Thesis (MSc (Physics))--Stellenbosch University, 2009. / ENGLISH ABSTRACT: This thesis aims to comprehensively discuss ultrafast electron di raction and its role in temporally resolving ultrafast dynamics on the molecular level. Theory on electron pulses and electron pulse propagation will be covered, but the main focus will be on the method, equipment and experimental setup required to generate sub-picosecond electron pulses, which are needed to perform time resolved experiments. The design and construction of an electron gun needed to produce the electron pulses will be shown in detail, while preliminary pulse characterization experiments will also be illustrated. An introduction into the theory of electron diffraction patterns and how to interpret these diffraction patterns will conclude the thesis. / AFRIKAANSE OPSOMMING: Hierdie tesis het ten doel om ultravinnige elektrondi raksie deeglik te bespreek asook die rol wat dit speel om ultravinnige tyd-dinamika op 'n molekulêre vlak op te los. Die teorie van elektonpulse en die voortplanting van elektronpulse sal gedek word, maar die fokus sal op die metode, gereedskap en eksperimentele opstelling wees wat benodig is om sub-pikosekonde elektronpulse te genereer. Die ontwerp en konstruksie van 'n elektrongeweer, wat benodig word om elektronpulse te produseer, sal in detail bespreek word, terwyl aanvanklike pulskarakterisasie eksperimente ook illustreer sal word. 'n Inleiding tot die teorie van elektrondi raksie patrone en hoe om hulle te interpreteer sal die tesis afsluit.

This work describes detailed convergent beam electron diffraction (CBED) studies of GdAlO3 and LaAlO3 perovskites. CBED patterns tilted away from major zone axes have been found to have high sensitivity to the presence of mirror or glide mirror symmetry. Such patterns confirm to high accuracy that the space group of GdAlO3 is orthorhombic, Pnma. Tilted patterns from this well characterised structure also serve as benchmarks against which similar patterns may be compared. In the case of LaAlO3, tilted patterns enable the space group to be confirmed as rhombohedral R3c, previously claimed to be cubic (Fm3c) by CBED. Furthermore, no evidence for the low symmetry (I2/a or F1) phases proposed for LaAlO3 has been observed. The LaAlO3 study also gives a careful assessment of the influence of tilted specimen surfaces on the CBED data. Within the qualitative scope of these experiments, no symmetry degrading effects could be observed. Some preliminary Quantitative CBED (QCBED) data from LaAlO3 is also presented. This shows it will be possible to make a detailed study of the bonding charge density (Δρ) in this material when combined with X-ray diffraction data. Also included is a brief CBED study of LaFeO3, a material that is isostructural with GdAlO3. Although this is restricted to exact zone axis patterns, it is noted that tilted patterns have significant potential to improve the quality of the symmetry determination.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Organic molecular salts have a wide range of physical properties which can be chemically tailored by minor variations of their substituents. These characteristics include high degrees of anisotropy, electrical conductivity ranging from superconducting to insulating, and structural changes in the crystal lattice during first order phase transitions brought about by minimal changes in temperature, effective pressure, and in some cases even light. Hence, these materials are particularly interesting for the development of molecular electronics and also as study materials in solid state physics. The family of copper-dimethyl-dicyanoquinone-diimine (Cu(DMe-DCNQI)2) salts forms part of the radical anion salt subclass of organic molecular crystals and is of particular interest due to its extraordinarily high conductivity compared to other quasi one-dimensional organic conductors. Its metal-to-insulator phase transition is characterised by conductivity jumps across several orders of magnitude within a few kelvin. Over the past three decades the metallic and insulating phases, as well as the transition behaviour have been investigated extensively utilising a broad spectrum of methods amongst others electrical conductivity, electron spin