Nanostructures in silicon (Si) induced by phase transformations have been investigated during the past 50 years. Performances of nanostructures are improved compared to that of bulk counterparts. Nevertheless, the confinement and loading conditions are insufficient to machine and fabricate high-performance devices. As a consequence, nanostructures fabricated by nanoscale deformation at loading speeds of m/s have not been demonstrated yet. In this study, grinding or scratching at a speed of 40.2 m/s was performed on a custom-made setup by an especially designed diamond tip (calculated stress under the diamond tip in the order of 5.11 GPa). This leads to a novel approach for the fabrication of nanostructures by nanoscale deformation at loading speeds of m/s. A new deformation-induced nanostructure was observed by transmission electron microscopy (TEM), consisting of an amorphous phase, a new tetragonal phase, slip bands, twinning superlattices, and a single crystal. The formation mechanism of the new phase was elucidated by ab initio simulations at shear stress of about 2.16 GPa. This approach opens a new route for the fabrication of nanostructures by nanoscale deformation at speeds of m/s. Our findings provide new insights for potential applications in transistors, integrated circuits, diodes, solar cells, and energy storage systems.

New Deformation-Induced Nanostructure in Silicon.

Colossal Permittivity Materials as Superior Dielectrics for Diverse Applications

Rational Design of Type-II Nano-heterojunctions for Nanoscale Optoelectronics

In this paper, we reported a new photosensitive material, Sm doped K0.5Na0.5NbO3 (KNN) ceramics, fabricated using a solid-sate reaction method, which exhibits both photochromism and luminescence switching properties. By alternating visible light irradiation (λ > 407 nm) and thermal stimulus, the samples show a reversible color change from the initial green to pale gray. Interestingly, luminescence emission intensity can be effectively tuned using photochromic reactions. Furthermore, the luminescence switching degree strongly depends on the firing temperature. These results suggest that KNN-based perovskite oxides with photochromism, luminescence switching and ferroelectric energy storage properties are particularly attractive for optical data storage applications as multi-functional materials.

(K,Na)NbO3 ferroelectrics: a new class of solid-state photochromic materials with reversible luminescence switching behavior

Synergistic effect of photocatalysis and pyrocatalysis of pyroelectric ZnSnO3 nanoparticles for dye degradation

Na0.5Bi0.5−x−yYbxPryTiO3 (NBT:xYb/yPr) ceramics with different Yb and Pr contents are prepared. Both the down-conversion (DC) and up-conversion (UC) photoluminescence (PL) of the ceramics via 453 and 980 nm excitation, respectively, are investigated. The effect of Yb3+ and Pr3+ doping contents on the DC and UC PL is significantly different from each other. Furthermore, the UC PL of the ceramics as a function of temperatures is measured to investigate the UC process in detail. Based on energy level diagram of Pr3+ and Yb3+ ions and the DC and UC PL spectra, the DC and UC PL mechanisms of Pr3+ and Yb3+ ions are discussed. Especially, the UC PL mechanism is clarified, which is different from the previously reported literature. Also, the temperature sensing properties of the ceramics are studied based on the photoluminescence ratio technique, using the thermal coupling energy levels of Pr3+.

The down-conversion and up-conversion photoluminescence properties of Na0.5Bi0.5TiO3:Yb3+/Pr3+ ceramics

Er3+ and Yb3+ co-doped (1 − x)K0.5Na0.5NbO3-xLiNbO3 (KNN-xLN:Er/Yb, x = 0.04–0.09) ceramics were prepared to investigate their phase structures and piezoelectric, ferroelectric, and up-conversion photoluminescence properties. With increasing LN content, x, KNN-xLN:Er/Yb ceramics at room temperature evolve from the orthorhombic phase to the polymorphic phase and finally to the tetragonal phase. All the ferroelectric and piezoelectric properties and the Ir/Ig ratio of integrated intensities of red and green emission bands reach maximum values within the polymorphic phase transition of the KNN-0.06LN:Er/Yb ceramic. In this work, we find a close correlation between the electrical properties, up-conversion photoluminescence, and phase structure of KNN-xLN:Er/Yb ceramics. This correlation is discussed based on the Judd-Ofelt and crystallographic symmetry theories.

