摘要:

Practical thermal desorption measurements require an ultrahigh vacuum (UHV) system with a simple method of calibrating the residual gas analyzer for a number of gases. The calibration system should be easy to move between systems. We describe how the gas injection method of Kendall has been used to calibrate an UHV system and present example measurements of the carbon dioxide and carbon monoxide evolution during the decomposition of a commercial triple carbonate used in cathode ray tube manufacture. The activation energy of the BaCO3component of the triple carbonate was found to be 94.7 kcal/mol.

ISSN:0734-2101    

DOI:10.1116/1.577123

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

An analysis for adsorbed gas on wall surfaces using an electron‐impact desorption (EID) technique was developed and applied to the evaluation of wall conditioning in the GAMMA 10 tandem mirror. The partial pressure rise due to EID (ΔPEID) was measured with a quadrupole mass analyzer installed near an electron emitting filament inserted in the central cell of GAMMA 10. The analysis using this method was performed during the wall‐conditioning period and the ΔPEIDrelated to light impurities (M=15, 28, 44) was observed to decrease by an order of magnitude with the progress of the wall conditioning. It was also observed that a good correlation exists between the ΔPEIDand the partial pressure rise induced by the plasma discharge (ΔPPID). The desorption efficiency of typically adsorbed gas molecules ξ was estimated by a simple balance equation for the partial pressures. A significant reduction of ξ due to the wall conditioning was observed.

ISSN:0734-2101    

DOI:10.1116/1.577131

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Adsorbate gases which are very reactive with chamber walls or which have low vapor pressures present serious difficulties in attaining precisely reproducible exposures in surface science experiments, especially if the desired exposures are small. Design considerations and details are described for an inexpensive gas dosing system which is excellently suited for precisely reproducing exposures of low vapor pressure and/or reactive gases to surfaces in UHV. Also presented is a method for calibrating the doser, such that even tiny exposures can be very accurately determined and reproduced.

ISSN:0734-2101    

DOI:10.1116/1.577108

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Metallic overlayers of platinum, copper, and gold on ap‐doped mercury cadmium telluride substrate have been depth profiled by 5 keV Ar+sputtering and analyzed with Auger and photoelectron spectroscopy, secondary ion, and secondary neutral mass spectroscopy. The dependence of the composition, diffusion behavior, and chemical state of the systems on different annealing conditions and substrate pretreatment procedures has been investigated. Depending on the metal, these features can differ very strongly, thus yielding different electronic properties of the metal–semiconductor contacts.

ISSN:0734-2101    

DOI:10.1116/1.577115

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The emission angle dependence of the depth distribution function of signal electrons in electron spectroscopies has been studied by means of a Monte Carlo simulation in which elastic scattering plays a significant role. Calculations were made for Si, InP, and In substrates at different emission angles (0°, and 40° to 80° off normal). The calculated depth distribution of signal electrons showed significant deviations from exponential attenuation at the more oblique emission angles. In consequence, the ‘‘attenuation length’’ of signal electrons loses its status of a material constant. A new empirical depth distribution function is proposed which consists of the sum of two exponential terms. This function describes the calculated Monte Carlo depth distribution as a function of the emission angle. The first term of this depth distribution function represents the contribution of those electrons which follow parallel straight‐line paths, whereas the second term accounts for a randomization of electron directions due to elastic scattering. Common to both terms is a parameter which we propose to call the attenuation parameter. A relationship is established between the attenuation parameter and the ‘‘effective attenuation length,’’ as proposed earlier [W. H. Gries and W. Werner, in Proceedings of the European Conference on Applied Surface and Interface Analysis, ECASIA, Antibes, France, 1989 (unpublished)]. The attenuation parameter is independent of the angle of emission, in contrast to the effective attenuation length. Evidence was found and is discussed, which indicates that the results apply equally to other materials. In special situations, the thickness dependence of the depth distribution function in the case of an overlayer situation is accounted for by using the new depth distribution function.

