氧化镓生长模拟中的流场与反应参数优化研究

建立了用于生长直径为15.24cm(6inch)的Ga₂O₃材料的氢化物气相外延(HVPE)生长腔的二维几何模型,对Ga₂O₃材料的生长进行了数值模拟。依次优化了GaCl进气速度、O₂进气速度、喷口到衬底间的距离等关键参数,在较高生长速率下使衬底上的Ga₂O₃膜厚相对均匀度达到7.02%。此外,对仿真中不同的反应活化能设置进行了对比实验,发现活化能参数虽然对平均生长速率有明显影响,但是对样品的生长速率分布及均匀性影响不大。     

Ca3Y2(Si3O9)2:Tb3+绿色荧光粉的光谱特性

采用高温固相法制备了Ca₃Y₂(Si₃O₉)₂: Tb³⁺绿色荧光粉,研究了材料的光学性能。X 射线衍射(XRD)结果显示,掺杂少量的Tb³⁺,并未影响Ca₃Y₂(Si₃O₉)₂材料 的晶相结构。Ca₃Y₂(Si₃O₉)₂:Tb³⁺ 荧光粉的激发光谱由较强的4f^75d1宽带吸收(200～300 nm )和较弱的4f-4f电子跃迁吸收 (300～500 nm)构成,主激发峰位于236nm。取波长分别为236、376和482nm的光 作为激发源时,发现样品的主发射峰均位于544 nm,对应Tb³⁺的⁵D 4→⁷F₅跃迁发射。以236nm 紫外光作为激发源,监测544nm主发射峰,随Tb³⁺浓度 的增大,Ca₃Y₂(Si ₃O₉)₂:Tb³⁺的荧光寿命逐渐减小,但在实验范围内并未出现浓度猝灭现象。     

CaSi2O2N2:Ce3+/Eu2+荧光粉的发光性能研究

采用高温固相反应法制备了CaSi₂O₂N₂:C e³⁺/Eu ²⁺荧光粉,研究了分别掺杂Ce³⁺、Eu²⁺及Ce³⁺/Eu²⁺共掺 杂时荧光粉 的发光特性。CaSi₂O₂N₂:Ce³⁺在333 nm激发下得到宽波段的发射谱,发射峰 位于395nm,随着Ce³⁺浓度的增大,发 射波长出现明显的红移,猝灭浓度为1mol%。CaSi₂O₂N₂:Eu²⁺在397nm激发下得到峰值位于540nm处的宽波段发射谱, 猝灭浓度为1mol%。对于Ca0.99－2xSi₂O₂N₂:xCe ³⁺,xLi⁺,0.01Eu²⁺荧光粉,在333nm激发下,位于395nm处的发射峰十分微 弱,在540nm处有宽带发射,随着Ce³⁺浓度增大,位于540nm处的Eu²⁺的特征 发射显著增强。对于Ca0.98－ySi₂O₂N₂: 0.01Ce³⁺,0.01Li⁺,yEu²⁺荧光粉,在激发光波长 为333nm,Eu²⁺浓度较低时,可以观察到两个发射带,峰值分 别位于395nm及540nm,随着Eu²⁺浓度增加,位于395nm的 发射强度一直减小,而540nm处的发射强度先增加后减小,猝灭浓 度为0.4mol%。证实了Ce³⁺,Eu²⁺之间发生了有效的能 量传递。计算出Ce 3+、Eu²⁺之间能量传递的效率ηT,在Eu²⁺浓 度为 1mol%时ηT趋于饱和,达到97.7%。通过计算,得到Ce3+ 与Eu²⁺之间的能量传递方式为电偶极-电偶极相互作用。     

用溶胶-凝胶法制备的Cu2Bi2Cr2O8薄膜 及其光学和铁磁性能研究

以硝酸铜Cu(NO₃)₂·3H₂O、硝酸铬Cr(NO₃)₃·9H₂O、硝酸铋Bi(NO₃)₃·3H₂O和乙二醇为原料,利用溶胶-凝胶工艺在石英衬底上制备了纳米Cu₂Bi₂Cr₂O₈薄膜。通过X射线衍射(X-Ray Diffraction, XRD)和拉曼测试对样品进行了表征。结果表明,Cu₂Bi₂Cr₂O₈薄膜具有良好的光学特性,其禁带宽度为1.49 eV;在磁性测试方面,Cu₂Bi₂Cr₂O₈薄膜呈现出了良好的铁磁性。     

