【作者】 陈义强；

【导师】 郑学军；

【作者基本信息】 湘潭大学 ， 材料科学与工程， 2011， 博士

【摘要】 随着元器件向小型化、智能化、高集成、高密度存储和超快传输方向发展,纳米材料独特、优异的物理化学性能,在微纳元器件中将有潜在、广泛的应用。因此,纳米材料与纳米技术备受国内外科研工作者的广泛关注。人们已经制备出了多种复杂纳米结构,如纳米纤维、纳米带、纳米线、纳米棒和纳米环等,并发现它们具有各种新奇特性,如量子尺寸效应、表面效应和介电限域效应等。本文以一维压电功能纳米材料为研究对象,首先对一维压电功能纳米材料的研究进展和应用背景进行了评述,主要讨论了:（1）功能纳米材料的各种制备方法。（2）功能纳米材料的光、力、电等物理耦合特性。然后按照从材料制备及其性能表征到器件应用的研究思路,通过系统的实验方法研究了一维压电Ⅱ-Ⅵ族半导体及NBT基功能纳米材料的光力电耦合性能,如一维压电功能纳米材料的制备工艺、力学性能、电学性能、光硬化（光塑性）效应、光伸缩效应和压电效应。主要内容和结果有如下五部分:1.采用热蒸发方法制备了ZnO和ZnS纳米带。运用纳米压痕仪、原子力显微镜（AFM）和光照系统研究了光照下ZnO和ZnS纳米带的光硬化（光塑性）效应。此外,还进一步探讨了ZnO和ZnS纳米带光硬化（光塑性）效应产生的物理机制。研究表明:（a）采用热蒸发法能成功制得截面为矩形状的ZnO和ZnS纳米带,其长度约几十到几百微米,具有六角纤锌矿晶体结构。（b） ZnO纳米带在紫外光和白光照射下光硬化效应最高分别可达45 %和348 %,而对于ZnS纳米带而言,在紫外光和白光照射下光硬化效应最高分别可达42 %和183 %,并发现它们有光塑性效应。（c）半导体纳米材料的高表体比效应、光电导效应以及电子应变效应是导致ZnO和ZnS纳米带产生光硬化效应的原因,而在光照下产生的大量电子空穴对使得位错在移动很短的距离内就能收集到足够多的电子,从而使佩尔斯势增加,进而导致纳米带发生光塑性效应。2.运用纳米压痕仪和光照系统,利用纳米压痕仪原位压入保载实验,通过在延长的保载时间阶段对纳米材料施加光场作用,研究了在紫外光照下ZnO和ZnS纳米带的光致伸缩性能。为了佐证光致伸缩实验,运用AFM和光照系统,通过AFM扫描成像方式,研究了ZnO纳米带在紫外光照下的光致伸缩性能。此外,还进一步探讨了ZnO和ZnS纳米带的光致伸缩效应产生的物理机制。研究表明:（a）当紫外光交替开与关的时候,ZnO和ZnS纳米带会产生两类变形,即不可逆压缩变形和可逆膨胀变形,其变形量最高可达10 nm。（b）运用位错滑移理论解释了ZnO和ZnS纳米带的不可逆压缩变形,运用光电导效应、光伏效应和逆压电效应的叠加效应对ZnO和ZnS纳米带的可逆光致伸缩特性进行了解释;（c）可逆光致伸缩实质上是一种光能转换成机械能的特性,笔者基于该特性提出了光弹簧的概念,光弹簧独特的可逆光致伸缩特性使其在光致传感器和执行器的研制和改良等方面有着潜在的应用前景。3.采用静电纺丝工艺成功制备出了掺杂浓度不同的V-ZnO纳米纤维。笔者运用扫描电镜（SEM）、X射线衍射仪（XRD）和透射电镜（TEM）对V-ZnO纳米纤维的表面形貌、晶体结构进行了表征。采用纳米压痕仪测试了V-ZnO纳米纤维的纳米力学性能。利用压电测试系统研究了V-ZnO纳米纤维的压电性能。研究表明:（a）经700℃煅烧后,V-ZnO纳米纤维形态结构依然保持较好,纤维直径约为50-200 nm,具有六角纤锌矿晶体结构。（b） V-ZnO纳米纤维的压电系数大,压电性能较好,其压电性能的大小与其掺钒量的多少有关。当掺钒量范围为0.015-0.025时,掺钒量越高,其压电性能越大;而当掺钒量范围为0.025-0.03时,其压电性能随掺钒量的增多而下降。这说明掺钒量为0.025时,V-ZnO纳米纤维的压电性能最好,其有效压电系数最高可达121 pm/V。（c） V-ZnO纳米纤维约简杨氏模量和硬度的统计平均值分别为58.7 GPa和3.3 GPa,与体材料相比较具有明显的尺寸效应,其约简杨氏模量值和硬度值分别下降了47.2 %和34.0 %,这与纳米材料的高表体比特性有关。此外,V-ZnO纳米纤维的约简杨氏模量和硬度的大小都与压痕深浅有关,这是由应变梯度效应所导致的。4.采用静电纺丝法成功制备出了(Na_0.5Bi_0.5)_0.94TiO₃-Ba_0.06TiO₃ （NBT-BT）和(Na_0.82K_0.18)_0.5Bi_0.5TiO₃ （NKBT）纳米纤维。运用SEM、XRD、TEM和能谱仪对制备出的NKBT和NBT-BT纳米纤维的表面形貌、晶体结构和元素组成进行了表征。采用压电测试系统对它们的压电性能进行了表征,获得了纳米纤维的有效压电系数。利用纳米压痕仪测试了它们的力学性能,获得了与纳米纤维的深度相关的杨氏模量和硬度特性。研究表明:（a）经温度为700℃烧结后,NBT-BT和NKBT纳米纤维形态结构依然保持较好,纤维直径约为50-600 nm,其晶体结构为钙钛矿相结构。（b） NBT-BT和NKBT纳米纤维的有效压电系数最高可达102和96 pm/V。NBT-BT和NKBT纳米纤维压电性能较好,优于多种无铅型压电材料。纳米纤维其优异的压电性能归因于:准同型相界区域附近外加电场容易使电畴发生倾斜和自发极化方向数目增加。（c）与其薄膜材料的杨氏模量（158.2 GPa）和硬度（7.3 GPa）相比,NKBT纳米纤维的杨氏模量（107.6 GPa）和硬度（4.9 GPa）分别下降了31.9 %和32.8 %,出现明显的尺寸效应。NBT-BT纳米纤维相关力学性能与之类似。综上可知,NBT-BT和NKBT纳米纤维是一种压电性能和力学性能优异的一维无铅型压电材料,在微机电系统中有着远大的应用前景。5.在SiO₂/Si基底上,采用光刻、溅射等微电子技术及工艺成功制作出了叉指状的Pt电极。将ZnS纳米带均匀分散在叉指电极表面,分别组装出了基于单根ZnS纳米带的光电导开关和基于ZnS纳米带薄膜的光电导开关,并使用半导体测试系统获得了这两种光电导开关的伏安特性和功能特性。研究表明:（a）叉指电极厚度为100 nm,电极宽度为55μm,电极间距为45μm。组装在叉指电极上的基于ZnS纳米带的两种光电导开关在无光照条件下绝缘性能较好,在紫外光照射下具有较大的光响应和光灵敏度。（b）把这两种开关接入测试电路后,当紫外光打开/关闭交替变换时,测试电路会在光电导开关的控制下实现“1”/“0”交替变换,故此,基于ZnS纳米带的光电导开关能较好地实现其开关功能。（c）运用氧吸附/解吸附理论、表面效应和光电导效应能对基于ZnS纳米带光电导开关特性的机理进行解释。该研究表明基于半导体纳米材料的光电导开关将有着很好的应用前景。更多还原

【Abstract】 With the development of device micromation, intelligence, high integration, high storage and high speed, there are potential applications in micro- and nano-devices for nanostructures due to their novel characteristics, therefore nanostructures and nanotechnology have attracted considerable attention. Many complex nanostructures, such as nanofibers, nanobelts （NBs）, nanowires, nanorods and nanorings, have been reported, and a lot of novel characteristics also have been explored, such as size effect, surface effect and dielectric confinement effect and so on. One-dimensional piezoelectric functional nanomaterials are investigated in this PhD dissertation. The advances of piezoelectric functional nanomaterials were reviewed in the introduction, and the review focuses on: （1） synthesis methods of functional nanomaterials; （2） optical/mechanical/electrical