新型石墨烯基LED器件：从生长机理到器件特性

III族氮化物因具有禁带宽度大、击穿电压高、电子饱和漂移速度大、稳定性高等优异特性而广泛应用在发光二极管(LED)、激光器以及高频器件中。目前III族氮化物薄膜通常是异质外延生长在蓝宝石衬底表面,但是由于蓝宝石与III族氮化物之间存在较大的晶格失配与热失配,使得外延生长的III族氮化物内部存在较大的应力与较高的位错密度,严重影响了器件性能;与此同时,蓝宝石衬底热导率差,限制了其在大功率器件方面的应用。近年来研究发现,石墨烯作为外延生长缓冲层,能够有效解决蓝宝石衬底与外延III族氮化物薄膜之间由于晶格失配和热失配导致的高应力与高位错密度等问题,进而获得了高品质薄膜,并提升了器件的性能。本文综述了石墨烯/蓝宝石衬底上III族氮化物生长与LED器件构筑的研究现状,着重介绍了本课题组提出的一种新型外延衬底—石墨烯/蓝宝石衬底的特点,阐明了III族氮化物在该新型衬底上的生长机理,总结了其对III族氮化物质量提升的作用,并对其发展前景进行了展望。     

Cu_3(PO_4)_2/TiO_2复合材料的制备及可见光催化性能研究

利用化学沉淀的方法,制备了一系列不同比例的Cu_3(PO_4)_2/TiO_2复合材料.采用紫外-可见漫反射谱(UV-Vis DRS)、X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)等手段,对Cu_3(PO_4)_2/TiO_2系列光催化剂进行了表征与分析.通过丙烯的光催化降解实验考察样品的可见光催化活性.结果表明,相比于纯Ti O2,Cu_3(PO_4)_2/TiO_2复合材料具有明显的可见光催化活性,当Cu3(PO4)2与Ti O2的质量比为2.5∶10时光催化活性最高,对丙烯的降解率达到46%.     

离子交换法制备LiCexEu1-xTiO4及其结构与电化学性能

选用六水合硝酸铈作为Ce源,利用溶胶凝胶结合离子交换法,成功合成了LiCe_xEu_(1-x)TiO_4,并利用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、循环伏安(CV)和充放电循环测试等方法对LiCe_x Eu_(1-x)TiO_4的结构、形貌和电化学性能方面做了系统地表征。研究结果表明,与未掺杂的LiEuTiO_4相比,在晶格中引入Ce~(3+)能显著改善材料的动力学性能,这可能与Ce-Eu-Ti协同效应有关。这种协同效应表现为晶格参数的复杂变化导致Ti和Ce处于混合价态。其中LiEu_(0.995)Ce_(0.005)TiO_4的电化学性能最好。     

Mn负载量对nMnO_x/TiO_2催化剂NH_3-SCR催化性能的影响

MnO_x/TiO_2催化剂由于具有优异的低温脱硝性能,已成为SCR催化剂的研究热点之一.我们通过浸渍法制备了一系列不同Mn负载量的nMnO_x/TiO_2(n=2.5%, 5%, 10%, 15%)(质量分数)催化剂,考察Mn负载量对催化剂脱硝性能的影响.利用N_2物理吸附, X-Ray Diffraction (XRD), Scanning Electron Microscope(SEM),Temperature Programmed Reduction with H_2(H_2-TPR),Temperature Programmed Desorption with NH_3(NH_3-TPD)和X-Ray Photoelectron Spectroscopy (XPS)对其结构进行表征.结果表明,催化剂的脱硝性能随着Mn负载量(2.5%～15%)(质量分数)的变化呈现"火山型"曲线,当Mn负载量为10%(质量分数)时,催化剂的脱硝性能最佳. H_2-TPR和XPS结果表明nMnO_x/TiO_2催化剂上表面氧比例和表面Mn~(4+)浓度均随着Mn负载量的增大,先增大后减小,具体顺序为10MnO_x/TiO_(2 ) 15MnO_x/TiO_(2 )5MnO_x/TiO_(2 ) 2.5MnO_x/TiO_2,与脱硝性能顺序完全一致.进一步关联表面氧的比例与T_(50)发现,催化剂的表面氧的比例与T_(50)呈线性关系,即表面氧比例越高, T_(50)越小,脱硝活性越高. NH_3-TPD结果表明,弱酸酸量的增加有助于低温脱硝活性的提高.这些结果揭示了Mn负载量影响脱硝性能的作用规律,为今后开发高效的锰基低温脱硝催化剂提供了技术支撑.     

