Chemical vapor deposition of Al, Fe and of the Al13Fe4 approximant intermetallic phase : experiments and multiscale simulations

Films containing intermetallic compounds exhibit properties and combination of properties which are only partially explored. They carry potential solutions to confer multifunctionality to advanced materials required by industrial sectors and to become a source of breakthrough and innovation.Metalorganic chemical vapor deposition (MOCVD) potentially allows conformal deposition on, and functionalization of complex surfaces, with high throughput and moderate cost. For this reason, it is necessary to control the complex chemical reactions and the transport mechanisms involved in a MOCVD process. In this perspective, computational modeling of the process, fed with experimental information from targeted deposition experiments, provides an integrated tool for the investigation and the understanding of the phenomena occurring at different length scales, from the macro- to the nanoscale. The MOCVD of Al-Fe intermetallic compounds is investigated in the present thesis as a paradigm of implementation of such a combined, experimental and theoretical approach. Processing of the approximant phase Al13Fe4 is particularly targeted, due to its potential interest as low-cost and environmentally benign alternative to noble metal catalysts in the chemical industry. The attainment of the targeted Al13Fe4 intermetallic phase passes through the investigation of the MOCVD of unary Al and Fe films. The MOCVD of Al from dimethylethylamine alane (DMEAA) in the range 139oC-241oC results in pure films. Increase of the deposition temperature yields higher film density and decreased roughness. The Aldeposition rate increases to a maximum of 15.5 nm/min at 185oC and then decreases. Macroscopic simulations of the process predictdeposition rates in sufficient agreement with experimental measurements, especially in the range 139oC-227oC. At higher temperatures, competitive gas phase and surface phenomena cannot be captured by the applied model. Multiscale modeling of the process predicts the RMS roughness of the films accurately, thus allowing the control of properties such as electrical resistivity which depend on the microstructure. The MOCVD of Fe from iron pentacarbonyl, Fe(CO)5, is investigated in the range 130oC-250oC for the possibility toobtain fairly pure Fe films with low Oand C contamination. The surface morphology depends strongly on the temperature and changes are observed above 200oC. The Fe deposition rate increases up to 200oC, to a maximum of 60 nm/min, and then decreases. Moreover, the deposition rate decreases sharply with increasing pressure. Computational predictions capture accurately the experimental behavior and they reveal that the decrease athigher temperatures and pressures is attributed to the high gas phase decomposition rate of the precursor and to inhibition of the surface fromCO. The multiscale model calculates RMS roughness in good agreement with experimental data, especially at higher temperatures. Upon investigation of the two processes, aseries of Al-Fe co-depositions performed at 200oC results in Al-rich films with a loose microstructure. They contain no intermetallic phases and they are O-contaminated due to the reaction of the Al with the carbonyl ligands. Sequential deposition of Al and Fe followed by in situ annealing at 575oC for 1 h is applied to bypass the Ocontamination. The process conditions of Fe are modified to 140oC, 40 Torr and 10 min resulting in O-free films with Al:Fe atomic ratio close to the targeted 13:4 one. Characterization techniques including X-ray diffraction, TEM an

Experimental and computational investigation of chemical vapor deposition of Cu from Cu amidinate

Experiments and computations are performed for the CuMOCVD fromcopper(I) N,N′-di-isopropylacetamidinate [Cu(iPr–Me–amd)]2 or [Cu(amd)]2 where amd = CH(CH3)2NC(CH3)NCH(CH3)2. The a priori choice of this precursor is dictated mainly by its oxygen and halogen–free ligands allowing co-deposition with oxophilic elements such as Al and by its ability to provide conformal Cu films in atomic layer deposition processes. The nucleation delay and the deposition rate as a function of deposition temperature and the evolution of the deposition rate along the radius of the substrate holder are experimentally determined with depositions performed at 1333 Pa in a vertical, warm wall, MOCVD reactor. With the aim to propose a kinetic scenario for Cu deposition, based on recently published experimental results for the decomposition of [Cu(amd)]2, a predictive 3D model of the process is built, based on the mass, momentum, energy and species transport equations. In agreement with the previously mentioned experimental results, it is demonstrated that a single surface reaction is responsible for the deposition of Cu. Two surface kinetics expressions are implemented depending on the deposition regime; a simple Arrhenius type expression in the reaction limited regime and a Langmuir–Hinshelwood type expression prevailing in the transport limited regimewhich takes into account the inhibition effects. The two different kinetics designate a modification in the surface reaction mechanism. The results show good agreement between experiments and computations. Complementary computations are performed, in order to compare the deposition rates of the Cu films deposited via the [Cu(amd)]2 and the (hfac)Cu(VTMS) and Cu(hfac)2 so as to determine relative advantages and disadvantages of Cu MOCVD from [Cu(amd)]2

