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Conrad Rizal

University of Victoria, Chemistry, Post-Doc

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Experienced and accomplished researcher and educator in the areas of Silicon nano-photonics, nano-electronics, magneto-optics and allied applied science and engineering fields. Research themes include (1) design and development of multifunctional nanocomposites using chemical
Phone: 6475704039
Address: North York, Ontario, Canada

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M.Saifur Rahman

Rajshahi University of Engineering and Technology

Khaleda Akter Rikta

Jannati Nabiha Nur

Mohammad Hasibul Hasan Hasib

Kamrun Shushama

University of Maryland, College Park

Conrad Rizal, PhD

University of California, San Diego

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Papers by Conrad Rizal

Magento-Optic-Plasmonic Sensors with Improved Performance

IEEE TRANSACTIONS ON MAGNETICS , 2021

In this paper, I propose a novel magneto-optic-plasmonic (MOP) surface plasmon resonance (SPR) ef... more In this paper, I propose a novel magneto-optic-plasmonic (MOP) surface plasmon resonance (SPR) effect-based sensor configuration using a conventional mutlilayer combination of metal and dielectrics, and compare the performance: sensitivity and detection limit of the proposed magneto-optic SPR (MOSPR) sensor (at the magnetic field, H = ±H) with the conventional SPR sensor (at H = 0) at the excitation wavelength, λ = 632.8 nm and 785 nm in air and Helium. Both the sensitivity and detection limit of the optimized MOSPR sensor showed significantly larger values over the sensitivity and detection limit of the SPR sensor, almost 4× h the performance of these sensors.

Surface Plasmon Resonance (SPR) to Magneto-Optic SPR

Condensed Matter, 2019

In this editorial, a brief background of the surface plasmon resonance (SPR) principle is discuss... more In this editorial, a brief background of the surface plasmon resonance (SPR) principle is discussed, followed by several aspects of magneto-optic SPR (MOSPR) and sensing schemes from the viewpoint of fundamental studies and potential technological applications. New sensitivity metrics are introduced that would allow researchers to compare the performance of SPR and MOSPR-based sensors. Merits of MOSPR over SPR based sensors and challenges faced by MOSPR sensors in terms of their practical use and portability are also considered. The editorial ends with potential new configurations and future prospects. This work is considered highly significant to device engineers, graduate and undergraduate students, and researchers of all levels involved in developing new classes of bio-devices for sensing, imaging, environmental monitoring, toxic gas detection, and surveying applications to name a few. 1. Background The interaction of optical radiation with surface plasmons (coherent delocalized electron oscillations at a metal-dielectric interface) in the absence and presence of a magnetic field (H) resulted in the discoveries of surface plasmon resonance (SPR) and magneto-optic SPR (MOSPR), respectively. The discovery of SPR phenomena dates to the early 20th century, between the years 1902 and 1912, first experimentally demonstrated by R.M. Wood [1], and later theoretically described by Lord Rayleigh in 1907 [2]. However, it was not until 1968 that a convenient approach for observing the SPR phenomenon was introduced by Kretschmann [3] and Otto [4]. Since then, several other researchers and companies continued investigating the phenomena for possible use in the medical field. However, it was only in 1990 that BIACORE commercially developed (first batch of 35 units) an SPR-based device for practical biosensing purposes [5]. Since then SPR has remained a primary choice for biosensing and drug discovery [6]. Surface plasmon polaritons (SPPs) are collective oscillations of the free-electron gas at the boundary/surface of metal and dielectric layers. The wave vector of these waves is given by k spp =

Improved Transition Metal Dichalcogenides-Based Surface Plasmon Resonance Biosensors

by Conrad Rizal, Kamrun Shushama, Mohammad Hasibul Hasan Hasib, and Jannati Nabiha Nur

Condensed MDPI Mater Special Issue on Magnetoplasmonics, 2019

Surface plasmon resonance (SPR) biosensors based on transition metal dichalcogenides (TMDC) mater... more Surface plasmon resonance (SPR) biosensors based on transition metal dichalcogenides (TMDC) materials have shown improved performance in terms of sensitivity, detection accuracy (DA), and quality factor (QF) over conventional biosensors. In this paper, we propose a five-layers model containing black phosphorus (BP) and TMDC (Ag/BP/WS 2) in Kretschmann configuration. Using TM-polarized light at 633 nm, we numerically demonstrate the highest sensitivity (375 • /RIU), DA (0.9210), and QF (65.78 1/RIU) reported so far over similar materials. Refractive index (RI) of the coupling prism has also played an essential role in enhancing the performance of these biosensors. The research on TMDC materials is still new, and these materials bring about opportunities to develop a new class of biosensor.

Design of a 2 × 4 Hybrid MMI-MZI Configuration with MMI Phase-shifters

by Conrad Rizal and Boris Niraula

This paper reports design of a 2 × 4 hybrid multimode interferometer-Mach-zehnder interferometer ... more This paper reports design of a 2 × 4 hybrid multimode interferometer-Mach-zehnder interferometer (MMI-MZI) configuration consiting of compact thermo-optical switches on the silicon-on-insulator (SOI) platform. The device consists of two identical MMI slab waveguides as power splitters and couplers that are connected with two identical MMI-based phase shifters, and linear tapers at both ends of the MMIs to minimize the power coupling loss. A thin Al pad is used as a heating element and a trench is created around this pad to prevent heat from spreading, and to minimize loss. The calculated average thermo-optical switching power consumption, excess loss, and power imbalance are 1.4 mW, 0.9 dB, and 0.1 dB, respectively. The overall footprint of the device is 6 × 304 µm 2. The new heating method has advantages of compact size, ease of fabrication on SOI platform with the current CMOS technology, and offers low excess loss and power consumption as demanded by devices based on SOI technology. The device can act as two independent optical switches in one device.

