Co-reporter:Lai-Guo WangZheng-Yi Cao, Xu Qian, Lin Zhu, Da-Peng Cui, Ai-Dong Li, Di Wu
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 7) pp:
Publication Date(Web):January 31, 2017
DOI:10.1021/acsami.6b16098
Al2O3- or HfO2-based nanocomposite structures with embedded CoPtx nanocrystals (NCs) on TiN-coated Si substrates have been prepared by combination of thermal atomic layer deposition (ALD) and plasma-enhanced ALD for resistive random access memory (RRAM) applications. The impact of CoPtx NCs and their average size/density on the resistive switching properties has been explored. Compared to the control sample without CoPtx NCs, ALD-derived Pt/oxide/100 cycle-CoPtx NCs/TiN/SiO2/Si exhibits a typical bipolar, reliable, and reproducible resistive switching behavior, such as sharp distribution of RRAM parameters, smaller set/reset voltages, stable resistance ratio (≥102) of OFF/ON states, better switching endurance up to 104 cycles, and longer data retention over 105 s. The possible resistive switching mechanism based on nanocomposite structures of oxide/CoPtx NCs has been proposed. The dominant conduction mechanisms in low- and high-resistance states of oxide-based device units with embedded CoPtx NCs are Ohmic behavior and space-charge-limited current, respectively. The insertion of CoPtx NCs can effectively improve the formation of conducting filaments due to the CoPtx NC-enhanced electric field intensity. Besides excellent resistive switching performances, the nanocomposite structures also simultaneously present ferromagnetic property. This work provides a flexible pathway by combining PEALD and TALD compatible with state-of-the-art Si-based technology for multifunctional electronic devices applications containing RRAM.Keywords: atomic layer deposition; CoPtx; ferromagnetic property; metal oxide; nanocrystal; nonvolatile memory; resistance random access memory;
Co-reporter:Wei Zhang;Ji-Zhou Kong;Zheng-Yi Cao
Nanoscale Research Letters 2017 Volume 12( Issue 1) pp:393
Publication Date(Web):08 June 2017
DOI:10.1186/s11671-017-2164-z
The HfO2/TiO2/HfO2 trilayer-structure resistive random access memory (RRAM) devices have been fabricated on Pt- and TiN-coated Si substrates with Pt top electrodes by atomic layer deposition (ALD). The effect of the bottom electrodes of Pt and TiN on the resistive switching properties of trilayer-structure units has been investigated. Both Pt/HfO2/TiO2/HfO2/Pt and Pt/HfO2/TiO2/HfO2/TiN exhibit typical bipolar resistive switching behavior. The dominant conduction mechanisms in low and high resistance states (LRS and HRS) of both memory cells are Ohmic behavior and space-charge-limited current, respectively. It is found that the bottom electrodes of Pt and TiN have great influence on the electroforming polarity preference, ratio of high and low resistance, and dispersion of the operating voltages of trilayer-structure memory cells. Compared to using symmetric Pt top/bottom electrodes, the RRAM cells using asymmetric Pt top/TiN bottom electrodes show smaller negative forming voltage of −3.7 V, relatively narrow distribution of the set/reset voltages and lower ratio of high and low resistances of 102. The electrode-dependent electroforming polarity can be interpreted by considering electrodes’ chemical activity with oxygen, the related reactions at anode, and the nonuniform distribution of oxygen vacancy concentration in trilayer-structure of HfO2/TiO2/HfO2 on Pt- and TiN-coated Si. Moreover, for Pt/HfO2/TiO2/HfO2/TiN devices, the TiN electrode as oxygen reservoir plays an important role in reducing forming voltage and improving uniformity of resistive switching parameters.
Co-reporter:Ji-Zhou Kong, Shan-Shan Wang, Guo-An Tai, Lin Zhu, Lai-Guo Wang, Hai-Fa Zhai, Di Wu, Ai-Dong Li, Hui Li
Journal of Alloys and Compounds 2016 Volume 657() pp:593-600
Publication Date(Web):5 February 2016
DOI:10.1016/j.jallcom.2015.10.187
•Ultrathin ZrO2 coating is deposited via ALD technology onto Li(Ni0.5Co0.2Mn0.3)O2.•Amorphous ZrO2 coated samples exhibit the significantly improved electrochemical performance.•ZrO2-coated electrode with 5 ALD cycles delivers excellent cycleability and rate capability.•EIS results demonstrate the ultrathin coating layer favors the lithium diffusion of the oxide.Ultrathin ZrO2 coatings are successfully adopted to modify the surface of the layered LiNi0.5Co0.2Mn0.3O2 cathode material via atomic layer deposition (ALD) technology. Compared with the bare LiNi0.5Co0.2Mn0.3O2, the ultrathin ZrO2-coated cathode materials exhibited a significantly improved discharge capacity and cycleability. Among all of the samples, ZrO2-coated LiNi0.5Co0.2Mn0.3O2 electrode with 5 ALD layers showed highest initial Coulombic efficiency, excellently electrochemical cycleability and high rate capability in the voltage range of 2.5–4.5 V at room temperature. Furthermore, this sample showed a discharge capacity of 155.1 mAh g−1 with a high retention of 88.1% at the current of 1000 mA g−1 (5C) after 60 cycles at the elevated temperature of 55 °C, which demonstrated a remarkable enhancement about 150% over that of the bare one. Such enhanced electrochemical performance can be attributed to the high-quality ultrathin ALD metal oxide coating for the cathode material, which protects the cathode material from the undesirable side reaction with the electrode and suppresses the increasing impedance in order to facilitate the diffusion of lithium ion into the host oxide.
