One important part of the motivation for this research work comes from the microelectromechanical systems (MEMS) technology. Its basic concept of high volume production and low unit cost can only be achieved when the devices made by microelectronics technique are reliable. The success in this area largely depends on the understanding of materials. However, the mechanicalcharacterization is lagged behind the theoretical work and designing software development. The standard characterization method is still not established. For MEMS actuators, especially for active materials, the desired characterization system for obtaining mechanical properties requires load control feature and the capability of doing dynamic tests. However, there is no such method among the currently available tools for mechanicalcharacterization.
62 3.2.3 Accounting for Non-uniformities
Unfortunately, there are many thin film deposition methods currently used that make it difficult to agree with all the assumptions used in the Stoney equation. For example, depending on the system parameters of magnetron sputter deposited films, film thickness, quality and deposition rates may be difficult to keep uniform across the area of a substrate. Magnetron sputtering systems have found wide application in commercial coating processes, particularly for the deposition of thin metallic films. Their acceptance is due to the possible combinations of high current densities at moderate voltages and reduced gas scattering of the sputtered atoms at low operating pressures, which results in higher depositions rates than non-magnetron systems. However, magnetron systems do have some disadvantages when it comes to film thickness uniformity. It has been widely studied that film thickness uniformity can be affected by non-uniform magnetic fields, gas pressure, target to substrate distance and shealth thickness in magnetron systems [28- 33].
2 Design of the biaxial tensile machine
The tensile machine has been designed to allow loading along two normal axes cruciform substrates coated by the studied films. The machine is composed of four identical module components. Each module contains a motor, a force sensor and a cylindrical fixation. The weight of the device is 3.5 kg and its size is 19×19×8.5 cm³ with a free space at the centre. The cruciform substrates were coated at their centre only and gripped by a cam rotating in the cylinder fixation. The machine can apply forces up to 200 N. A polymeric substrate is chosen to minimize its mechanical contribution to the total response of the film / substrate set since we are interested here in the film mechanical behaviour. Furthermore, the polyimide substrate is expected to behave elastically in the investigated strain range for metallic film (maximum of 0.4 %). Here, we used 125-µ m-thick polyimide substrate (sofimide® from MICEL). Fig. 1 shows the machine with a gripped cruciform specimen.
Imaging of the scratch path is used to correlate the type of mechanical failure mode with the applied normal force. Other measurements taken to characterize the failure
mechanism of the coating include the tangential force and acoustic emission.
It is important to note that this test although being relatively simple has its limitations. The principal limitation with this method is the thickness of the sample coating. Coatings with thickness’ below 0.1 µm and above 30 µm are not recommended for testing with this instrument. Test parameters, specimen condition and properties also have to be rigid for valid data to be obtained. For instance, a flat coating surface is recommended for the test. If the surface is not flat, it may result in skipping, bouncing and sticking of the stylus as it draws the scratch on the specimen surface. Consequently, critical data from the test may not be recordable or legitimate .
In this paper, the second harmonic method was applied to thin PMMA layers deposited onto silicon wafer. To calculate correctly the mechanical properties, it was necessary to recalculate the derivative of the contact stiffness with respect to the displacement in order to account for the variation of the elastic modulus versus indentation depth. This calculation was performed using the model of Bec et al. [10,11]. Experimental application shows precise properties measured at small indentation depths with both CSM and second harmonic methods, with a better accuracy for second harmonic method at low a/t ratio. At high indentation depth, a significant difference between experimental and numerical results was observed. A Finite Element investigation coupled with AFM observation of indentation print evidenced that classical contact models fail to compute accurately both h c /h ratio and dh c /dh leading thus to an overestimation of the mechanical properties.
heated water bath. Thiourea (SC (NH 2 ) 2 ) was then added into the mixed solution under stirring condition. Thereafter tin chloride solution, used as Sn source for doping of ZnS Was added. NH 4 OH was added drop-wise using a burette to maintain alkaline solution at a pH of 9. When the deposition temperature reached 80±1°C, pre-cleaned glass slides were introduced vertically inside the substrate holder, dipped into the solution and left for deposition for 30 minutes. After completion of film deposition, the samples were removed from the beaker and allowed to cool. The deposited films were then rinsed with de-ionized water to remove soluble impurities and dried. The film samples were prepared at different tin chloride concentration ratios by volume. The deposition parameters are summarized in table 1.