Combined Macro/Nanoscale Investigation of the Chemical Vapor Deposition of Fe from Fe(CO)5

Experiments and computations are performed to model the chemical vapor deposition of iron (Fe) from iron pentacarbonyl (Fe(CO)5). The behavior of the deposition rate is investigated as a function of temperature, in the range 130–250 °C, and pressure in the range 10–40 Torr. Furthermore, the evolution of the surface roughness is correlated with the deposition temperature. By combining previously published mechanisms for the decomposition of Fe(CO)5, a predictive 3D macroscale model of the process is built. Additionally, a nanoscale and a multiscale framework are developed for linking the evolution of the surface of the film with the operating conditions at the reactor scale. The theoretical predictions from the coupled macro/nanoscale models are in very good agreement with experimental measurements indicating poisoning of the surface from carbon monoxide and decrease of the film roughness when temperature increases

Multiscale modeling and experimental analysis of chemical vapor deposited aluminum films : Linking reactor operating conditions with roughness evolution

When composition and crystallographic structure remainconstant, film properties mainly depend on microstructure and surface morphology. In this case,the proper modeling of agrowing film allows linking the final surface features with the operating conditions at the reactor scale which in turn enables the control of theproperties of the final film. In this work, an experimentally supported,coarse-grained, multiscale framework is applied for the modeling of the surface roughness of aluminum thin films processed by chemical vapor deposition from dimethylethylaminealane. The multiscale framework is developed by linking macroscopic transport phenomena based on continuum mechanics models with nanoscale surface events which are simulated stochastically. The model reproduces experimentaldata successfully,thus validating the method with good statistics. Finally,modeling of surface roughness enables the estimation of the electrical resistivity in good agreement with corresponding measurements

Chemical Vapor Deposition of Al13 Fe4 Highly Selective Catalytic Films for the Semi-Hydrogenation of Acetylene

Catalytic properties of coatings containing the Al13Fe4 intermetallic phase are tested in the reaction of semi-hydrogenation of acetylene. The selectivity to ethylene is found as high as 74% close to the reported values for pure,unsupported Al13Fe4. The initial conversion of acetylene to ethylene is 84% and rapidly drops due to the catalytic formation of carbon-based by-products on secondary Al-Fe phases. Coatings are processed through sequential chemical vapor deposition (CVD) of aluminum (5 Torr, 180 °C) and iron(40 Torr, 140 °C) layers, followed by in situ annealing for 60 min at 575 °C.Deposition proceeds at high growth rate, resulting in 15 μm thick films. After annealing, coatings are composed of the Al13Fe4 phase, co-existing with minor secondary Al-Fe intermetallic phases. Overall, it is shown that films containing complex Al-Fe intermetallic phases can be processed by CVD, opening new routes to the engineering of pure, supported Al13Fe4 catalysts on 3D or porous supports

Growth of Carbon Nanofibers and Carbon Nanotubes by Chemical Vapour Deposition on Half-Heusler Alloys:A Computationally Driven Experimental Investigation

The possibility of directly growing carbon nanofibers (CNFs) and carbon nanotubes (CNTs) on half-Heusler alloys by Chemical Vapour Deposition (CVD) is investigated for the first time, without using additional catalysts, since the half-Heusler alloys per se may function as catalytic substrates, according to the findings of the current study. As a carbon source, acetylene is used in the temperature range of 700–750 °C. The n-type half-Heusler compound |(Zr0.4Ti0.6)0.33Ni0.33(Sn0.98Sb0.02)0.33 is utilized as the catalytic substrate. At first, a computational model is developed for the CVD reactor, aiming to optimize the experimental process design and setup. The experimental process conditions are simulated to investigate the reactive species concentrations within the reactor chamber and the activation of certain reactions. SEM analysis confirms the growth of CNFs with diameters ranging from 450 nm to 1 μm. Raman spectroscopy implies that the formed carbon structures resemble CNFs rather than CNTs, and that amorphous carbon also co-exists in the deposited samples. From the characterization results, it may be concluded that a short reaction time and a low acetylene flow rate lead to the formation of a uniform CNF coating on the surface of half-Heusler alloys. The purpose of depositing carbon nanostructures onto half-Heusler alloys is to improve the current transfer, generated from these thermoelectric compounds, by forming a conductive coating on their surface

Investigation of reaction mechanisms in the chemical vapor deposition of al from DMEAA

