures (T_an) of 500–1,100°C were investigated for thin Ta films which were sputter-deposited onto pure Si substrates and onto thermally oxidized Si. In the as-deposited state, the Ta layers predominantly consist of metastable tetragonal -Ta, whereby the [001] texture is independent of the substrate material. At lower annealing temperatures, the microstructural evolution is essentially the same for both Ta films. Incorporation of O atoms causes an increase of the intrinsic compressive stress, and diffusion of C atoms into the Ta layer leads to the formation of Ta₂C. Additionally, a partial transformation of the original -Ta phase into a second phase with tetragonal unit cell (denoted as -Ta) occurs. For the Ta/Si system, the formation of a Ta–Si intermixing layer is initiated at T_an=550°C, and nucleation of crystalline TaSi₂ occurs at T_an=620°C. The formation of a second Ta silicide was not detected up to T_an=900°C. In the case of the Ta film deposited onto the SiO₂ substrate, the metastable -Ta and the -Ta transform completely into the thermodynamically stable cubic -Ta at T_an=750°C. A marked reaction with the substrate indicated by the formation of Ta₂O₅ and Ta₅Si₃ occurs at T_an=1,000°C.     

Nitrogen depth distribution, interface and structure analysis of SiNx layers produced by low-energy ion implantation

Thin silicon nitride (SiN _x ) layers with the stoichiometric N/Si ratio of 1.33 in the maximum of the concentration depth distributions of nitrogen were produced by implanting 10 keV¹⁵N ₂ ⁺ in 100 silicon at room temperature under high vacuum conditions. The depth distribution of the implanted isotope was measured by resonance nuclear reaction analysis (NRA), whereas the layer structure of the implanted region and the geometrical thickness of the layers were characterised by high resolution transmission electron microscopy (TEM). SiN _x layers with a thickness of about 30 nm were determined by NRA. Channeling Rutherford backscattering spectrometry was used to determine the disorder in the silicon substrate. Sharp interfaces of a few nanometers between the highly disordered implanted region and the crystalline structure of the substrate thickness were observed by TEM. The high thermal stability of SiN _x layers with N/Si ratios from under to over stoichiometric could be shown by electron beam rapid thermal annealing (1100 °C for 15 s, ramping up and down 5 °C/s) and NRA.     

Characterization of iron-silicon thin films by means of electron diffraction and X-ray spectroscopy

Iron-silicon thin films have been characterized by means of analytical transmission electron microscopic methods. Under certain conditions — composition and annealing temperature — these films exhibit thermoelectric behavior. In particular, the morphology and phase formation which results from annealing of these films, and doping with oxygen and nitrogen, are of interest. The thermoelectric phase -FeSi₂ is formed at temperatures above 500°C. This phase is transformed into electrically conducting phases at about 1000°C. A small oxygen content does not influence this crystallization process. If the oxygen content is higher than 15 atom-% the electrically conducting phases exist even at 500°C. The presence of a small nitrogen content inhibits the formation of the -FeSi₂ phase. The development of silicon and iron nitrides is possible.     

Investigation of implanted gallium depth distributions in ZnSxSe-x by EPMA

In the present work EPMA combined with Monte Carlo simulation was applied to investigate implanted gallium depth distributions in ZnS_xSe_1–x layers. The layers of about 1 to 4 m thickness were grown by MOVPE on (100)-GaAs substrate. The overlap of the Ga and zinc L X-ray spectra and the low gallium net count rates were overcome by stripping the spectra of non implanted layers and by applying appropriate beam currents and counting times. Capabilities and limitations of the EPMA technique as applied to depth profile analysis are demonstrated.Despite the mentioned L interference, the detectability limit of EPMA for 340 keV Ga in ZnS_xSe_1–x is as low as 10¹⁴ cm^–2. The measured Ga L intensity versus beam energy curves reveal variations of the Ga depth profiles during annealing. Evaluation of the intensity curves by means of Monte Carlo simulations yields the implanted dose densities and the first two moments of the depth distributions, i.e. the projected range and its standard deviation. The nonannealed profiles agree well with expectations, but after thermal annealing the profiles were significantly shifted towards the surface. Comparison of EPMA and SIMS results with the example of a non annealed profile in ZnSe has shown good agreement.     

