Synthesis of Ferroelectric Thin Films with
Preferred Orientation
INTRODUCTION
Thin film processing is quite important for the development of device miniaturization, hybridization and lower working voltage. Several properties of functional materials are required for applications at a sub-micron level or less than that. Thin film processing techniques also have been receiving great attention for applications in semiconductor memories, opto-electronic devices, electronic components, display devices, magnetic devices, sensors and emerging area. The low temperature thin film processing also requires the precise control of chemical composition, the desired direction of crystal growth, and the high crystallinity. In this area, epitaxial single-crystal thin films with epitaxy are usually expected. Among several functional material thin films, ferroelectric thin films with preferred orientation have been mainly studied to improve ferroelectric properties and satisfy the requirements for device applications up to now. In addition, highly oriented electro-conductive including superconductive thin films have also been investigated to achieve high electrical conductivity and to use as a buffer layer of dielectric thin films with preferred orientation. In other examples, there are several magnetic and optical materials thin films with preferred orientation, etc. Recently, with the progress of thin film technology, intensive efforts have been focused on the preparation of epitaxial thin films mainly on single crystal substrates for making clear the properties of thin films with several functionalities.
Various techniques available today for the fabrication of thin films are noticeably more varied in type and in sophistication than couples of decades ago. Better equipment and more advanced techniques has, undoubtedly, led to higher quality films, and indeed, may be a primary factor in the now routine achievement of desired functionalities in thin films (50 nm or greater) prepared by a selection of different methods (Lee, 1971).
The chemical solution deposition (CSD), including sol–gel, process is one of the most common processes as the method of thin film fabrication. This process can be widely applied for optical, electrical, magnetical, mechanical, catalysis, etc. The most important advantages of chemical solution process are high purity, good homogeneity, lower processing temperature, precise composition control for the preparation of multicomponent compounds, versatile shaping and preparing by simple and cheap apparatus compared with other method. However, the larger the number of elements, the more complicated the solution chemistry, leading to difficulties in achieving the desired crystalline phases. Therefore, it is required to design the metal-alkoxide precursors through controlling the metal–oxygen–carbon bonds in component substances and to investigate the solution of multicomponent system in detail. Also, the crystallization behavior is complicated, so the investigation of crystallization process is a key for film synthesis. The films that are usually produced by chemical solution process are of polycrystalline nature, however, in many instances it is desirable to produce epitaxial film growth. The as-deposited gel films on the properly selected substrates undergo the atomic rearrangement during calcination and crystallization yielding epitaxial films.
In this chapter, therefore, we deals with various processing factors for preparing thin films with preferred orientation, such as (l) the control of the structure of metal-organic precursors with considering the stoichiometry in solution for coating, (2) the selection of the substrates for thin film fabrication, (3) the intermediate buffer layers (including a electrode layer) between the film and the substrate, (4) the heating (calcination and crystallization) conditions for LiNbO3(LN), K(Ta,Nb)O3(KTN) and tungsten bronze (Sr,Ba)Nb2O6(SBN), which are ferroelectric substances as case studies. Epitaxial LN, KTN and tungsten bronze SBN-based thin films are successfully synthesized on sapphire C, MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0), etc. substrates.
CASE STUDY 1: PREPARATION OF HIGHLY ORIENTED LiNbO3THIN FILMS
LiNbO3 Films with Preferred Orientation
Lithium niobate (LiNbO3) has a illumenite structure, and has various attractive properties, such as acoustic, piezoelectric, pyroelectric, acoustooptic and electro optic properties. LiNbO3 single crystals have generally been grown mainly by the Czochralski method. However, a LiNbO3 single crystal has been grown from a nonstoichometric melt of harmonic composition (Li2O/Nb2O5 = 48/52) by the Czochralski method. Recently, the development of a chemical solution processing route for epitaxial stoichiometric LiNbO3 thin films with high quality on appropriate substrates has been receiving great attentions, and strongly required for miniaturizing and integrating electrical and optical thin film devices (Weis, 1985; Hirano, 1988a, 1988b, 1988c, 1989, 1991, 1992a, 1993; Nashimoto, 1995). The stoichiometric LiNbO3films crystallized on Si substrates are usually polycrystalline, while the films on sapphire substrates are found to show preferred orientations depending upon crystallographic planes of sapphire. Only the 110, 012 and 006 reflections of LiNbO3 were observed on sapphire R, A and C substrates, respectively (Hirano, 1989, 1991, 1992a; Nashimoto, 1996). Also, the micro-patterning of oriented LiNbO3 film by the modification of ligands of the LiNbO3 precursor combined with UV irradiation have been demonstrated (Yogo, 1995a).
This section focuses on the orientation control of alkoxy-derived LiNbO3 thin films by controlling the structure (doing the molecular design) of metal-organic precursors in solution. The effect of modification of Li[Nb(OEt)6] double alkoxide is investigated for the synthesis of epitaxial LiNbO3thin films. LiNbO3films of excellent preferred orientation are successfully synthesized on substrates from the modified LiNbO3 precursors.
Effects of Modification of Ligands of Precursors on the Preparation of Epitaxially Grown LiNbO3 Films
PBD-Modified LiNbO3 Precursor. Non-modified LiNbO3 (STD-LiNbO3) precursor solutions are prepared from LiOEt and Nb(OEt)5 in ethanol (Hirano, 2002). The structure of the precursor was confirmed to consist of a complex alkoxide Li[Nb(OEt)6], which was reported by Eichorst et al. (1990) in detail (Eichorst et al., 1990). On the other hand, three types of β-diketone compounds are selected based upon the number of benzene rings (phenyl groups) in its structure. In this case, the coordination of l-phenyl-1,3-butanedione (PBD) to the LiNbO3precursor is confirmed by UV spectra. The similar
coordination is also realized in 2,4-pentanedione (PD)- and 1,3-diphenyl-1,3-propanedione (DPPD)-modified LiNbO3 precursors, which was confirmed by UV-spectra. The proposed structures of these β-diketone modified LiNbO3precursors are shown in Figure 17-1.
Sapphire C substrates are selected in order to fabricate highly oriented LiNbO3 thin films, because the c-plane of LiNbO3has the good crystallographic matching with c-plane of α-Al2O3. Figure 17-2 shows the XRD profile of the LiNbO3 thin film from the PBD-modified precursor on a sapphire C substrate crystallized at 550°C. This film shows a remarkable c-axis preferred orientation. The 006 reflection of LiNbO3 appears at as low as 400°C, and increases in intensity with increasing heat treatment temperature. However, the XRD evaluation is not proper for the judgement of the degree of precise orientations. Therefore, further investigation is required to examine the crystallographic relation between films and substrates as mentioned below.
Figure 17-1. Supposed structures of the STD-LiNbO3 and the β-diketone modified LiNbO3 (1 equiv of 2,4-pentanedion (PD), 1-phenyl-1,3-butanedion (PBD) and 1,3-diphenyl-1,3-propanedion (DPPD)) precursors.
Figure 17-2. XRD profile of the LiNbO3 thin film prepared on a sapphire C substrates from the 1 equiv. PBD modified LiNbO3 precursor solution at 550° C.
Figure 17-3. (a) X-ray pole figures of the LiNbO3thin films prepared on sapphire C substrates from STD-LiNbO3,(b) 1 equiv. PBD modified-LiNbO3precursor solutions and heat-treated at 550°C [2θ= 23.7°,for (0 12)].
X-ray pole figure measurement is commonly used to study the crystallographic alignment of oriented thin films on substrates. Figures 17-3(a) and (b) show (0 1 2) X-ray pole figures of the LiNbO3films prepared on sapphire C substrates from STD–LiNbO3and 1 equiv. PBD modified LiNbO3precursor solutions, respectively (Hirano, 2002). The pole figures are constructed for {0 1 2} planes. The term β is the rotation axis perpendicular to the film plane, and a is the rotation axis perpendicular to β and θ. The X-ray pole figures of (0 1 2) plane for the LiNbO3 single crystals and sapphire C show three spots at every 120°along β.However, the pole figure shown in Figure 17-3(a) exhibits additional spots than that of LiNbO3single crystal when non -modified STD-LiNbO3 precursor solutions are used. Six spots shown in Figure 17-3 (a) are composed of two groups of rotated three spots, one group with a stronger intensity and the other group with a weaker intensity. This ratio suggests that the structures appear at nucleation and grew through crystallization. Since LiNbO3 single crystals have triangular oxygen planes that are rotated by 60° around the c-axis, the misorientation should be formed easily at 60° along the c-axis during nucleation and growth. The similar twin structure of LiTaO3 films on sapphire substrate is reported to form by pulsed laser deposition (Agostinelli, 1993). On the other hand, the pole figure of the LiNbO3 film prepared on sapphire C from PBD-modified LiNbO3 precursor solution (Fig. 17-3(b)) is different from that shown in Figure 17-3(a).The figure shows the concentrated spots with a three-fold symmetry, which indicates the epitaxial growth of LiNbO3 films. The pole figure of LiNbO3 films fabricated by laser ablation is also reported to have a threefold symmetry for (0 1 2) (Shibata, 1993).
