Growth of antimony on copper : a scanning tunneling microscopy study
| dc.contributor.advisor | Hillie, K. T. | |
| dc.contributor.advisor | Roos, W. D. | |
| dc.contributor.author | Ndlovu, Gebhu Freedom | |
| dc.date.accessioned | 2015-09-08T10:04:44Z | |
| dc.date.available | 2015-09-08T10:04:44Z | |
| dc.date.copyright | 2012-01 | |
| dc.date.issued | 2012-01 | |
| dc.date.submitted | 2012-01 | |
| dc.description.abstract | English: The thesis deals with adsorption, self–assembly and surface reactions of Sb atoms on solid Cu(111) substrates. It is of genuine interest in materials science and technology to develop strategies and methods for reproducible growth of extended atomic and molecular assemblies with specific and desired chemical, physical and functional properties. When the mechanisms controlling the self-organized phenomena are fully disclosed, the self-organized growth processes can be steered to create a wide range of surface nanostructures from metallic, semiconducting and molecular materials. The experimental technique used to study ordered phases and phase transitions of Sb on Cu(111) substrates was the Scanning Tunneling Microscopy (STM) – an outstanding method to gain real space information of the atomic scale realm of adsorbates on crystalline surfaces. It is a general trend to conduct studies on well known structures before one begins working on complicated systems. Therefore, in this study, Si(111) Cu(111) and HOPG surfaces were studied in atomic detail to confirm the calibration and the resolution capabilities of the instrument. The acquired data were comparable to the reported theoretical and experimental data in literature. The investigated Cu(111) – Sb system is characterized by a complex interplay between adsorbate interactions and adsorbate substrate interactions which in this study manifests through self–assembly processes. Both low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) were utilized to determine the substrate cleanliness prior to the growth of a submonolayer Sb coverage (0.43 ± 0.02 ML Sb as calculated from the acquired STM data). The freely diffusing Sb adatoms on the copper surface were thermally excited from a random distribution of Sb atoms after growth to a finally rearrangement to more energetically stable configuration. The experimental results illustrated the presence of a surface alloy after annealing at ~360°C. The Cu – Cu spacing increased from 0.257 ± 0.01 nm (atomically clean Cu(111)) to 0.587 ± 0.02 nm after annealing at 360°C. At that temperature, the STM images showed the surface protrusions of different sizes and contrast, attributed to Cu and Sb atoms. In addition to the conventional ( 3 × 3)R30°–Sb structural phase acquired at ~400°C, new metastable structural phases: (2 3 × 2 3) R30°–Sb and (2 3 × 3)R30°– Sb were obtained for the first time after annealing at 600°C and 700°C, respectively. STM data after annealing at 600°C and 700°C was best described by a structural model involving an ordered p(2×2) and p(2×1) overlayer structures superimposed onto the ( 3 × 3)R30°–Sb surface, respectively. At elevated temperatures LEED showed ring shaped diffraction patterns composed of twelve equidistant spots which are consistent with the growth of a hexagonal film forming three equivalent rotational domains. All the superstructures were found to favour a structural model based on Sb atoms occupying substitutional rather than overlayer sites within the top Cu(111) layer. Other than the dissolution of Sb onto Cu(111), the study report also on the segregation of Sb on Cu together with STS measurements. The surface chemical reactivity on an atom–by–atom basis of the Cu sample surface was studied by current imaging tunneling spectroscopy (CITS). The local density of states (LDOS) were derived from dI/dV maps at low tunneling voltages by a simultaneous measurement of high resolution topographic micrographs. The use of surface sensitive techniques (LEED, AES, STM, STS) in studying the surface alloy in question has enabled more precise statements to be made about the surface structure of the system at various temperatures. Based on the experimental results, a comprehensive study of the adsorption and segregation behaviour of Sb on Cu(111), including the mechanisms for phase formation at the atomic scale is presented in this study. | en_ZA |