Co-reporter:Haifa Zhai, Jizhou Kong, Jien Yang, Jing Xu, Qingran Xu, Hongchen Sun, Aidong Li, Di Wu
Journal of Materials Science & Technology 2016 Volume 32(Issue 7) pp:676-680
Publication Date(Web):July 2016
DOI:10.1016/j.jmst.2016.03.011
The effect of Pt and Cu electrodes on the resistive switching properties and failure behaviors of amorphous ZrO2 films were investigated. Compared with Cu/ZrO2/Pt structures, the Pt/ZrO2/Pt structures exhibit better resistive switching properties such as the higher resistance ratio of OFF/ON states, the longer switching cycles and narrow distribution of OFF state resistance (Roff). The switching mechanism in the Pt/ZrO2/Pt structure can be attributed to the formation and rupture of oxygen vacancy filaments; while in the Cu/ZrO2/Pt structure, there exist both oxygen vacancy filaments and Cu filaments. The formation of Cu filaments is related to the redox reaction of Cu electrode under the applied voltage. The inhomogeneous dispersive injection of Cu ions results in the dispersive Roff and significant decrease of operate voltage. Schematic diagrams of the formation of conductive filaments and the failure mechanism in the Cu/ZrO2/Pt structures are also proposed.
Co-reporter:Guo-Yong Fang, Li-Na Xu, Yan-Qiang Cao, Lai-Guo Wang, Di Wu and Ai-Dong Li
Chemical Communications 2015 vol. 51(Issue 7) pp:1341-1344
Publication Date(Web):01 Dec 2014
DOI:10.1039/C4CC08004A
Plasma-enhanced atomic layer deposition (PE-ALD) has been applied to prepare high-quality ultrathin films for microelectronics, catalysis, and energy applications. The possible pathways for SiO2 PE-ALD using aminosilanes and O2 plasma have been investigated by density functional theory calculations. The silane half-reaction between SiH4 and surface –OH is very difficult and requires a high activation free energy of 57.8 kcal mol−1. The introduction of an aminosilane, such as BDMAS, can reduce the activation free energy to 11.0 kcal mol−1 and the aminosilane plays the role of a self-catalyst in Si–O formation through the relevant half-reaction. Among the various species generated in O2 plasma, 3O2 is inactive towards surface silane groups, similar to ordinary oxygen gas. The other three species, 1O2, 1O, and 3O, can strongly oxidize surface silane groups through one-step or stepwise pathways. In the 3O pathway, the triplet must be converted into the singlet and follow the 1O pathway. Meanwhile, both 1O and 3O can decay to 1O2 and enter into the relevant oxidation pathway. The concept of self-catalysis of aminosilanes may be invoked to design and prepare more effective Si precursors for SiO2 ALD. At the same time, the mechanism of strong surface oxidation by O2 plasma may be exploited in the PE-ALD preparation of other oxides, such as Al2O3, HfO2, ZrO2, and TiO2.
Co-reporter:Yan-Qiang Cao, Lin Zhu, Xin Li, Zheng-Yi Cao, Di Wu and Ai-Dong Li
Dalton Transactions 2015 vol. 44(Issue 33) pp:14782-14792
Publication Date(Web):09 Jul 2015
DOI:10.1039/C5DT00384A
Ti-based fumaric acid hybrid thin films were successfully prepared using inorganic TiCl4 and organic fumaric acid as precursors by molecular layer deposition (MLD). The effect of deposition temperature from 180 °C to 350 °C on the growth rate, composition, chemical state, and topology of hybrid films has been investigated systematically by means of a series of analytical tools such as spectroscopic ellipsometry, atomic force microscopy (AFM), high resolution X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The MLD process of the Ti-fumaric acid shows self-limiting surface reaction with a reasonable growth rate of ∼0.93 Å per cycle and small surface roughness of ∼0.59 nm in root-mean-square value at 200 °C. A temperature-dependent growth characteristic has been observed in the hybrid films. On increasing the temperature from 180 °C to 300 °C, the growth rate decreases from 1.10 to 0.49 Å per cycle and the XPS composition of the film's C:O:Ti ratio changes from 8.35:7.49:1.00 to 4.66:4.80:1.00. FTIR spectra indicate that the hybrid films show bridging bonding mode at a low deposition temperature of 200 °C and bridging/bidentate mixed bonding mode at elevated deposition temperatures of 250 and 300 °C. The higher C and O amounts deviating from the ideal composition may be ascribed to increased organic incorporation into the hybrid films at lower deposition temperature and temperature-dependent density of reactive sites (–OH). The composition of hybrid films grown at 350 °C shows a dramatic decrease in C and O elemental composition (C:O:Ti = 1.97:2.76:1.00) due to the thermal decomposition of the fumaric acid precursor. The produced by-product H2O changes the structure of the hybrid films, resulting in the formation of more Ti–O bonds at high temperatures. The stability of the hybrid films against chemical and thermal treatment, and long-term storage by vacuum-packing was explored carefully. It is found that the ultrathin hybrid film can be transformed into TiO2 nanoparticles via various post deposition annealing processes with different topographies. Finally, the charge trapping ability of the hybrid film is confirmed by fabricating a charge trapping memory capacitor in which the hybrid film was inserted as a charge trapping layer.