Magneto-Optic Surface Plasmon Resonance Ti/Au/Co/Au/P c Configuration and Sensitivity

Magneto-optic surface plasmon resonance (MOSPR)-based sensors are highly attractive as next-gener... more Magneto-optic surface plasmon resonance (MOSPR)-based sensors are highly attractive as next-generation biosensors. However, these sensors suffer from oxidation leading to degradation of performance, reproducibility of the sensor surface, because of the difficulty of removing adsorbed materials, and degradation of the sensor surface during surface cleaning and these limit their applications. In this paper, I propose MOSPR-based biosensors with 0 to 15 nm thick inert polycarbonate laminate plastic as a protective layer and theoretically demonstrate the practicability of my approach in water-medium for three different probing samples: ethanol, propanol, and pentanol. I also investigate microstructure and magnetic properties. The chemical composition and layered information of the sensor are investigated using X-ray reflectivity and X-ray diffraction analyses and these show distinct face-centered-cubic (fcc)-Au (111) phases, as dominated by the higher density of conduction electrons in Au as compared to Co. The magnetic characterization measured with the in-plane magnetic field to the sensor surface for both the as-deposited and annealed multilayers showed isotropic easy axis magnetization parallel to the multilayer interface at a saturating magnetic field of <100 Oersted (Oe). The sensor showed a maximum sensitivity of 5.5 × 10 4 %/RIU (refractive index unit) for water–ethanol media and the highest detection level of 2.5 × 10 −6 for water-pentanol media as the protective layer is increased from 0 to 15 nm. View Full-Text

Microstructure, Surface Plasmon, Magneto-Optic Surface Plasmon, and Sensitivity Properties of Magneto-Plasmonic Co/Au Multilayers

Micro-structure properties of (Co 1.2 nm/Au 2 nm) ×N = 20 multilayers (MLs) prepared using dc-mag... more Micro-structure properties of (Co 1.2 nm/Au 2 nm) ×N = 20 multilayers (MLs) prepared using dc-magnetron sputtering are reported using X-ray reflectivity (XRR) and X-ray diffraction (XRD) analysis. XRR profiles of these MLs showed excellent bilayer periodicity. The XRD spectra displayed Co layer thickness-dependent properties. Annealing increased lateral tensile strain, however, decreased compressive strain along the substrate normal direction. While surface roughness, crystallite grain size, and strain are affected by Co layer thickness, microstructure and periodicity are dominated by fcc-Au (111). Surface plasmon resonance (SPR) and magneto-optic SPR (MOSPR) study of an optimized Co/Au multilayer in Kretschmann configuration for air–He and water–methanol media showed an enhancement in sensitivity by over 4X when excited at λ = 785 nm compared to the conventional SPR configuration when excited at λ = 632.8 nm. This enhancement in MOSPR sensitivity means that the detection limit of this class of transducers can be substantially improved by tuning Co/Au layer thickness, wavelength, and incident angle of optical radiation. Index Terms— Co/Au, magneto-optic surface plasmon resonance (MOSPR), magneto-plasmonics, surface plasmon resonance (SPR), X-ray diffraction (XRD), X-ray reflection.

Improved Magneto-Optic Surface Plasmon Resonance Biosensors

The magneto-optic (MO) characteristics and sensing performance of noble metal (Ag, Au, Cu) or tra... more The magneto-optic (MO) characteristics and sensing performance of noble metal (Ag, Au, Cu) or transition metal (Fe, Ni, Co) single layers and Ag/Co or Au/Co bilayers have been studied and compared in both the standard plasmonic and MO plasmonic configurations at two different wavelengths (632.8 nm and 785 nm) and in two different sensing media (air and water). The sensing performance is found to be medium-specific and lower in biosensor-relevant water-based media. The sensitivities of MO-SPR sensors is found to be superior to SPR sensors in all cases. This enhancement in sensitivity means the detection limit of this class of transducers can be substantially improved by tuning Au/Co layer thickness, wavelength, and incident angle of optical radiation. The optimized bilayer showed an enhancement in sensitivity by over 30× in air and 9× in water as compared to the conventional Au SPR configuration. Notably, the best performance is 3× above that of MO-SPR sensors coupled to a photonic crystal previously reported in the literature and is found when the ferromagnetic layer is furthest from the sensing medium, as opposed to typical MO-SPR configurations. This proposed structure is attractive for next-generation biosensors.

IEEE TRANSACTIONS ON MAGNETICS Microstructure, Surface Plasmon, Magneto-Optic Surface Plasmon, and Sensitivity Properties of Magneto-Plasmonic Co/Au Multilayers

Micro-structure properties of (Co 1.2 nm/Au 2 nm) ×N = 20 multilayers (MLs) prepared using dc-mag... more Micro-structure properties of (Co 1.2 nm/Au 2 nm) ×N = 20 multilayers (MLs) prepared using dc-magnetron sputtering are reported using X-ray reflectivity (XRR) and X-ray diffraction (XRD) analysis. XRR profiles of these MLs showed excellent bilayer periodicity. The XRD spectra displayed Co layer thickness-dependent properties. Annealing increased lateral tensile strain, however, decreased compressive strain along the substrate normal direction. While surface roughness, crystallite grain size, and strain are affected by Co layer thickness, microstructure and periodicity are dominated by fcc-Au (111). Surface plasmon resonance (SPR) and magneto-optic SPR (MOSPR) study of an optimized Co/Au multilayer in Kretschmann configuration for air–He and water–methanol media showed an enhancement in sensitivity by over 4X when excited at λ = 785 nm compared to the conventional SPR configuration when excited at λ = 632.8 nm. This enhancement in MOSPR sensitivity means that the detection limit of this class of transducers can be substantially improved by tuning Co/Au layer thickness, wavelength, and incident angle of optical radiation. 10 11 Index Terms— Co/Au, magneto-optic surface plasmon resonance (MOSPR), magneto-plasmonics, surface plasmon resonance (SPR), X-ray diffraction (XRD), X-ray reflection.

