287 research outputs found

    Probing the Surface of Nanodiamonds at Stanford Synchrotron Radiation Lightsource and San Jose State University

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    The nitrogen-vacancy center in diamond is a promising tool in oncology, electric field sensing, and quantum cryptography. High-pressure high-temperature (HPHT) nanodiamonds (NDs) are prime contenders for these fields because they host nitrogen-vacancy centers (NVCs) which are applicable towards cancer detection and electric and magnetic field sensing. However, to apply HPHT NDs to these fields, the surface must first be functionalized—a difficult process because of the inert nature of the surface. The project at hand focuses on surface modification of HPHT NDs with amines to allow for further bioconjugation of small molecules and plasmonic shells. This is done via liquid-phase chemistry and high-temperature gas-phase chemistry. To characterize the surface of aminated NDs, samples are probed using synchrotron radiation at the Stanford Synchrotron Radiation Lightsource (SSRL) alongside the transmission edge spectroscopy (TES) detector. Aminated NDs were characterized using X-ray photoelectric spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) at SSRL. X-ray spectra are suggestive of multiple nitrogen moieties on the surface of the aminated NDs. With verification of a homogeneously amine-terminated surface, the NDs are prepared for further functionalization which can be targeted to enhance the properties of the NVC charge states for applications in enhanced electric field and voltage sensing

    Influence of Topology on the Ultrafast Carrier Dynamics in MoTe2

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    Transport properties of Weyl semimetals are intimately connected to the underlying band structure. The signature of Weyl semimetals are linear dispersing bands that touch, forming Weyl points that result in high charge carrier mobilities. The layered transition metal dichalcogenide MoTe2, undergoes a temperature dependent phase transition that directly converts the trivial 1Tprime phase to the nontrivial Td phase, providing an opportunity to understand how the formation of a Weyl point manifests in the ultrafast carrier dynamics. In this study, we use resonant X-ray photoemission to monitor the element specific evolution of excited carriers 1Tprime-MoTe2 and in the vicinity of the Weyl point in Td-MoTe2. We find that the delocalization time of 1Tprime-MoTe2 is a factor 1.5 times faster than in Td-MoTe2. We argue that this is a result of the change in the density of states and screening length, to a higher carrier scattering rate in Td-MoTe2. Our study tracks the fate of carriers in MoTe2 on sub-fs time-scales and with atomic site specificity

    Efficacy of atmospheric pressure dielectric barrier discharge for inactivating airborne pathogens

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    Atmospheric pressure plasmas have gained attention in recent years for several environmental applications. This technology could potentially be used to deactivate airborne microorganisms, surface-bound microorganisms, and biofilms. In this work, the authors explore the efficacy of the atmospheric pressure dielectric barrier discharge (DBD) to inactivate airborne Staphylococcus epidermidis and Aspergillus niger that are opportunistic pathogens associated with nosocomial infections. This technology uses air as the source of gas and does not require any process gas such as helium, argon, nitrogen, or hydrogen. The effect of DBD was studied on aerosolized S. epidermidis and aerosolized A. niger spores via scanning electron microscopy (SEM). The morphology observed on the SEM micrographs showed deformations in the cellular structure of both microor- ganisms. Cell structure damage upon interaction with the DBD suggests leakage of vital cellular materials, which is a key mechanism for microbial inactivation. The chemical structure of the cell surface of S. epidermidis was also analyzed by near edge x-ray absorption fine structure spectros- copy before and after DBD exposure. Results from surface analysis revealed that reactive oxygen species from the DBD discharge contributed to alterations on the chemistry of the cell membrane/ cell wall of S. epidermidis
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