3 research outputs found
Evolution of pseudo-spherical silicon nanocrystals to tetrahedra, mediated by phosphonic acid surfactants.
Silicon nanocrystals were synthesised at high temperatures and high pressures by the thermolysis of diphenylsilane using a combination of supercritical carbon dioxide and phosphonic acid surfactants. Size and shape evolution from pseudo-spherical silicon nanocrystals to well faceted tetrahedral-shaped silicon crystals with edge lengths in the range of 30-400 nm were observed with sequentially decreasing surfactant chain lenghts. The silicon nanocrystals were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), photoluminescence (PL), scanning electron microscopy (SEM) and Raman scattering spectroscopy
Effect of Boron Doping on the Wear Behavior of the Growth and Nucleation Surfaces of Micro- and Nanocrystalline Diamond Films
B-doped diamond has become the ultimate
material for applications
in the field of microelectromechanical systems (MEMS), which require
both highly wear resistant and electrically conductive diamond films
and microstructures. Despite the extensive research of the tribological
properties of undoped diamond, to date there is very limited knowledge
of the wear properties of highly B-doped diamond. Therefore, in this
work a comprehensive investigation of the wear behavior of highly
B-doped diamond is presented. Reciprocating sliding tests are performed
on micro- and nanocrystalline diamond (MCD, NCD) films with varying
B-doping levels and thicknesses. We demonstrate a linear dependency
of the wear rate of the different diamond films with the B-doping
level. Specifically, the wear rate increases by a factor of 3 between
NCD films with 0.6 and 2.8 at. % B-doping levels. This increase in
the wear rate can be linked to a 50% decrease in both hardness and
elastic modulus of the highly B-doped NCD films, as determined by
nanoindentation measurements. Moreover, we show that fine-grained
diamond films are more prone to wear. Particularly, NCD films with
a 3× smaller grain size but similar B-doping levels exhibit a
double wear rate, indicating the crucial role of the grain size on
the diamond film wear behavior. On the other hand, MCD films are the
most wear-resistant films due to their larger grains and lower B-doping
levels. We propose a graphical scheme of the wear behavior which involves
planarization and mechanochemically driven amorphization of the surface
to describe the wear mechanism of B-doped diamond films. Finally,
the wear behavior of the nucleation surface of NCD films is investigated
for the first time. In particular, the nucleation surface is shown
to be susceptible to higher wear compared to the growth surface due
to its higher grain boundary line density
Influence of the Chalcogen Element on the Filament Stability in CuIn(Te,Se,S)<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> Filamentary Switching Devices
In
this paper, we report on the use of CuInX<sub>2</sub> (X = Te, Se,
S) as a cation supply layer in filamentary switching applications.
Being used as absorber layers in solar cells, we take advantage of
the reported Cu ionic conductivity of these materials to investigate
the effect of the chalcogen element on filament stability. In situ
X-ray diffraction showed material stability attractive for back-end-of-line
in semiconductor industry. When integrated in 580 μm diameter
memory cells, more volatile switching was found at low compliance
current using CuInS<sub>2</sub> and CuInSe<sub>2</sub> compared to
CuInTe<sub>2</sub>, which is ascribed to the natural tendency for
Cu to diffuse back from the switching layer to the cation supply layer
because of the larger difference in electrochemical potential using
Se or S. Low-current and scaled behavior was also confirmed using
conductive atomic force microscopy. Hence, by varying the chalcogen
element, a method is presented to modulate the filament stability