Danish Hussain

Development of Three-Dimensional Atomic Force Microscope for Sidewall Structures Imaging With Controllable Scanning Density

In this paper, a three-dimensional atomic force microscope (3-D AFM) for imaging of the micro- and nanoscale sidewall structures is presented. The system mainly consists of two individual scanners, each with two degrees of freedom to drive the probe on YZ plane for the feedback control and the sample on XY plane for the raster scan. A slender optical fiber probe is used and can be laterally tilted with a rotary holder to access steep sidewalls with overhang or undercut features without any modification of the optical lever. Unlike the conventional AFM with the single-axis feedback control, the 3-D AFM is capable of tracking 3-D profiles of the sidewall structures with nonorthogonal scan due to the dual-axis feedback control with a vector probing scanning scheme. The motion vector angle of the probe is controllable, and varied according to the slope angle of the sample surface for accurate scan of the sidewall with a uniform image density. The 3-D AFM demonstrates great potential not only for characterization of 3-D surface topography, but also for critical dimension (CD) measurements of the sidewall structures. Three- dimensional imaging and CD measurement results of an AFM calibration grating, and a microcomb structure validate the capability and flexibility of the developed system.

Atomic force microscope caliper for critical dimension measurements of micro and nanostructures through sidewall scanning.

A novel atomic force microscope (AFM) dual-probe caliper for critical dimension (CD) metrology has been developed. The caliper is equipped with two facing tilted optical fiber probes (OFPs) wherein each can be used independently to scan either sidewall of micro and nanostructures. The OFP tip with length up to 500 μm (aspect ratio 10:1, apex diameter ⩾10 nm) has unique features of scanning deep trenches and imaging sidewalls of relatively high steps with exclusive profiling possibilities. The caliper arms-OFPs can be accurately aligned with a well calibrated opening distance. The line width, line edge roughness, line width roughness, groove width and CD angles can be measured through serial scan of adjacent or opposite sidewalls with each probe. Capabilities of the presented AFM caliper have been validated through experimental CD measurement results of comb microstructures and AFM calibration grating TGZ3.

Atomic force microscopy deep trench and sidewall imaging with an optical fiber probe

We report a method to measure critical dimensions of micro- and nanostructures using the atomic force microscope (AFM) with an optical fiber probe (OFP). This method is capable of scanning narrow and deep trenches due to the long and thin OFP tip, as well as imaging of steep sidewalls with unique profiling possibilities by laterally tilting the OFP without any modifications of the optical lever. A switch control scheme is developed to measure the sidewall angle by flexibly transferring feedback control between the Z- and Y-axis, for a serial scan of the horizontal surface (raster scan on XY-plane) and sidewall (raster scan on the YZ-plane), respectively. In experiments, a deep trench with tapered walls (243.5 μm deep) and a microhole (about 14.9 μm deep) have been imaged with the orthogonally aligned OFP, as well as a silicon sidewall (fabricated by deep reactive ion etching) has been characterized with the tilted OFP. Moreover, the sidewall angle of TGZ3 (AFM calibration grating) was accurately measured using the switchable scan method.

Towards MOOCs and Their Role in Engineering Education

Massive Open Online Courses (MOOCs) are the latest installment in the field of distance education. This paper discusses the pros and cons of MOOCs in the educational systems with a special emphasis on the engineering education. Since 2012, more and more universities have been joining MOOC revolution and the number of online courses has considerably increased over time. Engineering MOOCs are also increasing. Due to their access to large audience, massive online courses have been expanding their horizon of admission to engineering education at all levels and improving the in-campus learning.