Co-reporter:Yan-Qiang Cao, Jun Chen, Xiao-Jie Liu, Xin Li, Zheng-Yi Cao, Yuan-Jie Ma, Di Wu, Ai-Dong Li
Applied Surface Science 2015 Volume 325() pp:13-19
Publication Date(Web):15 January 2015
DOI:10.1016/j.apsusc.2014.11.073
Highlights
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Ge substrates were pretreated by in situ NH3 plasma in PEALD chamber.
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Native oxide GeOx can be transformed into GeOxNy by in situ NH3 plasma.
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GeOxNy has a better thermal stability and interface quality with Ge substrate.
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In situ NH3 plasma pretreatment effectively improves the electrical properties.
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Pt/HfO2/GeOxNy/Ge gate stacks exhibit a sub-nanometer CET of 0.96 nm.
Co-reporter:Xin Li, Xu Qian, Yan-Qiang Cao, Zheng-Yi Cao, Xiao-Jie Liu, Lin Zhu, Ai-Dong Li, Wen-Chao Liu, Di Wu
Materials Letters 2015 150() pp: 12-15
Publication Date(Web):
DOI:10.1016/j.matlet.2015.03.012
Co-reporter:Youpin Gong, Haifa Zhai, Xiaojie Liu, Jizhou Kong, Di Wu, Aidong Li
Applied Surface Science 2014 Volume 291() pp:35-39
Publication Date(Web):1 February 2014
DOI:10.1016/j.apsusc.2013.09.021
Highlights
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ZrO2 films were fabricated on GaAs substrates with ultrathin Gd2O3 control layer.
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Gd2O3 layer significantly improve the electrical properties of GaAs-based device.
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Conduction mechanism varied from Poole–Frenkel to Schottky–Richardson emission.
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Band alignments of interfaces for ZrO2/GaAs and ZrO2/Gd2O3/GaAs were established.
Co-reporter:Yan-Qiang Cao, Zheng-Yi Cao, Xin Li, Di Wu, Ai-Dong Li
Applied Surface Science 2014 Volume 291() pp:78-82
Publication Date(Web):1 February 2014
DOI:10.1016/j.apsusc.2013.10.133
Highlights
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It is difficult to deposit Al2O3 thin films on pristine graphene directly.
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H2O pulses pretreatment can enhance the Al2O3 coverage on pristine graphene.
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Uniform Al2O3 thin films can grow on the graphene after dipping pretreatment.
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No defects are produced in graphene after dipping pretreatment.
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It is easier to deposit Al2O3 on CVD graphene than exfoliated graphene.
Co-reporter:Zheng-Yi Cao, Ai-Dong Li, Xin Li, Yan-Qiang Cao, Di Wu
Thin Solid Films 2014 Volume 563() pp:6-9
Publication Date(Web):31 July 2014
DOI:10.1016/j.tsf.2014.02.024
•The charge trapping memory cells were fabricated by atomic layer deposition method.•The anneal temperature plays a key role in forming nanocrystals.•The memory cells annealed at 800 °C exhibit better memory performance.•The band alignment is beneficial to enhance the retention characteristics.Charge trapping memory cells using Ti–Al–O (TAO) film as charge trapping layer and amorphous Al2O3 as the tunneling and blocking layers were fabricated on Si substrates by atomic layer deposition method. As-deposited TAO films were annealed at 700 °C, 800 °C and 900 °C for 3 min in N2 with a rapid thermal annealing process to form nanocrystals. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize the microstructure and band diagram of the heterostructures. The electrical characteristics and charge storage properties of the Al2O3/TAO/Al2O3/Si stack structures were also evaluated. Compared to 700 °C and 900 °C samples, the memory cells annealed at 800 °C exhibit better memory performance with larger memory window of 4.8 V at ± 6 V sweeping, higher program/erase speed and excellent endurance.
Co-reporter:Mo-Yun Gao;Jun-Long Zhang
Journal of Sol-Gel Science and Technology 2014 Volume 71( Issue 2) pp:283-290
Publication Date(Web):2014 August
DOI:10.1007/s10971-014-3365-x
Hydrophilic FePt nanoparticles (NPs) have been embedded into the MgO-matrix systems via a sol–gel process to prevent FePt NPs from aggregating and sintering during the heat-treatment process required for the L10 ordering. The chemically ordered L10-phase FePt can be obtained after annealing at 700 °C for 60 min in atmosphere containing H2. The effect of the pH value of MgO collosol and FePt nanocrystal loading amount on the structure, morphology, and magnetic properties of FePt/MgO nanocomposites has been investigated. The neutral pH value of 7 in MgO sol is beneficial to stabilize FePt NPs and obtain higher chemical ordering parameter S for the face-centered tetragonal -FePt/MgO nanocomposites with larger coercivity. The FePt NPs loading amount also plays a key role in tuning the microstructure and magnetic properties of the nanocomposites. The relatively higher FePt NPs loading with FePt/MgO molar ratio (RFM) of 1:2 leads to relatively perfect hexagonal assembly and pure L10 phase. When the RFM is 1:5 and 1:10, the MgO-matrix in nanocomposites causes the Fe element loss in FePt NPs along with formation of secondary phases such as magnesioferrite or Pt3Fe during the annealing process. Under optimal processing of neutral pH value of 7 and RFM of 1:2, the presence of MgO matrix produces more homogeneous microstructures and better magnetic properties with higher room-temperature coercivity (HC = 4.65 kOe).
