322 research outputs found
Friction as Contrast Mechanism in Heterodyne Force Microscopy
The nondestructive imaging of subsurface structures on the nanometer scale
has been a long-standing desire in both science and industry. A few impressive
images were published so far that demonstrate the general feasibility by
combining ultrasound with an Atomic Force Microscope. From different excitation
schemes, Heterodyne Force Microscopy seems to be the most promising candidate
delivering the highest contrast and resolution. However, the physical contrast
mechanism is unknown, thereby preventing any quantitative analysis of samples.
Here we show that friction at material boundaries within the sample is
responsible for the contrast formation. This result is obtained by performing a
full quantitative analysis, in which we compare our experimentally observed
contrasts with simulations and calculations. Surprisingly, we can rule out all
other generally believed responsible mechanisms, like Rayleigh scattering,
sample (visco)elasticity, damping of the ultrasonic tip motion, and ultrasound
attenuation. Our analytical description paves the way for quantitative
SubSurface-AFM imaging.Comment: 7 pages main paper + 11 pages supplementary material
Spin-mediated dissipation and frequency shifts of a cantilever at milliKelvin temperatures
We measure the dissipation and frequency shift of a magnetically coupled
cantilever in the vicinity of a silicon chip, down to mK. The dissipation
and frequency shift originates from the interaction with the unpaired
electrons, associated with the dangling bonds in the native oxide layer of the
silicon, which form a two dimensional system of electron spins. We approach the
sample with a m-diameter magnetic particle attached to an ultrasoft
cantilever, and measure the frequency shift and quality factor as a function of
temperature and the distance. Using a recent theoretical analysis [J. M. de
Voogd et al., arXiv:1508.07972 (2015)] of the dynamics of a system consisting
of a spin and a magnetic resonator, we are able to fit the data and extract the
relaxation time ms and spin density
spins per nm. Our analysis shows that at temperatures mK magnetic
dissipation is an important source of non-contact friction.Comment: 5 pages, 3 figure
Mechanical properties of Pt monatomic chains
The mechanical properties of platinum monatomic chains were investigated by
simultaneous measurement of an effective stiffness and the conductance using
our newly developed mechanically controllable break junction (MCBJ) technique
with a tuning fork as a force sensor. When stretching a monatomic contact
(two-atom chain), the stiffness and conductance increases at the early stage of
stretching and then decreases just before breaking, which is attributed to a
transition of the chain configuration and bond weakening. A statistical
analysis was made to investigate the mechanical properties of monatomic chains.
The average stiffness shows minima at the peak positions of the
length-histogram. From this result we conclude that the peaks in the
length-histogram are a measure of the number of atoms in the chains, and that
the chains break from a strained state. Additionally, we find that the smaller
the initial stiffness of the chain is, the longer the chain becomes. This shows
that softer chains can be stretched longer.Comment: 6 pages, 5 figure
A method for mechanical generation of radio frequency fields in nuclear magnetic resonance force microscopy
We present an innovative method for magnetic resonance force microscopy
(MRFM) with ultra-low dissipation, by using the higher modes of the mechanical
detector as radio frequency (rf) source. This method allows MRFM on samples
without the need to be close to an rf source. Furthermore, since rf sources
require currents that give dissipation, our method enables nuclear magnetic
resonance experiments at ultra-low temperatures. Removing the need for an
on-chip rf source is an important step towards a MRFM which can be widely used
in condensed matter physics.Comment: 7 pages, 5 figures, to be submitted to Physical Review Applie
Determination of the complex microwave photoconductance of a single quantum dot
A small quantum dot containing approximately 20 electrons is realized in a
two-dimensional electron system of an AlGaAs/GaAs heterostructure. Conventional
transport and microwave spectroscopy reveal the dot's electronic structure. By
applying a coherently coupled two-source technique, we are able to determine
the complex microwave induced tunnel current. The amplitude of this
photoconductance resolves photon-assisted tunneling (PAT) in the non-linear
regime through the ground state and an excited state as well. The out-of-phase
component (susceptance) allows to study charge relaxation within the quantum
dot on a time scale comparable to the microwave beat period.Comment: 5.5 pages, 6 figures, accepted by Phys. Rev. B (Jan. B15 2001
Probing the magnetic moment of FePt micromagnets prepared by Focused Ion Beam milling
We investigate the degradation of the magnetic moment of a 300 nm thick FePt
film induced by Focused Ion Beam (FIB) milling. A rod is milled out of a film by a FIB process and is attached
to a cantilever by electron beam induced deposition. Its magnetic moment is
determined by frequency-shift cantilever magnetometry. We find that the
magnetic moment of the rod is , which implies that 70% of the magnetic moment is preserved
during the FIB milling process. This result has important implications for atom
trapping and magnetic resonance force microscopy (MRFM), that are addressed in
this paper.Comment: 4 pages, 4 figure
Vibration isolation with high thermal conductance for a cryogen-free dilution refrigerator
We present the design and implementation of a mechanical low-pass filter
vibration isolation used to reduce the vibrational noise in a cryogen-free
dilution refrigerator operated at 10 mK, intended for scanning probe
techniques. We discuss the design guidelines necessary to meet the competing
requirements of having a low mechanical stiffness in combination with a high
thermal conductance. We demonstrate the effectiveness of our approach by
measuring the vibrational noise levels of an ultrasoft mechanical resonator
positioned above a SQUID. Starting from a cryostat base temperature of 8 mK,
the vibration isolation can be cooled to 10.5 mK, with a cooling power of 113
W at 100 mK. We use the low vibrations and low temperature to demonstrate
an effective cantilever temperature of less than 20 mK. This results in a force
sensitivity of less than 500 zN/, and an integrated
frequency noise as low as 0.4 mHz in a 1 Hz measurement bandwidth
Deterministic nano-assembly of a coupled quantum emitter - photonic crystal cavity system
The interaction of a single quantum emitter with its environment is a central
theme in quantum optics. When placed in highly confined optical fields, such as
those created in optical cavities or plasmonic structures, the optical
properties of the emitter can change drastically. In particular, photonic
crystal (PC) cavities show high quality factors combined with an extremely
small mode volume. Efficiently coupling a single quantum emitter to a PC cavity
is challenging because of the required positioning accuracy. Here, we
demonstrate deterministic coupling of single Nitrogen-Vacancy (NV) centers to
high-quality gallium phosphide PC cavities, by deterministically positioning
their 50 nm-sized host nanocrystals into the cavity mode maximum with
few-nanometer accuracy. The coupling results in a 25-fold enhancement of NV
center emission at the cavity wavelength. With this technique, the NV center
photoluminescence spectrum can be reshaped allowing for efficient generation of
coherent photons, providing new opportunities for quantum science.Comment: 13 pages, 4 figure
Engineered arrays of NV color centers in diamond based on implantation of CN- molecules through nanoapertures
We report a versatile method to engineer arrays of nitrogen-vacancy (NV)
color centers in dia- mond at the nanoscale. The defects were produced in
parallel by ion implantation through 80 nm diameter apertures patterned using
electron beam lithography in a PMMA layer deposited on a diamond surface. The
implantation was performed with CN- molecules which increased the NV defect
formation yield. This method could enable the realization of a solid-state
coupled-spin array and could be used for positioning an optically active NV
center on a photonic microstructure.Comment: 12 pages, 3 figure
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