摘要:

The combined techniques of surface extended x‐ray absorption fine structure (SEXAFS) and high resolution core level photoelectron spectroscopy have been used to investigate the local bonding structure of the Sb/Si(111) interface. We find that the adsorption of 1 monolayer (ML) of Sb completely eliminates the surface components of the Si 2pcore level spectrum. The Sb induced Si 2pinterfacial core level has been found to be shifted 0.20±0.02 eV toward higher binding energy with an intensity that corresponds to the top 1 ML of surface atoms. The SEXAFS determination of the absolute surface coordination numbers and bond lengths within the first Sb shell is 2.1±0.3 Sb atoms at 2.86±0.02 Å and 2.0±0.4 Si atoms at 2.66±0.03 Å. Together, these results indicate that Sb trimers occupy the three fold atop sites of the Si(111) surface where each Sb atom is bonded to two Si atoms in a modified bridge configuration.

ISSN:0734-2101    

DOI:10.1116/1.577435

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

It has been reported that Cs adsorbed at low coverages on GaAs(110) forms linear one‐dimensional chains which usually appeared in pairs. The alkali metal atoms in the two chains (called primary and secondary) are shifted along the [11̄0] direction by an amounta/√2, whereais the bulk cubic lattice constant of GaAs. It is an unresolved issue as to why the chains appear in pairs adjacent to each other. We suggest that the primary and secondary chains can be really viewed as a single chain with a zig–zag structure. One can then compare the calculated total energy for a single linear chain (of double the density) with the total energy for a zig–zag chain. The latter is found to be a lower energy structure in agreement with the scanning tunneling microscopy observations. Physical interactions responsible for stabilizing the zig–zag structure are briefly discussed.

ISSN:0734-2101    

DOI:10.1116/1.577436

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Synchrotron radiation photoemission results for Sm/GaAs(110) interfaces formed and studied at 20 and 300 K show temperature dependencies that can be related to differences in surface growth structures and kinetic constraints. Submonolayer growth at 300 K produces two distinct ordered Sm chain configurations, as shown by scanning tunneling microscopy, and the photoemission results demonstrate that Sm atoms in these chains are divalent. These low‐surface‐density divalent configurations are precursors to surface disruption that, with additional Sm deposition, produce reacted clusters in which the Sm atoms are trivalent. Ultimately, Sm metal nucleation occurs on the reacted region and the overlayer thickens, with Ga and As atoms segregating to the surface region. For 20‐K growth, the valence‐band results show much slower conversion from divalent to trivalent Sm bonding, despite evidence that the amount of disruption is equivalent at 20 and 300 K. We attribute these differences, and those in the Ga and As core levels, to the freezing‐in of an amorphous Sm–Ga–As mixture at 20 K. Hence, kinetic factors curtail atom rearrangements that occur readily at 300 K. Annealing of thin overlayers to 300 K removes kinetic constraints and produces Ga, As, and Sm bonding that is spectroscopically equivalent to that observed for 300‐K growth. Sm/GaAs(110) interfaces formed by cluster assembly are shown to be unstable. Together, these results demonstrate that high‐atom‐density Sm contacts to GaAs are thermodynamically very unfavorable and that the instability generated by increasing the surface coverage provides the driving force for disruption.

ISSN:0734-2101    

DOI:10.1116/1.577437

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Momentum‐resolved inverse photoemission (KRIPES) and low energy electron diffraction (LEED) have been used to investigate the development at 300 K of the unoccupied electronic states and the overlayer morphology for growth of up to 15 ML of Bi on InP(110). KRIPES results reveal a Bi‐derived surface state atEF+1.35 eV onp‐type InP(110) for 1 monolayer (ML) coverage. This state is associated with zig–zag chain formation along the [11̄0] direction. The LEED seen for coverages above ∼6 ML suggests the formation of ordered Bi bulk‐like patches atop the initial monolayer with the crystallite basal planes oriented parallel to therelaxedInP(110) surface. The structure of the ordered, bulk‐like Bi patches originates from the two inequivalent sites for 1 ML Bi/InP(110), namely Bi–In and Bi–P bonding. The basal planes of the Bi crystallites are ∼20° from the normal of the unrelaxed (110) surface, toward [001]. The large InP(110) surface relaxation remaining after 1 ML growth of Bi and the slow strain relief upon subsequent growth are shown to account for the different evolution of the unoccupied states and overlayer morphology when compared to Bi/GaAs(110).

ISSN:0734-2101    

DOI:10.1116/1.577438

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Ionization gauges are commonly used for pressure measurement from the lowest achievable pressures to 10−2Torr. Two types exist: In the hot cathode gauge (HCG) the source of the ionizing electrons is a thermionic cathode. In the cold cathode gauge (CCG) it is a circulating space charge current of electrons trapped in crossed electric and magnetic fields. Indications of both types of gauge are gas dependent. Relative sensitivities for different gases are not the same for different HCGs or CCGs, or for HCGs compared to CCGs. Both types of gauge are susceptible to contamination. The filament heating power of the HCG is sufficient to cause local outgassing of adsorbed material, and possibly large pressure errors. Each has certain spurious effects. The lower limit of the HCG is set by x‐ray photocurrent and electron impact desorption. The CCG is subject to discontinuities in the current versus pressure characteristic. Starting of the discharge in a CCG may be delayed at ultrahigh vacuum (UHV). Pumping speeds of both types of gauge are of magnitude 10−2l/s, so that gauge pumping is usually negligible.