ISSN:0734-2101    

DOI:10.1116/1.577124

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The equilibrium surface compositions of Cu‐0.83 atomic percent (a/o) Ag and Cu‐0.61 a/o Ag have been determined by Auger electron spectroscopy over the temperature range 450–600 °C. These alloys show strong segregation of silver to the surface. Surface compositions have also been obtained by Monte Carlo simulations, performed in conjunction with an embedded atom method description of interatomic interactions. The results of the simulations have been interpolated by means of an analytical expression based on the regular solution approximation. Comparisons of the simulated surface compositions with experiment indicate reasonable quantitative agreement between calculated and measured surface compositions, but the temperature dependence of the computed surface composition is weaker than that observed experimentally. Possible reasons for the discrepancies are discussed.

ISSN:0734-2101    

DOI:10.1116/1.577125

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Fluorocarbon lubricants are of great interest in many applications where they are used in very thin layers. Control of the lubricant presence is easily performed by a surface analysis technique such as x‐ray photoelectron spectroscopy. However, the interpretation of the spectra is not straightforward. A simple electronegativity description of the charge shifts is developed from the group electronegativity and the Sanderson equalization approaches. It is applied to two types of high molecular weight molecules, and allows us to assign the experimental photoelectron spectra of the two fluorocarbon lubricants under study.

ISSN:0734-2101    

DOI:10.1116/1.577126

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The calcium catalyzed steam gasification of coal has been studied by a combination of a chemical microreactor working under technical conditions and surface analytical characterization (Auger and photoelectron spectroscopy, secondary ion and thermal desorption mass spectrometry) under ultra high vacuum conditions. The reaction model proposed by McKee was confirmed, and reaction products like calcium oxide, hydroxide and carbonate were detected after exposure to gasification conditions. The catalyst dispersion was studied as a function of reaction temperature and carbon conversion. The lowering of the CaCO3decomposition temperature and the decreasing sample charging at higher temperatures indicate the good contact between the catalyst and the substrate at reaction conditions. Deactivation of the catalyst is due to two processes: the inevitable sintering of calcium to CaO and catalyst poisoning by sulfur by forming calcium sulfide.

ISSN:0734-2101    

DOI:10.1116/1.577127

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We present a theory of the atomic resolution in scanning tunneling microscopy (STM) in terms of localized surface states on the tip. The tunneling matrix elements arising from these tip states are evaluated with thederivativerule. For example, apzsurface state on the tip generates a tunneling matrix element proportional to [∂ψ/∂z] at the nucleus of the apex atom, and ad3z2−r 2tip state generates a tunneling matrix element proportional to [3∂2ψ/∂z2−κ2ψ], (ψ is the sample wave function, κ is the decay constant of surface wave function, κ=(2meφ)1/2/ℏ ). To obtain analytic results of theoretical STM images, we further developed a simple independent‐orbital model to describe the wave functions of the sample surface. With this model, we present qualitative and quantitative explanations of the observed atomic resolution on metals and semiconductors, the spontaneous switching of instrument resolution during imaging, and various tip‐sharpening procedures.

ISSN:0734-2101    

DOI:10.1116/1.577128

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The ionization of fluorine with a field ion source is demonstrated. A fluorine(10%)–helium(90%) gas mixture and a (110) oriented tungsten emitter are used. The ion source is operated at a pressure of 1.5×10−5Torr and at temperatures between 7 and 80 K using a (110) plane of the emitter. Two current peaks in theI–Vcharacteristics are observed at temperatures over 46 K and one of them is confirmed to correspond to fluorine ion emission, which shows a maximum at 52 K and has an angular current density of 1.5×10−6A/sr and a brightness of 6×108A/cm2 sr. TheI–Vcharacteristics’ dependency on the crystal planes of the emitter tip such as (111) and (121) are also presented.

ISSN:0734-2101    

DOI:10.1116/1.577129

出版商:American Vacuum Society    

年代:1991

数据来源: AIP