Effect of Amount of Ligands for Modification. In order to investigate the effects of the amount of the ligands in LiNbO3 precursors on the degree of orientation of resultant thin films, three amounts of PBD are compared (Hirano, 2002). Figure 17-4 showsβscans of LiNbO3 thin films prepared on sapphire C substrates using LiNbO3 precursors modified with 0.1, 1.0 and 3.0 equivalents of PBD. When LiNbO3precursors are modified with 0.1 equiv of PBD, six peaks with two different intensities are observed as in the case of the non-modified STD-LiNbO3precursor solution (Fig. 17-4(a)). The degree of orientation is defined by I w/I s (I w: intensity of the weak peak, I s: intensity of the strong peak) as shown in Figure 17-4(a).The crystallinity is defined by FWHM (full width of half maximum) and FW1/10M (full width of 1/10 height of maximum). When 1.0 equiv of PBD is used for modification (Fig. 17-4(b)), almost one set of three peaks is observed, resulting in a smaller I w/I s value than that of Figure 17-4(a). At 3.0 equiv of PBD, both of the degree of orientation (I w/I s) and the crystallinity (FW1/10M) of LiNbO3 turn to be worse due to the difficulty in decomposition of the organics of the LiNbO3 precursor (Fig. 17-4(c)).
Figure 17-4. β scans of the LiNbO3 thin films prepared on sapphire C substrates from (a) 0.1 equiv, (b) 1 equiv. and (c) 3 equiv of PBD modified-LiNbO3precursor solutions and heat-treated at 550°C [2θ= 23.7°, for (0 1 2)]. *Orientation Degree = I w/I s.
Figure 17-5. X-ray pole figures of the LiNbO3 thin films prepared on sapphire C substrates from 1 eqiuv. of (a) PD and (b) DPPD modified-LiNbO3 precursor solutions and heat-treated at 550°C [2θ = 23.7°, for (0 1 2)].
Effect of Molecular Structure of Ligands. In order to study the effects of the molecular structure of ligands in LiNbO3precursors on the degree of orientation of resultant thin films, further two types of ligands are studied (Hirano, 2002). Figures 17-5(a) and (b)show X-ray pole figures of LiNbO3thin films prepared on sapphire C substrates from modified LiNbO3precursors with PD (1 equiv) and DPPD (1 equiv), respectively. Six spots with three strong and three weak intensities are observed in Figure 17-5(a).This result is similar to that of the LiNbO3thin film from the STD-LiNbO3 precursor solution. On the other hand, symmetric three spots are observed for the LiNbO3 film prepared from the DPPD-modified LiNbO3 precursor solution. This result is similar to that of the LiNbO3 thin film from the PBD-modified LiNbO3 precursor solution.
Figure 17-6. Dependence of the orientation degree and FW of 1/10 maximum on the amount of β-diketone (PBD, PD or DPPD) in the LiNbO3 precursor solutions [○,●:PBD, Δ, ▲: PD,□, ■:DPPD].
Orientation of Precursor Derived-LiNbO3Thin Films.The degree of orientation and the crystallinity of the synthesized LiNbO3 thin films are summarized in Figure 17-6 (Hirano, 2002). From this figure, the appropriate amount of PBD is found to be about 0.5–2 equivalent to LiNbO3precursor. The crystallinity of the synthesized films decreases with increasing PBD. This is attributed to the increase in the difficulty in elimination of the residual carbon in the film during crystallization. When l equiv. of PD without benzene rings is used for modification, the degree of orientation is low, where I w/I s is 0.28, which is comparable with that of the non-modified STD-LiNbO3. On the other hand, l equiv DPPD-modified LiNbO3precursor provides a higher degree of orientation, where I w/I s is as low as 0.01 as in the case with the l equiv. PBD-modified LiNbO3. This result indicates that the existence of benzene rings in the precursor plays an important role to improve the degree of orientation of LiNbO3 thin films on sapphire C substrates.
The reasons for the improvement in the degree of orientation by the addition of, β-diketone with benzene rings are considered on the basis of the molecular structure of the precursors. Supposed structure of the PBD modified LiNbO3precursor (LiNb(OEt)4(PBD)) is shown in Figure 17-1.The precursor has a large planar organic part of the benzene ring in its structure as is compared in the STD-LiNb(OEt)6and LiNb(OEt)4(PD). The complex alkoxide precursors are aligned on the substrate, yielding a gel film during coating and drying process. The STD-LiNbO3and PD- modified LiNbO3precursors might tend to be aligned randomly, whereas the PBD- or DPPD-modified LiNbO3 precursor is likely to be aligned in the ordered structure on the substrate to achieve the stable conformation. The alignment of the LiNbO3precursor on the substrate give a crucial effect on the nucleation and crystallization of LiNbO3during decomposition and combustion of the organic part of the precursors on the substrates, and the resultant degree of orientation. In addition, in the case of the PBD-modified LiNbO3, the crystallization temperature does not influence the degree of orientation compared with STD-LiNbO3. Therefore, the addition of β-diketone, especially with benzene rings in its structure, plays an important role for the improvement of the degree of orientation of alkoxy derived LiNbO3 films.
The epitaxally grown LiNbO3 thin films on sapphire C substrates are found to show high transparency over wide wavelength region. The surface roughness of the LiNbO3 films is confirmed to be below 5 nm by atomic force microscope (AFM). These results indicate that the current LiNbO3 films have a good quality for several applications, such as optical waveguides and second harmonic generation devices.
CASE STUDY 2: PREPARATION OF HIGHLY ORIENTED K(Ta,Nb)O3THIN FILMS
K(Nb,Ta)O3 Thin Films with Preferred Orientation
Potassium tantalate–niobate [K(Ta x Nb l–x)O3, KTN] is one of the ferroelectric materials with the perovskite structure, and is a solid solution of potassium tantalate (KTaO3) and potassium niobate (KNbO3). The Curie temperature of KTN for the cubic to tetragonal transition varies with Ta/Nb ratio, and is lowered with increasing Ta substitution (Triebwasser, 1959). The ferroelectric properties of KTN, therefore, can be controlled by the Ta/Nb ratio. The nonferroelectric cubic phase of KTN at x = 0.65 is known to show photorefractive effect based upon a large quadratic electro-optic coefficient at room temperature (Gausic, 1964; Orlowski, 1980).
KTN single crystals have been grown by a modified Kyropoulos method (Bonner, 1965; Gentile, 1967). However, the KTN crystals have the problems of compositional gradient and inhomogeneous Ta/Nb ratio. Highly oriented (epitaxial) perovskite KTN films have been of particular interest for application in electro-optic devices, such as band filters, IR detectors and light modulators (Chen, 1966; Stafsudd, 1972; Fox, 1975; Hirano, 1992b; Nazeri, 1992; Yoga, 1995b; Kuang, 1995).
This section describes the synthesis of epitaxial ferroelectric KTN films on MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0) substrates using complex metal alkoxide precursor solutions. Ferroelectric KTN films with (1 0 0) plane orientation were successfully synthesized on properly selected substrates for three Ta/Nb ratios (Ta/Nb = 65/35, 50/50, 35/65) by optimizing the heating conditions.
Synthesis of Epitaxially Grown Thin Films under Optimized Processing Conditions Effect of H2O/O2Vapor during Heating.Figure 17-7shows the experimental procedure for preparing KTN thin films (Yoga, 1995b). Substrates are dipped into the coating solution, and withdrawn at a fixed speed, producing the precursor films on the substrates. The precursor films are dried at room temperature for a few minutes under nitrogen, and are calcined and crystallized using two methods. In method A, the precursor films are calcined at 300°C and then crystallized at various temperatures in an O2 flow. Method B, on the other hand, includes the calcination of films in H2O/O2 gas. To increase the film thickness, the above procedures are repeated several times.
