ELECTROLUMINESCENCE SPECTRA OF GexSi1-x/Si SINGLE QUANTUM WELL

The electroluminescence of Ge_xSi_1-x/Si single quantum well was measured at temper-atures above room temperature along the growth direction and the direction normal to it. TO and NP peaks were resolved.     

RAMAN SCATTERING INTENSITIES OF FOLDED LONGITUDINAL ACOUSTIC PHONONS IN GexSi1-x/Si SUPERLATTICES

In terms of photoelastic mechanism we have investigated the Raman scattering intensities of the folded longitudinal acoustic (FLA) phonons in Ge_xSi_1-x/ Si superlattices (SLs), taking into account the differences between the acoustic and photoelastic parameters of the two constituents in the SLs. The relative intensities calculated for the FLA phonons are in excellent agreement with the experimental results at the frequencies up to about 50 cm^-1. The broadening of the linewidth arising from the so called strong acoustic attenuation, which was reported previously located around the frequency 15 cm^-1 in Ge_xSi_1-x/Si SLs(x≈0.5), has not been observed in this work.     

Optical properties of wavelength-tunable green-emitting color conversion glass ceramics

Color conversion glass ceramics are prepared by cosintering borosilicate glass frits and green 0.06Ce:Y_2.94(Al_1-xGa_x)₅O₁₂ phosphors. The crystal structures, the influence of Ga concentration on the photoluminescence (PL), and reliability properties of the color conversion glass ceramics are investigated. The PL emission wavelengths of 0.06Ce:Y_2.94(Al_1-xGa_x)₅O₁₂ glass ceramics show blue shift from 545 nm to 525 nm with increasing Ga content (x value) under excited at 460 nm. Reliability test results show that the quantum yield (QY) of 0.06Ce:Y_2.94(Al_1-xGa_x)₅O₁₂ glass ceramics decreases from 70.60% to 59.06% with x value increasing from 0.15 to 0.35 under the ambient condition of 85℃/RH85% for the exposure time of 168 h. And the quantum yield (QY) of 0.06Ce:Y_2.94(Al_1-xGa_x)₅O₁₂ glass ceramics decreases from 65.13% to 52.23% after being soaked into boiled water for 4 h. The finding reveals that the addition of Ga can deteriorate the reliability of the color conversion glass ceramics.     

Unified Treatment of Systematics for Even-Even Nuclei with A≥70

By the concept of effective boson numbers, systematics of E₂₁+E₄₁+E₆₁+, R=E₂₁+/E₄₁, B(E2, 0₁⁺→2₁⁺) and Q₀ for even-even nuclei with A≥70 are presented. New features of energy spectra are noticed and an intuitive understanding is given.     

ABNORMAL ENERGY DEPENDENCE OF AXIAL MINIMUM CHANNELING YIELDS IN GexSi1-x/Si(100) STRAINED

An energy dependence of the axial minimum channeling yield in Ge_xSi_1-x/Si(100) Strained-layer superlattice is observed in the energy range of impinging He⁺ ione from 1.2 to 3.0 MeV. For [100] axial channeling, the measurements ere in agreement with what have been known in a single crystal. However, for [110] axial channeling, it is found that the minimum channeling yields increase markedly with the increase of He⁺ ion energy, which is contrary to the general channeling behaviors in a single crystal. A tentative model is suggested to explain this aberrance.     

ORDER ALLOY IN GexSi1-x/Si(100) STRAINED-LAYER SUPERLATFICES

The Ge_xSi_1-x/Si(100) strained-layer superlattices have been investigated by means of the transmission electron microscopy of the cross-sectional specimen (XTEM) and the high resolution electron microscopy (HREM), The order alloy with a period of modulation twice as large as the lattice constant along <100> zone axis has been found in the alloy layers of the superlattices with x≈0.4-0.5. This order struc-ture makes the superlattices inhomogeneously strained. The result of the compuler simulation shows that the order alloy exhibits an altemating stack of 2 monolayers of Ge atoms and 2 monolayers of Si atoms along the <100> zone axis. Thc calculated elastic strain energy of the disorder alloy reported in the litera-ture is very close to that of the order alloy along <100> zone axis. Thus, during the MBE growth of the alloy layers, both the disorder and order alloys can be formed along <100> zone axis.     