PbTe(111)薄膜的分子束外延生长及其表面结构特性

采用分子束外延(MBE)方法在Ba F_2(111)衬底上直接外延生长了Pb Te薄膜。反射高能电子衍射(RHEED)实时监控的衍射图样揭示了Pb Te在Ba F_2(111)表面由三维生长向二维生长的变化过程。转动对称性的研究结合第一性原理密度泛函理论(DFT)的计算揭示了在富Pb及衬底温度(Tsub)为350°C的生长条件下,得到的Pb Te(111)薄膜具有稳定的(2×1)重构表面。Pb Te(111)-(2×1)表面覆盖Te膜后,通过300°C的退火处理,重构表面可完全复原,这为大气环境下Pb Te薄膜表面结构的保护提供了有效的方法。     

脉冲激光沉积制备La0.62Ca0.29K0.09MnO3外延膜及其磁热性能

采用脉冲激光沉积法在单晶SrTiO3(STO)基底上制备了La0.62Ca0.29K0.09MnO3(LCKMO)薄膜,通过调控基底温度获得了平整致密的膜层.利用二维面探X射线衍射仪和高分辨透射电子显微镜对薄膜结构进行了表征.结果表明,薄膜呈高质量取向外延生长,对应关系为{001}LCKMO||{001}STO.对薄膜的磁热性能研究表明,5 T下最大磁熵变为3.45 J/(kg·K),相对制冷效率为379.5 J/kg,磁熵半峰宽为110 K.     

具有高活性(001)晶面的Cr-TiO_2微球的制备及可见光催化性能

采用一步水热法制备了具有高裸露率(001)晶面的锐钛矿相Cr掺杂TiO2(Cr-TiO2)微球,利用场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)和X射线光电子能谱仪(XPS)等对样品进行了表征.结果表明,掺杂的Cr元素以Cr3+离子和CrO3团簇2种形式存在,Cr3+离子进入TiO2晶格,形成Cr3+→Ti4+电荷转移跃迁,Cr-TiO2在可见光区具有强烈吸收.少量的Cr掺杂有利于形成平整的高活性(001)晶面.以可见光降解酸性红染料作为探针反应研究了Cr-TiO2的催化活性.结果表明,具有(001)晶面的Cr-TiO2的催化效率明显优于普通的Cr-TiO2.     

脉冲激光沉积制备SrSn1-xCoxO3外延薄膜的微结构表征及能带调控

钙钛矿结构SrSnO₃因其独特的介电和半导体性质而备受关注,通过掺杂可显著调控其电学、磁学性能,拓宽其应用范围。本研究在单晶SrTiO₃(001)衬底上通过脉冲激光方法外延生长了SrSn_1-xCo_xO₃ (x = 0, 0.16, 0.33, 0.5) (SSCO)薄膜,探究了Co含量对薄膜结晶性、微观结构、光学性能以及介电性能的影响。结果表明, SrSn_1-xCo_xO₃薄膜可在SrTiO₃(001)衬底上外延生长, Co掺杂不会导致薄膜结晶质量的劣化。薄膜表面形貌平整、致密,膜厚200 nm,表面粗糙度为0.44 nm。随薄膜中Co掺杂量增加,薄膜透过率从90%降至25%,光学带隙从4.24 eV降至2.44 eV。介电性能测试表明,掺杂薄膜在10⁶Hz时介电常数为70.1,比无掺杂SrSnO₃薄膜提高57%。室温时SSCO薄膜表面电阻率为172 MΩ,在1000℃范围内薄膜结构稳定。     

薄膜CdSe及CdSexTe1-x电极的光电子能谱研究

用X射线光电子能谱(XPS)研究了不同含氧气氛中烧结的薄膜CdSe及Cdse_xTe_1-x电极表面,以及薄膜与Ti底基之间的界面。研究中发现,二种薄膜电极的表面形成了CdO,SeO₂及TeO₂氧化物,与薄膜接触的Ti底基表面上形成了TiO₂。用俄歇电子能谱(AES)对在电极表面及Ti表面所生成的氧化层分别进行了深度分析。结果表明,各种氧化物形成的程度有很大的不同,氧化层厚度也存在差异。对影响薄膜电极的光电性能的因素进行了讨论。     

