Black Silicon with high density and high aspect ratio nanowhiskers

Physical properties of black Silicon (b-Si) formed on Si wafers by reactive ion etching in chlorine plasma are reported in an attempt to clarify the formation mechanism and the origin of the observed optical and electrical phenomena which are promising for a variety of applications. The b-Si consisting of high density and high aspect ratio sub-micron length whiskers or pillars with tip diameters of well under 3 nm exhibits strong photoluminescence (PL) both in visible and infrared, which are interpreted in conjunction with defects, confinement effects and near band-edge emission. Structural analysis indicate that the whiskers are all crystalline and encapsulated by a thin Si oxide layer. Infrared vibrational spectrum of Si-O-Si bondings in terms of transverse-optic (TO) and longitudinal-optic (LO) phonons indicates that disorder induced LO-TO optical mode coupling can be an effective tool in assessing structural quality of the b-Si. The same phonons are likely coupled to electrons in visible region PL transitions. Field emission properties of these nanoscopic features are demonstrated indicating the influence of the tip shape on the emission. Overall properties are discussed in terms of surface morphology of the nano whiskers

The effect of equine-derived bone protein extract (Colloss-E) in the treatment of cavitary bone defects: An experimental study

Objective: Bone protein extract (BPE) usually requires a carrier or a scaffold for implantation. We aimed to compare the effect of equine-derived BPE, an osteoinductive agent composed of a high amount of type-I collagen and other bone proteins (Colloss-E), with that of human demineralized bone matrix (DBM) for treating cavitary bone defects not requiring scaffold use. Methods: Rabbit distal femoral condyle was used as a stable cavitary bone defect model. Bone defects of 6-mm diameter and 10-12-mm depth were created in the femoral condyles. Rabbits were assigned into the equine-derived BPE (BPE) , human-derived DBM (DBM), and control (C) groups. Approximately 20 mg of BPE was implanted into the defect in the equine-derived BPE group (n=6), whereas 0.3 cc of DBM was implanted in the DBM group (n=6). Defects were left empty in the C group (n=6). The defect area was histologically examined after 6 weeks. Results: There were no instances of macroscopic defect collapse or failure. Histopathological examination revealed that the BPE group had better scores (statistically significant) than both the other groups in terms of quality of union. The BPE group also had higher scores than the DBM group in terms of graft incorporation and new-bone formation. Conclusion: The current study revealed results consistent with those of the previous studies concerning BPEs. Equine-derived BPE was found to be successful for treating cavitary bone defects not requiring scaffold use. © 2015 Turkish Association of Orthopaedics and Traumatology

Controlled thinning and surface smoothening of silicon nanopillars

A convenient method has been developed to thin electron beam fabricated silicon nanopillars under controlled surface manipulation by transforming the surface of the pillars to an oxide shell layer followed by the growth of sacrificial ammonium silicon fluoride coating. The results show the formation of an oxide shell and a silicon core without significantly changing the original length and shape of the pillars. The oxide shell layer thickness can be controlled from a few nanometers up to a few hundred nanometers. While downsizing in diameter, smooth Si pillar surfaces of less than 10 nm roughness within 2 µm were produced after exposure to vapors of HF and HNO3 mixture as evidenced by transmission electron microscopy (TEM) analysis. The attempt to expose for long durations leads to the growth of a thick oxide whose strain effect on pillars can be assessed by coupled LO–TO vibrational modes of Si–O bonds. Photoluminescence (PL) of the pillar structures which have been downsized exhibits visible and infrared emissions, which are attributable to microscopic pillars and to the confinement of excited carriers in the Si core, respectively. The formation of smooth core–shell structures while reducing the diameter of the Si pillars has a potential in fabricating nanoscale electronic devices and functional components