A. Piotrowska

Fundamental and practical aspects of alloying encapsulated gold-based contacts to GaAs

Abstract Au/GaAs and Au(Zn)/GaAs protected with either SiO 2 or Al 2 O 3 overlayers were alloyed at temperatures of 400–500°C. Rutherford backscattering spectrometry, secondary ion mass spectrometry, scanning electron microscopy and X-ray diffraction show that the extent of interaction expressed in terms of the amount of gallium in the metal or the total volume of decomposed GaAs is reduced by a factor of 20 or more compared with unprotected contacts. A lower specific resistance of (SiO 2 )Au/Zn/Au ohmic contacts to p-GaAs is obtained over a wider range of processing temperatures. Also, the morphology of both the surface and the interface of the contact is significantly improved. The observed effects of encapsulation made it possible to formulate a revised model of interaction between gold and GaAs when annealed in the conventional open-system configuration. It is postulated that gold does not react directly with GaAs. The primary process responsible for decomposition of the semiconductor is the enhanced evaporation of arsenic through the metallic layer. Rapid reaction of the released gallium with gold is a secondary process which can be substantially limited by preventing the loss of arsenic.

Ohmic Contact to n-GaN with TiN Diffusion Barrier

The formation of n-GaN/Ti ohmic contacts with TiN diffusion barriers has been investigated by electrical measurements, x-ray diffraction and SIMS. It has been shown that the onset of the ohmic behaviour is associated with the thermally induced phase transformation of Ti into TiN at the GaN/Ti interface. It is suggested that the process is accompanied by an increase in the doping level in the semiconductor subcontact region. The presence of a TiN barrier is found to inhibit excessive decomposition of GaN and to confine the reaction between n-GaN and Ti.

Characterization of insomnia in patients with essential hypertension.

Introduction. Insomnia may increase risk of cardiovascular events. There is little data available reporting the prevalence and clinical relevance of insomnia in patients with essential hypertension. Therefore, the aim of the study was to investigate the relationship between insomnia and different clinical and biochemical parameters in essential hypertension patients. Methods. Four hundred and thirty‐two patients (mean age: 47±13 years; 253 male, 179 female) with essential hypertension were screened for insomnia using the Athens Insomnia Scale (AIS). Several variables including age, sex, known duration of hypertension, body mass index, creatinine, left ventricular mass index, coexisting disorders, smoking status and alcohol use were analysed. Twenty‐four‐hour ambulatory blood pressure measurements (ABPM) were performed. Results. Among patients included in the study, 207 subjects (mean age: 49±13 years; 47.9%) had an AIS score of 15 or higher and were identified as insomniacs. Insomnia was more frequent in women than in men (60.9% vs 38.7%, p<0.001) and was reported more frequently in patients with coronary artery disease. Subjects with insomnia were older and had longer duration of hypertension. There were no differences between insomniacs and non‐insomniacs in ABPM parameters. A relationship was found between the number of antihypertensive drugs and insomnia frequency. There were correlations between AIS score and age (r = 0.21; p<0.001) and duration of hypertension (r = 0.22; p<0.001). In the sub‐group of untreated essential hypertension patients, there were negative correlations between AIS score and night fall in systolic and diastolic blood pressure. Conclusion. Our results showed that insomnia is common in patients with essential hypertension and indicate an association between insomnia and gender, known duration of hypertension and number of antihypertensive drugs taken. Untreated essential hypertension insomniacs were characterized by less pronounced nocturnal fall in both systolic and diastolic blood pressure compared with non‐insomniacs.

On the nature of heart rate variability in a breathing normal subject: A stochastic process analysis.

