High-frequency gate manipulation of a bilayer graphene quantum dot

We report transport data obtained for a double-gated bilayer graphene quantum dot. In Coulomb blockade measurements, the gate dielectric Cytop(TM) is found to provide remarkable electronic stability even at cryogenic temperatures. Moreover, we demonstrate gate manipulation with square shaped voltage pulses at frequencies up to 100 MHz and show that the signal amplitude is not affected by the presence of the capacitively coupled back gate

Quantum capacitance and density of states of graphene

We report on measurements of the quantum capacitance in graphene as a function of charge carrier density. A resonant LC-circuit giving high sensitivity to small capacitance changes is employed. The density of states, which is directly proportional to the quantum capacitance, is found to be significantly larger than zero at and around the charge neutrality point. This finding is interpreted to be a result of potential fluctuations with amplitudes of the order of 100 meV in good agreement with scanning single-electron transistor measurements on bulk graphene and transport studies on nanoribbons

Raman spectroscopy on etched graphene nanoribbons

We investigate etched single-layer graphene nanoribbons with different widths ranging from 30 to 130 nm by confocal Raman spectroscopy. We show that the D-line intensity only depends on the edge-region of the nanoribbon and that consequently the fabrication process does not introduce bulk defects. In contrast, the G- and the 2D-lines scale linearly with the irradiated area and therefore with the width of the ribbons. We further give indications that the D- to G-line ratio can be used to gain information about the crystallographic orientation of the underlying graphene. Finally, we perform polarization angle dependent measurements to analyze the nanoribbon edge-regions

Transport through graphene double dots

We present Coulomb blockade measurements in a graphene double dot system. The coupling of the dots to the leads and between the dots can be tuned by graphene in-plane gates. The coupling is a non-monotonic function of the gate voltage. Using a purely capacitive model, we extract all relevant energy scales of the double dot system

Electron flow in split-gated bilayer graphene

We present transport measurements on a bilayer graphene sheet with homogeneous back gate and split top gate. The electronic transport data indicates the capability to direct electron flow through graphene nanostructures purely defined by electrostatic gating. By comparing the transconductance data recorded for different top gate geometries - continuous barrier and split-gate - the observed transport features for the split-gate can be attributed to interference effects inside the narrow opening

Quantum capacitance and density of states of graphene

Abstract We report capacitance measurements in top-gated graphene sheets as a function of charge carrier density. A measurement method using an LC-circuit provides high sensitivity to small capacitance changes and hence allows the observation of the quantum part of the capacitance. The extracted density of states has a finite value of 1 × 10 17 m −2 eV −1 in the vicinity of the Dirac point, which is in contrast to the theoretical prediction for ideal graphene. We attribute this discrepancy to fluctuations of the electrostatic potential with a typical amplitude of 100 meV in our device

Retrievals of the main phytoplankton groups at Lake Constance using OLCI, DESIS, and evaluated with field observations

Phytoplankton play an important role in the aquatic biogeochemical cycling such as for the formation of organic matter by photosynthetic processes through the fixation of carbon dioxide, and assimilation of macro- and micronutrients depending on their metabolic needs. These processes are common to all phytoplankton, however some phytoplankton groups have specific needs and thus play different functional roles in the biogeochemical cycle, which are used to classify phytoplankton into different phytoplankton functional types (PFTs). Information on the phytoplankton groups can be obtained from satellite observations such as the Ocean and Land Colour Instrument (OLCI) onboard of ISS and Sentinel-3. PFTs global ocean abundance can be estimated based on the OC-PFT algorithm (Hirata et al. 2011 and related updates to it) which is based on the assumption that a marker pigment for a specific PFT varies in dependence to the chlorophyll-a concentration. In this study, OC-PFT retrieval has been developed and adapted for estimation of PFT from Lake Constance by using a large collection of in-situ HPLC data set measured since 2000 at the largest German inland water by the regional authority and further analysed to derive PFT using the diagnostic pigment analysis following Vidussi et al. (2001) with adapted coefficients for Lake Constance. The PFT retrieved from OLCI are validated using independent in situ data derived from HPLC pigment measurements from 4 field campaigns performed in 2019 and 2020 at Lake Constance. Concentrations for five phytoplankton groups (diatoms, dinoflagellates, cryptophytes, green algae, and prokaryotes) are retrieved for Lake Constance, being the dominants diatoms and cryptophytes and at lesser degree green algae. In addition, evaluation of synergistic PFT products are presented to enlarge the capabilities of PFT data in inland and coastal waters analytically retrieved from high spectral and high spatial data such as DESIS, EnMAP or PRISMA by synergistic use with OLCI OC-PFT data sets is discussed