Highly selective photoenhanced wet etching of GaN for defect investigation and device fabrication

ABSTRACTPhotoenhanced electro-chemical (PEC) wet etching has been shown to be suitable for dislocation-density estimation in n-GaN films as well as for GaN-based device fabrication. We report on PEC etching of n-GaN samples grown by MBE and HVPE methods in unstirred aqueous KOH solution under He-Cd laser illumination. Characterization of the etched samples was carried out using atomic force microscopy (AFM) in both cross-sectional and plan-view configurations and scanning electron microscopy (SEM). At moderate illumination densities, the SEM and AFM analyses reveal sub-100 nm scale threading vertical wires on the etched surfaces. The calculated density (∼1×10 9cm−2) is in agreement with dislocation density found by transmission electron microscopy. Using cross-sectional AFM, we find that these vertical wires are ∼1[.proportional]m high and are perpendicular to the sapphire surface. Applying a higher illumination density or an external voltage, we obtain a higher etch rate with a smooth free-feature etched surface. Some highly resistive samples that cannot be etched under normal conditions because the band bending is too small to confine the holes to the surface for them to participate in the PEC process, can be etched with the application of a voltage to the sample. In this case, the etch rate depends on both the polarity and the magnitude of the voltage applied. In an MBE-grown sample with an AlN/GaN superstructure inside, we report on high selectivity between AlN and GaN (AlN is an etch stop); the selectivity is due to the etching mechanism of the PEC process

Vampires in the village Žrnovo on the island of Korčula: following an archival document from the 18th century

Središnja tema rada usmjerena je na raščlambu spisa pohranjenog u Državnom arhivu u Mlecima (fond: Capi del Consiglio de’ Dieci: Lettere di Rettori e di altre cariche) koji se odnosi na događaj iz 1748. godine u korčulanskom selu Žrnovo, kada su mještani – vjerujući da su se pojavili vampiri – oskvrnuli nekoliko mjesnih grobova. U radu se podrobno iznose osnovni podaci iz spisa te rečeni događaj analizira u širem društvenom kontekstu i prate se lokalna vjerovanja.The main interest of this essay is the analysis of the document from the State Archive in Venice (file: Capi del Consiglio de’ Dieci: Lettere di Rettori e di altre cariche) which is connected with the episode from 1748 when the inhabitants of the village Žrnove on the island of Korčula in Croatia opened tombs on the local cemetery in the fear of the vampires treating. This essay try to show some social circumstances connected with this event as well as a local vernacular tradition concerning superstitions

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Study and Characterization of Low-Pressure AsH\u3csub\u3e3\u3c/sub\u3e Cracking Cells in Gas Source MBE: Growth of GaAs and AlGaAs Epitaxy

MBE growth of GaAs and AlGaAs layers with good surface morphology and reasonably good PL spectral response has been achieved using two versions of a low-pressure, Calawa-type AsH3 cracker (long-quartz-tube containing a filamentary Ta catalyst) which produced predominately As4 and As2 and smaller concentrations of As1 for the MBE growth. Quadruple mass analyzer measurements of the cracking patterns and the As4, As2, and As1 molecular species produced by the gas cracking furnaces are also reported

Study and Characterization of Low-Pressure AsH\u3csub\u3e3\u3c/sub\u3e Cracking Cells in Gas Source MBE: Growth of GaAs and AlGaAs Epitaxy

MBE growth of GaAs and AlGaAs layers with good surface morphology and reasonably good PL spectral response has been achieved using two versions of a low-pressure, Calawa-type AsH3 cracker (long-quartz-tube containing a filamentary Ta catalyst) which produced predominately As4 and As2 and smaller concentrations of As1 for the MBE growth. Quadruple mass analyzer measurements of the cracking patterns and the As4, As2, and As1 molecular species produced by the gas cracking furnaces are also reported

Determination of Defect Pair Orientation in ZnO

The orientation of defect pairs with respect to the crystallographic axes was determined in ZnO. In a specific orientation of the strain with respect to the c axis of the crystal and the k-vector, the defect pair emission lines split, owing to combined strain and spin exchange. The polarization of the split components combined with knowledge of the specific orientation of the crystal and the k-vector allows one to determine the orientation of the defect pairs in the crystal. (C) 1999 Elsevier Science Ltd. All rights reserved

Determination of Defect Pair Orientation in ZnO

The orientation of defect pairs with respect to the crystallographic axes was determined in ZnO. In a specific orientation of the strain with respect to the c axis of the crystal and the k-vector, the defect pair emission lines split, owing to combined strain and spin exchange. The polarization of the split components combined with knowledge of the specific orientation of the crystal and the k-vector allows one to determine the orientation of the defect pairs in the crystal. (C) 1999 Elsevier Science Ltd. All rights reserved