The indirect forbidden fundamental absorption edge in single-crystal germanium sulphide

El‐Korashy, A.

doi:10.1088/0022-3719/21/13/021

Cited by 36 publications

(32 citation statements)

References 15 publications

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“…The decreased gap can only occur by association of three-fold coordinated SGe 3/3 clusters and formation of c-GeS micro-phases (room temperature optical energy gap of 1.57 eV was measured for theb b axis of c-GeS [36]), in excellent accordance with the results of Raman spectra in the 200-300 cm À1 region.…”

Section: Band Gaps and Absorption Edges Of G-gessupporting

confidence: 83%

Local structure of technologically modified g-GeS₂: resonant Raman and absorption edge spectroscopy combined withab initiocalculations

Holomb

Johansson

Міца

et al. 2005

Philosophical Magazine

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We have used resonant Raman and absorption edge spectroscopy together with first-principle calculations in order to study the structure of GeS 2 glasses (g-GeS 2 ). The glasses were prepared under different melt temperatures and cooling rates, which are shown to significantly influence the g-GeS 2 structure at the nano-scale. The combined use of Raman spectroscopy and ab initio calculations reveals the origin of the molecular level electronic structure and its connection to the interesting technological features of the g-GeS 2 . Local structure within the glasses is discussed in terms of atomic Ge n S m clusters. The band gaps computed for these clusters and their correlation to the experimental band gaps and the possible formation of band tail states are also discussed.

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Section: Band Gaps and Absorption Edges Of G-gessupporting

confidence: 83%

Local structure of technologically modified g-GeS₂: resonant Raman and absorption edge spectroscopy combined withab initiocalculations

Holomb

Johansson

Міца

et al. 2005

Philosophical Magazine

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show abstract

Section: Optical Constantsmentioning

confidence: 99%

“…On the basis of the above-mentioned model, the single oscillator parameters E , and Ed are connected to the imaginary part ci of the complex dielectric constant, and the -1 and -3 moments of the ci(E) optical spectrum, as defined in [5], can be derived from the relations Table 2 gives the values of the single effective oscillator parameters E,, Ed, Mfor the a-and b-crystallographic axes, calculated by the reflectance, interference, and prism methods. and M - In applying (14) to a SnS single crystal, there is some uncertainty about the coordination number of the anion which may be thought to be 6 (deformed NaCl structure) or 3 (taking account of the layer structure). The other parameters in (14) are well defined, namely 2, = 2, N , = 4 + 6 = 10.…”

Section: Absorption Coefficientmentioning

confidence: 99%

“…and M - In applying (14) to a SnS single crystal, there is some uncertainty about the coordination number of the anion which may be thought to be 6 (deformed NaCl structure) or 3 (taking account of the layer structure). The other parameters in (14) are well defined, namely 2, = 2, N , = 4 + 6 = 10. Wemple and Di Domenico [5] have found empirically that the coefficient /?…”

Section: Absorption Coefficientmentioning

confidence: 99%

“…Wemple and Di Domenico [5] have found empirically that the coefficient /? in (14) takes the values pi = 0.26 IfI 0.04 eV for ionic binding and p, = 0.37 k 0.05 eV for covalent binding and varies between these two limits for a large number of different materials. By considering these limiting values pi and p,, the limiting values of the coordination number N , of the cation nearest neighbor to the anion can be calculated.…”

Section: Absorption Coefficientmentioning

confidence: 99%

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Optical Constants of Tin Sulphide Single Crystals Measured by the Interference Method

El‐Korashy

1990

Physica Status Solidi (b)

