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High-quality microcrystals of trans -[Ru(SO 2 )(NH 3 ) 4 (H 2 O)][ p -TolSO 3 ] 2 photoisomers are embedded within thin films of polyvinylacrylate, which presents opportunities for optical data storage applications.
Photo-responsive metal–organic frameworks (MOFs) are one example of light controlled smart materials for use in advanced sensors, data storage, actuators and molecular switches. In this paper we show the design, synthesis and characterization of a photo-responsive linker that is subsequently reacted to yield MOF single crystals. The photo-responsive properties of the resulting UBMOF-2 arise from the photo-induced cyclization of the diarylethene moiety designed into the linker. Computational modeling to assess the relative energies of linker atropisomers reveals a large energetic barrier preventing facile interconversion between key species. The role of this barrier on the observed photo-induced fatigue provides useful insight into the development of advanced photo-responsive nanoporous materials.
It has been long sought to create magnetism out of simple non-magnetic materials, such as silicon and germanium. Here we show that intrinsic magnetism exists in bilayer silicene and germanene with no need to cut, etch, or dope. Unlike bilayer graphene, strong covalent interlayer bonding formed in bilayer silicene and germanene breaks the original π-bonding network of each layer, leaving the unbonded electrons unpaired and localized to carry magnetic moments. These magnetic moments then couple ferromagnetically within each layer while antiferromagnetically across two layers, giving rise to an infinite magnetic sheet with structural integrity and magnetic homogeneity. Furthermore, this unique magnetic ordering results in fundamental band gaps of 0.55 eV and 0.32 eV for bilayer silicene and germanene, respectively. The integration of intrinsic magnetism and spontaneous band gap opening makes bilayer silicene and germanene attractive for future nanoelectronics as well as spin-based computation and data storage.
Optical upconversion is a net process by which two low energy photons are converted into one higher energy photon. There is vast potential to exploit upconversion in applications ranging from solar energy and biological imaging to data storage and photocatalysis. Here, we link two upconverting chromophores together to synthesize a series of novel tetracene dimers for use as annihilators. When compared with the monomer annihilator, TIPS–tetracene, the dimers yield a strong enhancement in the triplet fusion process, also known as triplet–triplet annihilation, as demonstrated via a large increase in upconversion efficiency and an order of magnitude reduction of the threshold power for maximum yield. Along with the ongoing rapid improvements to sensitizer materials, the dimerization improvements demonstrated here open the way to a wide variety of emerging upconversion applications.
Phase-change materials such as Ge–Sb–Te compounds have attracted much attention due to their potential value in electrical data storage. In contrast to the amorphous and crystalline phases, supercooled liquids are far from being deeply understood despite their inevitable role in both amorphization and crystallization processes. To this end, we have studied the dynamics properties and structural characteristics of liquid and supercooled liquid Ge 3 Sb 2 Te 6 during the fast cooling process. As the temperature decreases, chemical bonds become more homogeneous, but coordination numbers of Ge, Sb and Te atoms change very little. Meanwhile, the structural order of short-range configuration is obviously enhanced. Further studies suggest that Ge-centered, Sb-centered and Te-centered configurations change to the more ordered defective octahedrons mainly by adjusting the bond-angle relationship and bond length, rather than just by changing the coordination environment. It is the more ordered octahedrons that promote the formation of medium-range order. Our findings provide a deep insight into the origin of local structural order in supercooled liquid Ge 3 Sb 2 Te 6 , which is of great importance for the comprehensive understanding of amorphization and crystallization processes.
Here, we investigate the local nanoscale changes of the magnetic anisotropy of a Ni film subject to an inverse magnetostrictive effect by proximity to a V 2 O 3 layer. Using temperature-dependent photoemission electron microscopy (PEEM) combined with X-ray magnetic circular dichroism (XMCD), direct images of the Ni spin alignment across the first-order structural phase transition (SPT) of V 2 O 3 were obtained. We find an abrupt temperature-driven reorientation of the Ni magnetic domains across the SPT, which is associated with a large increase of the coercive field. Moreover, angular dependent ferromagnetic resonance (FMR) shows a remarkable change in the magnetic anisotropy of the Ni film across the SPT of V 2 O 3 . Micromagnetic simulations based on these results are in quantitative agreement with the PEEM data. Direct measurements of the lateral correlation length of the Ni domains from XMCD images show an increase of almost one order of magnitude at the SPT compared to room temperature, as well as a broad spatial distribution of the local transition temperatures, thus corroborating the phase coexistence of Ni anisotropies caused by the V 2 O 3 SPT. We show that the rearrangement of the Ni domains is due to strain induced by the oxide layers’ structural domains across the SPT. Our results illustrate the use of alternative hybrid systems to manipulate magnetic domains at the nanoscale, which allows for engineering of coercive fields for novel data storage architectures.
