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Scanning tunneling microscopy and photoemission studies of Ag films on metal/semiconductor surfaces
Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).ORCID-id: 0000-0002-4361-2758
2020 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The research presented in this thesis has been focused on the study of thin Ag films, grown on metal-reconstructed Si(111) and Ge(111) surfaces.The films have been grown at room temperature, and the morphologiesand electronic structures of the films have been investigated using scanning tunneling microscopy and spectroscopy (STM/STS), low-energy electron diffraction (LEED) and angle-resolved photoelectron spectroscopy(ARPES).

On the Ga-, In-, and Sn/Si(111)-√3x√3 surfaces, the first layer of Ag forms a special interface which consists of short atomic rows, with slightly different appearances depending on the base surface. Starting from two monolayers (MLs), Ag grows as a thin film with bulk-like lattice parameters.

The electronic structures of the films reveal the behavior of the intrinsic quantum well states (QWSs). STS data show peaks in the filled states which move towards the Fermi level with increased thicknesses. These peaks have been compared with ARPES spectra and linked to the QWSs. The evolution of the QWSs with film thicknesses has been examined within, and extending upon, the established theoretical framework. The results point towards metal-reconstructed Si(111) surfaces using group III and IV elements as strong candidates for uniform film growth, and open up new avenues for studying electronic coupling effects between film/substrate.

On Sn/Si(111)-√3x√3, the Ag films grow in domains with two different lattice orientations, rotated 30° from each other. This is due to the interface consisting of two different structures, as revealed by the STM. One of the interfacial phases is a 3×3 honeycomb structure, and the other a line structure of short atomic rows with a three-fold symmetric 2√3×√3-R30° unit cell. Atomic models for the two interface phases have been proposed, based on two different spin configurations of the Sn/Si(111)-√3x√3 surface. The presence of two interfaces makes this system highly attractive for the study of interface related phenomena, and the difference in Ag filmson Sn/Ge(111) compared with Sn/Si(111) highlights the importance of electronic effects for the film growth.

Abstract [en]

From our everyday experiences, we are used to the world functioning in a certain way. As the size of things approach the nanometer scale, new physical phenomena and features arise that often contradict our intuition. One such phenomenon is the electron confinement. When the movement of electrons is restricted in space, the energy becomes quantized, so that only a few particular energy levels are allowed and all the energies between these levels are forbidden. This happens naturally in a metal thin film with a nanometer thickness. These allowed energy levels are called quantum well states. One way to create an artificial system is to grow thin metal films on semiconductor substrates.

This thesis presents research focused on Ag thin films on Si(111)- and Ge(111)-√3×√3 surfaces using Ga, In and Sn as adatoms. The morphologies and electronic structures of the interfaces and Ag films have been studied using a combination of scanning tunneling microscopy and photoelectron spectroscopy. The metal-reconstructed surfaces allow for Ag film formation to take place at room temperature. These surfaces also allow for layer-bylayer growth at very low coverages, which opens up the possibility to study coupling and interface related effects in the electronic structure of the films.

Ort, förlag, år, upplaga, sidor
Karlstad: Karlstads universitet, 2020. , s. 48
Serie
Karlstad University Studies, ISSN 1403-8099 ; 2020:23
Nyckelord [en]
Quantum well states, thin films, semiconductor, STM, STS, ARPES
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
URN: urn:nbn:se:kau:diva-79135ISBN: 978-91-7867-131-1 (tryckt)ISBN: 978-91-7867-136-6 (digital)OAI: oai:DiVA.org:kau-79135DiVA, id: diva2:1454453
Disputation
2020-09-11, 1B364, Frödingsalen, 10:15 (Engelska)
Opponent
Handledare
Anmärkning

Artikel 4 ingick som manuskript i avhandlingen, nu publicerad.

Tillgänglig från: 2020-09-11 Skapad: 2020-07-16 Senast uppdaterad: 2020-10-05Bibliografiskt granskad
Delarbeten
1. Quantum-well states in thin Ag films grown on the Ga/Si(111)-√3 x √3 surface
Öppna denna publikation i ny flik eller fönster >>Quantum-well states in thin Ag films grown on the Ga/Si(111)-√3 x √3 surface
2018 (Engelska)Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 19, s. 1-9, artikel-id 195430Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Silver thin films have been created by room temperature deposition on a Ga/Si(111)-√3 x √3 surface and their valence band structures and core levels have been measured by angle-resolved photoelectron spectroscopy (ARPES). Discrete quantum-well states (QWSs) quantized from the Ag sp valence band are observed already at 3 monolayers (ML). The characteristics of the QWSs have been examined in the phase accumulation model for thicknesses between 3 and 12 ML. The phase shift and QWSs binding energies dependence with Ag film thicknesses have all been consistently derived. In-plane energy dispersion follows a parabolic curve, and the effective mass of the QWSs shows an increasing trend with binding energies as well as with reduced film thicknesses. Furthermore, the ARPES measurements reveal umldapp mediated QWSs around the (M)over-bar points of the Si(111) 1 x 1 surface Brillouin zone. The study confirms that the Ga/Si(111)-√3 x √3 surface is a good substrate for growing uniform ultrathin Ag films in room temperature conditions.

