Coincident Doppler‐broadening spectroscopy of Si, amorphous SiO₂, and α‐quartz using mono‐energetic positrons

Abstract

Experiments on oxides and on silicon by coincident Doppler broadening spectroscopy (CDBS) using the mono‐ener‐ getic positron beam at the neutron induced positron source NEPOMUC are presented. Doppler‐broadening spectroscopy (DBS) as a function of positron implantation energy is applied in order to compare the crystalline quartz and single crystalline Si with amorphous quartz. More detailed information about the chemical surrounding at the positron annihilation site is gained by CDBS‐experiments. For this reason, the CDBS‐measurements are performed to detect the signature of positrons annihilating with electrons from oxygen. The comparison of the CDB spectra obtained for the quartz samples and ice with that of the Si surface clearly shows that the surface of single‐crystalline Si is terminated with oxygen. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Interstitial oxygen related defects and nanovoids in Au implanteda-SiO2glass depth profiled by positron annihilation spectroscopy

“…In figure 8 the ratio curve of Au and Herasil-1 silica glass, as obtained with equation ( 8), are shown. The ratio curve of Au has two peaks centred at ∼12 10 3 × − m 0 c and 35 10 3 × − m 0 c. Herasil-1 curve has a first peak at 10 10 3 × − m 0 c followed by a bump with a maximum around 40 10 3 × − m 0 c, which is in agreement with previous studies on both amorphous silica and crystalline quartz [57].…”

Asymmetric Positron Interactions with Chiral Quartz Crystals?

“…In selecting potential chiral materials, crystalline quartz came to the fore as an excellent material to study using positron experiments, since the enantiomorphs are available and can be compared to fused quartz [14][15][16]. Quartz in its α crystalline form occurs naturally in two chiral space groups; the quartz selected for our experiments is commercially available as RH or LH α-quartz rotators.…”

“…Beam Measurements. The "S parameter" of Doppler broadening energy spectra (DBES) was measured as a function of depth using a monoenergetic slow positron beam [16,23,24]. DBES spectra (Figure 2) were recorded as a function of positron implantation energy from around 0 to 30 keV using an HPGe detector (EG&G Ortec.…”

Caracterización de nanoestructuras sub-superficiales utilizando espectroscopía de aniquilación de positrones

“…5, podría inferirse que en los nanohuecos en los cuales se aniquilan los positrones, se encuentran decorados con átomos de Au ya que ambas curvas presentan características cualitativamente similares. Sin embargo, teniendo en cuenta que en la literatura se ha reportado que las curvas CDB correspondientes al SiO2 (tanto cuarzo como distintos tipos de vidrios) presentan un pico ancho y centrado en aproximadamente 30-35 (x10-3 m0c2) y que dicho pico fue atribuido a la aniquilación de positrones con electrones pertenecientes al core de oxígeno de la molécula SiO2 [23] es que el corrimiento de los picos podría explicarse considerando que los nanohuecos están decorados con átomos de Au y de oxígeno. Una discusión más refinada requiere del auxilio de cálculos teóricos del proceso de aniquilación electrón-positrón [24], tema en el cual nos encontramos trabajando en este momento.…”