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- ItemA Flashback on Control Logic Injection Attacks against Programmable Logic Controllers(Basel : MDPI, 2022) Alsabbagh, Wael; Langendörfer, PeterProgrammable logic controllers (PLCs) make up a substantial part of critical infrastructures (CIs) and industrial control systems (ICSs). They are programmed with a control logic that defines how to drive and operate critical processes such as nuclear power plants, petrochemical factories, water treatment systems, and other facilities. Unfortunately, these devices are not fully secure and are prone to malicious threats, especially those exploiting vulnerabilities in the control logic of PLCs. Such threats are known as control logic injection attacks. They mainly aim at sabotaging physical processes controlled by exposed PLCs, causing catastrophic damage to target systems as shown by Stuxnet. Looking back over the last decade, many research endeavors exploring and discussing these threats have been published. In this article, we present a flashback on the recent works related to control logic injection attacks against PLCs. To this end, we provide the security research community with a new systematization based on the attacker techniques under three main attack scenarios. For each study presented in this work, we overview the attack strategies, tools, security goals, infected devices, and underlying vulnerabilities. Based on our analysis, we highlight the current security challenges in protecting PLCs from such severe attacks and suggest security recommendations for future research directions.
- ItemTowards CMOS integrated microfluidics using dielectrophoretic immobilization(Basel : MDPI, 2019) Ettehad, Honeyeh Matbaechi; Yadav, Rahul Kumar; Guha, Subhajit; Wenger, ChristianDielectrophoresis (DEP) is a nondestructive and noninvasive method which is favorable for point-of-care medical diagnostic tests. This technique exhibits prominent relevance in a wide range of medical applications wherein the miniaturized platform for manipulation (immobilization, separation or rotation), and detection of biological particles (cells or molecules) can be conducted. DEP can be performed using advanced planar technologies, such as complementary metal-oxide-semiconductor (CMOS) through interdigitated capacitive biosensors. The dielectrophoretically immobilization of micron and submicron size particles using interdigitated electrode (IDE) arrays is studied by finite element simulations. The CMOS compatible IDEs have been placed into the silicon microfluidic channel. A rigorous study of the DEP force actuation, the IDE’s geometrical structure, and the fluid dynamics are crucial for enabling the complete platform for CMOS integrated microfluidics and detection of micron and submicron-sized particle ranges. The design of the IDEs is performed by robust finite element analyses to avoid time-consuming and costly fabrication processes. To analyze the preliminary microfluidic test vehicle, simulations were first performed with non-biological particles. To produce DEP force, an AC field in the range of 1 to 5 V (peak-to-peak) is applied to the IDE. The impact of the effective external and internal properties, such as actuating DEP frequency and voltage, fluid flow velocity, and IDE’s geometrical parameters are investigated. The IDE based system will be used to immobilize and sense particles simultaneously while flowing through the microfluidic channel. The sensed particles will be detected using the capacitive sensing feature of the biosensor. The sensing and detecting of the particles are not in the scope of this paper and will be described in details elsewhere. However, to provide a complete overview of this system, the working principles of the sensor, the readout detection circuit, and the integration process of the silicon microfluidic channel are briefly discussed. © 2019 by the authors.
- ItemDielectrophoresis: An Approach to Increase Sensitivity, Reduce Response Time and to Suppress Nonspecific Binding in Biosensors?(Basel : MDPI, 2022) Henriksson, Anders; Neubauer, Peter; Birkholz, MarioThe performance of receptor-based biosensors is often limited by either diffusion of the analyte causing unreasonable long assay times or a lack of specificity limiting the sensitivity due to the noise of nonspecific binding. Alternating current (AC) electrokinetics and its effect on biosensing is an increasing field of research dedicated to address this issue and can improve mass transfer of the analyte by electrothermal effects, electroosmosis, or dielectrophoresis (DEP). Accordingly, several works have shown improved sensitivity and lowered assay times by order of magnitude thanks to the improved mass transfer with these techniques. To realize high sensitivity in real samples with realistic sample matrix avoiding nonspecific binding is critical and the improved mass transfer should ideally be specific to the target analyte. In this paper we cover recent approaches to combine biosensors with DEP, which is the AC kinetic approach with the highest selectivity. We conclude that while associated with many challenges, for several applications the approach could be beneficial, especially if more work is dedicated to minimizing nonspecific bindings, for which DEP offers interesting perspectives.
- ItemA Review on Passive and Integrated Near-Field Microwave Biosensors(Basel : MDPI, 2017) Guha, Subhajit; Jamal, Farabi Ibne; Wenger, ChristianIn this paper we review the advancement of passive and integrated microwave biosensors. The interaction of microwave with biological material is discussed in this paper. Passive microwave biosensors are microwave structures, which are fabricated on a substrate and are used for sensing biological materials. On the other hand, integrated biosensors are microwave structures fabricated in standard semiconductor technology platform (CMOS or BiCMOS). The CMOS or BiCMOS sensor technology offers a more compact sensing approach which has the potential in the future for point of care testing systems. Various applications of the passive and the integrated sensors have been discussed in this review paper.