Human heart rate is moderated by the autonomous nervous system acting predominantly through the sinus node (the main cardiac physiological pacemaker). One of the dominant factors that determine the heart rate in physiological conditions is its coupling with the respiratory rhythm. Using the language of stochastic processes, we analyzed both rhythms simultaneously taking the data from polysomnographic recordings of two healthy individuals. Each rhythm was treated as a sum of a deterministic drift term and a diffusion term (Kramers-Moyal expansion). We found that normal heart rate variability may be considered as the result of a bidirectional coupling of two nonlinear oscillators: the heart itself and the respiratory system. On average, the diffusion (noise) component measured is comparable in magnitude to the oscillatory (deterministic) term for both signals investigated. The application of the Kramers-Moyal expansion may be useful for medical diagnostics providing information on the relation between respiration and heart rate variability. This interaction is mediated by the autonomous nervous system, including the baroreflex, and results in a commonly observed phenomenon--respiratory sinus arrhythmia which is typical for normal subjects and often impaired by pathology.

Gold-based ohmic contacts on III–V compounds: Thermally induced reactions between metallization and the semiconductor compound☆

Au/Zn/Au and Auue5f8Be layers were used to prepare ohmic contacts on p-type GaAs, GaP and InP. Rutherford backscattering spectrometry with 2 MeV He+ ions, secondary ion mass spectrometry, X-ray diffraction analysis and scanning electron microscopy were used to study the thermally induced reactions accompanying the formation of ohmic contacts. A change in the ohmic behaviour in the sequence GaAs, InP, GaP occurred upon heating. A marked ability of the group III element in the semiconductor substrate to react with gold appeared to be a common feature of the systems investigated. No reaction product involving the group V element was observed in contacts on GaAs and GaP, whereas the Au2P3 phase was identified in contacts on InP. The zinc dopant was found to form the intermetallic phases AuZn and Au3Zn with gold, and an increase in the content of the beryllium dopant resulted in the retardation of the metal-semiconductor reaction.

Sleepwalking episodes are preceded by arousal-related activation in the cingulate motor area: EEG current density imaging

OBJECTIVEnTo investigate local arousal fluctuations in adults who received ICSD-2 diagnosis of somnambulism.nnnMETHODSnEEG neuroimaging (eLORETA) was utilized to compare current density distribution for 4s epochs immediately preceding sleepwalking episode (from -4.0 s to 0 s) to the distribution during earlier 4s epochs (from -8.0 s to -4.0 s) in 20 EEG segments from 15 patients.nnnRESULTSnComparisons between eLORETA images revealed significant (t>4.52; p<0.05) brain activations before onset of sleepwalking, with greater current density within beta 3 frequency range (24-30 Hz) in Brodmann areas 33 and 24.nnnCONCLUSIONSnSleepwalking motor events are associated with arousal-related activation of cingulate motor area.nnnSIGNIFICANCEnThese results support the notion of blurred boundaries between wakefulness and NREM sleep in sleepwalking.

Sulfide treatment of GaSb surface: influence on the LPE growth of InGaAsSb/AlGaAsSb heterostructures

Abstract The influence of Na2S and (NH4)2S treatments on the surface properties of GaSb have been investigated through the etch rate, ellipsometry and Schottky barrier measurements. XRD and TEM analysis were performed to examine the effect of sulfide pretreatment of GaSb substrate on the LPE growth of InGaAsSb/AlGaAsSb heterostructures and their structural quality. Additionally, C–V characteristic of Hg-Schottky barriers were measured to evaluate carrier concentrations in non-intentionally doped InGaAsSb epilayers. Na2S preepitaxial treatment has been applied to LPE growth of n-In0.084Ga0.916As0.086Sb0.914/p-Al0.45Ga0.55As0.02Sb0.98 LED heterostructures for λp=2.06xa0μm and n-In0.23Ga0.77As0.18Sb0.82/p-Al0.24Ga0.76As0.02Sb0.98 PD heterostructures for wavelength λ=2.0–2.4xa0μm. As a result, LEDs which with increased by a factor of 4 quantum efficiency and total power of 6xa0mW were obtained. Mesa-structure photodiodes were characterised by detectivity D ∗ λ=2.2 μm =4×1010xa0cmHz1/2xa0W−1 at room temperature and dark current density jd=16xa0mA/cm2 at a reverse bias of −0.5xa0V.

