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You searched for subject:(Conduction AND valence bands). Showing records 1 – 3 of 3 total matches.

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1. Olar, Tetiana. Bewertung der elektronischen und chemischen Oberflächeneigenschaften von Kesterit.

Degree: 2017, Freie Universität Berlin

Kesterit-basierte Dünnschicht-Solarzellen mit der allgemeinen Zusammensetzung Cu2ZnSn(Se,S)4 sind in den letzten Jahren Gegenstand intensiver Forschungs-und Entwicklungsarbeiten gewesen. Kesterit kann wegen der ungiftigen und in der Erdkruste häufig vorkommenden Bestandteile und einer vergleichbaren Bandlücke ein guter Ersatz für Chalkopyrit (Cu(In,Ga)(Se,S)2) sein. Beim Übergang von der reinen Sulfid- zur reinen Selenidzusammensetzung verändert sich die Kesteritbandlücke von 1.5 auf 1 eV. In dieser Arbeit wurden die folgenden Fragen untersucht: wie ändern sich die elektronischen und chemischen Oberflächeneigenschaften von Kesterit, wenn wir das [S]/([S]+[Se])-Verhältnis ändern? Wie ändert sich die Bandanpassung mit der Pufferschicht? Was sind die relativen Valenzband- und Leitungsbandpositionen, wenn man von CZTS zu CZTSe geht? Um die elektronischen Eigenschaften von Kesterit zu untersuchen, wurden umfassende Analysen von Dünnschicht-Kesteritabsorbern unter Verwendung von oberflächensensitiven Techniken wie Röntgen-Photoelectronenspectroskopie (XPS) und Ultraviolett-Photoelektronenspectroskopie (UPS) sowie synchrotronbasierter Spektroskopie erfolgreich durchgeführt. Proben mit unterschiedlichen Konzentrationsverhältnissen von [S]/([S]+[Se]) wurden vor und nach der Anwendung spezieller nasschemischer Ätzverfahren untersucht. Es wurden starke Abweichungen zwischen der chemischen Zusammensetzung von unbehandelten und geätzten Oberflächen beobachtet. Generell unterscheiden sich Oberflächen und Volumenzusammensetzung. Die relativen Positionen der Valenzbandkante wurden mit UPS ausfühlich untersucht. Die dabei mit der Laborquelle erzielten Ergebnisse konnten mit Messungen mit unterschiedlichen Anregungsenergien am Synchrotron bestätigt wurden. Die experimentellen Ergebnisse stimmen gut mit theoretischen Werten zusammen, die in der Literatur verfügbar sind. Die Änderungen in der Anionenzusammensetzung bewirken eine Verschiebung nicht nur im Valenzbandmaximum (VBM), sondern auch im Leitungsbandminimum (LBM). Dies wurde mit Röntgennahkanten-Absorptionsspektroskopie (NEXAFS) gezeigt. Eine Serie von Absorptionskanten wurde für CZTS- und CZTSe-Proben erhalten: Cu, Zn K- and L-Kanten und die Sn L-Kante. Die relativen Verschiebungen zwischen den Spektren wurden der Verschiebung im LBM zugeschrieben. Der Wert der Verschiebung war für alle Kanten innerhalb der Fehlergrenze gleich. Neben den polykristallinen Dünnfilmproben wurden einphasige Pulverproben als Referenzen verwendet. Wir haben experimentelle Ergebnisse mit theoretischen Berechnungen korreliert und eine gute Übereinstimmung zwischen ihnen gefunden. Dichtefunktionaltheorie-Berechnungen der Leitungsbandzustände haben die in den Experimenten gesehene Tendenzbestätigt: Die relativen Positionen der unbesetzten-Zustände an der LB-Kante liegen in den Seleniden bei niedrigeren Energien als die des Schwefels. Unter Verwendung einer sogenannten GW- Annährung wurden die Werte der Verschiebung von VBM und LBM erhalten. Sie stimmen innerhalb der Fehlergrenzen mit den experimentellen… Advisors/Committee Members: [email protected] (contact), w (gender), Prof. Dr. M. Ch. Lux-Steiner (firstReferee), Prof. Dr. C. Roth (furtherReferee).

