8 research outputs found
Electrically Controlled Reversible Strain Modulation in MoS Field-effect Transistors via an Electro-mechanically Coupled Piezoelectric Thin Film
Strain can efficiently modulate the bandgap and carrier mobilities in
two-dimensional (2D) materials. Conventional mechanical strain-application
methodologies that rely on flexible, patterned or nano-indented substrates are
severely limited by low thermal tolerance, lack of tunability and/or poor
scalability. Here, we leverage the converse piezoelectric effect to
electrically generate and control strain transfer from a piezoelectric thin
film to electro-mechanically coupled ultra-thin 2D MoS. Electrical bias
polarity change across the piezoelectric film tunes the nature of strain
transferred to MoS from compressive 0.23% to tensile 0.14% as
verified through peak shifts in Raman and photoluminescence spectroscopies and
substantiated by density functional theory calculations. The device
architecture, built on a silicon substrate, uniquely integrates an MoS
field-effect transistor on top of a metal-piezoelectric-metal stack enabling
strain modulation of transistor drain current 130, on/off current ratio
150, and mobility 1.19 with high precision, reversibility and
resolution. Large, tunable tensile (1056) and compressive (-1498) strain gauge
factors, easy electrical strain modulation, high thermal tolerance and
substrate compatibility make this technique promising for integration with
silicon-based CMOS and micro-electro-mechanical systems.Comment: Manuscript and Supplementary Informatio
Interlayer-engineered high remnant polarization (2P > 70C/cm) in HfZrO thin films
In this letter, we report a high remnant polarization, 2P >
70C/cm in thermally processed atomic layer deposited
HfZrO (HZO) film on Silicon with NH plasma exposed thin
TiN interlayer and Tungsten (W) as a top electrode. The effect of interlayer on
the ferroelectric properties of HZO is compared with standard
Metal-Ferroelectric-Metal and Metal-Ferroelectric-Semiconductor structures. The
x-ray diffraction confirms that the thickness of the interlayer plays an
important role to enhance the orthorhombic ferroelectric phase. The HRTEM
images reveal that TiN acts as a seed layer for the local epitaxy in HZO and
hence a 2X improvement in remnant polarization. Finally, the HZO devices are
shown to be wake-up free, and exhibit endurance cycles. This study
opens a pathway to achieve epitaxial ferroelectric HZO films on Si with
improved memory performance.Comment: 4 pages, 4 figure
Understanding the Effects of Tetrahedral Site Occupancy by the Zn Dopant in Li-NMCs toward High-Voltage Compositional–Structural–Mechanical Stability via Operando and 3D Atom Probe Tomography Studies
Ni-containing “layered”/cation-ordered
LiTMO2s (TM = transition metal) suffer
from Ni-migration
to the Li-layer at the unit cell level, concomitant transformation
to a spinel/rock salt structure, hindrance toward Li-transport, and,
thus, fading in Li-storage capacity during electrochemical cycling
(i.e., repeated delithiation/lithiation), especially upon deep delithiation
(i.e., going to high states-of-charge). Against this backdrop, our
previously reported work [ACS Appl. Mater. Interfaces 2021, 13, 25836–25849] revealed a new concept toward blocking
the Ni-migration pathway by placing Zn2+ (which lacks octahedral
site preference) in the tetrahedral site of the Li-layer, which, otherwise,
serves as an intermediate site for the Ni-migration to the Li-layer.
This, nearly completely, suppressed the Ni-migration, despite being
deep delithiated up to a potential of 4.7 V (vs Li/Li+)
and, thus, resulted in significant improvement in the high-voltage
cyclic stability. In this regard, by way of conducting operando synchrotron
X-ray diffraction, operando stress measurements, and 3D atom probe
tomography, the present work throws deeper insights into the effects
of such Zn-doping toward enhancing the structural–mechanical–compositional
integrity of Li-NMCs upon being subjected to deep delithiation. These
studies, as reported here, have provided direct lines of evidence
toward notable suppression of the variations of lattice parameters
of Li-NMCs, including complete prevention of the detrimental “c-axis collapse” at high states-of-charges and concomitant
slower-cum-lower electrode stress development, in the presence of
the Zn-dopant. Furthermore, the Zn-dopant has been found to also prevent
the formation of Ni-enriched regions at the nanoscaled levels in Li-NMCs
(i.e., Li/Ni-segregation or “structural densification”)
even upon being subjected to 100 charge/discharge cycles involving
deep delithiation (i.e., up to 4.7 V). Such detailed insights based
on direct/real-time lines of evidence, which reveal important correlations
between the suppression of Ni-migration and high-voltage compositional–structural–mechanical
stability, hold immense significance toward the development of high
capacity and stable “layered” Li-TM-oxide
based cathode materials for the next-generation Li-ion batteries