RESUMEN
A multi-microscopy investigation of a GaN tunnel junction (TJ) grown on an InGaN-based light emitting diode (LED) has been performed. The TJ consists of a heavily Ge-doped n-type GaN layer grown by ammonia-based molecular-beam epitaxy on a heavily Mg-doped p-type GaN thin layer, grown by metalorganic vapor phase epitaxy. A correlation of atom probe tomography, electron holography and secondary ion mass spectrometry has been performed in order to investigate the nm-scale distribution of both Mg and Ge at the TJ. Experimental results reveal that Mg segregates at the TJ interface, and diffuses into the Ge-doped layer. As a result, the dopant concentration and distribution differ significantly from the nominal values. Despite this, electron holography reveals a TJ depletion width of â¼7 nm, in agreement with band diagram simulations using the experimentally determined dopant distribution.
RESUMEN
Strain can alter the properties of semiconductor materials. The selection of a strain measurement technique is a trade-off between sensitivity, resolution, and field of view, among other factors. We introduce a new technique based on the degree of polarization of cathodoluminescence (CL), which has excellent sensitivity (10-5), an intermediate resolution (about 100 nm), and an adjustable field of view. The strain information provided is complementary to that obtained by CL spectroscopy. Feasibility studies are presented. The experimental setup and the data treatment procedure are described in detail. Current limitations are highlighted. The technique is tested on the cross section of bulk indium phosphide samples strained by a patterned hard mask.
RESUMEN
We report the study of a resonant bandpass filter made of a very thin subwavelength metal patch array coupled to a high index dielectric waveguide. The spectral properties of those filters can easily be tuned by playing on the lateral dimensions of the grating. They exhibit high and narrow transmission peaks together with very good rejection of light out of the pass-band and low angular dependance. An experimental demonstration using standard large scale silicon microelectronics processes is presented in the mid infrared spectral range. This concept of filters can easily be scaled throughout the optical spectrum, and can be integrated within focal plane arrays of various imaging technologies, down to visible wavelengths.
RESUMEN
We report here for the first time the combination of x-ray synchrotron light and a micro-electro-mechanical system (MEMS). We show how it is possible to modulate in real time a MEMS mass distribution to induce a nanometric and tunable mechanical oscillation. The quantitative experimental demonstration we present here uses periodic thermal dilatation of a Ge microcrystal attached to a Si microlever, induced by controlled absorption of an intensity modulated x-ray microbeam. The mechanism proposed can be envisaged either for the detection of small heat flux or for the actuation of a mechanical system.
RESUMEN
Cibenzoline is a new antiarrhythmic agent with class 1 properties, and additional class 3 and 4 effects. We treated 28 patients with drug-refractory and recurrent ventricular tachycardia with up to 700 mg/day cibenzoline for periods up to 5.5 months. Cibenzoline prevented the recurrence of ventricular tachycardia in five patients (18%). In three patients (11%) the arrhythmia may have been worsened, in 23 patients (82%) cibenzoline was ineffective. Cibenzoline increased the PR interval by 18% and the QRS duration by 33%; the effect on the QT was variable and the corrected QT interval did not change significantly. Side-effects were observed in 21% of patients. We conclude that cibenzoline does not appear to be superior to conventional class 1 antiarrhythmic agents and that it cannot be recommended for general use in patients with ventricular tachycardia. Additional pharmacokinetic and electrophysiologic studies are required before cibenzoline is used in outpatients with severe ventricular arrhythmias.