Université Pierre et Marie Curie

MSc in Planetary Sciences Placement report

Space Research Centre, University of Leicester, UK.

Petrology of the NWA 2737 Martian and its carbonate

© Bruno Fectay & Carine Bidaut

Other project: Analysis of superconductor films

By Manon Le Testu

March-June 2009 Tutor: Dr John Bridges SRC Table of contents

ABSTRACT ...... - 2 - RESUME ...... - 3 - PART 1: PETROLOGY OF THE NWA 2737 AND ITS CARBONATE...... - 4 - PROBLEMATIC ...... - 5 - I. SNC PRESENTATION AND CHARACTERISTICS OF NWA 2737 METEORITE ...... - 6 - I. 1. Martian ...... - 6 - I. 2. NWA 2737 meteorite characteristics ...... - 7 - II. SAMPLES AND ANALYTICAL TECHNIQUES ...... - 9 - II. 1. Samples description ...... - 9 - II.1.a. Samples preparation ...... - 9 - II.1.b. Carbon Coating ...... - 9 - II. 2. Optic microscopy ...... - 9 - II. 3. Electronic microscopy analyses ...... - 10 - II. 3. a. Working principle ...... - 10 - II. 3. b. Samples analysed by SEM ...... - 11 - III. OBSERVATIONS AND DATA TREATMENTS ...... - 13 - III. 1. Optic imagery ...... - 13 - III.2. SEM analyses ...... - 13 - III.2.a. Samples general aspect ...... - 13 - III.2.b. Carbonates ...... - 14 - III.3. Data treatment ...... - 15 - III.3.a. Mineral composition ...... - 15 - III.3.b. Calculation of a chemical formula for carbonate and phosphate ...... - 15 - III.3.c. Mineral composition diagrams ...... - 16 - IV. RESULTS AND DISCUSSION ...... - 17 - IV. 1. Results and comparisons ...... - 17 - IV.1.a. Olivine and Pyroxene ...... - 17 - IV.1.b. Feldspar ...... - 18 - IV.1.c. Spinel ...... - 18 - IV.1.d. Phosphate ...... - 19 - IV.1.e. Carbonate ...... - 19 - IV. 2. Discussion ...... - 20 - IV.2.a. Mineral composition ...... - 20 - IV.2.b. About carbonates ...... - 21 - CONCLUSION PART 1 ...... - 23 - PART 2: ANALYSIS OF SUPERCONDUCTOR FILMS ...... - 24 - INTRODUCTION...... - 25 - I. METHOD ...... - 25 - I.1. Samples preparation ...... - 25 - I.2. Types of analyses made ...... - 25 - II. RESULTS ...... - 26 - II.1. Optical images ...... - 26 - II.2. SEM analyses ...... - 29 - III. DISCUSSION ...... - 32 - III.1. Samples preparation ...... - 32 - III.2. Analyses techniques used ...... - 32 - III.3. Results ...... - 32 - CONCLUSION PART 2 ...... - 33 - BIBLIOGRAPHY ...... - 34 - Acknowledgments ...... - 37 -

- 1 - ABSTRACT

This Master 2 placement subject, carried out at the Space Research Centre of Leicester University, UK entailed making precise quantitative analyses of NWA 2737 meteorite with the Scanning Electron Microscope (SEM). This meteorite, also known under the name of “Diderot”, is the second member of the Chassignite group, which is a sub-group of the Martian meteorites. It was discovered in 2000 in sands of the north west African desert, but its martian nature was recognized only in 2004. Thus, only a few petrologic and geochemical analyses have been carried out to date.

In a first time, accurate quantitative analyses of principal minerals composing NWA 2737 meteorite, were carried out under the SEM by energy-dispersive X-ray spectrometry. Then, the results of these analyses were indexed and treated in order to be compared with the results obtained by preceding research on this stone (Beck et al. 2005, Mikouchi et al. 2005, Treiman et al. 2007), and also on other Martian meteorites. Previous studies of NWA 2737 have described its general petrology and geochemistry (Beck et al., 2005-2006), its noble gazes (Marty et al. 2005), its age using the Ar-Ar dating technique (Bogard et al. 2006), and its shock events history (Mikouchi et al. 2005, Treiman et al., 2007, Van de Moortele et al. 2007).

We are particularly interested in the mineral origin carbonates that are present in NWA2737. All the studies undertaken on this meteorite show the presence of this mineral in interstices left between olivine crystals, or in veins. According to Beck et al. (2005), some of these carbonates could have a pre-terrestrial origin, because they are intersected by fractures which are preterrestrial. The Principal aim of our work is to test the hypothesis that these carbonates are Martian.

During our analyses, calcium-rich carbonates were found in small quantities in our samples. Some were indeed in cracks or between minerals. However others were discovered surrounding apatite minerals, a texture which has not been described before in NWA2737.

These various carbonate analyses did not reveal clues indicating their pre- terrestrial origin. However, more pushed studies must be carried out on this new type of carbonates which surround Apatite minerals to understand their formation process.

At the end of this report, some pages are devoted to the study carried out at the beginning of this placement on superconductor films. The objective was to check, by optical and electronic microscopy, if their structure was continuous enough to be able to explain some results obtained during previous studies of the Paramagnetic Meissner Effect (PME). Our SEM images have shown that most sample surfaces and edges were smooth and regular enough to explain the PME effects. However, it was also observed that some samples had been damaged after their PME experiences preparation, because they need to be roll up into small plastic tubes.

- 2 - RESUME

Le sujet de stage de Master 2, mené au Space Research Centre de l’Université de Leicester, est d’effectuer des analyses quantitatives précises de la météorite NWA 2737 au Microscope Electronique à Balayage. Cette météorite, aussi connue sous le nom de ‘Diderot’, est le second membre du groupe des Chassignites, sous groupe de météorites martiennes. Elle fut découverte en 2000 dans les sables du désert nord africain, mais sa nature ne fut reconnue qu’en 2004. Ainsi, seules peu d’analyses pétrologiques et géochimiques ont jusqu’alors été menées. Dans un premier temps, des analyses quantitatives précises des principaux minéraux composant la météorite NWA 2737, ont été effectués au Microscope Electronique à Balayage par spectroscopie de dispersion d’énergie des rayons X. Ensuite, les résultats de ces analyses ont été répertoriées puis traitées afin d’être comparée aux résultats obtenus par de précédent travaux de recherche sur cette pierre (Beck et al. 2005, Mikouchi et al. 2005, Treiman et al. 2007), ainsi que sur d’autres météorites martiennes. Les précédentes études menées sur la météorite NWA 2737 portaient sur sa pétrologie et géochimie (Beck et al., 2005-2006), sur l’analyse de ses gaz nobles (Marty et al. 2005), sur son âge en utilisant la technique de datation Ar-Ar (Bogard et al. 2006), et enfin sur les différents événements de choc qu’elle a subi (Mikouchi et al. 2005, Treiman et al., 2007, Van de Moortele et al. 2007). Nous nous sommes plus particulièrement intéressés à l’origine des carbonates présents dans cette météorite. Toutes les études menées sur cette météorite ont répertorié la présence de ce minéral dans des interstices laissés entre minéraux d’olivine, ou dans des veines. Selon Beck et al. (2005), certains de ces carbonates pourraient avoir une origine pré-terrestre, car étant entrecoupés de fractures pré-terrestres. L’objectif principal de nos travaux est de tester l’hypothèse que ces carbonates seraient martiens. Au cours de nos analyses, des carbonates riches en calcium ont été trouvés en petites quantités dans nos échantillons. Certains se trouvaient effectivement dans des veines ou entre des cristaux d’olivine. Cependant d’autres ont été découvert autours de minéraux d’Apatite, une localisation qui n’a pas encore été référencée dans la météorite NWA 2737. L’analyse de ces différents carbonates n’a pas révélé d’indices indiquant leur origine pré-terrestre. Cependant, des études plus poussées sur ce nouveau type de carbonates qui entourent des minéraux d’Apatites doivent être menées pour comprendre leur processus de formation.