Microstructure and magneto-optical surface plasmon resonance of Co/Au multilayers

IOP J. Physics Communication, 2018

Magneto-optical surface plasmon resonance (MOSPR) sensors benefit from a magneto-optic enhancemen... more Magneto-optical surface plasmon resonance (MOSPR) sensors benefit from a magneto-optic enhancement with respect to surface plasmon resonance (SPR) sensors, making these devices attractive for biosensing applications. Typical design compromises seek to balance magneto-optic effects and optical losses associated with surface plasmon waves extending to the ferromagnetic layer. Here, we demonstrate that Co/Au multilayers can yield sizeable MOSPR improvements in spite of the relative high total Co layer thickness. Co (t Co)/Au (2 nm) multilayers, with 1.2t Co 1.8 nm are prepared and characterized. X-ray analysis shows that the microstructure maintains high layer periodicity and improves upon annealing. The multilayer structures were then modeled to study their SPR/MOSPR sensitivities, suggesting that the MOSPR sensitivity is enhanced by a factor of up to 3 and 4 with respect to the SPR sensitivity when the devices are operated in Air and Water media, respectively. We find that multilayers provide a particular advantage when operating the sensors in Water-based media.

Compact Si-based asymmetric MZI waveguide on SOI as a thermo-optical switch

A compact low power consuming asymmetric MZI based optical modulator with fast response time has ... more A compact low power consuming asymmetric MZI based optical modulator with fast response time has been proposed on SOI platform. The geometrical and performance characteristics were analyzed in depth and optimized using coupled mode analysis and FDTD simulation tools, respectively. It was tested with and without implementation of thermo-optic (TO) effect. The device showed good frequency modulating characteristics when tested without the implementation of the TO effect. The fabricated device showed quality factor, Q ≈ 10,000, and this value is comparable to the Q of the device simulated with 25% transmission loss, showing FSR of 0.195 nm, FWHM ≈ 0.16 nm, and ER of 13 dB. With TO effect, it showed temperature sensitivity of 0.01 nm/ • C and FSR of 0.19 nm. With the heater length of 4.18 mm, the device required 0.26 mW per í µí¼ shift power with a switching voltage of 0.309 V, response time of 10 μ, and figure-of-merit of 2.6 mW μs. All of these characteristics make this device highly attractive for use in integrated Si photonics network as optical switch and wavelength modulator.

Perpendicular magnetic anisotropy and microstructure properties of nanoscale Co/Au multilayers

Nanoscale Silicon Waveguide Based Thermo‐Optic Sensor Using a Compact Mach‐Zehnder Interferometer

A compact Mach‐zehnder interferometer with a novel design of directional couplers and a phase shi... more A compact Mach‐zehnder interferometer with a novel design of directional couplers and a phase shifter has been presented as a thermo‐optical sensor. With the aim of reducing device size to micro and nano dimension silicon‐on‐insulator technology was employed. That allowed miniaturization of device size through the reduction of its cross sectional area to 0.066 μm 2 and the radius of curvature of both the arms of the directional coupler and S‐bends of the phase shifter to 5 μm and C‐bends to 3 μm. These nano size device dimensions made it possible to reduce the coupling gap to 0.2 μm, which resulted in a significant reduction in the coupling length. The device geometry and its performance characteristics were analyzed and optimized using coupled mode analysis and finite difference time domain simulation tools, respectively. The wavelength dependent transmission loss of the device was measured at different temperature to verify and validate its performance characteristics. Tested devices showed a remarkable temperature dependent transmission characteristic offering significant changes in transmission loss band – with as low as 0.45 0 C change in substrate temperature. The extinction ratio and the free spectral range of the device were 26 dB and 0.26 nm respectively in the wavelength range of 1549.5 nm – 1550.5 nm. These results imply that the devices presented here can be used as compact and highly sensitive thermal sensors and optical switches.

Magnetic properties of multilayers

by R. Zuberek, Elies Molins, and Conrad Rizal

Journal of Magnetism and Magnetic Materials, 1995

ABSTRACT Two Fe/Cu multilayer systems with ultra-thin Fe layers have been investigated by X-ray d... more ABSTRACT Two Fe/Cu multilayer systems with ultra-thin Fe layers have been investigated by X-ray diffraction, Mossbauer spectroscopy and strain modulated ferromagnetic resonance. Mossbauer spectra show the existence of alpha-Fe and gamma-Fe and also a ferromagnetic phase, which has been attributed to the interdifussion zone. The iron magnetic moment for the magnetic phases lies predominantly in the film plane. The magnetostriction constant increases with the iron thickness.

magnetochemistry Review Ferromagnetic Multilayers: Magnetoresistance, Magnetic Anisotropy, and Beyond

Obtaining highly sensitive ferromagnetic, FM, and nonmagnetic, NM, multilayers with a large room-... more Obtaining highly sensitive ferromagnetic, FM, and nonmagnetic, NM, multilayers with a large room-temperature magnetoresistance, MR, and strong magnetic anisotropy, MA, under a small externally applied magnetic field, H, remains a subject of scientific and technical interest. Recent advances in nanofabrication and characterization techniques have further opened up several new ways through which MR, sensitivity to H, and MA of the FM/NM multilayers could be dramatically improved in miniature devices such as smart spin-valves based biosensors, non-volatile magnetic random access memory, and spin transfer torque nano-oscillators. This review presents in detail the fabrication and characterization of a few representative FM/NM multilayered films—including the nature and origin of MR, mechanism associated with spin-dependent conductivity and artificial generation of MA. In particular, a special attention is given to the Pulsed-current deposition technique and on the potential industrial applications and future prospects. FM multilayers presented in this review are already used in real-life applications such as magnetic sensors in automobile and computer industries. These material are extremely important as they have the capability to efficiently replace presently used magnetic sensors in automobile, electronics, biophysics, and medicine, among many others.

