摘要:

We describe the construction of an UHV evaporator with two electron beam guns and a heated substrate turntable which is used for the preparation of composition‐modulated structures (CMS’s). Using a suitably controlled stepping motor, up to 20 different CMS’s can be prepared in the same run. The system has been used to deposit V/Fe CMS’s and preliminary structural measurements indicate the samples are of high quality.

ISSN:0734-2101    

DOI:10.1116/1.572618

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

A new type of effusion cell has been developed for thermal evaporation of materials up to 1300 °C under ultrahigh vacuum conditions. The evaporation rate, measured by a quadrupole mass spectrometer, is controlled by moving a mechanical shutter connected to the cell and not by varying the temperature. An electronic feedback circuit positions the shutter and allows computer programming of arbitrary profiles. Compared to common thermal control, any desired evaporation rate can be stabilized faster, for example, in less than 2 s.

ISSN:0734-2101    

DOI:10.1116/1.572626

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Thermal decomposition behavior of titanium hydride (TiH2) powder at temperatures between 250 and 330 °C (523 and 603 K) has been studied from both thermodynamic and kinetic viewpoints. Equilibrium hydrogen pressure measured in a closed system was found to vary from the order of 10−3to 10−2Torr (10−1to 1 Pa) and the enthalpy of formation of titanium hydride in the two phase (α+γ) region was evaluated to be 31 kcal/mol (130 kJ/mol). It has been found that steady state decomposition can be realized also in an open (continuously pumped) system as long as the two phases coexist. Hydrogen pressure at the steady state was in the order from 10−4to 10−3Torr (10−2to 10−1Pa) and the activation energy for the decomposition was determined to be 29 kcal/mol (122 kJ/mol). In addition, it has been demonstrated that hot titanium hydride can simply be applied to low pressure hydrogen control in vacuum systems.

ISSN:0734-2101    

DOI:10.1116/1.572617

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

The structure of fivefold particles is studied using single particle diffraction in a STEM microscope and lattice images. The results show excellent agreement with the rhombohedral and body‐centered orthohombic models for the particle. Theoretical calculations were carried out to study the influence of the number of atoms in the diffraction patterns.

ISSN:0734-2101    

DOI:10.1116/1.572619

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Energy spreads of Ar+beams extracted from a microwave ion source are investigated using a high resolution, cylindrical‐sector energy analyzer. The energy spread, measured from the spectrum width at half value of the peak, is about 5 eV, and is almost independent of microwave power, gas pressure, and extraction voltage. The excess energy of Ar+beam due to plasma floating potential is from about 10 to 20 eV, depending on gas pressure and microwave power. Comparison with other sources showed the microwave ion source to be suitable for obtaining high current beams of narrow energy spread.

ISSN:0734-2101    

DOI:10.1116/1.572620

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Zirconium overlayers were deposited onto a Pt(100) surface by electron beam evaporation in UHV, and the composition and structure of the surface was determined by AES and LEED. The overlayers were highly reactive towards oxygen, carbon monoxide, and hydrocarbons, forming oxide or carbide overlayers. Several metastable ordered structures were observed by LEED when oxidized overlayers were thermally annealed in UHV. Protracted annealing at>900 K results in reduction and dissolution of the oxidized overlayer with complete disappearance of zirconium from the surface. Oxygen dosing of annealed surfaces at 25 °C caused resegregation of zirconium to the surface, and the formation of an ordered PtZrxOysurface phase which may be a zirconia analog to the yttria ternary oxide PtYO3.5. This phase was stable in oxygen at 25–300 °C, but oxygen dosing at above 300 °C resulted in precipitation of ZrO2islands on top of the Pt(100)‐(1×1) substrate.

ISSN:0734-2101    

DOI:10.1116/1.572622

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Total pressure measurements below 10−10Torr, in an active residual gas, were made using a special hot‐cathode ionization gauge, without errors caused by electron‐stimulated ion desorption. The gauge can separate the two ion signals, i.e., the signal created from gas phase molecules and that from electron‐stimulated ion desorption, by using a new modulation and amplification system. In order to verify this separation effect, experiments were made with oxygen and nitrogen introduction in the 10−10Torr range.

ISSN:0734-2101    

DOI:10.1116/1.572624

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Radioactive85Kr was used in a closed volume under moderate vacuum to investigate mechanisms by which inert gas atoms are pumped in an electron‐impact ionization source of a simple diode design. Results are consistent with a mechanism involving the conversion of inert gas ions into energetic neutrals at the cathode followed by reflection and trapping of some of the neutral atoms in nearby surfaces. We discuss the possibility that the source pumping speed is enhanced due to burial of the trapped neutrals by material released in low‐energy sputtering processes. The implications of these results for reducing memory effects in UHV mass spectrometer systems are discussed.

ISSN:0734-2101    

DOI:10.1116/1.572625

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Several DP systems have been discussed and evaluated with respect to dynamic evacuation under actual operating conditions of an electron microscope. As a result, a cascade DP system has been found to be the most reasonable for an electron microscope where the column is evacuated by the first DP backed by the second DP, and for the camera chamber by the second DP with a large volume foreline backed by a mechanical pump. A spectrum of the residual gases in an electron microscope with a cascade DP system indicates a very clean vacuum with hydrocarbon partial pressures of less than 3×10−7Pa.

ISSN:0734-2101    

DOI:10.1116/1.572627

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

An electron beam column was designed and was used in experiments for a 50×50 mm2deflection area. The column consists of a condenser lens, a combined focusing and double deflection system, and dynamic focus and astigmatism coils. The system successfully reduced deflective coma and transverse chromatic aberrations that could not be dynamically corrected. The dynamic coils adroitly corrected not only inherent aberrations in the column but also irregular ones produced by misalignment of the beam, column manufacturing error, and so forth. A LaB6electron gun was employed at a brightness of 5×105A/cm2sr at 20 kV beam energy. After correction, the Gaussian beam diameter was less than 1.5 μm at 100 nA beam current in the deflection area. Test patterns including 4 μm minimum linewidths were exposed onto PMMA resist to demonstrate beam performance. Standard deviations (3σ) of the linewidths were 0.56 and 0.42 μm in thexandydirections, respectively.

ISSN:0734-2101    

DOI:10.1116/1.572628

出版商:American Vacuum Society    

年代:1984

数据来源: AIP