4 research outputs found
Magnetoresistance and Charge Transport in Graphene Governed by Nitrogen Dopants
We identify the influence of nitrogen-doping on charge- and magnetotransport of single layer graphene by comparing doped and undoped samples. Both sample types are grown by chemical vapor deposition (CVD) and transferred in an identical process onto Si/SiO<sub>2</sub> wafers. We characterize the samples by Raman spectroscopy as well as by variable temperature magnetotransport measurements. Over the entire temperature range, the charge transport properties of all undoped samples are in line with literature values. The nitrogen doping instead leads to a 6-fold increase in the charge carrier concentration up to 4 × 10<sup>13</sup> cm<sup>–2</sup> at room temperature, indicating highly effective doping. Additionally it results in the opening of a charge transport gap as revealed by the temperature dependence of the resistance. The magnetotransport exhibits a conspicuous sign change from positive Lorentz magnetoresistance (MR) in undoped to large negative MR that we can attribute to the doping induced disorder. At low magnetic fields, we use quantum transport signals to quantify the transport properties. Analyses based on weak localization models allow us to determine an orders of magnitude decrease in the phase coherence and scattering times for doped samples, since the dopants act as effective scattering centers
Reversible Photochemical Control of Doping Levels in Supported Graphene
Controlling the type and density
of charge carriers in graphene
is vital for a wide range of applications of this material in electronics
and optoelectronics. To date, chemical doping and electrostatic gating
have served as the two most established means to manipulate the carrier
density in graphene. Although highly effective, these two approaches
require sophisticated graphene growth or complex device fabrication
processes to achieve both the desired nature and the doping densities
with generally limited dynamic tunability and spatial control. Here,
we report a convenient and tunable optical approach to tune the steady-state
carrier density and Fermi energy in graphene by photochemically controlling
the concentration of adsorbed molecular O<sub>2</sub>, a p-dopant
in graphene, using femtosecond pulsed laser irradiation in the UV
range. As an all-optical approach, it allows spatial control over
doping levels. Combined terahertz (THz) spectroscopy and electrical
device measurements reveal that the Fermi level in laser-illuminated
graphene can be controllably and reversibly tuned between p- and n-type
in a large range (over ∼600 meV from −420 to +180 meV)
by readily tuning the peak intensity and the duration of the laser
irradiation treatment. Furthermore, we demonstrate that our photochemical
approach for doping of graphene allows one to optically write doping
structure with spatial control. Given the ease, effectiveness, and
simplicity of the method, this photochemical doping mechanism offers
a simple, reversible approach to control the steady-state electronic
and optical properties of graphene
Data_Sheet_1_Improved connectivity and cognition due to cognitive stimulation in Alzheimer’s disease.docx
BackgroundDue to the increasing prevalence of Alzheimer’s disease (AD) and the limited efficacy of pharmacological treatment, the interest in non-pharmacological interventions, e.g., cognitive stimulation therapy (CST), to improve cognitive dysfunction and the quality of life of AD patients are on a steady rise.ObjectivesHere, we examined the efficacy of a CST program specifically conceptualized for AD dementia patients and the neural mechanisms underlying cognitive or behavioral benefits of CST.MethodsUsing neuropsychological tests and MRI-based measurements of functional connectivity, we examined the (neuro-) psychological status and network changes at two time points: pre vs. post-stimulation (8 to 12 weeks) in the intervention group (n = 15) who received the CST versus a no-intervention control group (n = 15).ResultsAfter CST, we observed significant improvement in the Mini-Mental State Examination (MMSE), the Alzheimer’s Disease Assessment Scale, cognitive subsection (ADAS-cog), and the behavioral and psychological symptoms of dementia (BPSD) scores. These cognitive improvements were associated with an up-regulated functional connectivity between the left posterior hippocampus and the trunk of the left postcentral gyrus.ConclusionOur data indicate that CST seems to induce short-term global cognition and behavior improvements in mild to moderate AD dementia and enhances resting-state functional connectivity in learning- and memory-associated brain regions. These convergent results prove that even in mild to moderate dementia AD, neuroplasticity can be harnessed to alleviate cognitive impairment with CST.</p
Additional file 1: Figure S1. of Safety and in vivo immune assessment of escalating doses of oral laquinimod in patients with RRMS
Study MS-LAQ-101 flow chart. Figure S2. Average plasma concentrations of laquinimod on Day 21 after repeated daily administration. Figure S3. Exposure-dose plots of laquinimod after multiple dose administration. Table S1. Distribution of study drug termination reasons. Table S2. Biochemistry shift analysis to abnormal levels. Table S3. Hematology shift analysis. (DOCX 276 kb