高Tc超导体R_1Ba_2Cu_3O_(2-x)(R-rare earth)的磁性和超异电性研究

本论文合成了R_1Ba_2Cu_3O_(2-x) (R = La、Nd、Sm、Eu、Gd、Dr、Ho、Er、Tm、Yb)、Y_2Ba_2Cu_3O_(2-x) (x = 0.10～1.17)和Y_1Ba_2Cu_3O_(7-x)S_x (x = 0～2)，并对磁性和超导电性进行了较为系统的研究。R_1Ba_2Cu_3O_(2-x)的磁化率在T > Tc的很宽的温度范围内服从Curic-Weiss定律，求得的有效磁矩略大于理论值，差值与Y_1Ba_2Cu_3O_(2-x)中Cu~(2+)磁矩相近，说明Cu~(2+)的磁矩对体系磁性有额外贡献，这贡献随R~(3+)离子中自旋平行的电子权的增多而增大。其高温下的磁化率CT > 700K)相对Curic-Weiss定律发生较大偏离，这偏离可能的来源有三个：高温下稀土离子发生较大的能级反转效应，高温下结构相变对磁性的影响，高温下氧含量减少造成Cu~(2+)磁矩增大。R_1Ba_2Cu_3O_(2-x)磁化率在T < Tc时也服从Curic-Weiss定律，R~(3+)磁矩是定域的，表明超导与磁性相互独立。互不相关，稀土磁矩与传导电子间无相互作用。用Sr取代R_1Ba_2Cu_3O_(2-x)中的Ba，没能使体系产生磁有序的变化，但却使有效磁矩增大，并完全破坏了样品的超导电性。Sm~(3+)磁化率不服从Curic-Weiss定律，在Sm_1Ba_2Cu_3O_(2-x)中Sm~(3+)显示了典型Van VlccK离子的特性。Y_1Ba_2Cu_3O_(2-x)随氧含量减少发生超导体一半导体一绝缘体的转化，当氧含量由6.90减小至6.49时发生由正交到四方的结构相变。当(7-x) = 5.83时有较多杂质相出现，123相开始分解。样品磁化率均服从Curic-Weiss定律，并随氧含量增大磁化率－温度曲线越来越趋于平缓（直线），当(7-x) = 6.90时磁化率基本不随温度变化，这时Pauli顺磁性占主导地位，这说明氧含量增加定域磁矩减少，求得的有效磁矩Peff随氧含量增大总趋势减小。提出了电子“巡游”的观点，较好地解释了上述现象，并推测出Cu(2)的d电子是离域的，对样品磁矩没有贡献，样品Peff来源于部分Cu(1)的定域Cu~(2+)的磁矩，上述推测被EPR结果证实。正交相Y_1Ba_2Cu_3O_(2-x)的EPR谱显示了中心对称成准立方晶场中Cu~(2+)(d~9, S = 1/2, I = 3/2)的EPR物性。而四方相样品的EPR谱却出现了明显的各向异性，说明观察到的为Cu(1)的EPR信号，由Cu(1)~(2+)的写域磁矩产生。Y_1Ba_2Cu_3O_(2-x)的EPR信号束源于本体相，而非Y_2Cu_2O_5、BaCuO_2、Y_2BaCuO_5等杂质相。各样品EPR信号的自旋浓度远小于1spin/cu，并随氧含量减小而增大，当(7-x) = 6.49、6.40时自旋浓度出现陡增，这时伴随由正交到四方的转化，证明了电子“巡游”观点的正确。用硫部分取代Y_1Ba_2Cu_3O_2g中的氧，当Y_1Ba_2Cu_3O_(2-x)Sx中x = 0.11时Tc = 92.6K，比Y_1Ba_2Cu_3O_(7-x)升高2K，但由于杂质相的存在，ΔTc加宽。其他样品多为半导体和绝缘体。硫取代0，当x = 0.04，0.06，0.11和1.20时磁化率服从Curic-Weiss定律，并且x = 0.87，1.2时分别在230K、240K出现反铁磁有序。其他样品由于Cu被还原为＋1价而变成抗磁性。x = 0.11 (Tc = 92.6K)，EPR谱为正交场中Cu~(2+)的信号。自旋浓度与温度无关。当所有Cu均为Cu~(1+)时，测问的是-s-的EPR信号，而Cu为混合价态(+1和+2时)测问是上述两种信号的叠加。