37th Candian Medical and Biological Engineering Society Conference Series, Vancouver, BC, Canada. May 20-23, 2014.(Submitted)

Nanoscale multilayer structures built from sandwiching ferromagnetic Co, non-magnetic Au, and die... more Nanoscale multilayer structures built from sandwiching ferromagnetic Co, non-magnetic Au, and dielectric materials are interesting systems to investigate magnetoplasmonics (MP)a combined effect of plasmons, optical radiation, and applied magnetic field, H. 1 Co and Au possess large lattice mismatches below 693 K, 2, 3 and our experimental results have shown that they exhibit large magnetic anisotropies below H = 50 Oe and at room temperature 3 , allowing us to control the dielectric properties of the multilayers via H fields, incident angle,  of optical radiation, and layer thicknesses. We previously reported magnetic anisotropy and plasmonic properties of Co/Au/Glass multilayers. 3 , 4 In addition, we reported optical characteristics (e.g., reflectivity, etc.) of these structures as a function of . The multilayers exhibited minimum reflectivity characteristics at  = 43 0 , and it shifted towards higher angle when an antiferromagnetic, Cr layer is inserted between the Co and Au layers. In this work, we investigate the effect of , static and oscillating H fields, and layer thicknesses on the absorption and transmission characteristics of the Co/Au multilayers, and extend the work to the periodic arrays of nanoholes with the aim of using it for the biological samples. Due to the quantum nature of the magnetic spins (3d) in Co and the abundance of free conduction electrons (4s) in Au, Co/Au/Glass multilayers are expected to exhibit interesting magnetoplasmonics phenomena at small H fields that can have significant applications in biomedical engineering, especially in bio-magnetic and magnetoplasmonic sensing devices.

Effects of Annealing on Magnetization and Nanostructures of Cobalt-Gold

International Conference on Computer and Electrical Engineering 4th (ICCEE 2011), 2011

Effect of strain on magnetoresistance and magnetic properties of Co (tCo)/Ag nanostructures

2011 IEEE Nanotechnology Materials and Devices Conference, 2011

A series of [Co (tco) nm/Ag 1.5 nmlso

Magnetic Properties of Co/Au Multilayers

IEEE Transactions on Magnetics, 2014

We report on the magnetic anisotropy and magnetoresistance properties of [Co (tCo)/Au (tAu)] θ N ... more We report on the magnetic anisotropy and magnetoresistance properties of [Co (tCo)/Au (tAu)] θ N multilayers prepared by changing the incident angle of deposition, θ, the thicknesses tCo and tAu of Co and Au layers respectively, and the number of bilayers, N , while keeping N × tCo fixed at 20 nm. Although all of the multilayers showed magnetic anisotropies at low applied magnetic fields, H, and at room temperature, the ones deposited at θ = 45 • showed remarkable mgnetic anisotropies, which is further enhanced upon magnetic annealing. The [Co (1nm)/Au (2nm)] 45 20 multilayer showed a maximum magnetoresistance of 2.1% at room temperature and H = 1 kOe. Moreover, for the same field H and current I, the transverse (H ⊥ I) magnetoresistance is always larger than the longitudinal (H I) magnetoresistance.

Magnetotransport Properties of Co-Au Granular Alloys

International Journal of Applied Physics and Mathematics, 2011

A series of Cox-Au1-x granular alloys was grown using pulsed-current electrodeposition on polyimi... more A series of Cox-Au1-x granular alloys was grown using pulsed-current electrodeposition on polyimide substrates. The relationship between the giant magnetoresistance effect, saturation magnetization, and grain size was examined as the deposition current density and annealing temperatures were changed. A maximum magnetoresistance (MR) ratio of 4.5 % was obtained. The magnetization and ferromagnetic grain size of the as-deposited and annealed alloy films were examined against the deposition current density. The saturation magnetization decreased as the composition of Au was increased for both the alloys deposited at the current densities of 1 and 5 mA/cm2. The total magnetic moment further decreased on annealing. The grain size is found to be highly influenced by both the deposition current density and temperature. A low temperature magnetization measurement suggested that the ferromagnetic grain size decreases with increase in current densities. For the annealed samples, the ferromagnetic grain sizes were found to be dispersed in the Au matrix with different diameters. The decrease in magnetic moments with annealing is correlated with the grain size of the Co and its distribution in the gold matrix. The MR ratio increased with the increase in the deposition current density as a result of the formation of smaller grain size at higher deposition current densities.

Magnetic properties and magnetoresistance effect in Co/Au, Ag nano-structure films produced by pulse electrodeposition

physica status solidi (c), 2004

We have investigated the relationship between the magnetism and the magnetoresistance effect in t... more We have investigated the relationship between the magnetism and the magnetoresistance effect in the Co/Au, Ag multilayer films with layers produced in the atomic level by pulse electrodeposition method. The magnetoresistance effect is dependent on both the thickness of Co ferromagnetic layer and Ag,Au non-magnetic layers. The magnetization of these films shows the minimum value against the Ag and Au layer thickness. The Ag and Au layer thickness showing the maximum of MR ratio is not of necessary in agreement with the Ag and Au layer thickness showing the minimum of magnetization. Antiparallel alignment of magnetic spin is a necessary but not sufficient condition in order to generate the GMR of multilayer films. For the Co/Au multilayer films, the Au layer thickness showing the minimum of the magnetization shifts to higher side of the Au layer thickness.

Magento-Optic-Plasmonic Sensors with Improved Performance

IEEE TRANSACTIONS ON MAGNETICS , 2021

In this paper, I propose a novel magneto-optic-plasmonic (MOP) surface plasmon resonance (SPR) ef... more In this paper, I propose a novel magneto-optic-plasmonic (MOP) surface plasmon resonance (SPR) effect-based sensor configuration using a conventional mutlilayer combination of metal and dielectrics, and compare the performance: sensitivity and detection limit of the proposed magneto-optic SPR (MOSPR) sensor (at the magnetic field, H = ±H) with the conventional SPR sensor (at H = 0) at the excitation wavelength, λ = 632.8 nm and 785 nm in air and Helium. Both the sensitivity and detection limit of the optimized MOSPR sensor showed significantly larger values over the sensitivity and detection limit of the SPR sensor, almost 4× h the performance of these sensors.