The precursor films are prepared from the coating solutions of KTN65 (Ta/Nb = 65/35), KTN50 (Ta/Nb = 50/50) and KTN35 (Ta/Nb = 35/65). MgO(1 0 0) is selected as a suitable substrate due to the good lattice matching to KTN. The structures of the KTN precursors with various compositions are reported to consist of complex metal alkoxide precursors with a highly symmetric Nb–O octahedron as shown in Figure 17-8(Yoga, 1995b). The precursor films are heat-treated by the two methods mentioned above (Yogo, l995b; Suzuki, 1999a). Figure 17-9 shows the XRD profiles of the KTN65 films. The
pyrochlore phase is observed using method A as shown in Figure 17-9 (a). On the other hand, the perovskite KTN65 with the (1 0 0) preferred orientation is obtained by method B (Fig. l7-9(b)). Precursor films with KTN50 and 35 composition on MgO(1 0 0) are also calcined prior to crystallization at 300°C for l h in a gas mixture of water/oxygen. After heat treatment at 700°C for l h, the XRD of the films shows only 100 and 200 reflections of perovskite KTN (Suzuki, 1999a). The crystallinity of the film by method B is much superior to that by method A in terms of the direct formation of the perovskite phase. From these results, a mixture of H2O and O2 gases during calcination has a pronounced effect on the elimination of remaining organic components. The quality of the films prepared by the CSD method is generally affected by the decomposition and burn-out behaviors of organic species contained in the precursor film during heating. The schematic drawing of the elimination of organic groups by hydrolysis and the formation of –M–O–M–O–bonds in the precursor film is shown in Figure 17-10. The removal of the organic groups promotes the subsequent crystallization of perovskite KTN. The hydrolysis of precursor films on MgO is considered to promote the crystallization of perovskite KTN rather than the pyrochlore phase during the heating process. Similar effects are observed in (00l) oriented LiNbO3 (Hirano, 1988a, 1989), β-BaB2O4 (Yogo, 1997) and (1 1 1) oriented perovskite Pb(Zr,Ti)O3(Hirano, 1992c) and Pb(Mg,Nb)O3 (Hirano, 1994) films.
Figure 17-7. Experimental procedure for preparation of KTN thin films.
Figure 17-8. Proposed structure of the KTN precursor.
Figure 17-9. XRD profiles of KTN65 films crystallized at 700°C on MgO(1 0 0) substrates without H2O vapor (b) with H2O vapor.
Thin films are prepared on various substrates, such as Si(1 0 0) and sapphire(R), by method B. However, only the pyrochlore phase is observed by XRD analysis on these substrates even at 750°C. Therefore, the selection of MgO(1 0 0) as a substrate is also important to synthesize highly oriented perovskite KTN films.
Orientation of KTN Film on Substrate. Since the KTN65, KTN50 and KTN35 films on MgO(1 0 0) had (1 0 0) preferred orientation, X-ray pole figures are measured in order to investigate the three-dimensional regularity of the crystalline films (Yogo, 1995b). High density reflections of (1 1 0) poles are observed at a radius corresponding to α= 45° and every 90° along β. The fourfold symmetry indicates that the grains of KTN films are oriented in the same directions as MgO(1 0 0) surface along both the c and the a, b axes. Figure 17-11 illustrates the relation between the atomic alignment of MgO(1 0 0) and that in the a-plane of KTN. These two planes are well-matched to each other. The calculated lattice mismatch of oxygen-atom alignment between KTN(1 0 0) and MgO(1 0 0) is 3.6%, on the basis of the pole figure measurement.
Figure 17-10. Schematic drawing of the removal of organic groups promotes by hydrolysis and the formation –M–O–M–O–bonds in the precursor film.
Figure 17-11. The relation between the atomic alignment of MgO(1 0 0) and that in the a-plane of KTN.
Effect of Thin Seed Layer on the Crystallization of Oriented KTN Films. KTN films are also prepared on Pt(1 0 0)/MgO(1 0 0) substrates in order to evaluate the electric properties of the films (Suzuki, 1999a). In order to synthesize the oriented films, a buffer layer is precrystallized on the Pt(1 0 0)/MgO(1 0 0) substrates using a dilute
KTN precursor solution with a concentration of 0.01 mol/l. The crystallization of KTN film is influenced by the crystallization of the preapplied film on the Pt(1 0 0)/MgO(1 0 0) substrate. The underlying KTN film developed by a first dip coating is crystallized at 700°C after calcination in flows of water vapor and oxygen. The KTN films on the underlying film are crystallized in perovskite at 700°C. Figure 17-12shows the XRD profiles of the KTN films crystallized on Pt(1 0 0)/MgO(1 0 0) substrates at 700°C. The KTN65, 50 and 35 films are found to orient preferentially to (1 0 0) plane as is revealed in strong 100 and 200 reflections. The surface of the KTN films is observed by an atomic force microscope (AFM). The surface morphology and grain sizes are almost the same for the three compositions of KTN films. The surface morphology and the grain size of the KTN film on the underlayer is also the same as that without the underlayer.
Figure 17-12. XRD profiles of KTN films crystallized at 700°C on Pt(1 0 0)/MgO(1 0 0) substrates. (a) KTN65 film, (b) KTN50 film and (c) KTN35 film.
Furthermore, the KTN films on Pt(1 0 0)/MgO(1 0 0) substrates are analyzed by the X-ray pole figure method (Yoga, 1995b). Figure 17-13 shows the X-ray pole figures of (a) KTN65/Pt(1 0 0)/MgO(1 0 0) and (b) Pt(1 0 0)/MgO(1 0 0). Pt(1 0 0) grows on MgO(1 0 0) epitaxially as shown in Figure 17-13(b). When the X-ray pole figure of the KTN65 films on Pt(1 0 0)/MgO(1 0 0) is measured for {1 1 0} pole, clear spots with a fourfold symmetry are constructed at α= 45°. The KTN65 films are found to crystallize epitaxially on the Pt(1 0 0)/MgO(1 0 0) substrates as in the case of KTN65 films on MgO(1 0 0) as described above. The KTN50 and 35 films on Pt(1 0 0)/MgO(1 0 0) also reveal a clear spot pattern with fourfold symmetry. Therefore, the KTN films on Pt(1 0 0)/MgO(1 0 0) have not only the crystal structural arrangement having an axis perpendicular to the Pt(1 0 0) layer but also that with parallel one.
Crystallographic Matching between Film and Substrate.The orientation of the KTN films on MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0) substrates are ascribed to the lattice matching between KTN and substrates (Suzuki, l999a). The cubic phases of KTN65, KTN50 and KTN35 have lattice parameters of 400.8, 400.3 and 399.9 pm, respectively, and that of MgO is 421.3 pm. The lattice mismatch between KTN(1 0 0) and MgO(1 0 0) is from 4.5% to 5.2%. The deposited Pt layers on MgO(1 0 0) have a (1 0 0) orientation with a three-dimensional alignment confirmed by X-ray pole figure. Platinum has an fcc atomic packing with the lattice parameter 392.3 pm. The mismatch between KTN(1 0 0) and Pt(1 0 0) is from 1.8% to 2.5%, which is smaller than that between KTN and MgO. Thus, the crystallization of KTN with both in-plane and out-of-plane orientations results from the crystallographic matching of KTN (1 0 0) to MgO(1 0 0) and Pt(1 0 0).
Figure 17-13. X-ray pole figures of (a) KTN65/Pt(1 0 0)/MgO(1 0 0) and (b) Pt(1 0 0)/MgO(1 0 0). Electrical Properties of Highly Oriented K(Ta,Nb)O3 Films
KTN65(Ta/Nb = 65/35), KTN50(Ta/Nb = 50/50) and KTN35(Ta/Nb = 35/65) films are crystallized at 700°C on Pt(1 0 0)/MgO(1 0 0) substrates with (1 0 0)-preferred orientation described in previous sections. The electrical properties of films are measured using Au top electrodes deposited on the films and a sputtered Pt(1 0 0) layer on MgO(1 0 0) as a bottom electrode. The following dielectric measurements are conducted on 1.0 μm-thick KTN films (Suzuki, l999a).
Figure 17-14. Variation of Curie temperature with composition for the KTN films and single crystals.●: T c of the KTN films crystallized on Pt(1 0 0)/MgO(1 0 0) substrates at 700°C. ?: T c of the KTN single crystals after Triebwasser (1959).
