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Quantitative thin film analysis by EELS
Abstracts
The best fit is achieved for the quasi-chemical approximation of localized adsorption. For coverages ranging from 0 = 0 to 0 ~- 0.75 in each of the first three monolayers, this fit is very good. Thus, the adsorption can be concluded to be a localized one. By means of the quasi-chemical approximation the following data could be inferred from the experiments: adsorption energy, energy of lateral interaction, number of next neighbours and frequency of vibration.
The deposition treatment influence on structure properties of amorphous metallic thin films A Chrzastowski and H Jankowski, Department of Solid State Physics, Academy of Mining and Metallurgy, 30-059 Krak6w, al Mickiewicza 30, Poland. We have examined uhv evaporated and sputtered films of G d - C o alloys by transmission electron microscopy. Determination of radial distribution function and microstructure observations show the influence of substrate temperature and bias voltage on the structure of evaporated and sputtered films, respectively. Experimental technique and construction of vacuum deposition systems are also described.
Application of layer systems for optical components K Ehrig, U Ehrlich, G Gerlach and K Graef, VEB Hochvakuum Dresden, 8017 Dresden, Niedersedlitzer Str 63, East Germany By the use of layer systems, the optical properties of glasses (and plastic materials) can be varied in wide ranges, modern optical components like laser mirrors, beam splitters, heat reflectors, etc. are made by evaporation of various coating materials with defined refractive index and determined thickness. Coating materials are first of all dielectrics and metals. The number of single-layers can average up to 40 and more. A highly specialized hardware technique, which guarantees high quality of layers and reproducibility of layer attributes is the condition for the development and batch fabrication of complex layer systems. The fully automatic high-vacuum evaporation plant 'B 63 DM' developed by VEB HVD is especially suited for the fabrication of complex layer systems. Precise measuring and control technique (e.g. photometers, testglass changer, etc.) in combination with microprocessors and data memories allows variability of evaporating technologies and guarantees reproducibility, reliability and easy-to-use controls.
Imaging of the microtopography of silicon (111) surfaces by gold decoration D Katzer, Institute of Solid State Physics and Electron Microscopy of the Academy of Sciences of GDR, Weinberg 2, 4010 Halle, East Germany and G Srfrfin, Research Institute for Technical Physics of the Hungarian Academy of Sciences, H-325 Budapest, PO Box 76, Hungary A decoration method was developed for studying the microtopo-
graphy of Si (111) surfaces. The Si (111) single crystal surfaces were cleaned by heat treatment and decorated by gold deposition in an uhv system. A selective reaction of Au and Si occurred preferentially on the surface steps developed by sublimation at the 1220°C heat treatment. The gold-silicon alloy formation at the steps took place in a temperature range of 475 + 20°C, producing the 'reaction decoration' pattern. The decorated surface was studied in a STEM using secondary electron imaging. A crystallographic anisotropy was found in the velocity of step propagation during the sublimation.
Stability of sputtered NiCr thin films for strain gauge application A Banovec, K Po~un and M Kern, Ingtitut za Elektroniko in Vakuumsko Tehniko, Teslova 30, 61111 Ljubljana, Yugoslavia High electrical stability of thin resistive films under mechanical and thermal conditions is very important for practical strain gauge applications. Rf sputtered thin films with composition of NiCr alloy (50:50 wt %) were investigated. The layers were treated in combination with mechanical and thermal ageing. The process of thermal ageing was performed at 315°C in a N 2 atmosphere. Small differences in compositional-depth profiles of NiCr thin films due to the influence of selective chemical etching were observed with AES analysis. The influence of laser trimming gives rise to instability of resistance values. The results of electrical and environmental tests show high stability of sputtered NiCr strain gauges. The values of TCR measured between - 4 0 and + 80°C are less than + 5 ppm(°C) - 1 and temperature cycling resistance drifts by less than 0.1%.
