Investigation of native-oxide growth on HF-treated Si(111) surfaces by measuring the surface-state distribution

The evaluation of the surface state distribution of differently HF-treated Si(111) surfaces during the native-oxide growth in air is investigated by the large-signal field-modulated photovoltage technique. The surface state distribution consisting of intrinsic and extrinsic Si dangling bond defects is directly related to the state of oxidation of the Si surface. It is shown that the kind of HF treatment strongly influences the concentration of extrinsic defects with a lower state of oxidation. Special HF preparations for H termination of the Si(111) surface result in a nearly intrinsic surface state distribution. During the oxidation process three typical phases can be distinguished each characterized by specific defect structures. It was found that native-oxide growth is highly sensitive to the concentration of extrinsic defects directly after HF treatment.     

Molecule formation in electrothermal atomizers: Interferences and analytical possibilities by absorption, emission and fluorescence processes

Summary The formation of stable diatomic molecules in graphite tube furnaces is described. It is also shown that the new isothermal evaporation techniques in AAS do not lead to complete dissociation of molecules with dissociation energies > 3–4 eV. Systematic errors of AA results follow.Systematic studies of the application of diatomic molecules (MX-type) for trace analysis of non-metals (X) were carried out. Many results are given for molecular absorption with electrothermal evaporation (MAS-ETE). Trace determinations in ng level (l samples) for F, Cl, Br, S and I and their anions are possible. Examples for real analysis are given.Principles of over-excitation for improvement of detection limits of non-metals are applied to diatomic molecules.The application of the non-thermal FANES excitation leads to the development of the new method MONES-ETE (molecular non-thermal emission spectrometry with electrothermal evaporation) with detection limits below 1 ng for F, Cl, Br using InX molecules.The application of the principle of laser excited fluorescence leads to the new method LAMOFS-ETE (laser excited molecular fluorescence with electrothermal evaporation) with the upto now best detection limits for F, Cl, Br at pg level using AlBr, InCl, MgF molecules.

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Molekülbildung in elektrothermischen Atomisatoren: Störungen und analytische Möglichkeiten durch Absorptions-, Emissions- und Fluorescenzprozesse

Zusammenfassung Es wird die Bildung von stabilen, vorwiegend 2-atomigen Molekülen in Graphitrohrküvetten beschrieben. Es wird festgestellt, daß auch die modernen isothermen Verdampfungstechniken bei Molekülen mit Dissoziationsenergien > 3–4 eV nicht zur vollständigen Dissoziation führen. Systematische Fehler von AA-Resultaten sind die Folge.Systematische Untersuchungen zur Anwendung 2-atomiger Moleküle vom MX-Typ (z. B. AlF) für die Spurenanalyse von Nichtmetallen (X) werden beschrieben. Umfangreiche Ergebnisse werden zur Molekülabsorption mit elektrothermischer Verdampfung (MAS-ETV) angeführt. Spurenbestimmungen im Nanogramm-Bereich (Mikroliter-Proben) sind möglich für F, Cl, Br, S und I bzw. deren Anionen.Prinzipien der Überanregung werden zur Verbesserung der Nachweisgrenzen von Nichtmetallen auf 2-atomige Moleküle angewendet. Die Anwendung der nichtthermischen FANES-Anregung führt zur Entwicklung der neuen Methode MONES-ETV (Molekül-nichtthermische Emissionsspektroskopie mit elektrothermischer Verdampfung) mit Nachweisgrenzen unterhalb des Nanogramm-Bereichs für F, Cl und Br durch InX-Moleküle. Die Anwendung des Prinzips der laserangeregten Atomfluorescenz führt zur neuen Methode LAMOFS-ETV (laserangeregte Molekülfluorescenzspektrometrie mit elektrothermischer Verdampfung) mit den bisher besten Nachweisgrenzen von einigen Picogramm für F, Cl, Br durch Anwendung der AlBr, InCl und MgF-Moleküle.

     

Simultaneous determination of traces in solid samples with laser-AAS

Microamounts of solid samples are vaporized by focused laser radiation (Q-switch ruby). The solid aerosol is transported in an Ar gas stream to a hot graphite tube. The determination of trace metals is made by flameless AAS.A dual channel AA spectrometer is used for the investigation of the reproducibility of the absorbance values in indirect laser AAS. The simultaneous determination of Ag-Mn an Pb-Ag in copper standard metals and in pellets of organic powders show that the inhomogeneity of the materials and differences in the material vaporization by the laser light influence the analytical results.The results of the simultaneous determination of Ag, Al, Mn, Ni. and Pb in different solid samples are compared mutually and with the results of flameless AAS determinations of solutions.     

Matrix interference in laser atomic absorption spectrometry

The combination of graphite furnace atomic absorption spectrometry and ruby laser evaporation of solid samples is described. The influence of the matrix composition on analytical results is shown in the determination of Ag, Al, Cd, Ga, Mn and Pb. In the presence of halides a depression of the absorbance values of Al and Ga was observed. The formation of diatomic molecules and the dissociation of these in the laser plasma and in the hot graphite furnace are discussed.     

?quidensitometrie—eine methode zur Beurteilung der struktur von plasmen—IX. Einflu? von NaCl auf die Intensit?t von Spektrallinien und die axiale Teilchenverteilung in Gleichstrombogenplasmen1

The influence of an easily ionizable constituent (NaCl) on the intensities of atomic lines and the axial particle density distribution of Al, Sn, Ag, Si, Sb, and Be in a d.c. arc plasma was investigated. The following methods of investigation were employed: (i) intermediate imaging to determine the total intensity; (ii) direct imaging (with one lens) of the arc axis to establish the axial intensity distribution; (iii) direct imaging of the arc in a slitless spectrograph to obtain arc spectrograms and equidensitograms for the determination of the axial element density distribution and the geometrical shape of the plasma.A result of this investigation is the recognition that optimum total intensities occur even if there is a homogeneous element density distribution. This proves that the phenomena that govern the particle density distribution and intensity optima are interrelated. The results are discussed in detail.     

Atmosph?rische Luft

Ohne Zusammenfassung     

Untersuchungen zur atomspektroskopischen spurenanalyse in AIIIBV-halbleiter-mikroproben—IV: Vergleich der bestimmung von tellurspuren im GaP und GaAs durch AAS,AFS und AES

Methods are described for the determination of trace tellurium in acid solution in the absence and presence of the inorganic matrices As, P, Ga, GaP and GaAs and for the direct determination in solid GaP and GAs. The following methods were used: AAS with electrothermal atomization, AFS with electrothermal atomization, and AES with d.c. arc excitation. The conditions for each of the methods were optimized and the analytical results were compared. It is shown that AAS with electrothermal atomization gives the best absolute and also relative limit of detection for trace tellurium (90 pg Te, or 4 ppm Te in GaAs or GaP). Therefore this method is recommended for the determination of trace tellurium in very small samples of A^IIIB_V-semiconductors.