Dongxian Zhang

Tuning color by pore depth of metal-coated porous alumina

A simple and effective color tuning method has been developed by controlling the pore depth of the metal-coated porous alumina (PA) template. The mechanism for color tuning in this method was uncovered, which can be used to design a colorful complex pattern. A colorful world map was produced and exhibited on a PA template by this method. Such vivid color tuning is predominantly due to the interference enhancement of the nanostructure. This method has the potential for tuning colors and being widely applied in the fields of nanotechnology, physics and photonics.

Theoretical and experimental study of photo-thermal expansion using an atomic force microscope

This paper briefly presents a new idea of micro-drivers based on photo-thermal expansion (PTE). This kind of micro-driver consists of an expansion arm, a support arm and a motion block on the arm. While being heated by a laser beam, the expansion arm extends rapidly, and the motion block remains still due to its own inertia. When the heating beam is shut off, the expansion arm shrinks slowly and makes the block move along with it for a small step. Irradiated by a periodic laser, the block is able to move step by step in the micro/nanometer order. We first study the expansion and contracting mode of PTE in theory, and deduce some approximate formulae. Then the mechanism of PTE and its expansion waveform are observed and traced with an atomic force microscope (AFM) system. Experiments show that our theoretical formulae match experiment results well and the variable regularity of PTE satisfies the requirements of a micro-driver. The PTE amplitude is in the nanometer order, and its frequency is in accordance with the heating laser pulse. Furthermore, it is observed that the expansion amplitude can be adjusted by changing the power of the heating laser. The results show that the method of the micro-driver based on PTE is practically feasible.

Color tuning by local sputtering metal nanolayer on microstructured porous alumina

This article reports a novel color tuning method by local sputtering nanolayers on microstructured porous alumina (PA) templates with different pore depths. With the aid of scanning electron microscopy observation, physical models of the original and sputtered PA templates are set up, and the details of the color tuning method are further proposed. Two series of colors covering the whole visible range are first obtained by respectively sputtering Cr and Ag nanolayers on two groups of PA templates with pore‐depths ranging from 230 to 490 nm. A vivid colorful pattern of “Butterfly wings” is then prepared by local sputtering such Cr and Ag nanolayers on the surface of a PA with 310 nm pore‐depth. The scanning electron microscopy images of Cr and Ag sputtered PA surfaces show different microstructures, which is in agreement with different color exhibiting. This method is expected to have a potential of being widely applied in the fields of micro‐optics, microstructures, advanced materials, and micro/nanotechnology. Microsc. Res. Tech., 2012.

A Novel Atomic Force Microscope with High Stability and Scan Speed

Abstract A novel atomic force microscope (AFM) has been developed. Unlike conventional AFM systems, its cantilever and tip were set up in the X direction with respect to the sample. It can practically eliminate the crawling effect of the probe itself. Meanwhile, using a beam splitter, we devised a unique path optical beam deflection method for the measurement of the cantilevers displacement with its minimized structure and an optimal light‐amplifying ratio; the position of the sensitive detector (PSD) is just in front of the visual sight of operator. This makes observation and operation easier. Furthermore, the PSD attached to the translation stage can be adjusted and, thus, adapts the setpoint of imaging force to different samples. In this way, our new AFM provides high stability and scan speed. The highest scan rate is about 40 lines/s or 10s for a 400×400‐pixel, 3 µm×3 µm image.

An Effective Method for Extracting Capsule by Color Image Processing

In order to extract capsule defects and reduce the process time in the real-time capsule defects identification system, a novel method using color image processing has been presented. We take RGB color space as the image processing environment and build an algebra relationship among the R, G and B components to directly segment the capsule defects instead of transforming these components to HSI color space. The first step of this method is to remove the background and effectively extract the capsule from the CCD-captured image. Based on the color variation relationship between the defect regions and the surrounding ones, the capsule defects are further segmented. Experimental results show that the method can successfully extract capsules better than in HSI color space, meanwhile, it can greatly accelerate the process and finish extracting within 3.5 milliseconds in contrast with 29.3 milliseconds in HSI space. Using this method, we have effectively extracted the capsules as well as their defects. The method would be practically useful in capsule defect identification system.

