Ultra-high Vacuum Deposition Chamber Research Articles

Ultrahigh vacuum low temperature scanning tunneling microscope with ultrahigh vacuum deposition capability

An Omicron ultrahigh vacuum low temperature scanning tunneling microscope has been combined with an ultrahigh vacuum deposition chamber equipped with molecular beam sources and a rotatable liquid helium cooled sample holder. This configuration permits the growth of films and structures on either heated or cooled substrates with the possibility of subsequent study by scanning probe techniques at low temperatures without exposing them to air. The versatility of the fabrication process and the configuration of the equipment lends itself to easily exploring many physical systems. The apparatus has been used to investigate the electronic properties of metal clusters prepared using buffer layer assisted growth.

Tunneling spectroscopy in Fe-GaN-Fe trilayer structures grown by MBE using ECR microwave plasma nitrogen source

Epitaxy of Fe on GaAs by the MBE technique has a long tradition in magnetism research. This paper deals with the growth of epitaxial Fe–GaN–Fe trilayer structures whose intriguing magnetic properties were exploited for the evaluation of GaN as a spin-dependent tunneling barrier. The trilayers were grown on semi-insulating (0 0 1) GaAs using an ultra-high vacuum deposition chamber equipped with electron cyclotron resonance (ECR) microwave plasma nitrogen source.

Unusual crystallographic structure and its fluctuation of indium nanoparticles as-deposited and observed with HRTEM using the UHV-DC-TEM system

A UHV-DC-TEM system was developed for direct transportation of samples between an ultra-high vacuum deposition chamber (UHV-DC) and a UHV transmission electron microscope (UHV-TEM). Indium nanoparticles have been deposited onto Si(110) TEM samples at room temperature in UHV-DC and observed in UHV-TEM with high resolution transmission electron microscopy (HRTEM). Freshly made indium nanoparticles were found to be single, twinned, pseudo-twinned crystals and decahedral multiply-twinned particles (MTPs) with their size in the range 8–15 nm. The structure of single crystalline indium nanoparticles is body-centered tetragonal (bct), which is the same as that of bulk indium. In addition to the usual {011} type twins for bct structure, a pseudo-twin was observed to have an orientation relationship as [111] A//[100] B and (101̄) A//(01̄1̄) B. The structure of MTP indium is complicated because of the co-existence of bct and fcc structures within one nanocrystal. The structure fluctuation process has been examined using a video recorder with time scale down to 1/60 s. No complete liquid state was seen during this fluctuation.

Positive and negative low-energy ion beam deposition apparatus and applications

A dual ion beam deposition apparatus was newly developed. The machine consists of a positive ion beam line, a negative ion beam line and an ultra-high vacuum deposition chamber. The machine can generate mass-analyzed very low energy ion beams with positive and negative charges at the same time. Ion energy range covers 10 eV to 20 keV. It is possible to deposit these ions directly on a substrate not only simultaneously but also alternatively or independently. The machine has a wide possibility to fabricate such as ultra-pure materials or non- traditional materials. The machine is also useful to study fundamental processes of ion beam deposition and/or ion solid surface interactions. Using the new apparatus, isotopically pure carbon nitride (C x N y ) films were fabricated by simultaneous deposition of C − and N + ions. The ion energy was varied from 50 to 400 eV. The films were analyzed by Rutherford backscattering spectroscopy (RBS), Fourier transform infrared spectroscopy (FTIR) and Raman scattering. It was found that the maximum composition ratio (N/C) was about 0.9, the film structure was amorphous carbon-like and the amount of C-N triple bonds tended to decrease with decreasing nitrogen ion energy.

