共查询到20条相似文献,搜索用时 31 毫秒
1.
Mehmet Alper Sahiner Joseph C. Woicik Timothy Kurp Jeffrey Serfass Marc Aranguren 《Materials Science in Semiconductor Processing》2008,11(5-6):245
The thin film growth conditions are correlated with the local structures formed in HfxZr1−xO2 (x=0.0–1.0) high-k dielectric thin films on Si and Ge substrates during deposition. Pulsed laser deposition (PLD) technique has been used in the synthesis of the thin films with systematic variations of substrate temperature, Zr content of the targets and substrate selection. The local structural information acquired from extended X-ray absorption spectroscopy (EXAFS) is correlated with the thin film growth conditions. The response of the local structure around Hf and Zr atoms to growth parameters was investigated by EXAFS experiments performed at the National Synchrotron Light Source of Brookhaven National Laboratory. The competing crystal phases of oxides of Hf were identified and the intricate relation between the stabilized phase and the parameters as: the substrate temperature; Hf to Zr ratio; have been revealed. Specifically, HfO2 thin films on Si(1 0 0) exhibit a tetragonal to monoclinic phase transformation upon increase in the substrate temperature during deposition whereas, HfO2 PLD films on Ge(1 0 0) substrates remain in tetragonal symmetry regardless of the substrate temperature. 相似文献
2.
O. M. Orlov D. R. Islamov A. G. Chernikova M. G. Kozodaev A. M. Markeev T. V. Perevalov V. A. Gritsenko G. Ya. Krasnikov 《Russian Microelectronics》2016,45(5):350-356
The mechanism responsible for the charge transport in thin ferroelectric Hf0.5Zr0.5O2 films has been studied. It is shown that in these films the transport mechanism is phonon-assisted tunneling between the traps. The optimal thickness of dielectric film for TiN/Hf0.5Zr0.5O2/Pt structures is determined. As a result of comparing the experimental current–voltage (I–V) characteristics of TiN/Hf0.5Zr0.5O2/Pt structures with the calculated ones, the thermal and optical energies of the traps are determined and the concentration of the traps is estimated. A comparison between the transport properties of ferroelectric and amorphous Hf0.5Zr0.5O2 films is carried out. It is shown that the charge transport mechanism in this dielectric does not depend on its crystalline phase. A method for decreasing leakage currents in Hf0.5Zr0.5O2 is proposed. A study of the resource of repolarization cycles for TiN/Hf0.5Zr0.5O2/TiN metal-dielectric-metal (MDM) structures fully grown by atomic layer deposition (ALD) has been carried out. 相似文献
3.
Composition‐ and Shape‐Controlled Synthesis and Optical Properties of ZnxCd1–xS Alloyed Nanocrystals
Composition‐tunable ZnxCd1–xS alloyed nanocrystals have been synthesized by a new approach consisting of thermolyzing a mixture of cadmium ethylxanthate (Cd(exan)2) and zinc ethylxanthate (Zn(exan)2) precursors in hot, coordinating solvents at relatively low temperatures (180–210 °C). The composition of the alloyed nanocrystals was accurately adjusted by controlling the molar ratio of Cd(exan)2 to Zn(exan)2 in the mixed reactants. The alloyed ZnxCd1–xS nanocrystals prepared in HDA/TOP (HDA: hexadecylamine; TOP: trioctylphosphine) solution exhibit composition‐dependent shape and phase structures as well as composition‐dependent optical properties. The shape of the ZnxCd1–xS nanocrystals changed from dot to single‐armed rod then to multi‐armed rod with a decrease of Zn content in the ternary nanoparticles. The alloying nature of the ZnxCd1–xS nanocrystals was consistently confirmed by the results of high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), and UV‐vis absorption and photoluminescence (PL) spectroscopy. Further, the shape‐controlled synthesis of the ternary alloyed nanocrystals was realized by selecting appropriate solvents. Uniform nanodots in the whole composition range were obtained from TOPO/TOP solution, (TOPO: trioctylphosphine oxide) and uniform nanorods in the whole composition range were prepared from HDA/OA solution (OA: octylamine). The effect of the reaction conditions, such as solvent, reaction temperature, and reaction time, on the PL spectra of the alloyed ZnxCd1–xS nanocrystals was also systematically studied, and the reaction conditions were optimized for improving the PL properties of the nanocrystals. 相似文献
4.
