Atomic-scale study of the amorphous-to-crystalline phase transition mechanism in GeTe thin films.

The underlying mechanism driving the structural amorphous-to-crystalline transition in Group VI chalcogenides is still a matter of debate even in the simplest GeTe system. We exploit the extreme sensitivity of 57Fe emission Mössbauer spectroscopy, following dilute implantation of 57Mn (T½ = 1.5 min) at ISOLDE/CERN, to study the electronic charge distribution in the immediate vicinity of the 57Fe probe substituting Ge (FeGe), and to interrogate the local environment of FeGe over the amorphous-crystalline phase transition in GeTe thin films. Our results show that the local structure of as-sputtered amorphous GeTe is a combination of tetrahedral and defect-octahedral sites. The main effect of the crystallization is the conversion from tetrahedral to defect-free octahedral sites. We discover that only the tetrahedral fraction in amorphous GeTe participates to the change of the FeGe-Te chemical bonds, with a net electronic charge density transfer of ~ 1.6 e/a0 between FeGe and neighboring Te atoms. This charge transfer accounts for a lowering of the covalent character during crystallization. The results are corroborated by theoretical calculations within the framework of density functional theory. The observed atomic-scale chemical-structural changes are directly connected to the macroscopic phase transition and resistivity switch of GeTe thin films.

Solid-state dewetting of ultra-thin Au films on SiO2 and HfO2.

Ultra-thin Au films with thickness (h) ranging from 0.5 to 6.0 nm were deposited at room temperature (RT) by means of e-beam evaporation on SiO2 and HfO2. Due to the natural solid-state dewetting (SSD) of the as-deposited films, Au nanoparticles (NPs) were formed on the substrates. By properly adjusting the h value, the size and the density of the Au NPs can be finely tuned. For h = 0.5 nm, spherical-like Au NPs with diameter below 5 nm and density in the order of 10(12) Au NPs cm(-2) were obtained without any additional thermal treatment independently from the substrate. The dependence of the Au NPs characteristics on the substrate starts to be effective for h ≥ 1.0 nm where the Au NPs diameter is in the 5-10 nm range and the density is around 10(11) Au NPs cm(-2). The effect of a subsequent high temperature (400-800 °C) annealing in N2 atmosphere on the Au NPs was investigated as well. For h ≤ 1.0 nm, the Au NPs characteristics evidenced an excellent thermal stability. Whereas the thermal treatment affects the cristallinity of the Au NPs. For the thicker films (2.0 ≤ h ≤ 6.0 nm), the thermal treatment becomes effective to induce the SSD. The proposed methodology can be exploited for the synthesis of Au NPs with diameter below 10 nm on different substrates at RT.

Si nanocrystal synthesis in HfO2/SiO/HfO2 multilayer structures.

The synthesis of two-dimensional arrays of Si nanocrystals in an HfO2 matrix has been achieved by deposition of HfO2/SiO/HfO2 multilayer structures followed by high temperature (1100 degrees C) thermal treatment in nitrogen atmosphere. Silicon out-diffusion from the SiO layer through the HfO2 films has been shown to be the limiting factor in the formation of the Si nanocrystals. Suitable strategies have been identified in order to overcome this limitation. Si nanocrystal formation has been achieved by properly adjusting the thickness of the SiO layer.

[Local effects and changes in wound drainage in the free peritoneal cavity]. / Lokale Auswirkungen und Veränderungen von Wunddrainagen in der freien Bauchhöhle.

In a prospective randomised study 30 mongrel rabbits received two standard colon-resections. Three types of drains were tested: (latex-rubber-) Penrose-drains, rubbertube- and silicontube-drains, which were placed in the lower abdomen. As a closed drainage-system the extraperitoneal tip of the drain was placed in a closed subcutis-pocket. One of the two colon-anastomoses also was drained. The findings were recorded on the 7th postoperative day. A single mechanic alteration was found, an ulcer caused by a silicon-drain, that pushed against the abdominal wall. The other signs of mechanic irritation were microscopically unspecified inflammatory reactions to the foreign body drain. There was no ascending infection caused by the drain. All infections came from complications of the colon resections. In contrast to common opinions the drains in the lower abdomen showed no adhesions to the abdominal wall or organs. Only the entrance of the drain into the peritoneum and the cotton-gaze of Penrose-drains showed in nearly all cases adhesions. The large amount of adhesions to the anastomosis-drains came from complications of the colon-anastomoses. As a cause of material, rubber- and latex-rubber-drains showed large fibrin-clots on their surfaces. 7 days after the operation only about 20% of the drains had sufficient function. The rest was occluded by fibrin-clots in the lumen of the drain or the cotton-gaze. Over all there is no difference in changes and effects of the three different types of drains, but silicon as material showed advantages.