Possibility of photocurrent oscillation in Se-thin-layers J Kisprter, Food Industry College, Szeged, PO Box 557, H-6701
Szeged, Hungary We have found low temperature photocurrent oscillation in polycrystalline trigonal Se-thin-layers at the certain electric field strength, intensity of illumination and temperature chosen. The phenomenon was explained by a barrier model. In this work our purpose was to study photocurrent oscillation in Se-thin-layers having different crystalline forms, and purity of 99.996%. Photocurrent oscillation could not be detected in the evaporated Se-thin-layers examined, but results obtained by the kinetics of photoconductivity and the examination of I-V characteristics could well be explained by a barrier model treated for Semonocrystals.
Quantitative thin film analysis by EELS H D Bauer and W Scholz, AD W--Zentralinstitut ffir FestkSrper-
physik und Werkstofforschung, D D R-8027 Dresden, East Germany During recent years the electron energy loss spectroscopy obtained an increasing importance for the analytical transmission 193
Abstracts
electron microscope (TEM) by the capability to detect light elements, like B, C, N and O. For very thin samples the calculation of elemental concentrations due to Egerton (1978) leads to useful results. Solid state investigations at the TEM often employ sample foils thicker than 100 nm. There the mentioned quantification is in error because of the plural inelastic scattering, altering the intensity distribution of the characteristic edges. Usually, at first, the background has to be removed and then a deconvolution has to be accomplished. However, the background stripping is critical especially at the destroyed edges of thicker foils, leading to a dramatic uncertainty of quantification. We have developed a new technique, removing the background after the deconvolution. We use the hydrogenic approximation for the single loss profile as a statement, convolute this profile with the low loss region and compare the result with the measured edge region of the spectrum by a least-squares fit. The method is accomplished by the PDP-11/02 computer at our JEM-200 CX microscope. Even for strongly smeared spectra we obtain poor single loss edges well suitable for quantification. The basic principle of our technique is explained and data illustrating the results are presented.
Reflection electron energy loss spectroscopy (REELS) of some oxide films on substrates G Gergely and A Sulyok, Research Institute lor Technical Physics of the Hungarian Academy of Sciences, H-1325 Budapest, PO Box 76, Hungary REELS of thin oxide films on aluminium and silicon substrates has been done making use of elastic peak electron spectroscopy. In recent work, experimental evidence proved the dominant role of the two process model in REELS. The core level loss peak consists of inelastic scattering (IS) and elastic reflection (ER) processes: I S + E R or E R + I S within the thin film, IS in the film and ER in the substrate, before or after the loss event. The analysis is given of these processes, deducing formulas for evaluating REELS experimental results. The elastic peak consists of ER within the film and the substrate. Experiments have been carried out with a Riber OP C 103 CMA lock in on line computer system. Theoretical and experimental results vs the E primary electron energy are presented.
Adsorption and decomposition of NO on potassium promoted Rh(lll)
Pre-adsorbed potassium changed only slightly the rate and extent of NO uptake on R h(111 ) at 300 K up to 0 K_~0.3 coverage, but it promoted the dissociation of adsorbed NO. At higher potassium coverage the dissociation was almost complete. Adsorption of NO on Rh(111 ) at 100 K produced three losses at 6.4, 12 and 15 eV in EEL spectrum. The same losses were found on potassium covered surfaces. From the temperature dependence of these losses and from TD spectra it appeared that the effect of potassium is a twofold one: it slightly increases the temperature of the existence of NO on the R h and it promotes the dissociation at higher temperatures.
Adsorption of H20 and 02 on Rh surfaces studied by AES, ELS and TDS J Kiss and F Solymosi, Institute of Solid State and Radioehemistry,
University of Szeged: and Reaction Kinetics Research Group of the Hu,lqarian Academy of &'iences. PO Box 105, H-6701 Sze¢ted, Hunqary Water adsorption on metal surfaces is of fundamental interest in catalysis and electrochemistry. The interaction of water with clean, boron and oxygen pre-covered Rh surfaces was studied by AES, ELS (in electronic range) and TDS. Water vapour undergoes reversible molecular adsorption and desorption on clean R h ( l l l ) and Rh foil. The weakly chemisorbed layer desorbed with a peak temperature of 182 200 K. Above 0.5 1, exposure a second peak was developed at a peak maximum of 158 K, which corresponds to the formation of a multilayer of ice. The adsorbed water produced three losses at 14, 10.4 and 8.7 eV. The presence of surface boron caused the dissociation of adsorbed water which was indicated by evolution of H 2 and appearance of 9.4 eV loss above 200 K due to the formation of B O bonds. The adsorption of oxygen on boron-contaminated Rh foil also produced this loss. Adsorption of HzO in the presence of the electronegative oxygen additive on the Rh sample leads to formation of OH radicals. Upon heating, the dissociation process is followed by a disproportionation reaction, which results in a shift of the H 2 0 desorption peak towards higher temperatures:
T,> 220 K.
