Role of gallium diffusion in the formation of a magnetically dead layer at the Y3Fe5O12/Gd3Ga5O12 epitaxial interface

We have clarified the origin of a magnetically dead interface layer formed in yttrium iron garnet (YIG) films grown at above 700 degrees C onto a gadolinium gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The diffusion-assisted formation of a Ga-rich region at the YIG/GGG interface is demonstrated by means of composition depth profiling performed by x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and x-ray and neutron reflectometry. Our finding is in sharp contrast to the earlier expressed assumption that Gd acts as a migrant element in the YIG/GGG system. We further correlate the presence of a Ga-rich transition layer with considerable quenching of ferromagnetic resonance and spin wave propagation in thin YIG films. Finally, we clarify the origin of the enigmatic low-density overlayer that is often observed in neutron and x-ray reflectometry studies of the YIG/GGG epitaxial system

Comparative evaluation of surgical methods for low invasive surgical treatment of diseases of the kidneys and urinary tract

Background. The rapid development of laparoscopic surgery can significantly reduce trauma during operations in the retroperitoneal space. These goals are also achieved by retroperitoneoscopy (RPS), which has become widespread in the last twenty years. The main difficulties for surgeons were associated with a small workspace and a lack of clear anatomical landmarks. Different access methods have different features, advantages and disadvantages, the analysis of which helps to optimize surgical treatment and accelerate patient rehabilitation.Aim: to study the advantages and disadvantages of retroperitoneoscopic and transperitoneal laparoscopic surgical methods of treatment.Materials and methods: We analyzed 305  case histories of patients operated on for various kidney diseases. The patients were divided into 2 groups: Group 1 – patients who underwent surgery using an extraperitoneal retroperitoneoscopic approach, Group 2 – patients who used the transperitoneal laparoscopic approach. A comparison of two methods of surgical treatment of kidney diseases, retroperitoneoscopic and laparoscopic access, was carried out. The following indicators were compared: duration of surgery, length of hospital stay, need for analgesics, frequency of postoperative complications.Results. The duration of the operation with retroperitoneoscopic surgery was reduced by more than 15 % compared with the laparoscopic approach. Shorter periods of pain relief were required, and the number of complications also decreased. The duration of inpatient treatment did not differ significantly.Conclusion. Retroperitoneoscopic approach can be used as the method of choice for operations on the retroperitoneal space

Calcium Fluoride Barrier Layer in Tunnel Emitter Phototransistor

Owing to the optimized growth technology of the 1-2 nm calcium fluoride films on n-(111)-silicon, metal/tunnel-insulator/semiconductor phototransistors have been fabricated by the molecular beam epitaxy at the temperature 250°C. The characteristics of these transistors were measured in a wide range of voltages, and the proofs for current gain were found throughout the investigated range. The gain value exceeds $10^3$ approaching the theoretically estimated value in this system. The stability and reproducibility of the device characteristics were satisfactory. The results support the candidacy of calcium fluoride for being a vital dielectric in silicon-based functional electronics

Initial stages of CaF2 growth and wetting layer formation on Si[001]

It has been recently found that different types of CaF2 nanostructures can be formed on Si[001] substrates depending on the growth conditions. Below 500°C, nearly square-shaped dots nucleate on bare Si[001] surface; above 650°C, at submonolayer coverage, a so-called "wetting layer" forms. At higher coverage, formation of CaF2 stripes of a few nanometers in height and width takes place on top of the wetting layer. Interestingly, CaF2 [001]∥Si[001] in the dots and CaF2 [110]∥Si[001] in the stripes. In this work, initial stages of CaF2 epitaxial growth on Si[001] were studied by atomic force microscopy and photoemission spectroscopy with emphasis on formation and chemical composition of the wetting layer

Calcium fluoride on Si(001): adsorption mechanisms and epitaxial growth modes

Growth of CaF2 on Si(001) is studied as a function of the substrate temperature during deposition for coverages from fraction of a monolayer (ML) up to several monolayers. Structural and morphological studies using atomic force microscopy, low-energy electron diffraction, and reflection high-energy electron diffraction are combined with measurements of core-level photoemission and x-ray absorption. Bonding between CaF2 molecules and Si(001) substrates is followed by monitoring core-level shifts and x-ray absorption line shape. It is found that a dissociative reaction occurs at high deposition temperatures (similar to 750 degrees C), giving rise to a 1-ML-thick uniform wetting layer, which is bonded with the substrate through Ca atoms. This wetting layer changes the surface periodicity from double domain 2x1+1x2 to single domain 3x1. Three-dimensional CaF2 elongated islands develop on top of the wetting layer, with their (110) planes parallel to the Si surface plane. At temperatures below 600 degrees C no dissociative reaction takes place for CaF2; nanodimensional islands develop in the form of rectangular-based huts. The crystallographic orientation of these islands is parallel to that of the Si(001) substrate. The data are compared to results obtained on CaF2 deposited on Si(111)