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The refractive index, n, of SnS single crystals is measured from reflectance after being normalized to account for the pronounced rise below the energy gap. n is also measured by the interference method in the transparency region. An effective thickness smaller than the true one is introduced to account for the photon scattering by the layer structure of the material in this region. The effective thickness hypothesis gives a satisfactory explanation of the pronounced rise in reflectance for E < E,. The extinction coefficient, k, is calculated from the measured absorption coefficient. Measurements are performed at room temperature using plane polarized light with the plane of polarization parallel to the a-and b-crystallographic axes which lie in the plane of cleavage. The real and imaginary parts of the complex dielectric constant (er, ei) are calculated from the values of n and k. It is shown that SnS single crystals exhibit birefringence. Assuming that the SnS binding is partly ionic and partly covalent, the results of the optical constants are satisfactorly fitted to the model of a single effective oscillator.Der Brechungsindex n von SnS-Einkristallen wird aus dem Reflexionsvermogen nach Normierung des ausgepragten Anstiegs unterhalb der Energieliicke gemessen. n wird auch mittels lnterferenzmethode i m transparenten Bereich gemessen. Eine effektive Dicke, die geringer als die tatsachliche ist, wird eingefiihrt, urn die Photonenstreuung durch die Schichtstruktur des Materials in diesem Bereich zu beriicksichtigen. Die Hypothese der effektiven Dicke liefert eine befriedigende Erklarung des ausgepragten Anstiegs im Reflexionsvermogen fur E c E,. Der Extinktionskoeffizient k wird aus dem gemessenen Absorptionskoeffizienten berechnet. Messungen werden bei Zimmertemperatur mit ebenem polarisiertem Licht durchgefiihrt, wobei die Polarisationsebene parallel zur kristallografischen a-und b-Achse ist, die in der Spaltebene liegen. Der Real-und Imaginarteil der komplexen Dielektrizitatskonstante (e,,ei) wurden aus den Werten fur n und k berechnet. Es wird gezeigt, daO SnS-Einkristalle Doppelbrechung zeigen. Unter der Annahme, daD die SnS-Bindung teilweise ionisch und teilweise kovalent ist, lassen sich die optischen Konstanten befriedigend dem Modell eines isolierten effektiven Oszillators anpassen.

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Cathodoluminescence of Ultrathin Twisted Ge_1–_xSn_xS van der Waals Nanoribbon Waveguides

et al. 2020

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Ultrathin van der Waals semiconductors have shown extraordinary optoelectronic and photonic properties. Propagating photonic modes make layered crystal waveguides attractive for photonic circuitry and for studying hybrid light–matter states. Accessing guided modes by conventional optics is challenging due to the limited spatial resolution and poor out‐of‐plane far‐field coupling. Scanning near‐field optical microscopy can overcome these issues and can characterize waveguide modes down to a resolution of tens of nanometers, albeit for planar samples or nanostructures with moderate height variations. Electron microscopy provides atomic‐scale localization also for more complex geometries, and recent advances have extended the accessible excitations from interband transitions to phonons. Here, bottom‐up synthesized layered semiconductor (Ge1–xSnxS) nanoribbons with an axial twist and deep subwavelength thickness are demonstrated as a platform for realizing waveguide modes, and cathodoluminescence spectroscopy is introduced as a tool to characterize them. Combined experiments and simulations show the excitation of guided modes by the electron beam and their efficient detection via photons emitted in the ribbon plane, which enables the measurement of key properties such as the evanescent field into the vacuum cladding with nanometer resolution. The results identify van der Waals waveguides operating in the infrared and highlight an electron‐microscopy‐based approach for probing complex‐shaped nanophotonic structures.

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The indirect forbidden fundamental absorption edge in single-crystal germanium sulphide

Cited by 36 publications

References 15 publications

Local structure of technologically modified g-GeS₂: resonant Raman and absorption edge spectroscopy combined withab initiocalculations

Local structure of technologically modified g-GeS₂: resonant Raman and absorption edge spectroscopy combined withab initiocalculations

Optical Constants of Tin Sulphide Single Crystals Measured by the Interference Method

Cathodoluminescence of Ultrathin Twisted Ge_1–_xSn_xS van der Waals Nanoribbon Waveguides

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The indirect forbidden fundamental absorption edge in single-crystal germanium sulphide

Cited by 36 publications

References 15 publications

Local structure of technologically modified g-GeS2: resonant Raman and absorption edge spectroscopy combined withab initiocalculations

Local structure of technologically modified g-GeS2: resonant Raman and absorption edge spectroscopy combined withab initiocalculations

Optical Constants of Tin Sulphide Single Crystals Measured by the Interference Method

Cathodoluminescence of Ultrathin Twisted Ge1–xSnxS van der Waals Nanoribbon Waveguides

Contact Info

Product

Resources

About

Local structure of technologically modified g-GeS₂: resonant Raman and absorption edge spectroscopy combined withab initiocalculations

Local structure of technologically modified g-GeS₂: resonant Raman and absorption edge spectroscopy combined withab initiocalculations

Cathodoluminescence of Ultrathin Twisted Ge_1–_xSn_xS van der Waals Nanoribbon Waveguides