RESUMEN
We propose that the post-deposition oxidation of the IGZO surface is essential for improving the interface quality, with Al2O3 prepared by atomic layer deposition (ALD) employing a common metal precursor trimethylaluminum (TMA). Here, the ALD-Al2O3 process was conducted using H2O as an oxidant at a substrate temperature of 150 °C after IGZO deposition. The depth-resolved X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) data reveal the defect-rich and poor interface of the standard Al2O3/IGZO stack due to the redox reaction between the IGZO surface and TMA. The anion character of the IGZO was modified by introducing fluorine, which is known as a stability enhancer for oxide semiconductors. We highlight that the presence of the fluorine also improves the interface quality with ALD-Al2O3. As a consequence of the fluorine incorporation prior to the ALD-Al2O3 process, the chemical reduction reaction of the IGZO surface was effectively alleviated, resulting in a defect-passivated and sharp interface owing to the strong oxidizing nature of the fluorine.
RESUMEN
Collagen/chitosan composite microgranules were fabricated as bone substitutes for the purpose of obtaining high bone-forming efficacy. The microgranules have the flexibility to fill various types of defect sites with closer packing. The interconnected pores formed spaces between the microgranules, which allowed new bone ingrowth and vascularization. In addition, the transforming growth factor-beta 1 (TGF-beta1) was incorporated into the microgranules in order to improve bone-healing efficacy. The collagen/chitosan microgranules were fabricated by dropping a mixed solution into a NaOH/ethanol solution. TGF-beta1 was loaded into the collagen/chitosan microgranules by soaking the microgranules in a TGF-beta1 solution. Scanning electron microscopy (SEM) observations and experiments examining the release of TGF-beta1 from chitosan and the collagen/chitosan microgranules were performed. SEM was used to examine the cell morphologies on the microgranules and cell proliferation was evaluated using a dimethylthiazole tetrazolium bromide assay. The differentiated cell function was assessed by measuring the alkaline phosphatase (ALPase) activity as well as detecting an osteocalcin assay. The in vivo bone-regeneration experiments were performed using a rabbit calvarial defect model. TGF-beta1 was released from the collagen/chitosan microgranules at a therapeutic concentration for 4 weeks. SEM indicated that the seeded osteoblastic cells were firmly attached to the microgranules and proliferated in a multilayer manner. The proliferation of the osteoblasts on the TGF-beta1-loaded microgranules was the highest among the different types of microgranules tested. The ALPase activity and osteocalcin level of all the samples increased during the culture period, and the TGF-beta1-loaded microgranules had a significantly higher ALPase activity and osteocalcin content than the other microgranules. The TGF-beta1-loaded microgranules demonstrated a higher bone-regenerative capacity in the rabbit calvarial defects after 4 weeks than the TGF-beta1-unloaded microgranules.