Evolution of the microstructure of Au(Zn) metallization during formation of an ohmic contact to p-type GaAs

Abstract Structural processes occurring in thin Au(Zn) metallization during the formation of ohmic contact to p-type GaAs have been investigated by X-ray diffraction, secondary-ion mass spectrometry, transmission electron microscopy and high resolution electron microscopy. In order to examine the release of arsenic during thermal processing, a thin film collector method was applied. Emphasis was placed on the particular role of each of metallization constituents during consecutive stages of the formation of an ohmic contact. Pure Zn was found to penetrate the native oxide on GaAs surface and to form an ohmic contact after annealing at 220°C. The addition of Zn into the Au metallization suppresses the thermally induced decomposition of GaAs and stabilizes the size of Au grains, forming the α 3 -AuZn phase. The most important aspect of the GaAsue5f8Au reaction is the formation of Ga vacancies in the subcontact region. They are required to form a low resistance ohmic contact to p-type GaAs, since the specific resistance of the Au(Zn) contact is one order of magnitude lower than that of the pure Zn contact.

On the Robust Parametric Detection of EEG Artifacts in Polysomnographic Recordings

We present an open, parametric system for automatic detection of EEG artifacts in polysomnographic recordings. It relies on independent parameters reflecting the relative presence of each of the eight types of artifacts in a given epoch. An artifact is marked if any of these parameters exceeds a threshold. These thresholds, set for each parameter separately, can be adjusted via “learning by example” procedure (multidimensional minimization with computationally intensive cost function), which can be used to automatically tune the parameters to new types of datasets, environments or requirements. Performance of the system, evaluated on 103 overnight polysomnographic recordings, revealed concordance with decisions of human experts close to the inter-expert agreement. To make this statement well defined, we review the methodology of evaluation for this kind of detection systems. Complete source code is available from http://eeg.pl; a user-friendly version with Java interface is available from http://signalml.org.

Solid pseudopapillary tumor of the pancreas (Frantz’s tumor): two case reports and a review of the literature

IntroductionSolid pseudopapillary tumor of the pancreas is extremely rare in children; it usually occurs in young women between 18 and 35xa0years of age. It comprises less than 3xa0% of pancreatic tumors. It is of low malignancy; however, it may be locally aggressive. Surgical resection is the treatment of choice and its prognosis is excellent.Case presentationTwo Caucasian girls, 15 and 12xa0years of age were diagnosed with tumor of the pancreas. The first patient had severe abdominal pain. In the second case the tumor was asymptomatic, detected incidentally during ultrasound. Computed tomography confirmed pancreatic mass. In the first case, apart from the tumor located in the head and the body of her pancreas, focal change in her right kidney was found, which was an indication to biopsy that confirmed solid pseudopapillary tumor. In the second patient the tumor was located in the body of her pancreas, with portal vein occlusion and well-developed collateral circulation. In the first patient a pancreatoduodenectomy (Traverso-Longmire) was performed; there was no mass in her right kidney. In the second case, distal pancreatectomy and splenectomy were performed. In both cases histopathology revealed solid pseudopapillary tumor resected radically. Our first patient’s postoperative course was uneventful. In the second case, her postoperative course was complicated by necrosis of the remaining pancreatic head that needed pancreatoduodenectomy. Follow-up at 28 and 26xa0months revealed no evidence of tumor recurrence or metastases on magnetic resonance imaging.ConclusionsTypical radiological appearance of solid pseudopapillary tumor is an indication for surgery. The treatment of choice is tumor resection with sparing of pancreatic tissue. In one of our two cases we performed a preoperative biopsy because of an uncharacteristic mass in her right kidney. In our second patient, necrosis of her spared pancreatic head meant that we could not preserve pancreatic tissue. Our whole diagnostic process, treatment and possible complications analysis should be of interest and noteworthy not only to surgeons as the treatment of choice is radical resection, but also to pediatric oncologists because of differentiation from other pancreatic tumors in children.