Optimizing the Quality Factor of Quartz Tuning Fork Force Sensor for Atomic Force Microscopy: Impact of Additional Mass and Mass Rebalance

A force sensor in the heart of an atomic force microscope (AFM) plays a key role in the AFM measurements. Quartz tuning fork (QTF) based force sensor is attracting huge attention due to its peculiar traits such as self-actuating and sensing capability, high quality factor and high force sensitivity. Unfortunately, mounting a tip on a tine of the QTF degrades its quality (Q)-factor and sensitivity. Attaching an equivalent counter mass on the opposite tine (mass rebalance) can improve the Q-factor. We investigate the impact of the attached mass and counter mass on different traits of the QTF such as Q-factor, inherent relationship between excitation voltage and output as well as shift in the resonance frequency. We propose straight forward strategies to rebalance the QTF force sensor. Experimental results demonstrate that by attaching a counter mass (at the parallel position) on the opposite tine, the tip mass can be rebalanced. Q-factor is significantly improved after mass rebalance. The increase in the Q-factor depends on the mass of the tip, counter mass and position of the counter mass relative to the position of the tip (

Multiparametric Kelvin Probe Force Microscopy for the Simultaneous Mapping of Surface Potential and Nanomechanical Properties

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Characterization of spherical domains at the polystyrene thin film-water interface.

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Atomic Force Microscopy Sidewall Imaging with a Quartz Tuning Fork Force Sensor

We report high-resolution multiparametric kelvin probe force microscopy (MP-KPFM) measurements for the simultaneous quantitative mapping of the contact potential difference (CPD) and nanomechanical properties of the sample in single-pass mode. This method combines functionalities of the force-distance-based atomic force microscopy and amplitude-modulation (AM) KPFM to perform measurements in single-pass mode. During the tip-sample approach-and-retract cycle, nanomechanical measurements are performed for the retract part of nanoindentation, and the CPD is measured by the lifted probe with a constant tip-sample distance. We compare the performance of the proposed method with the conventional KPFMs by mapping the CPD of multilayer graphene deposited on n-doped silicon, and the results demonstrate that MP-KPFM has comparable performance to AM-KPFM. In addition, the experimental results of a custom-fabricated polymer grating with heterogeneous surfaces validate the multiparametric imaging capability of the MP-KPFM. This method can have potential applications in finding the inherent link between nanomechanical properties and the surface potential of the materials, such as the quantification of the electromechanical response of the deformed piezoelectric materials.

Fast Specimen Boundary Tracking and Local Imaging with Scanning Probe Microscopy

Summary Spherical domains that readily form at the polystyrene (PS)–water interface were studied and characterized using atomic force microscopy (AFM). The study showed that these domains have similar characteristics to micro- and nanobubbles, such as a spherical shape, smaller contact angle, low line tension, and they exhibit phase contrast and the coalescence phenomenon. However, their insensitivity to lateral force, absence of long-range hydrophobic attraction, and the presence of possible contaminants and scratches on these domains suggested that these objects are most likely blisters formed by the stretched PS film. Furthermore, the analysis of the PS film before and after contact with water suggested that the film stretches and deforms after being exposed to water. The permeation of water at the PS–silicon interface, caused by osmosis or defects present on the film, can be a reasonable explanation for the nucleation of these spherical domains.

Amplitude calibration of quartz tuning fork (QTF) force sensor with an atomic force microscope

Sidewall roughness measurement is becoming increasingly important in the micro-electromechanical systems and nanoelectronics devices. Atomic force microscopy (AFM) is an emerging technique for sidewall scanning and roughness measurement due to its high resolution, three-dimensional imaging capability and high accuracy. We report an AFM sidewall imaging method with a quartz tuning fork (QTF) force sensor. A self sensing and actuating force sensor is fabricated by microassembling a commercial AFM cantilever (tip apex radius ≤10 nm) to a QTF. The attached lightweight cantilever allows high-sensitivity force detection (7.4% Q factor reduction) and sidewall imaging with high lateral resolution. Owing to its unique configuration, the tip of the sensor can detect sidewall surface orthogonally during imaging, which reduces lateral friction. In experiments, sidewalls of a micro-electro-mechanical system (MEMS) structure fabricated by deep reactive ion etching process and a standard step grating are scanned and the sidewall roughness, line edge roughness and sidewall angles are measured.