Heterointerface-Driven Band Alignment Engineering and its Impact on Macro-Performance in Semiconductor Multilayer Nanostructures.

Interfaces in semiconductor heterostructures is of continuously greater significance in the trend of scaling materials down to the atomic limit. Since atoms tend to behave more irregularly around interfaces than in internal materials, accurate energy band alignment becomes a major challenge, which determines the ultimate performance of devices. Therefore, a comprehensive understanding of the interplay between heterointerface, energy band, and macro-performance is desiderated. Here, such interplay is explored by investigating asymmetric heterointerfaces with identical fabrication parameters in multiple-quantum-well lasers. The unexpected asymmetry derives from the atomic discrepancy around heterointerfaces, which ultimately improves the optical property through altered valence band offsets. Strain and charge distribution around heterointerfaces are characterized via geometric phase analysis and in situ bias electron holography, respectively. Combining experiments with theories, arsenic-enrichment at one of the interfaces is considered the origin of asymmetry. To reveal actual band alignment, valence band model is modified focusing on the transition around heterojunctions. The enhanced photoluminescence intensity reflects the alleviation of hole confinement insufficiency and the enlargement of valence band offset. The results help to advance the understanding of the general problem of interface in nanostructures and provide guidance applicable to various scenarios for micro-macro correlation.

Soft Ferrofluid Actuator Based on 3D-Printed Scaffold Removal.

Fabricating soft functional materials via additive manufacturing is an emerging field with a wide variety of applications due to their ability to respond to specifically engineered stimuli (e.g., mechanical, electrical, magnetic, chemical). This article describes an approach to engineering magnetically sensitive structures using three-dimensional printing of acrylonitrile butadiene styrene scaffolds. These scaffolds are encapsulated in polydimethylsiloxane (PDMS) and removed using organic solvents. The open channels that remain after removal are filled in with a ferrofluid to render the structure magnetically sensitive. A three-point flexural test shows that introducing a channel in this way only reduces the flexural modulus of the PDMS by a factor ∼8%. We perform magnetic deflection experiments on samples with three different channel diameters. Our results show a linear dependence between applied magnetic field strength and deflection. We also find that there is a minimum magnetic field strength that needs to be applied to achieve deflection. These results suggest that there is a minimum yield stress, beyond which deflection will occur. We perform experiments on a more complex channel geometry to find that there are multiple modes of deflection. A rational approach to channel design may enable us to tune the mechanical response and direct these actuators to undergo complex motion.

Note: Precision control of nano-positioning stage: An iterative learning-based model predictive control approach.

Due to mechanical vibration and nonlinearities such as hysteresis and creep effect, it is difficult to achieve precise control of nano-positioning stages for high-speed/bandwidth trajectory tracking. In this paper, we propose an iterative learning-based model predictive control (IL-MPC) approach to achieve this goal. IL-MPC strategically combines both model predictive control (MPC) and iterative learning control (ILC) tools: the MPC is applied to ensure that the tracking error is limited through all iterations and the ILC is applied to the system consisting of the MPC and the stage to guarantee high precision trajectory tracking with the existence of MPC modeling uncertainty and system nonlinearity. For experimental validation, IL-MPC was implemented to control a nano-piezo actuator to track both repetitive high-speed/broadband trajectories and trajectories with varying amplitude, phase, and frequency, respectively.