Bibliothek

Notizen: We have studied the influence of difference growth conditions on the two-dimensional to three-dimensional growth mode transition for a specific class of InGaAs/GaAs quantum dots (QDs) optimized for applications to optical devices operating around 1.3 μm (In content x(approximate)0.5). The dots are grown by low-pressure metalorganic chemical vapor deposition on GaAs substrates. We demonstrate that the critical layer thickness corresponding to optimized single-QD layer structures (i.e., with reduced wetting layer thickness and high uniformity) can be controlled by kinetic effects. The optimized growth conditions allow us to grow six-layers stacked QD structures as active material for the fabrication of a light emitting devices operating around 1.3 μm at room temperature. © 2001 American Institute of Physics.

Notizen: The metalorganic vapor phase epitaxy growth of ZnTe by di-isopropyl-telluride and di-methyl-zinc (Me2Zn) precursors is investigated by studying the epilayer growth rate as a function of both growth temperature and precursor transport rates. The ZnTe growth is a thermally activated process involving the heterogeneous pyrolysis of both Zn and Te alkyls onto the ZnTe surface. The growth rate dependence on growth conditions is explained in terms of surface adsorption-desorption reactions, assuming that the incorporation of Zn and Te atoms into ZnTe takes place through their selective adsorption on different surface lattice sites. There is also evidence that the occurrence of a competitive species for the surface adsorption of Zn atoms, which is identified as the CH3⋅ (methyl) radical, is produced by the pyrolysis of Me2Zn. Photoluminescence (PL) and absorption measurements performed on ZnTe allow to identify two new donor-acceptor pair (DAP) bands, originated from the recombination of a Ga donor with two acceptor centers, whose ionization energies are 56 meV for the higher energy band and around 140–150 meV for the lower energy one. Hall measurements show that the 56 meV acceptor is responsible of the p-type conductivity of the layers. The nature of the impurities originating such PL features is discussed with the support of secondary ion mass spectrometry. It is shown that Ga, Si, and C are dominant impurities in the layers, whereas Cu does not occur in our ZnTe. Unintentional C doping occurs in ZnTe as a consequence of the strong methyl and iso-propyl radical surface adsorption. We show that C is incorporated as an acceptor in ZnTe, originating the DAP bands observed in the PL spectra. Within this view, the 56 meV ionization energy acceptor is tentatively assigned to substitutional C atoms on Te lattice sites. © 1997 American Institute of Physics.

Notizen: The Stransky–Krastanow metalorganic vapor phase epitaxy growth of self-organized ZnTe islands on homoepitaxial (001)GaAs is demonstrated. The −7.4% lattice mismatch of the ZnTe/GaAs heterostructure leads to a strain-driven distribution of nanoscale ZnTe islands on top of a two-dimensionally (2D) grown wetting layer. Atomic force microscopy and Rutherford backscattering spectrometry are used to determine the island dimensions and the thickness of the wetting layer. The density of the islands, their average diameter, and aspect ratio turn out to be about 520 μm−2, 13.6 nm, and 0.20, respectively, for a 1.2 ML thick 2D layer. Furthermore, the average aspect ratio of the islands decreases by increasing the thickness of the wetting layer, as expected by the progressive extinction of the strain-driven island nucleation. © 1998 American Institute of Physics.

