33 research outputs found
Calibrated Microwave Reflectance in Low-Temperature Scanning Tunneling Microscopy
We outline calibrated measurements of the microwave reflection coefficient
from the tunnel junction of an ultra-high vacuum low temperature scanning
tunneling microscope. The microwave circuit design is described in detail,
including an interferometer for enhanced signal-to-noise and a demodulation
scheme for lock-in detection. A quantitative, in-situ procedure for impedance
calibration based on the numerical 3-error-term model is presented. Our
procedure exploits the response of the microwave reflection signal due to the
change of the tunneling conductance caused by sub-nm variation of the tunneling
distance. Experimental calibration is achieved by a least-squares numerical fit
of simultaneously measured conductance and microwave reflection retraction
curves at finite conductance. Our method paves the way for nanoscale microscopy
and spectroscopy of dielectric surface properties at GHz frequencies and
cryogenic temperatures. This opens a promising pathway even for dielectric
fingerprinting at the single molecule limit.Comment: The manuscript has been improved in response to reviewer comments.
Changes include addition of extra details and verification, updated figure
layout to improve clarity, and additional context added to the introduction
and conclusion. The conclusions and the underlying data remain the same. 12
pages, 4 figures, submitted to Review of Scientific Instrument
Dynamic electrostatic force microscopy in liquid media
We present the implementation of dynamic electrostatic force microscopy in liquid media. This implementation enables the quantitative imaging of local dielectric properties of materials in electrolyte solutions with nanoscale spatial resolution. Local imaging capabilities are obtained by probing the frequency-dependent and ionic concentration-dependent electrostatic forces at high frequency (>1 MHz), while quantification of the interaction forces is obtained with finite-element numerical calculations. The results presented open a wide range of possibilities in a number of fields where the dielectric properties of materials need to be probed at the nanoscale and in a liquid environment
Nanoscale measurement of the dielectric constant of supported lipid bilayers in aqueous solutions with electrostatic force microscopy
We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization forces which were measured using an electrostatic force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of Δr ⌠3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (Δr ⌠2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane electrostatics and other bioelectric phenomena
Effects of Dielectric Stoichiometry on the Photoluminescence Properties of Encapsulated WSe2 Monolayers
Two-dimensional transition-metal-dichalcogenide semiconductors have emerged
as promising candidates for optoelectronic devices with unprecedented
properties and ultra-compact performances. However atomically thin materials
are highly sensitive to surrounding dielectric media, which imposes severe
limitations to their practical applicability. Hence for their suitable
integration into devices, the development of reliable encapsulation procedures
that preserve their physical properties are required. Here, the excitonic
photoluminescence of WSe2 monolayer flakes is assessed, at room temperature and
10 K, on mechanically exfoliated flakes encapsulated with SiOx and AlxOy layers
employing chemical and physical deposition techniques. Conformal flakes coating
on untreated - non-functionalized - flakes is successfully demonstrated by all
the techniques except for atomic layer deposition, where a cluster-like oxide
coating is observed. No significant compositional or strain state changes in
the flakes are detected upon encapsulation by any of the techniques.
Remarkably, our results evidence that the flakes' optical emission is strongly
influenced by the quality of the encapsulating oxide - stoichiometry -. When
the encapsulation is carried out with slightly sub-stoichiometric oxides two
remarkable phenomena are observed. First, there is a clear electrical doping of
the monolayers that is revealed through a dominant trion - charged exciton -
room-temperature photoluminescence. Second, a strong decrease of the monolayers
optical emission is measured attributed to non-radiative recombination
processes and/or carriers transfer from the flake to the oxide. Power- and
temperature-dependent photoluminescence measurements further confirm that
stoichiometric oxides obtained by physical deposition lead to a successful
encapsulation.Comment: 30 pages, 6 figure
Nondestructive imaging of atomically thin nanostructures buried in silicon
It is now possible to create atomically thin regions of dopant atoms in silicon patterned with lateral dimensions ranging from the atomic scale (angstroms) to micrometers. These structures are building blocks of quantum devices for physics research and they are likely also to serve as key components of devices for next-generation classical and quantum information processing. Until now, the characteristics of buried dopant nanostructures could only be inferred from destructive techniques and/or the performance of the final electronic device; this severely limits engineering and manufacture of real-world devices based on atomic-scale lithography. Here, we use scanning microwave microscopy (SMM) to image and electronically characterize three-dimensional phosphorus nanostructures fabricated via scanning tunneling microscopeâbased lithography. The SMM measurements, which are completely nondestructive and sensitive to as few as 1900 to 4200 densely packed P atoms 4 to 15 nm below a silicon surface, yield electrical and geometric properties in agreement with those obtained from electrical transport and secondary ion mass spectroscopy for unpatterned phosphorus ÎŽ layers containing ~1013 P atoms. The imaging resolution was 37 ± 1 nm in lateral and 4 ± 1 nm in vertical directions, both values depending on SMM tip size and depth of dopant layers. In addition, finite element modeling indicates that resolution can be substantially improved using further optimized tips and microwave gradient detection. Our results on three-dimensional dopant structures reveal reduced carrier mobility for shallow dopant layers and suggest that SMM could aid the development of fabrication processes for surface code quantum computers.ISSN:2375-254
Local characterization of ferromagnetic resonance in bulk and patterned magnetic materials using scanning microwave microscopy
We have demonstrated the capabilities of the scanning microwave microscopy (SMM) technique for measuring ferromagnetic resonance (FMR) spectra in nanometric areas of magnetic samples. The technique is evaluated using three different samples, including a yttrium iron garnet (YIG) polycrystalline bulk sample and a thick YIG film grown by liquid phase epitaxy (LPE). Patterned permalloy (Py) micromagnetic dots have been characterized to assess the performance for imaging applications of the technique, measuring the variation of the magnetic properties of the sample along its surface. The proposed technique may pave the way for the development of high spatially resolved mapping of magnetostatic modes in different nanomagnetic and micromagnetic structures