resonance, and re ectivity measurements, x-ray photoelectron and infrared spectroscopy, x-ray diffraction, and dilatometry. Fast light-switching between phases has been observed in partially deuterated forms of Cu(DCNQI)2 on sub-100-ps time scales. Furthermore, the phase transition is believed to be induced by a deformation of the crystalline lattice and a charge density wave formation which are detectable in diffraction images. Therefore we want to investigate this metal-to-insulator phase transition structurally and temporally via ultrafast electron diffraction. The technique of ultrafast electron diffraction employs the fundamentals of pump-probe spectroscopy: One of the two femtosecond pulsed laser beams excites the thin, crystalline sample, while the other - after being converted into a pulsed electron beam via the photoelectric effect - forms a diffraction image of the sample's lattice structure. The arrival time of the two pulses at the sample can be varied by a few femtoseconds with respect to each other enabling the resolution of ultrafast structural dynamics of the crystal's atomic lattice via electron diffraction. During the work presented in this thesis the sample preparation and characterisation leading to a successful introduction of Cu(DCNQI)2 into our ultrafast electron diffraction setup is presented. A diffraction pattern of comparable quality to that of a commercially available transmission electron microscope was recorded of the metallic state of partially deuterated d6 Cu(DCNQI)2. Subsequent analysis of the obtained diffraction data and further studies of the low temperature state { including simulations as well as experiments { have narrowed down the factors still making the diffraction pattern evasive. Possible solutions to experimental challenges are proposed to make the documentation of structural ultrafast dynamics in these organic molecular salts an attainable goal in the future. / AFRIKAANSE OPSOMMING: Organiese molekulêre soute het `n wye verskeidenheid van fisiese eienskappe wat chemies verander kan word deur geringe variasie in die samestelling van die sout. Hierdie eienskappe sluit in `n hoë graad van anisotropie, elektriese geleidingsvermoë wat strek van supergeleiding tot elektriese isolasie, en strukturele veranderinge in die kristalstruktuur tydens eerste orde fase-oorgange wat veroorsaak word deur geringe veranderinge in temperature, effektiewe druk en in sommige gevalle selfs lig. Gevolglik is hierdie material besonder interessant vir die ontwikkeling van molekulêre elektronika en ook as studiemateriaal in vastetoestandfisika. Die familie van koperdimetieldisianokinoondiimien (Cu(DMe-DCNQI)2) soute vorm `n deel van die radikaal-anioon-sout subklas van organiese molekulêre kristalle en is van besondere belang as gevolg van hulle buitengewone hoë elektriese geleidingsvermoë in vergelyking met ander kwasi-eendimensionele organiese geleiers. Die metaal-na-isolator fase-oorgang van hierdie kristal word gekenmerk deur die verandering van die geleidingsvermoë met verskeie ordegroottes binne `n paar kelvin. Gedurende die laaste drie dekades is die metaal en isolator fases, asook die oorgangsgedrag deeglik ondersoek met behulp van `n wye verskeidenheid van metodes wat onder andere elektriese geleidingsvermoë, elektron-spin resonans en reeksiemetings, x-straal fotoelektron en infrarooi spektroskopie, x-straal diffraksie en dilatometrie insluit. Vinnige skakeling tussen fases is waargeneem in gedeeltelik gedeuteerde vorms van Cu(DCNQI)2 op `n sub-100-ps tydskaal. Daar word verder geglo dat die fase-oorgang geïnduseer word deur `n deformasie van die kristalstruktuur en die vorming van `n ladingsdigtheidgolf wat meetbaar is in elektrondiffraksiebeelde. Om hierdie rede wil ons die metaal-na-isolator fase-oorgang se struktuur- en tydafhanklikheid ondersoek deur gebruik te maak van ultra-vinnige elektron diffraksie. Die tegniek van ultra-vinnige elektron diffraksie maak gebruik van die beginsels van pomp-toets spektroskopie: Een van die twee femtosekonde laserpulse wek die dun kristallyne monster op, terwyl die ander na omskakeling in `n elektronpuls via die foto-elektriese effek `n diffraksiebeeld van die monster se kristalstruktuur vorm. Die aankomtyd van die twee pulse by die monster