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151.
Florian Klappenberger Dirk Kühne Matthias Marschall Stefan Neppl Wolfgang Krenner Alexei Nefedov Thomas Strunskus Karin Fink Christof Wöll Svetlana Klyatskaya Olaf Fuhr Mario Ruben Johannes V. Barth 《Advanced functional materials》2011,21(9):1631-1642
The ordering and conformational properties of dicarbonitrile‐para‐oligophenyls are studied with complementary methods, namely X‐ray structure analysis, low‐temperature scanning tunneling microscopy, and near‐edge X‐ray absorption fine‐structure spectroscopy. The packing of the functionalized variants differs from their technologically interesting para‐oligophenyl counterparts, both in the bulk crystal phase and in thin films grown by organic molecular beam epitaxy (OMBE) under ultra‐high vacuum conditions on the Ag(111) surface. In the crystal phase, the conformation depends on the number n of phenyl rings, exhibiting an intriguing screw‐like structure in the case of n = 4 at room temperature as well as at 180 K. For OMBE‐grown thin films, the whole series acquires the same type of conformation, characterized by alternately twisted phenyl rings, similar to the pure oligophenyl species. However, for all tested molecules, the orientation of the molecular reference plane is uniform within the entire film and coincides with the surface plane. This contrasts with the herringbone ordering adopted by the phenyl backbones without the carbonitrile groups. Our results demonstrate how the functionalization of moieties with extended conjugated electron systems can help to improve the structural homogeneity in technologically relevant organic thin films. 相似文献
152.
Andrei Kholkin Anna Morozovska Dmitry Kiselev Igor Bdikin Brian Rodriguez Pingping Wu Alexei Bokov Zuo‐Guang Ye Brahim Dkhil Long‐Qing Chen Marija Kosec Sergei V. Kalinin 《Advanced functional materials》2011,21(11):1977-1987
Relaxor ferroelectrics are a prototypical example of ferroic systems in which interplay between atomic disorder and order parameters gives rise to emergence of unusual properties, including non‐exponential relaxations, memory effects, polarization rotations, and broad spectrum of bias‐ and temperature‐induced phase transitions. Despite more than 40 years of extensive research following the original discovery of ferroelectric relaxors by the Smolensky group, the most basic aspect of these materials – the existence and nature of order parameter – has not been understood thoroughly. Using extensive imaging and spectroscopic studies by variable‐temperature and time resolved piezoresponse force microscopy, we find that the observed mesoscopic behavior is consistent with the presence of two effective order parameters describing dynamic and static parts of polarization, respectively. The static component gives rise to rich spatially ordered systems on the ～100 nm length scales, and are only weakly responsive to electric field. The surface of relaxors undergoes a mesoscopic symmetry breaking leading to the freezing of polarization fluctuations and shift of corresponding transition temperature. 相似文献
153.
154.
Wenhan Dong Bi-Xia Wang Yi Yuan Hua Wu Alexei A. Bokov Zuo-Guang Ye 《Journal of the American Ceramic Society》2022,105(7):4775-4783
To explore lead-reduced dielectric materials in the SrTiO3–PbTiO3–PbZrO3 ternary system, a novel solid solution between relaxor ferroelectric (Pb0.5Sr0.5)(Zr0.5Ti0.5)O3 and ferroelectric PbTiO3, namely (1 − x)(Pb0.5Sr0.5) (Zr0.5Ti0.5)O3–xPbTiO3 (lead–strontium–zirconate–titanate [PSZT]–PT), has been synthesized in the perovskite structure by high-temperature solid-state reaction method in the form of ceramics. The crystal structure and phase symmetry of the materials synthesized were analyzed and resolved based on X-ray powder diffraction (XRD) data through both the Pawley and Rietveld refinements. The results of the structural refinements indicate that at low PT-concentration end of the solid solution system, for example, x = 0.05, the PSZT–PT solid solution exhibits a cubic structural symmetry (with the space group Pm-3m). As the PT concentration (x) increases, the structure of (1 − x)PSZT–xPT gradually transforms from the cubic to a tetragonal (P4mm) phase. In the composition range of x = 0.10–0.25, a mixture of the cubic and tetragonal phases was identified. As the concentration of PT increases, the proportion of the tetragonal phase increases at the expense of the cubic phase. For a composition of x > 0.25, a pure tetragonal phase is observed. The dielectric properties of the materials were studied by measuring the permittivity as a function of temperature at various frequencies. For the composition of x = 0.05, the temperature dependence of dielectric constant shows typical relaxor behavior. For x = 0.35, the dielectric peaks indicate a normal ferroelectric phase transition. Overall, a structural transformation from a central-symmetric, nonpolar cubic phase to a non-centrosymmetric, polar tetragonal phase is induced by the substitution of PT for PSZT in the pseudo-binary solid solution of (1 − x)PSZT–xPT, which also reveals an interesting relaxor to ferroelectric crossover phenomenon. 相似文献
155.
