Department of Physics
Permanent URI for this community
Browse
Browsing Department of Physics by Type "Review"
Now showing 1 - 20 of 36
Results Per Page
Sort Options
Item Open Access 2D material liquid crystals for optoelectronics and photonics(Royal Society of Chemistry, 2017) Hogan, Ben T.; Kovalska, Evgeniya; Craciun, Monica F.; Baldycheva, AnnaThe merging of the materials science paradigms of liquid crystals and 2D materials promises superb new opportunities for the advancement of the fields of optoelectronics and photonics. In this review, we summarise the development of 2D material liquid crystals by two different methods: dispersion of 2D materials in a liquid crystalline host and the liquid crystal phase arising from dispersions of 2D material flakes in organic solvents. The properties of liquid crystal phases that make them attractive for optoelectronics and photonics applications are discussed. The processing of 2D materials to allow for the development of 2D material liquid crystals is also considered. An emphasis is placed on the applications of such materials; from the development of films, fibers and membranes to display applications, optoelectronic devices and quality control of synthetic processes. © 2017 The Royal Society of Chemistry.Item Open Access Active metamaterial nearly perfect light absorbers: A review [Invited](Optical Society of America, 2019) Hajian, Hodjat; Ghobadi, Amir; Bütün, Bayram; Özbay, EkmelAchieving nearly perfect light absorption from the microwave to optical region utilizing metamaterials has begun to play a significant role in photonics and optoelectronics due to their vital applications in thermal emitters, thermal photovoltaics, photovoltaics, sensing, filtering, and photodetection. However, employing passive components in designing perfect absorbers based on metamaterials and photonic crystals imposes some limits on their spectral operation. In order to overcome those limits, extensive research has been conducted on utilizing different materials and mechanisms to obtain active metamaterial light absorbers. In this review paper, we investigate the recent progress in tunable and reconfigurable metamaterial light absorbers through reviewing different active materials and mechanisms, and we provide a perspective for their future development and applications.Item Open Access Advances in plasmonic technologies for point of care applications(American Chemical Society, 2014) Tokel, Onur; İnci, Fatih; Demirci, UtkanInfectious diseases have considerable economic and societal impact on developing settings. For instance, malaria is observed more commonly in sub-Saharan Africa and India. The societal impact of acquired immune deficiency syndrome (AIDS) and tuberculosis is high, through targeting adults in villages and leaving behind declining populations. Highly sensitive and specific lab assays such as cell culture methods, polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA) are available for diagnosis of infectious diseases in the developed world. They require sample transportation, manual preparation steps, and skilled and well-trained technicians. These clinical conventional methods provide results in several hours to days, precluding rapid detection and response at the primary care settings. Another diagnostic challenge is identifying multiple pathogens.Item Open Access Beyond Poisson-Boltzmann : fluctuations and fluid structure in a self-consistent theory(Institute of Physics Publishing, 2016) Büyükdağlı, Şahin; Blossey, RalfPoisson-Boltzmann (PB) theory is the classic approach to soft matter electrostatics and has been applied to numerous physical chemistry and biophysics problems. Its essential limitations are in its neglect of correlation effects and fluid structure. Recently, several theoretical insights have allowed the formulation of approaches that go beyond PB theory in a systematic way. In this topical review, we provide an update on the developments achieved in the self-consistent formulations of correlation-corrected Poisson-Boltzmann theory. We introduce a corresponding system of coupled non-linear equations for both continuum electrostatics with a uniform dielectric constant, and a structured solvent - a dipolar Coulomb fluid - including non-local effects. While the approach is only approximate and also limited to corrections in the so-called weak fluctuation regime, it allows us to include physically relevant effects, as we show for a range of applications of these equations.Item Open Access Color science of nanocrystal quantum dots for lighting and displays(De Gruyter, 2013-02) Erdem, T.; Demir, Hilmi VolkanColloidal nanocrystals of semiconductor quantum dots (QDs) are gaining prominence among the optoelectronic materials in the photonics industry. Among their many applications, their use in artificial lighting and displays has attracted special attention thanks to their