| dc.description.abstract | Afrikaans: Die proefskrif handel oor die adsorpsie, selfrangskikking en oppervlakreaksie van Sb atome op ‘n soliede Cu(111) substraat. In die materiaalwetenskap en tegnologie is dit belangrik om strategieë en metodes te ontwikkel wat die reproduserende groei van ingewikkelde atomiese en molekulêre strukture, met spesifieke voorafbeplande chemiese, fisiese en funksionele eienskappe, vestig. Indien die meganismes, verantwoordelik vir die verskynsel van selfrangskikking, verstaan word, kan hierdie groeiprosesse gemanipuleer word om ‘n wye reeks nanostrukture op die oppervlak van metale, halfgeleiers en molekulêre materiale te bewerkstellig. In hierdie ondersoek oor geordende fases en fase oorgange van Sb op ‘n Cu(111) substraat, is die Skandeertonnelmikroskoop (STM) as eksperimentele tegniek gebruik. Dit is ‘n besonderse metode om inligting, op die atomiese vlak en in werklike ruimte, van ‘n geadsorbeerde stof op kristallyne oppervlakke te verkry. Dit is algemeen dat ondersoeke van hierdie aard eers op welbekende strukture gedoen word, voordat met meer komplekse studies begin word. In hierdie ondersoek is die Si(111), Cu(111) en HOPG oppervlakke op ‘n atomiese vlak ondersoek om die herhaalbaarheid, kalibrasie en oplosvermoë van die instrument te bevestig. Die gemete data was dan ook vergelykbaar met die gerapporteerde, teoretiese en eksperimentele, data in die literatuur. Die Cu(111) – Sb sisteem wat ondersoek is, is gekenmerk deur ‘n komplekse wisselwerking van reaksies tussen die adsorbate en ook tussen die geadsorbeerde stof en die substraat, wat manifesteer in selfrangskikkings prosesse. Beide lae-energieelektrondiffraksie (LEED) en Augerelektronspektroskopie (AES) is gebruik om die suiwerheid van die substraat te bepaal alvorens ‘n sub-monolaag Sb bedekking (0.43 ± 0.02 ML Sb soos bereken vanaf die STM data) gedeponeer is. Die geadsorbeerde Sb atome het willekeurige posisies op die oppervlak ingeneem, waarna dit termies gestimuleer is om na energeties meer stabiele konfigurasies te diffundeer. Die eksperimentele resultate dui die teenwoordigheid van ‘n oppervlaklegering na uitgloeiing by ~360°C aan. Die Cu – Cu spasiëring toon ‘n toename vanaf 0.257 ± 0.01 nm (atomies skoon Cu(111)) tot 0.587 ± 0.02 nm, na uitgloeiing. By hierdie temperature gee die STM-beelde oppervlak veranderings van verskillende groottes en kontraste, wat toegeskryf word aan die Cu en Sb atome. Bo en behalwe die konvensionele ( 3 × 3)R30°–Sb struktuur by ~400°C, is nuwe metastabiele strukture (2 3 × 2 3 ) R30°–Sb en (2 3 × 3)R30°–Sb na uitgloeiing by 600°C en 700°C respektiewelik vir die eerste keer waargeneem. Die STM data, na uitgloeiing by 600°C en 700°C, word die beste beskryf deur ‘n strukturele model, waar geordende oorstrukture van p(2×2) en p(2×1) respektiewelik gesuperponeer is op die ( 3 × 3) R30°–Sb oppervlak. By verhoogde temperature toon die LEED patrone ringvormige diffraksiepatrone bestaande uit twaalf kolle, ewe ver van mekaar, wat vereenselwig word met ‘n heksagonale lagie, met drie ekwivalente rotasie gebiede. Daar is gevind dat al die superstrukture ‘n strukturele model bevredig wat gebaseer is op Sb atome wat eerder substitusionele posisies as posisies bo-op die Cu(111) laag inneem. Die ondersoek rapporteer verder oor die segregasie van Sb op die Cu, tesame met STS metings. Die chemiese reaktiwiteit van die Cu-oppervlak, op ‘n atoom-totatoom grondslag, is met behulp van stroombeeldtonnelspektroskopie (SBTS) bestudeer. | afr |
| dc.description.sponsorship | Council for Scientific and Industrial Research (CSIR) | en_ZA |
| dc.description.sponsorship | Department of Science and Technology (DST) | en_ZA |
| dc.description.sponsorship | National Research Foundation (NRF) | en-ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/1199 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Self–assembly | en_ZA |
| dc.subject | Antimony | en_ZA |
| dc.subject | Copper | en_ZA |
| dc.subject | Organized growth | en_ZA |
| dc.subject | Scanning tunneling microscopy and spectroscopy | en_ZA |
| dc.subject | Adsorbates | en_ZA |
| dc.subject | Monolayers | en_ZA |
| dc.subject | Diffusion | en_ZA |
| dc.subject | Superstructure | en_ZA |
| dc.subject | Surface alloys | en_ZA |
| dc.subject | Surface tension | en_ZA |
| dc.subject | Root three by root three | en_ZA |
| dc.subject | Surface sensitive | en_ZA |
| dc.subject | Nanostructures | en_ZA |
| dc.subject | Annealing | en_ZA |
| dc.subject | Surfactant | en_ZA |
| dc.subject | Silicone | en_ZA |
| dc.subject | Highly oriented pyrolytic graphite | en_ZA |
| dc.subject | Segregation | en_ZA |
| dc.subject | Activation energy | en_ZA |
| dc.subject | Tip fabrication | en_ZA |
| dc.subject | Surface reconstruction | en_ZA |
| dc.subject | Structural phases | en_ZA |
| dc.subject | Density of states | en_ZA |
| dc.subject | Thesis (Ph.D. (Physics))--University of the Free State, 2012 | en_ZA |
| dc.title | Growth of antimony on copper : a scanning tunneling microscopy study | en_ZA |
| dc.type | Thesis | en_ZA |