The unique magnetic properties of iron oxide nanoparticles have paved the way for various biomedical applications, such as magnetic resonance cellular imaging or magnetically induced therapeutic hyperthermia. Living cells interact with nanoparticles by internalizing them within intracellular acidic compartments. Although no acute toxicity of iron oxide nanoparticles has been reported up to now, the mechanisms of nanoparticle degradation by the cellular environment are still unknown. In the organism, the long term integrity and physical state of iron-based nanoparticles are challenged by iron homeostasis. In this study, we monitored the degradation of 7 nm sized maghemite nanoparticles in a medium mimicking the intracellular environment. Magnetic nanoparticles with three distinct surface coatings, currently evaluated as MRI contrast agents, were shown to exhibit different kinetics of dissolution at an acidic pH in the presence of a citrate chelating agent. Our assessment of the physical state of the nanoparticles during degradation revealed that the magnetic properties, size distribution and structure of the remaining nanocrystals were identical to those of the initial suspension. This result suggests a model for nanoparticle degradation with rapidly dissolved nanocrystals and a reservoir of intact nanoparticles.
Continuous
development of Si photonics requires ecological and cost-effective
materials. In this work, SiGe nanocrystals (NCs) embedded in TiO2 are investigated as a photosensitive material for visible
(VIS) to short-wave infrared (SWIR) broad-range detection. The TiO2 matrix has the advantage of a lower band gap than SiO2, facilitating transport of photogenerated carriers in NCs.
The advantage of SiGe NCs over Ge NCs is emphasized by elucidating
the mechanisms involved in rapid thermal annealing (RTA)-induced nanocrystallization.
An efficiently increased NC stabilization is achieved by avoiding
the detrimental fast Ge diffusion. For this, the structure, morphology,
and composition were carefully characterized by high-resolution transmission
electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction,
and Raman spectroscopy. Two types of structures were investigated,
a film of SiGe–TiO2 alloy and a multilayer of a
stack of six SiGe/TiO2 pairs. The layers have been deposited
on Si wafers using magnetron sputtering of Si, Ge, and TiO2 followed by RTA in an inert atmosphere. The stabilization of SiGe
NCs is achieved by the formation during RTA of protective SiO2 thin layers through Si oxidation at the SiGe NC surface,
acting as a barrier for Ge diffusion. Thus, embedded Ge-rich SiGe
NCs are obtained, resulting in the SWIR extension of the spectral
photocurrent up to 1700 nm for films and 1600 nm for multilayers.
This study has shown that in multilayers, the local anisotropy of
crystallization is compensated by the stress field developed in the
SiGe lattice, highly visible in the bottom part. Also, SiGe crystallizes
faster than TiO2 in the rutile phase, and therefore, TiO2 remains mainly amorphous.
High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO /floating gate of single layer of Ge QDs in HfO/tunnel HfO /p-Si wafers. Both Ge and HfO are nanostructured by RTA at moderate temperatures of 600-700 °C. By nanostructuring at 600 °C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 × 10 m is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO NCs boundaries, while another part of the Ge atoms is present inside the HfO lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8 ± 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.
A strong focus on Superparamagnetic Iron Oxide Nanoparticles (SPIOs) has been appreciated recently especially for their use in Magnetic Resonance Imaging (MRI). However, some questions are being raised over these particles due to their long-term toxicity related to the production of toxic free iron during their biodegradation. Here we show by Electron Microscopy how SPIOs (P904) (Guerbet, Paris) are degraded after they are taken up by macrophages, so that iron from the SPIO core is progressively incorporated into the iron-storing protein ferritin (a nontoxic form of iron).
We
show that a simple ethanol (EtOH) refluxing treatment at mild temperature
(120 °C) allows producing blue-colored and reduced titanium dioxide
(TiO2–x
) exhibiting improved visible-light
(VIS) photocatalytic properties. The treatment causes an increase
in the density of Ti(III) species and the appearance of two optical
absorption features: a broad absorption bandresponsible for
the blue colorationextending from the green region (∼2.3
eV) up to the near-infrared and a subgap absorption tail close to
the band gap energy. The experimental results combined with a computation
of the density of states via hybrid Hartree–Fock density functional
support the hypothesis that the EtOH reflux treatment leads to formation
of surface and subsurface oxygen (O) vacancies. We also show that
the excitation-resolved photoluminescence technique allows a high-contrast
detection of a subgap optical excitation band peaked at about 430
nm (∼2.9 eV), associated with anatase photoluminescence, whose
intensity increases after the EtOH reflux treatment. This result gives
a very direct support to the debated hypothesis identifying O vacancy
states as the energy levels involved in the radiative transition of
anatase TiO2. Improved photocatalytic degradation by the
processed TiO2 under VIS illumination is demonstrated,
and the possible mechanism involved in the formation of surface O
vacancies is discussed. The method outlines a very simple, low-cost,
and fast procedure to target the formation of O vacancies in the TiO2 surface region.
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