111 research outputs found
Electromechanically Tunable Suspended Optical Nano-antenna
Coupling mechanical degrees of freedom with plasmonic resonances has
potential applications in optomechanics, sensing, and active plasmonics. Here
we demonstrate a suspended two-wire plasmonic nano-antenna acting like a
nano-electrometer. The antenna wires are supported and electrically connected
via thin leads without disturbing the antenna resonance. As a voltage is
applied, equal charges are induced on both antenna wires. The resulting
equilibrium between the repulsive Coulomb force and the restoring elastic
bending force enables us to precisely control the gap size. As a result the
resonance wavelength and the field enhancement of the suspended optical
nano-antenna (SONA) can be reversibly tuned. Our experiments highlight the
potential to realize large bandwidth optical nanoelectromechanical systems
(NEMS)
Unveiling the optical properties of a metamaterial synthesized by electron-beam-induced deposition
The direct writing using a focused electron beam allows for fabricating truly
three-dimensional structures of sub-wavelength dimensions in the visible
spectral regime. The resulting sophisticated geometries are perfectly suited
for studying light-matter interaction at the nanoscale. Their overall optical
response will strongly depend not only on geometry but also on the optical
properties of the deposited material. In case of the typically used
metal-organic precursors, the deposits show a substructure of metallic
nanocrystals embedded in a carbonaceous matrix. Since gold-containing precursor
media are especially interesting for optical applications, we experimentally
determine the effective permittivity of such an effective material. Our
experiment is based on spectroscopic measurements of planar deposits. The
retrieved permittivity shows a systematic dependence on the gold particle
density and cannot be sufficiently described using the common Maxwell-Garnett
approach for effective medium.Comment: 7 pages, 4 figure
Observation of strongly enhanced photoluminescence from inverted cone-shaped silicon nanostuctures
Silicon nanowires (SiNWs) attached to a wafer substrate are converted to
inversely tapered silicon nanocones (SiNCs). After excitation with visible
light, individual SiNCs show a 200-fold enhanced integral band-to-band
luminescence as compared to a straight SiNW reference. Furthermore, the
reverse taper is responsible for multifold emission peaks in addition to the
relatively broad near-infrared (NIR) luminescence spectrum. A thorough
numerical mode analysis reveals that unlike a SiNW the inverted SiNC sustains
a multitude of leaky whispering gallery modes. The modes are unique to this
geometry and they are characterized by a relatively high quality factor (Qâ~
1300) and a low mode volume (0.2â<â(λ/neff)3â<â4). In addition they show a
vertical out coupling of the optically excited NIR luminescence with a
numerical aperture as low as 0.22. Estimated Purcell factors FpâââQ/Vm of
these modes can explain the enhanced luminescence in individual emission peaks
as compared to the SiNW reference. Investigating the relation between the SiNC
geometry and the mode formation leads to simple design rules that permit to
control the number and wavelength of the hosted modes and therefore the
luminescent emission peaks
A Sub--Volume Cantilever-based Fabry-P\'erot Cavity
We report on the realization of an open plane-concave Fabry-P\'erot resonator
with a mode volume below at optical frequencies. We discuss some of
the less common features of this new microcavity regime and show that the
ultrasmall mode volume allows us to detect cavity resonance shifts induced by
single nanoparticles even at quality factors as low as . Being based on
low-reflectivity micromirrors fabricated on a silicon cantilever, our
experimental arrangement provides broadband operation, tunability of the cavity
resonance, lateral scanning and promise for optomechanical studies
InGaN/GaN multiquantum well nano-LEDs for a case study
The scattering in the light emission wavelength of semiconductor nano-emitters
assigned to nanoscale variations in strain, thickness, and composition is
critical in current and novel nanotechnologies from highly efficient light
sources to photovoltaics. Here, we present a correlated experimental and
theoretical study of single nanorod light emitting diodes (nano-LEDs) based on
InGaN/GaN multiquantum wells to separate the contributions of these intrinsic
fluctuations. Cathodoluminescence measurements show that nano-LEDs with
identical strain states probed by non-resonant micro-Raman spectroscopy can
radiate light at different wavelengths. The deviations in the measured optical
transitions agree very well with band profile calculations for quantum well
thicknesses of 2.07â2.72 nm and In fractions of 17.5â19.5% tightly enclosing
the growth values. The nanorod surface roughness controls the appearance of
