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Item Open Access Ab-initio atomic scale study of nearly frictionless surfaces(Elsevier, 2007) Çıracı, Salim; Yıldırım, T.; Dağ, S.; Gülseren, Oğuz; Erdemir, A.; Martin, J. -M.This chapter presents a comparative analysis of the dry sliding friction between the atomically flat and commensurate surfaces of two different systems: between two diamond (001) surfaces and between two BN (001) surfaces. The interaction between bare diamond (001) - (2 × 1) surfaces is strongly attractive until there is a small spacing d ∼ 1.5 Å, and the interaction forms strong chemical bonds between two surfaces. However, the interaction turns repulsive if two surfaces are pushed under high loading force. Upon hydrogenation, hydrogen atoms donate charge to the carbon atom and become positively charged. The interaction between surfaces carrying the same type of charge becomes repulsive. This appears to be the most important component of the superlow friction. The repulsive interaction persists at any relative position of the sliding surfaces and is strong even at large distance to prevent C-H bonds from merging. Strong and stiff C-H bonds and stiff diamond crystal by itself prevent excessive energy from dissipation. The oxygenation of surfaces in the atmospheric conditions finally destroys the steady repulsive interaction. However, the interaction between two bare reconstructed BN (001) surfaces is different from that of the diamond (001) surface because of the ionic nature of the crystal. BN being an ionic crystal with electron transfers from B to N, the bare surface is already negatively charged. Under these circumstances, the strong chemical interaction is canceled by the repulsive Coulombic interaction, resulting in a weak attractive interaction. © 2007 Elsevier B.V. All rights reserved.Item Open Access Aharonov-Bohm effect induced by light(Springer, Dordrecht, 1998) Kulik, Igor O.; Shumovsky, Alexander S.; Hunter, G.; Jeffers, S.; Vigier, J. -P.The quantum interferometry of normal metallic loops based on the Aharonov-Bohm effect is usually applied to measurements at low temperatures in the case of static or slowly time-varying magnetic fields (e.g., see [1]). Recently, an important case of an ac field of high frequency ω » v F /R (v F is the Fermi velocity and R is the radius of the metallic ring) has been considered [2]. This consideration is based on the assumption that the position dependent time-varying electromagnetic field produces the static electron energy minibands in the ring which appear due to electron motion in a time-averaged electrostatic potential periodic with coordinate along the ring circumference, produced by the square of an ac electric field [3]. it should be noted that, in the quantum case, an electron reflection from an oscillating potential causes a time-dependent phase shift, resulting in an effective chaotization of the phase of electron wave function, except at energy multiples of ħω.Item Open Access Applying förster-type nonradiative energy transfer formalism to nanostructures with various directionalities : dipole electric potential of exciton and dielectric environment(Springer Verlag, 2017) Hernández Martínez, P. L.; Govorov, A.; Demir, Hilmi Volkan[No abstract available]Item Open Access Background theory(Springer Verlag, 2016) Govorov A.; Hernández Martínez P.L.; Demir H.V.[No abstract available]Item Open Access Band-gap renormalization in quasi-one-dimensional systems(Kluwer Academic Publishers, 1997) Tanatar, Bilal; Abstreiter, G.; Aydınlı, Atilla; Leburton, J. -P.Item Open Access Biomedical and biochemical tools of förster resonance energy transfer enabled by colloidal quantum dot nanocrystals for life sciences(Springer Berlin Heidelberg, 2013) Şeker, Urartu Özgür Şafak; Demir, Hilmi VolkanSemiconductor quantum nanocrystals (NCs) provide the ability to control and fine-tune peak emission wavelength using the size effect, with a broad optical absorption band (excitation window) increasing toward UV wavelength range. Quantum dots with different peak emission wavelengths can be excited at the same wavelength and offer longer fluorescence lifetimes, which make them desirable donor molecules for Förster resonance energy transfer (FRET)-based applications. In this chapter, the tools of FRET using these quantum dot nanocrystals in life science applications are addressed.Item Open Access Colloidal semiconductor nanocrystals(Springer Singapore, 2022-10-28) Erdem, Onur; Demir, Hilmi VolkanIn this chapter, we review colloidal semiconductor nanocrystals (NCs) and their remarkable size-dependent properties. We emphasize on colloidal nanoplatelets and explain how they differ from NCs of other classes.Item Open Access Colorimetry for LED lighting(Springer, 2019-01) Erdem, Talha; Demir, Hilmi Volkan; Erdem, Talha; Demir, Hilmi VolkanIn this Chapter, we explain the basics of colorimetry and introduce the colorimetric tools useful for designing light sources.Item Open Access Common white light sources(Springer, 2019-01) Erdem, Talha; Demir, Hilmi Volkan; Erdem, Talha; Demir, Hilmi VolkanIn this Chapter we describe the features of common light sources. We first present the spectral features of the sun and discuss its colorimetric properties. Next, we summarize the properties of traditional light sources including incandescent lamps, fluorescent lamps, and high-pressure sodium lamps. Subsequently, we discuss the white light-emitting diodes of various types.Item Open Access Conclusions and future outlook(Springer Singapore, 2022-10-28) Erdem, Onur; Demir, Hilmi VolkanItem Open Access Conductance in nanowires(Kluwer Academic Publishers, 1997) Mehrez, H.; Çıracı, Salim; Abstreiter, G.; Aydınlı, Atilla; Leburton, J. -P.This paper presents a detailed analysis of conductance and atomic structure in metal nanowires under tensile stress. We calculate the variation of conductance with the