kan met `n paar femtosekondes ten opsigte van mekaar verander word om die tydresolusie van die ultra-vinnige strukturele dinamika van die kristal se atoomstruktuur deur elektrondiffraksie moontlik te maak. In hierdie tesis word die monstervoorbereiding en karakterisering wat gelei het tot suksesvolle eksperimente op Cu(DCNQI)2 in ons ultra-vinnige elektron diffraksie opstelling behandel. `n Diffraksie patroon waarvan die kwaliteit vergelykbaar is met die van `n kommersiëel beskikbare transmissie elektron mikroskoop is gemeet vir die metaalfase van gedeeltelik gedeuteerde d6 Cu(DCNQI)2. Daaropvolgende analiese van die gemete diffraksiedata en verdere studies van die lae temperatuur toestand wat simulasies sowel as eksperimente insluit het `n klein aantal faktore uitgewys wat steeds die deteksie van die isolatorfase se ladingsdigtheidgolf se kenmerkende diffraksiepatroon verhoed. Moontlike oplossings tot eksperimentele uitdagings word voorgestel om die dokumentering van strukturele ultra-vinnige dinamika in hierdie organiese molekulêre soute `n haalbare toekomstige doelwit te maak.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Trilayered transition metal dichalcogenides such as our sample (1T-TiSe2) have been studied for many years as systems with strong electron-electron and electron-phonon correlations. The main attraction to this family of compound is its potential to exhibit ground state phenomena known as charge density waves whose detailed physical origin has been controversially determined. In this study, we have used an ultrafast femtosecond laser based on a pump-probe technique, namely ultrafast electron diffraction, to investigate these exotic features associated with the crystal. A pump laser pulse photo-excites the crystal from its ground state and the probe pulse (ultrashort electron pulse) takes the snapshot of the evolution of the lattice generating an electron diffraction pattern of the crystal. Hence the dynamical structural behaviour can be observed in time with a subpicosecond temporal resolution. As a hexagonal close-packed structure, its signature is expected to be seen in the diffraction pattern in both a steady-state and electron time-resolved femtosecond electron diffraction. In addition, simulations of electron diffractions pattern for room and low temperature structural data via a software called Simulation and Analysis of Electron diffraction (SAED) have been carried out. Clear signatures of charge density waves were seen at low temperature. / AFRIKAANSE OPSOMMING: Drie-laag oorgangsmetaal dikhalkogeniedes soos ons voorbeeld (1T-TiSe2), word reeds vir baie jare bestudeer as sisteme met sterk elektron-elektron en elektron-fonon korrelasies. Die hoof aantrekkingskrag van hierdie sisteme is die verskynsel van ladingdigtheidsgolwe in die grondtoestand. Die fisiese oorsprong van hierdie ladingdigtheidsgolwe was bepaal te midde van verskeie teenstrydighede. In hierdie studie, maak ons gebruik van die ultravinnige femtosekonde laser gebaseerde aktiveer-interogeer tegniek, genaamd ultravinnige elektron diffraksie (UED) om unicke eienskappe wat met die kristal geassosieer is te bestudeer. In UED wek ’n ultravinnige laserpuls (aktivering) die kristal op vanaf die grondtoestand waartydens n ultravinnige elektronpuls (interogering) ’n foto neem van die evolusie van die elektron diffraksiepatroon wat deur die kristalrooster gegenereer word. Hierdie wisselwerking van die interogerings elektronpuls en die sisteem kan gevolglik teen verskeie vasgetelde tye toegelaat word. Dus kan die dinamiese strukturele gedrag waargeneem word met ’n tydresolusie in die orde van die elektronpuls (sub-pikosekondes). Siende dat die kristal ’n diggepakte-heksagonale struktuur vorm, behoort die kenmerkende diffraksiepatroon daarvan waarneembaar te wees in beide die bestendige diffraksie en femtosekonde elektron diffraksie tegnieke. In hierdie konteks was duidelike tekens van ladingdigtheidsgolwe waargeneem. Benewens was daar ook simulasies uitgevoer om die elektron diffraksiepatrone asook die strukturele data by kamer en lae temperature vas te pen. Die sagteware wat hiervoor gebruik word is genaamd Simulasie en Ontleding van Elektronendiffraksie (SAED) - Simulation and Analysis of Electron Diffraction (SAED).