high efficiency and narrow emission band, enabling spectral purity and fine tunability. By employing QDs in color-conversion LEDs, it is possible to simultaneously accomplish successful color rendition of the illuminated objects together with a good spectral overlap between the emission spectrum of the device and the sensitivity of the human eye, in addition to a warm white color, in contrast to other conventional sources such as incandescent and fluorescent lamps, and phosphor-based LEDs, which cannot achieve all of these properties at the same time. In this review, we summarize the color science of QDs for lighting and displays, and present the recent developments in QD-integrated LEDs and display research. First, we start with a general introduction to color science, photometry, and radiometry. After presenting an overview of QDs, we continue with the spectral designs of QD-integrated white LEDs that have led to efficient lighting for indoor and outdoor applications. Subsequently, we discuss QD color-conversion LEDs and displays as proof-of-concept applications - a new paradigm in artificial lighting and displays. Finally, we conclude with a summary of research opportunities and challenges along with a future outlook.Item Open Access Comment on "modeling the electrical conduction in DNA nanowires: Charge transfer and lattice fluctuation theories"(American Physical Society, 2016) Panahi, M.; Chitsazanmoghaddam, M.In a recent paper [S. Behnia and S. Fathizadeh, Phys. Rev. E 91, 022719 (2015)10.1103/PhysRevE.91.022719] an analytical approach is proposed for the investigation of the conductivity properties of DNA. The authors use mean Lyapunov exponent methods as the backbone of their approach and try to interpret properties of the system based on its behavior. Their interpretation regarding the change in nature of the mean Lyapunov exponent at the denaturation temperatures and discussions of stability and instability based on the mean Lyapunov exponent method are questioned. Moreover there is misunderstanding between mean Lyapunov exponent and Lyapunov exponent. © 2016 American Physical Society.Item Open Access Comparative analysis of zinc-blende and wurtzite GaN for full-band polar optical phonon scattering and negative differential conductivity(American Institute of Physics, 2000) Bulutay, C.; Ridley, B. K.; Zakhleniuk, N. A.For high-power electronics applications, GaN is a promising semiconductor. Under high electric fields, electrons can reach very high energies where polar optical phonon (POP) emission is the dominant scattering mechanism. So, we undertake a full-hand analysis of POP scattering of conduction-hand electrons based on an empirical pseudopotential band structure. To uncover the directional variations, we compute POP emission rates along high-symmetry directions for the zinc-blende (ZB) crystal phase of GaN. We also compare the results with those of the wurtzite phase. In general, the POP scattering rates in the zinc-blende phase are lower than the wurtzite phase. Our analysis also reveals appreciable directional dependence, with the Γ-L direction of ZB GaN being least vulnerable to POP scattering, characterized by a scattering time of 11 fs. For both crystal phases, we consider the negative differential conductivity possibilities driven by the negative effective mass part of the band structure. According to our estimation, for the ZB phase the onset of this effect requires fields above ∼ 1 MV/cm. © 2000 American Institute of Physics.Item Open Access Electromagnetically induced left-handedness in a dense gas of three-level atoms(The American Physical Society, 2004) Oktel, M. Ö.; Müstecaphoǧlu, Ö. E.Ways in which a three-level system can be used to change the frequency-dependent magnetic permeability of an atomic gas were discussed. The resulting macroscopic electrodynamics was also discussed. The two levels were separated at optical frequencies while having a nonvanishing magnetic dipole matrix element. It was found that such level splittings require large external magnetic fields.Item Open Access Electronic structure of Ge-Si superlattices grown on Ge (001)(1991) Gülseren, Oğuz; Çıracı, SalimThe authors have studied the electronic energy structure of pseudomorphic Gem/Sin superlattices by using the empirical tight-binding method. Effects of the band offset, sublattice periodicity and the lateral lattice constant on the transition energies have been investigated. They found that GemSin superlattices grown on Ge (001) can have a direct band gap, if m+n=10 and m=6. However, optical matrix elements for in-plane and perpendicular polarized light are negligible for the transition from the highest valence band to the lowest conduction band state at the centre of the superlattice Brillouin zone.Item Open Access Excitonics of semiconductor quantum dots and wires for lighting and displays(Wiley-VCH Verlag, 