Gd2O3:Yb3+,Er3+纳米粉体的水热合成及上转换发光研究

采用Gd₂O₃,Yb₂O₃,Er₂O₃,HNO₃,CO(NH₂)₂和C ₁₂H₂₅SO₄Na为实验原料,通过水热法合成了纳米Gd₂O₃:Yb³⁺,Er ³⁺上转换发光粉体。通过X射线衍射(XRD )、差示扫描量热 -热重分析(DSC-TGA )、傅里叶变换红外光谱(FT-IR ) 、透射电子显微镜(TEM )和 上转换发射光谱(UCL )等对样品进行表征。研究结果表明:CO(NH₂)₂与Gd ³⁺ 离子的摩尔比m影响前驱体的组成,当m=4时,前驱体是由晶态的 Gd₂(CO₃)₃·xH₂O构成。该 前驱体在空气气氛下800℃煅烧2h可获得单相的Gd₂O₃纳米粉体 ,粉体呈近球状,平均粒 径约为30～40nm。上转换发光光谱表明,在980nm波长红外光激发下,Gd₂O₃:Yb³⁺,Er³⁺的主发射峰 位于664nm波长处,呈红光发射,对应于Er³⁺的 ⁴F9/2→⁴I15/2跃迁。在波长为539 nm和562nm附近呈现绿光发射,分别对应于Er³⁺的²H11/2→⁴I15/2和⁴S3/2→⁴I15/2跃迁。Er³⁺的猝 灭浓度为1%。800℃煅烧合成的Gd₂O₃:Yb³⁺,Er³⁺ 纳米粉体的上转换发光机制为双光子模型, 而1200℃煅烧合成的Gd₂O₃:Yb³⁺,E r³⁺纳米粉体的上转换发光机制则为三光子模型。     

Ce3+对掺Er3+碲铌锌钠玻璃光谱性质的影响

用高温熔融法制备了摩尔组分百分比为75TeO₂- 10Nb₂O₅-10ZnO-5Na₂O-0.5Er₂O₃-xCe₂O₃(x=0.00、0.25、 0.50、0.75、1.00)的碲酸盐玻璃样品。测量了玻璃样品的吸收光谱、上转换 光谱、拉曼光谱和 荧光光谱。结合Judd-Ofelt(J-O)理论计算了玻璃样品的强度参数Ω_t(t=2、4、6)、自发辐射跃迁几率A、荧光分支比β和辐射寿命 τrad,并用McCumber理论计算得到了Er³⁺的受激发射截面。比 较了玻璃样品中Er³⁺的放大器带宽 品质因子(σpeak_e×FWHM)和增 益品质因子(σpeak_e×τm),分 析了Er³⁺/Ce³⁺间能量转移(ET)机 理以及Ce³⁺对上转换发光的抑制作用。研究表明,适量Ce³⁺的引入对于掺Er ³⁺碲铌锌钠玻璃的光谱特性有一定的提高作用。     

用于白光LED的KNaCa2(PO4)2:Eu2+蓝色荧光粉的发光特性

采用高温固相法合成了蓝色荧光粉KNaCa₂(PO₄)₂:Eu²⁺,利用X射线衍射(XRD)和光谱技术等表征了材料的性能。结果显示,少量Eu 2+的掺入并没有影响KNaCa₂(PO₄)₂的晶体结构。 在399nm近紫外光激发下,KNaCa₂(PO₄)₂:Eu²⁺材料发 射蓝光,发射光谱为400～600nm, 主发射峰位于471nm,对应Eu²⁺的4f^65d1→ 4f⁷跃迁发射;471nm发射峰,对应的激发光 谱为250～450nm,主激发峰位于399nm,与近紫外芯片匹配很好。 以365nm近紫外光作为 激发源时,KNaCa₂(PO₄)₂:Eu²⁺材料的发射强度约为商用蓝色荧光粉BAM:Eu 2+的85%;而以 399nm近紫外光作为激发源时,相较于BAM:Eu²⁺,KNaCa₂(P O₄)₂:Eu²⁺材料具有更强的发射强 度。此外,KNaCa₂(PO₄)₂:Eu²⁺和BAM:Eu²⁺的CIE色坐标接近,均位于蓝 色区域,色坐标分别 为(0.154,0.154)和(0.141,0.112)。研究结果 表明,KN aCa₂(PO₄)₂:Eu²⁺是一种在三基色白光LED中有应用前景的蓝色荧光粉。     

Co3O4/Fe2O3异质结复合材料的制备及其紫外光光电探测性能

分别采用旋涂法和水热法在FTO衬底上制备Co₃O₄种子层和Co₃O₄薄膜,再在Co₃O₄薄膜上水热生长Fe₂O₃纳米棒,获得了高质量的Co₃O₄/Fe₂O₃异质结复合材料。通过改变Fe₂O₃前驱体溶液浓度来改变异质结复合材料中Fe₂O₃组分的含量。结果表明,Fe₂O₃纳米棒覆盖在呈网状结构的Co₃O₄薄膜上,随着Fe₂O₃前驱体溶液浓度即Fe₂O₃组分含量的增加,Co₃O₄/Fe₂O₃异质结复合材料对紫外光的响应逐渐增强,当Fe₂O₃前驱体溶液浓度为0.015mol/L时,异质结复合材料有着很好的光电稳定性,并表现出较高的响应率(12.5mA/W)和探测率(4.4×10¹⁰Jones)。     