The dielectric constant (ε)–temperature (T) curves of the KTN films are found to be broad and to have a relaxor-type behavior. The Curie temperature (T c) of the films at l kHz–1 MHz is measured. Figure 17-14shows the variation of Curie temperature with composition for the KTN films and single crystals (Triebwasser, 1959). T c of KTN35, KTN50 and KTN65 films at 1 kHz are 100°C, 0°C and –60°C, respectively. The Curie temperature of the KTN films decreases with increasing Ta ratio. This tendency is the same as that of the single crystals (Triebwasser, 1959). This result is considered to be attributed to the stress imposed by substrates as reported (Suzuki, 1999a). This stress may affect the properties of the KTN films.
Figure 17-15 shows P–E hysteresis loops of the KTN films on Pt(1 0 0)/MgO(1 0 0) substrates measured at –180°C, where the ferroelectric phase is supposed to be stable to exhibit saturated P–E hysteresis loops (Suzuki, 1999a). At this temperature, all KTN films are ferroelectric. The hysteresis loops of the KTN films are nearly saturated. The value of remnant polarization of KTN35, KTN50 and KTN65 films are 5.0, 3.9 and 2.7 μC/cm2, respectively. The polarization of the KTN films decreases with increasing Ta ratio. Since KTN films with high Nb ratios are considered to have large strain along the polarized axis, the polarization of the KTN films is large in Nb-rich compositions. The remanent polarization (Pr) of the KTN films decreases gradually with increasing temperature to T c.The Pr is zero at T c,which is in good agreement with the Curie temperature obtained by dielectric measurement.
Figure 17-15. P–E hysteresis curves of the KTN films on Pt(1 0 0)/MgO(1 0 0) substrates at –180°C. (a) KTN35 film, (b) KTN50 film and (c) KTN65 film.
The epitaxally grown alkoxy-derived KTN thin films on substrates are found to show high transparency over wide wavelength region. Also, the pyroelectric properties of the KTN films are characterized (Suzuki, 1999b). These results indicate that the current ferroelectric KTN films have a good quality for several applications, such as infrared detectors, optical switching and light modulation utilizing their electrical and optical properties.
CASE STUDY 3: PREPARATION OF HIGHLY ORIENTED (Sr,Ba)Nb2O6-BASED THIN FILMS
Tungsten Bronze (Sr,Ba)Nb2O6-Based Thin Films with Preferred Orientation The tungsten–bronze materials consist of more than 190 individual end member compounds and numerous possible solid solutions with simple or complex compounds. The end members offer one of the most versatile, extensive and potentially useful families of ferroelectrics based on oxygen octahedra. Among those ferroelectrics, a number of niobates having tetragonal or orthorhombic tungsten–bronze structure such as (Sr,Ba)Nb2O6(SBN), (Ba,Sr)2(K,Na)Nb5O15(BSKNN), (Pb,Ba)Nb2O6(PBN), Ba2NaNb5O15 (BNN) and K3Li2Nb5O15 (KLN) have attracted a great deal of attention due to their potential applications in electrooptic, nonlinear optic, photorefractive, pyroelectric and SAW devices, because they have large pyroelectric coefficients, excellent piezoelectric and electro-optic properties. However, the growth of these crystals with sufficient sizes and quality is generally difficult because of the complex structures and high melting points. The preparation of dense polycrystals is also very difficult because of the anisotropic grain growth. Thus, the investigations about tungsten bronze niobate materials were limited to the growth of single crystals from melt and to the preparation of polycrystals by solid state reaction. One approach for the solution of this serious problem is the film synthesis with highly preferred orientation (or epitaxy) on easily available non-crystalline and single crystal substrates.
Tungsten bronze niobate compounds have large crystallographic anisotoropy. Therefore, the electrical and optical properties of tungsten bronze niobate depended upon the crystallographic directions. Highly c-axis oriented tungsten bronze niobate thin films are expected for pyroelectric, photorefractive and electro-optic applications, because c-axis is the direction of polarization and optic axis of these crystals. Also, the crystallization of tungsten bronze niobate at lower temperatures is required in order to fabricate thin films with high quality. Among the several tungsten bronze niobate compounds, the solid solution of strontium barium niobate (Sr1–x Ba x Nb2O6, SBN) exists in the BaNb2O6–SrNb2O6binary system with tetragonal tungsten bronze structure (Francombe, 1960; Jaffe, 1971). The solid solution is reported to have compositions from x= 0.25 to 0.75 (Ballman, 1967). SBN is one of the important ferroelectric materials because of the lead free composition with several excellent properties (Glass, 1967; Lenzo, 1967; Neurgaonkar, 1986; Ewbank, 1987; Rytz, 1989). In addition, SBN has been doped with rare-earth or alkali ions in order to improve its properties (Giess, 1969; Neurgaonkar, 1987; Umakantham, 1987; Bhanumathi, 1990).
This section focuses on the low temperature synthesis of highly oriented (Sr,Ba)Nb2O6 (SBN)-based thin films of tungsten bronze structure. The crystallographic phase, the mechanism of orientation on properly selected substrates and the characteristic electrical properties of SBN-based thin films with c-axis (direction of polarization) preferred orientation are mainly described.
Several Processing Factors and Characterization of Synthesis of Tungsten Bronze SBN-Based Thin Films
Crystalline SBN-Based Thin Films with Preferred Orientation.
SBN Thin Films on Single Crystal Substrates. Figure 17-16shows an experimental procedure for fabrication of strontium barium niobate (SBN)-based thin films (Sakamoto, 1996, 1997, 1998a). Films are fabricated using the metal alkoxide precursor solutions (0.2 M) on fused silica, MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0) substrates. A Pt(1 0 0) layer is deposited on MgO(1 0 0) by RF magnetron sputtering. A buffer layer is prepared on each substrate using a diluted precursor solution (0.02 M). The thin layer of the precursor on a substrate is heat-treated to the crystallization temperature in an oxygen flow. Then, the precursor film is deposited on the precrystallized buffer layer using the standard precursor solution (0.2 M). The electrical properties of films are measured using Au top electrodes deposited on the tungsten bronze niobate films and a sputtered Pt(1 0 0) layer on MgO(1 0 0) as a bottom electrode.
In this study, to achieve the improvement of the stability of the precursor solutions, the precursor solutions are stabilized by the modification of ligands. The homogeneity and stability of the coating solution are greatly improved by the properly selected stabilizing agent. A precursor including an appropriate amount of stabilizing agent (in this case, 2-ethoxyethanol) is found to have a sufficient long-term stability. The precise structure of the stabilized precursor in solution was analyzed by several spectroscopic analyses (Sakamoto, 1996, 1998a). The structure of precursor was found to consist of complex metal alkoxides with a highly symmetric Nb–O octahedron mixtured at a molecular level in solution. Proposed structure of SBN and KSBN precursor are shown in Figure 17-17 (Sakamoto, 1996, 1998a).
Figure 17-16. Experimental procedure for preparation of strontium barium niobate (SBN)-based thin films.
Figure 17-17. Proposed structures of the SBN and KSBN precursors.
In order to synthesize tungsten bronze SEN-based thin films with 00l preferred orientation, MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0) are selected as substrates, because MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0) has a good crystal matching with the c-plane of tungsten bronze SEN. Furthermore, Pt(1 0 0)/MgO(1 0 0) is used as a Pt/MgO part of the Pt(1 0 0) /MgO(1 0 0) /Si(1 0 0) structure for the compatibility of semiconductor processes.
Figure 17-18shows the XRD profiles of the Sr0.5Ba0.5Nb2O6(SEN50) films crystallized at 700°C and 1000°C on MgO(1 0 0) substrates. The SEN films on MgO(1 0 0) show strong 001 and 002 reflections as shown in Figure 17-18.From the XRD patterns, it is impossible to judge whether the SEN50 thin films on MgO(1 0 0) are crystallized to tetragonal of tungsten bronze or not, because SEN thin films crystallized at 700°C and 1000°C show only a few diffraction peaks due to the preferred orientation.
Characterization of Oriented Thin Films by Raman Spectroscopic Analysis.The crystallographic phases of the oriented SEN thin films are characterized further by Raman microprobe spectroscopy (Sakamoto, 1996). Figure 17-19shows the Raman microprobe spectra of the SEN thin films on MgO(1 0 0) substrates. The SEN thin film crystallized at 700°C is composed of two crystalline phases (orthorhombic low-temperature phase and tetragonal tungsten bronze phase) as shown in Figure 17-19(a). On the other hand, the SEN thin film heat-treated at 1000°C is tetragonal tungsten bronze (Fig. 17-19(b)). Raman spectra of these films are quite different depending upon the crystallographic phase (Sakamoto, 1996). This means that XRD analysis is not a sufficient method to determine the phase of SEN-based thin films on MgO(1 0 0) substrates. On the basis of XRD analysis, the SEN precursor powder crystallizes in the orthorhombic phase (Sakamoto, 1996, 1998a, 1998b) at 700°C, and began to be transformed to the tetragonal phase at 1000°C. Single-phase tetragonal SEN powder is found to form at 1200°C (Sakamoto, 1996, 1998a). Figure 17-19 shows that the film on a substrate does crystallize in the tetragonal phase more easily compared with powders.
