Quantitative Materials Contrast at High Spatial Resolution With a Novel Near-Field Scanning Microwave Microscope

A novel Near-Field Scanning Microwave Microscope (NSMM) has been developed where a Scanning Tunneling Microscope (STM) is used for tip-to-sample distance control. The technique is non-contact and non-destructive. The same tip is used for both STM and NSMM, and STM helps maintain the tip-to-sample distance at a nominal height of 1 nm. Due to this very small tip-to-sample separation, the contribution to the microwave signals due to evanescent (non-propagating) waves cannot be ignored. I describe different evanescent wave models developed so far to understand the complex tip-to-sample interaction at microwave frequencies. Propagating wave models are also discussed, since they are still required to understand some aspects of the tip-to-sample interaction. Numerical modeling is also discussed for these problems. I demonstrate the sensitivity of this novel microscope to materials property contrast. The materials contrast is shown in spatial variations on the surface of metal thin films, Boron-doped Semiconductor and Colossal Magneto-Resistive (CMR) thin films. The height dependence of the contrast shows sensitivity to nano-meter sized features when the tip-to-sample separation is below 100 nm. By adding a cone of height 4 nm to the tip, I am able to explain a 300 kHz deviation observed in the frequency shift signal, when tip-to-sample separation is less than 10 nm. In the absence of the cone, the frequency shift signal should continue to show the logarithmic behavior as a function of height. I demonstrate sub-micron spatial resolution with this novel microscope, both in tip-to-sample capacitance Cx and materials contrast in sheet resistance Rx. The spatial resolution in Cx is demonstrated to be at-least 2.5 nm on CMR thin films. The spatial resolution in Rx is shown to be sub-micron by measuring a variably Boron-doped Silicon sample which was prepared using the Focus Ion Beam (FIB) technique

Near-Field Microwave Microscopy on nanometer length scales

The Near-Field Microwave Microscope (NSMM) can be used to measure ohmic losses of metallic thin films. We report on the presence of a new length scale in the probe-to- sample interaction for the NSMM. We observe that this length scale plays an important role when the tip to sample separation is less than about 10nm. Its origin can be modeled as a tiny protrusion at the end of the tip. The protrusion causes deviation from a logarithmic increase of capacitance versus decreasing height of the probe above the sample. We model this protrusion as a cone at the end of a sphere above an infinite plane. By fitting the frequency shift of the resonator versus height data (which is directly related to capacitance versus height) for our experimental setup, we find the protrusion size to be 3nm to 5nm. For one particular tip, the frequency shift of the NSMM relative to 2 micrometers away saturates at a value of about -1150 kHz at a height of 1nm above the sample, where the nominal range of sheet resistance values of the sample are 15 ohms to 150 ohms. Without the protrusion, the frequency shift would have followed the logarithmic dependence and reached a value of about -1500 kHz.Comment: 6 pages, 7 figures (included in 6 pages

Identity and the politics of representation: the case of Muslim youth in Bradford

What are the dialectics of the endogenisation of ‘otherness’? This thesis is a study into the interaction between social representations, identities and power in relation to South Asian, Muslim, male youth in Bradford (UK) within the historical context of the ‘Rushdie affair’. The methodology is structured in order to investigate alternative locations of the identity-representation interaction. The studies include participant observation followed by 18 interviews with ‘specialists’, a rhetorical analysis of five television programmes that were aired on national television during and on the Rushdie affair, and an examination of the manner of reception of one of these programmes through 8 focus group discussions. The findings are that ‘otherness’ and difference are central to notions of identity for South Asian Muslim male youth, as they are surrounded by representations of themselves as ‘Muslim’ and ‘Paki’. Their identities take the form of three ideal-types – ‘coconuts’, ‘rude boys’ and ‘extremists’ – which rhetorically engage differentially with the representations. The Rushdie affair is interpreted firstly as a moment of subaltern contestation of its representation through ‘identity politics’ discourse, and secondly, dialogically as both rhetorical positions (hegemonic and subaltern) attempt to psychologically distance themselves from each other – through the construction of the ‘Bradford Muslim’ on the hegemonic side. However, both positions shared techniques of rhetoric, types of discourse, and a common narrative. Furthermore, ‘identity politics’ discourse (for two of the ideal-type identities) acted as the interpretative prism through which the reception of the programme made sense in relation to, for example, the content and manner of reception, the reception of representatives and the call for strategic essentialism. The thesis shows that attempts to escape negative evaluation result in the incorporation of representations, discourses and rhetorical techniques that position identities firmly within the hermeneutics of the hegemonic discourse

Nanometer-Scale Materials Contrast Imaging with a Near-Field Microwave Microscope

