EDTA辅助水热合成FeS2/NiSe2复合纳米晶及其薄膜光电性质

以EDTA为螯合剂，加入MX2结构化合物NiSe₂作为晶种，水热合成了FeS₂纳米晶. x射线衍射分析结果表明产物为单一相黄铁矿型FeS₂（pyrite）,平均粒径约40—50nm.丝网印刷成膜且高温退火后FeS₂薄膜光学直接带隙变宽.随晶种量的增加，吸收边在紫外—可见光谱区红移、方块电阻升高、霍尔迁移率上升和载流子浓度下降，实现了n型掺杂.并且对FeS₂的形成机理进行了讨论. 关键词： 2纳米晶')" href="#">FeS₂纳米晶 水热 诱导结晶 直接禁带宽度      

Sol-gel法制备Bi0.85Nd0.15FeO3多铁性薄膜

利用sol-gel法在Pt/Ti/SiO₂/Si衬底上制备出Bi_0.85Nd_0.15FeO₃薄膜.研究退火温度对其晶相形成的影响,发现在450 ℃退火时,Bi_0.85Nd_0.15FeO₃晶相开始形成,但是结晶较差,而且存在杂相;在500—600 ℃退火可以获得单相Bi_0.85Nd_0.15FeO₃薄膜,退火温度升高有利于其结晶.对600 ℃退火的Bi_0.85Nd_0.15FeO₃薄膜的介电、铁电和电磁性能进行了测试.在测试频率为1 MHz时,其介电常数和介电损耗分别为145,0.032;饱和磁化强度大约为44.8 emu/cm³;剩余极化值(2P_r)大约是16.6 μC/cm². 关键词： sol-gel法 0.85Nd_0.15FeO₃薄膜')" href="#">Bi_0.85Nd_0.15FeO₃薄膜 铁电性能 铁磁性能     

Ln2Sn2O7：Er3+纳米晶的制备及发光性能研究

采用溶胶-凝胶法合成Ln₂Sn₂O₇:Er³⁺(Ln=La,Gd,Y)纳米晶。通过X射线衍射和场发射扫描电子显微镜测试了样品的晶体结构和形貌,同时对样品的上转换发光性能进行了测试。结果表明:在980 nm连续激发光的激发下,样品主要表现为绿光发射。发射中心在528,549 nm的绿光和672 nm处的红光发射分别对应Er³⁺离子的⁴S_3/2→⁴I_15/2、²H_11/2→⁴I_15/2和 ⁴F_9/2→⁴I_15/2跃迁。以La₂Sn₂O₇:Er³⁺纳米晶为例,Er³⁺离子的摩尔分数为7%、退火温度为1 150℃是其制备的最佳条件,此时其各个发射峰的强度最高。对La₂Sn₂O₇:Er³⁺的发光强度与激发功率关系的研究表明,其绿光和红光发射均为双光子过程。激发光吸收和能量转移是La₂Sn₂O₇:Er³⁺纳米晶上转换发光的主要机制。     

La1.6(MoO4)3:Eu0.43+纳米晶合成及发光特性

采用燃烧法合成了La_1.6(MoO₄)₃:Eu_0.4³⁺纳米晶末,研究了其声子-掺杂-晶格相互作用和发光性质.X射线粉末衍射(XRD)分析表明,在500~900 ℃退火后,La_1.6(MoO₄)₃:Eu_0.4³⁺样品为单一晶相.对样品进行了光致发光(PL)测量,激发Mo⁶⁺-O^2-电荷迁移带,观察到Eu³⁺的系列发光,表明Mo⁶⁺-O^2-带和Eu³⁺间存在能量传递,中心波长分别在λ₁=469 nm和λ₂=426 nm处的两个one-phonon边带,相应的声子能量分别为767和1202 cm^-1,分别对应于 Mo=O 和Mo-O-Mo伸缩振动.同时,计算了两个局域模电子-声子耦合强度的黄昆因子分别为S₁=0.055和S₂=0.037,为揭示其三价离子高传导特性及其负热膨胀物理特性提供了实验基础.     