crossection of the constriction between two reservoirs, that is represented by three-dimensional circularly symmetric potentials. The absence of several observed features in the calculated conductance variations, in particular sudden jumps, suggests that the discontinuous rearrangements of atoms under stretch dominate the electron transport. To analyze the variations of atomic structure, we performed simulations based on the state of the art molecular dynamics simulations and revealed novel structural transformations. It is found that yielding and fracture mechanisms depend on the geometry, size, atomic arrangement and temperature. The elongation under uniaxial stress is realized by consecutive quasi elastic and yielding stages; the neck develops mainly by the implementation of a layer with a smaller crossection at certain stages of elongation. This causes to an abrupt decrease of the tensile force. Owing to the excessive strain at the neck, the original structure and atomic registry are modified; atoms show tendency to rearrange in closed-packed structures. In certain circumstances, a bundle of atomic chains or single atomic chain forms as a result of transition from the hallow site to the top site registry shortly before the break. The origin of the observed "giant" yield strength is explained by using results of present simulations and ab initio calculations of total energy and Young's modulus for an infinite atomic chain.Item Open Access A critique of the two level approximation(Springer New York, 2006) Hakioǧlu, Tuğrul; Savran, Kerim; Meşe, E.The conditions in favor and necessity of a realistic multileveled description of a decohering quantum system is examined. Under these conditions approximate techniques to simplify a multileveled system by its first two levels is unreliable and a realistic multilevel description in the formulation of decoherence is unavoidable. In this regard, the first crucial observation is that, the validity of the two level approximation of a multileveled system is not controlled purely by sufficiently low temperatures. That the type of system-environment coupling and the environmental spectrum have a dominant role over the temperature is demonstrated. Particularly, zero temperature quantum fluctuations induced by the Caldeira-Leggett type linear coordinate coupling can be influential in a wide energy range in the systems allowed transitions. The second crucial observation is that the decoherence times being among the system's short time scales are found to be dominated not by the resonant but non-resonant processes. © 2006 Springer Science+Business Media, Inc.Item Open Access Developing a transducer based on localized surface plasmon resonance (LSPR) of gold nanostructures for nanobiosensor applications(Trans Tech Publications, 2013) Turhan, Adil Burak; Ataman, D.; Çakmakyapan, S.; Mutlu, M.; Özbay, Ekmel; Vlachos, D. S.; Hristoforou, E.In this work, we report the nanofabrication, optical characterization, and electromagnetic modeling of various nanostructure arrays for localized surface plasmon resonance (LSPR) based biosensing studies. Comparison of the experimental results and simulation outputs of various nanostructure arrays was made and a good correspondence was achieved.Item Open Access Electromodulation of photoluminescence from CdSe nanorods film(World Scientific Publishing Co., 2007) Lutich, A.; Artemyev, M.; Ustinovich, E.; Soganci, Ibrahim Murat; Demir, Hilmi VolkanWe studied photoluminescence (PL) properties of CdSe nanorods integrated in a thin film sandwiched between transparent electrodes to which an electric field applied. Nearly 20 % of PL quenching accompanied with the weak Stark shift have been observed. This effect is proposed to be used for PL modulation, in particular in the wavelength range beyond the range that traditional optoelectronic devices may cover.Item Open Access Electronic and Optical Properties of Silicon Nanocrystals(Wiley-VCH, 2010) Bulutay, C.; Ossicini S.[No abstract available]Item Open Access Energy transfer review(Springer Verlag, 2016) Govorov A.; Hernández Martínez P.L.; Demir H.V.[No abstract available]Item Open Access Exciton dynamics of colloidal semiconductor quantum well stacks(Springer Netherlands, 2018) Erdem, O.; Guzelturk, B.; Olutas M.; Kelestemur Y.; Demir, Hilmi VolkanColloidal semiconductor nanoplatelets (NPLs) have recently emerged as a new class of colloidal nanocrystals. NPLs are quasi two-dimensional nanocrystals having atomically flat surfaces and have unique properties such as narrow photoluminescence (PL) emission (∼10 nm) and giant oscillator strength. NPLs can be self-assembled into stacks. These are one-dimensional superstructures that can contain tens or hundreds of NPLs in one chain. We studied how stacking modifies the optical properties of NPLs. We found that PL quantum yield and exciton lifetime are reduced with increased degree of stacking in NPL ensembles. Moreover, we showed that temperature-dependent behavior of stacked NPLs is significantly different than the nonstacked ones. We developed two statistical models that account for the ultra-fast nonradiative energy transfer within stacked NPL chains as well as nonemissive subpopulation of NPLs in the ensemble to explain the aforementioned changes when NPLs are stacked.Item Open Access First-Principles atomic-scale study of superlow friction(Springer, Berlin, Heidelberg, 2007) Çıracı, Salim; Dağ, S.; Gülseren, O.; Yıldırım, T.; Gnecco, E.; Meyer, E.Item Open Access Förster-Type nonradiative energy transfer models(Springer Verlag, 2016) Govorov A.; Hernández Martínez P.L.; Demir H.V.[No abstract available]Item Open Access Förster-type nonradiative energy transfer rates for nanostructures with various dimensionalities(Springer Verlag, 2017) Hernández Martínez, P. L.; Govorov, A.; Demir, Hilmi Demir[No abstract available]
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