Strong correlation of the electrical properties, up-conversion photoluminescence, and phase structure in Er3+/Yb3+ co-doped (1 − x)K0.5Na0.5NbO3-xLiNbO3 ceramics

Nanotwinned (nt) materials exhibit excellent mechanical properties, and have been attracting much more attention of late. Nevertheless, the fundamental mechanism of interaction between dislocations and a single nanotwin is not understood. In this study, in situ transmission electron microscopy (TEM) nanoindentation is performed, on a specimen of a nickel (Ni) alloy containing a single nanotwin of 89 nm in thickness. The specimen is prepared using focused ion beam (FIB) technique from an nt surface, which is formed by a novel approach under indentation using a developed diamond panel with tips array. The stiffness of the specimen is ten times that of the pristine counterparts during loading. The ultrahigh stiffness is attributed to the generation of nanotwins and the impediment of the single twin to the dislocations. Two peak loads are induced by the activation of a new slip system and the penetration of dislocations over the single nanotwin, respectively. One slip band is parallel to the single nanotwin, indicating the slip of dislocations along the nanotwin. In situ TEM observation of nanoindentation reveals a new insight for the interaction between dislocations and a single nanotwin. This paves the way for design and preparation of high-performance nt surfaces of Ni alloys used for aircraft engines, gas turbines, turbocharger components, ducts, and absorbers.

In Situ TEM Study of Interaction between Dislocations and a Single Nanotwin under Nanoindentation

Ceramics 0.94(K0.5Na0.5)NbO3−0.06LiNbO3:Er/xYb with x = 0, 0.002, 0.004, 0.006, 0.008 were fabricated in this study, and phase structure, dielectric, piezoelectric, ferroelectric, and upconversion photoluminescence properties of the ceramics were systematically studied. Results show that all ceramics are in the polymorphic phase transition region near room temperature. However, a relaxor-like phase transition was observed as Yb increasing to over x = 0.004. The optimized dielectric, piezoelectric, and ferroelectric properties, and maximized photoluminescence intensity ratio are obtained at x = 0.004. And the electrical and photoluminescence properties of the ceramics were discussed from the point view of the normal to relaxor-like ferroelectric phase transition. The present study demonstrates that both the electrical and upconversion photoluminescence properties of the ceramics have an intimate correlation with the normal to relaxor-like ferroelectric transition induced by Yb doping.

Effect of Yb Codoping on the Phase Transition, and Electrical and Photoluminescence Properties in KNLN:Er/xYb Ceramics

A small quantity of Eu3+ ions was doped in the lead-free ferroelectric K0.5Na0.5NbO3-xLiNbO3 (KNN-xLN, 0≤x≤0.08) ceramics to investigate the NbO6 octahedral distortion induced by the increasing LN content. In addition, the phase structure, ferroelectric and photoluminescence properties of K0.5Na0.5NbO3-xLiNbO3:0.006Eu3+ (KNN-xLN:0.006Eu3+) lead-free piezoelectric ceramics were characterized. All the X-ray diffraction, Raman spectra, dielectric constant versus temperature measurements and the photoluminescence of Eu3+ ions demonstrated that the prepared ceramics undergo a polymorphic phase transition (PPT, from orthorhombic to tetragonal phase transformation) with the rising LN content, and the PPT region locates at 0.05≤x≤0.06. The ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios show similar variations with the increasing LN content, all with a maximum value achieved at the PPT region. We believe that the close relationship among the ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios is caused by the NbO6 octahedral distortion. The photoluminescence of Eu3+ ion was discussed basing on the crystal-symmetry principle and Judd-Ofelt theory.

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Jia Wang

Papers

The down-conversion and up-conversion photoluminescence properties of Na0.5Bi0.5TiO3:Yb3+/Pr3+ ceramics

Strong correlation of the electrical properties, up-conversion photoluminescence, and phase structure in Er3+/Yb3+ co-doped (1 − x)K0.5Na0.5NbO3-xLiNbO3 ceramics

In Situ TEM Study of Interaction between Dislocations and a Single Nanotwin under Nanoindentation

Effect of Yb Codoping on the Phase Transition, and Electrical and Photoluminescence Properties in KNLN:Er/xYb Ceramics

The NbO6 octahedral distortion and phase structural transition of Eu3+-doped K0.5Na0.5NbO3–xLiNbO3 ferroelectric ceramics