20 research outputs found
A solid-state high harmonic generation spectrometer with cryogenic cooling
Solid-state high harmonic generation spectroscopy (sHHG) is a promising
technique for studying electronic structure, symmetry, and dynamics in
condensed matter systems. Here, we report on the implementation of an advanced
sHHG spectrometer based on a vacuum chamber and closed-cycle helium cryostat.
Using an in situ temperature probe, it is demonstrated that the sample
interaction region retains cryogenic temperature during the application of
high-intensity femtosecond laser pulses that generate high harmonics. The
presented implementation opens the door for temperature-dependent sHHG
measurements down to few Kelvin, which makes sHHG spectroscopy a new tool for
studying phases of matter that emerge at low temperatures, which is
particularly interesting for highly correlated materials
{\AA}ngstr\"om-resolved Interfacial Structure in Organic-Inorganic Junctions
Charge transport processes at interfaces which are governed by complex
interfacial electronic structure play a crucial role in catalytic reactions,
energy storage, photovoltaics, and many biological processes. Here, the first
soft X-ray second harmonic generation (SXR-SHG) interfacial spectrum of a
buried interface (boron/Parylene-N) is reported. SXR-SHG shows distinct
spectral features that are not observed in X-ray absorption spectra,
demonstrating its extraordinary interfacial sensitivity. Comparison to
electronic structure calculations indicates a boron-organic separation distance
of 1.9 {\AA}, wherein changes as small as 0.1 {\AA} result in easily detectable
SXR-SHG spectral shifts (ca. 100s of meV). As SXR-SHG is inherently ultrafast
and sensitive to individual atomic layers, it creates the possibility to study
a variety of interfacial processes, e.g. catalysis, with ultrafast time
resolution and bond specificity.Comment: 19 page
Polarization-Resolved Extreme-Ultraviolet Second-Harmonic Generation From Linbo3
Second harmonic generation (SHG) spectroscopy ubiquitously enables the investigation of surface chemistry, interfacial chemistry, as well as symmetry properties in solids. Polarization-resolved SHG spectroscopy in the visible to infrared regime is regularly used to investigate electronic and magnetic order through their angular anisotropies within the crystal structure. However, the increasing complexity of novel materials and emerging phenomena hampers the interpretation of experiments solely based on the investigation of hybridized valence states. Here, polarization-resolved SHG in the extreme ultraviolet (XUV-SHG) is demonstrated for the first time, enabling element-resolved angular anisotropy investigations. In noncentrosymmetric LiNbO3, elemental contributions by lithium and niobium are clearly distinguished by energy dependent XUV-SHG measurements. This element-resolved and symmetry-sensitive experiment suggests that the displacement of Li ions in LiNbO3, which is known to lead to ferroelectricity, is accompanied by distortions to the Nb ion environment that breaks the inversion symmetry of the NbO6 octahedron as well. Our simulations show that the measured second harmonic spectrum is consistent with Li ion displacements from the centrosymmetric position while the Nb─O bonds are elongated and contracted by displacements of the O atoms. In addition, the polarization-resolved measurement of XUV-SHG shows excellent agreement with numerical predictions based on dipole-induced SHG commonly used in the optical wavelengths. Our result constitutes the first verification of the dipole-based SHG model in the XUV regime. The findings of this work pave the way for future angle and time-resolved XUV-SHG studies with elemental specificity in condensed matter systems
Polarization-Resolved Extreme Ultraviolet Second Harmonic Generation from LiNbO
Second harmonic generation (SHG) spectroscopy ubiquitously enables the
investigation of surface chemistry, interfacial chemistry as well as symmetry
properties in solids. Polarization-resolved SHG spectroscopy in the visible to
infrared regime is regularly used to investigate electronic and magnetic orders
through their angular anisotropies within the crystal structure. However, the
increasing complexity of novel materials and emerging phenomena hamper the
interpretation of experiments solely based on the investigation of hybridized
valence states. Here, polarization-resolved SHG in the extreme ultraviolet
(XUV-SHG) is demonstrated for the first time, enabling element-resolved angular
anisotropy investigations. In non-centrosymmetric LiNbO, elemental
contributions by lithium and niobium are clearly distinguished by energy
dependent XUV-SHG measurements. This element-resolved and symmetry-sensitive
experiment suggests that the displacement of Li ions in LiNbO, which is
known to lead to ferroelectricity, is accompanied by distortions to the Nb ion
environment that breaks the inversion symmetry of the NbO octahedron as
well. Our simulations show that the measured second harmonic spectrum is
consistent with Li ion displacements from the centrosymmetric position by
0.5 Angstrom while the Nb-O bonds are elongated/contracted by