Surface Plasmon Resonance (SPR) to Magneto-Optic SPR

Condensed Matter, 2019

In this editorial, a brief background of the surface plasmon resonance (SPR) principle is discuss... more In this editorial, a brief background of the surface plasmon resonance (SPR) principle is discussed, followed by several aspects of magneto-optic SPR (MOSPR) and sensing schemes from the viewpoint of fundamental studies and potential technological applications. New sensitivity metrics are introduced that would allow researchers to compare the performance of SPR and MOSPR-based sensors. Merits of MOSPR over SPR based sensors and challenges faced by MOSPR sensors in terms of their practical use and portability are also considered. The editorial ends with potential new configurations and future prospects. This work is considered highly significant to device engineers, graduate and undergraduate students, and researchers of all levels involved in developing new classes of bio-devices for sensing, imaging, environmental monitoring, toxic gas detection, and surveying applications to name a few. 1. Background The interaction of optical radiation with surface plasmons (coherent delocalized electron oscillations at a metal-dielectric interface) in the absence and presence of a magnetic field (H) resulted in the discoveries of surface plasmon resonance (SPR) and magneto-optic SPR (MOSPR), respectively. The discovery of SPR phenomena dates to the early 20th century, between the years 1902 and 1912, first experimentally demonstrated by R.M. Wood [1], and later theoretically described by Lord Rayleigh in 1907 [2]. However, it was not until 1968 that a convenient approach for observing the SPR phenomenon was introduced by Kretschmann [3] and Otto [4]. Since then, several other researchers and companies continued investigating the phenomena for possible use in the medical field. However, it was only in 1990 that BIACORE commercially developed (first batch of 35 units) an SPR-based device for practical biosensing purposes [5]. Since then SPR has remained a primary choice for biosensing and drug discovery [6]. Surface plasmon polaritons (SPPs) are collective oscillations of the free-electron gas at the boundary/surface of metal and dielectric layers. The wave vector of these waves is given by k spp =

Improved Transition Metal Dichalcogenides-Based Surface Plasmon Resonance Biosensors

by Conrad Rizal, Kamrun Shushama, Mohammad Hasibul Hasan Hasib, and Jannati Nabiha Nur

Condensed MDPI Mater Special Issue on Magnetoplasmonics, 2019

Surface plasmon resonance (SPR) biosensors based on transition metal dichalcogenides (TMDC) mater... more Surface plasmon resonance (SPR) biosensors based on transition metal dichalcogenides (TMDC) materials have shown improved performance in terms of sensitivity, detection accuracy (DA), and quality factor (QF) over conventional biosensors. In this paper, we propose a five-layers model containing black phosphorus (BP) and TMDC (Ag/BP/WS 2) in Kretschmann configuration. Using TM-polarized light at 633 nm, we numerically demonstrate the highest sensitivity (375 • /RIU), DA (0.9210), and QF (65.78 1/RIU) reported so far over similar materials. Refractive index (RI) of the coupling prism has also played an essential role in enhancing the performance of these biosensors. The research on TMDC materials is still new, and these materials bring about opportunities to develop a new class of biosensor.

Design of a 2 × 4 Hybrid MMI-MZI Configuration with MMI Phase-shifters

by Conrad Rizal and Boris Niraula

This paper reports design of a 2 × 4 hybrid multimode interferometer-Mach-zehnder interferometer ... more This paper reports design of a 2 × 4 hybrid multimode interferometer-Mach-zehnder interferometer (MMI-MZI) configuration consiting of compact thermo-optical switches on the silicon-on-insulator (SOI) platform. The device consists of two identical MMI slab waveguides as power splitters and couplers that are connected with two identical MMI-based phase shifters, and linear tapers at both ends of the MMIs to minimize the power coupling loss. A thin Al pad is used as a heating element and a trench is created around this pad to prevent heat from spreading, and to minimize loss. The calculated average thermo-optical switching power consumption, excess loss, and power imbalance are 1.4 mW, 0.9 dB, and 0.1 dB, respectively. The overall footprint of the device is 6 × 304 µm 2. The new heating method has advantages of compact size, ease of fabrication on SOI platform with the current CMOS technology, and offers low excess loss and power consumption as demanded by devices based on SOI technology. The device can act as two independent optical switches in one device.

Magneto-Optic Surface Plasmon Resonance Ti/Au/Co/Au/P c Configuration and Sensitivity

Magneto-optic surface plasmon resonance (MOSPR)-based sensors are highly attractive as next-gener... more Magneto-optic surface plasmon resonance (MOSPR)-based sensors are highly attractive as next-generation biosensors. However, these sensors suffer from oxidation leading to degradation of performance, reproducibility of the sensor surface, because of the difficulty of removing adsorbed materials, and degradation of the sensor surface during surface cleaning and these limit their applications. In this paper, I propose MOSPR-based biosensors with 0 to 15 nm thick inert polycarbonate laminate plastic as a protective layer and theoretically demonstrate the practicability of my approach in water-medium for three different probing samples: ethanol, propanol, and pentanol. I also investigate microstructure and magnetic properties. The chemical composition and layered information of the sensor are investigated using X-ray reflectivity and X-ray diffraction analyses and these show distinct face-centered-cubic (fcc)-Au (111) phases, as dominated by the higher density of conduction electrons in Au as compared to Co. The magnetic characterization measured with the in-plane magnetic field to the sensor surface for both the as-deposited and annealed multilayers showed isotropic easy axis magnetization parallel to the multilayer interface at a saturating magnetic field of <100 Oersted (Oe). The sensor showed a maximum sensitivity of 5.5 × 10 4 %/RIU (refractive index unit) for water–ethanol media and the highest detection level of 2.5 × 10 −6 for water-pentanol media as the protective layer is increased from 0 to 15 nm. View Full-Text

Microstructure, Surface Plasmon, Magneto-Optic Surface Plasmon, and Sensitivity Properties of Magneto-Plasmonic Co/Au Multilayers