- ItemDesign and Fabrication of a BiCMOS Dielectric Sensor for Viscosity Measurements: A Possible Solution for Early Detection of COPD(Basel : MDPI, 2018) Soltani Zarrin, Pouya; Jamal, Farabi Ibne; Guha, Subhajit; Wessel, Jan; Kissinger, Dietmar; Wenger, ChristianThe viscosity variation of sputum is a common symptom of the progression of Chronic Obstructive Pulmonary Disease (COPD). Since the hydration of the sputum defines its viscosity level, dielectric sensors could be used for the characterization of sputum samples collected from patients for early diagnosis of COPD. In this work, a CMOS-based dielectric sensor for the real-time monitoring of sputum viscosity was designed and fabricated. A proper packaging for the ESD-protection and short-circuit prevention of the sensor was developed. The performance evaluation results show that the radio frequency sensor is capable of measuring dielectric constant of biofluids with an accuracy of 4.17%. Integration of this sensor into a portable system will result in a hand-held device capable of measuring viscosity of sputum samples of COPD-patients for diagnostic purposes.
- ItemThe role of substrate temperature and magnetic filtering for DLC by cathodic arc evaporation(Basel : MDPI, 2019) Lux, Helge; Edling, Matthias; Lucci, Massimiliano; Kitzmann, Julia; Villringer, Claus; Siemroth, Peter; De Matteis, Fabio; Schrader, SigurdDiamond-like carbon (DLC) films were deposited using two different types of high current arc evaporation. The first process used a magnetic particle filter to remove droplets from the plasma. For the second process, the samples were put into a metallic cage which was placed directly above the plasma source. For both processes, we varied the substrate temperature from 21 to 350 °C in order to investigate the temperature effect. The samples were characterized using SEM, AFM, XPS, Raman Spectroscopy, Ellipsometry, Photometry, and Nano Indentation in order to compare both methods of deposition and provide a careful characterization of such DLC films. We found that the sp3 content and the hardness can be precisely adjusted by changing the substrate temperature. Furthermore, in the case of unfiltered deposition, the optical constants can be shifted in the direction of higher absorbance in order to produce black and hard carbon coatings. © 2019 by the authors.
- ItemIntersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells(Basel : MDPI, 2020) Persichetti, Luca; Montanari, Michele; Ciano, Chiara; Di Gaspare, Luciana; Ortolani, Michele; Baldassarre, Leonetta; Zoellner, Marvin; Mukherjee, Samik; Moutanabbir, Oussama; Capellini, Giovanni; Virgilio, Michele; De Seta, Monican-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune, by design, the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are promising starting points towards a working electrically pumped light-emitting device. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemModeling the shape of ions in pyrite-type crystals(Basel : MDPI, 2014) Birkholz, MarioThe geometrical shape of ions in crystals and the concept of ionic radii are re-considered. The re-investigation is motivated by the fact that a spherical modelling is justified for p valence shell ions on cubic lattice sites only. For the majority of point groups, however, the ionic radius must be assumed to be an anisotropic quantity. An appropriate modelling of p valence ions then has to be performed by ellipsoids. The approach is tested for pyrite-structured dichalcogenides MX2, with chalcogen ions X = O, S, Se and Te. The latter are found to exhibit the shape of ellipsoids being compressed along the <111> symmetry axes, with two radii r
- ItemPlasma enhanced complete oxidation of ultrathin epitaxial praseodymia films on Si(111)(Basel : MDPI, 2015) Kuschel, Olga; Dieck, Florian; Wilkens, Henrik; Gevers, Sebastian; Rodewald, Jari; Otte, Christian; Zoellner, Marvin Hartwig; Niu, Gang; Schroeder, Thomas; Wollschläger, JoachimPraseodymia films have been exposed to oxygen plasma at room temperature after deposition on Si(111) via molecular beam epitaxy. Different parameters as film thickness, exposure time and flux during plasma treatment have been varied to study their influence on the oxygen plasma oxidation process. The surface near regions have been investigated by means of X-ray photoelectron spectroscopy showing that the plasma treatment transforms the stoichiometry of the films from Pr2O3 to PrO2. Closer inspection of the bulk properties of the films by means of synchrotron radiation based X-ray reflectometry and diffraction confirms this transformation if the films are thicker than some critical thickness of 6 nm. The layer distance of these films is extremely small verifying the completeness of the plasma oxidation process. Thinner films, however, cannot be transformed completely. For all films, less oxidized very thin interlayers are detected by these experimental techniques.
- ItemCurrent Modulation of a Heterojunction Structure by an Ultra-Thin Graphene Base Electrode(Basel : MDPI, 2018) Alvarado Chavarin, Carlos; Strobel, Carsten; Kitzmann, Julia; Di Bartolomeo, Antonio; Lukosius, Mindaugas; Albert, Matthias; Bartha, Johann Wolfgang; Wenger, ChristianGraphene has been proposed as the current controlling element of vertical transport in heterojunction transistors, as it could potentially achieve high operation frequencies due to its metallic character and 2D nature. Simulations of graphene acting as a thermionic barrier between the transport of two semiconductor layers have shown cut-off frequencies larger than 1 THz. Furthermore, the use of n-doped amorphous silicon, (n)-a-Si:H, as the semiconductor for this approach could enable flexible electronics with high cutoff frequencies. In this work, we fabricated a vertical structure on a rigid substrate where graphene is embedded between two differently doped (n)-a-Si:H layers deposited by very high frequency (140 MHz) plasma-enhanced chemical vapor deposition. The operation of this heterojunction structure is investigated by the two diode-like interfaces by means of temperature dependent current-voltage characterization, followed by the electrical characterization in a three-terminal configuration. We demonstrate that the vertical current between the (n)-a-Si:H layers is successfully controlled by the ultra-thin graphene base voltage. While current saturation is yet to be achieved, a transconductance of ~230 μS was obtained, demonstrating a moderate modulation of the collector-emitter current by the ultra-thin graphene base voltage. These results show promising progress towards the application of graphene base heterojunction transistors.