Jinchen Wei Lilai Jiang Menglin Huang Yuning Wu Shiyou Chen 《Advanced functional materials》2021,31(42):2104913
It is believed that promoting the fraction of ferroelectric orthorhombic phase (o-phase) through O-poor growth conditions can increase the spontaneous polarization of HfO2 and (Hf,Zr)O2 thin films. However, the first-principles calculations show that the growth may be limited by the easy formation of point defects in the orthorhombic and tetragonal phases of HfO2, ZrO2, and (Hf,Zr)O2. Their dominant defects, O interstitial (Oi) under O-rich conditions and O vacancy (VO) under O-poor condition, have low formation energies and quite high density (1016–1019 cm−3 for 800–1400 K growth temperature). Especially, Oi has negative formation energy in tetragonal HfO2 under O-rich condition, causing non-stoichiometry and limiting the crystalline-seed formation during o-phase growth. High-density defects can cause disordering of dipole moments and increase leakage current, both diminishing the polarization. These results explain the experimental puzzle that the measured polarization is much lower than the ideal value even in O-poor thin films and highlight that controlling defects is as important as promoting the o-phase fraction for enhancing ferroelectricity. The O-intermediate condition (average of O-rich and O-poor conditions) and low growth temperature are proposed for fabricating HfO2 and (Hf,Zr)O2 with fewer defects, lower leakage current, and stronger ferroelectricity, which challenges the belief that O-poor condition is optimal. 相似文献
5.
Y.C. Li H.Z. Zhong R. Li Y. Zhou C.H. Yang Y.F. Li 《Advanced functional materials》2006,16(13):1705-1716
The high‐yield fabrication of tetrapodal CdSe, CdTe, and CdSexTe1–x nanocrystals is systematically studied. CdSe nanocrystals are prepared by first controlling the synthesis of high‐quality wurtzite CdSe and zinc blende CdSe nanocrystals at a relatively high temperature (260 °C) by selecting different ligands. Then, based on the phase control of the CdSe nanocrystals, two nanoparticle‐tailoring routes (i.e., a seed‐epitaxial route and ligand‐dependent multi‐injecting route) are used, and a high yield of CdSe tetrapods is obtained. CdTe nanocrystals are prepared by adjusting the ligand composition and the ratio of Cd to Te; CdTe tetrapods are synthesized in high yield using a mixed ligand that does not contain alkylphosphonic acids. Moreover, the nanoscale Te powder (Te nanowires/nanorods), which is highly soluble in the ligand solvent, is first used as a Te source to synthesize CdTe nanocrystals, which remarkably enhanced the output of the CdTe nanocrystals in one reaction. Furthermore, composition‐tunable ternary CdSexTe1–x alloyed tetrapods are synthesized on a large scale, for the first time, by thermolyzing the mixture of the organometallic Cd precursor and the mixed (Se + Te) source in a mixed‐ligand solution. The CdSe, CdTe, and CdSexTe1–x nanocrystals are characterized by transmission electron microscopy (TEM), high‐resolution TEM, selected‐area electron diffraction, X‐ray diffraction, and UV‐vis and photoluminescence (PL) spectroscopy. Interesting nonlinear, composition‐dependent absorption and PL spectra are observed for the ternary CdSexTe1–x alloyed nanocrystals. The band‐edge positions of the nanocrystals of CdSe, CdSexTe1–x, and CdTe are systematically studied by cyclic voltammetry. 相似文献
6.
N.D. Afify G. Dalba U. Mahendra Kumar Koppolu C. Armellini Y. Jestin F. Rocca 《Materials Science in Semiconductor Processing》2006,9(6):1043
This paper reports a detailed structural study on the nucleation of t-HfO2 nanocrystals in thin films of 70SiO2–30HfO2 prepared by sol–gel route on v-SiO2 substrates. Thermal treatment was performed at different temperatures ranging from 900 to 1200 °C for short (30 min) or long (24 h) time periods. Crystallisation and microstructure evolutions were traced by X-ray diffraction (XRD). The local structure around hafnium ions was determined from Hf L3-edge extended X-ray absorption fine structure (EXAFS) measurements carried out at the BM08-GILDA Beamline of ESRF (France). XRD shows the nucleation of HfO2 nanocrystals in the tetragonal phase after heat treatment at 1000 °C for 30 min, and a partial phase transformation to the monoclinic phase (m-HfO2) starts after heat treatment at 1200 °C for 30 min. The lattice parameters as well as the average crystallites size and their distributions were determined as a function of the heat treatment. EXAFS results are in agreement with the XRD ones, with hafnium ions in the film heat treated at 1100 °C for 24 h are present in mixed phases. 相似文献
7.