NaGdF4纳米晶多元醇法的合成、表征与NaGdF4：Eu3+和NaGdF4：Yb3+, Er3+纳米晶的发光

通过多元醇法(polyol method)合成出NaGdF₄:Eu³⁺和NaGdF₄:Yb³⁺,Er³⁺纳米晶,利用X射线衍射(XRD)、场发射扫描电镜(FE-SEM)和傅立叶变换红外吸收光谱(FT-IR)对合成的样品进行了表征。研究了Eu³⁺掺杂样品的下转换发光和Yb³⁺/Er³⁺共掺杂样品的上转换发光。对未经退火和经过退火的样品进行了比较。     

掺铒Si/Al2O3多层结构中结晶形态对1.54 μm发光的影响

利用脉冲激光沉积的方法制备掺铒 Si/Al₂O₃多层结构薄膜,获得了由纳米结构的Si作为感光剂增强的Er³⁺在1.54 μm高效发光.利用拉曼散射、高分辨透射电镜和光致发光测量研究了在不同退火温度下（600—1000 ℃）纳米结构Si层的结晶形态变化,及对Er³⁺在1.54 μm的发光的影响特征.研究发现最佳发光是在退火温度600—700 ℃.在这个条件下纳米Si的尺寸和密度,Si和Er的作用距离以及Er^{3+ 关键词： 铒 纳米硅 能量转移 氧化铝}     

Y2O3:Eu纳米晶中能量传递相互作用的研究

通过浓度猝灭曲线确定了引起Y₂O₃纳米晶中Eu³⁺发光浓度猝灭的是交换相互作用.测量了两种颗粒尺寸下Eu³⁺的⁵D₀—⁷F₂跃迁发光衰减曲线随掺杂浓度的变化,利用交换相互作用的理论衰减曲线对实验衰减曲线进行拟合.计算Eu³⁺离子的交换相互作用能量传递的效率,分析了Y₂O_{3关键词： 能量传递 2}O₃Eu纳米晶')" href="#">Y₂O₃Eu纳米晶 发光衰减     

Si-Al2O3复合薄膜的室温铁磁性

在Si-Al₂O₃复合薄膜中观察到室温铁磁性.Si的体积百分比为15 %的Si-Al₂O₃复合薄膜的磁性最强.Si的含量影响样品的磁有序,在样品中观察到了明显的磁畴.在不同气氛下,对样品进行快速热退火.退火样品的磁性测试结果的差别表明氧空位不是样品铁磁性的主要来源.我们认为铁磁性来源于Si与Al₂O₃基质界面之间的缺陷的磁耦合.改变Si的含量可以改变缺陷密度,从而控制铁磁耦合强度. 关键词： 2O₃薄膜')" href="#">Al₂O₃薄膜 室温铁磁性 掺杂 交换相互作用     

简便合成相可调的CsPbBr3-Cs4PbBr6复合纳米晶及相转变过程的原位研究

通过改变四正辛基溴化铵(TOABr)用量和Cs/Pb摩尔比,在室温下采用一步单溶剂法成功制备出单斜相CsPbBr₃和六方相Cs₄PbBr₆两种相结构可调的钙钛矿纳米晶.研究发现,当TOABr浓度较低时(Cs/Pb/Br=1:1:4),体系中主要生成了单斜相的CsPbBr3纳米立方块,该立方块主要经历了快速成核、尺寸分布聚焦生长和Ostwald熟化生长3个阶段,最终尺寸为(11.8±1.6) nm.随着TOABr用量的增加,Br^-和Pb²⁺结合形成[PbBr₃]^-和少量的[PbBr₄[^2-络合物,两种络合物相互竞争.在成核期和生长早期体系中[PbBr3]-占主导,因而形成大量的CsPbBr₃纳米晶,随着反应的进行,体系中过量的Br-会与纳米晶中的Pb相互作用,导致CsPbBr₃纳米晶部分转变为具有六边形形状的Cs₄PbBr     

YZr2OZr3:Er3+纳米晶anti-Stokes发光性质的研究

采用均相沉积法制备了不同Er³⁺离子浓度掺杂的Y₂O₃纳米晶, 应用XRD，SEM和PL光谱对该体系材料进行了表征.在Y₂O₃:Er³⁺纳米材料体系中, 观察和研究了Stokes及anti-Stokes PL谱强度与Er³⁺离子摩尔浓度变化的关系, 当Er³⁺离子浓度为2.0mol%时, anti-Stokes PL强度最强.粉末X 关键词： 氧化钇纳米晶 anti-Stokes PL 双光子吸收     

Rapid thermal oxygen annealing formation of nickel silicide nanocrystals for nonvolatile memory

Discrete NiSi nanocrystals were synthesized by rapid thermal oxygen annealing of very thin Si/Ni/Si films on a SiO₂ tunneling layer. They were used to fabricate metal?Coxide?Csemiconductor capacitor memory. Electrical properties of the memory device such as programming, erasing and retention were characterized and good performance was achieved.     