Co-reporter:Xu Qian;Yanqiang Cao;Binglei Guo;Haifa Zhai ;Aidong Li
Chemical Vapor Deposition 2013 Volume 19( Issue 4-6) pp:180-185
Publication Date(Web):
DOI:10.1002/cvde.201207051
Abstract
Al-doped ZnO (AZO) films are deposited at 200°C by atomic layer deposition (ALD) on borosilicate glass and Si(001) substrates using diethylzinc (DEZ) and aluminum isopropoxide (AIP) as the Zn and Al precursors, respectively. The effect of the Zn/Al ALD cycle ratio and the AIP source temperature on the Al dopant concentration and resistivity of AZO films is carefully investigated. By changing the AIP temperature from 115°C to 135°C, at the optimal Zn/Al cycle ratio of 19:1, the Al dopant concentration ([Al]/([Al] + [Zn])) in AZO films varies from 0.15 at.-% to 2.32 at.-%. The 60 nm thick AZO films deposited at an AIP temperature of 120°C show the lowest resistivity of 9.4 × 10−4 Ω cm, with better optical transparency.
Co-reporter:Yan-Qiang Cao, Xue-Fei Li, Ai-Dong Li, Hui Li, Di Wu
Applied Surface Science 2012 Volume 263() pp:497-501
Publication Date(Web):15 December 2012
DOI:10.1016/j.apsusc.2012.09.092
Abstract
The self-cleaning effect of trimethylaluminium (TMA) and tetrakis (dimethyl-amino) hafnium (TDMAH) pretreatments on GaAs substrates was investigated deeply. The chemical states were carefully characterized by the X-ray photoelectron spectroscopy, which demonstrates that the pretreatment before ALD of dielectric films can suppress the formation of native oxides on GaAs substrates effectively. It is found that the combination of TMA and TDMAH pretreatments has better self-cleaning effect than single TMA pretreatment based on a ligand-exchange reaction mechanism between TMA/TDMAH and the native oxide. The transmission electron microscopy images also show a thinnest interlayer thickness of ∼0.2 nm for the TMA + TDMAH pretreated sample. TMA + TDMAH pretreated samples exhibit significantly improved interfacial and electrical properties such as the highest accumulation capacitance, the least stretch-out of capacitance–voltage curves, and the lowest interface trap density. These results indicate that the surface pretreatment by using the combination of TMA and TDMAH pulses may be a promising approach for the realization of high quality GaAs-based transistor devices.
Co-reporter:Ji-Zhou Kong, Mo-Yun Gao, Yi-Dong Xia, Ai-Dong Li, Jun-Long Zhang, You-Pin Gong, Qin-Yu Yan, Di Wu
Journal of Alloys and Compounds 2012 Volume 542() pp:128-131
Publication Date(Web):25 November 2012
DOI:10.1016/j.jallcom.2012.07.026
FePt nanoparticles (NPs) have been encapsulated in the insulating and protective oxide matrix, using a sol–gel process, in order to prevent particles from agglomerating and sintering during the heat-treatment process required for the L10 ordering. The microstructural and ferromagnetic properties of FePt/TiO2 nanocomposites were characterized. The presence of oxide-matrix leads to more homogeneous microstructures and better magnetic properties. The short range positional order of the FePt NPs can be preserved upon annealing at 700 °C to possess higher room-temperature coercivities (HC = 3.7 kOe). Such nanocomposites with assemblies of high-coercivity magnetic nanoparticles are attractive for realizing new types of ultra-high-density data storage devices and magneto-composites.Highlights► Well-monodispersed fcc-FePt nanoparticles were prepared via chemical reduction. ► FePt have been encapsulated in the insulating and protective oxide matrix. ► TiO2 matrix can prevent FePt from agglomerating and sintering during annealing. ► A high coercivity of 3.7 kOe is obtained for the nanocomposites annealed at 700 °C.
Co-reporter:Jun-Long Zhang;Ji-Zhou Kong
Journal of Sol-Gel Science and Technology 2012 Volume 64( Issue 2) pp:269-275
Publication Date(Web):2012 November
DOI:10.1007/s10971-010-2373-8
Superparamagnetic face-centered cubic (fcc) FePt nanoparticles were synthesized using a polyol process. The effect of reaction temperature and molar ratio of Fe(CO)5 to Pt(acac)2 on the structure, composition and morphology of nanoparticles has been investigated. The optimum processing condition has been obtained for producing well-monodisperse fcc-phase FePt nanoparticles with the 2:1 molar ratio of Fe-Pt at 220 °C. In order to circumvent the problem of FePt particle coalescence during high temperature annealing for the L10 ordering, FePt nanoparticle/SiO2-matrix composite films have been fabricated by sol–gel method. The experimental results confirm that the amorphous SiO2 matrix effectively inhibits the grain growth and particle aggregation during 700 °C annealing for 1 h. Well-monodisperse face-centered tetragonal (fct) FePt particles embedded in the SiO2 matrix can be obtained with the long-range chemical order parameter S of ~0.74, indicating partially ordered L10 phase transition in FePt/SiO2 composite films. The FePt/SiO2 system exhibits a hysteretic behavior with smaller coercive field of 1,450 Oe. The incomplete phase transition from cubic deredat height maxsium (A1-disordered phase to tetragonal L10-ordered phase) might be responsible for it.
