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

Photoluminescence from silicon nanoparticles embedded in ammonium silicon hexafluoride

Silicon (Si) nanoparticles (NPs) were synthesized by transforming a Si wafer surface to ammonium silicon hexafluoride (ASH) or (NH4)(2)SiF6 under acid vapor treatment. Si-NPs which were found to be embedded within the polycrystalline (ASH) layer exhibit a strong green-orange photoluminescence (PL). Differential PL measurements revealed a major double component spectrum consisting of a broad band associated with the ASH-Si wafer interfacial porous oxide layer and a high energy band attributable to Si-NPs embedded in the ASH. The origin of the latter emission can be explained in terms of quantum/spatial confinement effects probably mediated by oxygen related defects in or around Si-NPs. Although Si-NPs are derived from the interface they are much smaller in size than those embedded within the interfacial porous oxide layer (SiOx, x > 1.5). Transmission electron microscopy (TEM) combined with Raman scattering and Fourier transformed infrared (FTIR) analysis confirmed the presence of Si-NP and Si-O bondings pointing to the role of oxygen related defects in a porous/amorphous structure. The presence of oxygen of up to 4.5 at.% in the (NH4)(2)SiF6 layer was confirmed by energy dispersive spectroscopy (EDS) analysis

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

Microscopic Si whiskers

Physical properties of microscopic silicon whiskers formed 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. The silicon whiskers with diameters of well under 5 nm exhibit strong photoluminescence (PL) both in visible and infrared, which are related to quantum confinement, near band-edge and defects. Vibrational analysis indicate that disorder induced LO-TO optical mode coupling is very effective. Electric field emission properties of these microscopic features were also investigated to determine their potential for advanced technology applications. (C) 2011 Elsevier B.V. All rights reserved

Wood fuels consumption in households in Bosnia and Herzegovina

The paper shows research results for the consumption of all types of wood fuels in the households in Bosnia and Herzegovina and its entities in 2015. The research was conducted in the period from March 15th to August 26th, 2016 in 109 cities/municipalities in the entire Bosnia and Herzegovina. Complex methodological approach was used for conducting the research, which required field research on the sample of 8,602 households on the entire territory of Bosnia and Herzegovina as well as adequate statistical processing of the obtained data pursuant to the high statistical standards. Research results show that in 2015, 5.4 million m3 of firewood, 81,656 tones of wood pellets, and 6,780 tones of wood briquettes were consumed in the households in Bosnia and Herzegovina. Total expenses of households necessary for the supply of wood fuels in Bosnia and Herzegovina in 2015 were 239.8 M€, with the largest share of firewood (226.8 M€), followed by wood pellets (11.6 M€), and wood briquettes (720.9 thousand €). Average firewood consumption per household in Bosnia and Herzegovina is 6.43 m3. Compared to the surrounding countries it is on the level of Slovenia (6.5 m3 per household), less than in Serbia (7.3 m3 per household) and more than in Montenegro (5.49 m3 per household). Average consumption of energy from firewood expressed in kWh/m2 of the heated surface was 252.7 kWh, which is significantly higher than the average in the EU. One of the reasons for such high consumption of wood energy per 1 m2 of the heated surface is the fact that only 36.1% of the households using solid fuels have thermal insulation on their residential facilities

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 \ub5m 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