Notizen: A previously healthy 71-year-old Caucasian woman presented with an ulcer on her left leg. She had a 5-month history of bilateral, indurated erythematous, and had purplish nodules and plaques on both lower extremities. One of the plaques on the right leg had ulcerated and healed spontaneously. The present ulceration began as a small opening at an incisional biopsy site. Later, she developed two adjacent ulcers that coalesced into a larger ulcer. She was not taking any medication, and there was no history of exposure to tuberculosis. Examination of the right leg demonstrated two hyperpigmented, indurated plaques, one on the calf and one over the medial malleolus. On the left posterior calf there was another hyperpigmented, indurated plaque with a central area of ulceration measuring 9 × 2 cm. The ulcer bed had a mixture of fibrinous adherent tissue and granulation tissue. (〈link href="#f15801"〉Fig. 1) There was no peripheral edema, varicose veins, nor signs of peripheral neuropathy. Peripheral pulses and capillary refilling were within normal limits. The ankle brachial index was greater than 1.0 bilaterally. Biopsy of a subcutaneous nodule revealed a superficial and deep perivascular lymphocytic infiltrate with an admixture of neutrophils and numerous extravasated red blood cells. Mixed septal and lobular panniculitis consisting of an inflammatory infiltrate of histiocytes, giant cells, and neutrophils was observed. Focal neutrophilic microabscesses in the deep dermis and fibrinoid necrosis of small blood vessels were present in the deep dermis and subcutaneous tissue (〈link href="#f15802 #f15803"〉Figs 2 and 3). A smear was negative for acid fast bacilli.〈figure xml:id="f15801"〉1〈mediaResource alt="image" href="urn:x-wiley:00119059:IJD1580:IJD_1580_f1"/〉A hyperpigmented, indurated plaque with a central area of ulceration measuring 9 × 2 cm on the left posterior calf. The ulcer bed has a mixture of fibrinous adherent tissue and granulation tissue〈figure xml:id="f15802"〉2〈mediaResource alt="image" href="urn:x-wiley:00119059:IJD1580:IJD_1580_f2"/〉A scanning magnification〈figure xml:id="f15803"〉3〈mediaResource alt="image" href="urn:x-wiley:00119059:IJD1580:IJD_1580_f3"/〉Mixed septal and lobular panniculitis consisting of an inflammatory infiltrate of histiocytes, giant cells, and neutrophils. Focal neutrophilic microabscesses in the deep dermis and fibrinoid necrosis of small blood vessels in the deep dermis and subcutaneous tissueA diagnosis of nodular vasculitis was made. A complete blood count with differential and platelets was within normal limits, tuberculin testing was negative twice, and antineutrophil cytoplasmic antibodies (p-ANCA, c-ANCA) were also negative. Fungal, mycobacterial and bacterial cultures were negative. Chest X-rays were normal.The patient received supersaturated potassium iodide (SSKI) 15 drops per day with good response. With rapid tapering of SSKI, the ulcerations on the lower legs reappeared. Therapy was reinstituted with a more gradual taper. Two years after the initial diagnosis of nodular vasculitis the patient presented with new complaints of increased urinary frequency, increased abdominal girth, and weight gain. The patient was found to be borderline anemic, and a computer tomography scan revealed ascites, a normal liver, a normal uterus, and a soft tissue density in the region of the cecum. After an exploratory laparotomy she was found to have a moderately differentiated mucinous adenocarcinoma of the colon with metastases to periaortic lymph nodes, abdominal wall, and both ovaries. She is currently receiving adjuvant chemotherapy for stage IV colon carcinoma. Only one lesion of nodular vasculitis has remained active, and the patient is continuing treatment with SSKI at a low dose.

Notizen: As morphological basis for experimental surgery on the rabbit the roots of the phrenic nerve in 15 male and 15 female rabbits of the Norfolk 2,000 breed were studied. In sketches made of the dissections the modes of origin of the phrenic roots were demonstrated to arise from the fourth to the seventh cervical nerves. Four types could be distinguished. The phrenic nerve of the rabbit may have two, three or four roots.

Notizen: Background : Although administration of gastroprotective drugs may reduce the risk of peptic ulcers associated with the chronic use of non-steroidal anti-inflammatory drugs or aspirin, no consensus exists as to whether this co-therapy is effective for short-term prevention, particularly in old age.Aim : To evaluate the risk of peptic ulcer associated with acute and chronic non-steroidal anti-inflammatory drugs or aspirin therapy in elderly subjects, and the influence of antisecretory treatment on this risk.Methods : The study included 676 elderly non-steroidal anti-inflammatory drugs or aspirin users and 2435 non-users who consecutively underwent upper gastrointestinal endoscopy. The use of non-steroidal anti-inflammatory drugs and/or aspirin as well as antisecretory drugs (H2-blockers and proton-pump inhibitors) was evaluated by a structured interview. Diagnosis of gastric and duodenal ulcer as well as Helicobacter pylori infection were carried out by endoscopy and histological examination of the gastric mucosa.Results : About 47.3% of patients were acute and 52.7% chronic users of non-steroidal anti-inflammatory drugs or aspirin. The risk of peptic ulcer, adjusted for age, gender, H. pylori infection and antisecretory drug use was higher in acute (gastric ulcer: odds ratio, OR =4.47, 95% CI: 3.19–6.26 and duodenal ulcer: OR =2.39, 95% CI: 1.73–3.31) than chronic users (gastric ulcer: OR = 2.80, 95% CI: 1.97–3.99 and duodenal ulcer: OR = 1.68, 95% CI: 1.22–2.33). Proton-pump inhibitor treatment was associated with a reduced risk of peptic ulcer in both acute (OR = 0.70, 95% CI: 0.24–2.04) and chronic (OR = 0.32, 95% CI: 0.15–0.67) non-steroidal anti-inflammatory drugs/aspirin users. Conversely, concomitant treatment with H2-blockers was associated with a significantly higher risk of peptic ulcer both in acute (OR = 10.9, 95% CI: 3.87–30.9) and chronic (OR = 6.26, 95% CI: 2.56–15.3) non-steroidal anti-inflammatory drugs/aspirin users than non-users. Proton-pump inhibitor treatment resulted in an absolute risk reduction of peptic ulcer by 36.6% in acute and 34.6% in chronic non-steroidal anti-inflammatory drugs/aspirin users; indeed, the number needed to treat to avoid one peptic ulcer in elderly non-steroidal anti-inflammatory drugs/aspirin users was three both in acute and chronic users.Conclusions : These findings suggest that proton-pump inhibitor co-treatment is advisable in symptomatic elderly patients who need to be treated with non-steroidal anti-inflammatory drugs and/or aspirin for a short period of time.