We report topography-free materials contrast imaging on a nano-fabricated Boron-doped Silicon sample measured with a Near-field Scanning Microwave Microscope over a broad frequency range. The Boron doping was performed using the Focus Ion Beam technique on a Silicon wafer with nominal resistivity of 61 Ohm.cm. A topography-free doped region varies in sheet resistance from 1000Ohm/Square to about 400kOhm/Square within a lateral distance of 4 micrometer. The qualitative spatial-resolution in sheet resistance imaging contrast is no worse than 100 nm as estimated from the frequency shift signal.Comment: 5 pages, 3 figures, 1 tabl

Improved power quality operation of symmetrical and asymmetrical multilevel inverter using invasive weed optimization technique

Low switching frequency pulse width modulation (PWM) technique for modulation and control of multilevel inverter in medium voltage high power applications is preferred in order to reduce the switching losses. In this context, a multilevel inverter operated with Selective harmonics minimization PWM technique offers better quality waveform at reduced switching losses. After the Fourier series analysis, the system of non-linear simultaneous transcendental equations is obtained. These equations are then solved to obtain switching angles to have certain low order harmonics at minimum value and regulation in the fundamental voltage magnitude. In this paper, a novel invasive weed optimization (IWO) technique is proposed to compute switching angles. The proposed technique can compute switching angles for both symmetrical and asymmetrical multilevel inverters. Thus it has superiority over well-known optimization techniques such as GA, PSO, DE, and ACO, etc. Moreover, in certain modulation index ranges, it provides faster convergence and accurate results which have been demonstrated in the paper. The computational results have been verified with the experimental result on the prototype developed in the laboratory. The field programming gate arrays (FPGA) based controller is used to implement the proposed technique. The hardware results have been found in close agreement with the computed results. 2022This publication was made possible by NPRP grant #[ 13S-0108-20008 ] from the Qatar National Research Fund (A member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. The APC of the paper is funded by the Qatar National Library , Doha, Qatar.Scopu

Defense against Malicious Users in Cooperative Spectrum Sensing Using Genetic Algorithm

In cognitive radio network (CRN), secondary users (SUs) try to sense and utilize the vacant spectrum of the legitimate primary user (PU) in an efficient manner. The process of cooperation among SUs makes the sensing more authentic with minimum disturbance to the PU in achieving maximum utilization of the vacant spectrum. One problem in cooperative spectrum sensing (CSS) is the occurrence of malicious users (MUs) sending false data to the fusion center (FC). In this paper, the FC takes a global decision based on the hard binary decisions received from all SUs. Genetic algorithm (GA) using one-to-many neighbor distance along with z-score as a fitness function is used for the identification of accurate sensing information in the presence of MUs. The proposed scheme is able to avoid the effect of MUs in CSS without identification of MUs. Four types of abnormal SUs, opposite malicious user (OMU), random opposite malicious user (ROMU), always yes malicious user (AYMU), and always no malicious user (ANMU), are discussed in this paper. Simulation results show that the proposed hard fusion scheme has surpassed the existing hard fusion scheme, equal gain combination (EGC), and maximum gain combination (MGC) schemes by employing GA

A novel AI approach for optimal deployment of EV fast charging station and reliability analysis with solar based DGs in distribution network

The transportation sector is one of the most prevalent fossil fuel users worldwide. Therefore, to mitigate the impacts of carbon-dioxide emissions and reduce the use of non-environmentally friendly traditional energy resources, the electrification of the transportation system, such as the development of electric vehicles (EV), has become crucial. For impeccable EVs deployment, a well-developed charging infrastructure is required. However, the optimal placement of fast charging stations (FCSs) is a critical concern. Therefore, this article provides a functional approach for identifying the optimal location of FCSs using the east delta network (EDN). In addition, the electrical distribution network’s infrastructure is susceptible to changes in electrifying the transportation sector. Therefore, actual power loss, reactive power loss, and investment cost are three areas of consideration in deploying FCSs. Furthermore, including FCSs in the electricity distribution network increases the energy demand from the electrical grid. Therefore, this research paper recommends integrating solar-based distributed generations (SDGs) at selected locations in the distribution network, to mitigate the burden of FCSs on the system. Hence, making the system self-sustaining and reliable. In addition, the reliability of the distribution system is also analyzed after deploying the FCSs and SDGs. Furthermore, six case studies (CS) have been proposed to deploy FCSs with or without DG integration. Consequently, the active power loss went from 1014.48 kW to 829.68 kW for the CS-6

Impact of Foreign Direct Investment (FDI) Inflows on Equilibrium Real Exchange Rate of Pakistan

This study aims to analyze the impact of foreign exchange inflows on equilibrium real exchange rate of Pakistan for the period 1993 M7 to 2009 M3 through behavioral equilibrium real exchange rate (BEER) approach. The BEER approach uses econometric technique of cointegration to establish a behavioral link between the real exchange rate and relevant macroeconomic fundamentals. The study shall conclude that massive foreign direct investment inflows and workers ‘remittances have significantly appreciated equilibrium real exchange rate of Pakistan. The purpose of this paper is to investigate the impact of foreign exchange inflows in Pakistan in the form of FDI and workers’ remittances on equilibrium real exchange rate of Pakistan.&nbsp