Controlling the morphology of inorganic nanocrystals is important because many of their electronic attributes are highly sensitive to shape and aspect ratio. FePt nanocrystals have potential as advanced magnetic materials for ultrahigh-density memory. This is due to their high shape and/or magnetocrystalline anisotropy, which allows bits as small as 3 nm to be thermally stable over typical data storage periods of 10 years. Herein, nanocrystals were simply fabricated by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in properly chosen conditions of solvent/surfactant proportions and temperature for rational design of their shape and magnetic properties. This work has combined magnetometry measurements and micromagnetic simulations to illustrate the role of the external shape on the rotation of the magnetization vector for colloidal assemblies.
Disclosed is the design of a high speed two-dimensional optical beam position detector which outputs the X and Y displacement and total intensity linearly. The experimental detector measures the displacement from DC to 123 MHz and the intensity of an optical spot in a similar way as a conventional quadrant photodiode detector. The design uses four discrete photodiodes and simple dedicated optics for the position decomposition which enables higher spatial accuracy and faster electronic processing than conventional detectors. Measurements of the frequency response and the spatial sensitivity demonstrate high suitability for atomic force microscopy, scanning probe data storage applications, and wideband wavefront sensing. The operation principle allows for position measurements up to 20 GHz and more in bandwidth.
Through-focus scanning optical microscopy (TSOM) is a relatively new method that transforms conventional optical microscopes into truly three-dimensional metrology tools for nanoscale to microscale dimensional analysis. TSOM achieves this by acquiring and analyzing a set of optical images collected at various focus positions going through focus (from above-focus to under-focus). The measurement resolution is comparable to what is possible with typical light scatterometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM). TSOM method is able to identify nanometer scale difference, type of the difference and magnitude of the difference between two nano/micro scale targets using a conventional optical microscope with visible wavelength illumination. Numerous industries could benefit from the TSOM method--such as the semiconductor industry, MEMS, NEMS, biotechnology, nanomanufacturing, data storage, and photonics. The method is relatively simple and inexpensive, has a high throughput, provides nanoscale sensitivity for 3D measurements and could enable significant savings and yield improvements in nanometrology and nanomanufacturing. Potential applications are demonstrated using experiments and simulations.
Phase change materials have become significantly attractive due to its unique characteristics for its extensive applications. In this paper, a kind of phase change material, which consists of Fe and Te components, is developed. The crystallization temperature of the Fe-Te materials is 180 deg. C for Fe{sub 1.19}Te and can be adjusted by the Fe/Te ratio. High-speed phase change in the Fe-Te materials has been demonstrated by nanosecond laser irradiation. Comparing to conventional phase change materials, the Fe-Te materials exhibit an anomalous optical property that has higher reflectivity at amorphous than crystalline state, which is useful for data storage design.
Rapid thermal annealing was applied to transform sputter-deposited Fe{sub 51}Pt{sub 49}/Cu bilayers into L1{sub 0} chemically ordered ternary (Fe{sub 51}Pt{sub 49}){sub 100-x}Cu{sub x} alloys with (001) texture on amorphous SiO{sub 2}/Si substrates. It was found that for thin film samples, which were processed at 600 Degree-Sign C for 30 s, the addition of Cu strongly favors the L1{sub 0} ordering and (001) texture formation. Furthermore, it could be revealed by transmission electron microscopy and electron backscatter diffraction that the observed reduction of the ordering temperature with Cu content is accompanied by an increased amount of nucleation sites forming L1{sub 0} ordered grains. The change of the structural properties with Cu content and annealing temperature is closely related to the magnetic properties. While an annealing temperature of 800 Degree-Sign C induces strong perpendicular magnetic anisotropy (PMA) in binary Fe{sub 51}Pt{sub 49} films, the addition of Cu systematically reduces the PMA. However, due to the enhancement of both the A1-L1{sub 0} phase transformation and the development of the (001) texture with increasing Cu content, lowering of the annealing temperature leads to a shift of the maximum perpendicular magnetic anisotropy towards alloys with higher Cu content. Thus, for an annealing temperature of 600 Degree-Sign C, the highest perpendicular magnetic anisotropy energy is found for the (Fe{sub 51}Pt{sub 49}){sub 91}Cu{sub 9} alloy. The smooth surface morphology, adjustable PMA, and high degree of intergranular exchange coupling make these films suitable for post-processing required for specific applications such as for sensorics or magnetic data storage.
Spacer materials are often used to fabricate granular L1{sub 0} FePt media and reduce the grain size, however, at the expense of reduced out-of-plane coercivity. Here, we demonstrate a spacer-less method in which adding 1% helium to argon sputtering gas leads to a substantial improvement in the chemical ordering, as well as the magnetic and microstructural properties of FePt. This change is attributed to the modification in the ion current density of the plasma caused by the excited metastable helium species. Helium plays a pivotal role in providing the Fe and Pt atoms optimal adatom mobility, thereby, producing well-ordered L1{sub 0} FePt media. This leads to an enhancement of the out-of-plane coercivity from 15 to 22 kOe. Furthermore, exchange decoupled grains with a twofold reduction in their diameter to {approx}24 nm are also achieved. These properties are crucial for magnetic media of the future for data storage recording densities beyond 1 Tb/in{sup 2}.