Preparation and Optical Characterization of Sol-Gel Deposited Pb(Zr0.45Ti0.55)O3 Films

Homogeneous crack-free lead zirconate titanate (Pb(Zr_0.45Ti_0.55)O₃: PZT 45/55) films were prepared by a chemically modified sol-gel process using lead acetate trihydrate, zirconium n-propoxide, and titanium isopropoxide precursors. The coating solutions were modified by the addition of diethanolamine. Single and multilayer films were deposited with a 2000 rpm spin rate on fused silica and MgO(100) substrates. Multiple spin coating with an intermediate heat treatment in air at 400°C for 3 min between coatings was performed to obtain films up to 2 m in thickness. The formation of the tetragonal perovskite structure was found to depend on the intermediate firing temperature, final annealing temperature, and annealing time. A 650°C rapid thermal annealing treatment in oxygen was required to crystallize the PZT film into the perovskite structure. The films were characterized using optical spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermo-gravimetry and differential scanning calorimetry (TG-DSC). The optical constants of the PZT films were evaluated from spectral transmittance and reflectance measurements. Optical constants are presented over the visible and near infrared region.     

Growth of the Bismuth Titanate Films on Textured Oxide Electrode by the Spin Coating-Pyrolysis

Bismuth titanate films were fabricated onto highly oriented LaNiO₃ electrode grown on SrTiO₃(100) and LaAlO₃(012) substrates using spin-coating technique with metal naphthenates as starting materials. (00l)/(h00)-oriented bismuth titanate films on LaNiO₃/SrTiO₃ and LaNiO₃/LaAlO₃ were obtained by pyrolysis at 500°C, followed by annealing at 750°C. In-plane alignment and surface morphology of the films analyzed by pole-figure analysis ( scanning) and field emission scanning electron microscope showed an imperfect epitaxy with polycrystalline structure.An erratum to this article can be found at     

Oxygen diffusion in SrCe<Subscript>0.95</Subscript>Yb<Subscript>0.05</Subscript>O<Subscript>3−δ</Subscript>

¹⁸O/¹⁶O isotope exchange depth profiling (IEDP) combined with secondary ion mass spectrometry (SIMS) has been used to measure the oxygen tracer diffusivity of SrCe_0.95Yb_0.05O_3– between 800 °C and 500 °C at a nominal pressure of 200 mbar. The values of D* (oxygen tracer diffusion coefficient) and k (surface exchange coefficient) increase steadily with increasing temperature, and the activation energies are 1.13 eV and 0.96 eV, respectively. Oxygen ion conductivities have been calculated using the Nernst–Einstein equation. The transport number for oxide ions at 769 °C, the highest temperature studied, is only ~0.05. Moreover, SrCe_0.95Yb_0.05O_3– has been studied using impedance spectroscopy under dry O₂, wet O₂ and wet H₂ (N₂/10% H₂) atmospheres, over the range 850–300 °C. Above ~550 °C, SrCe_0.95Yb_0.05O_3– shows higher conductivity in dry O₂ than in wet O₂ or wet H₂; below that temperature the results obtained for the three atmospheres are comparable. Dry O₂ shows the highest activation energy (0.77 eV); the activation energies for wet O₂ and wet H₂ are identical (0.62 eV).Abbreviations HTPC high-temperature proton conductor - IEDP isotope exchange depth profiling - SIMS secondary ion mass spectrometryPresented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Selective solvation of copper(I) thiocyanate in acetonitrile-water mixtures at 30°C

The selective solvation of copper(I) thiocyanate has been studied in water-acetonitrile (AN) mixtures at 30°C by solubility and EMF measurements. The solubility of the salt increases continuously and changes only slightly beyond X _AN =0.7 mole fraction. The Gibbs energy of transfer of copper(I) ion from water to mixtures with acetonitrile (determined on the basis of the ferrocene reference method) decreases continuously, while that of the thiocyanate ion increases with the addition of acetonitrile. The solvent transport number of acetonitrile passes through a maximum (=6.4) at X _AN =0.25. These results were interpreted as arising due to a heteroselective solvation of the salt, the copper(I) ion being preferentially solvated by acetonitrile and the thiocyanate ion by water in these mixtures.     