钛酸钡薄膜生长初期粒子形态及其反应机理的模拟研究

在激光分子束外延生长钛酸钡(BaTiO₃,BTO)薄膜过程中,初期多粒子碰撞反应过程是薄膜形成的关键过程。本文采用密度泛函理论中的广义梯度近似(DFT/GGA),在PW91/DNP水平上研究了Ba、Ti、O、O₂、BaO、TiO₂以及BTO分子在真空中的优先反应形成与演化过程,计算研究了它们碰撞反应及其中间体的形成机理,获得了相应中间体的几何结构、过渡态及反应活化能,并运用前线轨道理论分析了BTO分子形成机理。对比BTO、SrTiO相似文献   

Dye-sensitized solar cells made from BaTiO3-coated TiO2 nanoporous electrodes

We reported on the preparation of a thin BaTiO₃-coated layer (2.27 nm) on the surface of TiO₂ and its further application in the dye-sensitized solar cells (DSCs). The as-prepared BaTiO₃–TiO₂ films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The performances of the DSCs with and without BaTiO₃ coating were analyzed by cyclic voltammograms (CVs), electrochemical impedance spectroscopy (EIS), and current–voltage measurements. It was found that the BaTiO₃–TiO₂ films with about 12 μm thickness increased the dye adsorption, resulting in increased J_sc. In the meantime, the BaTiO₃ modification on the TiO₂ surface is beneficial to the formation of an energy barrier against the electron transfer from TiO₂ to I₃⁻, providing the increase of V_oc due to the increased electron density in the TiO₂ that is caused by the increased electron lifetime.     

Oxidation of Anatase TiO2(001) (1×4) Surface

Anatase TiO₂(001) surface arouses lots of research interests since it is believed to be the most reactive surface. However, recent STM measurements showed that except the defect sites, anatase TiO₂(001) (1×4) reconstructed surface is inert to H₂O adsorption. It was indicated that oxidation could be the reason which induces the inert surface reactivity. Therefore, it is strongly motivated to understand the oxidation structures as well as the oxidation process on this surface. In this work, based on first principles calculations, we investigated the oxidized structures and processes of TiO₂ anatase (001) surface with (1×4) reconstruction. We have discovered two kinds of oxidized structures through the molecular adsorption and dissociated adsorption with different oxidation ratio. To understand the oxidation process, we studied the reaction barrier of oxidation process. We conclude the stability of different oxidized structures with different oxidation ratio by comparing the free energy of the system as a function of oxygen chemical potential. Based on that, a first-principles-based phase diagram of the low-energy oxidized surface structures is provided. The effects of the lattice stress are also studied. Results show that the oxidized structure and oxidation ratio strongly depend on the temperature and pressure. The lattice stress also plays an important role.     

阴离子对TiO2晶形的影响及光催化性能研究

以SO₄^2-、F^-、Cl^-和PO₄^3-作为阴离子来研究其对水热合成TiO₂(分别记为TiO₂-S、TiO₂-F、TiO₂-Cl和TiO₂-P)晶体的影响,并考察了其光催化性能.SEM显示TiO₂-S、TiO₂-F、TiO₂-Cl和TiO₂-P分别呈粒子、十面体、刺球和不规则块状.XRD图谱表明TiO₂-S和TiO₂-F为锐钛矿晶型,TiO₂-Cl为金红石晶型,而TiO₂-P为锐钛矿、金红石和板钛矿混合晶型,这一结论也被紫外-可见漫反射实验所证实.XPS能谱表明这4种TiO₂纳米材料都受到了各自阴离子掺杂的影响,光催化试验显示:它们的光催化活性顺序为: TiO₂-F>TiO₂-S>TiO₂-Cl>TiO₂-P,这表明锐钛矿的光催化活性要大于金红石和板钛矿,且具有{001}面,掺杂了F的锐钛矿光催化活性更强.     