Micro-structure properties of (Co 1.2 nm/Au 2 nm) ×N = 20 multilayers (MLs) prepared using dc-mag... more Micro-structure properties of (Co 1.2 nm/Au 2 nm) ×N = 20 multilayers (MLs) prepared using dc-magnetron sputtering are reported using X-ray reflectivity (XRR) and X-ray diffraction (XRD) analysis. XRR profiles of these MLs showed excellent bilayer periodicity. The XRD spectra displayed Co layer thickness-dependent properties. Annealing increased lateral tensile strain, however, decreased compressive strain along the substrate normal direction. While surface roughness, crystallite grain size, and strain are affected by Co layer thickness, microstructure and periodicity are dominated by fcc-Au (111). Surface plasmon resonance (SPR) and magneto-optic SPR (MOSPR) study of an optimized Co/Au multilayer in Kretschmann configuration for air–He and water–methanol media showed an enhancement in sensitivity by over 4X when excited at λ = 785 nm compared to the conventional SPR configuration when excited at λ = 632.8 nm. This enhancement in MOSPR sensitivity means that the detection limit of this class of transducers can be substantially improved by tuning Co/Au layer thickness, wavelength, and incident angle of optical radiation. Index Terms— Co/Au, magneto-optic surface plasmon resonance (MOSPR), magneto-plasmonics, surface plasmon resonance (SPR), X-ray diffraction (XRD), X-ray reflection.

Improved Magneto-Optic Surface Plasmon Resonance Biosensors

The magneto-optic (MO) characteristics and sensing performance of noble metal (Ag, Au, Cu) or tra... more The magneto-optic (MO) characteristics and sensing performance of noble metal (Ag, Au, Cu) or transition metal (Fe, Ni, Co) single layers and Ag/Co or Au/Co bilayers have been studied and compared in both the standard plasmonic and MO plasmonic configurations at two different wavelengths (632.8 nm and 785 nm) and in two different sensing media (air and water). The sensing performance is found to be medium-specific and lower in biosensor-relevant water-based media. The sensitivities of MO-SPR sensors is found to be superior to SPR sensors in all cases. This enhancement in sensitivity means the detection limit of this class of transducers can be substantially improved by tuning Au/Co layer thickness, wavelength, and incident angle of optical radiation. The optimized bilayer showed an enhancement in sensitivity by over 30× in air and 9× in water as compared to the conventional Au SPR configuration. Notably, the best performance is 3× above that of MO-SPR sensors coupled to a photonic crystal previously reported in the literature and is found when the ferromagnetic layer is furthest from the sensing medium, as opposed to typical MO-SPR configurations. This proposed structure is attractive for next-generation biosensors.

IEEE TRANSACTIONS ON MAGNETICS Microstructure, Surface Plasmon, Magneto-Optic Surface Plasmon, and Sensitivity Properties of Magneto-Plasmonic Co/Au Multilayers

Micro-structure properties of (Co 1.2 nm/Au 2 nm) ×N = 20 multilayers (MLs) prepared using dc-mag... more Micro-structure properties of (Co 1.2 nm/Au 2 nm) ×N = 20 multilayers (MLs) prepared using dc-magnetron sputtering are reported using X-ray reflectivity (XRR) and X-ray diffraction (XRD) analysis. XRR profiles of these MLs showed excellent bilayer periodicity. The XRD spectra displayed Co layer thickness-dependent properties. Annealing increased lateral tensile strain, however, decreased compressive strain along the substrate normal direction. While surface roughness, crystallite grain size, and strain are affected by Co layer thickness, microstructure and periodicity are dominated by fcc-Au (111). Surface plasmon resonance (SPR) and magneto-optic SPR (MOSPR) study of an optimized Co/Au multilayer in Kretschmann configuration for air–He and water–methanol media showed an enhancement in sensitivity by over 4X when excited at λ = 785 nm compared to the conventional SPR configuration when excited at λ = 632.8 nm. This enhancement in MOSPR sensitivity means that the detection limit of this class of transducers can be substantially improved by tuning Co/Au layer thickness, wavelength, and incident angle of optical radiation. 10 11 Index Terms— Co/Au, magneto-optic surface plasmon resonance (MOSPR), magneto-plasmonics, surface plasmon resonance (SPR), X-ray diffraction (XRD), X-ray reflection.

Microstructure and magneto-optical surface plasmon resonance of Co/Au multilayers

IOP J. Physics Communication, 2018

Magneto-optical surface plasmon resonance (MOSPR) sensors benefit from a magneto-optic enhancemen... more Magneto-optical surface plasmon resonance (MOSPR) sensors benefit from a magneto-optic enhancement with respect to surface plasmon resonance (SPR) sensors, making these devices attractive for biosensing applications. Typical design compromises seek to balance magneto-optic effects and optical losses associated with surface plasmon waves extending to the ferromagnetic layer. Here, we demonstrate that Co/Au multilayers can yield sizeable MOSPR improvements in spite of the relative high total Co layer thickness. Co (t Co)/Au (2 nm) multilayers, with 1.2t Co 1.8 nm are prepared and characterized. X-ray analysis shows that the microstructure maintains high layer periodicity and improves upon annealing. The multilayer structures were then modeled to study their SPR/MOSPR sensitivities, suggesting that the MOSPR sensitivity is enhanced by a factor of up to 3 and 4 with respect to the SPR sensitivity when the devices are operated in Air and Water media, respectively. We find that multilayers provide a particular advantage when operating the sensors in Water-based media.

