5 research outputs found
Dopant Induced Impurity Bands and Carrier Concentration Control for Thermoelectric Enhancement in p‑Type Cr<sub>2</sub>Ge<sub>2</sub>Te<sub>6</sub>
Our previous work demonstrated that Cr<sub>2</sub>Ge<sub>2</sub>Te<sub>6</sub> based compounds with a layered structure and
high symmetry are good candidates for thermoelectric application.
However, the power factor of only ∼0.23 mW/mK<sup>2</sup> in
undoped material is much lower than that of conventional thermoelectrics.
This indicates the importance of an electronic performance optimization
for further improvements. In this work, either Mn- or Fe-substitution
on the Cr site is investigated, with expectations of both carrier
concentration control and band structure engineering. First-principle
calculations indicate that an orbital hybridization between d orbitals
of the doping atom and the p orbital of Te significantly increases
the density of states (DOS) around the Fermi level. In addition, it
is found that Mn doping is more favorable to improve the electrical
properties than Fe doping. By tuning the carrier concentration via
Mn doping, the peak power factor rises rapidly from 0.23 mW/mK<sup>2</sup> to 0.57 mW/mK<sup>2</sup> at 830 K with <i>x</i> = 0.05. Combined with the intrinsic low thermal conductivity, Cr<sub>1.9</sub>Mn<sub>0.1</sub>Ge<sub>2</sub>Te<sub>6</sub> displays a
decent <i>zT</i> of 0.63 at 833 K, a 2-fold value as compared
to that of the undoped sample at the same direction and temperature
Observation of Exotic Domain Structures in Ferroelectric Nanodot Arrays Fabricated via a Universal Nanopatterning Approach
We
report a facile and cost-competitive nanopatterning route, using Ar
ion beam etching through a monolayer polystyrene sphere (PS) array
placed on a ferroelectric epitaxial thin film, to fabricate ordered
ferroelectric nanodot arrays. Using this method, well-ordered BiFeO<sub>3</sub> epitaxial nanodots, with tunable sizes from ∼100 to
∼900 nm in diameter, have been successfully synthesized. Interestingly,
a plethora of exotic nanodomain structures, e.g., stripe domains,
vortex and antivortex domains, and single domains, are observed in
these nanodots. Moreover, this novel technique has been extended to
produce PbÂ(Zr,Ti)ÂO<sub>3</sub> nanodots and multiferroic composite
Co/BiFeO<sub>3</sub> nanodots. These observations enable the creation
of exotic domain structures and provide a wide range of application
potentials for future nanoelectronic devices
Real-Time Observation of the Electrode-Size-Dependent Evolution Dynamics of the Conducting Filaments in a SiO<sub>2</sub> Layer
Conducting
bridge random access memory (CBRAM) is one of the most
promising candidates for future nonvolatile memories. It is important
to understand the scalability and retention of CBRAM cells to realize
better memory performance. Here, we directly observe the switching
dynamics of Cu tip/SiO<sub>2</sub>/W cells with various active electrode
sizes using <i>in situ</i> transmission electron microscopy.
Conducting filaments (CFs) grow from the active electrode (Cu tip)
to inert electrode (W) during the SET operations. The size of the
Cu tip affects the electric-field distribution, the amount of the
cation injection into electrolyte, and the dimension of the CF. This
study provides helpful understanding on the relationship between power
consumption and retention of CBRAM cells. We also construct a theoretical
model to explain the electrode-size-dependent CF growth in SET operations,
showing good agreement with our experimental results
Real-Time Observation of the Electrode-Size-Dependent Evolution Dynamics of the Conducting Filaments in a SiO<sub>2</sub> Layer
Conducting
bridge random access memory (CBRAM) is one of the most
promising candidates for future nonvolatile memories. It is important
to understand the scalability and retention of CBRAM cells to realize
better memory performance. Here, we directly observe the switching
dynamics of Cu tip/SiO<sub>2</sub>/W cells with various active electrode
sizes using <i>in situ</i> transmission electron microscopy.
Conducting filaments (CFs) grow from the active electrode (Cu tip)
to inert electrode (W) during the SET operations. The size of the
Cu tip affects the electric-field distribution, the amount of the
cation injection into electrolyte, and the dimension of the CF. This
study provides helpful understanding on the relationship between power
consumption and retention of CBRAM cells. We also construct a theoretical
model to explain the electrode-size-dependent CF growth in SET operations,
showing good agreement with our experimental results
Enhanced Metal–Insulator Transition Performance in Scalable Vanadium Dioxide Thin Films Prepared Using a Moisture-Assisted Chemical Solution Approach
Vanadium
dioxide (VO<sub>2</sub>) is a strong-correlated metal–oxide
with a sharp metal–insulator transition (MIT) for a range of
applications. However, synthesizing epitaxial VO<sub>2</sub> films
with desired properties has been a challenge because of the difficulty
in controlling the oxygen stoichiometry of VO<sub><i>x</i></sub>, where <i>x</i> can be in the range of 1 < <i>x</i> < 2.5 and V has multiple valence states. Herein, a
unique moisture-assisted chemical solution approach has been developed
to successfully manipulate the oxygen stoichiometry, to significantly
broaden the growth window, and to significantly enhance the MIT performance
of VO<sub>2</sub> films. The obvious broadening of the growth window
of stoichiometric VO<sub>2</sub> thin films, from 4 to 36 °C,
is ascribed to a self-adjusted process for oxygen partial pressure
at different temperatures by introducing moisture. A resistance change
as large as 4 orders of magnitude has been achieved in VO<sub>2</sub> thin films with a sharp transition width of less than 1 °C.
The much enhanced MIT properties can be attributed to the higher and
more uniform oxygen stoichiometry. This technique is not only scientifically
interesting but also technologically important for fabricating wafer-scaled
VO<sub>2</sub> films with uniform properties for practical device
applications