The low temperature formation of the tetragonal phase is attributed to the roles of the orientation of the substrate, the expansion mismatch and the stress in the films. However, the heat-treatment at 1000°C is found to be required to transform completely to the tetragonal SEN of tungsten bronze even on MgO(1 0 0) substrates (Sakamoto, 1996).
Figure 17-18. XRD profiles of the SBN50 thin films on MgO(1 0 0) substrates crystallized at (a) 700°C and (b) 1000°C.
Figure 17-19. Raman spectra of the SBN50 films on MgO(1 0 0) substrates heat-treated at (a) 700°C and (b) 1000°C (tetra.: tetragonal tungsten bronze phase; ortho.: orthorhombic low temperature phase).
Figure 17-20. XRD profiles of (a) K0.2SBN50 and (b) K0.4SBN50 thin films on MgO(1 0 0) substrates heat-treated at 700° C.
Potassium Substituted SBN Thin Films. For SEN film synthesis, the crystallization of ferroelectric tungsten bronze phase on substrates encounters the problem of the formation of a low temperature phase. In order to prepare tungsten bronze thin films at lower temperatures, the substitution of K+ for Sr2+ or Ba2+ site is investigated (Sakamoto, 1996, 1997).
Figure 17-20shows the XRD profiles of K0.4(Sr0.5Ba0.5)0.8Nb2O6(K0.4SBN50) and K0.2(Sr0.5Ba0.5)0.9Nb2O6 (K0.2SBN50) thin films on MgO(1 0 0) substrates crystallized at 700°C (Sakamoto, 1998a). The K0.4SBN50 and K0.2SBN50 films on MgO(1 0 0) have strong 001 and 002 reflections as shown in Figures 17-20(a) and (b). The K0.4SBN50 and K0.2SBN50 films on Pt(1 0 0)/MgO(1 0 0) crystallize above 600°C also show an excellent c-axis preferred orientation.
Figure 17-21 shows the Raman spectra of the K0.4SBN50 and K0.2SBN50 thin films on MgO(1 0 0) substrates heat-treated at 700°C, which reveal that the thin films are single-phase tungsten bronze, where the profiles are consistent with those of K0.4SBN50 and K0.2SBN5O powder samples (Sakamoto, 1998a). The KSBN film shows the Raman scatterings characteristic of tungsten bronze niobates, such as the Nb–O–Nb bending modes (220–300 cm–1) and the symmetric stretching mode of the NbO6 octahedron (580–700 cm–1). The Raman spectrum patterns of these films shown in Figure 17-21are in good agreement with that of the tetragonal tungsten bronze SEN single crystals, although the scattering positions are slightly shifted to each other (Burns, 1990). The formation of the tetragonal tungsten bronze phase is attributed to the substitution of potassium. The potassium substituted SBN thin films of tetragonal tungsten bronze do crystallize completely at much lower temperatures compared with the SBN thin films. Precise control of chemical composition of the film is very important for the synthesis of the desired films. The similar effect of potassium substitution in low temperature formation of 00l oriented tungsten bronze films is observed for (Pb,Ba)Nb2O6(PBN)-based thin films on MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0) (Sakamoto, 1998c, 1999a). KSBN thin films with other compositions, such as K0.4(Sr0.75Ba0.25)0.8Nb2O6(KSBN75) and
金屬氧化物透明導電材料的基本原理 一、透明導電薄膜簡介 如果一種薄膜材料在可見光範圍內(波長380-760 nm)具有80%以上的透光率，而且導電性高，其比電阻值低於1×10-3 ·cm，則可稱為透明導電薄膜。Au, Ag, Pt, Cu, Rh, Pd, A1, Cr等金屬，在形成3-15 nm厚的薄膜時，都有某種程度的可見光透光性，因此在歷史上都曾被當成透明電極來使用。但金屬薄膜對光的吸收太大，硬度低而且穩定性差，因此人們開始研究氧化物、氮化物、氟化物等透明導電薄膜的形成方法及物性。其中，由金屬氧化物構成的透明導電材料(transparent conducting oxide, 以下簡稱為TCO)，已經成為透明導電膜的主角，而且近年來的應用領域及需求量不斷地擴大。首先，隨著3C產業的蓬勃發展，以LCD為首的平面顯示器(FPD)產量逐年增加，目前在全球顯示器市場已佔有重要的地位，其中氧化銦錫(In2O3:Sn, 意指摻雜錫的氧化銦，以下簡稱為ITO)是FPD的透明電極材料。另外，利用SnO2等製成建築物上可反射紅外線的低放射玻璃(low-e window)，早已成為透明導電膜的最大應用領域。未來，隨著功能要求增加與節約能源的全球趨勢，兼具調光性與節約能源效果的electrochromic (EC) window (一種透光性可隨施加的電壓而變化的玻璃)等也可望成為極重要的建築、汽車及多種日用品的材料，而且未來對於可適用於多種場合之透明導電膜的需求也會越來越多。 二、常用的透明導電膜
一些目前常用的透明導電膜如表1所示，我們可看出TCO佔了其中絕大部分。這是因為TCO具備離子性與適當的能隙(energy gap)，在化學上也相當穩定，所以成為透明導電膜的重要材料。 表1 一些常用的透明導電膜 三、代表性的TCO材料 代表性的TCO材料有In2O3， SnO2， ZnO， CdO， CdIn2O4， Cd2SnO4，Zn2SnO4和In2O3-ZnO等。這些氧化物半導體的能隙都在3 eV以上，所以可見光(約1.6-3.3 eV)的能量不足以將價帶(valence band)的電子激發到導帶(conduction band)，只有波長在350-400nm(紫外線)以下的光才可以。因此，由電子在能帶間遷移而產生的光吸收，在可見光範圍中不會發生，TCO對可見光為透明。
