Peculiarities of electronic structure and composition in ultrasound milled silicon nanowires

The combined X-ray absorption and emission spectroscopy approach was applied for the detailed electronic structure and composition studies of silicon nanoparticles produced by the ultrasound milling of heavily and lowly doped Si nanowires formed by metal-assisted wet chemical etching. The ultrasoft X-ray emission spectroscopy and synchrotron based X-ray absorption near edges structure spectroscopy techniques were utilize to study the valence and conduction bands electronic structure together with developed surface phase composition qualitative analysis. Our achieved results based on the implemented surface sensitive techniques strongly suggest that nanoparticles under studies show a significant presence of the silicon suboxides depending on the pre nature of initial Si wafers. The controlled variation of the Si nanoparticles surface composition and electronic structure, including band gap engineering, can open a new prospective for a wide range Si-based nanostructures application including the integration of such structures with organic or biological systems

МИКРОСКОПИЧЕСКИЕ И РЕНТГЕНОСПЕКТРАЛЬНЫЕ ИССЛЕДОВАНИЯ МАССИВОВ СТОЛБИКОВ НИКЕЛЯ В МАТРИЦЕ ДИОКСИДА КРЕМНИЯ

Ni rods distributed in silicon dioxide matrix formed on silicon wafers have been characterized by means of scanning electron microscopy and X–ray absorption near edge structure (XANES) spectroscopy. Ni rods have been obtained by electrochemical deposition of the metal onto a silicon dioxide matrix pores formed with the tracking technique. Latent tracks have been obtained by SiO2 film irradiation  with heavy gold ions at the Hahn–Meitner–Institute (Berlin, Germany). Scanning electron microscopy has established the peculiarities of pore filling with metal and the specificity of Ni rod formation and their morphology (surface and cleavages). High intensity synchrotron radiation of the Helmholtz Zentrum Berlin has been used in the ultrasoft X–ray range for electron energy structure studies of the Ni rods with the XANES technique. The specific phase composition of the surface layers has been investigated using Si, Ni and O atom local surrounding analysis performed based on synchrotron XANES technique data including the rod/matrix interface. Possible Ni silicide formation has been demonstrated for a certain rod array formation mode in which partial SiO2 matrix destruction occurs and the metal contacts with the silicon wafer. Natural oxidation specificity has also been studied for the Ni rod/SiO2 heterostructure surface.Методом растровой электронной микроскопии (РЭМ) и спектроскопии ближней тонкой структуры края рентгеновского поглощения (X−ray absorption near edge structure — XANES) проведена диагностика массивов столбиков никеля, распределенных в матрице SiO2 на подложке кремния. Столбики Ni получены методом электрохимического осаждения металла в поры матрицы диоксида кремния, сформированные трековым методом. Латентные треки получены путем облучения слоя SiO2 тяжелыми ионами золота на ускорителе Института Хан−Майтнер (Берлин, Германия). Методом РЭМ установлены особенности заполнения пор металлом, показана специфика образования столбиков Ni, их морфология (поверхность и сколы). Электронно−энергетическое строение массивов столбиков Ni исследовано методом XANES с помощью высокоинтенсивного синхротронного излучения ультрамягкого рентгеновского диапазона накопительного кольца BESSY II Гельмгольц−центра г. Берлина. Путем анализа локального окружения атомов кремния, никеля и кислорода по данным синхротронного метода XANES изучена специфика фазового состава поверхностных слоев, включая границу раздела столбик−матрица. Возможное образование фазы силицида никеля показано лишь при определенных режимах формирования массивов столбиков: в случае частичного разрушения матрицы диоксида кремния и при контакте металла с подложкой Si. Изучена специфика естественного окисления поверхности гетероструктуры «столбик никеля — диоксид кремния»

Silicon Suboxides as Driving Force for Efficient Light Enhanced Hydrogen Generation on Silicon Nanowires

Efficient light stimulated hydrogen generation from top down produced highly doped n type silicon nanowires SiNWs with silver nanoparticles AgNPs in water containing medium under white light irradiation is reported. It is observed that SiNWs with AgNPs generate at least 2.5 times more hydrogen than SiNWs without AgNPs. The authors results, based on vibrational, UV vis, and X ray spectroscopy studies, strongly suggest that the sidewalls of the SiNWs are covered by silicon suboxides, by up to a thickness of 120 nm, with wide bandgap semiconductor properties that are similar to those of titanium dioxide and remain stable during hydrogen evolution in a water containing medium for at least 3 h of irradiation. Based on synchrotron studies, it is found that the increase in the silicon bandgap is related to the energetically beneficial position of the valence band in nanostructured silicon, which renders these promising structures for efficient hydrogen generatio