We used high-pressure Raman spectroscopy to study the evolution of vibrational frequencies of the phase change materials (PCMs) Ge{sub 2}Sb{sub 2}Te{sub 5}, GeSb{sub 2}Te{sub 4}, and SnSb{sub 2}Te{sub 4}. We found that the critical pressure for triggering amorphization in the PCMs decreases with increasing vacancy concentration, demonstrating that the presence of vacancies, rather than differences in the atomic covalent radii, is crucial for pressure-induced amorphization in PCMs. Compared to the as-deposited amorphous phase, the pressure-induced amorphous phase has a similar vibrational spectrum but requires much lower laser power to transform into the crystalline phase, suggesting different kinetics of crystallization, which may have implications for applications of PCMs in non-volatile data storage.
Theoretical understanding of the stability, ferromagnetism, and spin polarization of Mn{sub 5}Ge{sub 3} clusters has been performed by using the density functional theory with generalized gradient approximation for exchange and correlation. The magnetic moments and magnetic anisotropy energy (MAE) have been calculated for both bulk and clusters, and the enhanced magnetic moment as well as the enlarged MAE have been identified in clusters. The most attractive achievement is that Mn{sub 5}Ge{sub 3} clusters show a fine half-metallic character with large energy scales. The present results may have important implications for potential applications of small Mn{sub 5}Ge{sub 3} clusters as both emerging spintronics and next-generation data-storage technologies.
A resistive switching memory device consisting of reduced graphene oxide and indium tin oxide as top/bottom two electrodes, separated by dielectric MoS{sub 2} nanosphere assemblies as the active interlayer, was fabricated. This device exhibits the rewritable nonvolatile resistive switching with low SET/RESET voltage (∼2 V), high ON/OFF resistance ratio (∼10{sup 4}), and superior electrical bistability, introducing a potential application in data storage field. The resistance switching mechanism was analyzed in the assumptive model of the electron tunneling across the polarized potential barriers.
Near-field plates consist of non-periodically patterned surfaces that can overcome the diffraction limit and confine electromagnetic fields to subwavelength dimensions. Previous near-field plates experimentally demonstrated extreme field tailoring capabilities. However, their performance suffered from radiation/reflection in undesired directions, those other than the subwavelength focus. This issue can limit the practical use of near-field plates. In this paper, we address this issue by designing a unidirectional near-field plate that can form a subwavelength focal pattern, while suppressing the field radiated/reflected in other directions. The design and operation of the proposed unidirectional near-field plate are verified through full-wave simulation. The unidirectional near-field plate may find application in high resolution imaging and probing, high density data storage, and wireless power transfer systems. As an example, its utility as a high resolution probe is demonstrated through full-wave electromagnetic simulation.
We investigate the transitions of spin configurations in ultrathin nanostructures by tuning the perpendicular anisotropy (K{sub z}) and out-of-plane magnetic field (H), using the Monte Carlo simulation. It is revealed that enhancing the anisotropy K{sub z} can drive the evolution of in-plane vortex state into intriguing saturated magnetization states under various H, such as the bubble domain state and quadruple-block-domain state etc. The spin configurations of these states exhibit remarkable H-dependence. In addition, the strong effects of geometry and size on the spin configurations of nanostructures are observed. In particular, a series of edged states occur in the circular disk-shaped lattices, and rich intricate saturated magnetization patterns appear in big lattices. It is suggested that the magnetic states can be manipulated by varying the perpendicular anisotropy, magnetic field, and geometry/size of the nanostructures. Furthermore, the stability (retention capacity) of the saturated magnetization states upon varying magnetic field is predicted, suggesting the potential applications of these saturated magnetization states in magnetic field-controlled data storages.
Self-focusing is a well-researched phenomenon. Nanoscale spots can be achieved through self-focusing, which is an alternative method for achieving high-density data storage, high-resolution light imaging, and maskless nanolithography. Several research groups have observed that self-focusing spots can be reduced to nanoscale levels via incident laser power manipulation. Self-focusing spots can be analyzed by solving the nonlinear Schrödinger equation and the finite difference time domain method. However, both procedures are complex and time-consuming. In the present work, a multi-layer thin-lens self-focusing model that considers diffraction effects and changes of refractive index along the radial and film thickness directions is proposed to analyze the self-focusing behavior and traveling process of light beams intuitively. The self-focusing behaviors of As{sub 2}S{sub 3} are simulated, and results show that a nanoscale self-focusing spot with a radius of about 0.12 μm can be formed at the bottom of nonlinear sample when the incident laser power exceeds 4.25 mW. Our findings are basically consistent with experimental reports and provide a good method for analyzing and understanding the self-focusing process. An appropriate application schematic design is also provided.