第六章金属及金属材料专题复习 【教学目标】 知识目标： 1．了解金属的物理性质和金属材料的主要用途。 2．掌握金属的化学性质。 3. 掌握并熟练运用金属活动性顺序。 4．了解铁矿石炼铁的方法和金属防锈的原理和措施。 能力目标：培养学生归纳、解决问题的能力； 情感目标：培养学生严谨的学习态度，激发学生学习的积极性。 【教学重难点】金属活动性的应用 【教学方法】问题探究、合作展示、点评归纳 【教学过程】 【PPT】展示课题及复习目标 【师】同学们，这节课我们来复习《金属及金属材料》先请同学们看本章的复习目标。 第一阶段：考点知识梳理 【师】1、根据大屏幕上的考点提示进行基础知识复习。 2、同桌之间互相提问。 3、每个知识点复习2-3分钟不等。 【生】：根据大屏幕填空。（其他同学补充或矫正） 第二阶段：对应知识点简单应用 【师】PPT展示针对考点的简单应用题目（1-12题） 看哪位同学做的又快又正确，完成的举手 【生】做题，完成后举手 【师】分别找三名学生起立，展示答案。（7题、10题答案不一样）分别请认为第7题选A、B的同学起来解释理由； 【生】合成材料又称人造材料，是人为地把不同物质经化学方法或聚合作用加工而成的材料，其特质与原料不同，如塑料、玻璃等。 【师】这位同学解释的非常好,同学们要注意概念的差别。 【师】请认为第10题选C的同学起来解释理由； 【生】以前我们做过类似的题，此类型题解题方法是，抓住中间物质，要么选它的单质，其它两种金属用它们的盐溶液；要么选中间金属的盐溶液，其它两种金属用它们的单质。 【师】对于此题中物质的活动性排序我们还可以选用什么样的物质？ 【生】Zn、FeCl2、Cu 第三阶段：中考典例分析 考点一：金属与酸的反应的有关计算 【师】我们一起来回想一下金属与酸反应需要用到的知识点： 1.等质量的金属与足量酸反应，产生氢气的量由多到少依次是：铝、镁、铁、锌。 2.足量的金属与等质量的酸反应，产生氢气的量相等。
“薄膜晶体管的制备及电学参数”调研报告 （青岛大学物理科学学院，应用物理系） 摘要：20世纪平板显示技术的出现，把人类带入了信息社会，人类社会从此发生了质的飞跃。而平板显示的核心元件就是薄膜晶体管TFT(nlin Film Transistor)，一种在掺杂硅片或玻璃基底上通过薄膜工艺制作的场效应晶体管器件。将半导体氧化物作为有源层来制作TFT用于平板显示中，不仅能获得较高迁移率，器件性能优越，而且制造工艺简单、低温下可以获得，显示出了巨大的应用前景。本文综述了薄膜材料的制备方法，薄膜晶体管的发展历程与应用以及其结构、工作原理和测试表征方法。 关键词：薄膜材料，薄膜晶体管，制备，表征方法 Abstract:In the 20th century,the emergence of the flat panel display technology has brought human beings into the information society．Since then the human society happened a qualitative leap．The core component of flat panel display is the thin film transistor(TFT)，it is a field effect transistor device produced by thin film technology on the doped-silicon or glass．If we use the semiconductor oxide as the active layer，not only we can get a higher mobility，bu also the device performance call be enhanced．And the manufacturing process is simple，low temperatures also can be obtained,which shows a great prospect．The preparation method of thin film materials is reviewed in this paper, the development and application of thin film transistor and its structure, working principle and test method are characterized, Keywords: Thin film materials, thin film transistor, manufacture, characterization methods 前言 薄膜材料是指厚度介于单原子分子到几毫米间的薄金属或有机物层。当固体或液体的一维线性尺度远远小于它的其他二维尺度时，我们称这样的固体或液体为膜。薄膜材料具有良好的韧性、防潮性和热封性能，应用非常广泛。例如：双向拉伸聚丙烯薄膜（BOPP）、低密度聚乙烯薄膜（LDPE）、聚酯薄膜（PET）、镀铝薄膜、半导体氧化物薄膜等等。近几年来，以氧化锌、氧化铟、氧化锡等半导体氧化物及其合金为有源层的透明薄膜晶体管备受关注，并已取得了突破性进展。这些氧化物是优异的光电材料，具有高光学透过率、生长温度低、击穿电压高、电子迁移率高等优点，从而可以获得更好、成本更低的薄膜晶体管，并且也为新型薄膜晶体管的发展带来了契机。氧化物薄膜晶体管作为极具发展潜力的新型薄膜晶体管，具备了许多传统TFT无法比拟的优点，但是也存在诸多问题有待进一步解决。例如，如何解决外界环境对器件性能的影响，优化工艺从而降低成本，如何制作出性能优越、具有实用价值的器件等，这些都是现在研究面临的问题。本文的主要调研对象，包括氧化锌以及有机薄膜作为有源层的薄膜晶体管。 薄膜晶体管的发展历程 1925年，Julius Edger Lilienfeld首次提出结型场效应晶体管(Field
第44卷第5期2016年5月 硅酸盐学报Vol. 44，No. 5 May，2016 JOURNAL OF THE CHINESE CERAMIC SOCIETY https://www.doczj.com/doc/089950461.html, DOI：10.14062/j.issn.0454-5648.2016.05.15 多孔金属氧化物半导体薄膜的制备及其光催化性能 吴朵朵1，鲍艳2，马建中2，田万乐2 (1. 陕西科技大学化学与化工学院，西安 710021；2. 陕西科技大学资源与环境学院，西安 710021) 摘要：以垂直蒸发沉积法制备的聚苯乙烯(PS)胶态晶体为模板，采用溶胶-凝胶法制备多孔ZnO和TiO2薄膜，分别考察其对罗丹明B(RhB)溶液的光催化降解效果。使用扫描电子显微镜观察PS胶态晶体以及多孔ZnO和TiO2薄膜的形貌，以紫外-可见吸收光谱仪表征光催化降解效果。结果表明：PS分散液浓度对PS胶态晶体的组装层数有显著影响；PS胶态晶体的组装层数及ZnO和TiO2溶胶的浓度对多孔ZnO和TiO2薄膜的光催化降解效果有显著影响。 关键词：PS胶态晶体；多孔ZnO薄膜；多孔TiO2薄膜；光催化降解 中图分类号：TB32 文献标志码：A 文章编号：0454–5648(2016)05–0000–06 网络出版时间：网络出版地址： Preparation and Photocatalytic Activity of Porous Metal Oxides Films WU Duoduo1, BAO Yan2, MA Jianzhong2, TIAN Wanle2 (1. College of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China; 2. College of Resources and Environment, Shaanxi University of Science and Technology, Xi’an 710021, China) Abstract: Porous ZnO and TiO2 films were fabricated on ITO conductive glass by sol-dipping method using polystyrene colloidal crystal as template, which was prepared via vertical deposition method. The effect of porous ZnO and TiO2 films on photocatalysis degradation to Rhodamine B solution was investigated. Scanning electron microscopy was used to observe the structure of polystyrene colloidal crystal templates, porous ZnO and TiO2 films. Photocatalysis degradation ability of porous ZnO and TiO2 films was evaluated by ultraviolet-visible spectrometer. The results show that the concentration of polystyrene suspension has a significant influence on colloidal crystal layer. Simultaneously, PS colloidal crystal layer and sol concentration affects greatly to the photocatalytic degradation ability of ZnO and TiO2 films. Keywords: polystyrene colloidal crystal; porous ZnO films; porous TiO2 films;photocatalysis degradation 常用的金属氧化物半导体材料有ZnO和TiO2，半导体材料在受到光照射时产生的电子和空穴具有较强的还原和氧化能力，可以有效地催化降解有机污染物，最终使之生成无毒、无味的二氧化碳和水。目前，已经成功制备出不同形貌的ZnO和TiO2，且已被广泛用于光催化领域中[1-4]。然而常用的ZnO 和TiO2是粉体材料，纳米粉末在应用过程中存在容易团聚从而降低光催化效果的缺陷。同时，光催化结束后从悬浮液中分离出不可溶解的纳米粉末非常困难。多孔金属氧化物薄膜具有比表面积大、分散性好、易于回收等优点，在光催化领域具有潜在的应用。 迄今为止，已有大量文献报道了多孔材料的制备方法。如可利用模板分子的立体效应进行制备，Lupo等[5]以呫吨染料曙红作为结构诱导剂，通过电化学沉积法制备了多孔ZnO。也可以聚合物为模板制备多孔材料[6–7]，Zhao等[6]以一种生物质作为硬模板，嵌段式聚醚作为软模板制备了多孔ZnO，可有 收稿日期：2015–10–13。修订日期：2016–02–28。第一作者：吴朵朵(1993—)，女，硕士研究生。 通信作者：马建中(—)，男，教授。Received date: 2015–10–13. Revised date: 2016–02–28. First author: WU Duoduo (1993–), female, Master candidate. E-mail: wuduoduo3@https://www.doczj.com/doc/089950461.html, Corresponding author: MA Jianzhong(), male, Professor. E-mail: majz@https://www.doczj.com/doc/089950461.html,
