Paramagnetic MgF₂ Nanocrystals for ¹⁹F Magnetic Resonance Imaging

MgF2-based formulations have unique physicochemical properties, making them attractive for diverse applications. Here, we show the ability to control the morphology of Sm3+-doped, paramagnetic MgF2 nanocrystals (Sm:MgF2 NCs) for use as nanosized imaging agents for 19F-magnetic resonance imaging (19F-MRI). By reducing the temperature of the reaction mixture from 160 to 110 °C and shortening the reaction time from 16 to 3 h, the morphology of the fabricated oleate-coated Sm:MgF2 NCs was transitioned from rod-shaped to spherical-shaped nanofluorides, both with a characteristic high-resolution liquid-state 19F-NMR resonance at −198 ppm. Further coating the surface of the spheric Sm:MgF2 NCs with a phospholipid layer resulted in a water-soluble formulation that was used to show its detectability with 19F-MRI

Electrically Driven Plasmons in Metal–Insulator–Semiconductor Tunnel Junctions: The Role of Silicon Amorphization

We investigate electrically driven plasmon (EDP) emission in metal–insulator–semiconductor tunnel junctions. We find that amorphization of the silicon crystal at a narrow region near the junction due to the applied voltage plays a critical role in determining the nature of the emission. Furthermore, we suggest that the change in the properties of the insulating layer above a threshold voltage determines the EDP spatial properties, from being spatially uniform when the device is subjected to low voltages, to a spotty pattern peaking at high voltages. We emphasize the role of the high-energy emission as an unambiguous tool for distinguishing between EDP and radiative recombination of electrons and holes in the semiconductor

Guided CdTe Nanowires Integrated into Fast Near-Infrared Photodetectors

Infrared photodetectors are essential devices for telecommunication and night vision technologies. Two frequently used materials groups for this technology are III–V and II–VI semiconductors, notably, mercury-cadmium-telluride alloys (MCT). However, growing them usually requires expensive substrates that can only be provided on small scales, and their large-scale production as crystalline nanostructures is challenging. In this paper, we present a two-stage process for creating aligned MCT nanowires (NWs). First, we report the growth of planar CdTe nanowires with controlled orientations on flat and faceted sapphire substrates via the vapor–liquid–solid (VLS) mechanism. We utilize this guided growth approach to parallelly integrate the NWs into fast near-infrared photodetectors with characteristic rise and fall times of ∼100 μs at room temperature. An epitaxial effect of the planar growth and the unique structure of the NWs, including size and composition, are suggested to explain the high performance of the devices. In the second stage, we show that cation exchange with mercury can be applied, resulting in a band gap narrowing of up to 55 meV, corresponding to an exchange of 2% Cd with Hg. This work opens new opportunities for creating small, fast, and sensitive infrared detectors with an engineered band gap operating at room temperature

Curved Nanoflakes of Alkane-Grafted Ti₃C₂T_<i>x</i> MXene Thin Flims for Enhanced Terahertz Electromagnetic Interference Shielding

The sixth-generation wireless communication (6G) extends the electromagnetic pollution up to the terahertz band. The two-dimensional titanium carbide of intercalated structure Ti3C2Tx MXene attracts much attention because it exhibits high terahertz electromagnetic interference (EMI) shielding effectiveness (SE) due to the large intrinsic electrical conductivity as well as few-atom monosheet thickness. Scientists worldwide are making continuous efforts to optimize the MXene structures for EMI shielding application. Innovatively, we demonstrate a chemical method to bend the nanoflake by grafting two types of alkane, octane (C8H18) and dodecane (C12H26), onto the surface terminals. The chain length of alkane exceeds the bond length of surface functionalities Tx (=O, −OH, −F) to introduce intrananoflake and internanoflake strains into Ti3C2Tx MXene. The nanoflake’s deformation leads to Raman peak redshift and broader line width. The element distribution shows that the alkane increases the oxygen–fluorine ratio of Ti3C2Tx MXene from 3:2 to 3:1 (Ti3C2Tx-C8H18) and even up to 4:1 (Ti3C2Tx-C12H26). Electronic microscopy (SEM/TEM) shows obvious edge-fold and tensile/compressive deformation of the nanoflake. The EMI SE of Ti3C2Tx-C12H26 achieves 35 dB, which is higher than those of Ti3C2Tx-C8H18 (26 dB) and Ti3C2Tx MXene (22 dB). The alkane grafting increases the absorption coefficient of the MXene thin film by more than 50% but has negligible contribution to the refractive index. Meanwhile, the conductivity of Ti3C2Tx-C8H18 MXene is over twice higher than that of Ti3C2Tx MXene, whereas the conductivity of Ti3C2Tx-C12H26 is three times higher than that of Ti3C2Tx MXene. The nanoflake curvature of alkane grafted Ti3C2Tx MXene enlarges the specific surface area and causes topological defects, which increase the absorption as well as the conductivity so that the terahertz EMI SE is enhanced correspondingly. The realization of Ti3C2Tx MXene of curved nanoflake for the enhancement of terahertz EMI SE is valuable for 6G electromagnetic protection