A la fin de ce rapport, quelques pages sont consacrées à l’étude réalisée en début de stage sur des films supraconducteurs. L’objectif était de vérifier, par microscopie optique et électronique, si leur texture était suffisamment régulière pour pouvoir prendre en compte les résultats obtenues suite à de précédentes études portant sur l’effet Meissner paramagnétique. Les images obtenues ont montre que la surface et les bords des échantillons était suffisamment lisse et régulière. Cependant, il a également été observé que certains échantillons avaient été fortement endommagés suite a leur préparation pour les expériences de PME, car ils doivent être enroulés sur eux même dans de petits tubes en plastiques.

- 3 -

PART 1:

PETROLOGY OF THE NWA 2737 MARTIAN METEORITE AND ITS CARBONATE

- 4 - PROBLEMATIC

The Martian carbonates study is essential for the comprehension of the red planet’s paleo-climate. From their formation mode, i.e. the basaltic rocks alteration in the presence of and carbon dioxide, the carbonates can inform us about the CO2 atmospheric content and the presence of water on the planet at a time given by dating of the carbonate (e.g. Borg et al. 1999 for ALH 84001). It is then possible to determine the atmospheric pressure over Mars, CO2 being the chemical species most abundant in its atmosphere, like deducting the quantity and the mode of water run-off then presents on this planet.

Thanks to Mars surface images given by high resolution cameras flying onboard mission (like HiRISE on Mars reconnaissance Orbiter, and HRSC on Mars Express), it is today possible to affirm that water was present on this planet surface. Indeed, morphological features as valley networks were necessarily caused by the flow of this fluid.

Thanks to the data transmitted by instrument CRISM (Compact Recognition Imaging Spectrometer for Mars) of the probe Mars Reconnaissance Orbiter, a team of researchers from Brown University highlighted (Ehlmann et al. 2008) the presence of magnesium-rich carbonate deposits at the surface of Mars, in the Nili Fossae region. However, while waiting for the future Mars Sample Return mission, the only rocks available for analyses are the Martian meteorites (SNC).

The Space Research Centre of Leicester University (UK) has several samples of the Martian meteorite NWA 2737, the second Chassignite. This meteorite having been identified only five years ago has not yet been studied thoroughly.

Thus, the prime objective of this placement will be to carry out accurate quantitative analyses of the composition of major minerals making up the NWA 2737 meteorite, then comparing them with preceding results. Then, it will be a question of determining the terrestrial or pre-terrestrial origin of rare carbonates which can be found in this meteorite.

This work will give a report of pre-research for possible future studies concerning the clues which Martians carbonates could give us about the processes related to water on this planet. Nevertheless, if they seem to have been formed by terrestrial , it will be interesting to analyze them to understand their formation in a Martian rock. Indeed, they would constitute a good analogue to understand the carbonates formation in , whose martian origin has been confirmed (Wright et al. 1992, Harvey et al. 1992, Treiman et al. 1993).

- 5 - I. SNC PRESENTATION AND CHARACTERISTICS OF NWA 2737 METEORITE

I. 1. Martian meteorites The source of Martian meteorites was determined for the first time by studying the isotopic composition of the couple nitrogen/argon of these meteorites and by comparing the results with those obtained by the Viking probes in 1976. Until now they represent a group of 32 meteorites, derived from Mars by a product of 4 to 7 ejection events, probably from Tharsis and Elysium-Amazonis.

Names of these Martian meteorites groups are coming from the name of 3 famous meteorites of this class, respectively fallen in Shergotty (1865, in India), Nakhla (1911, Egypt) and (1815, the Haute-Marne, France). Martian meteorites are very young and have a crystallization age lower than 1,5 Ga, except for the meteorite ALH84001, the only orthopyroxenite Martian meteorite, whose age seems to be close to 4 Ga (e.g. Ash et al. 1996, Bogard and Garrison 1997-1999, Turner et al. 1997, Ilg et al. 1997).

The principal identifiable minerals in these stones are olivine, pyroxenes and feldspars. Nevertheless, all these groups have well determined characteristics that differentiated one from each other.

• Shergottites They are now classified in three sub-groups, for it became more than obvious with the new members discoveries that it represent a rather heterogeneous group, even if all are basaltic in nature. The original one gathers 10 members which make it the most abundant type of Martian meteorites. They all are igneous rocks of volcanic origin primarily made up of pyroxenes, olivine and plagioclases which were transformed into by the high pressure generated at the time of the impact which the ejection produced. Another one named the Lherzolites, is composed by 6 igneous cumulates stones primarily made up by medium-grained olivines and chromites that are poikilitically enclosed by large orthopyroxene crystals. They have probably crystallized as cumulates from residual basaltic melts in magma chambers. Finally, the newest one is named picritic shergottites as it gathers 9 stones with olivine-phyric texture, made up by olivine phenocrysts set in a basaltic groundmass of pigeonite, plagioclase shock-converted to maskelynite, minor augite, and olivine. Recent theories suggest that they originated from olivine-saturated magmas parental to basaltic Shergottites (Barrat et al. 2002). .

• Nakhlites All 7 members of this group are of a very similar appearance, and homogenous composition. They are Ca-rich clinopyroxenites, consisting of green cumulate augite crystals (more than 80% vol.) with ~10% olivine in a very fine-grained mesostasis.

- 6 - This mesostasis is made up of plagioclase, alkali feldspar, pyroxenes, iron-titanium oxides, sulfides and phosphates together with some carbonate (Bridges and Grady, 2000) Two theories are discussed about their origin: some think they were formed from magma plutons deep inside the Martian crust (e.g. Bunch and Reid, 1975), whereas some others (e.g. Friedman Lentz et al. 1999) advanced they would come from a lava flow near the Martian surface.

