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We present a novel bonding process for gallium nitride-based electronic devices on diamond heat spreaders. In the proposed technology, GaN devices are transferred from silicon (Si) onto single (SCD) and polycrystalline diamond (PCD) substrates by van der Waals bonding. Load-pull measurements on Si and SCD heat spreaders at 3 GHz and 50 V drain bias show comparable power-added-efficiency and output power (Pout) levels. A thermal analysis of the hybrids was performed by comparison of 2 × 1mm2 AlGaN/GaN Schottky diodes on Si, PCD, and SCD, which exhibit a homogeneous field in the channel in contrast to gated transistors. Significantly different currents are observed due to the temperature dependent mobility in the 2DEG channel. These measurements are supported by a 3D thermal finite element analysis, which suggests a large impact of our transfer technique on the thermal resistance of these devices. In summary, we show a promising new GaN-on-diamond technology for future high-power, microwave GaN device applications.
Group III nitrides are promising materials for light emitting diodes (LEDs). The occurrence of structural defects strongly affects the efficiency of these LEDs. We investigate the optical properties of basal plane stacking faults (BFSs), and the assignment of specific spectral features to distinct defect types by direct correlation of localized emission bands measured by cathodoluminescence in a scanning electron microscope with defects found in high resolution (scanning) transmission electron microscopy and electron beam induced current at identical sample spots. Thus, we are able to model the electronic structure of BSFs addressing I1, I2, and E type BSFs in GaN and AlGaN with low Al content. We find hints that BSFs in semipolar AlGaN layers cause local changes of the Al content, which strongly affects the usability of AlGaN as an electron blocking layer in nitride based LEDs.
We aimed to investigate whether changes in high-energy phosphate metabolism after treatment of children and young adults with anthracycline can be demonstrated non-invasively by 31P magnetic resonance spectroscopy.
Abnormal myocardial energy metabolism has been suggested as a mechanism for anthracycline-induced cardiotoxicity. Deterioration in such has been shown in animal studies by resonance spectroscopy.
We studied 62 patients, with a mean age of 13.5 ±5 years,3.7±4.3 years after a cumulative anthracycline dose of 270±137 mg/m2. Normal echocardiographic findings had been elicited in 54 patients. The control group consisted of 28 healthy subjects aged 20±7 years. Resonance spectrums of the anterior left ventricular myocardium were obtained at 1.5 Tesla using an image-selected in vivo spectroscopy localization technique.
The ratio of phosphocreatine to adenosine triphosphate after blood correction was 1.09±0.43 for the patients, and 1.36±0.36 (mean±SD)for controls (p = 0.005), with a significantly reducedmean ratio even in the subgroup of patients with normal echocardiographic results ( l.11 ± 0. 44 versus1.36±0.36, p=0.01). The ratio did not correlate with the cumulative dose of anthracycline. The ratio of phosphodiester to adenosine triphosphate was similar in patients and controls (0.90±0.56 versus 0.88±0.62).
In patients treated with anthracyclines in childhood, myocardial high-energy phosphate metabolism may be impaired even in the absence of cardiomyopathy. Our data support the concept that anthracycline-induced cardiotoxicity is not clearly dose dependent.
Aberration correctors using hexapole fields have proven useful to
correct for the spherical aberration in electron microscopy. We
investigate the limits of the present design for the hexapole corrector
with respect to minimum probe size for the scanning transmission electron
microscope and discuss several ways in which the design could be improved
by rather small and incremental design changes for the next generation of
advanced probe-forming systems equipped with a gun monochromator.
Planar defects in a polycrystalline diamond film were studied by
high-resolution transmission electron microscopy (HRTEM) and
high-resolution scanning transmission electron microscopy (STEM). In both
modes, sub-Ångström resolution was achieved by making use of
two aberration-corrected systems; a TEM and a STEM
CS-corrected microscope, each operated at 300 kV. For
the first time, diamond in 〈110〉 zone-axis orientation was
imaged in STEM mode at a resolution that allows for resolving the atomic
dumbbells of carbon at a projected interatomic distance of 89 pm. Twin
boundaries that show approximately the Σ3 CSL structure reveal at
sub-Ångström resolution imperfections; that is, local
distortions, which break the symmetry of the ideal Σ3 type twin
boundary, are likely present. In addition to these imperfect twin
boundaries, voids on the atomic level were observed. It is proposed that
both local distortions and small voids enhance the mechanical toughness of
the film by locally increasing the critical stress intensity factor.