新型红色荧光粉Ca0.5Sr0.5MoO4:Sm3+的制备及光学性能

为了得到发光效率较好的长波长红色荧光粉,采用 高温固相法成功地合成了适合紫外激发的红色荧光粉 Ca0.5－xSr0.5MoO₄:xSm³⁺,研究了其晶体结构和发 光性质。X射线衍射(XRD)测量结果显示,制备的样品为纯相Ca0.5Sr0.5MoO₄晶体。其激发 光谱包括一个宽带峰和一系列尖峰,通过不同波长激发的发射谱和与Ca0. 5－xSr0.5MoO₄:xEu³⁺的发射 谱比较分析得出激 发宽带为最有效激发带,归属于Mo⁶⁺－O2－的电荷迁移跃迁。在275nm的激发 下,发射峰由峰值为564nm(⁴G5/2→⁶H 5/2)、 606nm(4G5/2→⁶H7/2) 、647nm (⁴G5/2→⁶H9/2)、707nm(4G5/2→⁶H11/2)的4个峰组成,最大发射 峰位于647nm处,呈现红光 发射。Sm³⁺掺杂高于6%时Ca0.5－xSr0.5Mo O₄:xSm³⁺出现浓度猝灭,分析表明,其猝灭机 理是最邻近离子间的能量传递。同时,添加电荷补偿剂可增强材料的发射强度,以添加Na +的效果最明显。     

白光LED用Ba0.955Al2Si2-xGexO8∶Eu2+荧光粉的晶体结构和光谱特性研究

采用高温固相法在弱还原气氛下制备了Ba0.955Al₂Si2－xGexO₈∶E u²⁺(x=0.0～1.0)系列荧 光粉,研究了Ge⁴⁺置换Si⁴⁺对其晶体结构和光谱特性的影响。Ge⁴⁺以类 质同相替代Ba长石(BaAl₂Si₂O₈) 晶格中的Si⁴⁺形成连续固溶体,晶胞参数a、b、c、β和晶胞体积V随Ge⁴⁺置换量呈线性递 增。荧光激发谱为宽带,位于230～400nm处,可拟合成4个峰,最大 峰值位于332nm;随着 Ge⁴⁺置换量的增加,半高宽(FWHM)从93nm减小到80nm。发射光谱位于375～600nm,可由422nm 和456nm两峰拟合而成,最大峰值位于434nm;随着Ge⁴⁺置换量Si⁴⁺进入基质晶格,造成 Eu-O距离变小,发光中心Eu²⁺所处晶体场增强,5d轨道 能级分裂变大,最低发射能级下移,两拟合峰均线性红移。     

New TIT capacitor with ZrO2/Al2O3/ZrO2 dielectrics for 60 nm and below DRAMs

New ZrO₂/Al₂O₃/ZrO₂ (ZAZ) dielectric film was successfully developed for DRAM capacitor dielectrics of 60 nm and below technologies. ZAZ dielectric film grown by ALD has a mixture structure of crystalline phase ZrO₂ and amorphous phase Al₂O₃ in order to optimize dielectric properties. ZAZ TIT capacitor showed small Tox.eq of 8.5 Å and a low leakage current density of 0.35 fA/cell, which meet leakage current criteria of 0.5 fA/cell for mass production. ZAZ TIT capacitor showed a smaller cap leak fail bit than HAH capacitor and stable leakage current up to 550 °C anneal. TDDB (time dependent dielectric breakdown) behavior reliably satisfied the 10-year lifetime criteria within operation voltage range.     

Research of SiO2/InP structure prepared by photo-CVD

The SiO₂ film as an insulator in InP MOS structure was grown by mercury-sensitized photo induced chemical-vapor deposition (photo-CVD) utilizing gaseous mixture of monosilane (SiH₄) and nitrous oxide (N₄O) under 253.7 nm ultraviolet light irradiation. The PHOTOX SiO₂ film (i.e., SiO₂ film prepared by photo-CVD system) deposited at 250° C has a refractive index of 1.46 and breakdown field strength of 7.0 MV/cm. The 1 MHz capacitance-voltage characteristics of the InP MOS diode was measured to study the interface state densities. The minimum value is 1.2 × 10¹¹ cm⁻²eV⁻¹ for the sample prepared at a substrate temperature of 250° C.     