The nature of the adsorption states of hydrogen on surfaces of thin transition metal films
L Bugyi and F Solymosi, Institute of Solid State and Radio-
R Dug, Institute of Physival Chemistry Polish Academy ,!/Science.s ul Kasprzaka 44.01-224 Warszawa. Poland
chemistry, University of Szeged; and Reaction Kinetics Research Group of the Hun qarian Academy of Sciences, PO Box 105, H-670 I Sze.qed, Hun~tary
and E Nowicka, Space Research Centre, Polish Academy of Sciences. ul Ordona 21, 01-237 Warszawa. Poland
The interaction of NO with clean and potassium covered Rh(1111 surfaces has been investigated by LEED, Auger electron, electron energy loss (in the electronic range) and thermal desorption spectroscopy in the temperature range between !00 and 1200 K. After saturation of the clean surface with NO at 300 K two NO desorption peaks were observed, at T , = 397 and 447 K. At the same time, N 2 also desorbed, at Tp=460 and 773 K indicating that NO dissociates on R h ( l l l ) surface at higher temperatures.
One can expect that essentially three kinds of the adsorption states of different physical character, e.g. binding energy, electrical properties, etc. and probably different chemical reactivity, can be formed on transition metal surfaces due to: (i) adsorption on surface sites of different bonding potential; (ii) mutual interaction within the adsorbate: (iii) adsorbate-adsorbent chemical reaction leading to new compound formation on the surface. The aim of this work was to find what adsorption states arc
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The best fit is achieved for the quasi-chemical approximation of localized adsorption. For coverages ranging from 0 = 0 to 0 ~- 0.75 in each of the first three monolayers, this fit is very good. Thus, the adsorption can be concluded to be a localized one. By means of the quasi-chemical approximation the following data could be inferred from the experiments: adsorption energy, energy of lateral interaction, number of next neighbours and frequency of vibration.
The deposition treatment influence on structure properties of amorphous metallic thin films A Chrzastowski and H Jankowski, Department of Solid State Physics, Academy of Mining and Metallurgy, 30-059 Krak6w, al Mickiewicza 30, Poland. We have examined uhv evaporated and sputtered films of G d - C o alloys by transmission electron microscopy. Determination of radial distribution function and microstructure observations show the influence of substrate temperature and bias voltage on the structure of evaporated and sputtered films, respectively. Experimental technique and construction of vacuum deposition systems are also described.
Application of layer systems for optical components K Ehrig, U Ehrlich, G Gerlach and K Graef, VEB Hochvakuum Dresden, 8017 Dresden, Niedersedlitzer Str 63, East Germany By the use of layer systems, the optical properties of glasses (and plastic materials) can be varied in wide ranges, modern optical components like laser mirrors, beam splitters, heat reflectors, etc. are made by evaporation of various coating materials with defined refractive index and determined thickness. Coating materials are first of all dielectrics and metals. The number of single-layers can average up to 40 and more. A highly specialized hardware technique, which guarantees high quality of layers and reproducibility of layer attributes is the condition for the development and batch fabrication of complex layer systems. The fully automatic high-vacuum evaporation plant 'B 63 DM' developed by VEB HVD is especially suited for the fabrication of complex layer systems. Precise measuring and control technique (e.g. photometers, testglass changer, etc.) in combination with microprocessors and data memories allows variability of evaporating technologies and guarantees reproducibility, reliability and easy-to-use controls.