Annealing is a thermal treatment used for several purposes: to active dopants, to modify bonds of bonded wafers, to densify films and to reduce residual stress in materials. Annealing changes physical and chemical properties of thinfilms since annealing induces modification of film composition, reduction of pin-holes, increasing of grain sizes. Therefore, annealing influences the crystallinity and to the mechanical properties of materials. However, if thin film is deposited at temperatures comparable to the annealing temperature, then only minor residual stress changes can be observed after annealing. This is associated due to low thermal stress induced by annealing. For instance, LPCVD films have stable tensile stress during and after annealing. In contrast, if films are grown at lower temperatures than of annealing and have different expansion coefficients from a substrate, dramatic stress changes can take place. For example, the residual stress of PECVD silicon oxide films after annealing >800 °C become more compressive since the thermal expansion coefficient of silicon oxide is much lower than of silicon substrate (3.08 ppm/°C for silicon versus 0.55 ppm/°C for silicon oxide) and therefore the film is unable to shrink as much as silicon during cooling to room temperature, leading to compression of the film. If annealing of PECVD silicon oxide is performed at 500–550°C, then most of hydrogen and moisture diffuse out, and film can even experience tensile stress due to microstructure changes induced by hydrogen reduction from the film. PECVD silicon nitride films exhibit different behavior from PECVD silicon oxide upon annealing at temperatures >600°C due to very small difference of thermal expansion coefficients with silicon (the difference is only 0.8 ppm/°C). During the annealing, silicon nitride film losses hydrogen and stress rapidly changes from compressive to tensile and stays tensile after the cooling to the room temperature . Figure 20 displays schematic representation of the mechanism of hydrogen loss in PECVD Si 3 N 4 film during annealing.
A scanning electron microscope, performed with a SEM model EVO-MA10 (Zeiss) was necessary to observe the morphology of the films.
During the depositions, a piece of silicon wafer was placed on the sample in order to produce a step to determine the thickness of the deposited films with a mechanical profilometer model Tencor Instruments Alpha-Step 500.
undergraduate education, Mahmut’s intention was to become a mechanical engineer like his father and his brother in law. He later recognized that he likes science more than engineering and hoping that he would be more involved in science he took lots of courses related to micro-electronics. As he learned more about the operation of micro- electronic devices, Mahmut started to think that revolutionary advancements in micro- electronics technology are strongly tied to advancements in materials chemistry and physics. Therefore he selected Material Science and Engineering as a major and Physics as his minor. During his undergraduate education, he had the chance to preform research with brilliant scientists who migrated to Turkey from the USA and Soviet Russia. This way, he was able to see that there can be lot of different
2 Professor, Department of Mechanical Engineering, R.V.College of Engineering, Bangalore, Karnataka, India Abstract - Pure Zno,2% and 4% Ag doped ZnO (SZO) thinfilms synthesized on silicon substrate by varying parameters like doping concentration, number of layers , spinning speed and annealing temperature using low cost sol-gel method. The effect of silver doping on structural, morphological, and electrical properties of SZO films were investigated. The X-Ray Diffraction (XRD) indicated the poly crystalline nature having hexagonal wurtzite crystal structure. Scanning Electron Microscopy (SEM) shows uniform distribution of spherical grains and increasing annealing temperature increases the c-axis orientation and crystal size of the film. The morphologies, surface roughness and film thickness were observed by Atomic Force Microscopy (AFM). Analysis of variance showed, Silver doping concentration was influenced by 80.71 % for roughness, 85.56 % for thickness and 90.84 % for conductivity. Regression model R 2 value indicated 87.92 % for roughness, 89.27 % for thickness and 98.04 % for conductivity. Comparison of initial process parameter with Grey theory prediction showed that roughness increased from 14.20 nm to 21.34 nm, thickness decreased from 226.21 nm to 198.33 nm, and conductivity increased from 136.24 nA to 328.61 nA.
