Defect information is critical for both fundamental research and industrial analysis of metals and semiconductors. Diffraction contrast is the basis for defect imaging using either X-ray or electron microscopy. Taking the advantage of high resolution in electron microscopy techniques, here we evaluate the efficiency for diffraction contrast imaging based on scanning transmission electron microscopy. The working principle and application are demonstrated using the typical semiconductor material silicon as an example. The efficiency is improved at least an order of magnitude compared with conventional electron microscopy method.
Detection of dopamine, an important neurotransmitter, is vital for understanding its roles in mammals and disease diagnosis. However, commonly available methods for dopamine detection typically rely on a single signal readout, which can be susceptible to interference by internal or external factors. Here, we report a dual-signal detection of dopamine based on label-free luminescent NaGdF4:Tb nanoparticles. In the presence of dopamine, the NaGdF4:Tb nanoparticles exhibit luminescence quenching under the excitation of 272 nm, while they give enhanced luminescence under 297 nm excitation, realizing both turn off and turn on detection of dopamine. The nanoparticle-based dual-signal sensors exhibit high sensitivity, with a detection limit of â¼30 nM, and good selectivity, which offers the possibility to identify potential interferents in the samples. We further demonstrate that the dual-signal response results from different energy-transfer processes within the nanoparticles under the excitation of different light. The new strategy demonstrated here should pave the way for the development of multiresponse nanosensors based on lanthanide-doped luminescent nanomaterials.
Dopamine/analysis , Luminescent Agents/chemistry , Luminescent Measurements/methods , Metal Nanoparticles/chemistry , Neurotransmitter Agents/analysis , Dopamine/blood , Dopamine/radiation effects , Dopamine/urine , Energy Transfer , Gadolinium/chemistry , Gadolinium/radiation effects , Humans , Limit of Detection , Luminescence , Luminescent Agents/radiation effects , Metal Nanoparticles/radiation effects , Neurotransmitter Agents/blood , Neurotransmitter Agents/radiation effects , Neurotransmitter Agents/urine , Terbium/chemistry , Terbium/radiation effects , Ultraviolet Rays
Enhancing upconversion emission is critical for small-sized lanthanide doped upconversion nanocrystals. A promising way is increasing the doping concentration of excitation energy absorbers, the Yb3+ sensitizer. However, it is still a challenge to obtain small-sized hexagonal NaLnF4 (Ln: lanthanide) upconversion nanocrystals with a high Yb3+ concentration due to the fast growth of NaYbF4 crystals, which hinders their applications particularly in biology. We here demonstrate a highly repeatable and controllable method for tuning the size of hexagonal NaYbF4 nanocrystals, down to â¼7 nm, without the assistance of additional impurity doping. By monitoring the reaction process, we found that ultrasmall hexagonal NaYbF4 nanocrystals were formed through an in situ transformation of their cubic counterparts. We observed an enhanced upconversion emission of NaYbF4:Tm nanocrystals when compared to that of NaYbF4:Y/Tm nanocrystals with less Yb3+ doping. After coating a thin layer of a NaYF4 shell on NaYbF4:Tm nanocrystals, a â¼100 times upconversion emission enhancement with over 800 times stronger emission in the ultraviolet and blue ranges was observed. This versatile method, together with the strong upconversion emission of the as-prepared ultrasmall nanocrystals, should facilitate the future applications of upconversion nanocrystals.