• Chassignites Chassignites group is formed by 2 cumulate rocks, resembling terrestrial dunites, and peridotites. They consist of about 90% Fe-rich olivine, minor clinopyroxene, feldspar, plagioclase, chromite, melt inclusions, and other accessory minerals and phases (Prinz et al. 1974, Beck et al. 2005,2006) Crystallization ages of about 1.36 Gy, (Jagoutz (1996), Misawa et al. (2005) and Marty et al. (2005)) and compositional and elemental trends indicate a relationship between the Chassignites and the Nakhlites, suggesting an origin from the same parent magma on Mars. However, the Chassignites show noble gas values different to those found in other SNC members or in the Martian atmosphere. It is suspected that these gases might originate from the Martian mantle, suggesting a formation within magma plutons deep inside the Martian crust for the Chassignites.

• Orthopyroxenite The only member of this Martian meteorite group is ALH 84001. This is a crystalline rock quite exclusively made up by orthopyroxene. The rock must has been formed they are 4.5 Gy from a magmatic room hidden in the depth of Martian crust. With the cooling of the silicated bath, pyroxene crystals started to be formed, before forming a deposit at the bottom of the magmatic room, where they accumulated and cemented to form an orthopyroxenite. ALH 84001 became famous because of the presence of certain microscopic structures in the shape of tubes which were considered during a certain time remainders of forms of bacterial life (McKay et al. 1996)

I. 2. NWA 2737 meteorite characteristics NWA 2737 is the second member of the Chassignite group. It has been found in the Moroccan Sahara in August 2000 by Carine Bidaut and Bruno Fectay. The stone appears as a black rock, fragmented in several pieces, with a total weight of 611g. Its typical color, due to a submission at extreme pressure which transformed olivine into a dark material, didn’t help scientists to recognize it as a meteorite. Its real nature has been revealed only four years later by chemical analyses: they have revealed that its isotopic composition well plot on the single O isotopic fractionation line of Martian meteorites. Furthermore, Fe/Mn (= 55) and Ga/Al (= 3.10-4) ratios correspond to those of the other Martian meteorites (Beck et al.2006; Connolly et al. 2006). It was then named Diderot, thus paying homage to the famous French encyclopaedist and the area of Langres (birthplace of Diderot), a few kilometers distant from the Chassigny village. But the only name recognized by the Meteoritical

- 7 - Society is NWA 2737, as this meteorite is the 2737th one found in Northern West Africa.

NWA 2737 is not highly altered by weathering. It has low U, Sr and Ba, which are the usual indicators or desert weathering (Barrat et al. 2003). However, the isotopic composition of Sr indicates at least some alteration (Misawa et al. 2005). This meteorite material originally crystallized ~ 1.3 b.y., but was severely shocked ~ 170 m.y. ago.

With 90% modal olivine, it is akin to a dunite, as is Chassigny (Beck et al. 2005; Mikouchi et al. 2005). However, it has a somewhat higher Mg/Fe ratio than that of Chassigny and is highly shocked (Van de Mooretele et al. 2007). Other important minerals are Pyroxene (Augite and Pigeonite), Chromite, Feldspar (mostly Sanadine), and Phosphate. Note as well Carbonate presence which certain are found to be offset by shock features (Beck et al. 2005, 2006); evidence that they may be from Mars.

Here is a table showing three studies about the volume percentage of most abundant minerals found in NWA 2737 (table from The Mars Meteorite Compendium, compiled by Charles Meyer).

Mineralogical Mode of NWA2737

Mikouchi et al. Treiman et al. Beck et al. 2005 2005 2007 Olivine 89.6 vol%. 89 85.1 Augite 3.1 3 5 Pigeonite 1.0 4 4 Chromite 4.6 3 2.9 Sanadine 1.6 Glass 1 2.2 Phosphate 0.2 Carbonate 0.9 Nanophase iron tr.

- 8 - II. SAMPLES AND ANALYTICAL TECHNIQUES

II. 1. Samples description

II.1.a. Samples preparation

All NWA 2737 analyses discussed hereafter were carried out starting from three samples. Those had already been prepared before the beginning of this placement. The first one hereafter called “Sample 1”, is a polished thin section of the meteorite. The other two ones, called “Sample 2” and “Sample 3” have been incorporated in resin, and then polished.

Figure 1 Figure 2

1 cm 1 cm

Figure 1: photo of the polished thin section (sample 1), which actually show two pieces of NWA 2737but only one has been analyzed Figure2: photo the polish block containing sample 2 (same appearance as sample3).

II.1.b. Carbon Coating

For their study with the Scanning Electron Microscope, samples surface have to be made conducting.

The three samples have been metalized by carbon coating. This technique consists in causing evaporation in the vacuum of carbon atoms contained in a stick, by heating it until its vaporization temperature, by an electrical current which crosses it. The carbon atoms are propagated then to the cold surface of the sample. Furthermore, for sample 2 and 3, silver-rich paint had already been spread on the polished block surface, from the sample to the metal support. That helps to reduce charging in the SEM chamber.

II. 2. Optical microscopy

Only the thin section, sample 3, has been the object of pre-analysis by optic microscopy. We used a reflectance and a transmission optical microscope with a digital camera connected to a PC in order to capture still images. These instruments allow magnification from 5x to 100x and a good resolution to image the films. It provides a useful set of context images before the Scanning Electron Microscope analyses.

- 9 - II. 3. Electronic microscopy analyses

II. 3. a. Working principle

Scanning electronic microscopy is an electronic microscopy technique based on the electron-matter interaction principle, offering some high resolution images of the sample surface. An SEM image, gives information about the samples’ topography and chemical composition. An SEM is composed by (see Appendix 1): - an optic electronic column, assembled on the sample chamber, in wich an electron beam is accelerated and rastered allowing the scanning of the sample. - a pumping circuit for a secondary vacuum. - a scintillator / photomultiplier to detect the secondary electrons. - a diode to detect backscattered electrons - two devices for analysis of photonic radiation: cathodoluminescence detector and x- ray spectrometer with energy selection (Si/Li diode cooled by liquid nitrogen connected to an amplifier system).

Electron beam emission

The source of electrons consists of a tungsten wire cathode in the shape of a V, which is directly heated by the joule effect (at a temperature of 2700K). The beam is then focused by a Wehnelt diaphragm. Finally, an anode, allows the electron beam to be accelerated through a potential of 10 to 20 kV.