Graduation date: 1997

The dynamics of atomic scale structures during structural change can be studied by Ultrafast Electron Diffraction (UED). The time resolution needed to reveal the fastest dynamics is 100 fs. Sub-angstrom structural resolution becomes possible with 1-1000 pC of charge necessary for diffraction pattern analysis during subtle structural changes. This combination of requirements cannot currently be realized due to the space-charge temporal broadening inherent to bunches of electrons of high fluence and short temporal duration. Simulations show that the incorporation of a specially designed Radio-Frequncy (RF) cavity into the UED apparatus removes this technical limitation. The RF cavity reverses the near linear position-momentum distribution of the temporally broadened electron bunch, causing the bunch to recompress itself as it propagates. It is found that our proposed method allows for sub-100 fs bunches with maximum charge of 0.6 pC, almost 3 orders of magnitude improvement over today's state of the art.

No description available.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Low-dimensional materials are known to undergo phase transitions to differently or- dered states, when cooled to lower temperatures. These phases often show a periodic modulation of the charge density (called a charge density wave – CDW) coupled with a periodic perturbation of the crystal lattice (called a periodic lattice distortion – PLD). Although many experiments have been performed and much has been learnt about CDW phases in low-dimensional materials, the reasons for their existence are still not fully understood yet. Many processes, involving either strong electron–electron or electron–lattice coupling, have been observed which all might play a role in explaining the formation of different phases under different conditions. With the availability of femtosecond lasers it has become possible to study materials under highly nonequilibrium conditions. By suddenly introducing a known amount of energy into the system, the equilibrium state is disturbed and the subsequent relax- ation processes are then observed on timescales of structural and electronic responses. These experiments can deliver valuable information about the complex interactions between the different constituents of condensed matter, which would be inaccessible under equilibrium conditions. We use time resolved electron diffraction to investigate the behaviour of a CDW system perturbed by a short laser pulse. From the observed changes in the diffraction patterns we can directly deduce changes in the lattice structure of our sample. A femtosecond electron diffraction setup was developed at the Laser Research In- stitute in Stellenbosch, South Africa. Short laser pulses produce photo electrons which are accelerated to an energy of 30 keV. Despite space charge broadening effects, elec- tron pulses shorter than 500 fs at sample position can be achieved. Technical details of this system and its characterisation as well as sample preparation techniques and analysis methods are described in detail in this work. Measurements on two members of the quasi-two-dimensional transition metal di- chalcogenides, namely 4Hb-TaSe2 and 1T-TaS2, are shown and discussed. Both show fast (subpicosecond) changes due to the suppression of the PLD and a rapid heating of the lattice. When the induced temperature rise heats the sample above a phase tran- sition temperature, a complete transformation into the new phase was observed. For 4Hb-TaSe2 we found that the recovery to the original state is significantly slower if the PLD was completely suppressed compared to only disturbing it. On 1T-TaS2 we could not only study the suppression of the