24 research outputs found
Biocompatible chitosan nanofibers functionalized with silver nanoparticles for SERS based detection
Electrospun chitosan nanofibrous substrates are functionalized with silver nanoparticles by reduction of silver from Tollens reagent using glucose. Filling factor is estimated through developed protocol by using analysis of scanning electron microscopy images. Obtained nanocomposite silver-chitosan plasmonic films display reliable surface enhanced Raman scattering signal of rhodamine B with the concentration 10(-5) M adsorbed onto the surface of functionalized substrates
Conditional statistics of electron transport in interacting nanoscale conductors
Interactions between nanoscale semiconductor structures form the basis for
charge detectors in the solid state. Recent experimental advances have
demonstrated the on-chip detection of single electron transport through a
quantum dot (QD). The discreteness of charge in units of e leads to intrinsic
fluctuations in the electrical current, known as shot noise. To measure these
single-electron fluctuations a nearby coherent conductor, called a quantum
point contact (QPC), interacts with the QD and acts as a detector. An important
property of the QPC charge detector is noninvasiveness: the system physically
affects the detector, not visa-versa. Here we predict that even for ideal
noninvasive detectors such as the QPC, when a particular detector result is
observed, the system suffers an informational backaction, radically altering
the statistics of transport through the QD as compared to the unconditional
shot noise. We develop a theoretical model to make predictions about the joint
current probability distributions and conditional transport statistics. The
experimental findings reported here demonstrate the reality of informational
backaction in nanoscale systems as well as a variety of new effects, such as
conditional noise enhancement, which are in essentially perfect agreement with
our model calculations. This type of switching telegraph process occurs
abundantly in nature, indicating that these results are applicable to a wide
variety of systems.Comment: 16 pages, 3 figures, to appear in Nature Physic
Allowed and forbidden transitions in artificial hydrogen and helium atoms
The strength of radiative transitions in atoms is governed by selection
rules. Spectroscopic studies of allowed transitions in hydrogen and helium
provided crucial evidence for the Bohr's model of an atom. Forbidden
transitions, which are actually allowed by higher-order processes or other
mechanisms, indicate how well the quantum numbers describe the system. We apply
these tests to the quantum states in semiconductor quantum dots (QDs), which
are regarded as artificial atoms. Electrons in a QD occupy quantized states in
the same manner as electrons in real atoms. However, unlike real atoms, the
confinement potential of the QD is anisotropic, and the electrons can easily
couple with phonons of the material. Understanding the selection rules for such
QDs is an important issue for the manipulation of quantum states. Here we
investigate allowed and forbidden transitions for phonon emission in one- and
two-electron QDs (artificial hydrogen and helium atoms) by electrical
pump-and-probe experiments, and find that the total spin is an excellent
quantum number in artificial atoms. This is attractive for potential
applications to spin based information storage.Comment: slightly longer version of Nature 419, 278 (2002
Measurement of finite-frequency current statistics in a single-electron transistor
Electron transport in nano-scale structures is strongly influenced by the
Coulomb interaction which gives rise to correlations in the stream of charges
and leaves clear fingerprints in the fluctuations of the electrical current. A
complete understanding of the underlying physical processes requires
measurements of the electrical fluctuations on all time and frequency scales,
but experiments have so far been restricted to fixed frequency ranges as
broadband detection of current fluctuations is an inherently difficult
experimental procedure. Here we demonstrate that the electrical fluctuations in
a single electron transistor (SET) can be accurately measured on all relevant
frequencies using a nearby quantum point contact for on-chip real-time
detection of the current pulses in the SET. We have directly measured the
frequency-dependent current statistics and hereby fully characterized the
fundamental tunneling processes in the SET. Our experiment paves the way for
future investigations of interaction and coherence induced correlation effects
in quantum transport.Comment: 7 pages, 3 figures, published in Nature Communications (open access
Probing quantum and thermal noise in an interacting many-body system
The probabilistic character of the measurement process is one of the most
puzzling and fascinating aspects of quantum mechanics. In many-body systems
quantum mechanical noise reveals non-local correlations of the underlying
many-body states. Here, we provide a complete experimental analysis of the
shot-to-shot variations of interference fringe contrast for pairs of
independently created one-dimensional Bose condensates. Analyzing different
system sizes we observe the crossover from thermal to quantum noise, reflected
in a characteristic change in the distribution functions from Poissonian to
Gumbel-type, in excellent agreement with theoretical predictions based on the
Luttinger liquid formalism. We present the first experimental observation of
quasi long-range order in one-dimensional atomic condensates, which is a
hallmark of quantum fluctuations in one-dimensional systems. Furthermore, our
experiments constitute the first analysis of the full distribution of quantum
noise in an interacting many-body system
Theory and numerical modelling of parity-time symmetric structures in photonics: introduction and grating structures in one dimension
A class of structures based on PT PT-symmetric Bragg gratings in the presence of both gain and loss is studied. The basic concepts and properties of parity and time reversal in one-dimensional structures that possess idealised material properties are given. The impact of realistic material properties on the behaviour of these devices is then investigated. Further extension to include material non-linearity is used to study an innovative all-optical
memory device
Polylactic acid nano- and microchamber arrays for encapsulation of small hydrophilic molecules featuring drug release via high intensity focused ultrasound
The authors would like to thank the following funding agencies which partly supported this work: the National Natural Science Foundation of China (grant no. 21503058) (J. F.), the State Key Laboratory Foundation (project no. 2016KM008), the Key Laboratory of Micro-/Nanotechnology Research Center, HIT, (J. F.), the Chinese Scholarship Council (CSC) Grant No. 201406120038 (M. G.), and the Queen Mary University of London (M. G.). The work was also supported by The Government of the Russian Federation (grant 14.Z50.31.0004) to support scientific research projects implemented under the supervision of leading scientists at Russian institutions and Russian institutions of higher education, A.V.P., V.V.P., G.B.S)
Composite SERS-based satellites navigated by optical tweezers for single cell analysis
Herein, we have designed composite SERS-active micro-satellites, which exhibit a dual role: (i) effective probes for determining cellular composition and (ii) optically movable and easily detectable markers. The satellites were synthesized by the layer-by-layer assisted decoration of silica microparticles with metal (gold or silver) nanoparticles and astralen in order to ensure satellite SERS-based microenvironment probing and satellite recognition, respectively. A combination of optical tweezers and Raman spectroscopy can be used to navigate the satellites to a certain cellular compartment and probe the intracellular composition following cellular uptake. In the future, this developed approach may serve as a tool for single cell analysis with nanometer precision due to the multilayer surface design, focusing on both extracellular and intracellular studies