Memory characteristics and tunneling mechanism of Pt nano-crystals embedded in HfAlOx films for nonvolatile flash memory devices

A non-volatile flash memory device based on metal oxide semiconductor (MOS) capacitor structure has been fabricated using platinum nano-crystals(Pt–NCs) as storage units embedded in HfAlO_x high-k tunneling layers. Its memory characteristics and tunneling mechanism are characterized by capacitance–voltage(C–V) and flat-band voltage-time(ΔV_FB-T) measurements. A 6.5 V flat-band voltage (memory window) corresponding to the stored charge density of 2.29 × 10¹³ cm⁻² and about 88% stored electron reserved after apply ±8 V program or erase voltage for 10⁵ s at high frequency of 1 MHz was demonstrated. Investigation of leakage current–voltage(J–V) indicated that defects-enhanced Pool-Frenkel tunneling plays an important role in the tunneling mechanism for the storage charges. Hence, the Pt–NCs and HfAlO_x based MOS structure has a promising application in non-volatile flash memory devices.     

Low voltage program-erasable Pd-Al_2O_3-Si capacitors with Ru nanocrystals for nonvolatile memory application

Pd-Al2O3-Si capacitors with Ru nanocrystals are fabricated and electrically characterized for nonvolatile memory application.While keeping the entire insulator Al2O3thickness fixed,the memory window has a strong dependence on the tunneling layer thickness under low operating voltages,whereas it has weak dependence under high operating voltages.As for the optimal configuration comprised of 6-nm tunneling layer and 22-nm blocking layer,the resulting memory window increases from 1.5 V to 5.3 V with bias pulse increasing from 10 5s to 10 2s under±7 V.A ten-year memory window as large as 5.2 V is extrapolated at room temperature after±8 V/1 ms programming/erasing pulses.     

基于Ni电极和ZrO_2/SiO_2/ZrO_2介质的MIM电容的导电机理研究

研究了基于Ni电极和原子层淀积的ZrO_2/SiO_2/ZrO_2对称叠层介质金属-绝缘体-金属(MIM)电容的电学性能.当叠层介质的厚度固定在14nm时,随着SiO_2层厚度从0增加到2nm,所得电容密度从13.1 fF/μm~2逐渐减小到9.3fF/μm~2,耗散因子从0.025逐渐减小到0.02.比较MIM电容的电流-电压(I-V)曲线,发现在高压下电流密度随着SiO_2厚度的增加而减小,在低压下电流密度的变化不明显,还观察到电容在正、负偏压下表现出完全不同的导电特性,在正偏压下表现出不同的高、低场I-V特性,而在负偏压下则以单一的I-V特性为主导.进一步对该电容在高、低场下以及电子顶部和底部注入时的导电机理进行了研究.结果表明,当电子从底部注入时,在高场和低场下分别表现出普尔-法兰克(PF)发射和陷阱辅助隧穿(TAT)的导电机理;当电子从顶部注入时,在高、低场下均表现出TAT导电机理.主要原因在于底电极Ni与ZrO_2之间存在镍的氧化层(NiO_x),且ZrO_2介质层中含有深浅两种能级陷阱(分别为0.9和2.3 eV),当电子注入的模式和外电场不同时,不同能级的陷阱对电子的传导产生作用.     

Resistance switching properties of In2O3 nanocrystals memory device with organic and inorganic hybrid structure

A memory device with In₂O₃ nanocrystals embedded in a biphenyl-tertracarboxylic dianhydride-phenylen diamine (BPDA-PDA) polyimide layer on a ZnO layer was fabricated, and its electrical properties were evaluated. Then, the transmittance efficiency in the structure of the BPDA-PDA polyimide/In₂O₃ nanocrystals/ZnO/ITO/double polishing sapphire substrate was measured to be about 80% between 440 to 800 nm by ultraviolet-visible transmittance spectroscopy. A bipolar switching current bistability by difference resistance appeared in the sweep voltage rage from −7 to 7 V. It was considered that the bipolar behavior of current-voltage may originate from a resistance fluctuation because of the electron charging effect in In₂O₃ nanocrystals by voltage sweeping, Fowler–Nordheim tunneling, space-charge-limited current, and the migration of O²⁻ ions.     

Discharge mechanisms modeling in LPCVD silicon nanocrystals usingC–Vand capacitance transient techniques

Charging and discharging phenomena from silicon nanocrystals have been studied by means of capacitance–voltage characteristics on P-type metal-oxide-semiconductor (P-MOS) capacitors with embedded self-assembled silicon quantum dots. The dots have a floating gate behavior as shown by the hysteresis onC –V curves. The Si-dots are charged or discharged by direct tunneling of carriers through a 3 nm thick oxide. The nanocrystals could be charged by electrons or holes, depending on the charging bias conditions. The discharge is studied by constant bias method and shows a logarithmic variation with time. Retention times higher than several hours are observed. A simple model is developed in order to evaluate the electric field within the tunneling oxide layer. Then, complete simulations are done for the different discharge paths. The barrier heights are extracted from the discharge data and possible confinement effects are discussed. The results confirm the high potentiality of silicon nanocrystal-floating gates for memory applications.     