稀土络合物的合成及还原反应的研究

本工作用无水SmCl_3和YbCl_3每二摩尔比的叔丁基环戊二烯基钠在四氢呋喃中反应，合成了二（叔丁基环戊二烯基稀土氧化物(t-C_4H_9C_5H_4)_2Sm(DME)和(t-C_4H_9C_5H_4)_2YbCl(THF)，配合物得到元素分析及~1H-NMR的鉴定。通过(t-C_4H_9C_5H_4)_2SmCl(DME)和(t-C_4H_9C_5H_4)_2YbCl(THF)分别每金属钠在四氢呋喃中的还原反应，分离得到了相应的二价稀土络合物(t-C_4H_9C_5H_4)_2Sm(DME)和(t-C_4H_9C_5H_4)_2Yb(THF)_2。络合物经元素分析，~1H-NMR鉴定，并通过对络合物具有弯曲的夹心式结构，中心金属离子Yb~(2+)除每两个五元环络合外，还与两个THF的氧配位，形成稳定的8配位结构。本工作还研究了二价络合物(t-C_4H_9C_5H_4)_2Sm（DME）的还原性，并通过(t-C_4H_9C_5H_4)_2Sm（DME）每phc≡CH在甲苯中反应，证明了(t-C_4H_9C_5H_4)_2Sm（DME）具有很强的还原性，能每phC≡CH发生单电子转移反应，从此瓜体系中分离得到了一个新的三价Sm~(3+)络俣物[(t-C_4H_9C_5H_4)_2Sm(u-C≡Cph)]_2。经X光单晶结构的鉴定，证明此络合物具有双分子结构，中心金属离子Sm~(3+)除了与两个叔丁基环戊二烯基负离子络合外，还与两个桥炔配位，构成八配位的结构。二价Yb~(2+)络合物(t-C_4H_9C_5H_4)_2Yb(THF)_2能与三苯氧膦在甲苯溶液中反应，发生配体交换，使络合物中的一个THF分子被三苯氧膦取代，得到(t-C_4H_9C_5H_4)_2Yb(opph_3)(THF)。此外，我们还研究了(C_tMe)_2Nd(u-Cl)_2Na(DME)_2与甲基萘钠在溶剂DME中的反应，结果表明，在这一体系中，发生了甲基萘钠对溶剂分子CH_3OCH_2CH_2OCH_3中CH_3-O键的断裂反应断裂反应产生的CH_3ONa能与(C_5Me_5)_2Nd(u-Cl)_2Na(DME)_2发生交换反应得到(C_5Me_5)_2Nd(u-Cl)_2Na(DME)_2。络合物经元素分析，水解色质（GC-MC）谱及~1H-NMR鉴定，并通过X光单晶结构的测定证明具有弯曲夹心式结构。