锌掺杂对SrTiO_3光催化性能的影响

制备了锌掺杂的SrTiO3光催化剂,测试了掺杂样品在400 W高压汞灯照射下,分解纯水制氢的活性。考察了锌的掺杂量及样品的焙烧温度对其光催化活性的影响,并对掺锌与未掺杂样品进行了XRD、UV-vis、XPS及SEM表征分析。结果表明,Zn掺入可显著提高SrTiO3的光催化活性,适宜的锌掺杂摩尔分数为1%左右,相应的掺杂量下,适宜的焙烧温度为950℃左右,上述条件制得掺锌SrTiO3的产氢速率较未掺杂样品提高了120%左右。表征结果显示,掺摩尔分数1%的锌未改变SrTiO3的晶体结构及结晶完整性,但样品表面发生了锌的富集,而且在一定的掺杂范围内,锌掺杂使SrTiO3催化剂的粒度有所增大。推测掺入的Zn与存在于SrTiO3表面的富钛相反应生成Zn2TiO4,使SrTiO3表面的缺陷浓度降低,光催化活性提高。     

部分还原二氧化钛的NMR和EPR研究

Partially reduced TiO₂ nanomaterials have attracted significant interest because of their visible-light activity for catalysis and photodegradation. Herein, we prepared a partially reduced anatase TiO₂ (Re-A-TiO₂) nanoparticle material using a fast combustion method, demonstrating good activity toward decomposing methyl orange under visible light irradiation. The surface structure of the prepared material, after being surface-selectively ¹⁷O-labeled with H₂¹⁷O (¹⁷O-enriched water), was studied via ¹⁷O and ¹H solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, and the obtained results were compared to those of non-reduced anatase TiO₂ (A-TiO₂). The EPR results showed that the concentrations of paramagnetic species (i.e., oxygen vacancies (OV) and Ti³⁺) in Re-A-TiO₂ were much higher than that in A-TiO₂, while the former was associated with a higher OV/Ti³⁺ ratio. The intensities of the EPR signals were significantly affected by the adsorbed water, and this phenomenon was explored in combination with ¹H NMR spectroscopy. The ¹H species on Re-A-TiO₂ appeared at larger chemical shifts, denoting the increased acidity of the sample, and these ¹H species on Re-A-TiO₂ were more difficult to remove than those on A-TiO₂. On the other hand, different features were observed for the signals arising from the two-coordinated oxygen atoms (μ₂-O) in ¹⁷O NMR, suggesting a typical anatase TiO₂(101) surface on A-TiO₂, but a more complex surface environment for Re-A-TiO₂. Furthermore, a larger amount of hydroxyl groups (OH) were observed on Re-A-TiO₂ compared to that on A-TiO₂, indicating a larger proportion of exposed (001) facets on Re-A-TiO₂. However, the μ₂-O signals broadened and became similar when the drying temperature was increased to 100 ℃, indicating a non-faceted anatase TiO₂ surface in such conditions. Based on the EPR and NMR results, a significant fraction of the OH species is believed to be formed from the reaction of the paramagnetic centers and adsorbed water molecules. The ¹H→¹⁷O cross polarization (CP) MAS and two-dimensional heteronuclear correlation (2D HETCOR) NMR spectra were used to verify the spatial proximity of the hydrogen and oxygen species, confirming the spectral assignments of a strongly adsorbed water and one type of surface OH species. In particular, the ¹H NMR signals at approximately 11 ppm were ascribed to the hydrogen species in the intramolecular hydrogen bond. In summary, this study investigated the paramagnetic species and surface structure of anatase TiO₂ materials by combining EPR along with ¹H and ¹⁷O solid-state NMR spectroscopy. The differences in the surface structures of Re-A-TiO₂ and A-TiO₂ should be closely related to their different properties toward the photodegradation of methyl orange.     

可见光下高催化活性不同结构Sr/TiO2催化剂的制备和表征

采用分步沉积法制备不同Sr/Ti 摩尔比例的Sr/TiO₂催化剂, 以X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、傅里叶变换红外(FT-IR) 光谱、紫外-可见漫反射光谱(UV-Vis RDS)等手段对样品进行了表征, 以可见光催化降解亚甲基蓝为模型反应考察样品光催化活性. 结果表明, 催化剂的活性和结构随Sr/Ti 摩尔比(n(Sr)/n(Ti))的变化而变化, 当n(Sr)/n(Ti)≤3/2 时, 催化剂呈由TiO₂和SrTiO₃组成的球状结构; 而当n(Sr)/n(Ti)在3/2 与4/1 之间时, 催化剂呈片状结构, 且随着n(Sr)/n(Ti)增大, 催化剂组成由SrTiO₃ 和Sr₂₄ 变为Sr₂₄和Sr(OH)₂·H₂O; 当n(Sr)/n(Ti)=9/1 时, 催化剂呈以Sr(OH)₂·H₂O为主的针状结构. 其中, n(Sr)/n(Ti)=4/1的样品表现出最高的光催化活性, 一级反应速率为SrTiO₃钙钛矿催化剂的5.0倍, 商用P25的86.7倍.     