Oxygen Transport in the SOFC Cathode

The impedance of the La_0.75Sr_0.2MnO₃-cathode/electrolyte interface for cathodes with different porosity is measured. The impedance spectra are fitted using a developed model of the oxygen transport at this interface. After the measurements, the cathode is removed from the electrolyte. The contact area and the three-phase boundary length (TPBL) at the interface are estimated from SEM images of the electrolyte surface. The dependence of the interfacial electrical resistance on the microstructure is discussed. It is shown that the bulk diffusion of oxygen vacancies at the interface at 950°C is high enough to use the whole La_0.75Sr_0.2MnO₃/YSZ contact area F for the oxygen transport into the electrolyte for microstructures with 2F/TPBL 2 m. The impact of the surface diffusion of oxygen species on polarization resistance at operation temperatures <900°C is discussed. The polarization resistance and the morphology of composite cathodes made from La_0.75Sr_0.2MnO₃/YSZ and yttria- or scandia-stabilized zirconia powders (3YSZ, 8YSZ, 10ScSZ) are investigated by impedance spectroscopy at 800–950°C. The polarization (interfacial) resistance decreases gradually with addition of electrolyte powder in the uLSM cathode material independent of the electrolyte powder used. The interfacial resistance of the uLSM/3YSZ, uLSM/8YSZ, and uLSM/10ScSZ composite cathodes is almost the same. The interaction between uLSM and doped zirconia particles is discussed on the basis of the interfacial resistance, activation energies, and high-frequency impedance.     

Synthesis of new dinuclear dicopper(II) and dinickel(II) complexes. The kinetics of catechol oxidase and electrochemistry of a dicopper(II) complex

A new dinuclear ligand L, ethylene[OO-bis-salicylidene--diketone] bearing two symmetrical coordination sites was synthesized by the condensation of salicylaldehyde and acetylacetone, L, with 1,2-dibromoethane under reflux. The ligand L in a 1:1 ratio was treated with CuCl₂ and NiCl₂ to yield the complexes, tetrachloro bis[OO-bis- salicylidene--diketone copper(II)] and bis[OO-bis-salicylidene--diketone nickel(II)] chloride. The complexes were subsequently characterized by spectroscopic techniques, elemental analysis, i.r., ¹H-n.m.r., ¹³C-n.m.r., u.v.–vis., e.p.r. spectroscopy, and conductance measurements. The conductance measurements in DMF reveal that the Cu^II complex is covalent while the Ni^II complex is ionic and the spectral data support the Cu^II complex to be distorted octahedral whereas the Ni^II complex has square-planar geometry. The dioxygen binding was studied spectrophotometrically by the oxidation of tetrachloro bis[OO-bis-salicylidene--diketone copper(II)] with pyrocatechol in the presence of oxygen. The kinetic experiments were performed with the copper complex in DMF by monitoring the increase in absorbance over time at pH 8.0 in the presence of pyrocatechol at 25 °C. The kinetic parameters V_max and K_M were determined on the Michaelis–Menten Approach. Redox behavior of the dinuclear copper(II) complex was investigated by cyclic voltammetry in the presence of O₂ with the pyrocatechol (substrate) and also without the substrate. The large difference in potentials E⁰ is indicative of reversible oxygen binding of the complex and distinct catalytic activity.     

Diffusion kinetics for methanol in polycrystalline ice

Quantitative analyses of the isothermal desorption kinetics from methanol-doped H2O films on Pt(111) reveal that transport kinetics for CH3OH in polycrystalline ice are much slower than previously reported. They also indicate that MeOH displays first-order desorption kinetics with respect to its instantaneous surface concentration below 0.1 mole fraction in ice. These observations allow isothermal desorption rate measurements to be interpreted in terms of a depth profiling analysis providing one-dimensional concentration depth profiles from methanol-doped polycrystalline ice films. Using a straightforward approach to inhibit ice sublimation, transport properties are extracted from the evolution of concentration depth profiles obtained after thermal annealing of binary ice films at high temperature. Heterodiffusion coefficients for methanol in polycrystalline (cubic) ice Ic films are reported for temperatures between 145 and 195 K and for concentrations below 10(-3) mole fraction. Finally, diffusion kinetics for methanol in ice are shown to display a very strong concentration dependence that may contribute, in addition to variations in laboratory samples microstructure, to the disagreements reported in the literature regarding the transport properties of ice.     