J. Müller T.S. Böscke U. Schröder M. Reinicke L. Oberbeck D. Zhou W. Weinreich P. Kücher M. Lemberger L. Frey 《Microelectronic Engineering》2009,86(7-9):1818-1821
A broad compositional range of the dielectric material Zr1?xHfxO2 was evaluated with respect to its applicability in DRAM storage capacitors. The paper reports on phase composition, crystallization behavior, and electrical properties of the mixed system in planar metal-insulator-metal (MIM) capacitors. Admixture of HfO2 into ZrO2 proved to stabilize the deposition process at high temperatures without degrading the dielectric properties of the film. Compared to pure ZrO2 the 30–40% HfO2 containing films showed improved scalability (capacitance equivalent thickness 0.73 nm at 8 * 10?9 A/cm2) as well as improved reliability. 相似文献
8.
Pavan Pujar Haewon Cho Srinivas Gandla Muhammad Naqi Seongin Hong Sunkook Kim 《Advanced functional materials》2021,31(43):2103748
The fabrication of Hf0.5Zr0.5O2-ferroelectric negative capacitor using solution combustion is presented for the first time. The starting materials used for the solution combustion to form equimolar Hf0.5Zr0.5O2 are to act as both combustible elements and cation sources. Jain's method, which is used for estimating the stoichiometric quantities of precursors in propellant chemistry, has also been modified and applied. The conventional assumption for this method that molecular oxygen does not take part in the reaction is refuted and stoichiometric combustion in the presence of molecular oxygen is proposed. This reaction is followed by post-rapid thermal processing to stabilize the metastable, non-centrosymmetric orthorhombic phase. The thin film stacks, Hf0.5Zr0.5O2/HfO2, are used to achieve sub-thermionic swing (forward sweep: 25.42 ± 8.05 mV dec−1, reverse sweep: 42.56 ± 4.87 mV dec−1) in MoS2 negative capacitance field effect transistors with a hysteresis of ≈ 40 mV at 1 nA, resulting in ultra-low-power operation. 相似文献
9.
Run Zhao Weiwei Li Joon Hwan Lee Eun Mi Choi Yan Liang Wei Zhang Rujun Tang Haiyan Wang Quanxi Jia Judith L. MacManus‐Driscoll Hao Yang 《Advanced functional materials》2014,24(33):5240-5245
Self‐assembled nanocomposite films and coatings have huge potential for many functional and structural applications. However, control and manipulation of the nanostructures is still at very early stage. Here, guidelines are established for manipulating the types of composite structures that can be achieved. In order to do this, a well studied (YBa2Cu3O7‐δ)1‐x:(BaZrO3)x ‘model’ system is used. A switch from BaZrO3 nanorods in YBa2Cu3O7‐δ matrix to planar, horizontal layered plates is found with increasing x, with a transitional cross‐ply structure forming between these states at x = 0.4. The switch is related to a release in strain energy which builds up in the YBa2Cu3O7‐δ with increasing x. At x = 0.5, an unusually low strain state is observed in the planar composite structure, which is postulated to arise from a pseudo‐spinodal mechanism. 相似文献
10.
S. Sakurai S. Kuroki H. Tokoro K. Hashimoto S. Ohkoshi 《Advanced functional materials》2007,17(14):2278-2282
A series of ?‐InxFe2–xO3 nanorods are prepared by combining the reverse‐micelle and the sol–gel methods. Metal replacement was achieved in the region of 0 ≤ x ≤ 0.24. The crystal structures are orthorhombic structures (space group: Pna21), which are pyroelectric with an electric polarization along the c axis. The transmission electron microscopy images show that the particle sizes are (80 ± 40) × (23 ± 5) nm (x = 0), (65 ± 30) × (30 ± 10) nm (x = 0.12), and (80 ± 40) × (35 ± 15) nm (x = 0.24). The magnetization versus temperature curves of the samples with x = 0, x = 0.12, and x = 0.24 show spontaneous magnetization with Curie temperatures of 495 K, 456 K, and 414 K, respectively. Their coercive fields at 300 K are 20 kOe (x = 0), 14 kOe (x = 0.12), and 9 kOe (x = 0.24). These samples show a spin reorientation with reorientation temperatures (Tp) of 102 K (x = 0), 149 K (x = 0.12), and 180 K (x = 0.24). In particular, the samples with x = 0.12 and x = 0.24 show antiferromagnetic behavior below Tp. This series of ?‐InxFe2–xO3 is the first example of a pyroelectric material that exhibits a phase transition between ferrimagnetism and antiferromagnetism. 相似文献
11.
