114 research outputs found
Spin-Dependent Electron Transmission Model for Chiral Molecules in Mesoscopic Devices
Various device-based experiments have indicated that electron transfer in
certain chiral molecules may be spin-dependent, a phenomenon known as the
Chiral Induced Spin Selectivity (CISS) effect. However, due to the complexity
of these devices and a lack of theoretical understanding, it is not always
clear to what extent the chiral character of the molecules actually contributes
to the magnetic-field-dependent signals in these experiments. To address this
issue, we report here an electron transmission model that evaluates the role of
the CISS effect in two-terminal and multi-terminal linear-regime electron
transport experiments. Our model reveals that for the CISS effect, the
chirality-dependent spin transmission is accompanied by a spin-flip electron
reflection process. Furthermore, we show that more than two terminals are
required in order to probe the CISS effect in the linear regime. In addition,
we propose two types of multi-terminal nonlocal transport measurements that can
distinguish the CISS effect from other magnetic-field-dependent signals. Our
model provides an effective tool to review and design CISS-related transport
experiments, and to enlighten the mechanism of the CISS effect itself
Circuit-Model Analysis for Spintronic Devices with Chiral Molecules as Spin Injectors
Recent research discovered that charge transfer processes in chiral molecules
can be spin selective and named the effect chiral-induced spin selectivity
(CISS). Follow-up work studied hybrid spintronic devices with conventional
electronic materials and chiral (bio)molecules. However, a theoretical
foundation for the CISS effect is still in development and the spintronic
signals were not evaluated quantitatively. We present a circuit-model approach
that can provide quantitative evaluations. Our analysis assumes the scheme of a
recent experiment that used photosystem~I (PSI) as spin injectors, for which we
find that the experimentally observed signals are, under any reasonable
assumptions on relevant PSI time scales, too high to be fully due to the CISS
effect. We also show that the CISS effect can in principle be detected using
the same type of solid-state device, and by replacing silver with graphene, the
signals due to spin generation can be enlarged four orders of magnitude. Our
approach thus provides a generic framework for analyzing this type of
experiments and advancing the understanding of the CISS effect
Detecting chirality in two-terminal electronic devices
Central to spintronics is the interconversion between electronic charge and
spin currents, and this can arise from the chirality-induced spin selectivity
(CISS) effect. CISS is often studied as magnetoresistance (MR) in two-terminal
(2T) electronic devices containing a chiral (molecular) component and a
ferromagnet. However, fundamental understanding of when and how this MR can
occur is lacking. Here, we uncover an elementary mechanism that generates such
a MR for nonlinear response. It requires energy-dependent transport and energy
relaxation within the device. The sign of the MR depends on chirality, charge
carrier type, and bias direction. Additionally, we reveal how CISS can be
detected in the linear response regime in magnet-free 2T devices, either by
forming a chirality-based spin-valve using two or more chiral components, or by
Hanle spin precession in devices with a single chiral component. Our results
provide operation principles and design guidelines for chirality-based
spintronic devices and technologies
Detecting chirality in two-terminal electronic devices
Central to spintronics is the interconversion between electronic charge and
spin currents, and this can arise from the chirality-induced spin selectivity
(CISS) effect. CISS is often studied as magnetoresistance (MR) in two-terminal
(2T) electronic devices containing a chiral (molecular) component and a
ferromagnet. However, fundamental understanding of when and how this MR can
occur is lacking. Here, we uncover an elementary mechanism that generates such
a MR for nonlinear response. It requires energy-dependent transport and energy
relaxation within the device. The sign of the MR depends on chirality, charge
carrier type, and bias direction. Additionally, we reveal how CISS can be
detected in the linear response regime in magnet-free 2T devices, either by
forming a chirality-based spin-valve using two or more chiral components, or by
Hanle spin precession in devices with a single chiral component. Our results
provide operation principles and design guidelines for chirality-based
spintronic devices and technologies
Reply to "Comment on 'Spin-dependent electron transmission model for chiral molecules in mesoscopic devices'"
Here we emphasize once more the distinction between generating CISS
(spin-charge current conversion) in a chiral system and detecting it as
magnetoresistance in two-terminal electronic devices. We also highlight
important differences between electrical measurement results obtained in the
linear response regime and those obtained in the nonlinear regime
Semiconductor channel mediated photodoping in h-BN encapsulated monolayer MoSe2 phototransistors
In optically excited two-dimensional phototransistors, charge transport is
often affected by photodoping effects. Recently, it was shown that such effects
are especially strong and persistent for graphene/h-BN heterostructures, and
that they can be used to controllably tune the charge neutrality point of
graphene. In this work we investigate how this technique can be extended to h
BN encapsulated monolayer MoSe_2 phototransistors at room temperature. By
exposing the sample to 785 nm laser excitation we can controllably increase the
charge carrier density of the MoSe_2 channel by {\Delta}n {\approx} 4.45
{\times} 10^{12} cm^{-2}, equivalent to applying a back gate voltage of 60 V.
We also evaluate the efficiency of photodoping at different illumination
wavelengths, finding that it is strongly correlated with the light absorption
by the MoSe_2 layer, and maximizes for excitation on-resonance with the A
exciton absorption. This indicates that the photodoping process involves
optical absorption by the MoSe_2 channel, in contrast with the mechanism
earlier described for graphene/h-BN heterostroctures
High-grade, Compact spectrometers for Earth observation from smallsats
The market for nano- and microsatellites is developing rapidly. There is a strong focus on 2D imaging of the Earth\u27s surface, with limited possibilities to obtain spectral information. More demanding applications, such as monitoring trace gases and aerosols, or water quality still require advanced spectral imaging instruments, which are large, heavy and expensive.
In recent years TNO has investigated and developed different innovative designs to realize advanced spectrometers for space applications in a more compact and cost-effective manner. This offers multiple advantages: A compact instrument can be flown on a much smaller platform (nano- or microsatellite); a low-cost instrument opens up the possibility to fly multiple instruments in a satellite constellation, improving both global coverage and temporal sampling (e.g. multiple overpasses per day to study diurnal processes); in this way a constellation of low-cost instruments may provide added value to the larger scientific and operational satellite missions (e.g. the Copernicus Sentinel missions); and a small, lightweight spectrometer can easily be mounted on a high-altitude UAV (offering high spatial resolution).
Moreover, a low-cost instrument may allow us to break through the \u27cost spiral\u27: lower cost will allow us to take more risk and thus progress faster. This may lead to a much faster development cycle than customary for current Earth-observation instruments.
Finally, the TNO designs offer flexibility to tune the performance (spectral range, spectral resolution) of the spectrometer to a specific application. Thus, based on the same basic system design, these instruments offer a wide range of applications to a variety of clients, both inside and outside the scientific community using a quasi-recurrent instrument.
In this presentation we will illustrate this innovative approach, using the most mature design of a hyperspectral imaging spectrometer (named \u27Tropolite\u27) as an example. Other, less developed, designs will be presented briefly. We will discuss the different design and manufacturing techniques that were used to realize these very compact and low-cost concepts. The first laboratory test results of a Tropolite breadboard will be presented and commented upon. Based on these test results the feasibility to use Tropolite for different applications (e.g. air quality, water quality, …) will be discussed further. Currently, efforts are being made to realize an in-orbit demonstration of Tropolite
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