Subjects/Keywords: kesterite; solar cells; absorption spectroscopy; valence band; conduction band; 500 Naturwissenschaften und Mathematik::530 Physik::530 Physik

…different band gaps, a discontinuity of the conduction and the valence bands exist together… …layer? What are the relative positions of conduction (CB) and valence band (VB… …valence band offset X-ray absorption spectroscopy X-ray photoelectron spectroscopy conduction… …the conduction and valence band discontinuities [41]: (3.1.)… …NEXAFS spectra 4.3. Theoretical methods for the conduction band evaluation 4.3.1. Ab-initio… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Olar, T. (2017). Bewertung der elektronischen und chemischen Oberflächeneigenschaften von Kesterit. (Thesis). Freie Universität Berlin. Retrieved from http://dx.doi.org/10.17169/refubium-6722

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Olar, Tetiana. “Bewertung der elektronischen und chemischen Oberflächeneigenschaften von Kesterit.” 2017. Thesis, Freie Universität Berlin. Accessed October 23, 2020. http://dx.doi.org/10.17169/refubium-6722.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Olar, Tetiana. “Bewertung der elektronischen und chemischen Oberflächeneigenschaften von Kesterit.” 2017. Web. 23 Oct 2020.

Vancouver:

Olar T. Bewertung der elektronischen und chemischen Oberflächeneigenschaften von Kesterit. [Internet] [Thesis]. Freie Universität Berlin; 2017. [cited 2020 Oct 23]. Available from: http://dx.doi.org/10.17169/refubium-6722.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Olar T. Bewertung der elektronischen und chemischen Oberflächeneigenschaften von Kesterit. [Thesis]. Freie Universität Berlin; 2017. Available from: http://dx.doi.org/10.17169/refubium-6722

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


University of Alabama

2. Mackey, Frederick D. Electron tunneling in the tight-binding approximation.

Degree: 2016, University of Alabama

In this thesis, we treat tunneling similar to a scattering problem in which an incident wave on a barrier is partially transmitted and partially reflected. The transmission probability will be related to the conductance using a model due to Landauer. Previously tunneling has been treated using a simple barrier model, which assumes the electron dispersion is that of free electrons. In this model it is not possible to investigate tunneling in the gap between a valence band and a conduction band. We shall remedy this limitation by using the tight-binding model to generate a barrier with a gap separating a valence band and a conduction band. To do this, we constructed a model consisting of semi-infinite chains of A atoms on either side of a semi-infinite chain of B-C molecules. The B-C chain has a gap extending between the onsite energy for the B atom and the onsite energy for the C atom. Tunneling through the gap has been calculated and plotted. We present exact closed form solutions for the following tunneling systems: (i) A-B interface, (ii) A-(B-C) interface, (iii) A-B-A tunnel barrier, (iv) A-(B-C) interface with the orbitals on B having s-symmetry and those on C having p-symmetry, (v) A-(B-C)-A tunnel barrier. (Published By University of Alabama Libraries) Advisors/Committee Members: Butler, William H., Mewes, Claudia, Gupta, Arunava, University of Alabama. Dept. of Physics and Astronomy.

Subjects/Keywords: Electronic Thesis or Dissertation;  – thesis; Condensed matter physics; Materials Science; Information technology; conduction band; landauer conductanc formula; quantum tunneling; simple barrier model; tight-binding; valence band

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Mackey, F. D. (2016). Electron tunneling in the tight-binding approximation. (Thesis). University of Alabama. Retrieved from http://purl.lib.ua.edu/163874

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Mackey, Frederick D. “Electron tunneling in the tight-binding approximation.” 2016. Thesis, University of Alabama. Accessed October 23, 2020. http://purl.lib.ua.edu/163874.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Mackey, Frederick D. “Electron tunneling in the tight-binding approximation.” 2016. Web. 23 Oct 2020.