Mauro Epifani Teresa Andreu Sara Abdollahzadeh‐Ghom Jordi Arbiol Joan R. Morante 《Advanced functional materials》2012,22(13):2867-2875
Ceria–zirconia solid solution nanocrystals, (1‐x)CeO2–xZrO2, 0 ≤ x ≤ 1, are prepared by sol–gel processing in dodecylamine of solutions obtained by forced hydrolysis of inorganic salts. The as‐prepared nanoparticles have a ceria cubic structure, up to x = 0.35, or are amorphous. Heat‐treatment is carried out at temperatures ranging from 500 to 800 °C, the latter temperature begin suitable to obtain solid solutions throughout the composition range. For all the heating temperatures and x values, the fluorite cubic structure of pure CeO2 transforms to a mixture (c′) of the cubic c and tetragonal t″ phases for x = 0.35, and to tetragonal t phase only for x = 0.8 at 650 °C, x = 0.65 at 800 °C, and, to a very limited extent, x = 0.5 at 1000 °C. No evidence is obtained at low x values of the t phase, which is detrimental to the oxygen storage capacity. Prolonged heating at 1000 °C demonstrates that only for x = 0.65 a limited separation of CeO2‐rich nanocrystals occurs. The samples undergo the same transition without simultaneous occurrence of different phases, apart for the two mentioned limited cases. This result is attributed to the intimate mixing of the metal cations even in the early stages of processing. In as‐prepared samples the Zr distribution becomes inhomogeneous when going from x = 0.2 to x = 0.35, but no early phase separations appear. The oxygen storage capacity is favorably influenced by the persistence of the cubic c′ phase. 相似文献
12.
Puqi Hao Shuaizhi Zheng Binjian Zeng Tao Yu Zhibin Yang Luocheng Liao Qiangxiang Peng Qijun Yang Yichun Zhou Min Liao 《Advanced functional materials》2023,33(31):2301746
The next-generation semiconductor memories are essentially required for the advancements in modern electronic devices. Ferroelectric memories by HfO2-based ferroelectric thin films (FE-HfO2) have opened promising directions in recent years. Nevertheless, improving the polarization switching speed of FE-HfO2 remains a critical task. In this study, it is demonstrated that the composition-graded Hf1-xZrxO2 (HZO) ferroelectric thin film has more than two times faster polarization switching speed than the conventional composition-uniform one. Meanwhile, it has excellent ferroelectricity and improved endurance characteristics. It is also discovered that when the HZO thin film has a gradient composition, the polarization-switching dynamics shifts from the nucleation-limited-switching mechanism to the domain-wall growth mechanism. Moreover, the transition of switching dynamics is responsible for the faster speed and better endurance of the composition-graded HZO thin film. These findings not only reveal the physical mechanisms of this material system but also provide a new strategy for memory devices having faster speed and higher endurance. 相似文献
13.
The objective of this research is the development of chemical routes for the preparation of high‐temperature superconducting powders. A simple sol–gel synthesis technique for preparing the superconducting compound Hg1−xTlxBa2Ca2Cu3O8+δ (Hg,Tl‐1223) has been refined. A systematic study of the influence of synthesis conditions on the phase purity of the obtained superconducting material is described. We have demonstrated that superconducting Hg1−xTlxBa2Ca2Cu3O8+δ phase of good quality can be obtained by this sol–gel synthesis method. Replacing Hg by Tl in the bulk material significantly increased the superconducting transition temperature. An as‐prepared sample showed TC(onset)=136 K, but after oxygen treatment the critical temperature of Hg1−xTlxBa2Ca2Cu3O8+δ superconductor increased to 140 K. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
14.
