Direct chemical in-depth profile analysis and thickness quantification of nanometer multilayers using pulsed-rf-GD-TOFMS

Nanometer depth resolution is investigated using an innovative pulsed-radiofrequency glow discharge time-of-flight mass spectrometer (pulsed-rf-GD-TOFMS). A series of ultra-thin (in nanometers approximately) Al/Nb bilayers, deposited on Si wafers by dc-magnetron sputtering, is analyzed. An Al layer is first deposited on the Si substrate with controlled and different values of the layer thickness, t _Al. Samples with t _Al = 50, 20, 5, 2, and 1 nm have been prepared. Then, a Nb layer is deposited on top of the Al one, with a thickness t _Nb = 50 nm that is kept constant along the whole series. Qualitative depth profiles of those layered sandwich-type samples are determined using our pulsed-rf-GD-TOFMS set-up, which demonstrated to be able to detect and measure ultra-thin layers (even of 1 nm). Moreover, Gaussian fitting of the internal Al layer depth profile is used here to obtain a calibration curve, allowing thickness estimation of such nanometer layers. In addition, the useful yield (estimation of the number of detected ions per sputtered atom) of the employed pulsed-rf-GD-TOFMS system is evaluated for Al at the selected operating conditions, which are optimized for the in-depth profile analysis with high depth resolution.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

Precipitation polymerization of <Emphasis Type="Italic">N-tert</Emphasis>-butylacrylamide in water producing monodisperse polymer particles

The precipitation polymerizations of N-tert-butylacrylamide (NtBAM) in water are demonstrated; for example, the polymerization with potassium peroxodisulfate using a 15 g L⁻¹ (118 mmol L⁻¹) concentration of NtBAM in the feed ([NtBAM]₀) was performed at 70 °C for 12 h, quantitatively producing poly(N-tert-butylacrylamide) particles with a number-average diameter (d _n) of 203 nm and a coefficient of variation (C _v) of 4.7%. The particle sizes were controlled in the d _ns range between 75 and 494 nm by changing the monomer feeds or adding an electrolyte such as NaCl. The solid contents in the resulting aqueous latex solutions ranged from 0.1 to 1.5%, whereas it increased to 4.8% by applying a “shot-growth” technique. The polymerization in water under a somewhat unique condition is described, which was started from a heterogeneous system due to the presence of significantly large amounts of monomers ([NtBAM]₀ = 50 g L⁻¹). This also provided monodisperse latexes with the d _n of 370 nm in 96% yield, in which the solid content reached 4.9%.     

Determination of the Mg-Concentration Profile in Near-Surface Layers of Materials Using the 24Mg(α,p)27Al Nuclear Reaction

 The ²⁴Mg(α, p)²⁷ Al nuclear reaction was applied for the determination of the magnesium distribution in near-surface layers of materials. The cross sections of this reaction were determined in the energy region between 4.5 and 5.5 MeV in steps of 5 to 10 KeV (θ_lab : 158°) using thin magnesium films. The investigated projectile energy region included five main resonances allowing the determination of magnesium. The uncertainty of the cross-section determination was of the order of 7%. The applicability of the technique was tested using Mg-implanted AISI 321 steel samples. Depth resolution of 100 nm and detection limits of the order of 0.1 ppm were achieved for the determination of magnesium in steel samples using the 4805 keV resonance of the ²⁴Mg(α, p)²⁷ Al nuclear reaction. The shape and height of the magnesium depth-profile in the Mg-implanted steel samples were compared with corresponding values obtained by X-ray photoelectron spectroscopy. Received July 15, 1999. Revision March 30, 2000.     

Photocurrent and differential capacity measurements at polybithienyl and poly(3-butylthiophene) films

Photocurrent and differential capacity measurements have been carried out at polybithienyl (PBT) and poly(3-butylthiophene) (PBuT) films on platinum. The photocurrents are cathodic, similar to inorganic p-type semiconductors. The band gap energy was determined from the photocurrent spectra (E _g=1.7 eV for PBT and E _g=1.9 eV for PBuT). The dependence of the differential capacity on the potential could be presented as Mott-Schottky plot, at least in a limited potential region. The flatband potential was determined (E _fb= 0.67 V for PBT and E _fb=0.58 V for PBuT). Received: 9 June 1998 / Accepted: 22 August 1998     