Compact Si-based asymmetric MZI waveguide on SOI as a thermo-optical switch

A compact low power consuming asymmetric MZI based optical modulator with fast response time has ... more A compact low power consuming asymmetric MZI based optical modulator with fast response time has been proposed on SOI platform. The geometrical and performance characteristics were analyzed in depth and optimized using coupled mode analysis and FDTD simulation tools, respectively. It was tested with and without implementation of thermo-optic (TO) effect. The device showed good frequency modulating characteristics when tested without the implementation of the TO effect. The fabricated device showed quality factor, Q ≈ 10,000, and this value is comparable to the Q of the device simulated with 25% transmission loss, showing FSR of 0.195 nm, FWHM ≈ 0.16 nm, and ER of 13 dB. With TO effect, it showed temperature sensitivity of 0.01 nm/ • C and FSR of 0.19 nm. With the heater length of 4.18 mm, the device required 0.26 mW per í µí¼ shift power with a switching voltage of 0.309 V, response time of 10 μ, and figure-of-merit of 2.6 mW μs. All of these characteristics make this device highly attractive for use in integrated Si photonics network as optical switch and wavelength modulator.

Perpendicular magnetic anisotropy and microstructure properties of nanoscale Co/Au multilayers

Nanoscale Silicon Waveguide Based Thermo‐Optic Sensor Using a Compact Mach‐Zehnder Interferometer

A compact Mach‐zehnder interferometer with a novel design of directional couplers and a phase shi... more A compact Mach‐zehnder interferometer with a novel design of directional couplers and a phase shifter has been presented as a thermo‐optical sensor. With the aim of reducing device size to micro and nano dimension silicon‐on‐insulator technology was employed. That allowed miniaturization of device size through the reduction of its cross sectional area to 0.066 μm 2 and the radius of curvature of both the arms of the directional coupler and S‐bends of the phase shifter to 5 μm and C‐bends to 3 μm. These nano size device dimensions made it possible to reduce the coupling gap to 0.2 μm, which resulted in a significant reduction in the coupling length. The device geometry and its performance characteristics were analyzed and optimized using coupled mode analysis and finite difference time domain simulation tools, respectively. The wavelength dependent transmission loss of the device was measured at different temperature to verify and validate its performance characteristics. Tested devices showed a remarkable temperature dependent transmission characteristic offering significant changes in transmission loss band – with as low as 0.45 0 C change in substrate temperature. The extinction ratio and the free spectral range of the device were 26 dB and 0.26 nm respectively in the wavelength range of 1549.5 nm – 1550.5 nm. These results imply that the devices presented here can be used as compact and highly sensitive thermal sensors and optical switches.

Magnetic properties of multilayers

by R. Zuberek, Elies Molins, and Conrad Rizal

Journal of Magnetism and Magnetic Materials, 1995

ABSTRACT Two Fe/Cu multilayer systems with ultra-thin Fe layers have been investigated by X-ray d... more ABSTRACT Two Fe/Cu multilayer systems with ultra-thin Fe layers have been investigated by X-ray diffraction, Mossbauer spectroscopy and strain modulated ferromagnetic resonance. Mossbauer spectra show the existence of alpha-Fe and gamma-Fe and also a ferromagnetic phase, which has been attributed to the interdifussion zone. The iron magnetic moment for the magnetic phases lies predominantly in the film plane. The magnetostriction constant increases with the iron thickness.

magnetochemistry Review Ferromagnetic Multilayers: Magnetoresistance, Magnetic Anisotropy, and Beyond

Obtaining highly sensitive ferromagnetic, FM, and nonmagnetic, NM, multilayers with a large room-... more Obtaining highly sensitive ferromagnetic, FM, and nonmagnetic, NM, multilayers with a large room-temperature magnetoresistance, MR, and strong magnetic anisotropy, MA, under a small externally applied magnetic field, H, remains a subject of scientific and technical interest. Recent advances in nanofabrication and characterization techniques have further opened up several new ways through which MR, sensitivity to H, and MA of the FM/NM multilayers could be dramatically improved in miniature devices such as smart spin-valves based biosensors, non-volatile magnetic random access memory, and spin transfer torque nano-oscillators. This review presents in detail the fabrication and characterization of a few representative FM/NM multilayered films—including the nature and origin of MR, mechanism associated with spin-dependent conductivity and artificial generation of MA. In particular, a special attention is given to the Pulsed-current deposition technique and on the potential industrial applications and future prospects. FM multilayers presented in this review are already used in real-life applications such as magnetic sensors in automobile and computer industries. These material are extremely important as they have the capability to efficiently replace presently used magnetic sensors in automobile, electronics, biophysics, and medicine, among many others.

37th Candian Medical and Biological Engineering Society Conference Series, Vancouver, BC, Canada. May 20-23, 2014.(Submitted)

Nanoscale multilayer structures built from sandwiching ferromagnetic Co, non-magnetic Au, and die... more Nanoscale multilayer structures built from sandwiching ferromagnetic Co, non-magnetic Au, and dielectric materials are interesting systems to investigate magnetoplasmonics (MP)a combined effect of plasmons, optical radiation, and applied magnetic field, H. 1 Co and Au possess large lattice mismatches below 693 K, 2, 3 and our experimental results have shown that they exhibit large magnetic anisotropies below H = 50 Oe and at room temperature 3 , allowing us to control the dielectric properties of the multilayers via H fields, incident angle,  of optical radiation, and layer thicknesses. We previously reported magnetic anisotropy and plasmonic properties of Co/Au/Glass multilayers. 3 , 4 In addition, we reported optical characteristics (e.g., reflectivity, etc.) of these structures as a function of . The multilayers exhibited minimum reflectivity characteristics at  = 43 0 , and it shifted towards higher angle when an antiferromagnetic, Cr layer is inserted between the Co and Au layers. In this work, we investigate the effect of , static and oscillating H fields, and layer thicknesses on the absorption and transmission characteristics of the Co/Au multilayers, and extend the work to the periodic arrays of nanoholes with the aim of using it for the biological samples. Due to the quantum nature of the magnetic spins (3d) in Co and the abundance of free conduction electrons (4s) in Au, Co/Au/Glass multilayers are expected to exhibit interesting magnetoplasmonics phenomena at small H fields that can have significant applications in biomedical engineering, especially in bio-magnetic and magnetoplasmonic sensing devices.