Figure 3 Electron-matter interactions

Figure 3: Diagram of the electron-matter interactions

• The backscattered electrons are primary beam electrons that have reacted with the sample’s atoms in a quasi elastic way. They are returned in a direction close to their original direction with little loss of energy. Because of the fact that the probability of backscattering increase with the atomic number of the target atom, it is these electrons which are used to highlight the chemical contrast. Their energy is much more important (until 30 kV) than that of secondary electrons.

- 10 - • The secondary electrons result from the target atom ionization by an incident electron. Their energy is low. - it is possible to divert them to easily retrieve a large number on the detector and thus obtain an image with a good signal to noise ratio. - they can only go a small way in the sample because they are quickly arrested and therefore originate from a near surface layer giving an image with a very good resolution (with a beam diameter of 30Å, the resolution is about 40Å). So show the surface morphology and also have a relatively large depth of field.

• X-ray Photons During lifting of different electronics layers electrons of target atoms by the incident beam of electrons, the upper layers of electrons are energized to replace these ejected electrons, and thus produceX-ray photons. Their energy is equal to the difference in energy between the layer of the excited electron and the layer which will position the electron after de-excitation. Because these energy differences are specific to each atomic species they can be used to show the composition of the sample.

II. 3. b. Samples analysed by SEM

The prime objective of the analyses carried out with the SEM was to recognize the different component minerals in our NWA2737 meteorite samples. Three samples had a total surface area studied of approximately 16mm2. All composition studies were made with an EDX analyzer (Inca Oxford). First, we began to make spectral analyses, but this method proved to take too much time while it was then simply required to have an overall Figure of present minerals. So, elementary maps of several zones presenting a fitting of various minerals were carried out. Different parameters exploiting clearness from the results were modified. These parameters are: acquisition duration, the number of pixels per image, the number of scans. The principals elements to be quantified by energy dispersive technique, during analyses carried out on this type of Martian meteorite are oxygen, silicon, magnesium, potassium, iron, suffer, chromium, phosphorus, sodium and calcium.. These elements were mapped at the same time and each map obtained only corresponds to one element. This method allowed us to recognize pyroxene, chromite, phosphate, and feldspar minerals. Moreover, this method was enabled us to find carbonate grains in these zones rich in various minerals. Because calcium and phosphorus elements distribution seemed to be very closed, the interesting grains were identified by superimposing Ca and P elements maps on the studied zones Figures.

- 11 - The second objective was to carry out analyses of all minerals type composition (even carbonates found riming phosphates). In order to have very accurate results, we used standard to calibrate and verify the electron beam constancy. The standard used was pure nickel. Furthermore, for olivine, we had the possibility to use a sample of the Barwell chondritic meteorite, recognized as an international olivine standard, to check the calibration. In practice, the standard and the sample have to be in the chamber in the same time.

The quant optimization of a standard has to be done after a stabilisation of the electron beam and its environment (count 30 min after the sample was put in the chamber). During samples analyses, it’s possible to know if a new quant optimization is necessary by watching at the total weight % of all measured species: if this total has a too low value from expected one (near 100%), it means that a quant optimization has to be done. Thus, it is very important to not normalize the weight % results. During these measures, it appears that a quant optimization have often to be done, approximately every three analyses. All these analyses were performed with an accelerating voltage of 15kV and a 5.0µm-sized beam spot. Furthermore, because we know the sample is oxidized, we chose the oxygen element, as the combined element for stoichiometry in processing options. These really accurate analyses which need a very high magnification also revealed the presence of carbonates in very thin veins. Lastly, photos of interesting sites (mostly contenting carbonates), have been taken in back scattered electron (BSE). Furthermore, in order to keep a general detailed view of each sample, montages of all of them have been made with BSE Figures taken at a magnification of 250x or 350x.

- 12 - III. OBSERVATIONS AND DATA TREATMENTS

III. 1. Optic imagery

Most clear and detailed images of sample 1 (thin section) were obtained using the optical petrographic microscope, see Figures 4 and 5. First thing that appear is the cracked texture of the sample. These cracks seem to follow two perpendicular directions. Furthermore, although NWA 2737 meteorite has a dark appearance, images 4 and 5 reveal a brown colour of the olivine crystals. According to Treiman and al. (2007), these two phenomenon have the same origin: a shock event there at 170 Ma.

Figure 4 Figure 5

Figure 4 and 5: photos of sample 1 taken with a transmission microscope

These images also show the discolouration of olivine at certain areas. Picture 5 even exhibit broad colourless stripes (see Appendix 2 for other Figures of these features at a higher magnification). On these Figures, some chromite crystals can also be seen; they appear opaque.

III.2. SEM analyses

III.2.a. Samples general aspect

Sample 1 SEM analyses do not show longer these colourless stripes. Texture of sample 2 and sample 3 appear to differ from the thin section one. There are no apparently interstices between the olivine crystals.

- 13 - Figure 6 0.5mm Figure 7 0.5mm

Figure 6 and 7: montage of numerously BSE photos, of sample 1 and sample 2 respectively magnification 350x. Bulk mineral is olivine, and big minerals in light grey are chromite.

III.2.b. Carbonates

SEM analyses allowed us to find out two “types” of carbonates into NWA 2737 meteorite.

The first one was discovered riming phosphate (apatite) nodules, in sample 1 and 2

Figure 8 Figure 9

30 µm 30 µm

Figure 8: superposition of a BSE Figure and elements maps of Ca (red) and P (green), magnification 2000x. Yellow mineral is both Ca and P rich: it is a phosphate. Mineral in grey is feldspar, and the one in white is Ilmenite. Accurate chemical analyses prove that red zones correspond to carbonates. These carbonates width do not exceed 5 µm. Figure 9: original BSE Figure

- 14 - Second type has been found in veins or interstice between minerals.

Figure 10 Figure 11

60 µm 60 µm

Figure 10: superposition of a BSE Figure and elements maps of Ca (red) and P (green), magnification 2000x (high contrasted for a better see of the carbonate-rich veins and interstices between minerals). Yellow mineral is both Ca and P rich: it is a phosphate. Mineral in grey is feldspar, and pale red is pyroxene. Figure 11: original BSE photo, magnification 2000x.

III.3. Data treatment

III.3.a. Mineral composition

The minerals which mainly constitute NWA 2737 meteorite have all been the object of accurate chemical analyses. For most abundant minerals (i.e. olivine, feldspar, pyroxene and chromite), 10 analyses points were carried out on each sample in a random way (with an exception of 3 more for pyroxenes of sample2). For carbonates and phosphates, as many analyses as possible were done, there number differ according to the sample. All results were reported in Excel tables for then carry out calculation to obtain minerals composition. Data obtained for atomic % are normalized, on the contrary of weight % values.