original phase but also the formation of the higher energetic CDW phase. Long (100 ps) time constants were found for the tran- sition between the two phases. These suggest the presence of an energy barrier which has to be overcome in order to change the CDW phase. Pinning of the CDW by de- fects in the crystal structure result in such an energy barrier and consequently lead to a phase of domain growth which is considerably slower than pure electron or lattice dynamics. / AFRIKAANSE OPSOMMING: Dit is bekend dat lae-dimensionele materie fase oorgange ondergaan na anders ge- ori¨enteerde toestande wanneer afgekoel word tot laer temperature. Hierdie fases toon dikwels ’n periodiese modulasie van die elektron digtheid (genoem ’n “charge density wave” – CDW), tesame met ’n periodiese effek op die kristalrooster (genoem ’n “peri- odic lattice distortion” – PLD). Alhoewel baie eksperimente al uitgevoer is en al baie geleer is oor hierdie CDW fase, is die redes vir hul bestaan nog steeds nie ten volle verstaan nie. Baie prosesse, wat of sterk elektron–elektron of elektron–fonon interaksie toon, is al waargeneem en kan ’n rol speel in die verduideliking van die vorming van die verskillende fases onder verskillende omstandighede. Met die beskikbaarheid van femtosekonde lasers is dit nou moontlik om materie onder hoogs nie-ewewig voorwaardes te bestudeer. Deur skielik ’n bekende hoeveel- heid energie in die stelsel in te voer, word die ewewigstaat versteur en word die daar- opvolgende ontspanning prosesse waargeneem op die tydskaal van atomies struktu- rele en elektroniese bewiging. Hierdie eksperimente kan waardevolle inligting lewer oor die komplekse interaksies tussen die verskillende atomiese komponente van ge- kondenseerde materie, wat ontoeganklik sou wees onder ewewig voorwaardes. Ons gebruik elektrondiffraksie met tyd resolusie van onder ’n pikosekonde om die gedrag van ’n CDW stelsel te ondersoek nadat dit versteur is deur ’n kort laser puls. Van die waargenome veranderinge in die diffraksie patrone kan ons direk aflei watse veranderinge die kristalstruktuur van ons monster ondergaan. ’n Femtosekonde elektronendiffraksie opstelling is ontwikkel by die Lasernavors- ingsinstituut in Stellenbosch, Suid-Afrika. Kort laser pulse produseer foto-elektrone wat dan na ’n energie van 30 keV versnel word. Ten spyte van Coulomb afstoting ef- fekte, kan elektron pulse korter as 500 fs by die monster posisie bereik word. Tegniese besonderhede van hierdie opstelling, tegnieke van die voorbereiding van monsters asook analise metodes word volledig in hierdie tesis beskryf. Metings op twee voorbeelde van kwasi-tweedimensionele semi-metale, naamlik 4Hb-TaSe2 en 1T-TaS2, word gewys en bespreek. Beide wys ’n vinnige (subpikosekon- de) verandering as gevolg van die versteuring van die PLD en ’n vinnige verhitting van die kristalrooster. Wanneer die ge¨ınduseerde temperatuur bo die fase oorgang tempe- ratuur styg, is ’n volledige transformasie na die nuwe fase waargeneem. Vir 4Hb-TaSe2 het ons gevind dat die herstelling na die oorspronklike toestand aansienlik stadiger is as die PLD heeltemal viernietig is in vergelyking met as die PLD net versteur is. Met 1T-TaS2 kon ons nie net alleenlik die vernietiging van die oorspronklike fase sien nie, maar ook die vorming van ’n ho¨er energie CDW fase. Lang (100 ps) tydkonstante is gevind vir die oorgang tussen die twee fases. Hierdie dui op die teenwoordigheid van ’n energie-versperring wat eers oorkom moet word om die CDW fase voledig te ver- ander. Vaspenning van die CDW deur defekte in die kristalstruktuur veroorsaak so’n energie versperring en gevolglik lei dit tot ’n fase van groeiende CDW gebiede wat heelwat stadiger as pure elektron of kritalrooster dinamika is.