156.
Ohheum Bak Theodor S. Holstad Yueze Tan Haidong Lu Donald M. Evans Kasper A. Hunnestad Bo Wang James P. V. McConville Petra Becker Ladislav Bohatý Igor Lukyanchuk Valerii M. Vinokur Antonius T. J. van Helvoort J. Marty Gregg Long‐Qing Chen Dennis Meier Alexei Gruverman 《Advanced functional materials》2020,30(21)
Application of scanning probe microscopy techniques such as piezoresponse force microscopy (PFM) opens the possibility to re‐visit the ferroelectrics previously studied by the macroscopic electrical testing methods and establish a link between their local nanoscale characteristics and integral response. The nanoscale PFM studies and phase field modeling of the static and dynamic behavior of the domain structure in the well‐known ferroelectric material lead germanate, Pb5Ge3O11, are reported. Several unusual phenomena are revealed: 1) domain formation during the paraelectric‐to‐ferroelectric phase transition, which exhibits an atypical cooling rate dependence; 2) unexpected electrically induced formation of the oblate domains due to the preferential domain walls motion in the directions perpendicular to the polar axis, contrary to the typical domain growth behavior observed so far; 3) absence of the bound charges at the 180° head‐to‐head (H–H) and tail‐totail (T–T) domain walls, which typically exhibit a significant charge density in other ferroelectrics due to the polarization discontinuity. This strikingly different behavior is rationalized by the phase field modeling of the dynamics of uncharged H–H and T–T domain walls. The results provide a new insight into the emergent physics of the ferroelectric domain boundaries, revealing unusual properties not exhibited by conventional Ising‐type walls. 相似文献
157.
This work proposes a technique for the controlled incorporation of nanoinclusions into a polymer matrix, which, as expected, will help resolve the contradiction in the requirements asked of polymer film coats, that is, good adhesion and above-average tribological properties, including the high wear resistance. The study introduces and puts to the test an approach by performing the controlled incorporation of fullerene-like nanoinclusions. The results of experimental verification, that is, the tribological profile of resultant nanocomposite were presented. It was found that a polyacetal matrix reinforced with the fullerene-like nanoinclusions demonstrated a more stable behavior in tribological tests. These polymer films showed slightly lower coefficients of friction. This result can be considered successful and promising; without changing the nanocomposite composition, a tribological enhancement was achieved by manipulating the nanoparticle distribution within the polymer matrix. This study sought to create a three-dimensional structure of nanoinclusions, specifically a graphite-like hexagonal structure, that is, “columns” with a height equal to the film thickness and located at the nodes of the hexagonal lattice. The research concept was experimentally verified by comparing polymer films with a different distribution of nanoinclusions integrated into them. The filler fractions were 2 wt% in all films regardless of nanoparticle distribution. A polymer film with a uniform distribution of nanoinclusions was regarded as a baseline. A film with an ordered arrangement of nanoinclusions showed a 40% greater wear resistance (the number of cycles to film fragmentation) and a 39% lower coefficient of friction. 相似文献
158.
