Enhancement of near-field phase-shifting contact lithography by immersion technique

Near-field phase-shifting contact lithography is theoretically modeled incorporating the immersion technique for improvement of photoresist features. The absorption patterns in the photoresist layer, which correspond to the resolution of features after development, are found to be localized in a more compact and uniform fashion with the immersed lithographic system than with the dry system. Therefore, the resolution and profiles of the high-aspect-ratio features can be notably enhanced by immersion lithography.     

Lifetime determination of materials that exhibit a stretched exponential luminescent decay

We report frequency- and time-domain luminescent lifetime measurements for materials that exhibit a broad spectrum of lifetimes, specifically, those for which the observed decay dynamics can be described by a stretched exponential function. The spectrum of lifetimes of such materials can be characterized by an average lifetime, and in principle this average can be extracted from either time- or frequency-domain measurements. In practice, this requires some care, because the extent to which the various states are excited depends on how long their lifetime is relative to the excitation pulse width or period. For the complex luminescent materials ZnS:Cu,Al and CdS quantum dots we compare the average lifetime obtained from frequency-domain data and from time-domain data under both pulsed laser excitation and steady-state, dc excitation. The agreement between the average measured lifetimes is good, but not perfect, showing that quoted average lifetimes for complex materials can be dependent on the measurement technique. Finally, a spectrum of lifetimes is given that gives rise to stretched exponential relaxation and this spectrum is used to compute frequency-domain data for a stretched exponential material.     

Theoretical study of electric conductance through nanostructures in terms of the phase-shift

A simple expression of the electric conductance through a nanostructure connected to two electrodes is obtained by using the phase-shift analysis. The Green function theory applicable to the nonequilibrium system is employed to formulate the electric conductance. The 0 bias limit, i.e., the linear response approximation is taken. The relation between Green functions and phase-shifts is obtained by extending the method applied to the single impurity problem in the metal. It is shown that a channel does not contribute to the conductance if its phase-shift is an integer multiple of π. Also shown is the importance of the effect due to multiple orbitals in nanostructures. Some concrete examples leading to simpler forms are given.     

二维超外差条纹处理技术

本文从超外差式调频接受机的原理出发,提出一个适合于各种灵敏度测量的二维超外差条纹处理方法.与超外差式调频接受机的优点对应,该条纹处理方法有兼顾各种灵敏度,具有统一的中频处理与鉴相模块等优点.与其它采用条纹骨架的处理方法相比较,该方法实际上是直接的位相检测,其鉴相部分运用普通的phase-shift原理,因而具有测量精高度、灵敏度高的优点.此外,该方法也便于用硬件实现.     

Synchronization of four coupled van der Pol oscillators

It is possible that self-excited vibrations in turbomachine blades synchronize due to elastic coupling through the shaft. The synchronization of four coupled van der Pol oscillators is presented here as a simplified model. For quasilinear oscillations, a stability condition is derived from an analysis based on linearizing the original equation around an unperturbed limit cycle and transforming it into Hill’s equation. For the nonlinear case, numerical simulations show the existence of two well-defined regions of phase relationships in parameter space in which a multiplicity of periodic attractors is embedded. The size of these regions strongly depends on the values of the oscillator and coupling constants. For the coupling constant below a critical value, there exists a region in which a diversity of phase-shift attractors is present, whereas for values above the critical value an in-phase attractor is predominant. It is observed that the presence of an anti-phase attractor in the subcritical region is associated with sudden changes in the period of the coupled oscillators. The convergence of the coupled system to a particular periodic attractor is explored using several initial conditions. The study is extended to non-identical oscillators, and it is found that there is synchronization even over a wide range of difference among the oscillator constants.