Co-reporter:Ji-Zhou Kong, You-Pin Gong, Xue-Fei Li, Ai-Dong Li, Jun-Long Zhang, Qing-Yu Yan and Di Wu
Journal of Materials Chemistry A 2011 vol. 21(Issue 13) pp:5046-5050
Publication Date(Web):21 Feb 2011
DOI:10.1039/C0JM03268A
Self-assembled face-centered cubic FePt nanoparticles on Si substrates were embedded into amorphous Al2O3 capping layers with various thicknesses in the range 5–20 nm using atomic layer deposition (ALD) technology. The effect of the Al2O3 layer thickness on the structure, mono-dispersibility, and magnetic properties of the FePt/Al2O3-matrix composite films was investigated. After annealing at 700 °C in a reducing atmosphere for 1 h, well-dispersed face-centered tetragonal (fct) FePt particles could be obtained for the samples with 10 nm-thick and greater Al2O3 layers. Experimental results suggest that the protection of the amorphous 10 nm-thick Al2O3 matrix can effectively inhibit grain growth and particle aggregation, and preserve the ordered domains of FePt nanoparticles during the L10 ordering transition through annealing. The 5 nm fct FePt-nanoparticles/10 nm-thick Al2O3-matrix sample shows higher coercivity of 5.9 kOe. The combination of ALD-capping layer and self-assembled FePt nanoparticles provides a potential new approach to fabricate patterned magnetic recording media with ultrahigh areal density.
Co-reporter:Hai-Fa Zhai, Xu Qian, Ji-Zhou Kong, Ai-Dong Li, You-Pin Gong, Hui Li, Di Wu
Journal of Alloys and Compounds 2011 Volume 509(Issue 42) pp:10230-10233
Publication Date(Web):20 October 2011
DOI:10.1016/j.jallcom.2011.08.077
Triclinic β-BiNbO4 prepared below 750 °C and above 1040 °C (denoted as Low-β and High-β, respectively) and pure orthorhombic α-BiNbO4 at 900 °C were successfully derived from a citrate method and the phase transition from β-BiNbO4 to α-BiNbO4 was first observed in BiNbO4 powders. This phenomenon proves that the abnormal phase transition from β-BiNbO4 to α-BiNbO4 exists in BiNbO4 powder system. The synthesis of Low-β powders can be attributed to the formation of the intermediate phase of Bi5Nb3O15 by the citrate method. With increasing temperature, the Low-β phase gradually turns into α-BiNbO4 due to the thermodynamically metastable state of Low-β. We also identified that the stress in pellet format can accelerate the phase transition from Low-β to α phase of BiNbO4 in comparison with powder samples. It brings us new understanding of the BiNbO4 system and also provides a simple way to obtain BiNbO4 for microwave and photocatalytic applications.Highlights► Pure BiNbO4 powders were successfully prepared by a citrate method using home-made Nb-citrate (Nb-CA) aqueous solution. ► Abnormal phase transition from β-BiNbO4 to α-BiNbO4 was first observed in BiNbO4 system. ► The synthesis of Low-β can be attributed to the formation of the intermediated phase Bi5Nb3O15 and the mechanism of the phase transition from β-BiNbO4 to α-BiNbO4 was proposed. ► We identified that the stress in pellet format can accelerate the phase transition compared with powder samples.
Co-reporter:Ji-Zhou Kong, Ai-Dong Li, Xiang-Yu Li, Hai-Fa Zhai, Wen-Qi Zhang, You-Pin Gong, Hui Li, Di Wu
Journal of Solid State Chemistry 2010 Volume 183(Issue 6) pp:1359-1364
Publication Date(Web):June 2010
DOI:10.1016/j.jssc.2010.04.005
A photocatalyst of Ta-doped ZnO was prepared by a modified Pechini-type method. The structural, morphological properties and photocatalytic activity of 1 mol % Ta-doped ZnO samples annealed at different temperatures were characterized. The photo-oxidation of methylene blue under the visible-light irradiation followed the pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. It is found that the photocatalysis of 1% Ta-doped ZnO annealed at 700 °C showed excellent performance of the photodegradation of methylene blue, which was attributed to a competitive trade-off among the crystallinity, surface hydroxyl groups, and specific surface area. The processing parameter such as the pH value also played an important role in tuning the photocatalytic activity. The maximum photodecomposed rate was achieved at pH=8, and an novel model about the absorption of methylene blue on the surface of the catalysts was proposed.This model describes the adsorption between the amphoteric behavior of the metal oxide and the cationic dye methylene blue (MB) on the surface of the catalyst at the acidic and alkaline condition.
Co-reporter:Haifa Zhai, Yidong Xia, Aidong Li, Youpin Gong, Jizhou Kong, Xiangyu Li, Qiyue Shao, Qingyu Yan, Jan Ma, Di Wu
Thin Solid Films 2010 Volume 518(Issue 14) pp:3929-3932
Publication Date(Web):3 May 2010
DOI:10.1016/j.tsf.2009.12.098
B-site modification lead strontium zirconate titanate Pb0.4Sr0.6ZrxTi1 − xO3 (PSZT, x = 0–0.7) thin films were prepared on Pt/TiO2/SiO2/Si substrates by a sol–gel method. The XRD results indicate that paraelectric PSZT thin films at room temperature are obtained as x approaches 0.2. The temperature-dependent dielectric and hysteresis loop measurements reveal that the thin films have diffuse phase transition characteristics and relaxor-like behavior with nano-polar regions in the paraelectric films at room temperature. The Curie temperature of the PSZT thin films varies with the Zr contents, exhibiting a complex trend. This can be attributed to two competitive factors: higher mobility of Ti4+ than Zr4+ and smaller open space left for the displacement of Ti ions with the increase of Zr content. The further increase of the Zr contents leads to the simultaneous decrease of dielectric constant, dielectric loss and tunability. PSZT (x = 0.4) thin film shows the largest figure of merit of 24.3 with a moderate tunability of 55.8% and a dielectric loss of 0.023. This suggests that B-site ions have different roles in modifying the electrically tunable performance of PSZT thin films for tunable microwave device applications.