Depth profiling of Irganox‐3114 nanoscale delta layers in a matrix of Irganox‐1010 using conventional Cs+ and O2+ ion beams

Depth profiling of an organic reference sample consisting of Irganox 3114 layers of 3 nm thickness at depths of 51.5, 104.5, 207.6 and 310.7 nm inside a 412 nm thick Irganox 1010 matrix evaporated on a Si substrate has been studied using the conventional Cs⁺ and O₂⁺ as sputter ion beams and Bi⁺ as the primary ion for analysis in a dual beam time‐of‐flight secondary ion mass spectrometer. The work is an extension of the Versailles Project on Advanced Materials and Standards project on depth profiling of organic multilayer materials. Cs⁺ ions were used at energies of 500 eV, 1.0 keV and 2.0 keV and the O₂⁺ ions were used at energies of 500 eV and 1.0 keV. All four Irganox 3114 layers were identified clearly in the depth profile using low mass secondary ions. The depth profile data were fitted to the empirical expression of Dowsett function and these fits are reported along with the full width at half maxima to represent the useful resolution for all the four delta layers detected. The data show that, of the conditions used in these experiments, an energy of 500 eV for both Cs⁺ beam and O₂⁺ beam provides the most useful depth profiles. The sputter yield volume per ion calculated from the slope of depth versus ion dose matches well with earlier reported data. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface transient effects in ultralow‐energy O2+ sputtering of silicon

It is known that by lowering the impact energy the sputter rate and surface transient width in SIMS will be reduced. However, few studies have been done at ultralow energies over a wide range of impact angles. This study examines the dependence of sputter rate and transient width as a function of O₂⁺ primary ion energy (E_p = 250 eV, 500 eV and 1 keV) and incidence angles of 0–70°. The instrument used is the Atomika 4500 SIMS depth profiler and the sample was Si with 10 delta‐layers of Si_0.7Ge_0.3. We observed that the lowest transient width of 0.7 nm is obtainable at normal and near‐normal incidence with E_p ～ 250 eV and E_p ～ 500 eV. There is no significant improvement in transient width going down in energy from E_p ～ 500 to ～250 eV. The onset of roughening is also not obvious at E_p ～ 250 eV over the whole angular range studied. Although the sputter rate during the surface transient is normally different from that at steady state, only at E_p ～ 250 eV was it observed that the sputter rate remained fairly independent of depth. We conclude that the best working ranges to achieve a narrow transient width and accurate depth calibration are at E_p ～ 250 eV/0° < θ < 20°and 500 eV/0°< θ < 10°. Copyright © 2005 John Wiley & Sons, Ltd.     

A UV-visible spectroelectrochemical study of the electropolymerisation of N-benzylaniline

The electropolymerisation of N-benzylaniline (NBA) at transparent ITO glass electrodes was investigated with in situ UV-visible spectroelectrochemistry. An intermediate was found to be generated during electrolysis as the precursor of poly(N-benzylaniline) (PNBA). The intermediate, which shows an absorbance band at λ = 460 nm, is able to react spontaneously with NBA, forming a polymeric end product, which is deposited on the electrode surface. UV-Vis spectra were obtained with PNBA-modified electrodes at various electrode potentials. It was shown that the colouration of the PNBA film after a positive-going potential step proceeds ca. 5 times slower than its discolouration after the reverse negative-going potential step. Anodic degradation of PNBA film was shown to proceed when holding the electrode at a sufficiently high positive potential. A linear dependence between the first-order degradation rate constant (k/s⁻¹) and electrode potential (E/V) was found in the potential range of E _RHE = +0.8 to +1.1 V: log k = a + bE, where a = −8.75 and b = 5.45 are empirical coefficients. In the whole spectral range investigated, the degradation of PNBA was found to proceed faster as compared to that of polyaniline (for polyaniline, coefficients a = −12.7 and b = 8.96 were obtained in the potential range of E _RHE = +0.85 to +1.1 V). The electrooxidation of hydroquinone, as well as the electroreduction of benzoquinone, were shown to proceed at PNBA-modified electrodes. In these processes, PNBA was shown to play the role of an electron mediator between the ITO electrode and solution phase redox species. Received: 8 January 1999 / Accepted: 27 January 1999     