卤素离子对TiO2薄膜光致亲水性的影响

将卤化钾盐KX(X＝I、Br、Cl、F)分别引入至TiO₂溶胶中, 利用提拉法在载玻片上制得含有卤素离子的TiO₂-X薄膜样片, 通过测试样片紫外光照下水滴接触角的变化, 考察了不同浓度的KI以及不同卤素离子对TiO₂薄膜光致亲水性能的影响, 并通过测试光照后的亲水薄膜样片暗处放置不同时间后接触角的变化, 比较了含TiO₂-I和TiO₂-F薄膜样片亲水性能的持久性. 结果表明, 适量的KI有助于提高TiO2薄膜的光致亲水性, 当TiO₂溶胶中KI浓度为1.0×10^-5 mol•L^-1时, 其所制得TiO₂薄膜的光致亲水性最好, 继续增大KI浓度时, 薄膜的光致亲水性逐步下降, 当KI浓度达1.0×10^-2 mol•L^-1时, 其光致亲水性较纯TiO₂薄膜差；同时, 适量的KBr、KCl加入也有助于提高TiO₂薄膜的光致亲水性, 且随KI＞KBr＞KCl的顺序逐渐减弱, 但KF的加入降低了薄膜的光致亲水性；另外, 卤素离子的加入还有助于提高TiO₂薄膜亲水性能的持久性, 且KF＞KI. 分析认为, 卤素离子对TiO₂薄膜光致亲水性的影响与其给电子或捕获光致电子作用有关, 并提出了其作用模型, 而卤素离子与亲水基团(羟基)的氢键作用是使KX-TiO₂薄膜能够延长亲水性时间的原因.     

富含本征缺陷的新型锐钛矿TiO2纳米管的制备

为阻止纳米管钛酸在转变为新型锐钛矿TiO₂时管状结构的破坏,先在纳米管钛酸的内、外表面化学吸附一层物质,用以保护纳米管钛酸在脱水转变为新型锐钛矿TiO₂的过程中,管状结构不断裂、不塌陷,然后再除去表面的吸附物质,即可制得纯净的新型TiO₂纳米管。新型TiO₂纳米管有望应用于可见光"全"分解水制H₂、药物缓释剂以及纳米反应器等研究。     

过渡金属离子的掺杂对TiO2光催化活性的影响

考察了过渡金属离子对TiO₂ 光催化性能的影响,结果发现:第二过渡系列金属离子对TiO₂ 膜的修饰作用比第一过渡系列金属离子的修饰作用更加明显;第二、六副族的金属离子对TiO₂ 膜的修饰效果较好.通过X射线衍射(XRD)、电镜分析 (SEM)、光电能谱分析 (XPS)及差热分析 (DTA)对催化剂表面进行了表征,结果表明:TiO₂ 的晶型为锐钛矿型,粒子半径为 32.58nm.     

Tunable Synthesis of Core-shell α-Fe2O3/TiO2 Composite Nanoparticles and Their Visible-light Photocatalytic Activity

Uniform α-Fe₂O₃/amorphous TiO₂ core-shell nanocomposites were prepared via a hydrolysis method and α-Fe₂O₃/anatase TiO₂ core-shell nanocomposites were obtained via a post-calcination process. The structure and morphology of the products were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and scanning electron microscopy. Amorphous TiO₂ nanoparticles with diameters of ten to several tens nanometer were formed on the surface of α-Fe₂O₃ nanoparticles and the coverage density of the secondary TiO₂ nanoparticles in the composite can be controlled by varying the concentration of Ti(BuO)₄ in the ethanol solution. The visible-light photocatalytic properties of different products towards Rhodamine B(RhB) were investigated. The results show that the α-Fe₂O₃/amorphous TiO₂ exhibits a good photocatalytic property owing to the extension of the light response range to visible light and the efficient separation of photogenerated electrons and holes between α-Fe₂O₃ and amorphous TiO₂.