For the four main minerals, calculations were directly made from atomic% values. On the other hand, composition calculations for carbonates and phosphates were not possible to be directly done from atomic% values. In carbonates case, because samples are carbon coated, real carbon content can not be given, and light elements are difficult to detect. Furthermore, for this last mineral as for phosphate, other anions than oxygen, chlorine and fluorine, were also measured. Because of there presence, atomic% values, which are normalized, are modified from the reality. Thus several intermediary calculations from weight% values were done to find their chemical formula.

III.3.b. Calculation of a chemical formula for carbonate and phosphate

The problem is that each element is directly determined as a weight percentage of oxide, even though the oxides doesn’t exist as such in the mineral.

- 15 - Chlorine and fluorine are shown as a weight percentage of oxide. For simplicity, we assume that these two elements are bonded to P atoms only, and yet the same atoms of P are recorded as a combined with oxygen in P2O5.. This implies an excess of recorded oxygen. To obtain a real total, a correction has to be done, by subtracting oxygen equivalent of chlorine and fluorine. When the real weight % of oxides is found, it is then possible to find the number of each ion in the chemical formula, by recover first the number of anions for each present oxide. See Appendix 3 where the followed procedure to calculate the chemical formula from a mineral analysis is reported and described by means of a phosphate example.

Note that for carbonates, when first corrections are done, carbon weight % is calculate assuming that this value represents the difference between total value normally expected (100 wt%), and the total value really obtained.

III.3.c. Mineral composition diagrams

In order to make rapid and visual comparisons between our results and ones previously obtained on this meteorite or on other Martian meteorite, composition diagrams were made for olivine, pyroxene and carbonate using the Triangular diagram plotting (TRI-PLOT) program (copyright © 2003 David Graham and Nicholas Midgley) of Loughborough University.

- 16 - IV. RESULTS AND DISCUSSION

IV. 1. Results and comparisons

IV.1.a. Olivine and Pyroxene

Calculated results from atomic% values show that olivine crystals are highly Mg-rich, with an Mg# range really equilibrated, between 76.6 and 80.5 for an average of 79.3 mol% (see Appendix 4-6). This result is consistent with the one found by Beck et al. (2005) which was Fo = 78.7±0.5 mol%. Note that, experimental errors were not calculated but according to the Barwell olivine analyses, they have to be sensible. Indeed, we exactly found the same Fo# as

recorded (Hutchison et al. 1988), as to say Fo75.5.

Concerning pyroxenes, most of the 33 analysed points, correspond to

orthopyroxene with a composition range from En81.5Wo3.9Fs20.8 to En77.3Wo1.2Fs16.4. There is also augite from En57.4Wo44.9Fs12.5 to En47.6Wo30.1Fs47.0, and only 2 analysed points of pigeonite from En75.1Wo7.7Fs16.9 to En74.1Wo9.3Fs16.6 (see Appendix 7-9).

Picture 4 Figure 12 Figure 13

Fo Fa

Figure 12: Major element compositions of pyroxenes and olivines in NWA 2737 (solid circles and solid square). The range of compositions for these minerals in the Chassigny meteorite (grey areas and grey square) is also shown for comparison (Floran et al. 1978). The dashed curves are the calculated isotherms for equilibrium relationships between coexisting pyroxenes in the Wo-Fs-En system (Lindsley, 1983). Beck et al. 2005-2006, Mikouchi et al. 2006. Figure 13: pyroxenes and olivine composition obtained during our analyses of NWA 2737.

The two diagrams clearly show that pyroxene and olivine have a similar Mg/Fe ratio. This implies that the rock has experienced a long period at high temperature which allowed the ions to migrate from one mineral to another and lastly made the whole rock homogeneous in Mg.

By comparing these two diagrams, it clearly appears that analysed pyroxenes are falling along the same tie-line. However, the orthopyroxene we analysed tends to be less Ca-rich than reported by Beck et al. Since no pyroxene standards were used during our analyses, these results differences could be explained by a calibration defect.

- 17 - Our results can also be compared to some Shergottites and Nakhlites composition (see Appendix 10). It shows that the meteorites whose pyroxene compositions are similar to NWA 2737 are the two olivine-phyric Shergottites SaU005 and DaG476.

IV.1.b. Feldspar

Feldspar analyses show mineral composition range from An16.1Ab77.5Or24.7 to An0Ab64.2Or18.0, (see Appendix 11-13).

Figure 14 Figure 15 at% at%

Figure 14: compositions of maskelynite (filled circles) and melt inclusion glass (open circles) in NWA 2737 (atomic molar proportions) For comparison, the compositional range of Chassigny maskelynites is indicated (grey area) as well as glasses from melt inclusions in Chassigny (dashed area). The data for Chassigny are taken from Floran et al., 1978. Beck et al. 2006. Figure 15: feldspar composition obtained during our analyses of NWA 2737.

These two diagrams show a quite good correspondence between our results for feldspar analyses, and those obtained by Beck et al. (2006) (their results range is An1-13Ab68-79Or15-23). However, no melt inclusions have been found during our analyses. These feldspars are only analbite. Comparing to Chassigny, feldspar range is really more restricted. As Beck et al., we didn’t find any plagioclase.

IV.1.c. Spinel

The only spinel present in NWA 2737 is chromite (see Appendix 14-16). Accurate analyses revealed an average number of Cr# 81.2 (100Cr/(Cr+Al)). Because of a lack of time, no specify studies have been led on chromite. However, these first results appear to be consistent with the chromite composition found for spinel in NWA2737 by Beck et al., that is Cr # between 72.0 and 83.4. Note that according to Beck et al. 2006, Chromite is zoned from core to rim. This hasn’t been studied during our analyses. This can explain the high value found for Cr # average comparing to the range found by Beck et al. can be explained by the fact that analyses have mostly been done in the core of chromite crystals.

- 18 - IV.1.d. Phosphate

Phosphate type determination was a bit difficult because the stoichiometry doesn’t perfectly correspond to one of these minerals. However, while comparing to other analyses carried out on phosphates, it appeared that our values (see Appendix 17-21) are closer from the apatite mineral. All contain both chlorine and fluorine (no hydroxide), with values up to 3.25 wt% for Cl and 5.29 wt% for F. These values are a little bit higher than those of Beck et al., who found apatite contains up to 2.7 wt%, and did not detect fluorine.

IV.1.e. Carbonate

Obtained results for carbonates composition (see Appendix 22-34) show very homogeneous values. Carbonates are clearly calcium-rich, with the following average composition: Ca# 93.07, Mg# 6.38, and Fe# 0.55. It is not yet possible to say if it’s question of calcite or aragonite, because grains are too little to be analysed at the transmission microscope using a polarized light which would help to determine their crystallisation system.

In order to compare carbonates found during our analyses to Martian carbonates, whole carbonates composition has been plotted on a diagram for carbonates found in ALH 84001, The ALH84001 carbonates are pre-terrestrial according to Knott et al. (1995), and Wadhwa and Lugmair (1996). We have also added results for NWA2737 carbonates riming apatite only (corresponding to site 1-3 of sample 1 and sites 1-9 of sample 2, see Appendix 22, 26-28, 32, 33) for comparing them to the ones found in veins or interstices.