半绝缘GaAs的双调制反射光谱研究

半导体材料电子能带结构的确定对研究其物理性质及其在半导体器件方面的应用有重要意义.光调制反射光谱是一种无损和高灵敏度的表征半导体材料电子能带结构的光学手段.光调制反射光谱中激光调制导致的材料介电函数的变化在联合态密度奇点附近表现得更为明显.通过测量这些变化,可以得到有关材料能带结构临界点的信息.然而在传统的单调制反射光谱中,激光调制信号的光谱线型拟合和临界点数目的分析往往被瑞利散射和荧光信号所干扰.本文将双调制技术与双通道锁相放大器结合,消除了瑞利信号和荧光信号的干扰,获得了具有较高信噪比的调制反射光谱信号.双通道锁相放大器可以同时解调出反射光谱信号及其经泵浦激光调制后的细微变化量,避免了多次采集时可能存在的系统误差.利用这种技术,在可见激光(2.33 eV)泵浦下,我们测量了半绝缘GaAs体材料从近红外至紫外波段(1.1-6.0 eV)的双调制反射光谱,获得了多个能带结构临界点的信息.探测到了高于泵浦能量之上的与GaAs能带结构高阶临界点对应的特征光谱信号,说明带隙以上高阶临界点的光调制反射光谱本质是光生载流子对内建电场的调制,并不是来自该临界点附近的能带填充效应.这一结果表明双调制反射光谱能够对半导体材料能带结构带隙及其带隙以上临界点进行更准确的表征.     

Magnetic entropy change and magnetic properties of LaFe_(11.5)Si_(1.5) after controlling the Curie temperature by partial substitution of Mn and hydrogenation

Magnetic properties and magnetic entropy changes of La(Fe_(1-x)Mn_x)_(11.5)Si_(1.5)H_y compounds are investigated. Their Curie temperatures are adjusted to room temperature by partial Mn substitution for Fe and hydrogen absorption in 1-atm(1 atm = 1.01325×10~5Pa) hydrogen gas. Under a field change from 0 T to 2 T, the maximum magnetic entropy change for La(Fe_(0.99)Mn_(0.01))_(11.5)Si_(1.5)H_(1.61)is-11.5 J/kg. The suitable Curie temperature and large value of ?S_m make it an attractive potential candidate for the room temperature magnetic refrigeration application.     

Gd1-xEuxAl3(BO3)4纳米晶的合成及其发光性能

以高温固相反应法合成了Gd_1-xEu_xAl₃(BO₃)₄:Eu³⁺纳米荧光粉。使用XRD分析确定了样品的物相,并根据谢乐公式计算出其微晶的纳米粒度。采用了“粉末悬浮法”以甘油为分散介质,在RF540荧光光度计上测试了纳米晶荧光粉的激发光谱和发射光谱。GdAl₃(BO₃)₄基质本身发光,GdAl₃(BO₃)₄:Eu纳米荧光粉表现了Eu³⁺的特征发射光谱,其中最强峰为⁵D₀→⁷F₂发射,表明晶体结构中没有对称中心格位。实验表明在GdAl₃(BO₃)₄:Eu纳米晶荧光粉中,存在Gd³⁺对Eu³⁺发光的基质敏化作用。     

Quantum critical behavior in an antiferromagnetic heavy-fermion Kondo lattice system(Ce_(1-x)La_x)_2Ir_3Ge_5

The measurements on temperature dependences of magnetic susceptibility χ(T), specific heat C(T), and electrical resistivity ρ(T) were carried out for the antiferromagnetic(AFM)(Ce_(1-x)La_x)_2Ir_3Ge_5(0 ≤ x ≤ 0.66) system. It was found that the Neel temperature TNdecreases with increasing La content x, and reaches 0 K near a critical content xcr =0.6. A new phase diagram was constructed based on these measurements. A non-Fermi liquid behavior in ρ(T) and a log T relationship in C(T) were found in the samples near xcr, indicating them to be near an AFM quantum critical point(QCP) with strong spin fluctuation. Our finding indicates that(Ce_(1-x)La_x)_2Ir_3Ge_5 may be a new platform to search for unconventional superconductivity.     

La3Co29-xFexSi4B10的择优占位、电子结构和晶格振动性质的理论研究

分别用第一性原理及原子间相互作用势对初始模型进行几何优化, 所得稳定结构的晶格参数均与实验值符合较好. 通过第一性原理密度泛函理论, 计算了稳定结构La₃Co_29-xFe_xSi₄B₁₀化合物择优占位情况, 计算结果表明, Fe原子最择优替代Co 原子的2c晶位, 择优占位顺序为2c > 8j1 > 8i2 > 8j2 > 8i3 > 16k > 8i1, 这与实验结果非常符合. Fe原子每次只替代不同晶位的一个Co原子时, La₃Co_29-xFe_xSi₄B₁₀ 体系的晶格常数几乎不变, 磁矩却发生了有趣的变化. 当Fe原子沿着择优顺序依次替代不同晶位的所有Co原子时, 随着La₃Co_29-xFe_xSi₄B₁₀体系中Fe原子含量的增多, 其电子态密度整体向左移动. Fe原子完全替代Co时, 与未掺杂时相比体系的总磁矩增加. 最后, 利用原子间相互作用势进一步预测了La₃Co_29-xFe_xSi₄B₁₀体系的晶格振动及热力学性质. 在低频部分, 振动模式主要由质量较大的Co, Fe和La元素作贡献; 随着掺杂原子Fe的增多, 体系的截止频率先减小后增多, 中频部分由Si元素引起的振动模式减少; B-B强相互作用引起了高频部分的振动模式. 基于声子态密度预测了不同数量Fe掺杂后体系的比热、熵和德拜温度的变化, 当Fe 含量大于Co时, 德拜温度明显升高.     

Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe_(3-x)Se_x

It was found that selenium doping can suppress the charge-density-wave(CDW) order and induce bulk superconductivity in ZrTe_3. The observed superconducting dome suggests the existence of a CDW quantum critical point(QCP) in ZrTe_3-xSex near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe_(3-x)Se_x single crystals(x = 0.044 and 0.051) down to 80 m K. For both samples, the residual linear term κ_0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ_0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe_(3-x)Se_x,which indicates conventional superconductivity despite of the existence of a CDW QCP.     

(Ga,Mn)As光调制反射光谱

室温下我们研究了稀磁半导体(Ga,Mn)As的光调制反射(PR)光谱,观测到来自样品的Franz-Keldysh振荡(FKO)信号。随着Mn原子浓度的增加,PR线形展宽,但是临界点E₀和E₀+Δ₀没有明显的移动。根据FKO振荡数据,计算得到样品表面电场强度随Mn原子掺杂浓度的增加而增强。测量到与Mn原子掺杂相关的杂质带,其能量位置离GaAs价带边~100 meV。根据样品的表面电场强度和表面耗尽层模型,估算样品的空穴浓度为~10¹⁷cm^-3,较低的空穴浓度可能与样品具有较低的居里温度有关,或测量的PR信号来自于样品中外延层的部分耗尽区域。     

铁基超导体的量子临界行为

铁基超导体呈现丰富的电子相图, 各种有序态相互交叠. 本文主要介绍利用核磁共振手段在空穴型和电子型掺杂的BaFe₂As₂以及LaFeAsO_1-xF_x这三种具有代表性的铁基超导体中探测到的反铁磁序与超导序的微观共存、量子临界点和量子临界行为. 实验发现, 无论在空穴型还是电子型掺杂的铁基超导体中, 反铁磁相变温度都随着掺杂被抑制, 并最终在某个掺杂量降到零温而形成量子临界点. 在反铁磁转变温度之上存在结构相变, 其转变温度也随着掺杂而降低. 核磁共振谱证实结构相变也形成一个量子临界点. 本文介绍核磁共振及输运测量揭示的这两种量子临界点附近存在的量子临界行为, 共存态下奇异的超导性质等.     

硅锗量子阱结构在硅异质结太阳电池中应用的数值模拟

利用半导体工艺和器件仿真软件silvaco TCAD(Technology Computer Aided Design),模拟研究了采用硅/硅锗合金(silicon/silicon germanium alloy,Si/Si_(1-x)Ge_x)量子阱结构作为吸收层的薄膜晶体硅异质结太阳电池各项性能.模拟结果显示,长波波段光学吸收随锗含量的增加而增加,而开路电压则因Si_(1-x)Ge_x)层带隙的降低而下降.锗含量为0.25时,短路电流密度的增加补偿了开路电压的衰减,效率提升0.2%.氢化非晶硅/晶体硅(a-Si:H/c-Si)界面空穴密度以及Si_(1-x)Ge_x)量子阱的体空穴载流子浓度制约着空穴费米能级的位置,进而影响到开路电压的大小.随着锗含量增加,a-Si:H/c-Si界面缺陷对开压的影响降低,Si_(1-x)Ge_x)量子阱的体缺陷对开压的影响则相应增加.高效率含Si_(1-x)Ge_x)量子阱结构的硅异质结太阳电池的制备需要a-Si:H/c-Si界面缺陷的良好钝化以及高质量Si_(1-x)Ge_x)量子阱的生长.     