Ort, förlag, år, upplaga, sidor
American Physical Society, 2018
Nyckelord
Quantum well states, Thin films, Semiconductor, ARPES
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-67486 (URN)10.1103/PhysRevB.97.195430 (DOI)000433009300010 ()
Tillgänglig från: 2018-06-07 Skapad: 2018-06-07 Senast uppdaterad: 2020-10-05Bibliografiskt granskad
2. STM/STS and photoemission study of Ag thin films on Ga/Si(111)(√3 × √3)R30°
Öppna denna publikation i ny flik eller fönster >>STM/STS and photoemission study of Ag thin films on Ga/Si(111)(√3 × √3)R30°
2019 (Engelska)Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 682, s. 25-32Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Silver thin films have been formed by room temperature deposition of Ag on a Ga/Si(111) (√3 × √3)R30° surface. Scanning tunneling microscopy and spectroscopy (STM/STS) have been used to study both the clean Ga/Si(111) (√3 × √3)R30° surface and Ag films with different coverages. For the film formation, Ag first grows into 2D islands on Ga/Si(111) (√3 × √3)R30°. The first layer of the islands forms atomic lines with three-fold symmetry in the 1 × 1 direction of the underlying Si(111) substrate. From a 2 ML coverage, the growth becomes layer-by-layer mode. STS measurements have been performed on Ag films with different coverages inorder to investigate their electronic structures. Between 2–4 ML, the STS spectra reveal 2 and 3 peaks below the Fermi level. These peaks move towards the Fermi level with increased film thicknesses and thus share the same behavior as those of quantum well states (QWSs). The energy positions of the peaks have been compared with valence band photoelectron spectra in order to assign them to various parts of the QWSs. In addition, the photoemission results also confirm the existence of QWSs for a 2 ML Ag film on Ga/Si(111) (√3 × √3)R30°.

Ort, förlag, år, upplaga, sidor
Elsevier, 2019
Nyckelord
Quantum well states, Thin films, Semiconductor, STM STS
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-79131 (URN)10.1016/j.susc.2018.12.009 (DOI)000462690900004 ()
Tillgänglig från: 2020-07-16 Skapad: 2020-07-16 Senast uppdaterad: 2020-10-05Bibliografiskt granskad
3. Initial quantum well states in Ag thin films on the In/Si(111)- √3 × √3 surface
Öppna denna publikation i ny flik eller fönster >>Initial quantum well states in Ag thin films on the In/Si(111)- √3 × √3 surface
2020 (Engelska)Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 692, s. 1-7, artikel-id 121531Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Silver thin films have been formed by room temperature deposition of Ag on In/Si(111)-√3 × √3. The Ag films have been investigated using both angle-resolved photoelectron spectroscopy (ARPES) and scanning tunnelingmicroscopy and spectroscopy (STM/STS). This creates a powerful link between the electronic structures and the film morphology. The valence band spectra show a clear evidence of quantum well state (QWS) formation already for a 2 monolayer (ML) film. This QWS moves towards the Fermi level for the 3 ML film, which also reveals a second QWS. The QWSs’ dispersions have been plotted along the ΓM and ΓK symmetry lines of the 1×1 surface Brillouin zone (SBZ), where the ΓM direction shows the umklapp-mediated QWSs. The valence band spectra for the 3 ML Ag film also show a strong Ag sp band close to the edge of the Ag(111) 1×1 SBZ. In the STS spectrum from 2 ML, two peaks are visible below the Shockley surface state. These peaks are compared with the ARPES data and attributed to different features of the QWS

Ort, förlag, år, upplaga, sidor
Elsevier, 2020
Nyckelord
Quantum well states, Thin films, Semiconductor, ARPES, STM/STS
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-79132 (URN)10.1016/j.susc.2019.121531 (DOI)000502892900008 ()2-s2.0-85074996429 (Scopus ID)
Tillgänglig från: 2020-07-16 Skapad: 2020-07-16 Senast uppdaterad: 2021-11-29Bibliografiskt granskad
4. Layer-by-layer control of Ag film growth on Sn/Si(111)-(√3 ×√3)-R30°
Öppna denna publikation i ny flik eller fönster >>Layer-by-layer control of Ag film growth on Sn/Si(111)-(√3 ×√3)-R30°
2020 (Engelska)Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 701, s. 1-9, artikel-id 121697Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Silver thin films have been formed on the Sn/Si(111)-(√3 ×√3)-R30 degrees surface at room temperature. The film morphologies, growth and electronic structures have been studied by scanning tunneling microscopy/spectroscopy (STM/STS), low-energy electron diffraction (LEED) and angle-resolved photoelectron spectroscopy (ARPES). The first layer of Ag forms an interface which consists of atomic rows with three-fold symmetry oriented along the Si(111)-1 x 1 directions. On top of the interface, Ag grows as an uniform thin film, following a layer-by-layer mode. The electronic structures of the films have been studied by STS for coverages between 1-5 monolayers (MLs). The STS spectra show peaks in the occupied electronic states which move towards the Fermi level with increased film thicknesses. These peaks have been attributed to quantum well states. ARPES measurements have been performed for 1 and 2 ML Ag coverage on Sn/Si(111)-(√3 ×√3)-R30 degrees, where the resulting thicknesses were confirmed by STM. The spectra reveal that quantum well states appear first for the 2 ML film.

Ort, förlag, år, upplaga, sidor
Elsevier, 2020
Nyckelord
Quantum well states; Thin films; Semiconductor; STM; STS; ARPES
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-79133 (URN)10.1016/j.susc.2020.121697 (DOI)000566758600013 ()2-s2.0-85088897183 (Scopus ID)
Tillgänglig från: 2020-07-16 Skapad: 2020-07-16 Senast uppdaterad: 2022-05-11Bibliografiskt granskad
5. Ag film growth on Sn/Ge(111)-√3 ×√3
Öppna denna publikation i ny flik eller fönster >>Ag film growth on Sn/Ge(111)-√3 ×√3
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:kau:diva-79134 (URN)
Tillgänglig från: 2020-07-16 Skapad: 2020-07-16 Senast uppdaterad: 2021-05-06Bibliografiskt granskad

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