Co-reporter:Ji-Zhou Kong, Ai-Dong Li, Hai-Fa Zhai, You-Pin Gong, Hui Li, Di Wu
Journal of Solid State Chemistry 2009 Volume 182(Issue 8) pp:2061-2067
Publication Date(Web):August 2009
DOI:10.1016/j.jssc.2009.03.022
This paper describes a novel catalyst of the Ta-doped ZnO nanocrystals prepared by a modified polymerizable complex method using the water-soluble tantalum precursor as the sources of Ta. The catalysts were characterized by means of various analytical techniques as a function of Ta content (x=0–4 mol%) systematically. A remarkable advantage of the results was confirmed that dopant Ta enhanced the visible-light absorption of ZnO and the low-solubility tantalum doping could restrain the growth of crystal and minish the particle size. The relationship between the physicochemical property and the photocatalytic performance was discussed, and it was found that the photocatalytic activity in the photochemical degradation of methylene blue under visible-light irradiation (λ⩾420 nm) was dependent on the contents of the dopant, which could affect the particle size, concentration of surface hydroxyl groups and active hydrogen-related defect sites, and the visible-light absorption. The highest photocatalytic activity was obtained for the 1.0 mol% Ta-doped ZnO sample.The addition of the tantalum into ZnO prepared by a modified polymerizable complex method not only restrains the growth of crystal, minish the particle size, but also changes the nanocrystal morphology.
Co-reporter:Wen-Qi Zhang, Ai-Dong Li, Qi-Yue Shao, Yi-Dong Xia, Di Wu, Zhi-Guo Liu, Nai-Ben Ming
Applied Surface Science 2008 Volume 254(Issue 6) pp:1583-1586
Publication Date(Web):15 January 2008
DOI:10.1016/j.apsusc.2007.07.067
Abstract
Pb(Zr0.52Ti0.48)O3 (PZT) thin films with large remanent polarization and SrBi2Ta2O9 (SBT) thin films with excellent fatigue-resisting characteristic have been widely studied for non-volatile random access memories, respectively. To combine these two advantages, bilayered Pb(Zr0.52Ti0.48)O3/SrBi2Ta2O9 (PZT/SBT) thin films were fabricated on Pt/TiO2/SiO2/Si substrates by chemical solution deposition method. X-ray diffraction patterns revealed that the diffraction peaks of PZT/SBT thin films were completely composed of PZT and SBT, and no other secondary phase was observed. The electrical properties of the bilayered structure PZT/SBT films have been investigated in comparison with pure PZT and SBT films. PZT/SBT bilayered thin films showed larger remanent polarization (2Pr) of 18.37 μC/cm2 than pure SBT and less polarization fatigue up to 1 × 109 switching cycles than pure PZT. These results indicated that this bilayered structure of PZT/SBT is a promising material combination for ferroelectric memory applications.
Co-reporter:Hai-Rong Guo;Yuan Gao;Zhong Yan
Journal of Sol-Gel Science and Technology 2008 Volume 45( Issue 3) pp:315-318
Publication Date(Web):2008 March
DOI:10.1007/s10971-008-1680-9
Pb0.56Sr0.44Zr0.52Ti0.48O3 (PSZT) inverse opal photonic crystals (PCs) have been synthesized by a process of self-assembly in combination with a sol–gel procedure. PSZT inverse opals show pure perovskite structure with good orders in three dimensions. The evident photonic band gaps have been observed in the transmittance spectra with a blue-shift phenomenon due to the decrease of opal template periods. PSZT inverse opals also exhibit the reflection peaks in basic agreement with the calculated results. This three-dimensional (3D) ordered PSZT inverse opals have shown interesting optical characteristics and potential applications in optoelectronic and photonic devices.
Co-reporter:Ai-Dong Li, Jin-Bo Cheng, Hui-Qing Ling, Di Wu, Nai-Ben Ming
Applied Surface Science 2006 Volume 253(Issue 3) pp:1154-1159
Publication Date(Web):30 November 2006
DOI:10.1016/j.apsusc.2006.01.057
Abstract
Bi4Ti3O12 (BIT) films were prepared on Pt/TiO2/SiO2/Si substrates by the sol–gel method. A low electric field was in-situ applied to BIT films during rapid thermal annealing (RTA). It was first found that a bias electric field has great influence on the structure, orientation, and morphology of BIT films at proper temperatures. Under the electric field of very low V/cm, BIT films show highly c-axis-oriented growth with second phase of bismuth oxide at 600 and 650 °C. The possible origin is proposed. On one hand, the electrostatic energy provides an extra driving force and the co-interaction of the electrostatic energy and interface energy promotes the c-axis-oriented growth of the BIT grains. On the other hand, the second phase of bismuth oxide produced during RTA in an electric field also plays an important role in the control of film orientation.