Figure 16 at%

Figure 16: composition diagram for carbonates found in ALH 84001 Corrigan and Harvey 2004. Here is added in red the composition of whole carbonates found during our analyses, and in blue the composition of carbonates riming apatite.

While looking at this diagram, it appears that carbonates analysed in NWA 2737 do not show a compositional range as wide as theALH 84001 carbonate. However, the calcium-rich carbonates composition is exactly the same.

Comparing carbonates riming apatite, to those from veins and interstice, it appears that their composition is really similar. Thus there is no evidence to prove that these carbonates do not have a similar fluid origin.

- 19 - These results can also been compared to carbonate composition of some meteorites.

Figure 17

Figure 17: Composition (at%) of carbonate in the nakhlites. (A) Ca–Mg–FeCO3 of Lafayette (n=20). (B) Mn–Mg–FeCO3 of Governador Valadares (open squares within dashed ellipse, n=12) and Nakhla (n=41, triangles). Bridges and Grady, 2000.

These two Nakhlites carbonate composition diagrams show this mineral to not be as calcium-rich as in NWA 2737, but rather more iron-rich. Thus, there is no evidence for these carbonates to have a similar origin.

Figure 19 IV. 2. Discussion

IV.2.a. Mineral composition

Overall results of mineral composition analyses show quite similar values to those found by Beck et al. (2006).

Concerning pyroxene, the fact that they seem to better plot with two olivine- phyric Shergottites, is unexpected because normally clues indicate a closer origin between Chassignites and Nakhlites. This point has to be clarified later.

According to Bridges et al. (2002), chromite is a characteristic mineral to crystallize from basaltic or ultrabasic melts. The Cr# value found during our analyses appear to be less high than those of basaltic and lherzolitic shergotites (Cr# 74-87, Bridges et al. 2002) but similar to ALH 840001 and Chassigny. Thus NWA 2737 appears to be less primitive than lherzolitic and basaltic shergotites.

The apatite found in NWA 2737show a major atomic content of F and Cl and no OH: that is not completely consistent with values for Martian apatite. According to Filiberto and Treiman (2009), Martian meteorite apatite contains little OH with an average Cl:F:OH ratio of ~5:3:2, whereas terrestrial basaltic rocks contain little Cl and variable OH:F ratios. Thus, it may be possible that apatite analysed was weathered, which is consistent with a terrestrial weathering origin of carbonate (see bellow).

- 20 - IV.2.b. About carbonates

Contrary to the conclusions of Beck et al. (2006), we have not seen textural evidence of a pre-terrestrial origin such as shock-induced fractures dislocating a carbonate vein. Thus, we have to support that their origin is more likely to be terrestrial weathering. However though this process is not thought to have been very extensive on this meteorite, because it has low U, Sr and Ba, which are the usual indicators for desert weathering (Barrat et al. 2003). Furthermore, carbonates found using the CRISM instrument of the Mars Reconnaissance Orbiter, show a magnesium-rich composition (Ehlmann et al. 2008).

However, carbonates range of ALH84001 meteorite spreads from magnesium- rich carbonates to high-Ca carbonates whose composition is very similar to the ones found in NWA 2737 meteorite. Carbonates of this particular meteorite are supposed to be pre-terrestrial (according to Knott et al. 1995, and Wadhwa and Lugmair 1996), thus the possibility that NWA 2737 carbonates are pre-terrestrial cannot be ruled out completely

However, studies led by Lee and Bland (2004) about the weathering effect on meteorites recovered from hot deserts, show production of Fe-rich minerals, jarosite, Ca-sulphate, silica, barite and Ca-carbonates in the Acfer 019 meteorite (ordinary ), which has a terrestrial age of 19.8 ± 1.3 ka (Blend et al. 1998). Studies revealed that Ca-carbonate is compositionally relatively pure, containing an average of 98.6 wt.% CaCO3, 0.4 wt.% MgCO3, 0.9 wt.% FeCO3 and 0.1 wt.% MnCO3 (n=11 analyses). These carbonate compositions are close to those found in NWA 2737. That supports the idea that NWA 2737 carbonates are terrestrial in origin.

Composition similarity of carbonates found around apatite minerals with those located in veins or interstices lead us to think that those carbonates are from a terrestrial origin too. According to experimental studies led by Lee et al. (2006) on ordinary , chlorapatite (and feldspar) are especially susceptible to dissolution during terrestrial weathering on meteorites. Their results show that even very short periods of subaerial exposure will lead to dissolution of primary minerals and crystallization of weathering products that are likely to include Ca-carbonates among other things. Furthermore, this phenomenon can be amplified by a pH decrease (see Guidry and Mackenzie, 2003).

According to Ash and Pillinger (1995), although deserts are defined by their aridity, they are not entirely devoid of precipitation. Furthermore, NWA 2737 were found in Morocco, so at the edges of Sahara desert, where rain can be heavier than in the middle of the desert. Thus, NWA 2737 carbonate formation can be explained by fluids precipitation, following interactions with minerals contained in the meteorite. Moreover, fluid percolation can be enhanced in a desert since meteorite porosity can be increased by dilatation-contraction cycles due to very high temperature variation of the Saharan surface sand (from more than +80°C down to sub-zero) and even more for a black body (excess of 16°C hotter). This fluid may come from the meteorite surrounding environment and has been enriched in Ca and C elements during its crossing in the soil.

- 21 -

Thus, even if weathering on this meteorite was expected to be low, it must have been important enough to allow carbonate formation.

The theory of possible pre-terrestrial carbonates in the NWA 2737 meteorite comes from Beck et al. studies (2006). They made the assumption that parallel fractures apparently displacing carbonates veins showed that carbonates were pre- terrestrial (see Figure below).

Figure 18

Figure 18: Reflected light image of a possible pre- terrestrial (Martian) calcite vein in NWA 2737 (black arrows). The parallel shock-induced fractures crossing the pyroxene crystal (Px) may have dislocated the carbonate vein, and post-date calcite formation. No scale was provided. Beck et al., 2006.

Figure 19 Figure 19, taken during our analyses, also show orthogonal fractures. But on this Figure, it appears that the fluid filled the cracks.

Figure 19 Figure 19: BSE Figure of sample 3, showing a crack crossed by fractures and filled by carbonate. These seem to not have been affected by the fractures.

Site 3, sample 2 Ol

We suggest that the findings of Beck et al. may be explained by carbonate fluid filling the fractures rather than postdating them.