Density functional study on zerovalent lanthanide bis(arene)-sandwich complexes

Several zerovalent lanthanide bis(arene)-sandwich complexes, Ln(η⁶-C₆H₆)₂, Ln = La, Ce, Eu, Gd and Lu, have been studied by means of density functional theory. The calculated geometries are in good agreement with experiment. The calculated dissociation energies of the bond Ln-(η⁶-C₆H₆) may be considerably underestimated, but they correctly reveal the variation regularity. The bonding in these molecules can be described in terms of a relatively weak π-electron donation from benzene to Ln and a stronger electron back-donation from Ln 5d to the benzene π* orbitals. During bond formation, there is electron promotion from Ln 6s to 5d instead of from 4f to 5d, in opposition to the proposal of Anderson et al. The relativistic effect only slightly influences the molecular geometry, but decreases the bonding energy considerably through lowering the Ln 6s level and raising the 5d level. It enhances the trend of the bonding energy to decrease along the lanthanide series. Received: 22 June 1998 / Accepted: 9 September 1998 / Published online: 17 December 1998     

On Water Structure in Concentrated Salt Solutions

In concentrated salt solutions the average distances between the ions, d ^av=1.1844⋅(∑ν _i c _i )^−1/3 nm, are commensurate with the sizes of the solvated ions, so that no ‘bulk solvent’ remains. This is illustrated with two saturated aqueous solutions, where 16.67 mol⋅dm⁻³ CsF at 75 °C has d ^av(Cs–F)=0.368 nm and 14.54 mol⋅dm⁻³ LiI at 80 °C has d ^av(Li–I)=0.385 nm. The minimal distance required for the bare ions (sum of their radii) are 0.303 nm for CsF and 0.289 nm for LiI. Hence no water molecule, diameter 0.276 nm, can be fitted between the ions to form linear or slightly bent hydrogen bonds. Some recent work ignoring such constraints, even in 3–6 mol⋅dm⁻³ solutions, is criticized on this account.     

The L Spectrum of Fe and Fe3O4

The intensities of the Fe L lines/bands l = L₃M₁, η = L₂M₁, α_1,2 = L₃M_4,5, β₁ = L₂M₄, and β_3,4 = L₁M_2,3 were measured for pure Fe and Fe₃O₄ using a TAP crystal as the dispersing element. The energy of the exciting electrons, E₀, was varied in the range 5 ≤ E₀ ≤ 25 keV. For pure Fe the following results were obtained. The net peak height ratio Ll/Lα remains relatively constant with varying E₀ at approximately 14%. The E₀ dependence of Lη is similar to that of Ll, although Lη is less intense than Ll by a factor of 7. Lβ₁/Lα decreases from 20% for E₀ = 5 keV to about 5% for 25 keV. Lβ_3,4 behaves like Lβ₁ but is weaker by a factor of 15. For Fe₃O₄ a much weaker intensity of Lα was observed which can be partially explained by its stronger absorption. Again, the E₀ dependence of Ll and Lη is similar with Ll/Lα = 19% and Lη/Lα = 4%. Lβ₁ and Lβ_3,4 show a comparable E₀ dependence. Lβ₁/Lα decreases from 50% for E₀ = 5 keV to 34% for 25 keV. Lβ_3,4 is weaker than Lβ₁ by a factor of about 25. The observed E₀ dependence of the different lines was used to estimate a set of mass absorption coefficients. Our value for Lα in Fe agrees well with other data which were deduced from variable E₀ measurements but differs considerably from data given by Heinrich and Henke.     

Analysis of photocurrent spectra at polybithienyl film coated on Pt

Photoelectrochemical measurements have been performed at a polybithienyl (PBT) film (doping level of 1 × 10¹⁸/cm³) deposited on a platinum electrode. The cathodic photocurrents and negative slope of the Mott-Schottky plot indicate that the PBT film has the features of a p-type semiconductor. The cathodic photocurrents are interpreted in terms of the Gaertner-Butler model on the basis of the theory of the semiconductor|solution interface. The (i _ph hν)^2/n vs. hν plots taken from the photocurrent spectra show two linearities for n=1 in the wavelength range from 460 nm to 490 nm and for n=4 in the wavelength range λ > 490 nm. The band gaps of the PBT film were determined to be 2.05 ± 0.05 eV for n=1 and 1.55 ± 0.05 eV for n=4. The flat-band potential is 0.33 V (vs SCE). From the slope of the Mott-Schottky plot at the modulation frequency of 3 kHz, the dielectric constant ɛ of the film and the thickness of the depletion layer W ₀ of the PBT film were determined to be 7.4 and 0.29 μm, respectively. Received: 6 January 1999 / Accepted: 6 June 1999     