Xin Gu Liang Chen Zhicheng Ju Huayun Xu Jian Yang Yitai Qian 《Advanced functional materials》2013,23(32):4049-4056
Hierarchical nanocomposites rationally designed in component and structure, are highly desirable for the development of lithium‐ion batteries, because they can take full advantages of different components and various structures to achieve superior electrochemical properties. Here, the branched nanocomposite with β‐MnO2 nanorods as the back‐bone and porous α‐Fe2O3 nanorods as the branches are synthesized by a high‐temperature annealing of FeOOH epitaxially grown on the β‐MnO2 nanorods. Since the β‐MnO2 nanorods grow along the four‐fold axis, the as‐produced branches of FeOOH and α‐Fe2O3 are aligned on their side in a nearly four‐fold symmetry. This synthetic process for the branched nanorods built by β‐MnO2/α‐Fe2O3 is characterized. The branched nanorods of β‐MnO2/α‐Fe2O3 present an excellent lithium‐storage performance. They exhibit a reversible specific capacity of 1028 mAh g?1 at a current density of 1000 mA g?1 up to 200 cycles, much higher than the building blocks alone. Even at 4000 mA g?1, the reversible capacity of the branched nanorods could be kept at 881 mAh g?1. The outstanding performances of the branched nanorods are attributed to the synergistic effect of different components and the hierarchical structure of the composite. The disclosure of the correlation between the electrochemical properties and the structure/component of the nanocomposites, would greatly benefit the rational design of the high‐performance nanocomposites for lithium ion batteries, in the future. 相似文献
15.
《Progress in Photovoltaics: Research and Applications》2017,25(1):113-122
Because of its tunable band gap and band position, Sb2(Se1 − x Sx )3 (0 ≤ x ≤ 1) is a promising light‐absorbing material for photovoltaic device applications. However, no systematic study on the synthesis and characterization of single‐phase polycrystalline Sb2(Se1 − x Sx )3 thin films has been reported. Through introducing in situ sulfurization into the rapid thermal evaporation process, a series of single‐phase, highly crystalline Sb2(Se1 − x Sx )3 films with x = 0.09, 0.20, 0.31, and 0.43 were successfully obtained, with the corresponding band gap, band position and film morphology fully revealed. Futhermore, solar cells with superstrate ITO/CdS/Sb2(Se1 − x Sx )3/Au structure were fabricated and carefully optimized. Finally, a champion device having 5.79% solar conversion efficiency was obtained employing uniform Sb2(Se0.80S0.20)3 absorber layer. Our experimental investigation confirmed that Sb2(Se1 − x Sx )3 is indeed a very promising absorber material worth further optimization. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
16.
Guodong Du Neeraj Sharma Vanessa K. Peterson Justin A. Kimpton Dianzeng Jia Zaiping Guo 《Advanced functional materials》2011,21(20):3990-3997
Synchrotron X‐ray diffraction data were used to determine the phase purity and re‐evaluate the crystal‐structure of Li4Ti5O12‐xBrx electrode materials (where the synthetic chemical inputs are x = 0.05, 0.10 0.20, 0.30). A maximum of x′ = 0.12 Br, where x′ is the Rietveld‐refined value, can be substituted into the crystal structure with at least 2% rutile TiO2 forming as a second phase. Higher Br concentrations induced the formation of a third, presumably Br‐rich, phase. These materials function as composite anodes that contain mixtures of TiO2, Li4Ti5O12‐xBrx, and a Br‐rich third, unknown, phase. The minor quantities of the secondary phases in combination with Li4Ti5O12‐xBrx where x′ ~ 0.1 were found to correspond to the optimum in electrochemical properties, while larger quantities of the secondary phases contributed to the degradation of the performance. In situ neutron diffraction of a composite anatase TiO2/Li4Ti5O12 anode within a custom‐built battery was used to determine the electrochemical function of the TiO2 component. The Li4Ti5O12 component was found to be electrochemically active at lower voltages (1.5 V) relative to TiO2 (1.7 V). This enabled Li insertion/extraction to be tuned through the choice of voltage range in both components of this composite or in the anatase TiO2 phase only. The use of composite materials may facilitate the development of multi‐component electrodes where different active materials can be cycled in order to tune power output. 相似文献
17.
Chang-Ta Yang Kuei-Shu Chang-Liao Hsin-Chun Chang Tzu-Chen Wang Wen-Fa Wu 《Microelectronic Engineering》2007,84(12):2916-2920
Interaction of HfxTayN metal gate with SiO2 and HfOxNy gate dielectrics has been extensively studied. Metal-oxide-semiconductor (MOS) device formed with SiO2 gate dielectric and HfxTayN metal gate shows satisfactory thermal stability. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis results show that the diffusion depths of Hf and Ta are less significant in SiO2 gate dielectric than that in HfOxNy. Compared to HfOxNy gate dielectric, SiO2 shows better electrical properties, such as leakage current, hysteresis, interface trap density and stress-induced flat-band voltage shift. With an increase in post metallization annealing (PMA) temperature, the electrical characteristics of the MOS device with SiO2 gate dielectric remain almost unchanged, indicating its superior thermal and electrical stability. 相似文献
18.