Analysis and experimentation of novel asymmetric photo-thermal micro-actuator

In this article, an innovative micro-actuator based on photo-thermal heating is introduced. The basic ideas are to apply a new way to get large actuation power from laser source. When a beam of laser irradiates a thin sheet, the sheet temperature increases and volume expands. Besides irradiation laser power, convection coefficient and the parameters of sheet material, the length-width ratio of sheet also influences the heating process. Applying this characteristic, an asymmetric photo-thermal actuator was manufactured by the excimer laser micromaching system. Steady-state thermal analysis is presented. Feasibility experiments with a laser diode (655 nm) as the power source were carried out, and the data of deflection have been measured under different laser power. The experiment results prove the availability of these novel photo-thermal micro-actuators, and demonstrate that the deflection can be 11.8 μm at 10 mW laser power. This mirco-actuator doesnt need of the old power supply modes of external electric wire or small battery, and can be operated in non-focused uniform irradiation, so it has more mobility and can be controlled remotely. Furthermore, this actuator can be applied in many special environments.

Atomic force microscope in liquid with a specially designed probe for practical application

An atomic force microscope (AFM) in liquid was developed. The specially designed AFM probe was composed of a tip attached to a cantilever, a cantilever-tip pedestal, a circular Plexiglas window, and a scanner which is made up of three perpendicular tube piezos. When the instrument works, the liquid level is between the upper and lower surface of the window, and a circular meniscus is established around the Plexiglas window, preventing the tip from being affected or destroyed by surface tension of the liquid. In this setup, the cantilever tip and the sample are completely immersed in fluid. Meanwhile, during the cantilever-tip scanning over the sample during measurement, this system has no restriction on the sample’s size and weight and has a high scanning speed, which can be up to 40lines∕s or 10s for a 400×400pixel image. Some experiments were carried out on the system to demonstrate the elegant performance. The results show that the AFM (i) enables the whole canitlever tip to dive into the fluid; (ii) t...

Theoretical modelling and experimental study of novel photothermal microactuators

We present a category of novel photothermal (PT) microactuators. Each microactuator consists of two PT arms that are jointed at the free end and connected to an anchor at the fixed end. When a laser beam irradiates one of the arms (called hot arm, and the other is cold arm), light energy is absorbed and converted into heat. The asymmetric thermal expansion of the hot and cold arms results in lateral deflection. Based on conduction heat transfer theory and heat dissipation mechanism, we study the PT effects and establish the theoretical model of PT expansion for the microactuators. The temperature distribution and the linear thermal expansion can be numerically calculated. The analytical solution provides an insight into the operation of the actuators and predicts the performance of the actuators with new designs. A symmetry microactuator and a microswitch as the prototypes have been fabricated and tested. The experimental results are in good agreement with the theoretical predictions and prove the feasibility of the novel PT microactuators.

Dual imaging-unit atomic force microscope for nanometer order length metrology based on reference scales

This article reports results from a dual imaging-unit atomic force microscope (DIU-AFM) used for length metrology based on reference scales. The DIU-AFM, suitable for most samples with different conductivity, was developed in view of the fact that the application field of a dual tunneling-unit scanning tunneling microscope was strongly limited by sample conductivity. Two atomic force microscopy (AFM) units were combined in the DIU-AFM, one as a reference unit, and the other a test one. Their probes with Z piezoelements and tips were horizontally set in parallel at the same height to reduce errors due to geometric asymmetry. A reference sample and a test sample were attached to one single XY scanner on same surface, and were imaged by the AFM units at the same time. The two images have the same lateral size, and thus, the length of the test sample image could be accurately measured by counting the periodic features in the reference one. The most remarkable advantages of the DIU-AFM include: Scanning errors...

A study of color modulation of porous alumina processed by physical vapor deposition

With the development of the porous alumina(PA)fabrication technology, more and more scholars plough into the research of its properties, especially optical properties. Recently, we observed an interesting phenomenon that the PA templates processed by Physical Vapor Deposition (PVD) show color differences related to light path difference. Our work attempts to make the principle clear and to find an effective method to modulate the color of PA samples. This article describes the details of our experimental and theoretical results. We successfully prepared some PA templates with different pore-depth by controlling the time of anodization in oxalic acid solution. In order to enhance the reflectivity of air-PA interface, a layer of TiO2 film of 18 nm is coated with PVD technique, which makes PA templates display quite distinct colors with different hole-depth. By modelling and analyzing PA samples, we make the interpretation of this optical property by taking the PA sample with 150 nm pore-depth as an example, and then put forward a way to simulate samples color within its hole-depth and material refraction-index. The results are in good agreement with our theoretical analysis, which proves the feasibility of our simulation mode.