Imaging of the microtopography of silicon (111) surfaces by gold decoration D Katzer, Institute of Solid State Physics and Electron Microscopy of the Academy of Sciences of GDR, Weinberg 2, 4010 Halle, East Germany and G Srfrfin, Research Institute for Technical Physics of the Hungarian Academy of Sciences, H-325 Budapest, PO Box 76, Hungary A decoration method was developed for studying the microtopo-
graphy of Si (111) surfaces. The Si (111) single crystal surfaces were cleaned by heat treatment and decorated by gold deposition in an uhv system. A selective reaction of Au and Si occurred preferentially on the surface steps developed by sublimation at the 1220°C heat treatment. The gold-silicon alloy formation at the steps took place in a temperature range of 475 + 20°C, producing the 'reaction decoration' pattern. The decorated surface was studied in a STEM using secondary electron imaging. A crystallographic anisotropy was found in the velocity of step propagation during the sublimation.
Stability of sputtered NiCr thin films for strain gauge application A Banovec, K Po~un and M Kern, Ingtitut za Elektroniko in Vakuumsko Tehniko, Teslova 30, 61111 Ljubljana, Yugoslavia High electrical stability of thin resistive films under mechanical and thermal conditions is very important for practical strain gauge applications. Rf sputtered thin films with composition of NiCr alloy (50:50 wt %) were investigated. The layers were treated in combination with mechanical and thermal ageing. The process of thermal ageing was performed at 315°C in a N 2 atmosphere. Small differences in compositional-depth profiles of NiCr thin films due to the influence of selective chemical etching were observed with AES analysis. The influence of laser trimming gives rise to instability of resistance values. The results of electrical and environmental tests show high stability of sputtered NiCr strain gauges. The values of TCR measured between - 4 0 and + 80°C are less than + 5 ppm(°C) - 1 and temperature cycling resistance drifts by less than 0.1%.
Possibility of photocurrent oscillation in Se-thin-layers J Kisprter, Food Industry College, Szeged, PO Box 557, H-6701
Szeged, Hungary We have found low temperature photocurrent oscillation in polycrystalline trigonal Se-thin-layers at the certain electric field strength, intensity of illumination and temperature chosen. The phenomenon was explained by a barrier model. In this work our purpose was to study photocurrent oscillation in Se-thin-layers having different crystalline forms, and purity of 99.996%. Photocurrent oscillation could not be detected in the evaporated Se-thin-layers examined, but results obtained by the kinetics of photoconductivity and the examination of I-V characteristics could well be explained by a barrier model treated for Semonocrystals.
Quantitative thin film analysis by EELS H D Bauer and W Scholz, AD W--Zentralinstitut ffir FestkSrper-
physik und Werkstofforschung, D D R-8027 Dresden, East Germany During recent years the electron energy loss spectroscopy obtained an increasing importance for the analytical transmission 193
Abstracts
electron microscope (TEM) by the capability to detect light elements, like B, C, N and O. For very thin samples the calculation of elemental concentrations due to Egerton (1978) leads to useful results. Solid state investigations at the TEM often employ sample foils thicker than 100 nm. There the mentioned quantification is in error because of the plural inelastic scattering, altering the intensity distribution of the characteristic edges. Usually, at first, the background has to be removed and then a deconvolution has to be accomplished. However, the background stripping is critical especially at the destroyed edges of thicker foils, leading to a dramatic uncertainty of quantification. We have developed a new technique, removing the background after the deconvolution. We use the hydrogenic approximation for the single loss profile as a statement, convolute this profile with the low loss region and compare the result with the measured edge region of the spectrum by a least-squares fit. The method is accomplished by the PDP-11/02 computer at our JEM-200 CX microscope. Even for strongly smeared spectra we obtain poor single loss edges well suitable for quantification. The basic principle of our technique is explained and data illustrating the results are presented.