The interfacial structures of (Ba, Sr)TiO3 films deposited by radio frequency magnetron sputtering

Ba_0.6Sr_0.4TiO₃ (BST) films were deposited on Pt/SiO₂/Si substrates by radio frequency magnetron sputtering. The deposited films were crystallized by conventional thermal annealing (CTA) and rapid thermal annealing (RTA). The interfacial structures of BST/Pt were studied. High-resolution transmission electron microscopy (HRTEM) observation shows that there is a transition layer at BST/Pt interface, and the layer is 4-5 nm thick for CTA and 2-3 nm for RTA. X-ray photoelectron spectroscopy (XPS) investigations show that the layer is composed of perovskited BST phase and non-perovskited BST phase. The content of the non-perovskited BST phase is most for CTA, whereas that of the perovskited BST phase is most for RTA. It is found that the transition layer thickens with the increase of annealing temperature, and CTA corresponds to faster thickening rate. XPS shows that the non-perovskited BST phase does not come from the absorbed CO₂ or CO contaminations, but from other interfacial elements. Also, it is indicated that the RTA-annealed BST film capacitor shows much better dielectric properties, with an average value of 150 higher dielectric constant and almost two orders of magnitude lower leakage current density than the CTA-annealed film capacitor. Grazing X-ray diffraction (GXRD) patterns exhibit that the RTA-annealed BST films present more compact structure. It is such a compact structure that can effectively prevent the absorbed elements further diffusing toward two sides, and cause thinner transition layer, thus result in higher dielectric constant and lower leakage current density.     

Formation of high density TiN nanocrystals and its application in non-volatile memories

Non-volatile memory based on TiN nanocrystal （TiN-NC） charge storage nodes embedded in SiO2 has been fabricated and its electrical properties have been measured. It was found that the density and size distribution of TiN-NCs can be controlled by annealing temperature. The formation of well separated crystalline TiN nano-dots with an average size of 5 nm is confirmed by transmission electron microscopy and x-ray diffraction, x-ray photoelectron spectroscopy confirms the existence of a transition layer of TiNxOy/SiON oxide between TiN-NC and SiO2, which reduces the barrier height of tunnel oxide and thereby enhances programming/erasing speed. The memory device shows a memory window of 2.5V and an endurance cycle throughout 10^5. Its charging mechanism, which is interpreted from the analysis of programming speed （dVth/dt） and the gate leakage versus voltage characteristics （Ig vs Vg）, has been explained by direct tunnelling for tunnel oxide and Fowler Nordheim tunnelling for control oxide at programming voltages lower than 9V, and by Fowler-Nordheim tunnelling for both the oxides at programming voltages higher than 9V.     

Charge storage and electron/light emission properties of silicon nanocrystals

Monodispersed silicon nanocrystals show novel electrical and optical characteristics of silicon quantum dots, such as single-electron tunneling, ballistic electron transport, visible photoluminescence and high-efficiency electron emission.Single-electron memory effects have been studied using a short-channel MOSFET incorporating Si quantum dots as a floating gate. Surface nitridation of Si nanocrystal memory nodes extends the charge-retention time significantly. Single-electron storage in individual Si dots has been evaluated by Kelvin probe force microscopy.Photoluminescence and electron emission are observed for surface-oxidized silicon nanocrystals. Efficiency of the no-phonon-assisted transition increases with decreasing core Si size. Electron emission efficiency as high as 5% has been achieved for the Si-nanocrystal-based cold electron emitter devices. The non-Maxwellian energy distribution of emitted electrons suggests that the mechanism of electron emission is due to ballistic transport through arrays of surface-oxidized Si nanocrystals. Combined with the ballistic electron emission, the quasi-direct light emission properties can be used for developing Si-based lasers.     

High-performance amorphous In-Ga-Zn-O thin-film transistor nonvolatile memory with a novel p-SnO/n-SnO2 heterojunction charge trapping stack

Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor (TFT) memories with novel p-SnO/n-SnO₂ heterojunction charge trapping stacks (CTSs) are investigated comparatively under a maximum fabrication temperature of 280 ℃. Compared to a single p-SnO or n-SnO₂ charge trapping layer (CTL), the heterojunction CTSs can achieve electrically programmable and erasable characteristics as well as good data retention. Of the two CTSs, the tunneling layer/p-SnO/n-SnO₂/blocking layer architecture demonstrates much higher program efficiency, more robust data retention, and comparably superior erase characteristics. The resulting memory window is as large as 6.66 V after programming at 13 V/1 ms and erasing at -8 V/1 ms, and the ten-year memory window is extrapolated to be 4.41 V. This is attributed to shallow traps in p-SnO and deep traps in n-SnO₂, and the formation of a built-in electric field in the heterojunction.