ABSTRACT
Mg doping of GaAs nanowires has been established as a viable alternative to Be doping in order to achieve p-type electrical conductivity. Although reports on the optical properties are available, few reports exist about the physical properties of intermediate-to-high Mg doping in GaAs nanowires grown by molecular beam epitaxy (MBE) on GaAs(111)B and Si(111) substrates. In this work, we address this topic and present further understanding on the fundamental aspects. As the Mg doping was increased, structural and optical investigations revealed: i) a lower influence of the polytypic nature of the GaAs nanowires on their electronic structure; ii) a considerable reduction of the density of vertical nanowires, which is almost null for growth on Si(111); iii) the occurrence of a higher WZ phase fraction, in particular for growth on Si(111); iv) an increase of the activation energy to release the less bound carrier in the radiative state from nanowires grown on GaAs(111)B; and v) a higher influence of defects on the activation of nonradiative de-excitation channels in the case of nanowires only grown on Si(111). Back-gate field effect transistors were fabricated with individual nanowires and the p-type electrical conductivity was measured with free hole concentration ranging from 2.7 × 1016 cm-3 to 1.4 × 1017 cm-3. The estimated electrical mobility was in the range ≈0.3-39 cm2/Vs and the dominant scattering mechanism is ascribed to the WZ/ZB interfaces. Electrical and optical measurements showed a lower influence of the polytypic structure of the nanowires on their electronic structure. The involvement of Mg in one of the radiative transitions observed for growth on the Si(111) substrate is suggested.
ABSTRACT
Describir los hallazgos del ECG en mayores de 18 años con síncope al ingreso a urgencias, entre junio 1 de 2012 y junio 1 de 2013 en el Hospital de San José de Bogotá DC. Materiales y métodos: estudio de corte transversal retrospectivo con datos de variables sociodemográficas clínicas y hallazgos del ECG reportados en forma independiente por un médico de urgencias y un cardiólogo. Resultados: 60 pacientes cumplieron los criterios según las guías de la Sociedad Europea de Cardiología. Los hallazgos del ECG más frecuentes fueron cambios del intervalo QT (11.7%), bradicardia sinusal (6.7%), bloqueo bifascicular (5%), bloqueo aurículo ventricular de segundo grado (1.7 %), taquicardia ventricular no sostenida (1.7 %), ondas Q sugestivas de necrosis miocárdica (1.7 %) y otros cambios (20%). La concordancia entre médico general versus cardiólogo fue 41.5%. Conclusión: la edad mediana y el género son similares a los reportados en otros estudios, pero hay notoria diferencia en la interpretación del ECG entre el médico de urgencias y el cardiólogo, lo cual puede cambiar el pronóstico y aumentar la probabilidad de desenlaces negativos.Abreviaturas: ECG, electrocardiograma(s)...
To describe the initial electrocardiogram (ECG) findings in emergency room (ER) patients aged 18 years or more with syncope, between June 1 2012 and June 1 2013 at Hospital de San José, Bogotá DC. Materials and Methods: cross-sectional, retrospective study with data on clinical socio-demographic variables and ECG findings reported independently by an ER physician and a cardiologist. Results: the European Society of Cardiology criteria were met by 60 patients. The most common ECG findings include: QT interval changes (11.7%), sinus bradycardia (6.7%), bifascicular block (5%), grade II atrioventricular block (1.7 %), nonsustained ventricular tachycardia (1.7 %), Q waves suggestive of myocardial necrosis (1.7 %) and other changes (20%). Concordance between the general practitioner and the cardiologist was 41.5%. Conclusion: the median for age and gender are similar to those reported in other studies, but there is a significant difference between the ER physician and the cardiologist ECG interpretation which may change the prognosis and increase the risk for adverse outcomes...