ceramics also have high acoustic impedance and low flexibility . Necessary care should be taken for the preparation of such PT based materials. So to avoid these difficulties, substitution of cations in sites A or B in PT composition has been extensively required. Otherwise this will cause the micro or macro cracking in the material. These micro-cracking are considered to be responsible for the decrease in the dielectric and piezoelectric properties of the materials. This material has poor mechanical properties due to its large tetragonal strain. Hence in order to reduce the large tetragonal strain and maintain the high mechanical stability there is need to dope PT systems with proper substituent.
atmosphere from 450°C during heating or at the beginning of the cooling phase. Composite films with different phase ratios could be obtained, depending on the temperature for changing from inert to oxidizing atmosphere. Both the heat-treatment atmospheres and the film thickness, which decreases with increasing spin velocity and with decreasing concentration of the precursor solution, were found to be important parameters in controlling the phase ratios of the films. The results open for tailoring of chemical and physical properties through control of thickness and phase compositions in cobalt oxide and composite films. This is interesting for practical application such as catalysis, as well as for fundamental
Drjyotsna Chauhan 1 , And Roopal Soni
1 Hod Nanotechnology Rajiv Ganhi Techanical University, Bhopal (M.P.) Corresponding auther: Drjyotsna Chauhan
ABSTRACT: With Reduction In Size, Novel Electrical, Mechanical, Chemical, Magnetic, And Optical Properties Can Be Introduced. The Resulting Structure Is Then Called A Low-Dimensional Structure (Or System). The Confinement Of Particles, Usually Electron S Or Holes, To A Low- Dimensional Structure Leads To A Dramatic Change In Their Behavior And To The Manifestation Of Size Effects That Usually Fall Into The Category Of Quantum-Size Effects. The Low Dimensional Materials Exhibit New Physicochemical Properties Not Shown By The Corresponding Large-Scale Structures Of The Same Composition. Nanostructures Constitute A Bridge Between Molecules And Bulk Materials. Suitable Control Of The Properties And Responses Of Nanostructures Can Lead To New Devices And Technologies. Lead Selenide ThinFilms Were Successfully Prepared Varying Ph By Chemical Bath Deposition Technique On Glass Substrates. The Variations Were Found To Affect Thickness Of The Deposited Films. The Structural And Electrical Properties Of The Films Were Found To Be Thickness Dependent. The X-Ray Diffraction Studies Revealed That All Films Had FCC Crystal Structure With A (111) Preferred Orientation. Optical Studies Indicated That The Band Gap Decreased With Increasing Thickness Of The Films. The Electrical Conductivity Decreases With Thickness While The Dielectric Constant Increases With Thickness
The content of the dissertation will be organized in several chapters. The dissertation begins with a brief introduction and research objectives.
Chapter 2 describes the fundamental properties of the InN thinfilms. In addition to the principle of sol-gel spin coating method, other major fabrication approaches are reviewed. Factors such as substrates, buffer layers, and nitridation conditions that influence InN crystal growth are emphasized. Lastly, the potential application of the sol-gel spin coated InN-based IR photodetectors is introduced.
Film deposition of technologically important materials aims at providing better functionality and eventually applications to a variety of substrates. Such property enhancements may appear in the form of longer lifetime or higher reliability. The purpose of these modifications is to introduce better properties such as wear resistance and lubrication to the surface while at the same time retaining the strength, toughness and other bulk properties of the material. It is essential that films maintain a high degree of surface adhesion. The films must be virtually nonreactive in the surrounding environment and resistant to mechanical damage owing to exposure of the bare substrate to harsh process environment. A number of thin film deposition techniques were developed in the last century, in parallel with the improvement of electronics, vacuum- and measurement-technologies. Lately, the fast development of these techniques has initiated an exponentially growing research activity focusing on deposition of thinfilms for a largely diversified field of technologically important applications.
