When the atomic layers in a non-centrosymmetric van der Waals structure slide against each other, the interfacial charge transfer results in a reversal of the structure’s spontaneous polarization. This phenomenon is known as sliding ferroelectricity and it is markedly different from conventional ferroelectric switching mechanisms relying on ion displacement. Here, we present layer dependence as a new dimension to control sliding ferroelectricity. By fabricating 3 R MoS2 of various thicknesses into dual-gate field-effect transistors, we obtain anomalous intermediate polarization states in multilayer (more than bilayer) 3 R MoS2. Using results from ab initio density functional theory calculations, we propose a generalized model to describe the ferroelectric switching process in multilayer 3 R MoS2 and to explain the formation of these intermediate polarization states. This work reveals the critical roles layer number and interlayer dipole coupling play in sliding ferroelectricity and presents a new strategy for the design of novel sliding ferroelectric devices.
Large decreases in the conductivity of arsenic-doped silicon have been observed during 500–970°C heat treatments. The rate of conductivity change depends upon the prior quenching rate from diffusion temperature to room temperature. These conductivity changes are reversed by higher-temperature treatments. The relationship between the electrically active arsenic, as calculated from the conductivity, and the total arsenic is shown to be consistent with a model of substitutional arsenic atoms being nonionized when in a cluster or in a complex involving one or more vacancies.
Phosphorus-, arsenic-, and boron-implanted junctions have been investigated with special emphasis on their annealing behavior of the junction-leakage currents. It is shown that a minimum of about 900°C and 30 min annealing is required for junction qualities equal to that of diffused ones. Hall-effect measurements of the implanted region show that about 900°C for phosphorus annealing and 1000°C for arsenic and boron annealing are required to restore carrier concentrations corresponding to the implanted impurities, respectively. The relative importance of surface area and perimeter contribution to the junction leakage is identified. It is shown that for an area-to-perimeter ratio smaller than about 1 mil, the perimeter contribution dominates. There are indications that the distribution of the leakage contributing g-r centers coincide with the implanted impurities.
Aiming to accomplish synchronous optical temperature measurements in the first, second, and third biological windows, this work has carefully designed a novel ratiometric optical thermometer based on ZrO 2 :Er 3+ /Yb 3+ nanocrystals synthesized by a gel combustion method. Under 980 nm excitation, the luminescence spectra consist of emissions centered at 531, 568, 660, and 1528 nm from Er 3+ ions as well as the luminescence located at ∼1000 nm from Yb 3+ ions. The temperature-sensing behaviors were investigated on the basis of the valley-to-peak ratio (VPR) technique. Linear temperature dependencies VPR-1 (I 668 /I 682 ), VPR-2 (I 1023 /I 1036 ), and VPR-3 (I 1492 /I 1528 ) were deduced from the homogeneous broadening of the peak line width, showing the advantages of high sensitivity and accuracy. This study provides a novel approach to exploring optical nanothermometers with luminescence covering the three biological windows, which is important in the fields of biology and medicine.
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