2013) Guzelturk, B.; Martinez, P. L. H.; Zhang, Q.; Xiong, Q.; Sun, H.; Sun, X. W.; Govorov, A. O.; Demir, Hilmi VolkanIn the past two decades, semiconductor quantum dots and wires have developed into new, promising classes of materials for next-generation lighting and display systems due to their superior optical properties. In particular, exciton-exciton interactions through nonradiative energy transfer in hybrid systems of these quantum-confined structures have enabled exciting possibilities in light generation. This review focuses on the excitonics of such quantum dot and wire emitters, particularly transfer of the excitons in the complex media of the quantum dots and wires. Mastering excitonic interactions in low-dimensional systems is essential for the development of better light sources, e.g., high-efficiency, high-quality white-light generation; wide-range color tuning; and high-purity color generation. In addition, introducing plasmon coupling provides the ability to amplify emission in specially designed exciton-plasmon nanostructures and also to exceed the Forster limit in excitonic interactions. In this respect, new routes to control excitonic pathways are reviewed in this paper. The review further discusses research opportunities and challenges in the quantum dot and wire excitonics with a future outlook.Item Open Access Forward tunneling current in Pt/p-InGaN and Pt/n-InGaN Schottky barriers in a wide temperature range(Elsevier, 2012-07-27) Arslan, E.; Çakmak, H.; Özbay, EkmelThe current-transport mechanisms of the Pt contacts on p-InGaN and n-InGaN were investigated in a wide temperature range (80-360 K) and in the forward bias regime. It was found that the ideality factor (n) values and Schottky barrier heights (SBHs), as determined by thermionic emission (TE), were a strong function of temperature and Φb0 show the unusual behavior of increasing linearly with an increase in temperature from 80 to 360 K for both Schottky contacts. The tunneling saturation ( JTU(0)) and tunneling parameters (E 0) were calculated for both Schottky contacts. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. The results indicate that the dominant mechanism of the charge transport across the Pt/p-InGaN and Pt/n-InGaN Schottky contacts are electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-360 K.Item Open Access High power gain for stimulated Raman amplification in CuAlS2(American Institute of Physics, 1996) Bairamov, B. H.; Aydınlı, Atilla; Bodnar', I. V.; Rud', Yu. V.; Nogoduyko, V. K.; Toporov, V. V.The spontaneous Raman spectra of the chalcopyrite structure crystal CuAlS2, which is promising for nonlinear optical applications, has been investigated at 8 and 300 K. The main aim of this study is to compare the absolute spontaneous Raman scattering efficiency in CuAlS2 crystals with that of their isomorphous analog, zinc-blende structure GaP crystals, known as one of the most efficient materials for Raman amplification. Observation of a high value of absolute scattering efficiency S/L dΩ (where S is the fraction of incident power that scatters into the solid angle d Ω and L is the optical path length with S/L dΩ=9.5×10-5 cm-1 sr-1), together with relatively narrow linewidth (Γ=5.1 cm-1, full width at half maximum at room temperature and Γ=1.5 cm-1 at 8 K for the strongest Γ1 phonon mode of CuAlS2 at 314 cm-1) indicate that CuAlS2 has the highest value of the stimulated Raman gain coefficient gs/I where I is the incident laser power density. The calculated value of this gain is gs/I=2.1×10-6 cm-1/W at 300 K and 5.0×10-6 cm/W, at 8 K for 514.5 nm laser excitation, and is larger than those for the appropriate vibrational modes of various materials (including GaP, LiNbO3, Ba2NbO5O15, CS2, and H2) investigated so far. The calculations show that cw Raman oscillator operation in CuAlS2 is feasible with low power threshold of pump laser. © 1996 American Institute of Physics.Item Open Access A highly sensitive atomic force microscope for linear measurements of molecular forces in liquids(American Institute of Physics, 2005) Patil, S.; Matei, G.; Dong, H.; Hoffmann, P. M.; Karaköse, M.; Oral, A.We describe a highly improved atomic force microscope for quantitative nanomechanical measurements in liquids. The main feature of this microscope is a modified fiber interferometer mounted on a five axis inertial slider which provides a deflection sensitivity that is significantly better than conventional laser deflection based systems. The measured low noise floor of 572.0 fmHz provides excellent cantilever amplitude resolution. This allows us to operate the instrument far below resonance at extremely small cantilever amplitudes of less than 1 Å. Thus linear measurements of nanomechanical properties of liquid systems can be performed. In particular, we present measurements of solvation forces in confined octamethylcyclotetrasiloxane and water with amplitudes