铜（III）及相关化合物的合成和性质的研究，稀土复合氟化物电性、氧敏和氢敏性质

本论文包括两部分内容。第一部分为“Cu(III)及相关化合物的合成和性质的研究”；第二部分为“稀土复合氟化物的电性、氧敏和氢敏性质”。第一部分的主要内容有：1.制备了Na_4H[Cu(H_2TeO_6)_2]·17H_2O和Na_4K[Cu(HIO_6)_2]·12H_2O的Cu(III)单晶配合物。2.在比较相应的Cu(II)化合物的条件下，详细地研究了这二个Cu(III)配合物的电子光谱和Cu2p光电子能谱，由于价态升高，场强参数增大，Cu(III)化合物的d-d跃迁相对于Cu(II)化合物d-d跃迁，发生“蓝移”。3.成功地实现了用O_3和电化学方法对强碱溶液中Cu(II)配合物的氧化，获得了二个新的Cu(III)固态配合物Ba_4K[Cu(H_2TeO_6)_2] (OH)_4·6H_2O和Ba_3K[Cu(HIO_6)_2] (KOH)_(0.5)(OH)_2·8H_2O利用化学分析、磁学性质、电子光谱和Cu2p XPS，对这二个化合物进行了表征。4.对BaCuO_(2.5)的合成、电学性质、磁学性质、Cu(III) ESR和Cu2p XPS进行了研究。5.以Na_4K[Cu(HIO_6)_2]·12H_2O和BaCuO_(2.5)为参照物，用电子光谱和Cu2p XPS，确认了YBa_2Cu_3O_(7-5)中的高价态的铜。6.考察了以Cu（III）化合物作为Cu部分原料所合成的YBCO系超导材料的电学性质。第二部分的主要内容有：1.测试了元件“BiF_3(Bi)/Ce_(0.95)Ca_(0.05)F_(2.95)/Pt”的氧敏、氢敏等性能。从室温到130 ℃，元件的氧敏机理为“双电子反应”，电动势（EMF）与氧分压遵循Nernst关系式。室温时，元件对空气中100Pa或1000Pa氢气的响应时间仅为15秒或短于5秒；氢分压在16Pa～1000Pa范围内，EMF与氢分压的对数呈线性关系，斜率为-116mV/decade, 敏感机理表现为“混合电极电势”。元件具有良好的氢敏性能，并有一定的选择性。2.合成并测试了La_(1-x)Pb_xF_(3-x)(X = 0.00 ～ 0.15)的电导率，La_(0.95)Pb_(0.05)F_(2.95)的电导率最高，比LaF_3高约一个数量级。以La_(0.95)Pb_(0.05)F_(2.95)为固体电解质材料，Pd或Pt为敏感电极，BiF_3(Bi)或PbF_2(Pb)为参比电极，制成了四个元件。其中，“BiF_3(Bi)/La_(0.95)Pb_(0.05)F_(2.95)/Pt”具有最好的氧敏、氢敏性能。从室温到150 ℃，元件的EMF与1gPo_2附合Nernst关系式。150 ℃时，元件对氧气的响应时间仅为80秒。室温下，元件对空气中100Pa或1000Pa氢气的响应时间仅为75秒或15秒，元件的电动势EMF与氢分压的关系可表示为“E=E_o-96lgP_(H2)(mV)”。元件对CO有较差的敏感性能，而对空气中甲烷、乙烷或乙炔（≤1000Pa）不具敏感性能。3.合成并测试了Ln_(1-x)Pb_xF_(3-x)(Ln=Ce、Pr、Nd和Gd、Dy、Ho、Yb)的电性。前四个系列为离子导体材料，后三个系列可能为P型半导体。随着Ln原子序数增大，LnF_3导电性能变差；La~(3+)、Ce~(3+)、Pr~(3+)、Nd~(3+)与Pb~(2+)离子半径差异较小，LnF_3和PbF_2可以形成固溶体；而Gd~(3+)、Dy~(3+)、Ho~(3+)、Yb~(3+)与Pb~(2+)离子半径差异较大，LnF_3和PbF_2难以形成固溶体。

