4 research outputs found
Room-Temperature Lasing from Monolithically Integrated GaAs Microdisks on Silicon
Additional functionalities on semiconductor
microchips are progressively important in order to keep up with the
ever-increasing demand for more powerful computational systems. Monolithic
IIIâV integration on Si promises to merge mature Si CMOS processing
technology with IIIâV semiconductors possessing superior material
properties, <i>e</i>.<i>g</i>., in terms of carrier
mobility or band structure (direct band gap). In particular, Si photonics
would strongly benefit from an integration scheme for active IIIâV
optoelectronic devices in order to enable low-cost and power-efficient
electronicâphotonic integrated circuits. We report on room-temperature
lasing from AlGaAs/GaAs microdisk cavities monolithically integrated
on Si(001) using a selective epitaxial growth technique called template-assisted
selective epitaxy. The grown gain material possesses high optical
quality without indication of threading dislocations, antiphase boundaries,
or twin defects. The devices exhibit single-mode lasing at <i>T</i> < 250 K and lasing thresholds between 2 and 18 pJ/pulse
depending on the cavity size (1â3 ÎŒm in diameter)
Fingerprinting electronic molecular complexes in liquid
Predicting the electronic framework of an organic molecule under practical conditions is essential if the
molecules are to be wired in a realistic circuit. This demands a clear description of the molecular energy
levels and dynamics as it adapts to the feedback from its evolving chemical environment and the surface
topology. Here, we address this issue by monitoring in real-time the structural stability and intrinsic
molecular resonance states of fullerene (C60)-based hybrid molecules in the presence of the solvent.
Energetic levels of C60 hybrids are resolved by in situ scanning tunnelling spectroscopy with an energy
resolution in the order of 0.1 eV at room-temperature. An ultra-thin organic spacer layer serves to limit
contact metal-molecule energy overlap. The measured molecular conductance gap spread is statistically
benchmarked against first principles electronic structure calculations and used to quantify the diversity
in electronic species within a standard population of molecules. These findings provide important
progress towards understanding conduction mechanisms at a single-molecular level and in serving as
useful guidelines for rational design of robust nanoscale devices based on functional organic molecules
Sub-10 Nanometer Feature Size in Silicon Using Thermal Scanning Probe Lithography
High-resolution
lithography often involves thin resist layers which
pose a challenge for pattern characterization. Direct evidence that
the pattern was well-defined and can be used for device fabrication
is provided if a successful pattern transfer is demonstrated. In the
case of thermal scanning probe lithography (t-SPL), highest resolutions
are achieved for shallow patterns. In this work, we study the transfer
reliability and the achievable resolution as a function of applied
temperature and force. Pattern transfer was reliable if a pattern
depth of more than 3 nm was reached and the walls between the patterned
lines were slightly elevated. Using this geometry as a benchmark,
we studied the formation of 10â20 nm half-pitch dense lines
as a function of the applied force and temperature. We found that
the best pattern geometry is obtained at a heater temperature of âŒ600
°C, which is below or close to the transition from mechanical
indentation to thermal evaporation. At this temperature, there still
is considerable plastic deformation of the resist, which leads to
a reduction of the pattern depth at tight pitch and therefore limits
the achievable resolution. By optimizing patterning conditions, we
achieved 11 nm half-pitch dense lines in the HM8006 transfer layer
and 14 nm half-pitch dense lines and L-lines in silicon. For the 14
nm half-pitch lines in silicon, we measured a line edge roughness
of 2.6 nm (3Ï) and a feature size of the patterned walls of
7 nm
Disorder-Induced Magnetotransport Anomalies in Amorphous and Textured Co<sub>1â<i>x</i></sub>Si<sub><i>x</i></sub> Semimetal Thin Films
In recent times the chiral semimetal cobalt monosilicide
(CoSi)
has emerged as a prototypical, nearly ideal topological conductor
hosting giant, topologically protected Fermi arcs. Exotic topological
quantum properties have already been identified in CoSi bulk single
crystals. However, CoSi is also known for being prone to intrinsic
disorder and inhomogeneities, which, despite topological protection,
risk jeopardizing its topological transport features. Alternatively,
topology may be stabilized by disorder, suggesting the tantalizing
possibility of an amorphous variant of a topological metal, yet to
be discovered. In this respect, understanding how microstructure and
stoichiometry affect magnetotransport properties is of pivotal importance,
particularly in case of low-dimensional CoSi thin films and devices.
Here we comprehensively investigate the magnetotransport and magnetic
properties of â25 nm Co1âxSix thin films grown on a MgO substrate
with controlled film microstructure (amorphous vs textured) and chemical
composition (0.40 x < 0.60). The resistivity
of Co1âxSix thin films is nearly insensitive to the film microstructure
and displays a progressive evolution from metallic-like (dÏxx/dT > 0) to semiconducting-like
(dÏxx/dT < 0)
regimes of conduction upon increasing the silicon content. A variety
of anomalies in the magnetotransport properties, comprising for instance
signatures consistent with quantum localization and electronâelectron
interactions, anomalous Hall and Kondo effects, and the occurrence
of magnetic exchange interactions, are attributable to the prominent
influence of intrinsic structural and chemical disorder. Our systematic
survey brings to attention the complexity and the challenges involved
in the prospective exploitation of the topological chiral semimetal
CoSi in nanoscale thin films and devices