第六章金属及合金的塑性变形和断裂 2）求出屈服载荷下的取向因子，作出取向因子和屈服应力的关系曲线，说明取向因子对屈服应力的影响。 答： 1）需临界临界分切应力的计算公式：τk=σs cosυcosλ，σs为屈服强度=屈服载荷/截面积 需要注意的是：在拉伸试验时，滑移面受大小相等，方向相反的一对轴向力的作用。当载荷与法线夹角υ为钝角时，则按υ的补角做余弦计算。 2）c osυcosλ称作取向因子，由表中σs和cosυcosλ的数值可以看出，随着取向因子的增大，屈服应力逐渐减小。cosυcosλ的最大值是υ、λ均为45度时，数值为0.5，此时σs为最小值，金属最易发生滑移，这种取向称为软取向。当外力与滑移面平行（υ=90°）或垂直（λ=90°）时，cosυcosλ为0，则无论τk数值如何，σs均为无穷大，表示晶体在此情况下根本无法滑移，这种取向称为硬取向。 6-2 画出铜晶体的一个晶胞，在晶胞上指出： 1）发生滑移的一个滑移面 2）在这一晶面上发生滑移的一个方向 3）滑移面上的原子密度与{001}等其他晶面相比有何差别 4）沿滑移方向的原子间距与其他方向有何差别。 答： 解答此题首先要知道铜在室温时的晶体结构是面心立方。 1）发生滑移的滑移面通常是晶体的密排面，也就是原子密度最大的晶面。在面心立方晶格中的密排面是{111}晶面。 2）发生滑移的滑移方向通常是晶体的密排方向，也就是原子密度最大的晶向，在{111}晶面中的密排方向<110>晶向。 3）{111}晶面的原子密度为原子密度最大的晶面，其值为2.3/a2，{001}晶面的原子密度为1.5/a2 4）滑移方向通常是晶体的密排方向，也就是原子密度高于其他晶向，原子排列紧密，原子间距小于其他晶向，其值为1.414/a。 6-3 假定有一铜单晶体，其表面恰好平行于晶体的（001）晶面，若在[001]晶向
第6章金属材料 一、学习指导 （一）内容提要 本章介绍钢的冶炼与分类；建筑钢材的主要技术性能；钢的组织与化学成分对其性能的影响；钢材的强化机理及强化方法；建筑钢材的分类、标准与选用；钢材的防护；铝合金与铜合金 （二）基本要求 1、了解钢的分类； 2、掌握钢的冶炼对钢材质量的影响；熟练掌握建筑钢材的技术性能（包括：抗拉性能、冲击韧性、耐疲劳性、硬度、冷弯性能、焊接性能、冷加工及热处理等）； 3、熟悉建筑钢材的强化机理及强化方法； 4、掌握钢材的化学成分对钢材性能的影响； 5、掌握土木工程中常用建筑钢材的分类、主要品种及其选用原则； 6、了解建筑钢材的晶体组织对钢材性质的影响； 7、熟悉钢材的锈蚀与防护方法以及钢材的防火。 （三）重、难点提示 1、重点提示：钢材的冶炼对钢材质量的影响；建筑钢材的主要技术性能：抗拉性能、冲击韧性、冷弯性能；化学成分对其性能的影响；钢材的强化机理及强化方法；建筑钢材的分类、主要品种、标准与选用。 2、难点提示：钢材的强化机理及强化方法；化学成分对其性能的影响。 二、习题 （一）判断题 1、钢材的屈强比越大，反映结构的安全性越高，但钢材的有效利用率越低。 （） 2、钢材的伸长率表明钢材的塑性变形能力，伸长率越大，钢材的塑性越好。（） 3、钢材在焊接时产生裂纹，原因之一是钢材中含磷较高所致。（） 4、建筑钢材的基本晶体组织是随着含碳质量分数的提高而珠光体增加渗碳体减少。（） 5、钢中含磷影响钢材的塑性变形能力，而含硫则影响钢材的冷脆性。（） 6、钢中N、O等杂质越多，越容易引起钢材的时效敏感性。（） 7、钢材冷拉是指在常温下将钢材拉断，且以伸长率作为性能指标。（） 8、某厂生产钢筋混凝土梁，配筋需用冷拉钢筋，但现有冷拉钢筋不够长，因此将此钢
2019-2020学年度第六章金属测试题 可能用到的相对原子质量：C—12 O—16 H—1 Zn—65 Fe—56 一、选择题（本题包括20小题，每小题2分，共40分，每小题有四个选项，其中只有一个选项符合题意。） 1.下列应用在高铁列车上的材料，不属于金属材料的是（） A.不锈钢 B.玻璃 C.铝合金 D.铜线 2.下列有关金属和金属材料的说法不正确的是（） A.不锈钢的抗腐蚀性强，可用来制作炊具、医疗器械 B.黄铜属于合金，它的硬度比铜小 C.铁的导热性好，可以制成锅 D.铝表面易形成致密的氧化膜，可阻止铝进一步被氧化 3.下列关于金属利用的说法错误的是（） A.用铝制高压电线 B.用钨制灯丝 C.用纯铁制机床底座 D.用铝粉制防锈漆 4.下列说法正确的是（） A.铁在潮湿的空气中容易生锈 B.金属的活动性：Zn＞Ag＞Cu C.合金属于纯净物 D.铝是地壳中含量最多的元素 5.新农村建设如火如荼，许多村庄道路两侧安装了太阳能路灯，关于太阳能路灯所用材料的叙述不正确的是（） A.铝合金灯柱属于金属材料 B.透明的塑料灯罩属于有机合成高分子材料 C.灯泡中填充氮气做保护气 D.硅电池板中的硅元素是地壳中含量最多的金属元素 6.下列有关合金的说法正确的是（） A.一般来说，合金的硬度比其纯金属大 B.一般来说，合金的熔点比其纯金属高 C.合金的性能都比纯金属好 D.合金是只由金属熔合而成的混合物 7.下表是一些金属熔点的数据： 金属锡铅铋镉 熔点/ 231.9 327.5 271.3 320.9 日常所用保险丝由铋、铅、锡、镉等金属组成，其熔点约为( ) A.300-320℃ B.230-250℃ C.60-80℃ D.20-40℃ 8.下列对金属和金属材料的认识中，错误的是（）
Chapter 6 Metallic Materials 1.名词解释：Explain the concepts: 1）黑色金属: 指铁、铬、锰金属及其合金，以铁及铁合金为主。Blank metals: refers to Fe, Cr, Mn and their alloys, mainly are Fe and its alloy. 2）有色金属：除铁、铬、锰以外的金属成为有色金属。Non-ferrous metals: refers to metals except iron, chromium, manganese and their alloys. 3）奥氏体：碳溶解在γ－Fe中的间隙固溶体，它仍保持γ－Fe的面心立方晶格，晶界比较直，呈规则多边形。Austenite: interstitial solid solution formed by carbon dissolves in γ-Fe, it remains face-centered cubic lattice of γ-Fe, the grain boundary is relatively straight, and is regular polygon. 4）马氏体：碳在α－Fe中的过饱和固溶体，晶体结构为体心四方结构，中高碳钢中加速冷却通常能够得到这种组织。Martensite: supersaturated solid solution formed by the carbon dissolves in α-Fe, the crystal structure is body-centered tetragonal structure, it can be obtained by accelerated cooling the high-carbon steel. 5）超耐热合金：在700～1200℃高温下能长时间保持所需力学性能，具抗氧化、抗腐蚀能力，且能满意工作的金属材料。Super heat-resistant alloys: materials that can maintain the required mechanical properties at high temperature of 700 to 1200 ℃ for a long time. They are antioxidant, corrosion resistant and can work satisfactory. 6）金属固溶体：指一种溶质元素（金属或非金属）原子溶解到另一种溶剂金属元素（较大量的）的晶体中形成的一种均匀的固态溶液。Metal solid solutions: refers to a homogeneous solid solution that formed by a solute elements (metal or nonmetal) atoms dissolve into a solvent metal element (relatively large). 7）金属间化合物：指金属和金属之间，类金属和金属原子之间以共价键形式结合生成的化合物，具有不同于其组成元素的长程有序晶体结构和金属基本特性。Intermetallic compounds: refers to compounds that formed between the metal and the metal atoms by covalent binding. They have basic characteristics of metal and long-range ordered crystal structure. 2.简述形状记忆合金原理。Describe the principle of shape memory alloys. 答：形状记忆合金是指具有一定初始形状的材料经形变并固定成另一形状后，通过热、光、电等物理刺激或化学刺激的处理又可恢复成初始形状的合金。其形状记忆效应源于某些特殊