氟化物体系新型无机闪烁材料制备特性及若干基础问题研究

本文综述了无机闪烁材料研究的进展，着重了氟化物体系中几种新型无机闪烁材料的制备、性能及辐照损伤等特性。运用B－S法生长了BaF_2及BaF_2:Ce晶体，研究了其室温以上的TSL特性，发现BaF_2的TSL曲线是由381K和402K的双峰结构组成Ce的掺入使TSL强度降低，同时提高了其抗辐照性能。运用高温固相反应法合成了KMgF_3、KCaF_3、BaLiF_3微晶，用TSL和ESR研究了其辐照损伤及其恢复情况。纠正了文献中对KMgF_3热释峰归属的错误，发现在KMgF_3、KCaF_3中杂质Al~(3+)一方面引入新的缺陷而导致新的热释峰，另一方面抑制了F心的形成。在BaLiF_3中La~3、Yb~(3+)的掺入会抑制F心，同时使H心增强，观察到了大剂量（10~8Rad）辐照时BaLiF_3中FA心形成及其在加热和紫外光照射时向F心的转化。发现它们的X射线辐照损伤极易恢复，而γ射线辐照损伤则较难恢复。通过对ESR峰高与Eu掺杂浓度的研究，运用数学拟合法求得了Eu~(3+)掺入KMgF_3制备KMgF_3:Eu~(2+)的饱和掺杂浓度为0.29mol%。首次发现BaLiF_3:Eu~(2+)的PSL现象，并证明它是一种很有发展前途的新型X射线存贮材料。运用B－S法探索了KMgF_3、BaLiF_3、单晶生长工艺，用X射线四园衍射法发现La~(3+)、Tm~(3+)掺入KMgF_3时分另占据K~+、Mg~(2+)的格位，用SEM观察了浓H_2SO_4cf KMgF_3单晶的侵蚀形貌和BaLiF_3单晶生长中经常出现的包裹体。研究了LaF_3:Ce~(3+)的发光特性及其它三价稀土离子的共掺杂对Ce~(3+)发光特性的影响，发现其它三价稀土离子的共掺杂都会使Ce~(3+)的发光猝灭，并分别归结为能量传递和电荷转移。用B－S法生长了CeF_3单晶，但因原料纯度低，衰减常数和光子产额都比文献值要低，说明在闪烁晶体制备时，提高原料纯度是十分必要的。

环戊烷基环戊二烯基均配及其与环辛四烯基混配稀土配合物的合成和表征

本文合成表征了11种共16个新型的环戊烷基环戊二烯基稀土氯化物、环戊烷基环戊二烯基稀土甲基配合物、环戊烷基环戊二烯基与环辛四烯基烯土混配配合物和2，4-二甲基戊二烯基与环辛四烯基稀土混配配合物，并研究了基结构特征，同时还采用2，4-二甲基戊二烯基钾还原Yb~(3+)的方法，得到+2价镱的环戊二烯基和茚基的配合物，并测定了其晶体结构。本文共报道了14个配合物的晶体结构。

酸性磷（膦）酸酯萃取稀土、相关元素的机理及萃合物结构研究

本文研究了酸性磷（膦）酸酯对稀土及相关元素的萃取（包括协同萃取）机理，利用核磁共振（NMR）测试手段对HEH/EHP(III)、BTMPPA－Yb(III)的萃合物结构进行了~1H、~(13)C、~31P NMR谱的测定，获得了一些新的结构信息。

Persistent Photoconductivity in n-type GaN

The persistent photoconductivity（PPC） phenomena in n-type GaN Films grown by metalorganic chemical vapor deposition（MOCVD） have been studied. After using some testing and analysis methods, such as the double crystal X-ray diffraction（DCXRD）, the photolumineseence（PL） spectra, etc, it is found that the issue which influences PPC in n-type GaN is not relative to the dislocations and yellow band （YB）, and is caused by the doping level of Si most likely.

Photovoltage and luminescence study of stacked InAs/GaAs self-organized quantum dots

The ground and excited state excitonic transitions of stacked InAs self-organized quantum dots (QDs) in a laser diode structure are studied. The interband absorption transitions of QDs are investigated by non-destructive PV spectra, indicating that the strongest absorption is related to the excited states with a high density and coincides with the photon energy of lasing emission. The temperature and excitation (electric injection) intensity dependences of photoluminescence and electroluminescence indicate the influence of state filling effect on the luminescence of threefold stacked QDs. The results indicate that different coupling channels exist between electronic states in both vertical and lateral directions.

