Terahertz imaging and spectroscopy of large-area single-layer graphene

We demonstrate terahertz (THz) imaging and spectroscopy of a 15x15-mm^2 single-layer graphene film on Si using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is characterized by a flat spectral response. A theoretical analysis based on the Fresnel coefficients for a metallic thin film shows that the local sheet conductivity varies across the sample from {\sigma}s = 1.7x10^-3 to 2.4x10^-3 {\Omega}^-1 (sheet resistance, {\rho}s = 420 - 590 {\Omega}/sq).Comment: 6 pages, 5 figure

High-Contrast Imaging of Graphene via Time-Domain Terahertz Spectroscopy

We demonstrate terahertz (THz) imaging and spectroscopy of single-layer graphene deposited on an intrinsic Si substrate using THz time-domain spectroscopy. A single-cycle THz pulse undergoes multiple internal reflections within the Si substrate, and the THz absorption by the graphene layer accumulates through the multiple interactions with the graphene/Si interface. We exploit the large absorption of the multiply reflected THz pulses to acquire high-contrast THz images of graphene. We obtain local sheet conductivity of the graphene layer analyzing the transmission data with thin-film Fresnel formula based on the Drude model.Keywords: Graphene, Time-domain spectroscopy, Multiple internal reflections, Terahertz imagin

Translocation of silver nanoparticles in the ex vivo human placenta perfusion model characterized by single particle ICP-MS

With the extensive use of silver nanoparticles (AgNPs) in various consumer products their potential toxicity is of great concern especially for highly sensitive population groups such as pregnant women and even the developing fetus. To understand if AgNPs are taken up and cross the human placenta, we studied their translocation and accumulation in the human ex vivo placenta perfusion model by single particle ICP-MS (spICP-MS). The impact of different surface modifications on placental transfer was assessed by AgNPs with two different modifications: polyethylene glycol (AgPEG NPs) and sodium carboxylate (AgCOONa NPs). AgNPs and ionic Ag were detected in the fetal circulation in low but not negligible amounts. Slightly higher Ag translocation across the placental barrier for perfusion with AgPEG NPs and higher AgNP accumulation in placental tissue for perfusion with AgCOONa NPs were observed. Since these AgNPs are soluble in water, we tried to distinguish between the translocation of dissolved and particulate Ag. Perfusion with AgNO3 revealed the formation of Ag containing NPs in both circulations over time, of which the amount and their size in the fetal circulation were comparable to those from perfusion experiments with both AgNP types. Although we were not able to clarify whether intact AgNPs and/or Ag precipitates from dissolved Ag cross the placental barrier, our study highlights that uptake of Ag ions and/or dissolution of AgNPs in the tissue followed by re-precipitation in the fetal circulation needs to be considered as an important pathway in studies of AgNP translocation across biological barriers

Translocation of silver nanoparticles in the ex vivo human placenta perfusion model characterized by single particle ICP-MS

With the extensive use of silver nanoparticles (AgNPs) in various consumer products their potential toxicity is of great concern especially for highly sensitive population groups such as pregnant women and even the developing fetus. To understand if AgNPs are taken up and cross the human placenta, we studied their translocation and accumulation in the human ex vivo placenta perfusion model by single particle ICP-MS (spICP-MS). The impact of different surface modifications on placental transfer was assessed by AgNPs with two different modifications: polyethylene glycol (AgPEG NPs) and sodium carboxylate (AgCOONa NPs). AgNPs and ionic Ag were detected in the fetal circulation in low but not negligible amounts. Slightly higher Ag translocation across the placental barrier for perfusion with AgPEG NPs and higher AgNP accumulation in placental tissue for perfusion with AgCOONa NPs were observed. Since these AgNPs are soluble in water, we tried to distinguish between the translocation of dissolved and particulate Ag. Perfusion with AgNO3 revealed the formation of Ag containing NPs in both circulations over time, of which the amount and their size in the fetal circulation were comparable to those from perfusion experiments with both AgNP types. Although we were not able to clarify whether intact AgNPs and/or Ag precipitates from dissolved Ag cross the placental barrier, our study highlights that uptake of Ag ions and/or dissolution of AgNPs in the tissue followed by re-precipitation in the fetal circulation needs to be considered as an important pathway in studies of AgNP translocation across biological barriers

Photo-Thermoelectric Effect at a Graphene Interface Junction. Nano Lett

ABSTRACT We investigate the optoelectronic response of a graphene single-bilayer interface junction using photocurrent (PC) microscopy. We measure the polarity and amplitude of the PC while varying the Fermi level by tuning a gate voltage. These measurements show that the generation of PC is by a photothermoelectric effect. The PC displays a factor of ∼10 increase at the cryogenic temperature as compared to room temperature. Assuming the thermoelectric power has a linear dependence on the temperature, the inferred graphene thermal conductivity from temperature dependent measurements has a T 1.5 dependence below ∼100 K, which agrees with recent theoretical predictions. KEYWORDS Graphene, photocurrent, photo-thermoelectric effect D evices that convert photons to electrical current, such as photodetectors and photovoltaic devices, are the backbone of optoelectronics. For semiconductor optoelectronic devices, photocurrent (PC) generation is mainly due to separation of the excited electron-hole pair by a built-in electric field, as shown in Graphene is an interesting potential optoelectronic material with unusual electronic, optical, and thermal properties. A graphene interface junction, formed by single-bilayer graphene (G1/G2) as shown i

Onjuist geneesmiddelgebruik bij ouderen opsporen: de herziene STOPP- en START-criteria

- Het gebruik van potentieel ongeschikte geneesmiddelen door ouderen en potentiële omissies in de voorgeschreven geneesmiddelen vormen een omvangrijk probleem. Dit verhoogt het risico op bijwerkingen, maar is deels beïnvloedbaar. - Het gebruik van de in Ierland ontwikkelde STOPP- en START-criteria voor het optimaliseren van farmacotherapie bij ouderen vermindert het aantal geneesmiddelbijwerkingen en medicatiefouten. - Registratie van nieuwe geneesmiddelen, uitbreiding van het aantal potentieel ongeschikte geneesmiddelen en de beschikbaarheid van nieuwe literatuur gaven aanleiding tot herziening van de eerste versie van de STOPP- en START-criteria, die in 2008 verscheen. - Om een breder toepasbaar screeningsinstrument te ontwikkelen werd bij de 2e versie van de STOPP- en START-criteria gekozen voor een consensuspanel met experts op het gebied van farmacotherapie bij ouderen uit 14 Europese landen, waaronder 2 uit Nederland. - De vertaling van de 2e versie van de STOPP- en START-criteria is aangepast aan de Nederlandse situatie, onder meer door geneesmiddelen die in Nederland niet geregistreerd zijn, weg te laten