Polygermanosilyne Calcium Hydroxide Intercalation Compounds Formed by Topotactic Transformation of Ca(Si 1 − x Ge x )2 Alloy Zintl Phases in Ambient Atmosphere

Summary.   Epitaxial thin films of Ca(Si _1 − x Ge _x )₂ with 0 < x ≤ 1 are found to react with the moisture of ambient atmosphere to form new Ca-Si-Ge-O-H compounds which were studied by X-ray diffraction, energy dispersive X-ray analysis, infrared absorption, and thermally induced hydrogen desorption measurements. Pure CaGe₂ forms the polygermyne calcium hydroxide intercalation compound Ca(OH)₂(GeH)₂ upon exposure to humidity, with a trigonal tr6 crystal lattice with a = 4.00(1) and c = 65.3(1)?. In mixed Ca(Si _1 − x Ge _x )₂ with smaller Ge content, the group-14 layers are subject to intense oxidation leading to decreased crystallinity. The products exhibit characteristic colours and intense photoluminescence, the peak luminescence varying from 1.35 eV for the reaction product of Ca(Si_0.3Ge_0.7)₂ to 2.6 eV for that of Ca(Si_0.5Ge_0.5)₂. Received March 12, 2001. Accepted (revised) May 2, 2001     

High-resolution photofragment translational spectroscopy for the UV photodissociation of C<Subscript>2</Subscript>H<Subscript>5</Subscript>I

The photodissociation of ethyl iodide at 279.71, 281.73, 304.02 and 304.67 nm has been studied on our new mini-photofragment translational spectrometer with a total flight path of only 5 cm. Some vibrational peaks are firstly resolved in the TOF spectra of I*(2P1/2) and I(2P3/2) channels. These vibrational peaks are assigned to the excitation states (v2 = 0, 1, 2,…) of the umbrella mode (v2, 540 cm-1) of the photofragment C2H5, and the distribution of the vibrational states is obtained. The dissociation energy has been determined to be D0(C-I)=2.314 ±0.03 eV. The energy partitioning of the available energy (Eavl=ET Eint=ET EV,R) calculated from our experimental data (-E)int/Eavl= 22.1% at 281.73 nm, 22.4% at 304.02 nm for the I* channel, and (-E)int/Eavl = 25.2% at 279.71 nm, 25.9% at 304.67 nm for the I channel, seem to be more reliable.     

The equivalence of bond-energy schemes and the determination of resonance energies

 It is argued that the preservation of algebraic equivalence between the Allen and Laidler bond-energy schemes for nonconjugated alkenes logically determines that the Allen scheme should apply to a classical structure of a conjugated hydrocarbon exactly as it stands, i.e. no additional parameters are needed. Extending the requirement of equivalence to conjugated alkenes implies that, in the Laidler scheme, the bond energy of the pure single CC bond in a conjugated system is a combination of the bond-energies of the semiconjugated and normal CC single bonds: E(C_d—C_d)=2E(C_d—C)−E(C—C). This result is a deduction and is not an independent hypothesis. The equivalence of the two schemes for conjugated hydrocarbons is demonstrated numerically, by calculating the resonance energies of some selected molecules by both methods. Received: 5 December 1999 / Accepted: 5 March 2000 / Published online: 5 June 2000     

EPMA and Quantitative MCs+-SIMS of Metal-DLC Coating Materials

 Compositional characterization of metal-DLC (metal-containing diamond-like carbon) hard coatings is carried out by (WDS)-EPMA and MCs⁺-SIMS. EPMA enables accurate (± 5% relative) quantitative analysis including minor concentrations (0.1–10 at%) of N, O and Ar. Under conditions of “near-surface” EPMA (E₀ < 10 keV) the influence of surface oxide films on “pure” metal standards may be a limiting factor in respect of accuracy. Depth profiling of sufficiently “thick” layered structures (film thickness ≥ 2 μm) is carried out by EPMA-line scans along mechanically prepared bevels. The depth resolution is about 0.2 μm. SIMS in the MCs⁺-mode enables high resolution (< 20 nm) depth profiling of metal-DLC layered structures including the determination of H (1–20 at%). MCs⁺-SIMS, i.e. employing Cs⁺ primary ions and monitoring MCs⁺ molecular secondary ions (M is the element of interest) is presented as a promising route towards sufficiently accurate (10–20%) SIMS-quantification. Matrix-independent relative sensitivity factors for MCs⁺-SIMS are derived from homogeneous coating materials defined by EPMA. EPMA proves to be also useful to detect problems related to SIMS of Ar in metal-DLC materials. The combination EPMA-SIMS is demonstrated as an effective analytical strategy for quality control in industrial production and to support the development of metal DLC layered structures with optimum tribological properties.     