displacements of the O atoms by 0.1 Angstrom. In addition, the
polarization-resolved measurement of XUV-SHG shows excellent agreement with
numerical predictions based on dipole-induced SHG commonly used in the optical
wavelengths. This constitutes the first verification of the dipole-based SHG
model in the XUV regime. The findings of this work pave the way for future
angle and time-resolved XUV-SHG studies with elemental specificity in condensed
matter systems
Geleneksel olmayan ortamlarda elektrokimyasal iyon taşınmasının sorgulanması
Cataloged from PDF version of article.Thesis (M.S.): Bilkent University, Department of Chemistry, İhsan Doğramacı Bilkent University, 2018.Includes bibliographical references. (leaves 139-151).Ion transport is a critical process that occurs routinely in all electrochemical devices. Especially the new generation batteries extensively utilized in portable devices, Li-Ion batteries, operate simply through Li+ transport. Although, a multitude of similar energy storage and conversion devices are prevalent in both the industry and the electrochemical literature, these devices are not the only technologies that ion transport is critical. Other technologies such as electrochromic devices, organic electronics and next generation display panels also involve electrochemical processes that are inherently dependent on or limited by ion transport. Conventional electrochemical methods enable interrogation of the various interfaces these devices possess however limited information on the behavior of the concentrated-like media investigated in this thesis compared to the well documented behavior of the dilute media, limits their applicability.
In this thesis we not only offer investigations on possible esoteric materials that have unique ion transport properties that show emergent behavior in the systems they are employed at through fundamental electrochemical studies but also we outline the development of new electroanalytical tools to better interrogate ion transport in variety of electrochemical systems. The attempts at understanding and explaining the ion transport in various media and to leverage its benefits towards better devices is outlined. Electrochemical noise measurements for Li-Ion batteries is shown as a potential tool for ion transport interrogation, while the ion transport behavior of Liquid Crystals and Ionic Liquids are investigated. A new electroanalytical tool to separate counter ion diffusion from electron transfer is also shown. Finally, an electrochemical method to visualize corrosion that utilizes ion transport is outlined in this thesis.by Can Berk Uzundal.M.S
Lyotropic Liquid Crystalline Mesophase of Sulfuric Acid–Nonionic Surfactant Stabilizes Lead(II) Oxide in Sulfuric Acid Concentrations Relevant to Lead Acid Batteries
Aksaray'da hurdacılık ve dökümcülük ekonomiye etkileri
Ankara : İhsan Doğramacı Bilkent Üniversitesi İktisadi, İdari ve Sosyal Bilimler Fakültesi, Tarih Bölümü, 2016.This work is a student project of the The Department of History, Faculty of Economics, Administrative and Social Sciences, İhsan Doğramacı Bilkent University.by Emiroğlu, Kudret
X-ray Photoelectron Spectroscopy with Electrical Modulation Can Be Used to Probe Electrical Properties of Liquids and Their Interfaces at Different Stages
Operando X-ray photoelectron spectroscopy (o-XPS) has been used to record the binding energy shifts in the C 1s peak of a pristine poly(ethylene glycol) (PEG) liquid drop in an electrowetting on dielectric (EWOD) geometry and after exposing it to several high-voltage breakdown processes. This was achieved by recording XPS data while the samples were subjected to 10 V dc and ac (square-wave modulation) actuations to extract electrical information related to the liquid and its interface with the dielectric. Through analysis of the XPS data under ac actuation, a critical frequency of 170 Hz is extracted for the pristine PEG, which is translated to a resistance value of 14 MΩ for the liquid and a capacitance value of 60 pF for the dielectric, by the help of simulations using an equivalent circuit model and also by XPS analyses of a mimicking device under similar conditions. The same measurements yield an increased value of 23 MΩ for the resistance of the liquid after the breakdown by assuming that the capacitance of the dielectric stays constant. In addition, an asymmetry in polarity dependence is observed with respect to both the onset of the breakdown voltage and also the leakage behavior of the deteriorated (PEG + dielectric) system such that deviations are more pronounced at positive voltages. Both dc and ac behaviors of the postbreakdown system can also be simulated, but only by introducing an additional element, a diode or a polarity- and magnitude-dependent voltage source (VCVS), which might be attributed to negative charge accumulation at the interface. Measurements for a liquid mixture of PEG with 8% ionic liquid yields an almost 2 orders of magnitude smaller resistance for the drop as a result of the enhanced conductivity by the ions. Coupled with modeling, XPS measurements under dc and ac modulations enable probing unique electrochemical properties of liquid/solid interfaces