Effects of Annealing on Magnetization and Nanostructures of Cobalt-Gold

International Conference on Computer and Electrical Engineering 4th (ICCEE 2011), 2011

Effect of strain on magnetoresistance and magnetic properties of Co (tCo)/Ag nanostructures

2011 IEEE Nanotechnology Materials and Devices Conference, 2011

A series of [Co (tco) nm/Ag 1.5 nmlso

Magnetic Properties of Co/Au Multilayers

IEEE Transactions on Magnetics, 2014

We report on the magnetic anisotropy and magnetoresistance properties of [Co (tCo)/Au (tAu)] θ N ... more We report on the magnetic anisotropy and magnetoresistance properties of [Co (tCo)/Au (tAu)] θ N multilayers prepared by changing the incident angle of deposition, θ, the thicknesses tCo and tAu of Co and Au layers respectively, and the number of bilayers, N , while keeping N × tCo fixed at 20 nm. Although all of the multilayers showed magnetic anisotropies at low applied magnetic fields, H, and at room temperature, the ones deposited at θ = 45 • showed remarkable mgnetic anisotropies, which is further enhanced upon magnetic annealing. The [Co (1nm)/Au (2nm)] 45 20 multilayer showed a maximum magnetoresistance of 2.1% at room temperature and H = 1 kOe. Moreover, for the same field H and current I, the transverse (H ⊥ I) magnetoresistance is always larger than the longitudinal (H I) magnetoresistance.

Magnetotransport Properties of Co-Au Granular Alloys

International Journal of Applied Physics and Mathematics, 2011

A series of Cox-Au1-x granular alloys was grown using pulsed-current electrodeposition on polyimi... more A series of Cox-Au1-x granular alloys was grown using pulsed-current electrodeposition on polyimide substrates. The relationship between the giant magnetoresistance effect, saturation magnetization, and grain size was examined as the deposition current density and annealing temperatures were changed. A maximum magnetoresistance (MR) ratio of 4.5 % was obtained. The magnetization and ferromagnetic grain size of the as-deposited and annealed alloy films were examined against the deposition current density. The saturation magnetization decreased as the composition of Au was increased for both the alloys deposited at the current densities of 1 and 5 mA/cm2. The total magnetic moment further decreased on annealing. The grain size is found to be highly influenced by both the deposition current density and temperature. A low temperature magnetization measurement suggested that the ferromagnetic grain size decreases with increase in current densities. For the annealed samples, the ferromagnetic grain sizes were found to be dispersed in the Au matrix with different diameters. The decrease in magnetic moments with annealing is correlated with the grain size of the Co and its distribution in the gold matrix. The MR ratio increased with the increase in the deposition current density as a result of the formation of smaller grain size at higher deposition current densities.

Magnetic properties and magnetoresistance effect in Co/Au, Ag nano-structure films produced by pulse electrodeposition

physica status solidi (c), 2004

We have investigated the relationship between the magnetism and the magnetoresistance effect in t... more We have investigated the relationship between the magnetism and the magnetoresistance effect in the Co/Au, Ag multilayer films with layers produced in the atomic level by pulse electrodeposition method. The magnetoresistance effect is dependent on both the thickness of Co ferromagnetic layer and Ag,Au non-magnetic layers. The magnetization of these films shows the minimum value against the Ag and Au layer thickness. The Ag and Au layer thickness showing the maximum of MR ratio is not of necessary in agreement with the Ag and Au layer thickness showing the minimum of magnetization. Antiparallel alignment of magnetic spin is a necessary but not sufficient condition in order to generate the GMR of multilayer films. For the Co/Au multilayer films, the Au layer thickness showing the minimum of the magnetization shifts to higher side of the Au layer thickness.

Ferromagnetic Hybrid Nanostructure for Potential Clinical Applications

This book presents the theory, design, fabrication, measurement, and characterization of ferromag... more This book presents the theory, design, fabrication, measurement, and characterization of ferromagnetic hybrid multilayers and granular alloys consisting of magnetic, non-magnetic, and dielectric material that are significant in the development of next generation state-of-the-art magnetic sensors. Topics on artificial generation of magnetic anisotropy through oblique angle deposition and induced strain are also covered. It also covers topics on nanocomposite material and high-magnetic-moment biocompatible alloys, artificially produced on polyimide, and considered useful for potential clinical applications.
The future of magneto-optic based ferromagnetic nanostructures is extremely bright. The exceptional properties displayed by magneto-optic nanostructures, such as strong enhancement of electromagnetic fields, high sensitivity, and large signal-to-noise-ratio, make them unique, outstanding, and sought for material for biosensing, imaging and many other applications. New chapters are added on surface plasmon resonance (SPR) and MO-SPR configurations and bio-sensing.

Magneto-Optic Surface Plasmon Resonance Ti/Au/Co/Au/Pc Configuration and Sensitivity 3

Magneto-optic surface plasmon resonance (MOSPR) based sensors are highly attractive as next gener... more Magneto-optic surface plasmon resonance (MOSPR) based sensors are highly attractive as next generation biosensors. However, these sensors suffer from oxidation leading to degradation of performance, reproducibility of the sensor surface because of the difficulty of removing adsorbed materials, and degradation of sensor surface during surface cleaning, and these limit their applications. In this paper, I propose MOSPR-based biosensors with 0 to 15 nm thick inert polycarbonate laminate plastic as a protective layer and theoretically demonstrate the practicability of our approach in water-medium for three different probing samples: ethanol, propanol, and pentanol. I also investigate microstructure and magnetic properties. The chemical composition and ayered information of the sensor are investigated using X-ray reflectivity and X-ray diffraction analyses and these show distinct fcc-Au (111) phases, as dominated by the higher density of conduction electrons in Au as compared to Co. The magnetic characterization measured with the in-plane magnetic field to the sensor surface for both the as-deposited and annealed multilayers showed isotropic easy axis magnetization parallel to the multilayer interface at a saturating magnetic field of < 100 Oe. The sensor showed a maximum sensitivity of 5.5 × 10 4 % / RIU for water-ethanol media and the highest detection level of 2.5×10-8 for water-pentanol media as the protective layer is increased from 0 to 15 nm.