smaller than the size of the respective molecules. In general, the development of the instrument is important in the context of quantitative nanomechanical measurements in liquid environments.Item Open Access An Introduction to Practical Laboratory Optics, by J. F. James: Scope: monograph, manual, guide. Level: early career researcher, researcher, specialist(Taylor and Francis Ltd., 2015) Volpe, Giovanni[No abstract available]Item Open Access Kümmel et al. Reply(American Physical Society, 2014-05-19) Kümmel, F.; Hagen, B. T.; Wittkowski, R.; Takagi, D.; Takagi, I.; Eichhorn, R.; Volpe, G.; Löwen, H.; Bechinger, C.Item Open Access LEDs using halide perovskite nanocrystal emitters(Royal Society of Chemistry, 2019) Yan, F.; Demir, Hilmi VolkanThe emerging family of lead–halide perovskite (LHP) nanocrystal emitters has shown impressive achievements in solid-state light-emitting applications. With luminous efficiency comparable to that of organic light-emitting diodes, LHP light-emitting diodes (PeLEDs) have demonstrated a wide colour gamut with high colour purity and a widely tunable range of emissive wavelengths across the whole visible range. Herein, the understanding of LHP nanocrystals in light emission and the resulting PeLEDs are reviewed. Additionally, key features of LHP nanocrystal emitters applied in PeLEDs and guidelines towards realizing high-performance devices are discussed.Item Open Access Light generation in lead halide perovskite nanocrystals: LEDs, color converters, lasers, and other applications(WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Yan, F.; Tan, S.; Li, X.; Demir, Hilmi VolkanFacile solution processing lead halide perovskite nanocrystals (LHP‐NCs) exhibit superior properties in light generation, including a wide color gamut, a high flexibility for tuning emissive wavelengths, a great defect tolerance and resulting high quantum yield; and intriguing electric feature of ambipolar transport with moderate and comparable mobility. As a result, LHP‐NCs have accomplished great achievements in various light generation applications, including color converters for lighting and display, light‐emitting diodes, low threshold lasing, X‐ray scintillators, and single photon emitters. Herein, the considerable progress that has been made thus far is reviewed along with the current challenges and future prospects in the light generation applications of LHP‐NCs.Item Open Access Oligonucleotide-based label-free detection with optical microresonators: strategies and challenges(Royal Society of Chemistry, 2016) Toren, P.; Ozgur E.; Bayındır, MehmetThis review targets diversified oligonucleotide-based biodetection techniques, focusing on the use of microresonators of whispering gallery mode (WGM) type as optical biosensors mostly integrated with lab-on-a-chip systems. On-chip and microfluidics combined devices along with optical microresonators provide rapid, robust, reproducible and multiplexed biodetection abilities in considerably small volumes. We present a detailed overview of the studies conducted so far, including biodetection of various oligonucleotide biomarkers as well as deoxyribonucleic acids (DNAs), ribonucleic acids (RNAs) and proteins. We particularly advert to chemical surface modifications for specific and selective biosensing.Item Open Access On the quantization of the chiral solitonic bag model(American Physical Society, 1990) Pak, N. K.; Yilmaz, T.A consistent quantization scheme for the two-flavor chiral solitonic bag model with unequal quark masses is developed employing a propagator formulation. © 1990 The American Physical Society.Item Open Access Optical trapping and manipulation of nanostructures(Nature Publishing Group, 2013) Maragò, O. M.; Jones, P. H.; Gucciardi, P. G.; Volpe, G.; Ferrari, A. C.Optical trapping and manipulation of micrometre-sized particles was first reported in 1970. Since then, it has been successfully implemented in two size ranges: the subnanometre scale, where light-matter mechanical coupling enables cooling of atoms, ions and molecules, and the micrometre scale, where the momentum transfer resulting from light scattering allows manipulation of microscopic objects such as cells. But it has been difficult to apply these techniques to the intermediate-nanoscale-range that includes structures such as quantum dots, nanowires, nanotubes, graphene and two-dimensional crystals, all of crucial importance for nanomaterials-based applications. Recently, however, several new approaches have been developed and demonstrated for trapping plasmonic nanoparticles, semiconductor nanowires and carbon nanostructures. Here we review the state-of-the-art in optical trapping at the nanoscale, with an emphasis on some of the most promising advances, such as controlled manipulation and assembly of individual and multiple nanostructures, force measurement with femtonewton resolution, and biosensors.