We reveal the existence of two different
crystalline phases, i.e.,
the metastable rock salt and the equilibrium zinc blende phase within the CdS-shell of PbS/CdS core/shell
nanocrystals formed by cationic exchange. The chemical composition
profile of the core/shell nanocrystals with different dimensions is
determined by means of anomalous small-angle X-ray scattering with
subnanometer resolution and is compared to X-ray diffraction analysis.
We demonstrate that the photoluminescence emission of PbS nanocrystals
can be drastically enhanced by the formation of a CdS shell. Especially,
the ratio of the two crystalline phases in the shell significantly
influences the photoluminescence enhancement. The highest emission
was achieved for chemically pure CdS shells below 1 nm thickness with
a dominant metastable rock salt phase fraction matching
the crystal structure of the PbS core. The metastable phase fraction
decreases with increasing shell thickness and increasing exchange
times. The photoluminescence intensity depicts a constant decrease
with decreasing metastable rock salt phase fraction
but shows an abrupt drop for shells above 1.3 nm thickness. We relate
this effect to two different transition mechanisms for changing from
the metastable rock salt phase to the equilibrium zinc blende phase depending on the shell thickness.
Midinfrared electroluminescence of epitaxial PbTe quantum dots in CdTe with emission in the 2–3 μm wavelength range is demonstrated up to room temperature. The light-emitting diode structures were grown by molecular beam epitaxy with the active PbTe quantum dots embedded in the intrinsic zone of a CdTe/CdZnTe p-i-n junction on GaAs (100) substrates. The current and temperature dependences of the electroluminescence emission are presented. The comparison with photoluminescence measurements shows that midinfrared light-emission from the diodes originates from the quantum dots.
Customized 2D wires are designed for high throughput electromigration testing on model Al and Cu thin films. Two direct writing approaches for defining the 2D wires are compared with photolithography. Electromigration effects on Al and Cu thin films are studied on 2D wires obtained applying both methods. A self‐developed four‐point probe is used to apply current through the test wires while measuring the potential drop along the wires. Photolithography is selected as the main method to outline the wires in order to have reproducible results in a high throughput manner. The errors of electromigration assessment are empirically evaluated by analyzing the data scattering for a large number of measured 2D wires. Inductively coupled plasma optical emission spectrometry (ICP‐OES) is performed on the photoresist removal solution before and after the lift‐off process. No traces of metallic elements are detected in both cases confirming the proposed mechanism.
Ultraviolet (UV) Nanoimprint Lithography (NIL) is a replication method that is well known for its capability to address a wide range of pattern sizes and shapes. It has proven to be an efficient production method for patterning resist layers with features ranging from a few hundred micrometers and down to the nanometer range. Best results can be achieved if the fundamental behavior of the imprint resist and the pattern filling are considered by the equipment and process parameters. In particular, the material properties and pattern size and shape play a crucial role. For capillary force-driven filling behavior it is important to understand the influencing parameters and respective failure modes in order to optimize the processes for reliable full wafer manufacturing. In this work, the nanoimprint results obtained for different pattern geometries are compared with respect to pattern quality and residual layer thickness: The comprehensive overview of the relevant process parameters is helpful for setting up NIL processes for different nanostructures with minimum layer thickness.
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