coupled properties of functional nanomaterials. Based on these reviews, according to the idea of fabrication-characterization-application optical/mechanical/electrical coupled properties of one-dimensional piezoelectricⅡ-Ⅵ/NBT-based functional nanomaterials are investigated systematically by the experimental methods, such as the fabrication, mechanics, electrics, photostiffening （photoplastic） effect, photoinduced deformation and piezoelectric properties. The main results are summarized as follows:1. ZnO and ZnS wool like NBs were synthesized by thermal evaporation at high temperature without the presence of the catalyst. The photoinduced stiffening （PIS） and photoplastic effect （PPE） of ZnO and ZnS individual NBs were observed by using a nanoindenter, atomic force microscope （AFM） in conjunction with an incident ultraviolet （UV） light source system. Meanwhile, the mechanisms of PIS and PPE were also explored. The results show: （a） the NBs with square cross section are of several tens to several hundreds of micrometers in length, and they are of the hexagonal wurtzite structure; （b） under UV illumination and visible light, the elastic moduli of ZnO individual NBs are up to 45 % and 348 % larger than that in darkness, while for ZnS individual NB they are up to 42 % and 183 % larger than that in darkness. For ZnO and ZnS individual NBs, the PPE were observed under UV illumination and visible light; （c） the high surface-to-volume ratio, photoconductive and electronic strain lead to the PIS, while the dislocation can collect more electrons to increase the Peierls barrier under illumination. Then, it leads the PPE of the ZnO and ZnS individual NBs under illumination.2. Photostrictive deformations of ZnO and ZnS individual NBs were investigated by using a nanoindenter in conjunction with an incident UV light source system, and under the in-situ nanoindentation a modulated UV laser was introduced into the load-holding segment extended. In order to confirm the photostrictive experiment, AFM in conjunction with an incident UV light source system were used to detect the photostrictive deformations of ZnO individual NBs under scanning mode. The mechanisms of photostrictive deformation were also discussed. The results show: （a） when the UV laser was periodically turned“on”and“off”, the irreversible contraction and the reversible dilatation were observed for both ZnO and ZnS individual NBs, and they are up to 10 nm; （b） the irreversible contraction was interpreted by dislocation theory, while the reversible dilatation was explained by the combination mechanisms of photoconductive effect, photovoltaic effect and converse piezoelectric effect; （c） the reversible dilatation is corresponding to the direct conversion of photonic to mechanical motion, and a photospring was designed. There may be potentially applied into photostrictive sensors and actuators.3. V-ZnO nanofibers with different vanadium-doped concentration were synthesized by sol-gel process and electrospinning. The morphology, crystallized phase and crystal structure were investigated by scanning electron microscopy （SEM）, X-ray diffractometer （XRD） and high resolution transmission electron microscopy （TEM）, respectively. The reduced modulus and hardness of V-ZnO piezoelectric nanofibers were investigated by nanoindenter. The butterfly-shaped piezoelectric response was measured by scanning force microscopy （SPM）. The results show: （a） the diameters of V-ZnO nanofibers with hexagonal wurtzite phase are in the range of 50 to 200 nm, while the lengths are several hundreds of micrometers; （b） the average effective piezoelectric coefficient ( d₃₃^*) value increases with