shows the variations of surface roughness of NiO films measured by atomic force microscopy (AFM). The depend-
ence of deposition rate and surface morphology at various substrate temperatures can be reasoned as follows. Since more nickel atoms could be ejected from the target at higher RF power, the deposition rate increases with RF power increasing. The substrate temperature controls the mobility of the absorbed atoms on the surface. Depositing in cooler substrate has low atomic mobility and tends to form preferred crystallite structure, which leads to a rougher surface. Hence, the adsorbed atoms prefer to stack on the energetic favor crystalline plane site rather than random stacking. This result leads to a rougher surface. Increasing the substrate temperature, adsorbed atoms gain extrathermal energy and have the motivity to move to another preferred sites. The roughness decreases because of free atomic motion. On the other hand, the higher substrate temperature provides extrathermal energy for the adsorbed atoms and enhances atomic mobility that could minimize the preferred orientation and hence the roughness. At higher RF power and substrate temperature conditions, the sputtered atoms obtained more kinetic energy when they arrived at the substrate surface because of extrathermal energy provided by the heated substrate and high power. Hence, they have a higher probability to reach the equilibrium positions and leads to a more perfect crystalline structure. But the adsorpted atoms also have higher probability to desorb from the surface at higher substrate temperature because of the thermal energy. The roughness of surface is more probable to be reduced and lead to a dense structure at high RF power with elevated substrate temperature. Therefore, the deposition rate and surface roughness were reduced at 200 W RF power with elevated substrate temperature conditions.
Devonshire functional. Both choices quantify the 2-D polarization P as a function of 2-D stress and field inputs. The third choice is similar to that employed for SMA [26, 42, 44] in the sense that it is 1-D with three wells cor- responding to ± 180 ◦ and 90 ◦ equilibria. The construction of this functional is phenomenological but the resulting decrease in dimension significantly di- minishes implementation time. In all three cases, the functionals are directly minimized to provide kernels for characterization in the absence of thermal relaxation or balanced with the relative thermal energy through Boltzmann principles to incorporate relaxation phenomena.
Since contact resonance frequency depends on tip-sample mechanical coupling, it is sensitive to the material‟s stiffness, with higher resonance frequency corresponding to higher stiffness. The sensitivity has been used in the past to evidence contrast in Young‟s Modulus between domains of different ferroelastic orientation, - but the technique was thought to be blind with respect to polarization sign. Our results, however, show that there is a measurable difference between the contact resonance frequency of oppositely-polarized domains (Figure 3), with down-polarized domains resonating at higher frequencies (stiffer) than up-polarized ones, in agreement with the nanoindentation results. This result is explained by the same arguments as in the indentation experiment: inhomogeneous deformation under the AFM tip induces a flexoelectric polarization that either adds to or subtracts from the piezoelectricity of the domains depending on their ferroelectric sign, resulting in asymmetric energy costs of deformation and thus different stiffness and contact resonance frequency.
The study of semiconductor nanoparticles has been an interesting field of research for more than two decades. The confinement effect is observed for CdS particles when the particle sizes are equal to or less than 50 Å . Bulk CdS is widely used as a commercial photodetector in the visible spectrum. It is also used as a promising material for buffer layers in thin film solar cells. The optical properties of CdS nanoparticles have been extensively studied in recent years as this material exhibits pronounced quantum size effects. The present work involves the study of nanocrystalline CdS thinfilms by sol-gel spin coating deposition techniques, studying growth, microstructure, and morphology and from that correlating the microstructure to its physical, electrical and optical properties.
The polypyrrole synthesized using chemical polymeriza- tion process. The films had a uniform granular morphol- ogy. The structure of the films is confirmed by FTIR and XRD techniques. UV-Vis studies showed that the PPy films exhibit absorption peak at 446 nm (2.77 eV). The PPy shows a thermally activated behavior of conductivi- ty.