Researches On The Growth Dynamics Of Crystalline Scheelite-Structure Films Prepared By Electrochemical Method

Electrochemical processing is an important technique for functional thin films fabrication in recent years, and also this technique is one of the Soft Solution Processing (SSP) methods. Compare to the conventional processing for functional thin films, electrochemical processing has not only the outstanding advantages in equipment simpleness, prepared processing simpleness, and one step formation of the thin films, but also the great potentional to the application because of the advantages for low cost, low energy consumption, high yield and the impact to environment etc.Using electrochemical technique to prepare the tungstate and molybdate thin films with scheelite-structure is the frondose application of electrochemical technique in functional thin films fabrication. Some international research groups have reported the crystalline thin films prepared by electrochemical technique, but that is only localization in the research on the preparation technics and technology, so the research on the growth propensity and the growth dynamics of the crystalline thin films is very lack.In fact, the experiment and theory research on the growth propensity and the growth dynamics of the crystalline thin films by using electrochemical technique has very important academic and realistic senses. This is because that: at first, the growth characteristic of crystalline thin films prepared by this technique have some common properties of the crystal (granules) free growth as well as some growth characteristics of crystalline thin films because of their unique preparation technique; then the substrates of the thin films participate in the electrochemical reaction as one of film's basic elements, thus this processing must has the characteristics of electrochemical reaction and the relevant growth dynamics . In a word, the study on its growth characteristic needs to consider not only crystal growth and crystalline thin films growth but also some relative problems of electrochemistry. So the research is different from the crystal growth, and different from the crystalline thin films growth prepared by other techniques.In this thesis, a serial of molybdate and tungstate thin films (including BaMoO₄, SrMoO₄, BaWO₄, SrWO₄, Ba_1-XSr_XMoO₄, Ba_1-x-ySr_XCa_yMoO₄ etc.) with scheelite structure which were prepared at suitable conditions in different time were directly prepared on molybdenum and tungsten metal substrates by electrochemical technique; the physical and chemical characteristics (including crystalline nucleus, granules, phase structure, surface morphology, composition and composition ratio) of prepared films were characterized by using XRD, SEM, XPS, AFM, FESEM, EDX; these prepared thin films were compared by landscape and portrait orientation; the growth propensity and the growth dynamics of the thin films were discussed; some problems (such as the growth unit, anionic coordination-polyhedra and complexation form ect) were discussed. The main conclusions with outstanding innovative features acquired from the present work are mainly as follows:(1) By using the control variable quantitative method, we control the physical quantities and correlated conditions (such as current density, surface roughness of substrate, reaction time, the pH value of solution, reaction temperature ect) as invariant except prepare time, and prepare vast scale initial growth thin films, medium-term growth thin films and confectioning thin films. A series of prepare work against the research on the growth propensity of the crystalline thin films isn't reported(2) The physical and chemical characteristics (including crystalline nucleus, granules, phase structure, surface morphology, composition and composition ratio) of prepared films were characterized by using XRD, SEM, XPS, FESEM, EDX, and have found some important experiment phenomenon which provides experiment proof for the discussion on the growth propensity of the crystalline thin films by using electrochemical technique. It is found that the growth of the crystalline thin films by using electrochemical method at their early stages possesses special characteristics as follows:â‘ There are integrated crystalline nucleuses at the beginning of growth;â‘¡The places where these crystalline nucleus and granules pile up and grow prior are those of the defects such as the fold, nick, disfigurement, and cave and convex inequality etc at the substrate;â‘¢The quantity and the size of the crystalline granules increase with the preparation time;â‘£The crystalline granules are dispersed gradually to all over of the substrate;⑤The {111} faces of the crystalline granules always appear during the growth;â‘¥The crystalline granule grows in the direction that its C axis is perpendicular to the surface of the substrate; and along with the extension of deposition time, the growth direction of the crystalline granule trends to its C axis being in the surface of the film. It is sure that the results are of great significance for crystal growth and for controlling the growth of crystalline films by using electrochemical method.The correlate research is not reported.(3) We compared the prepared thin films by landscape (different positively ion or negative ion) and portrait (different prepare time) orientation, and get a series of "the common characteristics"and "the individual characteristics" about the growth propensity of tungstate thin films, and molybdate thin films with scheelite-structure.The common characteristics are:â‘ The mechanism of the crystalline growth of the film is the same;â‘¡The shape of the crystalline nucleuses is integrated at the beginning of the formation of the nucleuses;â‘¢The places where these crystalline nucleus and granules pile up and grow are those of the defects such as the fold, nick, disfigurement, and cave and convex inequality at the substrate;â‘£The quantity and the size of the crystalline granules increase with the preparation time, the crystalline granules are dispersed gradually from sparseness to all over of the substrate; and⑤The {111} faces of the crystalline granules always appear during the growth. The individual characteristics are:â‘ The speed of nucleation of BaMoO₄ and SrMoO₄ crystalline thin films at their early stages is different; and the speed of crystal growth of the films is also different;â‘¡The shape and size of crystalline grains of the films are different; andâ‘¢The orientation of the crystalline grains of the films is differentThese results provide the classify proof for the discussion on the growth dynamics of the crystalline thin films by using electrochemical technique. This research is not reported.â‘£We have proceeded detailed discussion about some probloms of the crystalline thin films (such as nucleation velocity, granules growth velocity, film forming velocity, density of thin films ect) from the growth dynamics specialllly energy, and explain some new experiment phenomenon. This research is not reported.⑤Some probloms about scheelite-structure crystalline thin film which contain crystal nucleus formation and growth, anionic coordination-polyhedra growth units, structure of granules, crystal trend, growth orientation, thin film formation process, thin film growth mode, crystalline thin film structure etc. This research is not reported.