ISSN:0734-2101    

DOI:10.1116/1.577439

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Remarkable variation of the sensitivity of a triode gauge with emission current and pressure was revealed to be due to the space charge effect of gas ions and electrons. An experimental attempt to reduce the space charge effect on the sensitivity was made. Triode gauges with a simple auxiliary electrode installed between the ion collector and the anode were fabricated and tested. The dependence of the sensitivity on emission current of the gauge was drastically reduced for most pressure ranges of high and medium vacuum. This result can be applied in the development of a new gauge with less dependence of the sensitivity on pressure.

ISSN:0734-2101    

DOI:10.1116/1.577440

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Measurement of the performance of mass spectrometers is required to determine which model best meets the requirements of a process. For this study, the instruments under test were adjusted according to manufacturers’ recommendations and these settings were maintained throughout the tests. Only Faraday cup data were collected. Scan speed/damping combinations were set to give low noise, moderate scan speed, and no peak clipping. Pressure decay through a molecular leak and calibrated leaks generated partial pressures from 10−4to 10−11Torr in a chamber pumped by conductance‐limited turbomolecular pumps. Ten parameters were measured. Peak shape and peak top structure were analyzed by least‐squares programs. Baseline and peak top noise were determined. Short‐ and long‐term stability of peak height, half peak height, and peak position were measured. Sensitivities to eight gases were determined. Linearities within and between electrometer ranges were calculated. The upper and lower pressure limits of linear response were found. Interferences of gases varied unpredictably. The instruments tested showed wide variations in performance.

ISSN:0734-2101    

DOI:10.1116/1.577441

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Two turbopumped vacuum systems were each equipped with connections for up to three residual gas analyzers (RGAs) of different types. One system allowed comparisons of two commercial quadrupole RGAs with a time‐of‐flight (TOF) instrument of roughly similar performance; the other provided a comparison of a TOF‐RGA with a 5 cm radius magnetic sector‐field instrument. This TOF‐RGA was tested with flight path lengths of 29 and 82 cm. The magnetic RGA was tested in both accelerating‐voltage scan and magnetic‐scan variants, and with both first and second‐order direction focusing magnets. For each type of RGA, the adjustments essential for optimum performance were identified. For reliable quantitative data, it seems desirable to use some form of constant‐transmission mode for quadrupoles, magnetic scan or at least magnetic range change for sector‐field instruments, and modern transient recorder/averagers for TOF‐RGAs. It appears that minimum detectable partial pressures and resolving powers can be roughly similar for the three basic types of RGAs. Mass limits and maximum scan rates, on the other hand, are very different. We conclude that the ‘‘best’’ type of RGA is very much a function of the specific application.

ISSN:0734-2101    

DOI:10.1116/1.577442

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Many instruments used in vacuum technology for the measurement and diagnosis of the gas content of systems use electrons and ions directed by electric and magnetic fields. Examples include mass spectrometer leak detectors, residual gas analyzers, and ion gauge tubes. Microchannel technology, originally developed to implement night vision devices for the military, can be used to make beams of electrons and ions visible. This technology is very useful in the development and improvement of devices that depend on the electric and magnetic optics to form and guide such beams. The development of a new tube for a leak detector provides a good example of the application of this technology. The basic structure of microchannel devices requires special vacuum enclosures and electrical circuitry; some examples used in the development of the new tube are presented, along with photographs of ion beam images. The images demonstrate a previously unrecognized focusing phenomenon, a good example of the utility of the approach.

ISSN:0734-2101    

DOI:10.1116/1.577443

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

In semiconductor device manufacturing, the use of toxic, corrosive gases and the generation of large amounts of solid by‐products make frequent maintenance inevitable, as the mechanical pump stops pumping. The requirements of semiconductor device manufacturers, especially those in the production areas, were foremost in mind to the pump manufacturer when the development of a new rotary vacuum pump line was started. The new ‘‘Quick Release’’ pumps reduce shutdown time by about one order of magnitude when compared with the currently available pumping system. This cost saving feature is due to the Quick Release concept; for the first time, the pumping module and the drive module are completely separate units, which combine into a single operating unit. When the pumping module is removed to undergo the necessary maintenance, the drive module remains connected to the pumping station, ready to receive the spare pumping module. All the power, control, and vacuum connections to or from the drive module are untouched. There is no dispersion of contaminated oil, as it is contained in the removed module. There is no need of complex checking of the equipment at start‐up. Simply lock the pumping module in place, and flip the start switch to operate.

ISSN:0734-2101    

DOI:10.1116/1.577444

出版商:American Vacuum Society    

年代:1991

数据来源: AIP