Search

The Nanomaterials Editorial Office retracts the article, “Manufacturing of Conductive, Wear-Resistant Nanoreinforced Cu-Ti Alloys Using Partially Oxidized Electrolytic Copper Powder” [...]

The article analyzes the nuances of the changes in Soviet-Lithuanian relations after the coup d'etat staged in December 1926. The coming to power of the leaders of the Lithuanian Nationalist and Republican Union A. Smetona and A. Voldemaras initially contributed to the situation of uncertainty in bilateral relations. Moscow was extremely concerned about Voldemaras' desire to exacerbate the Polish-Soviet contradictions in order to solve the Vilnius problem in Polish-Lithuanian relations. The Soviet diplomats feared that Voldemaras could provoke an armed conflict with Poland and that the Soviet Union would inevitably be involved in the conflict. On the other hand, Soviet diplomacy was interested in maintaining both the independence of Lithuania and the maintenance of some tension between Poland and Lithuania, as this situation created obstacles to Poland’s spread of influence throughout the Baltic East. By the late 1920s, it became apparent to Moscow that dissatisfaction with Voldemaras’ policy in Lithuania had reached its climax and that Voldemaras was to be forced out of Lithuanian political life in the near future. As a result, a few months before Voldemaras’ resignation, the political leadership of the USSR categorically opposed contacts with him by the leadership of the People’s Commissariat for Foreign Affairs.

Inscription of embedded photoluminescent microbits inside micromechanically positioned bulk natural diamond, LiF and CaF2 crystals was performed in sub-filamentation (geometrical focusing) regime by 525 nm 0.2 ps laser pulses focused by 0.65 NA micro-objective as a function of pulse energy, exposure and inter-layer separation. The resulting microbits were visualized by 3D-scanning confocal Raman/photoluminescence microscopy as conglomerates of photo-induced quasi-molecular color centers and tested regarding their spatial resolution and thermal stability via high-temperature annealing. Minimal lateral and longitudinal microbit separations, enabling their robust optical read-out through micromechanical positioning, were measured in the most promising crystalline material, LiF, as 1.5 and 13 microns, respectively, to be improved regarding information storage capacity by more elaborate focusing systems. These findings pave a way to novel optomechanical memory storage platforms, utilizing ultrashort-pulse laser inscription of photoluminescent microbits as carriers of archival memory.

Optical-range bulk diffraction nanogratings were fabricated via challenging direct inscription by ultrashort (femtosecond, fs) laser pulses inside heat-shrinkable polymers (thermoplastics) and VHB 4905 elastomer. The inscribed bulk material modifications do not emerge on the polymer surface, being visualized inside the materials by 3D-scanning confocal photoluminescence/Raman microspectroscopy and by the multi-micron penetrating 30-keV electron beam in scanning electron microscopy. The laser-inscribed bulk gratings have multi-micron periods in the pre-stretched material after the second laser inscription step, with their periods continuously reduced down to 350 nm on the third fabrication step, using thermal shrinkage for thermoplastics and elastic properties for elastomers. This three-step process allows facile laser micro-inscription of diffraction patterns and their following controlled scaling down as a whole pattern to pre-determined dimensions. In elastomers, utilizing the initial stress anisotropy, the post-radiation elastic shrinkage along the given axes could be precisely controlled until the 28-nJ threshold fs-laser pulse energy, where elastomer deformation ability is dramatically reduced, producing wrinkled patterns. In thermoplastics, the fs-laser inscription does not affect their heat-shrinkage deformation up to the carbonization threshold. The measured diffraction efficiency of the inscribed gratings increases during the elastic shrinkage for the elastomers and slightly decreases for the thermoplastics. High 10% diffraction efficiency was demonstrated for the VHB 4905 elastomer at the 350 nm grating period. No significant molecular-level structural modifications were observed by Raman micro-spectroscopy in the inscribed bulk gratings in the polymers. This novel few-step method paves the way for facile and robust ultrashort-pulse laser inscription of bulk functional optical elements in polymeric materials for diffraction, holographic and virtual reality devices.

