A figure of merit for optimization of nanocrystal flash memory design

Nanocrystals can be used as storage media for carriers in flash memories. The performance of a nanocrystal flash memory depends critically on the choice of nanocrystal size and density as well as on the choice of tunnel dielectric properties. The performance of a nanocrystal memory device can be expressed in terms of write/erase speed, carrier retention time and cycling durability. We present a model that describes the charge/discharge dynamics of nanocrystal flash memories and calculate the effect of nanocrystal, gate, tunnel dielectric and substrate properties on device performance. The model assumes charge storage in quantized energy levels of nanocrystals. Effect of temperature is included implicitly in the model through perturbation of the substrate minority carrier concentration and Fermi level. Because a large number of variables affect these performance measures, in order to compare various designs, a figure of merit that measures the device performance in terms of design parameters is defined as a function of write/erase/discharge times which are calculated using the theoretical model. The effects of nanocrystal size and density, gate work function, substrate doping, control and tunnel dielectric properties and device geometry on the device performance are evaluated through the figure of merit. Experimental data showing agreement of the theoretical model with the measurement results are presented for devices that has PECVD grown germanium nanocrystals as the storage media.     

Vertical Phase Separation in Small Molecule:Polymer Blend Organic Thin Film Transistors Can Be Dynamically Controlled

Blending of small‐molecule organic semiconductors (OSCs) with amorphous polymers is known to yield high performance organic thin film transistors (OTFTs). Vertical stratification of the OSC and polymer binder into well‐defined layers is crucial in such systems and their vertical order determines whether the coating is compatible with a top and/or a bottom gate OTFT configuration. Here, we investigate the formation of blends prepared via spin‐coating in conditions which yield bilayer and trilayer stratifications. We use a combination of in situ experimental and computational tools to study the competing effects of formulation thermodynamics and process kinetics in mediating the final vertical stratification. It is shown that trilayer stratification (OSC/polymer/OSC) is the thermodynamically favored configuration and that formation of the buried OSC layer can be kinetically inhibited in certain conditions of spin‐coating, resulting in a bilayer stack instead. The analysis reveals here that preferential loss of the OSC, combined with early aggregation of the polymer phase due to rapid drying, inhibit the formation of the buried OSC layer. The fluid dynamics and drying kinetics are then moderated during spin‐coating to promote trilayer stratification with a high quality buried OSC layer which yields unusually high mobility >2 cm² V^?1 s^?1 in the bottom‐gate top‐contact configuration.     

Application of local error method to SSSF simulation of vector propagation in dispersion compensated optical links

A local error method based on an analytical scheme previously developed for the scalar optical fiber channel is applied to the second-order symmetrized split-step Fourier simulation of polarization multiplexed signal propagation through dispersion compensated optical fiber links. It is found that the global simulation accuracy for the vector propagation can be satisfied using the local error bound from a scalar propagation model for the same global error over a large range of simulation accuracy, chromatic dispersion, and differential group delay. Furthermore, carefully designed numerical simulations are used to show that similar local simulation error are obtained for vector simulations and that the similar local error leads to higher computational efficiency compared to other prevalent step-size selection schemes. The scaling of the global simulation error with respect to the number of optical fiber spans is demonstrated, and global error control for multi-span simulations is proposed. Combining the local error and global error control, the developed simulation scheme can significantly speed up the time-consuming simulations in coherent optical fiber communication system analysis and design.     

Silicon‐Modified Rare‐Earth Transitions—A New Route to Near‐ and Mid‐IR Photonics

Silicon underpins microelectronics but lacks the photonic capability needed for next‐generation systems and currently relies on a highly undesirable hybridization of separate discrete devices using direct band gap semiconductors. Rare‐earth (RE) implantation is a promising approach to bestow photonic capability to silicon but is limited to internal RE transition wavelengths. Reported here is the first observation of direct optical transitions from the silicon band edge to internal f‐levels of implanted REs (Ce, Eu, and Yb); this overturns previously held assumptions about the alignment of RE levels to the silicon band gap. The photoluminescence lines are massively redshifted to several technologically useful wavelengths and modeling of their splitting indicates that they must originate from the REs. Eu‐implanted silicon devices display a greatly enhanced electroluminescence efficiency of 8%. Also observed is the first crystal field splitting in Ce luminescence. Mid‐IR silicon photodetectors with specific detectivities comparable to existing state‐of‐the‐art mid‐IR detectors are demonstrated.     

Composite Nanostructures of TiO2 and ZnO for Water Splitting Application: Atomic Layer Deposition Growth and Density Functional Theory Investigation

The commercialization of solar fuel devices requires the development of novel engineered photoelectrodes for water splitting applications which are based on redundant, cheap, and environmentally friendly materials. In the current study, a combination of titanium dioxide (TiO₂) and zinc oxide (ZnO) onto nanotextured silicon is utilized for a composite electrode with the aim to overcome the individual shortcomings of the respective materials. The properties of conformal coverage of TiO₂ and ZnO layers are designed on the atomic scale by the atomic layer deposition technique. The resulting photoanode shows not only promising stability but also nine times higher photocurrents than an equivalent photoanode with a pure TiO₂ encapsulation onto the nanostructured silicon. Density functional theory calculations indicate that segregation of TiO₂ at the ZnO surfaces is favorable and leads to the stabilization of the ZnO layers in water environments. In conclusion, the novel designed composite material constitutes a promising base for a stable and effective photoanode for the water oxidation reaction.     

Robust state feedback $$H_\infty $$ control for uncertain 2-D continuous state delayed systems in the Roesser model

This paper is concerned with the problem of robust state feedback \(H_\infty \) stabilization for a class of uncertain two-dimensional (2-D) continuous state delayed systems. The parameter uncertainties are assumed to be norm-bounded. Firstly, a new delay-dependent sufficient condition for the robust asymptotical stability of uncertain 2-D continuous systems with state delay is developed. Secondly, a sufficient condition for \(H_\infty \) disturbance attenuation performance of the given system is derived. Thirdly, a stabilizing state feedback controller is proposed such that the resulting closed-loop system is robustly asymptotically stable and achieves a prescribed \(H_\infty \) disturbance attenuation level. All results are developed in terms of linear matrix inequalities. Finally, two examples are provided to validate the effectiveness of the proposed method.     

Development and application of C60-fullerene bound silica for solid-phase extraction of biomolecules

Sample pretreatment is the most important procedure to remove the matrix for interfacing with mass spectrometry (MS). Additionally, for the samples with low concentration, the process of preconcentration is required before MS analysis. We have newly developed a solid-phase extraction stationary phase based on C60-fullerene covalently bound to silica for purification of biomolecules of different characteristics. Silica particles of different porosity are modified with aminopropyl linker and then covalently bound to C60-fullerenoacetic acid or C60-epoxyfullerenes. The developed materials have been successfully applied as an alternative to commercially available reversed-phase materials for solid-phase extraction. C60-fullerene silica is able to retain small and hydrophilic molecules like phosphopeptides, which can be easily lost by reversed-phase sorbents. The novel materials are applied for desalting and preconcentration of proteins and peptides, especially phosphopeptides. In addition, the C60-fullerene silica is applied for the solid-phase extraction of selected flavonoids with recoveries of approximately 99%. The recoveries are compared with the commercially available solid-phase extraction materials.