A. V. Ermakov

A NOVEL AFM/STM/SEM SYSTEM

An atomic force/scanning tunneling (AFM/STM) microscope intended for operation inside a scanning electron microscope(SEM) is described. This AFM/STM/SEM system enables us to image a sample conventionally by SEM as well as to investigate the local surface topography by AFM or STM. This device incorporates a new method for monitoring AFM cantilever deflection that utilizes the focused electron beam of the SEM.

Cu(001) to HD energy transfer and translational to rotational energy conversion on surface scattering

Intense peaks are observed in angular intensity distributions for HD scattering from the Cu(001) surface. These can be ascribed to coherent diffraction with translational energy transfers of ΔE=0, −11.0, or 33.11 meV to molecular rotational energy. Time-of-flight spectra, at other scattering angles, display inelastic peaks that are assigned to phonon creation or annihilation processes with either the HD rotationally elastic or inelastic transitions. The HD phonon dispersion curves suggest a strong HD coupling both with surface Rayleigh modes and with bulk phonon modes of the metal surface. Comparisons of both elastic and inelastic scattering intensities are also made with those reported for the Ni(001) surface. To explain an apparent anomalous diffraction peak intensity ratio for Ni, a preferential coupling for the HD J=0 rotational state into a predissociation channel above the Ni surface is proposed.

An electrostatic autoresonant ion trap mass spectrometer

A new method for ion extraction from an anharmonic electrostatic trap is introduced. Anharmonicity is a common feature of electrostatic traps which can be used for small scale spatial confinement of ions, and this feature is also necessary for autoresonant ion extraction. With the aid of ion trajectory simulations, novel autoresonant trap mass spectrometers (ART-MSs) have been designed based on these very simple principles. A mass resolution approximately 60 is demonstrated for the prototypes discussed here. We report also on the pressure dependencies, and the (mV) rf field strength dependencies of the ART-MS sensitivity. Importantly the new MS designs do not require heavy magnets, tight manufacturing tolerances, introduction of buffer gases, high power rf sources, nor complicated electronics. The designs described here are very inexpensive to implement relative to other instruments, and can be easily miniaturized. Possible applications are discussed.

APPLICATION OF A NOVEL CONTACTLESS CONDUCTIVITY SENSOR IN CHEMICAL VAPOR DEPOSITION OF ALUMINUM FILMS

A novel contactless method for conductivity sensing is introduced that utilizes a driving coil and two tunable and near resonant coils. The design uses only inexpensive electronic components and a variable frequency rf generator. An algebraic expression for the response has been derived and simulations indicate a linear response to surface conductivity changes over at least four orders of magnitude. The sensitivity is shown to depend on the conductivity of the substrate, with a limit to conductivity changes as low as 10−4 Ω−1 for insulating substrates. An ultrahigh vacuum compatible version of this probe has been used to monitor in situ aluminum thin film growth by chemical vapor deposition on a native oxide covered, highly doped, Si(111) wafer. On this semiconducting substrate (3 Ω−1) a sensitivity to sheet conductivity changes as low as ∼2×10−2 Ω−1 has been demonstrated. The Al films show a discrete jump in differential sheet conductivity associated with Al cluster coalescence during growth.

Phosphine adsorption and the production of phosphide phases on Cu(001)

Abstract The adsorption and thermal decomposition of PH 3 on a Cu(0xa00xa01) surface has been investigated by means of high-resolution helium atom scattering, Auger electron spectroscopy and temperature programmed desorption. Phosphine adsorption at T x 3 , and desorption of hydrogen between T x =250 K and T x =320 K. Molecular phosphine was not seen to desorb. Phosphine deposition at room temperature or above produces well-ordered copper–phosphorus phases exhibiting either c(6×8) or c(6×6) diffraction patterns, depending upon the deposition conditions. Auger electron spectra indicate that these ordered phases contain approximately 1/3 ML or more of phosphorus. Possible atomic models for the overlayer structures are discussed.

Surface intercalation of graphite by lanthanum

Abstract Investigation of La - adsorption onto the (0001) graphite surface with following annealing was performed by AES and STM. It was shown that the low temperatre annealing leads to formation of La - carbide phase, and the high temperature annealing is followed by La - intercalated graphite formation. The C(KVV) Auger line of carbide shows the characteristic triplet structure. La - intercalated graphite is characterized by reconstruction of the surface crystalline structure and appearance in C(KVV) Auger spectra of the high energy feature connected with formation of the high density of states near the Fermi-level.

Oxidation induced stress in SiO2/SiC structures

Physical stress in SiO2/SiC stacks formed by the thermal oxidation of SiC is studied experimentally through both room temperature ex-situ and variable temperature (25–1150u2009°C) in-situ investigations. Mechanisms giving rise to the stress are a thermal component, associated with differences in thermal expansion coefficients of the oxide and the substrate, and an intrinsic component associated with the different atomic densities and structure of the film and substrate. Ex-situ results show a ∼108u2009Pa compressive stress in the SiO2 film in a SiO2/SiC stack with a strong crystal face dependence (C face(000ī) and Si face (0001)) and processing (temperature, growth rate) dependence. Real-time stress determination demonstrates that at temperatures above ∼900u2009°C, the total intrinsic stress and a portion of the thermal stress may be relieved. On the basis of these findings, a viscous model is proposed to discuss the stress relaxation.

Adsorption of PF3 on Cu(001): Ordered overlayer structures and frustrated translational modes

The adsorption of PF3 on Cu(001) was studied by means of high resolution helium atom scattering (HAS) and SPALEED. PF3 adsorbs at surface temperatures below 210 K and forms a lattice gas at exposures less than 0.8 L. Saturation is reached for exposures greater than 3 L. At these coverages PF3 forms an ordered c(4×2) layer for surface temperatures above 145 K. For temperatures below 145 K an incommensurate, hexagonal PF3 layer was observed that necessarily excludes uniquely on-top site PF3 molecule to surface coordination. A new vibrational mode in the thermal energy regime corresponding to the frustrated translation parallel to the surface was identified; the energies of excitation were 3.3 meV and 3.5 meV, respectively, for the isolated molecules and the c(4×2) structure. No dispersion of the frustrated translation in the ordered c(4×2) phase was found. The results are discussed in terms of adsorbate–adsorbate and adsorbate–substrate interactions.

Scanning tunneling microscope with large scan range

Abstract A new design is described for a scanning tunneling microscope (STM) intended for the detailed characterization of surfaces of industrial or technological interest. The instrument used was designed specifically for modern technology and precision engineering: large scan range (up to 200 μm lateral, 12 μm vertical) at low operating voltage (below 300 V), operation in ambient air, automated and computerized control.

Device for direct writing and reading-out of information based on the scanning tunneling microscope

Abstract A scanning tunneling microscope has been applied to the microprocessing of nanometer-sized craters in gold films on flat silicon substrates by mechanically driving the STM tip into the surface. It has been shown that reproducible nanometer-scale modifications of the surface in air are possible. The compact device (100 × 100 × 20 mm 3 ) for writing as well as for reading-out of the information bits, using a direct indentation principle, has been designed for data storage. The developed device is based on a small STM with a large scanning area (≈ 400 × 400 μm 2 ) to provide easy operation for both tip and small-size interchangeable memory diskettes. With an average craters diameter and spacing of 300 A an available memory of 10 MB per diskette can be obtained with a surface information density of about 10 10 bits/cm 2 .