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Emergence of dark ZnO nanorods by hydrogen plasma treatment
Remeš, Zdeněk ; Buryi, Maksym ; Sharma, Dhananjay K. ; Artemenko, Anna ; Mičová, J. ; Rezek, B. ; Poruba, A. ; Hsu, H.S. ; Potocký, Štěpán ; Babin, Vladimir
We employed a custom-built inductively coupled plasma (ICP) 13.56 MHz reactor with up to 300 W RF discharge power. Hydrothermally grown ZnO nanorods were exposed to the ICP plasma with a mixture of hydrogen and argon for up to 30 min, followed in-situ by plasma oxidation. Plasma properties were monitored by optical emission spectroscopy (OES) and by measuring the self-bias potential of the stainless steel sample holder separated from the ground by a blocking capacitor. The exciton-related UV photoluminescence of ZnO nanorods and optical absorption increases significantly after the plasma treatment. We attribute it to the complex changes of ZnO surface electronic states that also give rise to its black color visually.
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Comparison of microbial interactions of zinc oxide nanomaterials in various size and shape
Rutherford, D. ; Jíra, J. ; Mičová, J. ; Remeš, Zdeněk ; Hsu, H.S. ; Rezek, B.
Zinc oxide nanoparticles (ZnO NP) have shown great potential as a novel antibacterial material at a time when resistance towards conventional antibiotics is becoming more prevalent. We report bacteria inactivation by ZnO NP with novel hedgehog-like morphology using model gram-negative (E. coli) and gram-positive (S. aureus) bacteria. E. coli exposed to the novel ZnO hedgehog NP during growth resulted in 4 orders of magnitude reduction in viable cell concentration after 24 h, which is more than 2 orders higher reduction compared to commercially available ZnO NPs with nominal sizes from 50 nm to 20 um. There was a positive correlation between hedgehog NP concentration and bacteria cell concentration reduction within the range tested 0.1 – 1.0 mg/mL. S. aureus was less sensitive to ZnO NP exposure and inactivation effect of various ZnO NP, was comparable. The effect can be thus attributed to direct mechanical damage of the bacterial mebrane that is the most effective for the novel hedgehog ZnO NP. This conclusion was corroborated also by disk diffusion assays.\n
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The hydrogen plasma doping of ZnO thin films and nanoparticles
Remeš, Zdeněk ; Neykova, Neda ; Potocký, Štěpán ; Chang, Yu-Ying ; Hsu, H.S.
The optical absorptance and photoluminescence studies has been applied on the hydrogen and oxygen plasma treated, nominally undoped ZnO thin films and aligned nanocolumns grown on the nucleated glass substrate by the hydrothermal process in an oil bath containing a flask with ZnO nutrient solution. The localized defect states at 2.3 eV below the optical absorption edge were detected by photothermal deflection spectroscopy (PDS) in a broad spectral range from near UV to near IR. The optical absorptance spectroscopy shows that hydrogen doping increases free electron concentration changing ZnO to be electrically conductive (hydrogen doping).\n
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