Vancouver:

Mackey FD. Electron tunneling in the tight-binding approximation. [Internet] [Thesis]. University of Alabama; 2016. [cited 2020 Oct 23]. Available from: http://purl.lib.ua.edu/163874.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Mackey FD. Electron tunneling in the tight-binding approximation. [Thesis]. University of Alabama; 2016. Available from: http://purl.lib.ua.edu/163874

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


University College Cork

3. Hartnett, Mark C. Role of sulfur in vibration spectra and bonding and electronic structure of GeSi surfaces and interfaces.

Degree: 2016, University College Cork

A quantum mechanical density functional theory approach was used to investigate the structural atomic configuration, vibration mode frequencies and electronic structure of surfaces and interfaces using germanium. Initially, we investigated the H2S and H2Opassivated germanium surfaces. A supercell approach is used with the local density (LDA), generalized gradient (GGA) approximations and van der Waals (vdW) interactions. The frozen phonon method was used to calculate the vibrational mode frequencies of these surfaces. The calculated frequencies produce stretch, bond bending and wag modes. The differences between the functionals including vdW terms and the LDA or GGA are less than the differences between LDA and GGA for the vibrational mode frequencies. Some of these modes provide useful vibrational signatures of bonding of both sulfur and oxygen on germanium surfaces, which may be compared with vibrational spectroscopy measurements. A bare germanium surface is bonded to a bare silicon surface to form a Ge-Si interface. As germanium has a 4% larger lattice constant than silicon this implies there are regions on the interface where the germanium and silicon match perfectly (aligned) and are completely mismatched (misaligned). The atomic structure of the GeSi aligned interface shows the original crystal structure and the projected band structure (PBS) shows no interface states in the band gap. The GeSi misaligned structure forms a (2x1) configuration. The electronic PBS shows interface states in the band gap. To remove the interface states seen in the GeSi interface, sulfur with its six valence electrons and its flexible chemical bonds is suggested to improve the interface bonding and remove interface states. The PBS in both the aligned and misaligned GeSSi interfaces shows states around the germanium and silicon interface atomic layers and a charge density localised around the sulfur interface atoms. A sulfur terminated germanium surface results in a (1x1) configuration with surface states present in the band gap. However, a H2S terminated germanium surface results in a (2x1) configuration with symmetric Ge-Ge dimers and pushes the surface states into the bulk region, implying the presence of hydrogen results in no surface states. Including hydrogen on our GeSSi interfaces, the atomic configuration remains the same with the hydrogen molecule in the channels. However, upon looking at the PBS, states are clearly visible in the band gap and when we investigate the charge density contour plots, interface states do exist. Therefore, the presence of hydrogen here does not influence the interfaces. Advisors/Committee Members: Fahy, Stephen B..

Subjects/Keywords: Germanium; Silicon; Vibrational; Mode; Frequencies; Surfaces; Interfaces; Band structure; Sulfur; Hydrogen; Interface states; Conduction and valence bands; Density functional theory

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Hartnett, M. C. (2016). Role of sulfur in vibration spectra and bonding and electronic structure of GeSi surfaces and interfaces. (Thesis). University College Cork. Retrieved from http://hdl.handle.net/10468/3665

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Hartnett, Mark C. “Role of sulfur in vibration spectra and bonding and electronic structure of GeSi surfaces and interfaces.” 2016. Thesis, University College Cork. Accessed October 23, 2020. http://hdl.handle.net/10468/3665.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Hartnett, Mark C. “Role of sulfur in vibration spectra and bonding and electronic structure of GeSi surfaces and interfaces.” 2016. Web. 23 Oct 2020.

Vancouver:

Hartnett MC. Role of sulfur in vibration spectra and bonding and electronic structure of GeSi surfaces and interfaces. [Internet] [Thesis]. University College Cork; 2016. [cited 2020 Oct 23]. Available from: http://hdl.handle.net/10468/3665.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Hartnett MC. Role of sulfur in vibration spectra and bonding and electronic structure of GeSi surfaces and interfaces. [Thesis]. University College Cork; 2016. Available from: http://hdl.handle.net/10468/3665

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.