Oxygen as a surfactant in the growth of giant magnetoresistance spin valves

We have found a novel method for increasing the giant magnetoresistance (GMR) of Co/Cu spin valves with the use of oxygen. Surprisingly, spin valves with the largest GMR are not produced in the best vacuum. Introducing 5×10−9 Torr (7×10−7 Pa) into our ultrahigh vacuum deposition chamber during spin-valve growth increases the GMR, decreases the ferromagnetic coupling between magnetic layers, and decreases the sheet resistance of the spin valves. It appears that the oxygen may act as a surfactant during film growth to suppress defects and to create a surface which scatters electrons more specularly. Using this technique, bottom spin valves and symmetric spin valves with GMR values of 19.0% and 24.8%, respectively, have been produced. These are the largest values ever reported for such structures.

Thin Film Formation by Positive and Negative Ion Beams Simultaneously Irradiated Deposition.

A dual ion beam deposition apparatus was newly developed, which consists of a positive ion beam line, a negative ion beam line and an ultra-high vacuum deposition chamber. The machine can generate mass-analyzed very low energy ion beams with positive and negative charges at the same time with the ion energy range from 10 eV to 20 keV. It is possible to deposit both ions not only simultaneously but also alternatively. The machine has a wide possibility to fabricate ultra-pure materials or non-traditional materials, and is also useful to study fundamental processes of ion beam deposition and/or ion solid surface interactions. Using this new equipment, carbon nitride films were fabricated by simultaneous deposition of C- and N+ ions with the ion energy varying from 50 to 400 eV. The films were analyzed by Rutherford backscattering (RBS), Fourier Transform Infrared Spectroscopy (FTIR) and Raman scattering. It was found that the maximum composition ratio (N/C)c was about 0.9, the film structure was like amorphous carbon and the amount of C-N triple bonds tended to decrease with decreasing nitrogen ion energy.

Measurements of stress during vapor deposition of copper and silver thin films and multilayers

Copper and silver single layer and multilayered thin films were thermal vapor deposited onto cantilevered substrates [Si(100) with native oxide] near room temperature in ultrahigh vacuum. The total force per unit width (F/w) in the film during and after deposition was determined from the change in substrate curvature measured in situ by a laser scanning technique. The intrinsic component of F/w was obtained by subtraction of the thermal component, which was obtained by measuring the product of the biaxial modulus of the film (Yf) and the difference in coefficients of thermal expansion of the substrate and the film (Δαs−f) while each sample was still in the ultra-high vacuum deposition chamber. For all samples, the measured value of YfΔαs−f was substantially lower than the calculated value based on the {111} biaxial modulus and the coefficients of thermal expansion of the bulk materials, even though x-ray diffraction indicated strong {111} film texture. During deposition, a general trend in F/w was found regardless of the initial surface material as long as a heterogeneous interface was formed: following an initial compressive transient, F/w goes through a broad tensile maximum, then decreases and eventually becomes net compressive. This work conclusively demonstrated the presence of a compressive component of F/w. The evolution of the general features is unaffected by stopping and then resuming deposition of the same material. When a Ag/Cu multilayer is deposited continuously or intermittently (i.e., with periods of time without deposition between deposition of each layer), the evolution of the features of F/w is different during deposition of Cu layers from that during deposition of Ag layers, but is the same for each Cu layer and each Ag layer. After deposition ends, F/w changes with time in the tensile direction regardless of whether the final F/w during deposition is tensile or compressive. This change is reversed upon further deposition of the same material and therefore is a surface change from a dynamic to a static configuration (not a bulk change such as grain growth). The magnitude of the change in F/w after deposition increases linearly with the thickness of the top layer (the layer that was most recently deposited). The (111) Ag/Cu interface stress was determined for the first time, to the best of our knowledge, based on measured discontinuities in F/w associated with interface formation during deposition of multilayers. These discontinuities were different for Cu onto Ag and Ag onto Cu, and were repeatably reproduced for each interface during continuous deposition of multilayered films. A value of −0.21±0.10 N/m was found for the (111) Ag/Cu interface stress. The sign (compressive) is significant; it is the same as that of earlier experimental determinations, but opposite to that of theoretical calculations. The absolute value of the interface stress is low due to the incomplete formation of each interface at the early stage of layer formation.