A rapid and universal bacteria-counting approach using CdSe/ZnS/SiO2 composite nanoparticles as fluorescence probe

In this paper, a rapid, simple, and sensitive method was described for detection of the total bacterial count using SiO₂-coated CdSe/ZnS quantum dots (QDs) as a fluorescence marker that covalently coupled with bacteria using glutaraldehyde as the crosslinker. Highly luminescent CdSe/ZnS were prepared by applying cadmium oxide and zinc stearate as precursors instead of pyrophoric organometallic precursors. A reverse-microemulsion technique was used to synthesize CdSe/ZnS/SiO₂ composite nanoparticles with a SiO₂ surface coating. Our results showed that CdSe/ZnS/SiO₂ composite nanoparticles prepared with this method possessed highly luminescent, biologically functional, and monodispersive characteristics, and could successfully be covalently conjugated with the bacteria. As a demonstration, it was found that the method had higher sensitivity and could count bacteria in 3 × 10² CFU/mL, lower than the conventional plate counting and organic dye-based method. A linear relationship of the fluorescence peak intensity (Y) and the total bacterial count (X) was established in the range of 3 × 10²–10⁷ CFU/mL using the equation Y = 374.82X − 938.27 (R = 0.99574). The results of the determination for the total count of bacteria in seven real samples were identical with the conventional plate count method, and the standard deviation was satisfactory.     

Spectrophotometric Investigation of the Complexing Reaction between Rutin and Titanyloxalate Anion in 50% Ethanol

Summary.  In the present work, rutin (3,3′ ,4′ ,5,7-pentahydrohyflavone-3-rhamnoglucoside) was determinated via a complexing reaction with a titanyloxalate anion. K₂[TiO(C₂O₄)₂] and rutin react in 50% ethanol forming a 1:2 complex in a pH range from 4.00 to 11.50, in which the TiO(C₂O₄)₂ ²⁻ ion is linked to rutin through the 4-carbonyl and 5-hydroxyl group. The thermodynamic stability constant log β₂ ⁰ of the complex is determined to 10.80 at pH = 6.50. The change of the standard Gibbs free energy Δ G⁰ amounts to −61 kJċ mol⁻¹, indicating that the process of complex formation is spontaneous. The optimal conditions for the spectrophotometric determination of microconcentrations of rutin are at pH=6.40 and λ= 430 nm, where the complex shows an absorption maximum with a molar absorption coefficient a ₄₃₀=(60±2)ċ10³ dm³ċ mol⁻¹ċ cm⁻¹. The method is applied rutin determination from tablets. Received January 4, 2000. Accepted (revised) February 17, 2000     

Spectrophotometric Investigation of the Complexing Reaction between Rutin and Titanyloxalate Anion in 50% Ethanol

 In the present work, rutin (3,3′ ,4′ ,5,7-pentahydrohyflavone-3-rhamnoglucoside) was determinated via a complexing reaction with a titanyloxalate anion. K₂[TiO(C₂O₄)₂] and rutin react in 50% ethanol forming a 1:2 complex in a pH range from 4.00 to 11.50, in which the TiO(C₂O₄)₂ ²⁻ ion is linked to rutin through the 4-carbonyl and 5-hydroxyl group. The thermodynamic stability constant log β₂ ⁰ of the complex is determined to 10.80 at pH = 6.50. The change of the standard Gibbs free energy Δ G⁰ amounts to −61 kJċ mol⁻¹, indicating that the process of complex formation is spontaneous. The optimal conditions for the spectrophotometric determination of microconcentrations of rutin are at pH=6.40 and λ= 430 nm, where the complex shows an absorption maximum with a molar absorption coefficient a ₄₃₀=(60±2)ċ10³ dm³ċ mol⁻¹ċ cm⁻¹. The method is applied rutin determination from tablets.