New approaches to the synthesis of hybrid materials InP - organic stabilizer

         The project aims to create a hybrid semiconductor materials - organic stabilizer representing quantum dots InP. Such materials are nanocrystalline electronic transitions in the visible and near infrared range, and have high recombination efficiency of luminescence, and therefore are used for the creation of photodetectors solar batteries electroluminescent devices, the devices for transmitting the signal via fiber optic telecommunications link , as well as biotechnology as fluorescent markers - biomarkers . Hybrid materials based on A3B5 compounds are especially useful as biomarkers . For use in biomedical hybrid materials based A3B5 is necessary that they be water soluble and emit at wavelengths minimally absorbed and scattered in biological fluids and tissues. Last condition corresponds to the so -called biological transparency window within 700-900 nm. Currently used in practice only a very limited range of organic dyes (Cy7, IRDye78, indocyanine green), which , in contrast to materials based on nanocrystals do not have sufficient photostability and are characterized by low quantum yield of luminescence.
    An important step is to obtain biomarkers perevedeniem received fluorescent structures in the aqueous phase . The water-soluble quantum dots can be obtained in two ways - either by synthesis of the quantum dots themselves when used as a surface stabilizer nanocrystals bifunctional ligands polar or non-polar by substitution at the shell are synthesized CT polar . During the first scan method is attempted to produce CT stabilized geptandikarbonovoy and 6 - aminocaproic acid in the presence of myristic acid , which led to unsatisfactory results - obtained nanocrystals stitched together these bifunctional molecules. In connection with this work has focused on ways to obtain the second water-soluble RT. To replace the membranes using standard samples CT InP, myristic acid, stabilized, and samples heterostructures InP / ZnSe with two monolayers Accrued zinc selenide and also stabilized myristic acid. Initial samples were mixed mixed with 5 -fold excess of mercaptoacetic 3- mercaptopropionate, and 6 - aminocaproic acid . If merkaptokislot as InP, and InP / ZnSe QDs immediately coagulated and precipitated , which means almost instant replacement myristic shell on bipolar mercapto- shell. Selected samples were dissolved in aqueous ammonia to pH 10-11. For InP samples turbidity and discoloration was observed due to irreversible degradation of - apparently merkaptostabilizatory weakly bound to the surface of pure nanokrstallov InP, or In-S bond on the surface is easily hydrolyzed such colloids . It should be noted that aqueous solutions heterostructures InP / ZnSe are stable , no degradation was observed during the months of storage . In experiments on membranes replacing 6 - aminocaproic acid sludge formation were observed. Extraction of the aqueous phase also failed. IR spectra of the samples which have undergone the replacement of the shell not differ from the IR spectrum of the original sample InP, stabilized MA, and on said characteristic spectra missing band oscillations and NH_2- NH₃  groups. It can be concluded that the replacement of the shell does not occur, apparently due to a rather strong binding of myristic acid core CT, and low solubility in non-polar amino acid environments in which the experiments were carried out by replacing the shell.
    Study of the luminescence of the studied samples showed its complete lack of InP- aqueous solutions , which is a result of poor stabilization of surface defects merkaptokislotami . For InP / ZnSe- samples observed red- orange luminescence with a maximum at about 650 nm and a quantum yield of less than 1% . These results also reflect a weak stabilization nanostructure surface , but more severe than in the case of pure InP by the presence of atoms on the surface of Zn, forming a rather strong bonds with sulfur.
    An important objective is to obtain InP quantum dots with high quantum yield of luminescence. Photoetching uncoated InP samples described earlier. Photoetching xenon lamp purified and dissolved in THF sample InP / ZnSe led to an increase in the quantum yield up to 29% for 1 hour there is a gradual increase in luminescence with a slight shift to the red (up to 10 nm). In the process took fototrafleniya add a slight excess of TOP / TOPO, without which received luminescent nanostructures precipitated . Myristic acid, apparently poorly bonded to the surface and nanocrystalls during etching "washed" with samples and excess TOP / TOPO stabilizes again well prepared surface.


KEYWORDS
Indium phosphide quantum dots, biomarkers, nanocrystalline semiconductors, photoetching