2 research outputs found
Integrating AlN with GdN Thin Films in an in Situ CVD Process: Influence on the Oxidation and Crystallinity of GdN
The
application potential of rare earth nitride (REN) materials has been
limited due to their high sensitivity to air and moisture leading
to facile oxidation upon exposure to ambient conditions. For the growth
of device quality films, physical vapor deposition methods, such as
molecular beam epitaxy, have been established in the past. In this
regard, aluminum nitride (AlN) has been employed as a capping layer
to protect the functional gadolinium nitride (GdN) from interaction
with the atmosphere. In addition, an AlN buffer was employed between
a silicon substrate and GdN serving as a seeding layer for epitaxial
growth. In pursuit to grow high-quality GdN thin films by chemical
vapor deposition (CVD), this successful concept is transferred to
an in situ CVD process. Thereby, AlN thin films are included step-wise
in the stack starting with Si/GdN/AlN structures to realize long-term
stability of the oxophilic GdN layer. As a second strategy, a Si/AlN/GdN/AlN
stacked structure was grown, where the additional buffer layer serves
as the seeding layer to promote crystalline GdN growth. In addition,
chemical interaction between GdN and the Si substrate can be prevented
by spatial segregation. The stacked structures grown for the first
time with a continuous CVD process were subjected to a detailed investigation
in terms of structure, morphology, and composition, revealing an improved
GdN purity with respect to earlier grown CVD thin films. Employing
thin AlN buffer layers, the crystallinity of the GdN films on Si(100)
could additionally be significantly enhanced. Finally, the magnetic
properties of the fabricated stacks were evaluated by performing superconducting
quantum interference device measurements, both of the as-deposited
films and after exposure to ambient conditions, suggesting superparamagnetism
of ferromagnetic GdN grains. The consistency of the magnetic properties
precludes oxidation of the REN material due to the amorphous AlN capping
layer
Photoactive Zinc Ferrites Fabricated via Conventional CVD Approach
Owing
to its narrow band gap and promising magnetic and photocatalytic
properties, thin films of zinc ferrite (ZFO, ZnFe<sub>2</sub>O<sub>4</sub>) are appealing for fabrication of devices in magnetic recording
media and photoelectrochemical cells. Herein we report for the first
time the fabrication of photactive zinc ferrites via a solvent free,
conventional CVD approach, and the resulting ZFO layers show promise
as a photocatalyst in PEC water-splitting. For large scale applications,
chemical vapor deposition (CVD) routes are appealing for thin film
deposition; however, very little is known about ZFO synthesis following
CVD processes. The challenge in precisely controlling the composition
for multicomponent material systems, such as ZFO, via conventional
thermal CVD is an issue that is caused mainly by the mismatch in thermal
properties of the precursors. The approach of using two different
classes of precursors for zinc and iron with a close match in thermal
windows led to the formation of polycrystalline spinel type ZFO. Under
the optimized process conditions, it was possible to fabricate solely
ZFO in the desired phase. This work demonstrates the potential of
employing CVD to obtain photoactive ternary material systems in the
right composition. For the first time, the application of CVD grown
ZFO films for photoelectrochemical applications is being demonstrated,
showing a direct band gap of 2.3 eV and exhibiting activity for visible
light driven photoelectrochemical water splitting