Cecilia I. Ventura Jose D. Querales Flores Javier D. Fuhr Rafael A. Barrio 《Progress in Photovoltaics: Research and Applications》2015,23(1):112-118
Ternary group‐IV alloys have a wide potential for applications in infrared devices and optoelectronics. In connection with photovoltaic applications, they are among the most promising materials for inclusion in the next generation of high‐efficiency multijunction solar cells, because they can be lattice matched to substrates as GaAs and Ge, offering the possibility of a range of band gaps complementary to III–V semiconductors. Apart from the full decoupling of lattice and band structures in Ge1 − x − ySixSny alloys, experimentally confirmed, they allow preparation in a controllable and large range of compositions, thus enabling to tune their band gap. Recently, optical experiments on ternary alloy‐based films, photodetectors measured the direct absorption edges and probed the compositional dependence of the direct gap. The nature of the fundamental gap of Ge1 − x − ySixSny alloys is still unknown, as neither experimental data on the indirect edges nor electronic structure calculations are available, as yet. Here, we report a first calculation of the electronic structure of Ge1 − x − ySixSny ternary alloys, employing a combined tight‐binding and virtual crystal approximation method, which proved to be useful to describe group‐IV semiconductor binary alloys. Our results confirm predictions and experimental indications that a 1eV band gap is indeed attainable with these ternary alloys, as required for the fourth layer plan to be added to present‐day record‐efficiency triple‐junction solar cells, to further increase their efficiency, for example, for satellite applications. When lattice matched to Ge, we find that Ge1 − x − ySixSny ternary alloys have an indirect gap with a compositional dependence reflecting the presence of two competing minima in the conduction band. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
Giulio Ferrari J.R. Watling S. Roy J.R. Barker P. Zeitzoff G. Bersuker A. Asenov 《Materials Science in Semiconductor Processing》2006,9(6):995
HfO2-based high-κ dielectrics are among the most likely candidates to replace SiO2 and the currently favoured oxinitride in the next generation of MOSFETs. High-κ materials allow the use of a thicker gate dielectric, maintaining the gate capacitance with reduced gate leakage. However, they lead to a fundamental mobility degradation due to the coupling of carriers to surface soft (low-energy) optical phonons. Comparing the vertical field dependence of the mobility for HfO2 and SiO2, the severe degradation in mobility in the presence of high-κ becomes evident. The introduction of a SiO2 interfacial layer between the channel and the HfO2 mitigates this degradation, by increasing the effective distance between the carriers and the SO phonons, thus decreasing the interaction strength, this does though lead to an increase in the equivalent oxide thickness (EOT) of the gate dielectric. The material of choice for the first commercial introduction of high-κ gate stacks is Hafnium Silicate (SixHf1-xO2). This alloy stands up better to the processing challenges and as a result suffers less from dielectric fluctuations. We show that as the fraction of Hf increases within the alloy, the inversion layer mobility is shown to decrease due to the corresponding decrease in the energy of the surface optical phonons and increase in the dielectric constant of the oxide. 相似文献
20.
Huajun Liu Ping Yang Kui Yao Khuong Phuong Ong Ping Wu John Wang 《Advanced functional materials》2012,22(5):937-942
A tetragonal BiFeO3 phase with giant c/a of approximately 1.25 has been of great interest recently as it potentially possesses a giant polarization and much enhanced electromechanical response. This super‐tetragonal phase is known to be a stable phase only under high compressive strains of above approximately 4.5%, according to first principle calculations. However, in previous work, this super‐tetragonal BiFeO3 phase was obtained in films deposited at high growth rate on SrTiO3 substrates with compressive strain of only around 1.5%. By detailed structure analysis using high resolution synchrotron X‐ray diffraction, atomic force microscopy, and transmission electron microscopy, the parasitic β‐Bi2O3 phase is identified as the origin inducing the formation of super‐tetragonal BiFeO3 phase on SrTiO3 substrates. In addition, ab initio calculations also confirm that this super‐tetragonal phase is more stable than monoclinic phase when Bi2O3 is present. Using Bi2O3 as a buffer layer, an alternative route, not involving strain engineering, is proposed to stabilize this promising super‐tetragonal BiFeO3 phase at low growth rates. 相似文献