vanadium concentration in the range of 0.015 to 0.025, while decreases in the range of 0.025 to 0.03 due to structural deterioration by over-doping. The large d₃₃^* of 121 pm/V was obtained, and the high piezoelectric property may be attributed to the switchable spontaneous polarization induced by V dopants and the easier rotation of V-O bonds under electric field; （c） the statistical average values of reduced modulus and hardness are 58.7 GPa and 3.3 GPa for the nanofibers, and they decrease by 47.2 % and 34.0 % in comparison with those of bulk ZnO. It indicates that size effect of the mechanical behavior was obviously observed for the nanofibers, and the mechanism was discussed in conjunction with their high surface-to-volume ratio. Indentation depth-dependent reduced modulus and hardness properties were observed, and it was attributed to the strain gradient effect during nanoindentation.4. (Na_0.5Bi_0.5)_0.94TiO₃-Ba_0.06TiO₃ （NBT-BT） and (Na_0.82K_0.18)_0.5Bi_0.5TiO₃ （NKBT） piezoelectric nanofibers were synthesized by sol-gel process and electrospinning technique. The morphology, crystallized phase and crystal structure were investigated by SEM, XRD, TEM and Energy-Dispersive X-ray Spectroscopy. To characterize the piezoelectricity, the d₃₃^* of nanofibers was measured by SPM. The nanoscale mechanical behaviors of piezoelectric nanofibers, such as reduced modulus and hardness properties, were investigated by nanoindentation technique in detail. The results show: （a） NBT-BT and NKBT nanofibers with perovskite phase were formed, and the diameter and length of nanofibers are in the range of 50 to 600 nm and several tens to several hundreds of micrometer; （b） the average values of d₃₃^* are 102 and 96 pm/V for NBT-BT and NKBT nanofibers, and the high piezoelectric property may be attributed to the easiness for electric field to tilt polar vector of domain and the increase of possible spontaneous polarization direction; （c） in comparison with the reduced modulus （158.2 GPa） and hardness （7.3 GPa） of NKBT thin film, the reduced modulus and hardness are 107.6 GPa and 4.9 GPa for the nanofibers, and they decrease by 31.9 % and 32.8 %. The size effect of the mechanical behavior was obviously observed for the nanofibers, and it is similar for the NBT-BT nanofibers. Due to their well piezoelectric and mechanical properties, they are a candidate of one-dimensional piezoelectric nanomaterials for potential appllication in micro-electro-mechanical systems.5. Photolithography and radio frequency magnetron sputtering were utilized to fabricate Pt interdigital electrodes on the SiO₂/Si substrate. The ZnS NBs were assembled onto the interdigital electrodes to fabricate photoconductive semiconductor switches （PCSS’s） based on individual NB and PCSS based on NBs film. The current-voltage （Ⅰ-Ⅳ） and functional characteristics of the PCSS’s were measured by Keithley system. The results show: （a） the separation between interdigital electrodes and the electrode width are 45μm and 55μm, and the thickness is 100 nm. The PCSS’s based on ZnS NBs have high photoresponse, well off-state and large photosensitivity; （b） the PCSS’s were applled into a test circuit to control the circuit state under UV-light with different wavelengths. The PCSS’s can reversibly control the circuit state conversion between“1”and“0”when UV-light was tured“on”and“off”, thus, the PCSS’s are of switching function; （c） oxygen chemisorption, surface effect and photoconductive effect were used to successfully explain the photoconductivity mechanism of PCSS’s. The results indicate that the PCSS’s based on semiconducting nanomaterials are a promising candidate for future integration.更多还原