surface optical phonon modes with direct implications on the design of phonon
assisted nano-LED devices. This work establishes a new, simple, and powerful
methodology for fundamental understanding as well as quantitative analysis of
the strain â light emission relationship and surface-related phenomena in the
emerging field of nano-emitters.1\. Auflag
A novel copper precursor for electron beam induced deposition
A fluorine free copper precursor, Cu(tbaoac)2 with the chemical sum formula CuC16O6H26 is introduced for focused electron beam induced deposition (FEBID). FEBID with 15 keV and 7 nA results in deposits with an atomic composition of Cu:O:C of approximately 1:1:2. Transmission electron microscopy proved that pure copper nanocrystals with sizes of up to around 15 nm were dispersed inside the carbonaceous matrix. Raman investigations revealed a high degree of amorphization of the carbonaceous matrix and showed hints for partial copper oxidation taking place selectively on the surfaces of the deposits. Optical transmission/reflection measurements of deposited pads showed a dielectric behavior of the material in the optical spectral range. The general behavior of the permittivity could be described by applying the MaxwellâGarnett mixing model to amorphous carbon and copper. The dielectric function measured from deposited pads was used to simulate the optical response of tip arrays fabricated out of the same precursor and showed good agreement with measurements. This paves the way for future plasmonic applications with copper-FEBID
Effect of rapid thermal annealing on barrier height and 1/f noise of Ni/GaN Schottky barrier diodes
Current-voltage (as a function of temperature), capacitance-voltage, and 1/f
noise characteristics of Ni/GaN Schottky barrier diodes (SBDs) as function of
rapid thermal annealing (RTA) are studied. It is found that RTA treatments of
SBDs at 450â°C for 60âs resulted in a significant improvement of ideality
factor and Schottky barrier height: the ideality factor decreased from 1.79 to
1.12 and the barrier height increased from 0.94 to 1.13âeV. The spectral power
density of current fluctuations in the diode subjected to RTA at 450â°C is
found to be two orders of magnitude lower as compared to the as-deposited
diode. Improved diode characteristics and decreased 1/f noise in RTA treated
(450â°C/60âs) diode are attributed to reduced level of barrier inhomogeneities
at the metal-semiconductor interface and explained within the framework of the
spatial inhomogeneity model
Interfacing transitions of different alkali atoms and telecom bands using one narrowband photon pair source
Quantum information technology strongly relies on coupling of optical photons
with narrowband quantum systems, such as quantum dots, color centers, and
atomic systems. This coupling requires matching the optical wavelength and
bandwidth to the desired system, which presents a considerable problem for most
available sources of quantum light. Here we demonstrate coupling of alkali
dipole transitions with a tunable source of photon pairs. Our source is based
on spontaneous parametric down-conversion in a triply-resonant
whispering-gallery mode resonator. For this, we have developed novel wavelength
tuning mechanisms, which allow for a coarse tuning to either cesium or rubidium
wavelength with subsequent continuous fine-tuning to the desired transition. As
a demonstration of the functionality of the source, we performed a heralded
single photon measurement of the atomic decay. We present a major advance in
controlling the spontaneous down-conversion process, which makes our bright
source of single photons now compatible with a plethora of narrow-band resonant
systems.Comment: 8 pages, 5 figure
Bioactivity and corrosion behavior of magnesium barrier membranes
In the current research, magnesium and its alloys have been intensively studied as resorbable implant materials. Magnesium materials combine their good mechanical properties with bioactivity, which make them interesting for guided bone regeneration and for the application as barrier membranes. In this study, the in vitro degradation behavior of thin magnesium films was investigated in cell medium and simulated body fluid. Three methods were applied to evaluate corrosion rates: measurements of (i) the gaseous volume evolved during immersion, (ii) volume change after immersion, and (iii) polarization curves. In this comparison, measurements of H2 development in Dulbecco's modified Eagle's medium showed to be the most appropriate method, exhibiting a corrosion rate of 0.5âmm·yearâ1. Observed oxide and carbon contamination have a high impact on controlled degradation, suggesting that surface treatment of thin foils is necessary. The bioactivity test showed positive results; more detailed tests in this area are of interest
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