Effects of residual C and O impurities on photoluminescence in undoped GaN epilayers

Photoluminescence (PL) was investigated in undoped GaN from 4.8 K to room temperature. The 4.8 K spectra exhibited recombinations of free exciton, donor-acceptor pair (DAP), blue and yellow bands (Ybs). The blue band (BB) was also identified to be a DAP recombination. The YB was assigned to a recombination from deep levels. The energy-dispersive X-ray spectroscopy show that C and O are the main residual impurities in undoped GaN and that C concentration is lower in the epilayers with the stronger BB. The electronic structures of native defects, C and O impurities, and their complexes were calculated using ab initio local-density-functional (LDF) methods with linear muffin-tin-orbital and 72-atomic supercell. The theoretical analyses suggest that the electron transitions from O-N states to C-N and to V-Ga states are responsible for DAP and the BB, respectively, and the electron transitions between the inner levels of the C-N-O-N complex may be responsible for the YB in our samples. (C) 2002 Elsevier Science B.V. All rights reserved.

Photocurrent derivative spectra of ZnCdSe-ZnSe double multi-quantum wells

Photocurrent (PC) spectra of ZnCdSe-ZnSe double multi-quantum wells are measured at different temperature. Its corresponding photocurrent derivative (PCD) spectra are obtained by computing, and the PCD spectra have greatly enhanced the sensitivity of the relative weak PC signals. The polarization dependence of the PC spectra shows that the transitions observed in the PC spectra are heavy-hole related, and the transition energy coincide well with the results obtained by envelope function approximation including strain. The temperature dependence of the photocurrent curves indicates that the thermal activation is the dominant transport mechanism of the carriers in our samples. The concept of saturation temperature region is introduced to explain why the PC spectra have different temperature dependence in the samples with different structure parameters. It is found to be very useful in designing photovoltaic devices.

Experimental Study on the Subthreshold Swing of Silicon Nanowire Transistors

SOI based wrap-gate silicon nanowire FETs are fabricated through electron beam lithography and wet etching. Dry thermal oxidation is used to further reduce the patterned fins cross section and transfer them into nanowires. Silicon nanowire FETs with different nanowire widths varying from 60 nm to 200 nm are fabricated and the number of the nanowires contained in a channel is also varied. The on-current (I-ON) and off-current (I-OFF) of the fabricated silicon nanowire FET are 0.59 mu A and 0.19 nA respectively. The subthreshold swing (SS) and the drain induced barrier lowering are 580 mV/dec and 149 mVN respectively due to the 30 nm thick gate oxide and 1015 cm(-3) lightly doped silicon nanowire channel. The nanowire width dependence of SS is shown and attributed to the fact that the side-gate parts of a wrap gate play a more effectual role as the nanowires in a channel get narrower. It seems the nanowire number in a channel has no effect on SS because the side-gate parts fill in the space between two adjacent nanowires.

Electrical bistability and negative differential resistance in diodes based on silver nanoparticle-poly(N-vinylcarbazole) composites

An electrically bistable device has been fabricated using nanocomposite films consisting of silver nanoparticles and a semiconducting polymer by a simple spin-coating method. The current-voltage characteristics of the as-fabricated devices exhibit an obvious electrical bistability and negative differential resistance effect. The current ratio between the high-conducting state and low-conducting state can reach more than 103 at room temperature. The electrical bistability of the device is attributed to the electric-filed-induced charge transfer between the silver nanoparticles and the polymer, and the negative differential resistance behavior is related to the charge trapping in the silver nanoparticles. The results open up a simple approach to fabricate high quality electrically bistable devices by doping metal nanoparticles into polymer.