Thesis (PhD (Physics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Ultrafast Electron Diffraction (UED) is a rapidly maturing field which allows investigation of the evolution of atomic arrangement in solids on timescales comparable to the vibrational period of their constituent atoms (~10-13 s). The technique is an amalgamation of conventional high energy electron diffraction methods and pump-probe spectroscopy with femtosecond (1 fs = 10-15 s) laser pulses. Ultrafast pulsed electron sources generally suffer from limitations on the attainable electron number per pulse (brightness) due to Coulomb repulsion among the electrons. In this dissertation, the design and construction of a compact UED source capable of delivering sub-300 fs electron pulses suitable for diffraction experiments and containing about 5000 electrons per shot is described. The setup has been characterised by measurement of the transverse beam size and angular spread, and through recording and analyzing an electron diffraction pattern from a titanium foil. Measurement of the temporal duration of fs electron pulses is not trivial, and a specialised compact streak camera operating in accumulation mode has been developed as part of this study. A sub-200 fs temporal resolution has been achieved, and the dependence of temporal duration on electron number per pulse was investigated for the current UED source. The observed trends correlate well with detailed electron bunch simulations. In order to investigate ultrafast processes on samples that cannot be probed repeatedly, it becomes necessary to significantly increase the brightness of current state of the art compact sources such as the one constructed in the present study. UED sources employing electron pulse compression techniques offer this possibility. Traditional pulse compression schemes based on RF cavities, while simple in principle, pose significant technical challenges in their realisation. The current thesis describes two novel UED pulse compression methods developed by the author: achromatic reflectron compression and pulsed cavity compression. Both concepts are expected to be easier to realise than conventional RF compression. Detailed simulations predict that such sources can attain a brightness improvement of more than one order of magnitude over compact sources that do not employ compression techniques. In addition, such sources show much promise for the attainment of pulse durations in the sub-100 fs range. / AFRIKAANSE OPSOMMING: Ultra vinnige elektron diffraksie is ‘n meettegniek wat tans in die proses is om vinnige ontwikkeling te ondergaan. Die tegniek het ten doel om strukturele omsettingsprosesse op ‘n lengteskaal van atoombindings en ‘n tydskaal van die vibrasie periode van atome in materie, ongeveer 10-13 s, te ondersoek. Dit word bewerkstellig deur die spasieresolusievermoë van gewone hoë energie elektron diffraksie met die tydresolusievermoë van femtosekonde (1 fs = 10-15 s) laserspektroskopie te kombineer. Die aantal elektrone per puls (intensiteit) van ultravinnige gepulsde elektronbronne word beperk deur die Coulomb afstootingskragte tussen die elektrone. Hierdie dissertasie beskryf die ontwerp en konstruksie van ‘n kompakte ultravinnige elektron bron. Die elektronpulse wat geproduseer word bevat tot 5000 elektrone per puls met ‘n tyd durasie van minder as 300 fs, en is geskik vir diffraksie eksperimente. Die aparaat is gekarakteriseer deur die volgende metings: elektronpulsdiameter, straaldivergensie, en ‘n titaan foelie se statiese diffraksie patroon. Dit is nie triviaal om die durasie van femtosekonde elektronpulse te meet nie, en n spesiale kompakte akkumulerende “streak camera” is vir die doeleindes van hierdie projek onwikkel. Die tydresolusie van hierdie “streak camera” is beter as 200 fs, en die afhanklikheid van die pulsdurasie wat deur die ultravinnige elektron bron geproduseer word as n funksie van die elektrongetal per puls is met behulp van hierdie toestel bepaal. Die resultate klop redelik goed met gedetaileerde simulasies van die elektron puls dinamika. Die karakterisasie van monsters wat nie herhaaldelik gemeet kan word nie vereis verkieslik ‘n nog hoër pulsintensiteit as wat met huidige bronne bereik kan word. ‘N verdere doelstelling is dus om ultravinnige elektron bronne te ontwikkel wat pulse met meer elektrone per puls kan genereer. Dit kan bewerkstellig word deur bronne wat van elektron puls kompressie tegnieke gebruik maak. Die tradisionele manier waarop dít gedoen word is deur middel van n kontinu gedrewe radio frekwensie holte. Hierdie metode gaan egter gepaard met aanmerklik hoë tegniese uitdagings. Om hierdie rede het die outeur twee alternatiewe puls kompressie konsepte ontwikkel: akromatiese reflektron kompressie and gepulsde holte kompressie. Albei konsepte sal waarskeinlik makliker wees om te realiseer as die tradisionele radio frekwensie kompressie, en is deur middel van gedetaileerde simulasies geverifiseer. Hierdie simulasies voorspel dat die intensiteit van genoemde bronne met ten minste n grooteorde meer kan wees as wat tans met kompakte ultravinnige elektron bronne moontlik is. Verder blyk dit dat sulke bronne n pulsdurasie van minder as 100 fs kan bereik.