近紫外宽带激发LED用红色荧光粉(Gd_(1-x)Eu_x)6(Te_(1-y)Mo_y)O_(12)的制备与性能

利用高温固相法制备了一种新型红色荧光粉(Gd_(1-x)Eu_x)_6(Te_(1-y)Mo_y)O_(12),研究了Eu~(3+)单掺和Eu~(3+),Mo~(6+)共掺Gd_6TeO_(12)荧光粉的结构、形貌和荧光性能.实验结果表明,所合成的粉体为纯相.在393 nm近紫外光激发下,(Gd_(1-x)Eu_x)_6(Te_(1-y)Mo_y)O_(12)荧光粉发出特征红光,位于632 nm处的发射主峰属于Eu~(3+)的~5D_0→~7F_2跃迁.当Eu~(3+)掺杂浓度超过20%(物质的量分数)时发光出现浓度淬灭,经证实这是由电偶极-电偶极相互作用造成的.随着工作温度升高,荧光粉发光强度减小,计算得到Eu~(3+)热淬灭过程中的激活能为0.1796 eV.当(Gd_(0.8)Eu_(0.2))_6TeO_(12)中共掺Mo~(6+_(取代Te~(6+)),该荧光粉发射光谱的峰位、强度变化不大,但是Mo~(6+)-O~(2-)电荷迁移态显著增大了近紫外波段的激发带宽度,可以有效提高激发效率.具有近紫外宽带激发特征的(Gd_(0.8)Eu_(0.2))_6(Te_(0.6)Mo_(0.4))O_(12)是一种潜在的白光LED用荧光粉材料.     

Validity of the Counting Schemes of Boson Number in the Interacting Boson Model and Regularities in Systematic Studiesfor Even-Even Nuclei

The E₂₁+, E₄₁+, E₆₁+, B(E2,0₁⁺ → 2₁⁺) systematics are presented by using the total np interaction V_Np and the ratio betwyn V_Np and the total pairing strength V_pair to have a richer understanding of the wel&known N_πN_V and N_nN_p/(N_n + N_p) schemes. The different counting schemes for effective bosoh numbers and some regularities uncovered in previous studies are tested by the figures of V_NP/V_pair schemes. The systematics in the V_NP/V_pair scheme suggest that-the N_nN_p/(N_n + N_p) scheme holds for A ≥ 100 even-even nudei.     

硼组分在BaAl2Si2O8:Eu2+发光材料中的作用

采用高温固相法在弱还原气氛下制备Ba0.955Al2-xBxSi2O8:Eu2+(x=0～0.5)系列荧光粉,研究B3+置换Al3对晶体结构和光谱特性的影响.B3+以类质同相替代BaAl2Si2O8晶格中的Al3+形成部分连续固溶体,随着B3+置换量的增加,晶胞参数a,b,c和晶胞体积V呈线性递减,晶面夹角β呈线性递增...     

Formation of L10-FeNi hard magnetic material from FeNi-based amorphous alloys

L1₀-FeNi hard magnetic alloy with coercivity reaching 861 Oe was synthesized through annealing Fe₄₂Ni_41.3Si₈B₄P₄Cu_0.7 amorphous alloy, and the L1₀-FeNi formation mechanism has been studied. It is found the L1₀-FeNi in annealed samples at 400 ℃ mainly originated from the residual amorphous phase during the second stage of crystallization which could take place over 60 ℃ lower than the measured onset temperature of the second stage with a 5 ℃/min heating rate. Annealing at 400 ℃ after fully crystallization still caused a slight increase of coercivity, which was probably contributed by the limited transformation from other high temperature crystalline phases towards L1₀ phase, or the removal of B from L1₀ lattice and improvement of the ordering quality of L1₀ phase due to the reduced temperature from 520 ℃ to 400 ℃. The first stage of crystallization has hardly direct contribution to L1₀-FeNi formation. Ab initio simulations show that the addition of Si or Co in L1₀-FeNi has the effect of enhancing the thermal stability of L1₀ phase without seriously deteriorating its magnetic hardness. The non-monotonic feature of direction dependent coercivity in ribbon segments resulted from the combination of domain wall pinning and demagnetization effects. The approaches of synthesizing L1₀-FeNi magnets by adding Si or Co and decreasing the onset crystallization temperature have been discussed in detail.     

M_2Eu_xLn_(1-x)AlO_5(M=Ca,Sr,Ba,Ln=La,Gd,Lu)红色荧光粉发光性质的研究

用高温固相反应法合成了M_2Eu_xLn_(1-x)AlO_5(M=Ca,Sr,Ba,Ln=La,Lu,Gd)荧光粉,研究了荧光粉的发光性质。在紫外光和近紫外光激发下,样品的发射光谱由Eu~(3+)的5D0→7FJ(J=0,1,2,3,4)特征发射组成。其中Eu3+离子位于590 nm附近的5D0→7F1和位于620 nm附近的5D0→7F2跃迁发射的强度最强。荧光粉的激发光谱都是由O~(2-)-Eu~(3+)电荷迁移带和Eu~(3+)的f-f跃迁构成的。M_2Eu_xLa_(1-x)AlO_5(M=Ca,Sr,Ba)的O2--Eu~(3+)的电荷迁移带的峰位按Ca、Sr、Ba顺序向长波方向移动。研究了用La、Gd和Lu替代M_2Eu_xLn_(1-x)AlO_5中Ln的位置对样品发光的影响。给出了Eu~(3+)浓度对发光强度的影响。分析了M_2Eu_xLn_(1-x)AlO_5和M_2Eu_xLn_(1-x)AlO_5的荧光寿命。