An ultrashort-pulse laser inscription of embedded birefringent microelements was performed inside bulk fluorite in pre-filamentation (geometrical focusing) and filamentation regimes as a function of laser wavelength, pulsewidth and energy. The resulting elements composed of anisotropic nanolattices were characterized by retardance (Ret) and thickness (T) quantities, using polarimetric and 3D-scanning confocal photoluminescence microscopy, respectively. Both parameters exhibit a monotonous increase versus pulse energy, going over a maximum at 1-ps pulsewidth at 515 nm, but decrease versus laser pulsewidth at 1030 nm. The resulting refractive-index difference (RID) Δn = Ret/T ~ 1 × 10−3 remains almost constant versus pulse energy and slightly decreases at a higher pulsewidth, generally being higher at 515 nm. The birefringent microelements were visualized using scanning electron microscopy and chemically characterized using energy-dispersion X-ray spectroscopy, indicating the increase of calcium and the contrary decrease of fluorine inside them due to the non-ablative inscription character. Dynamic far-field optical diffraction of the inscribing ultrashort laser pulses also demonstrated the accumulative inscription character, depending on the pulse energy and the laser exposure. Our findings revealed the underlying optical and material inscription processes and demonstrated the robust longitudinal homogeneity of the inscribed birefringent microstructures and the facile scalability of their thickness-dependent retardance.

A new additive (polytetrafluoroethylene, PTFE) to typical sugar precursors for hard carbon (HC) preparation via hydrothermal carbonization has been proposed and investigated. The HC samples obtained from sugars (D-glucose and pectin) with and without PTFE were characterized with X-ray powder diffraction, Raman spectroscopy, scanning and transmission electron microscopy, energy-dispersive X-ray and electron energy loss spectroscopy, specific surface area measurements. Adding PTFE to sugars significantly improves the HC yield from

The ultrafast interaction of tightly focused femtosecond laser pulses with bulk dielectric media in direct laser writing (inscription) regimes is known to proceed via complex multi-scale light, plasma and material modification nanopatterns, which are challenging for exploration owing to their mesoscopic, transient and buried character. In this study, we report on the first experimental demonstration, analysis and modeling of hierarchical multi-period coupled longitudinal and transverse nanogratings in bulk lithium niobate inscribed in the focal region by 1030 nm, 300 fs laser pulses in the recently proposed sub-filamentary laser inscription regime. The longitudinal Bragg-like topography nanogratings, possessing the laser-intensity-dependent periods ≈ 400 nm, consist of transverse birefringent nanogratings, which are perpendicular to the laser polarization and exhibit much smaller periods ≈ 160 nm. Our analysis and modeling support the photonic origin of the longitudinal nanogratings, appearing as prompt electromagnetic and corresponding ionization standing waves in the pre-focal region due to interference of the incident and plasma-reflected laser pulse parts. The transverse nanogratings could be assigned to the nanoscale material modification by interfacial plasmons, excited and interfered in the resulting longitudinal array of the plasma sheets in the bulk dielectric material. Our experimental findings provide strong support for our previously proposed mechanism of such hierarchical laser nanopatterning in bulk dielectrics, giving important insights into its crucial parameters and opening the way for directional harnessing of this technology.

Ferroelectric nanodomains were formed in bulk lithium niobate single crystals near nanostructured microtracks laser-inscribed by 1030-nm 0.3-ps ultrashort laser pulses at variable pulse energies in sub- and weakly filamentary laser nanopatterning regimes. The microtracks and related nanodomains were characterized by optical, scanning probe and confocal second-harmonic generation microscopy methods. The nanoscale material sub-structure in the microtracks was visualized in the sample cross-sections by atomic force microscopy (AFM), appearing weakly birefringent in polarimetric microscope images. The piezoresponce force microscopy (PFM) revealed sub-100 nm ferroelectric domains formed in the vicinity of the embedded microtrack seeds, indicating a promising opportunity to arrange nanodomains in the bulk ferroelectric crystal in on-demand positions. These findings open a new modality in direct laser writing technology, which is related to nanoscale writing of ferroelectric nanodomains and prospective three-dimensional micro-electrooptical and nanophotonic devices in nonlinear-optical ferroelectrics.