We propose a novel reaction scheme for the chemical vapor deposition (CVD) of Al films on substrates from dimethylethylamine alane (DMEAA), supported by the prediction of the Al deposition rate as a function of process temperature. The scheme is based on gas phase oligomerizations of alane which form a substantial amount of intermediates. Combined with reversible surface dehydrogenation steps, the global deposition reaction is composed of a set of 12 chemical reactions. This new scheme entails four intermediates and includes side reactions that play an important role in the formation of Al thin films. The chemistry mechanism is incorporated in a 2D Computational Fluid Dynamics (CFD) model of the CVD reactor setup used for the experimental investigation. The simulation predictions of the Al deposition rate are in good agreement with corresponding experimental measurements. The success of this novel reaction pathway lies in its ability to capture the abrupt decrease of the deposition rate at temperatures above 200 °C, which is attributed to the gas phase consumption of alane along with its increased desorption rate from the film surface

A study of the Chemical Vapor Deposition (CVD) of copper and aluminum

108 σ.Στην εργασία εξετάζεται η χημική απόθεση χαλκού και αλουμινίου από ατμό τόσο μέσω πειραμάτων όσο και με προσομοιώσεις και υπολογιστική ανάλυση. Σκοπός της εργασίας είναι η εξαγωγή διαγραμμάτων ρυθμού απόθεσης υμενίων χαλκού και αλουμινίου πάνω σε υποστρώματα καθώς και διαγραμμάτων Arrhenius βασιζόμενα στο ρυθμό απόθεσης. Τα διαγράμματα αυτά προκύπτουν από τη διεξαγωγή πειραμάτων αλλά και από τη διεξαγωγή υπολογιστικών προσομοιώσεων. Η μελέτη της χημικής απόθεσης αλουμινίου από ατμό είναι συνέχεια πρόσφατης εργασίας, τόσο για το πειραματικό μοντέλο όσο και για τις υπολογιστικές αναλύσεις. Μέσω των υπολογιστικών αναλύσεων εξετάζεται στην παρούσα εργασία η κινητική Arrhenius που χρησιμοποιεί ο υπολογιστικός κώδικας Fluent, για να εφαρμοστεί στη συνέχεια στο υπολογιστικό μοντέλο της χημικής απόθεσης χαλκού από ατμό. Τα πειράματα διεξήχθησαν στην Τουλούζη της Γαλλίας στο "Master Reactor" του εργαστηρίου Centre Interuniversitaire de Recherche et d'Ingénierie des Matériaux (CIRIMAT) του πανεπιστημίου Institut National Polytechnique de Toulouse (INPT) μόνο για το χαλκό, ενώ για το αλουμίνιο χρησιμοποιήθηκαν δεδομένα πειραμάτων που είχαν πραγματοποιηθεί παλαιότερα στον ίδιο αντιδραστήρα. Οι υπολογιστικές προσομοιώσεις έγιναν με τη χρήση του υπολογιστικού κώδικα Fluent. Στην εργασία επιχειρείται προσαρμογή του ρυθμού αντίδρασης, ώστε να επιτυγχάνεται καλύτερη προσέγγιση των πειραμάτων. Παρουσιάζεται ο ρυθμός απόθεσης του χαλκού και του αλουμινίου κατά μήκος του υποστρώματος (wafer) και τα συγκριτικά διαγράμματα Arrhenius των υπολογιστικών προσομοιώσεων και των πειραμάτων.In this thesis the Chemical Vapor Deposition (CVD) of copper and aluminum is studied, through experiments and computational simulations. In particular the deposition rate of these two materials on the surface of wafers is measured and theoretically predicted. Copper deposition is studied trough experiments and computational simulations. The aluminum deposition is simulated in order to validate the model with existing experimental results. The experiments were carried out at the reactor CMA of the Centre Interuniversitaire de Recherche et d'Ingénierie des Matériaux (CIRIMAT) in Institut National Polytechnique de Toulouse (INPT). For the computational simulations the code FLUENT was used. The results include the fitting of the pre-exponential factor in the reaction rate so as to get a reasonable agreement of theoretically predictions with experimental measurements. The deposition rate along the wafer and the comparative Arrhenius plots for computational simulations and experiments are presented.Ιωάννης Γ. Αβιζιώτη