多晶硅薄膜晶体管特性研究 摘要 多晶硅薄膜晶体管（polysilicon thin film transiston）因其高迁移率、高速高集成化、p 型和n型导电模式、自对准结构以及耗电小、分辨率高等优点，近年来被广泛的应用于液晶显示器。随着器件尺寸减小至深亚微米，热载流子退化效应所致器件以及电路系统的可靠性是器件的长期失效问题。 本文主要研究热载流子效应。首先，研究热载流子退化与栅极应力电压，漏极应力电压及应力时间的依赖关系。其次，漏极轻掺杂（Light Doped Drain，LDD）结构是提高多晶硅薄膜晶体管抗热载流子特性的一种有效方法，研究了LDD结构多晶硅薄膜晶体管的结构参数对器件可靠性的影响。 关键词：多晶硅薄膜晶体管热载流子效应可靠性
Study on Characteristics of polysilicon thin film transistor Abstract Today, p-Si TFTs are used broadly in display devices because of its high field effect mobility,high integration and high speed,high definition display,n channel and p channel capability,low power consumption and self-aligned structures. With the device scaling down to deep-submicrometer, the reliability of the device circuit system induced by hot carrier effect is long-term failure. Hot carrier effects is studied. Firstly,we mainly study the dependence between hot carrier degradation and gate-stress voltage,drain-stress voltage and stress time.Secondly,the structure of Light Doped Drain is an effective means to resist hot carrier effect ,the influence of parameters of LDD structures on reliability of p-Si TFT was investigated. Keywords：p-Si TFT;hot carrier effect;reliability
第六章答案 1．用 45 钢制造机床齿轮，其工艺路线为：锻造—正火—粗加工一调 质一精加工—高频感应加热表面淬火一低温回火—磨加工。说明各热处理 工序的目的及使用状态下的组织。 答：锻造后的 45 钢硬度较高，不利于切削加工，正火后将其硬度控制 在 160-230HBS 围，提高切削加工性能。组织状态是索氏体。粗加工后， 调质处理整个提高了 45 钢强度、硬度、塑性和韧性，组织状态是回火索氏 体。高频感应加热表面淬火是要提高 45 钢表面硬度的同时，保持心部良好 的塑性和韧性。低温回火的组织状态是回火马氏体，回火马氏体既保持了 45 钢的高硬度、高强度和良好的耐磨性，又适当提高了韧性。2．常用的合金元素有哪些？其中非碳化物形成元素有一一一：碳化物 形成元素有一一一；扩大 A 区元素有——；缩小 A 区元素在一一。答：常用的合金元素有：锰、铬、钼、钨、钒、铌、锆、钛、镍、硅、铝、钴、镍、氮等。其中非碳化物形成元素有：镍、硅、铝、钴等；
形成元素有：锰、铬、钼、钨、钒、铌、锆、钛等；扩大 A 区元素有：镍、 锰、碳、氮等；小 A 区元素有：铬、铝、硅、钨等。 3．用 W18Cr4V 钢制作盘形铣刀，试安排其加工工艺路线，说明各热加工工序的目的，使用状态下的显微组织是什么？为什么淬火温度高达 1280℃？淬火后为什么要经过三次 560℃回火？能否用一次长时间 回火代 替？ 答：工艺路线: 锻造十球化退火→切削加工→淬火+多次 560℃回火→喷砂→磨 削加工→成品 热处理工艺： 球化退火:高速钢在锻后进行球化退火，以降低硬度，消除锻造应力，便于切削加工，并为淬火做好组织准备。球化退火后的组织为球状珠光体。 淬火和回火:高速钢的优越性能需要经正确的淬火回火处理后才能获得。 淬火温度高（1220-1280℃）的原因是：合金元素只有溶入钢中才能有 效提高红硬性，高速钢量的 W、MO、Cr、V 的是难熔碳化物，它们只
1 滑移与孪生的区别及它们在塑性变形过程中的作用。 答：滑移与孪生的区别： （1）滑移是晶体两部分发生相对滑动，不改变晶体位向，孪生是晶体一部分相对另一部分发生均匀切变，发生位向的改变，孪生面两侧原子呈镜面对称。 （2）滑移面上的原子移动的距离是原子间距的整数倍，而孪生方向移动的原子不是原子间距的整数倍。 （3）滑移是个缓慢的过程，孪生产生速度极快。 （4）滑移是在晶体内各晶粒内部产生不均匀，而孪生在整个孪生区内部都是均匀的切变。 作用：晶体产生塑性变形过程主要依靠滑移机制来完成的；孪生所需的临界应力要高很多，对塑性变形的贡献比滑移小得多，但孪生改变了部分晶体的空间取向，使原来处于不利取向的滑移系转变为新的有利取向，激发晶体滑移。 2面心立方、体心立方、密排六方金属的主要塑性变形方式是什么？温度、变形速度对其有何影响？铝、铁、鎂中哪种金属的塑性最好？哪种最差？ 答：面心立方、体心立方有较多的滑移系，塑性变形以滑移为主，而密排六方金属对称性低，滑移系少，塑性变形方式主要是孪生。变形温度越高，滑移越容易，孪生产生的几率越小，反之变形温度越高，滑移越困难，产生孪晶的几率越大。变形速度越大，滑移常来不及产生足够大的变形，因此导致切应力增大，产生孪晶的几率也增大。铝为面心立方结构、铁为体心立方结构、镁为密排六方结构，因此铝的塑性最好，镁的塑性最差。 3绘图说明常见fcc、bcc结构金属的滑移系有哪些？这两种晶体结构的密排面、密排方向是哪些？与滑移系之间有何关系？ 答：FCC晶格：滑移面就是最密排面：｛111｝包括(111), (111), (111), (111); 滑移方向就是最密排方向：〈110〉每个滑移面上有三个，如图中箭头所示。 一个滑移面与滑移面上的一个滑移方向构成一个滑移系，因此滑移系数: 4×3=12 BCC晶格：滑移面：｛110｝ (110), (011), (101), (110), (011), (101)共6个 滑移方向：〈111〉，每个滑移面上两个，如图箭头所示。 所以共有滑移系数：6×2=12
第六章耐热钢 1.在耐热钢的常用合金元素中，哪些是抗氧化元素？哪些是强化元素？哪些是奥氏体形成元素？说明其作用机理。 答：①Cr：提高钢抗氧化性的主要元素，Cr能形成附着性很强的致密而稳定的氧化物Cr2O3，提高钢的抗氧化性。 ②Al：是提高钢抗氧化性的主要元素，含铝的耐热钢在其表面上能形成一层保护性良好的Al2O3膜，它的抗氧化性能优于Cr2O3膜。 ③Si：是提高抗氧化性的辅助元素，效果比Al还要有效。高温下，在含硅的耐热钢表面上形成一层保护性好、致密的SiO2膜。钢中含硅量达1％～2％时，就有较明显的抗氧化效果。 ④Mo、W：是提高低合金耐热钢热强性能的重要元素，Mo溶入基体起固溶强化作用，能提高钢的再结晶温度，也能析出稳定相，从而提高热强性。W的作用于Mo相似。 ⑤Ti、Nb、V：是强碳化物形成元素，能形成稳定的碳化物，提高钢的松弛稳定性，也提高热强性。当钢中有Mo、Cr等元素时，能促进这些元素进入固溶体，提高高温强度。 ⑥Ni：是奥氏体形成元素，获得奥氏体组织。 2.为什么锅炉管子用珠光体热强钢的含C量都较低（<0.2%）？有一锅炉管子经运行两年后，发现有“起瘤”现象，试分析原因，并提出改进设想。 答：因为含碳量高了，使珠光体球化和聚集速度加快，石墨化倾向增大，合金元素的再分配加速，并且钢的焊接、成型等工艺性能有所降低。在保证有足够强度的前提下，尽可能降低碳量。 3.提高钢热强性的途径有哪些？ 答：(1)强化基体：耐热温度要求越高，就要选用熔点越高的金属作基体。合金元素的多元适量复合加入，可显著提高热强性。 (2)强化晶界:①净化晶界:在钢中加入稀土、硼等化学性质比较活泼的元素；②填充晶界空位：晶界上空位较多，原子易快速扩散。B易偏聚于晶界，减少晶界空位。 (3)弥散相强化：金属基体上分布着细小、稳定、弥散分布的第二相质点，能有效地阻止位错运动，而提高强度。获得弥散相的方法有直接加入难熔质点和时效析出两种。 (4)热处理：珠光体耐热钢进行热处理，一方面可获得需要的晶粒度，另一方面可以提高珠光体热强钢的蠕变强度。 4.为什么y-Fe基热强钢比a-Fe基热强钢的热强性要高？ 答：因为金属或合金的晶格类型也影响原子间结合力。对Fe基合金来说，面心立方晶体的原子间结合力较强，体心立方晶体较弱。所以奥氏体型钢要比铁素体型钢、马氏体型钢、珠光体型钢的蠕变抗力高。因为奥氏体晶体y-Fe的原子排列比较致密，合金元素在y-Fe晶体中不容易扩散，并且y-Fe晶界上原子有序度比较好，晶界强度较高。 5.什么叫抗氧化钢？常用在什么地方？ 答：抗氧化钢：在高温下有较好的抗氧化能力且具有一定强度的钢。 常用于工业炉子中的构件、炉底板、料架、炉罐等。 6.为什么低合金热强钢都用Cr、Mo、V合金化？ 答:因为Cr是提高钢抗氧化性的主要元素，Cr能形成附着性很强的致密而稳定的氧化物Cr2O3，提高钢的抗氧化性。Cr也能固溶强化，提高钢的持久强度和蠕变极限。Mo是提高低合金耐热钢热强性能的重要元素，Mo溶入基体起固溶强化作用，能提高钢的再结晶温度，也能析出稳定相，从而提高热强性。V是强碳化物形成元素，能形成稳定的碳化物，提高钢的松弛稳定性，也提高热强性。当钢中有Mo、Cr等元素时，能促进这些元素进入固溶体，提高高温强度。