Ol

- 22 - CONCLUSION PART 1

This placement had as a prime objective to carry out precise chemical analyses of various minerals within the NWA 2737 Martian meteorite (second Chassignite), The results are compared to previous studies carried out on this meteorite and on other Martian meteorites. The second objective was to make a more detailed study of rare minerals contained in this meteorite, the carbonates, in order to determine their origin and their formation process.

The analyses were carried out at the SEM on three samples of NWA 2737 meteorite and revealed that principal minerals compositions, i.e. olivine, pyroxene (augite, pigeonite and orthopyroxene), spinel (chromite), feldspar (analbite) and phosphate (apatite), are really similar to the studies undertaken by Beck et al. (2006).

During our study of the carbonate, we discovered a new textural location of this mineral. I only found carbonate in veins or interstices between minerals, and rimming apatite nodules. All these carbonates have the same composition and are high-calcium.

As this particular composition has already been revealed in other meteorites to be of terrestrial origin, and no textural features suggesting a preterrestrial origin were found, we assumed that these carbonates were product from terrestrial weathering. Furthermore, terrestrial weathering explains carbonate rimming apatite. Thus, we do not support the conclusions of Beck et al. (2006) who suggested a preterrestrial carbonate origin.

Nevertheless, it would be interesting to study the relationship between carbonate and apatite by analyzing FIB-SEM section with a Transmission Electron Microscope (TEM). Furthermore, other carbonate composition checks have to be done on more materials, by analyzing a biggest surface area, because the possibility to find pre-terrestrial carbonate in NWA 2737 is still not lost.

- 23 -

PART 2:

ANALYSIS OF SUPERCONDUCTOR FILMS

- 24 - INTRODUCTION

An essential property of superconductors is their capability to expel magnetic flux when they are placed in a magnetic field and cooled down: this is called the Meissner effect. However, some superconducting samples also show another phenomenon: they attract the magnetic field, because of the Paramagnetic Meissner Effect (PME). It is already known that this last effect is a function of the magnetic field. Furthermore, some new research has shown that the PME depends on the critical temperature and on the surface superconductivity itself (Geim et al. 1998). In this project we study some conventional superconducting films (low-Tc superconductors). All films are made of lead and sandwiched between silicon oxide layers. Some previous PME analyses have already been performed on these samples by Dr. Daniel Brandt, and revealed interesting results. The objective of the work discussed here is to analyse the structure and the composition of the superconductors themselves. By using different types of microscopy, we aim to determine if the films are islanded or continuous, and if their edges are continuous or irregular.

I. METHOD

I.1. Samples preparation

All five superconducting films have a lead layer above a silicon oxide one, but their structures differ because of the thickness of those layers and the composition of other layers deposited on it. Here are the five samples’ characteristics: . Sample 1: 51nm SiO; 300nm Pb ; 52nm SiO . Sample 2: 52nm SiO; 5nm Pb; 52nm SiO . Sample 3: 500nm Au; 10.3nm SiO; 200nm Pb; 11.1nm SiO; 220nm Au . Sample 4: 52nm SiO; 20nm Pb; ~50nm SiO . Sample 5: 150nm Pb; 10nm SiO . All these samples have been deposited on VICTREX® PEEK™, a thermoplastic film especially designed to improve the semiconductor fabrication process, thanks to its specific properties such as wear resistance, electrostatic discharge control and tight tolerance.

I.2. Types of analyses made

Initially, the SEM was used to take pictures of the film edges, in order to see, at the same time, how the layers are superposed and what the sample surfaces look like. Additional images were taken while trying to tilt samples inside the chamber of the SEM so as to have a better view of the edges. Different parameters influencing image clarity were modified. It has been proven that the best pictures are achieved by the BSE detector, with an electron beam of 20kV, a

- 25 - spot size of 5 units, in a wet vacuum at approximately 1 Torr pressure. A wet vacuum is used so as to allow charge to dissipate and thus allow the electron beam to penetrate deeper (films only become superconducting at very low temperatures, near absolute zero). After these preliminary studies, different types of x-ray analyses were carried out. Initially, precise spectral analyses were made on diverse points of the edge area, along a line perpendicular to the sample boundary, in order to see the evolution of the film composition toward the border. Following this edge analysis, EDX maps of selected zones were made. These maps are a good means to map elemental distribution (Si, O and Pb). In order to have sufficient contrast within comparatively short exposure times, the maps were taken at a medium resolution of 256*208 and a process time of 5 units.

II. RESULTS

II.1. Optical images

Optical images allow us to see the different zones of the samples, especially thanks to the fact that the pictures obtained are coloured. The first thing that appeared on these pictures is the sample surface structure. Thus, sample 1 shows quite a continuous surface as compared to sample 2 which has lots of fractures on its surface (Pictures 19 and 20 respectively).

Figure 19 Figure 20

Figure 19: photo of sample 1 taken at the optic microscope, film in black, magnetisation 10x. Figure 20: photo of sample 2 taken at the optic microscope, film in blue, magnetisation 10x.

However, samples 4 and 5 (Figures 21, 22) seem to have a granular surface.

- 26 - Figure 21 Figure 22

Figure 21: Photo of sample 4 taken at the optic microscope, film in black, magnification 20x. Figure 22: Photo of sample 5 taken at the optic microscope, film in black, magnification 20x.

Note that sample 3 (Figure 23), which has gold layers, is in a very bad state to be analysed as it had been detached in large part from the PEEK™, when it was wrapped for PME measures. Nevertheless, Figures of still attached zones were taken at the optic microscope, but only at a little magnification, and no SEM analyses were made because a big part of the film rises perpendicularly to the PEEK™.

Figure 23 Figure 23: Photo of sample 3 taken at the optic microscope, magnification 10x. This image shows the film is very crinkled.

As has already been seen on previous photos, it appeared that the edges of most films are marked by a compositional gradient towards the boundaries which showed that the border of these films is not clear. That means all the layers from a same sample must not measure the same surface (Figures 24 to 31).

- 27 - Figure 24 Figure 25

Figure 24 and 25: Photos of sample 1 taken at the optic microscope, film in dark grey, magnification 20x and 50x respectively. These photos show the sample border is not composed like the entire sample surface: there is a clearer band which marks the film contours.

Figure 26 Figure 27

Figure 26 and 27: Photos of sample 2 taken at the optic microscope, film in blue, magnification 20x and 50x respectively. A thin band at the film border can be seen on these images.

Figure 28 Figure 29

Figure 28 and 29: Photos of sample 4 taken at the optic microscope, film in black and orange, magnification 20x and 50x respectively. It can be seen on these images that the film loses matter to the edges. There is also a thin blue border, with spherical grains on it. Note that these last grains are not found anywhere on this band witch it is all around the film.

- 28 - Figure 30 Figure 31

Figure 30 and 31: photos of sample 5 taken at the optic microscope, the films are granular, magnification 50x for the both figures. These two photos show two borders types. It can be seen on Figure 12, a loss of material toward the edge and a fractured grey band in border, whereas on Figure 13, the edges are very clear.