Co-reporter:Q. Shao;A. Li;W. Zhang;D. Wu;Z. Liu;N. Ming
Chemical Vapor Deposition 2006 Volume 12(Issue 7) pp:
Publication Date(Web):6 JUL 2006
DOI:10.1002/cvde.200506480
A novel Zr/Ti mixed metal nitrate[ZrxTi1–x(NO3)4] has been successfully developed as a single-source precursor to deposit multicomponent metal oxide films. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses confirm that Zr0.65Ti0.35O2 films are successfully prepared from this anhydrous nitrate precursor using CVD. The basal dielectric properties of Zr0.65Ti0.35O2 films are studied, and well-defined C–V curves with negligible hysteresis are achieved. Compared to pure TiO2 and ZrO2 films, the Zr0.65Ti0.35O2 films exhibit a trade-off of dielectric properties with a moderate bandgap value of 4.3 eV and a value for k of 47. ZrxTi1–xO2 is, therefore, a promising candidate for gate-dielectric application, and an anhydrous mixed-metal nitrate can be a potential single-source precursor for high-k materials derived from CVD.
Co-reporter:Ai-Dong Li, Hui-Qing Ling, Di Wu, Tao Yu, Zhi-Guo Liu, Nai-Ben Ming
Solid State Communications 2003 Volume 125(Issue 9) pp:469-473
Publication Date(Web):March 2003
DOI:10.1016/S0038-1098(02)00888-8
SrBi2Ta2O9 (SBT) films were prepared on Pt/TiO2/SiO2/Si substrates at 750 °C in oxygen by metalorganic decomposition method. A low electric field was in situ applied during the film crystallization. It was first found that a low electric field and its direction have significant influence on the microstructures and ferroelectric properties of SBT films. Under a positive electric field (assuming that the bottom electrode is electrically grounded), the films show stronger c-axis-preferred orientation than without electric field and under a negative electric field. As a possible origin is proposed that the interface-induced nucleation growth between SBT and Pt coated substrate with application of low electric field plays a key role. Above all, an in situ applied low electric field during the film crystallization is a promising technique controlling film orientation for film preparation by wet chemical method.
Co-reporter:Ai-Dong Li, Di Wu, Hui-Qin Ling, Tao Yu, Zhi-Guo Liu, Nai-Ben Ming
Microelectronic Engineering 2003 Volume 66(1–4) pp:654-661
Publication Date(Web):April 2003
DOI:10.1016/S0167-9317(02)00979-6
SrBi2Ta2O9 (SBT) thin films were prepared on Pt/TiO2/SiO2/Si substrates by metalorganic decomposition method. Impact of interfacial diffusion on structural and electrical properties of SBT film capacitors has been investigated by X-ray diffraction (XRD), scanning electron microscopy, Auger electron spectroscopy (AES) and electrical measurements. Interfacial layer model was used to fit measured electrical properties. XRD results confirm the interfacial diffusion leads to secondary phase formation such as Bi2Pt and Bi4Ti3O12 (BTO) between SBT films and Pt and the main interfacial phase is BTO. The electrical measurements indicate that moderate interfacial diffusion acts as a stable barrier layer with the enhanced breakdown voltage and the decreased leakage current whereas remnant polarization decreases slightly and coercive field increases slightly. Films with moderate interfacial diffusion show good fatigue behavior and retention property. However, the severe interfacial diffusion deteriorates the electrical properties, leading to small remnant polarization and dielectric constant of SBT capacitors.
Co-reporter:Di Wu, Aidong Li, Zhiguo Liu, Huiqin Ling, Chuan Zhen Ge, Xiaoyong Liu, Hong Wang, Min Wang, Peng Lü, Naiben Ming
Thin Solid Films 1998 Volume 336(1–2) pp:172-175
Publication Date(Web):30 December 1998
DOI:10.1016/S0040-6090(98)01223-1
Metallic LaNiO3 (LNO) films were prepared on LaAlO3 (LAO) and Si substrates by metal-organic decomposition (MOD) and their application as the bottom electrode for sol-gel derived (BaSr)TiO3 (BST) thin films was studied. X-ray diffraction, atomic force microscope and electrical measurements were used to characterize the multilayer films of BST/LNO/substrates. BST film on LNO-coated LAO substrate exhibited preferred (100) orientation. Smooth and dense surface with fine grains (∼50 nm) was observed. The electrical measurement results on BST films using LNO and stainless steel as the bottom electrodes, respectively, showed BST/LNO/substrates have higher dielectric constant, lower loss tangent, lower leakage current and higher breakdown voltage.
Co-reporter:Aidong Li, Di Wu, Zhiguo Liu, Chuanzhen Ge, Xiaoyong Liu, Guoxin Chen, Naiben Ming
Thin Solid Films 1998 Volume 336(1–2) pp:386-390
Publication Date(Web):30 December 1998
DOI:10.1016/S0040-6090(98)01289-9
Perovskite conductive LaNiO3 (LNO) films were prepared by metalorganic decomposition. The films were obtained by spin-on pyrolysis on NaCl and SrTiO3(STO) substrates and then annealing at various temperature. The effect of different thermal treatments and annealing temperature on crystallinity, orientation and surface morphology of LNO films was studied. The results obtained by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray photoelectron spectrometry (XPS) indicated that in the thermal treatment process the oxygen diffusion into the film is the critical step in the fabrication of good metallic LNO films at lower growth temperature. Epitaxial LNO films could be fabricated on STO. The surface morphology of LNO film on STO including the film roughness was recorded by atomic force microscopy (AFM).
