MoO3修饰氧化石墨烯作为空穴注入层影响研究

研究了MoO₃修饰氧化石墨烯(GO)作为空穴注入层的影响。采用旋涂的方法制备了GO, 再真空蒸镀修饰层MoO₃,得到了空穴注入能力强和透过率高的复合薄膜。MoO₃的厚分 别采用0、3、5和8nm。通过优化MoO₃的厚度发现,当MoO₃的厚为5nm时,复合薄膜 的透过率达到最大值,在 550nm的光波长下透光率为88%,且此时采用 复合薄膜作为空穴注入层制备的结构为 ITO/GO/MoO₃(5nm)/NPB(40nm)/Alq₃(40nm)/LiF(1nm)/Al(100nm)的有机电致发光器件(OLED)性能 最佳。通过对OLED进一步的优化,改变Alq₃的厚度,分别取50、60和70nm,测量其电压 、电流、亮度、色坐标和电致发光(EL)光谱等参数发现,当Alq₃的厚为50nm时器件性能最 佳。最终制备了结构为ITO/GO/MoO₃(5nm)/NPB(50nm)/Alq₃(50nm)/LiF(1nm)/Al(100 nm)的OLED,在电压为10V时,最大电流效率达到5.87cd/A,与GO单独作为空穴注入层制备的器件相比,提高了50%。     

三氧化钼修饰银透明电极的光电性能及其应用研究

银(silver,Ag)纳米薄膜具有优异的导电性、延 展性、易制备等优点,是极具潜力的柔性透明电极材 料。通过真空热蒸镀制备不同厚度的银薄膜(6 nm、10 nm、14 nm、18 nm、20 nm、24 nm),由于光散射和 光吸收的共同作用, 其透过率随厚度的增加呈先减小、再增加、再减小的趋势,厚度为18 nm时最优,最高透过率约60%; 而面电阻则随厚度的增加逐渐减小。为提升银膜的透过率,引入高折射率(2.1)电介质三氧化钼(m olybdenum trioxide,MoO₃)对银膜进行修饰,制备了MoO₃/Ag/MoO₃(MAM)多层膜。结 果表明:引入MoO₃可以平滑 银膜表面,降低面电阻,并改善电导率;更重要的是“MoO₃/Ag”界面处会发生折射率耦合 ,大大提升多 层膜的整体透过率,透过率普遍增加至少10%。当银层的厚度为14 nm时,MAM多层膜的透过率最优, 可接近70%。最后,以银作为透明阴极,成功制备了双侧发光的绿光 有机发光二极管(organic light-emitting diode,OLED)。     

基于石墨烯的光控太赫兹调制器

研究了锗基单层石墨烯结构宽带光控太赫兹调制器。利用实验室搭建的太赫兹时域光谱系统,实验证明了在1 550 nm飞秒光泵浦下,该太赫兹调制器工作带宽为0.2~1.5 THz。当泵浦光功率从0增加到250 mW时,该太赫兹波调制器的平均透过率从40%下降到22%,平均吸收系数从19 cm-1增加到44 cm-1,在0.2~0.7 THz,调制深度均高于50%,最大调制深度为62%（0.38 THz）。实验结果表明,相比于纯锗基太赫兹调制器,单层石墨烯的引入能增强对太赫兹波的调制效果。     

二维材料异质结增强的硅基太赫兹光调制器

研究了石墨烯/氮化硼二维异质结增强的硅基太赫兹波光调制器。利用太赫兹波时域谱系统和实验室自主搭建的太赫兹波动态测试系统分别测试了808 nm激光对太赫兹波的静态和动态调制。当照射在太赫兹波调制器上的激光功率从0增加至500 mW时,平均太赫兹波透过率从58%下降到13%,静态调制深度最高达到76%(500 mW)。动态测试获得的最大调制速度为15 kHz (100 mW)。实验结果表明,与单层石墨烯增强的硅基调制器相比,石墨烯/氮化硼异质结可以更大地提高硅对于太赫兹波的调制深度,并提升调制速度。     

导电聚苯胺在太赫兹波段的光电性能研究

导电聚苯胺是一种掺杂高分子半导体,内部含有大量的自由载流子,同时含有大量被束缚的载流子。本文利用太赫兹时域光谱装置测量了不同电导率的聚苯胺在0.3～2.8 THz的光谱特性,得到了其在太赫兹波段的吸收系数、折射率和介电常数等光电参数。研究了电导率对其吸收系数、折射率和介电常数的影响,对半导体材料中载流子与太赫兹波的相互作用的研究具有重要意义。     