Reflection electron energy loss spectroscopy (REELS) of some oxide films on substrates G Gergely and A Sulyok, Research Institute lor Technical Physics of the Hungarian Academy of Sciences, H-1325 Budapest, PO Box 76, Hungary REELS of thin oxide films on aluminium and silicon substrates has been done making use of elastic peak electron spectroscopy. In recent work, experimental evidence proved the dominant role of the two process model in REELS. The core level loss peak consists of inelastic scattering (IS) and elastic reflection (ER) processes: I S + E R or E R + I S within the thin film, IS in the film and ER in the substrate, before or after the loss event. The analysis is given of these processes, deducing formulas for evaluating REELS experimental results. The elastic peak consists of ER within the film and the substrate. Experiments have been carried out with a Riber OP C 103 CMA lock in on line computer system. Theoretical and experimental results vs the E primary electron energy are presented.
Adsorption and decomposition of NO on potassium promoted Rh(lll)
Pre-adsorbed potassium changed only slightly the rate and extent of NO uptake on R h(111 ) at 300 K up to 0 K_~0.3 coverage, but it promoted the dissociation of adsorbed NO. At higher potassium coverage the dissociation was almost complete. Adsorption of NO on Rh(111 ) at 100 K produced three losses at 6.4, 12 and 15 eV in EEL spectrum. The same losses were found on potassium covered surfaces. From the temperature dependence of these losses and from TD spectra it appeared that the effect of potassium is a twofold one: it slightly increases the temperature of the existence of NO on the R h and it promotes the dissociation at higher temperatures.
Adsorption of H20 and 02 on Rh surfaces studied by AES, ELS and TDS J Kiss and F Solymosi, Institute of Solid State and Radioehemistry,
University of Szeged: and Reaction Kinetics Research Group of the Hu,lqarian Academy of &'iences. PO Box 105, H-6701 Sze¢ted, Hunqary Water adsorption on metal surfaces is of fundamental interest in catalysis and electrochemistry. The interaction of water with clean, boron and oxygen pre-covered Rh surfaces was studied by AES, ELS (in electronic range) and TDS. Water vapour undergoes reversible molecular adsorption and desorption on clean R h ( l l l ) and Rh foil. The weakly chemisorbed layer desorbed with a peak temperature of 182 200 K. Above 0.5 1, exposure a second peak was developed at a peak maximum of 158 K, which corresponds to the formation of a multilayer of ice. The adsorbed water produced three losses at 14, 10.4 and 8.7 eV. The presence of surface boron caused the dissociation of adsorbed water which was indicated by evolution of H 2 and appearance of 9.4 eV loss above 200 K due to the formation of B O bonds. The adsorption of oxygen on boron-contaminated Rh foil also produced this loss. Adsorption of HzO in the presence of the electronegative oxygen additive on the Rh sample leads to formation of OH radicals. Upon heating, the dissociation process is followed by a disproportionation reaction, which results in a shift of the H 2 0 desorption peak towards higher temperatures:
T,> 220 K.
The nature of the adsorption states of hydrogen on surfaces of thin transition metal films
L Bugyi and F Solymosi, Institute of Solid State and Radio-
R Dug, Institute of Physival Chemistry Polish Academy ,!/Science.s ul Kasprzaka 44.01-224 Warszawa. Poland
chemistry, University of Szeged; and Reaction Kinetics Research Group of the Hun qarian Academy of Sciences, PO Box 105, H-670 I Sze.qed, Hun~tary
and E Nowicka, Space Research Centre, Polish Academy of Sciences. ul Ordona 21, 01-237 Warszawa. Poland
The interaction of NO with clean and potassium covered Rh(1111 surfaces has been investigated by LEED, Auger electron, electron energy loss (in the electronic range) and thermal desorption spectroscopy in the temperature range between !00 and 1200 K. After saturation of the clean surface with NO at 300 K two NO desorption peaks were observed, at T , = 397 and 447 K. At the same time, N 2 also desorbed, at Tp=460 and 773 K indicating that NO dissociates on R h ( l l l ) surface at higher temperatures.
One can expect that essentially three kinds of the adsorption states of different physical character, e.g. binding energy, electrical properties, etc. and probably different chemical reactivity, can be formed on transition metal surfaces due to: (i) adsorption on surface sites of different bonding potential; (ii) mutual interaction within the adsorbate: (iii) adsorbate-adsorbent chemical reaction leading to new compound formation on the surface. The aim of this work was to find what adsorption states arc
1 94