II.2. SEM analyses

. Sample 1 SEM images of sample 1 (Figures 14 and 15) show that the film surface seems to be quite granular at high magnifications. The band lighter in colour, seen on the optical microscope photos, does not appear clearly here. Actually, the film seems to gradually get thinner toward the edges.

Figure 32 Figure 33

Figure 32 and 33: Photos of sample 1 taken in backscattered electrons, film is in clearer grey. Lighter forms indicated by the blue arrows are artefacts due to water content in the chamber.

The spectra analyses of diverse points along a perpendicular line to the border are reported on Appendix 35. Data show a gradual reduction of Pb and Si quantity toward the edge, whereas the O element has a steady increase. This phenomenon can also be seen on X-ray maps from Appendix 36. Data for Si elements were expected, but not the increase of O to the outside of the film; normally, Si and O should have the same evolution. Furthermore, it appears that Si and Pb elements seem to have the same evolution whereas the Pb layer has to be

- 29 - below the first SiO layer. Thus it was rather expected that Pb would not appeared while Si is present in high quantity. . Sample 2 The SEM revealed that sample 2 (Figures 34 and 35) seems to be quite smooth, in spite of fractures at certain places. Note that these fractures are quite distant from one to another, with fracture separations of order 50 µm.

Figure 34 Figure 35

Figure 34 and 35: Photos of sample 2 taken in backscattered electrons, film is in clearer grey.

It appears on Figure 34 that grains were deposited on the film, especially towards the edges and in the fractures. From visual inspection, these grains appear to have been deposited on the film rather than being truly integrated with it. This is supported by some of the grains being located on or in the cracks. Figure 35 revealed a strange sort of border. Some spectral analyses were made on it to identify where the boundary between the film and the PEEK™ is. These analyses (see Appendix 37) show a quite constant decrease of the three elements towards the film border. Elements maps (see Appendix 38) show a similar pattern for Si and O, with a slight concentration decrease towards the edge. Conversely, it seems that Pb element is gaining in concentration towards the outside of the film. This may very well be explained by the thinning of the SiO layer surface, which helps reveal the layer of film Pb. Finally, the film border is well marked by a total disappearance of these three elements.

. Sample 4 As expected following the optic microscope analyses, sample 4 surface is highly granular.

- 30 - Figure 36 Figure 37

Figure 36 and 37: Photos of sample 4 taken in backscattered electrons, film is in clearer grey. The lighter form indicated by the blue arrow is an artefact due to water content in the chamber.

Figure 36 revealed fractures that are also present on few locations in the film. It also shows a clear band at the edge of the film (red arrow), which certainly corresponds to the ‘orange’ band already seen on photos taken with the optic microscope. Figure 37 shows another sort of border, less clear, with an already seen, on optic microscope photos, thin black band with unidentified white grains inside (yellow arrow). Some precise spectral analyses and elements maps were made on this last border (see Appendix 39 and 40). They globally show the same pattern of SI, O and Pb elements with a quite clear border.

. Sample 5 This sample shows a sort of mosaic structure, with smaller shapes on its contours.

Figure 38 Figure 39

Figure 38 and 39: Photos of sample 5 taken in backscattered electrons, film is in clearer grey. The lighter form indicated by the blue arrow is an artefact due to water content in the chamber.

The area photographed in Figure 38 seems to have a different structure from the rest of the film; rounded shapes are spaced on one another revealing a clear layer. Figure 39 shows important fractures that are certainly due to the assembly. We also see that the edge of this place is lightly detached exactly along the boundary between the biggest and the smallest forms. This confirms the structure variation of edges compared to the rest of the film. Some spectral analyses and elements maps of a similar region without fractures were made (see Appendix 41, 42). It reveals that the lead layer is well defined with a clear border. However, it is not the case for the

- 31 - SiO layer: Si abundance decreases little by little towards the edges but is still significant in spite of the supposed boundary, and oxygen is very abundant throughout the image. The fact that Si and O elements are decoupled is not understood yet.

III. DISCUSSION

III.1. Samples preparation

In light of the samples analysis, it appears clearly that rolling the film for the PME measures can damage them. Indeed, it creates fractures (sample 2), or a weakening of the film (sample 5), or even a detachment of some layers (sample 3).

III.2. Analyses techniques used

Images taken by optical microscope are interesting for a large true colour optical image of the samples, and to have a first idea of the structure surface of them, but these samples requires a much more powerful and accurate instruments for the film’s outlines analyses. The use of wet vacuum for the SEM analyses is necessary to stop the raster charging on the sample, but in the same time, shapes appear on the films due to water when the electrons beam remains on a long time on a zone. This brings important difficulties to analyses because the study area becomes very light and artefacts appear. Thus, the spectral analyses could be truncated by this phenomenon. Moreover, it appears that the electrons beam does not remain fixed during the spectral analyses. This has to be considerate in the case of element maps taken over a long time, and that could explain the fact that the edges viewed on elements maps do not coincide with the film’s one viewed on the image taken before the start of the mapping.

III.3. Results

All four samples, analyses with the SEM, seem to have a good enough quality for their PME experiments are taken in account. The surfaces are continuous; even if granular structures are seen on some samples, they are the structure of the entire layer itself and not the appearance of the layer below. Concerning the fractures of certain samples, they do not appear to be an issue because they are distant enough from one to another. As for the borders, they are well defined.

- 32 - CONCLUSION PART 2

These conventional superconductors analyses have been made in order to determine if the Paramagnetic Meissner Effect, which had already been measured on them, could be take in account. Thus, by using an optic microscope and a Scanning Electron Microscope, surfaces and edges of all samples were investigated. It appears that rolling these films for PME measures had damaged them, and made analysis of the one with gold layers analysis impossible. However, the used instruments were effective in getting good images of the films and studying their overall structure. Thus, it clearly appeared that the films’ surfaces were continuous and not fragmented. Moreover, even if the spectral analysis performed on SEM were not perfectly accurate, they are still sufficient to judge the films edges have a good enough quality. The studies led on the PME conducted on these samples can be taken into account. Nevertheless, it would be necessary to repeat this analysis with another sample of the film with gold layer.

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- 36 - Acknowledgments

I am most grateful to John Bridges for allowing me to work on rare Martian meteorites samples. I have also much appreciated his patience and comprehension given my difficulties in English.

I must also address my thanks to George Fraser without whom I wouldn’t have been able to come to the Space Research Centre and work on this subject I love.

Many thanks to Graham Clark for his invaluable technical assistance during SEM sessions and to Hitesh Changela for all the helpful discussions we had about Martian meteorites.

Lastly, I would like to thank Eric Chassefière who helped me a lot to find this placement.

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