High pressure in situ Raman scattering and electrical resistivity measurements were performed to investigate the phase transitions in a semimetal 1T-TiTe2 single crystal up to 17 GPa. Combining anomalous experimental results with the electronic band structures and Z2 topological invariants in calculations, two topological phase transitions and one structural phase transition were confirmed at 1.7 GPa, 3 GPa, and 8 GPa, respectively. These two topological transformations are due to the enhanced orbital hybridization followed by a few of band inversions near the Fermi level, and the further parity analysis manifested that the phases II and III correspond to a strong topological state and a weak topological state, respectively. The rich topology variation of 1T-TiTe2 under high pressure provides a potential candidate for understanding the relevant topology physics and probable applications. The current results also demonstrate that Raman spectroscopy and electrical transport measurements are efficient tools to detect the topological phase transition under high pressure.
The emission properties of Mn 2+ ions with direct and indirect excitation in MnS/ZnS core/shell quantum dots are investigated under high pressure. A transition from the zincblende to rock salt phase is observed at 16.1 GPa. The intensity of the Mn 2+ emission peak attenuates significantly from 7.5 to 9.6 GPa due to the crossing of 2 T 2 ( 2 I) and 4 T 1 ( 4 G) energy levels and subsequent enhancement of nonradiative relaxation. Pressure-induced anomalous emission behaviors are observed and explained by the competition between two types of Mn 2+ emissions: a major one from coupled Mn 2+ ions and a minor one from isolated Mn 2+ ions. The corresponding mechanism is discussed. These findings can provide insights into the fundamental physics and better design/applications of this kind of material.
In this work, Mn2+-doped ZnS nanorods were synthesized
by a facile hydrothermal method. The morphology, structure, and composition
of the as-prepared samples were investigated. The temperature-dependent
photoluminescence of ZnS:Mn nanorods was analyzed, and the corresponding
activation energies were calculated by using a simple two-step rate
equation. Mn2+-related orange emission (4T1 → 6A1) demonstrates high stability
and is comparatively less affected by the temperature variations than
the defect-related emission. A metal–semiconductor–metal
junction ultraviolet photodetector based on the nanorod networks has
been fabricated by a cost-effective method. The device exhibits visible
blindness, superior ultraviolet photodetection with a responsivity
of 1.62 A/W, and significantly fast photodetection response with the
rise and decay times of 12 and 25 ms, respectively.
Temporary bonding and debonding (TBDB) is a key technology
in the
semiconductor field to enable 2.5D/3D integration of devices. However,
the conventional polyimides, which serve as the laser-response material
in TBDB, exhibit extremely poor solubility in aprotic polar solvents
due to high-temperature imidization, limiting the cleaning process
for wafers after debonding. Herein, a feasible method of controlling
the curing temperature to enhance the solubility of thermoplastic
polyimide (TPI) has been developed. The results proved that the ultimate
solubility of TPI cured at 200 °C (TPI-200 °C) could be
as high as 28.4 wt %. Besides, TPI-200 °C exhibits excellent
heat resistance, outstanding mechanical properties, and ultrahigh
absorptivity (99.96%) at a 355 nm UV wavelength. Meanwhile, we demonstrate
the feasibility of the as-prepared TPI material for application in
the TBDB process, showing excellent efficiency and low cost, and the
follow-up elemental analysis of the cleaned wafer surfaces proved
that TPI-200 °C can be completely removed after debonding. All
these results demonstrate that TPI materials that can be used for
TBDB are promising for ultrathin chip packaging and wafer level packaging
(WLP) in the field of advanced electronic packaging.
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