Electrothermal investigation of the switching effect in p-Type TllnSe2, TllnTe2, and TIGaTe2 chain chalcogenide semiconductors

Large p-type TlInSe₂, TlInTe₂, and TlGaTe₂ single crystals have been grown by the Bridgman-Stockbarger method, starting from stoichiometric melts. The first observations of the switching process in p-type TlGaTe₂ single crystal are reported. Current-voltage (I-V) characteristics of symmetrical In/p-TlInSe₂/In, In/p-TlInTe₂/In, and In/p-TlGaTe₂/In structures exhibit two distinct regions: an ohmic region at low current densities and nonlinear regions (S-shape) having negative differential resistance (NDR) at moderate and higher current densities. An electrothermal model was used to explain the nonlinear behavior. The nonlinear behavior of the I–V curves was studied at different ambient temperatures in the 100–340K region; the sample temperature and the threshold voltage of the NDR region were examined as a function of the current density and the ambient temperature, respectively. The electrothermal model is a satisfactory explanation.     

Transport properties of thermoelectric materials for coolers

The Seebeck coefficient, thermal conductivity, electrical conductivity and Hall coefficient of cooler grade, p-and n-type ternary alloys of Bi₂Te₃-Sb₂Te₃-Sb₂Se₃ were measured between 10 and 300 K. Between 300 K and about 150 K the temperature dependence of the transport properties can be explained by assuming nondegeneracy and a lattice scattering mechanism. The difference between the temperature dependence of the Hall effect in n-and p-type alloys can be explained by the presence of sub-bands of light and heavy holes in the valence band of p-type alloys.     

Excellent performance of gas sensor based on In2O3-Fe2O3 nanotubes

In₂O₃-Fe₂O₃ nanotubes are synthesized by an electrospinning method. The as-synthesized materials are characterized by scanning electron microscope and X-ray powder diffraction. The gas sensing results show that In₂O₃-Fe₂O₃ nanotubes exhibit excellent sensing properties to acetone and formaldehyde at different operating temperatures. The responses of gas sensors based on In₂O₃-Fe₂O₃ nanotubes to 100 ppm acetone and 100 ppm formaldehyde are 25 (240℃) and 15 (260℃), and the response/recovery times are 3/7 s and 4/7 s, respectively. The responses of In₂O₃-Fe₂O₃ nanotubes to 1 ppm acetone (240℃) and formaldehyde (260℃) are 3.5 and 1.8, respectively. Moreover, the gas sensor based on In₂O₃-Fe₂O₃ nanotubes also possesses an excellent selectivity to acetone and formaldehyde.     

不同深宽比GaAs衬底的Al22O3/HfO2复合薄膜材料原子层沉积及能谱分析

利用热原子层沉积（Atomic Layer Deposition, ALD）技术在不同深宽比GaAs衬底上进行了Al2₂O₃/HfO₂复合薄膜的沉积。通过对其表面和能谱进行分析发现,沉积温度对复合薄膜的摩尔比具有较大的影响。随着深宽比的增大,其沉积表面和沟槽内会出现残留物;随着ALD沉积温度的上升,其沉积表面和沟槽内的残留物减少,摩尔比趋向均匀。当深宽比为2.2并利用150 ℃的低沉积温度时,表面及底面基本无残留物。但当深宽比为4.25时,150 ℃沉积明显有大量残留物。只有当温度升高到300 ℃时,表面和沟槽里复合薄膜的残留物才被明显消除。ALD技术可以实现各种器件结构的全方位钝化,这是其他化学气相沉积法无法比拟的。     

The effect of Tl2Te3 on the properties of the solid solution (Sb2Te3)0.75.(Bi2Te3)0.25

The effect on transport properties of the addition of 0.5-5% Tl₂Te₃ to p-type solid solutions of antimony and bismuth tellurides was studied. It was found that the addition of Tl₂Te₃ caused a lessening of the increase of hole concentration as low temperatures were approached, resulting in a slower decrease of the Seebeck coefficient with a decrease in temperature. In partial fulfillment of M.Sc. degree, Hebrew University, Jerusalem. Permanent address, Dept. of Inorganic and Analytical Chemistry, Hebrew University, Jerusalem.     

Powder processing of high temperature ceramic superconductor Tl2Ba2Ca2Cu3O10

We have developed a technique to produce high quality Tl₂Ba₂Ca₂Cu₃O₁₀ powders used for making superconducting wire, tape, lead, shield, and other large scale bulk applications. Starting with T1₂O₃, BaO₂, CaO, and CuO, we mix and grind these chemicals with a machine ball mill and then press the ground mixture into pellets. The pellets are sintered at about 895‡C for at least 30 h in an oxygen atmosphere. The sintered material is mainly the Tl₂Ba₂Ca₂Cu₃O₁₀ compound. To get more homogeneous superconductor powders, we pulverize the sintered material and use a magnetic superconducting material selector to separate and grade the material. Finally, the top grade material has a phase purity of <98% and a T_c(r < 0) of 123–126K.