Crystal and Molecular Structure of Cu(II) Bis-(2-methoxy-2,6-dimethyl-3-imino-5-heptanonate)

A new compound from the series of alkoxyketoiminates, Cu(II) bis-(2-methoxy-2,6-dimethyl-3-imino-5-heptanonate), has been synthesized and studied by X-ray crystallography. Crystal data for CuO₄N₂C₂₀H₃₆: a=10.154(1), b=9.921(1), c=11.684(2) , =96.17(1)°, space group P2₁/c, Z=2, dcalc =1.226 g/cm³, R=0.037. The structure is molecular and built from isolated trans-complexes. The copper atom has a plane square environment of two oxygen atoms (Cu–O 1.93 ) and two nitrogen atoms (Cu–N 1.90 ). The O–Cu–N chelate angle is 91.7°. The complex has an intramolecular hydrogen bond, N–H...O 2.16 , involving the alkoxy oxygen atom. The molecular packing in the crystal is close to that of copper(II) dipivaloylmethanate. The calculated van der Waals intermolecular interaction energies and thermogravimetric characteristics of the complexes are compared.     

Verfeinerung der Kristallstruktur von Kupfer(II)-hydroxichlorid,Cu(OH)Cl

The crystal structure of Cu(OH)Cl [a=5.555 (2) Å,b=6.671 (4) Å,c=6.127 (2) Å, =114.88 (3)°, space group P2_I/a,Z=4] was refined for 810 observed reflections with sin /0.80 Å^–1 toR=0.035. Crystals were synthesized under hydrothermal conditions. The copper atom is planar four coordinated by three oxygen atoms and one chlorine atom; two further chlorine atoms complete its coordination. The copper polyhedra share edges to build up sheets, which are connected by hydrogen bonds to the chlorine atoms of adjacent sheets.

     

Surface cosegregation on Fe-3%V-C, Fe-3%V-C,N and Fe-15%Cr-N (110) single crystals

Surface cosegregation has been studied on (110) oriented Fe-3%V-C, Fe-3%V-C,N and Fe-15%Cr-N single crystals applying AES and LEED. The surface compounds VC,V(C,N) and CrN are formed upon annealing in the temperature range from 450 to 750° C depending on the alloy. The stoichiometries of the binary surface compounds correspond to VC_1.2 and approximately CrN_0.8 as determined by quantitative evaluation of Auger peak height ratios. The composition of the V(C,N) surface compound varies between V(C_0.6N_0.6) at 450° C and V(C_0.2N_1.0) at 640° C. Three-dimensional precipitates are not formed as indicated by Ar⁺ depth profiling. After short annealing times streaking LEED patterns are observed indicating partial disorder in one direction of the direct space. Upon sufficient annihilation of surface defects sharp (4 × 1) patterns appear. A missing and added row model is proposed for the surface compounds on bcc(110) substrate surfaces.     

Synthesis and characterization of dithienobenzothiadiazole-based donor–acceptor conjugated polymers for organic solar cell applications

New donor–acceptor conjugated polymers (P1 and P2) containing a fused-ring dithienobenzothiadiazole (DT-BTD building block) were synthesized by using the Stille copolymerization method. The synthesized polymers were characterized by ¹H NMR, GPC, and elemental analysis. The optical band gaps of the polymers were found to be 1.86 and 1.9 eV, respectively, as calculated from their film onset absorption edge. Upon annealing both produced a distinct shoulder peak in their film absorption spectra. The electrochemical studies of P1 and P2 revealed that the HOMO and LUMO energy levels of the polymer were −5.3, −5.1 eV, and −3.4, −3.2 eV, respectively. The polymers are thermally stable up to 250–350 °C.     

Photoluminescence as a Function of Aggregated Size from n-Butyl-Terminated Silicon Nanoclusters

Photoluminescence (PL) from alkyl-terminated silicon nanocrystallites as a function of size has been studied. Ultraviolet–blue luminescence (390–410 nm) is observed from as-prepared silicon nanoclusters with diameters from 3 to 8 nm. After 1 h of annealing at 162°C in 2-methoxyethyl ether (diglyme), the _max of PL shifts from 360 to 420 nm. High-resolution transmission electron microscopy (HRTEM) images show that individual silicon nanoparticles are fused to form pairs of nanoparticles. FTIR spectra show that the alkyl groups remain on the surface of silicon nanoparticles. As the temperature is raised to 250°C for 1 h, the PL no longer shows any peak in the visible light region. TEM images show that the silicon nanoparticles are aggregated and fused uniformly in one single dimension, to form a strip, and these strips parallel each other. When the temperature is raised to 350°C these silicon nanoparticles form a large piece of silicon textile network, showing that functionalized alkyl surface does not persist above this temperature. A strong Si–O–Si asymmetric stretching vibration appears between 1000 and 1100 cm^–1 at the expense of the C–H vibrational modes and there is no more change after 3 h of annealing at 250 or 350°C. These results provide strong evidence that the PL originates from quantum confinement.