Dmitry S. Lugvishchuk Vladimir Z. Mordkovich Edward B. Mitberg Aida R. Karaeva Boris A. Kulnitskiy Alexei N. Kirichenko 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(4):250-255
AbstractOnion-like carbon (OLC) particles were produced as a byproduct of thermal partial oxidation of methane under different O2/Natural Gas (NG) ratio. It was established that the particles have quasi-spherical morphology and concentric shell structure. The particles have an outer diameter of 20–60?nm while the inner cage is rather typical for onions and has a diameter below 1?nm. The concentric graphitic structure and spherical symmetry along with the absence of amorphous carbon were confirmed by transmission electron microscopy, electron diffraction, EDX spectroscopy and Raman investigation. Variation of O2/NG ratio was proved a powerful tool for controlling OLC particles yield and structure. The formation of single-core or multicore OLC can be controlled by thermal partial oxidation process. 相似文献
159.
Ivan M. Petyaev Dmitry V. Pristensky Elena Y. Morgunova Nailya A. Zigangirova Valeriy V. Tsibezov Natalia E. Chalyk Victor A. Klochkov Victoria V. Blinova Tatiana M. Bogdanova Alexei A. Iljin Larisa S. Sulkovskaya Marina P. Chernyshova Marina V. Lozbiakova Nigel H. Kyle Yuriy K. Bashmakov 《Food Science & Nutrition》2019,7(4):1157-1165
Lycopene is a dietary antioxidant known to prevent skin photodamage. This study aimed to examine age‐dependent presence of this carotenoid on the surface of the facial skin and in the serum as well as to measure the same parameters during supplementation with lycopene. Serum samples and samples from facial skin surface were obtained from 60 young (under 25 years old) and 60 middle‐aged (over 50 years old) volunteers. Similar samples were taken from 15 middle‐aged subjects during 4‐week supplementation with lycopene (7 mg/day). Serum lycopene levels and isomer profiles were analyzed by HPLC. Lycopene in desquamated corneocytes and the sebum from facial skin surface was determined using lycopene‐specific fluorescent monoclonal antibodies. The results demonstrated that there was no age‐related difference in serum lycopene levels, but a higher proportion of (all‐E)‐lycopene was detected in the “young” group (37.5% vs 26.2% in the “middle‐aged” group; p < 0.0001). “Young” volunteers also had a higher lycopene level in both corneocytes (p = 0.0071) and the sebum (p = 0.0139) from the skin surface. Supplementation with lycopene resulted in a sharp increase of lycopene concentrations in both serum and skin surface samples. There was also a clear change in the pattern of lycopene isomers in the serum manifested by a significant increase in the proportion of (all‐E)‐lycopene (from 22.1% to 44.0% after supplementation, p < 0.0001). It can be concluded that dietary supplementation with lycopene results in its accumulation in the serum and skin. This process is accompanied by significant changes in the circulating lycopene isomer profile which becomes similar to that typical for young individuals. 相似文献
160.
Tianxiang Nan Jia‐Mian Hu Minyi Dai Satoru Emori Xinjun Wang Zhongqiang Hu Alexei Matyushov Long‐Qing Chen Nian Sun 《Advanced functional materials》2019,29(6)
Magnetization dynamics induced by spin–orbit torques in a heavy‐metal/ferromagnet can potentially be used to design low‐power spintronics and logic devices. Recent computations have suggested that a strain‐mediated spin–orbit torque (SOT) switching in magnetoelectric (ME) heterostructures is fast, energy‐efficient, and permits a deterministic 180° magnetization switching. However, its experimental realization has remained elusive. Here, the coexistence of the strain‐mediated ME coupling and the SOT in a CoFeB/Pt/ferroelectric hybrid structure is shown experimentally. The voltage‐induced strain only slightly modifies the efficiency of SOT generation, but it gives rise to an effective magnetic anisotropy and rotates the magnetic easy axis which eliminates the incubation delay in current‐induced magnetization switching. The phase field simulations show that the electric‐field‐induced effective magnetic anisotropy field can reduce the switching time approximately by a factor of three for SOT in‐plane magnetization switching. It is anticipated that such strain‐mediated ME‐SOT hybrid structures may enable field‐free, ultrafast magnetization switching. 相似文献