[Can the diffractive multifocal posterior chamber lens be implanted in routine lens implantation?]. / Kann die diffraktive multifokale Hinterkammerlinse als Routinelinse implantiert werden?

Three different types of diffractive IOLs were implanted in the eyes of 140 patients who were followed up for 2 years. The latest follow-up included: near and distance visual acuity, glare and low-contrast visual acuity. We ask the patients when they wear glasses. All patients with the most advanced model of diffractive IOL obtained full visual acuity in far and near distance without additional correction. More then 50% of the patients only use glasses rarely. The glare visual acuity was not statistically different compared to patients with standard IOLs. Also, low-contrast acuity was no different.

[Clinical results after implantation of a multifocal diffractive posterior chamber lens]. / Klinische Ergebnisse nach Implantation einer multifokalen diffraktiven Hinterkammerlinse.

45 diffractive multifocal posterior chamber lenses were implanted in 41 patients. The follow-up time amounted to 12 months. With one correction good visual acuity for far and as well as near distances could be achieved. A significant loss of visual acuity with glare and low contrast and of contrast sensitivity was observed. Future has to show whether the advantages of this multifocal PCL will equal the disadvantages to the modern standard PMMA-PCL.

[Implantation of folding posterior chamber lenses]. / Implantation faltbarer Hinterkammerlinsen.

The implantation of foldable intraocular lenses (IOL) takes advantages of the benefit of small incision cataract surgery provided by phacoemulsification. However, even experienced surgeons may find the new implantation techniques required initially difficult. Advantages of small incision techniques include maintaining stability of the globe during surgery, especially in the case of acute IOP elevation caused by choroidal effusion or expulsive hemorrhage, as well as improved postoperative healing. Small incision surgery minimizes induced astigmatism, to less than 1.0 dpt change. Therefore, the patients physical and visual rehabilitation can be accelerated. Soft IOL's composed of p-HEMA or Silicone materials have been investigated for the past ten years and appear to be well biocompatible. The p-HEMA lens most often implanted is the IO-GEL, manufactured by Alcon. 120 p-HEMA IOL's were implanted in our clinic over the past 2 years. Our experiences with this foldable IOL are reported.

[Tonography and fluorophotometry in the clinical study of aqueous humor dynamics]. / Tonographie und Fluorophotometrie zur klinischen Untersuchung der Kammerwasserdynamik.

We used Grant's tonography and fluorophotometry (the Jones and Maurice method) to study the aqueous humor dynamics in normal and glaucomatous eyes. The results of the two methods were compared. The mean facility and rate of aqueous flow in normal eyes were similar. In glaucomatous eyes the tonographic outflow facility (C-value) varied greatly, and the calculated rate of aqueous flow (F-value) also had a large standard deviation. To study the inflow rate, fluorophotometry is a more accurate method. Further calculation of uveoscleral flow and the "pseudofacility" from the tonographic F-value and fluorophotometric C-value was therefore of only limited accuracy.

Influence of imipenem on the serum resistance of enterobacteriaceae.

Following growth in a subinhibitory concentration of imipenem and additional incubation in a 20% dilution of normal human serum (NHS) for 90 minutes, five of 12 serum-resistant strains of enterobacteriaceae showed a decrease in colony-forming units of two or more logs of growth compared with the control. Two strains (of Escherichia coli and Enterobacter aerogenes) showed this phenomenon even with incubation in 5% NHS. Treatment with imipenem did not change the serum resistance of the other seven strains (two strains each of Enterobacter cloacae, Klebsiella pneumonia, and Serratia marcescens, and one strain of Proteus morganii). The phenomenon of induced serum susceptibility is dose dependent and reversible. Other beta-lactam antibiotics either caused only a slight decrease of resistance (cefsulodin, cefoxitin, cefuroxime, cefodizime-HR221) or did not influence the serum resistance at all (cefotaxime, mecillinam). Killing of the induced serum-sensitive strains appeared to be antibody dependent.