Coarse-grained computation for cell polulation balances

58 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Υπολογιστική Μηχανική”Βασικός στόχος της παρούσας εργασίας είναι η ανάπτυξη μιας υπολογιστικής μεθοδολογίας που επιτρέπει την αποτελεσματική μελέτη της μακροσκοπικής συμπεριφοράς συστημάτων, η περιγραφή των οποίων είναι διαθέσιμη σε επίπεδο μικρο-κλίμακας, χωρίς την ανάγκη εξαγωγής ενός μοντέλου διαφορικών εξισώσεων που να περιγράφει τη δυναμική συμπεριφορά σε επίπεδο μακρο-κλίμακας. Αντιμετωπίστηκαν προβλήματα ισοζυγίων κυτταρικών πληθυσμών, στα οποία διερευνάται η επίδραση της κυτταρικής ετερογένειας στο φαινότυπο κυττάρων που φέρουν το ίδιο ρυθμιστικό γενετικό δίκτυο. Η μελέτη αυτή αναδεικνύει ένα δρόμο για τη γεφύρωση του χάσματος μεταξύ κλιμάκων που διαφέρουν κατά τάξεις μεγέθους (κύτταρο – φαινότυπος κυτταρικού πληθυσμού). Στο πρώτο στάδιο της εργασίας κατασκευάστηκε ένας στοχαστικός αλγόριθμος kinetic Monte Carlo ο οποίος περιγράφει τη συμπεριφορά κυτταρικών πληθυσμών. Πραγματοποιήθηκαν προσομοιώσεις με τη χρήση του αλγορίθμου, οι οποίες οδήγησαν στη χρονική εξέλιξη του εξεταζόμενου συστήματος μέχρι αυτό να φτάσει στη μόνιμη κατάσταση. Στη συνέχεια, αναπτύχθηκε υπολογιστικός κώδικας για την αδρομερή προσομοίωση του συστήματος. Κατά τους αδρομερείς υπολογισμούς ενδιαφερόμαστε για τα στατιστικά μεγέθη του πληθυσμού (μέση τιμή, τυπική απόκλιση-ροπές χαμηλότερης τάξης), τα οποία αποτελούν τη μακροσκοπική πληροφορία που εξάγεται από τις στοχαστικές προσομοιώσεις που έχουν διεξαχθεί σε επίπεδο μικρο-κλίμακας. Οι αδρομερείς υπολογισμοί απαιτούν σημαντικά λιγότερο υπολογιστικό κόστος από την ευθεία εφαρμογή του στοχαστικού αλγορίθμου. Μέσω αυτών εξετάζεται το κατά πόσο οι προκύπτουσες κατανομές είναι ακριβείς στην περιγραφή της συμπεριφοράς του πληθυσμού. Μετά την ανάπτυξη του αδρομερούς προσομοιωτή, πραγματοποιήθηκε παραμετρική ανάλυση, με σκοπό να διαπιστωθεί αν για κάποιες τιμές παραμέτρων ο φαινότυπος του κυτταρικού πληθυσμού εμφανίζει πολλαπλότητα λύσεων (συγκεκριμένα διπλο-ευστάθεια). Σε πρώτη φάση έχει επιτευχθεί μόνο ο υπολογισμός ευσταθών καταστάσεων, με τη χρήση της επαναληπτικής μεθόδου Newton-Raphson που διαμορφώνεται κατάλληλα για να ενσωματώσει την αδρομερή περιγραφή του συστήματος. Για τον υπολογισμό καταστάσεων που ανήκουν στον ασταθή κλάδο είναι απαραίτητη η μελλοντική εφαρμογή της μεθόδου μήκους-τόξου (arc-length continuation), η οποία, επίσης, πρέπει να διαμορφωθεί λαμβάνοντας υπόψη τις αδρομερείς προσομοιώσεις.The main objective of this thesis was the development of a computational methodology that allows the efficient analysis of the macroscopic behavior of systems, the description of which is available only at the micro-scale level, without the need to extract a set of differential equations describing the dynamic behavior at the macro-scale level. For this purpose, cell populations were considered, where the effect of the cellular heterogeneity in cell phenotype carrying the same regulatory network, was investigated. The analysis of cell population balances reveals a path for bridging the gap between scales, varying over few orders of magnitude (cell-phenotype of the cell population). At first, a kinetic Monte Carlo algorithm was developed that describes the behavior of the cell population. Simulations using this algorithm were performed to observe the time evolution of the investigated system until it reaches steady state. Then, an algorithm for coarse-grained simulations was built. In these simulations we are interested for the statistics of the cell population (mean value, standard deviation-generally for low-order moments), which are the macroscopic information extracted from the micro-scale through stochastic simulations. Coarse-grained computations require significantly less computer time compared to the direct implementation of the detailed algorithm and result to distributions which are accurate in describing the dynamics of the cell population. In the last part of this thesis, a bifurcation analysis was attempted with the purpose to determine the existence of bistability regions in the phenotype of the cell population, for a range of parameter values. In this work, we were able to compute only stable branches by means of Newton-Raphson iteration appropriately designed as to incorporate the coarse-grained description of the system. Along the same lines, an arc-length continuation algorithm is necessary to enable the calculation of phenotypes on unstable branches.Ιωάννης Γ. Αβιζιώτη