Co-reporter:Guo-Yong Fang, Li-Na Xu, Yan-Qiang Cao, Lai-Guo Wang, Di Wu and Ai-Dong Li
Chemical Communications 2015 - vol. 51(Issue 7) pp:NaN1344-1344
Publication Date(Web):2014/12/01
DOI:10.1039/C4CC08004A
Plasma-enhanced atomic layer deposition (PE-ALD) has been applied to prepare high-quality ultrathin films for microelectronics, catalysis, and energy applications. The possible pathways for SiO2 PE-ALD using aminosilanes and O2 plasma have been investigated by density functional theory calculations. The silane half-reaction between SiH4 and surface –OH is very difficult and requires a high activation free energy of 57.8 kcal mol−1. The introduction of an aminosilane, such as BDMAS, can reduce the activation free energy to 11.0 kcal mol−1 and the aminosilane plays the role of a self-catalyst in Si–O formation through the relevant half-reaction. Among the various species generated in O2 plasma, 3O2 is inactive towards surface silane groups, similar to ordinary oxygen gas. The other three species, 1O2, 1O, and 3O, can strongly oxidize surface silane groups through one-step or stepwise pathways. In the 3O pathway, the triplet must be converted into the singlet and follow the 1O pathway. Meanwhile, both 1O and 3O can decay to 1O2 and enter into the relevant oxidation pathway. The concept of self-catalysis of aminosilanes may be invoked to design and prepare more effective Si precursors for SiO2 ALD. At the same time, the mechanism of strong surface oxidation by O2 plasma may be exploited in the PE-ALD preparation of other oxides, such as Al2O3, HfO2, ZrO2, and TiO2.
Co-reporter:Yan-Qiang Cao, Lin Zhu, Xin Li, Zheng-Yi Cao, Di Wu and Ai-Dong Li
Dalton Transactions 2015 - vol. 44(Issue 33) pp:NaN14792-14792
Publication Date(Web):2015/07/09
DOI:10.1039/C5DT00384A
Ti-based fumaric acid hybrid thin films were successfully prepared using inorganic TiCl4 and organic fumaric acid as precursors by molecular layer deposition (MLD). The effect of deposition temperature from 180 °C to 350 °C on the growth rate, composition, chemical state, and topology of hybrid films has been investigated systematically by means of a series of analytical tools such as spectroscopic ellipsometry, atomic force microscopy (AFM), high resolution X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The MLD process of the Ti-fumaric acid shows self-limiting surface reaction with a reasonable growth rate of ∼0.93 Å per cycle and small surface roughness of ∼0.59 nm in root-mean-square value at 200 °C. A temperature-dependent growth characteristic has been observed in the hybrid films. On increasing the temperature from 180 °C to 300 °C, the growth rate decreases from 1.10 to 0.49 Å per cycle and the XPS composition of the film's C:O:Ti ratio changes from 8.35:7.49:1.00 to 4.66:4.80:1.00. FTIR spectra indicate that the hybrid films show bridging bonding mode at a low deposition temperature of 200 °C and bridging/bidentate mixed bonding mode at elevated deposition temperatures of 250 and 300 °C. The higher C and O amounts deviating from the ideal composition may be ascribed to increased organic incorporation into the hybrid films at lower deposition temperature and temperature-dependent density of reactive sites (–OH). The composition of hybrid films grown at 350 °C shows a dramatic decrease in C and O elemental composition (C:O:Ti = 1.97:2.76:1.00) due to the thermal decomposition of the fumaric acid precursor. The produced by-product H2O changes the structure of the hybrid films, resulting in the formation of more Ti–O bonds at high temperatures. The stability of the hybrid films against chemical and thermal treatment, and long-term storage by vacuum-packing was explored carefully. It is found that the ultrathin hybrid film can be transformed into TiO2 nanoparticles via various post deposition annealing processes with different topographies. Finally, the charge trapping ability of the hybrid film is confirmed by fabricating a charge trapping memory capacitor in which the hybrid film was inserted as a charge trapping layer.
Co-reporter:Ji-Zhou Kong, You-Pin Gong, Xue-Fei Li, Ai-Dong Li, Jun-Long Zhang, Qing-Yu Yan and Di Wu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 13) pp:NaN5050-5050
Publication Date(Web):2011/02/21
DOI:10.1039/C0JM03268A
Self-assembled face-centered cubic FePt nanoparticles on Si substrates were embedded into amorphous Al2O3 capping layers with various thicknesses in the range 5–20 nm using atomic layer deposition (ALD) technology. The effect of the Al2O3 layer thickness on the structure, mono-dispersibility, and magnetic properties of the FePt/Al2O3-matrix composite films was investigated. After annealing at 700 °C in a reducing atmosphere for 1 h, well-dispersed face-centered tetragonal (fct) FePt particles could be obtained for the samples with 10 nm-thick and greater Al2O3 layers. Experimental results suggest that the protection of the amorphous 10 nm-thick Al2O3 matrix can effectively inhibit grain growth and particle aggregation, and preserve the ordered domains of FePt nanoparticles during the L10 ordering transition through annealing. The 5 nm fct FePt-nanoparticles/10 nm-thick Al2O3-matrix sample shows higher coercivity of 5.9 kOe. The combination of ALD-capping layer and self-assembled FePt nanoparticles provides a potential new approach to fabricate patterned magnetic recording media with ultrahigh areal density.