Orientador: Richard Landers / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-09T10:50:19Z (GMT). No. of bitstreams: 1 Pancotti_Alexandre_M.pdf: 2977317 bytes, checksum: 914d690fda86677fcc9c894c6f408409 (MD5) Previous issue date: 2005 / Resumo: Nesse trabalho nos propomos a estudar a estrutura eletrônica e geométrica de ligas de superfície à partir de filmes ultra finos, da ordem de monocamada atômica , crescidos por MBE sobre substratos monocristalinos. Os filmes finos foram crescidos in situ e analizados por XPS (X-Ray Photoelectron Spectroscopy), PED (Photoelectron Diffraction), LEED (Low Energy Electron Diffraction) e UPS (Ultra Violet Photoelectron Spectroscopy). As ligas de superfície estudas foram InPd, SnPd e SbPd sempre sobre um substrato de Pd(111). Os resultados das medidas PED dos sistemas InPd e SnPd foram interpretadas usando programas tipo MSCD[1]. Foi mostrado que Sn e In em baixa cobertura formam uma estrutura (raiz2 3 x raiz2 3) R 30o ( e o In mostrou uma estrutura (1x1) para filmes com mais de 2 monocamadas, provavelmente na forma de ilhas sobre a superfície do Pd. Estudos anteriores mostraram que Sb sobre Pd(111) também apresenta a fase (raiz2 3 x raiz2 3)R 30o para baixas coberturas[2]. Os modelos que melhor se adequaram aos dados sugerem fortemente que os metais sp(In, Sn,e Sb) não difundem além da segunda monocamada. Durante estes estudos foi observado que a intensidade do satélite de shake-up do Pd tendia a zero para os átomos em contato direto com os metais s / Abstract: The purpose of this report is to present a study of the electronic and geometric structure of surface alloys grown by MBE (Molecular Beam Epitaxy) on single crystal substrates in the sub monolayer regime. The films were grown "in-situ" in the analysis chamber and analyzed by XPS (X-Ray Photoelectron Spectroscopy), PED (Photoelectron Diffraction), LEED (Low Energy Electron Diffraction) and UPS (Ultra Violet Photoelectron Spectroscopy). The alloys studied were InPd, SnPd e SbPd, all grown on the (111) face of a Pd crystal. The PED measurements for InPd and SnPd were analyzed using the MSCD code[3]. It was possible to show that for low coverages both metals formed a (raiz2 3 x raiz2 3) R 30o ( reconstruction and the first inter-planar distances were determined. For films with over two monolayers the In grew with a (1x1) structure probably in the form of islands separated by clean Pd. Previous studies showed that Sb[4] at low coverage also forms a (raiz2 3 x raiz2 3) R 30o ( structure. Our simulations suggest that In, Sn and Sb for the coverages studied do not diffuse beyond the second atomic layer. We also observed that the intensity of the Pd shake up satellite tends to zero for the Pd atoms in contact with these sp metals / Mestrado / Física da Matéria Condensada / Mestre em Física