氧氩流量比对RF溅射ZnO:Mg薄膜结构及光学性能的影响

利用射频(RF)磁控溅射技术,采用单质Zn靶和 MgO陶瓷靶共溅射,在O₂和Ar气的混合气氛下制备了Mg掺杂ZnO(ZnO:Mg)薄膜,并通过改变O₂和Ar的流量比O ₂/Ar,研究了 对ZnO:Mg薄膜的物相结构、表面形貌及光学性能的影响。结果表明,室 温下O₂/Ar在1∶1～3∶1 范围内制备的薄膜均为单相的ZnO(002)薄膜,薄膜具有三维(3D)的结核生长模式;沉积的 ZnO:Mg薄膜在 N₂氛下200℃退火处理后,O₂/Ar为3∶1制备的薄膜在380～1200nm光谱范围内具有较高的透过率,可见光区平 均透过率约为85%、最大透过率达90%;薄膜的光学带隙 Eg为3.51eV,Mg掺杂对ZnO薄膜的光学带隙具有 较为明显的调制作用;采用极值包络线法计算表明,薄膜在589.3nm 处的折射率为1.963,膜厚约285nm。     

砷化镓类半导体材料在太赫兹波段的透射特性研究

首先给 出了利用光电导天线产生的太赫兹波的时域和频域光谱,进而,基于搭建的太赫 兹时域光谱系统, 并采用透射光谱法分别测量了砷化镓类型的三种半导体材料在太赫兹波段的透过率。结果表 明,基于光电导 天线产生的太赫兹波在0~2THz范围内,光谱比较稳定,频率带宽比 较宽;砷化镓半导体材料在0~2.0THz 范围内的透过率的变化相对较小,具有较高的透过率(>60%),并且 明显优于碲化锌以及碲化镉半导体 材料在太赫兹波段的透过率。因此,相比于碲化锌以及碲化镉半导体材料而言,砷化镓半导 体材料更适用于设计宽频带的太赫兹功能器件。     

空芯带隙型光子晶体光纤残余双折射特性研究

采用磁控溅射法, 在玻璃基底上一步沉积In₂S₃薄膜。研究了溅射功率对In₂S₃薄膜的成分、结构、表面形貌和光电性能的影响。结果表明: 所制备的所有薄膜均为β-In₂S₃, 无杂相存在, 且具有(222)面择优生长特性。溅射功率对薄膜的成分、厚度和结晶度具有明显的影响, 并因此影响薄膜的光学和电学性能。薄膜在100W沉积时最接近化学计量比, 薄膜的透过率随着溅射功率增大在500nm波段附近显著提高, 禁带宽度达到2.45eV, 同时电流密度增大两个数量级。     

光诱导氧化钒薄膜原位太赫兹波调制特性研究

采用磁控溅射及快速热氧化法在c-Al2O3基底制备出高质量的氧化钒薄膜。首先,分析结果表明所制备的氧化钒薄膜表面颗粒大小均匀,表面均方根粗糙度约为16.75 nm,主要成分为VO2和V2O5,V4+离子的含量为78.59%,所制备的氧化钒薄膜具有稳定的热致相变特性;其次,光诱导下薄膜的THz波调制特性研究结果显示,随着激励光功率增大,薄膜的THz透过率逐渐减小;最后,经过多次原位反复测试结果表明所制备的氧化钒薄膜具有稳定可逆的THz波调制特性,可应用于太赫兹开关和调制器等集成式太赫兹功能器件。     

二维铁电材料调控下的石墨烯超灵敏太赫兹探测器

石墨烯具有缺陷密度低、易大面积转移,载流子迁移率高等优异特性,但石墨烯具有的零带隙能带结构导致光生载流子寿命不高,制约了其在高灵敏光电探测器的应用。本工作中利用铁电材料CuInP₂S₆（CIPS）做顶栅来调控石墨烯的光电特性,探索了提升石墨烯太赫兹探测器灵敏度的可能性,研究了基于铁电调控下的石墨烯光热电效应和等离子体波自混频效应的探测机理,得到了高性能的石墨烯太赫兹探测器。在40 mV的偏置电压和2.12 V的栅压下,该器件在0.12 THz波段辐射下达到了0.5 A/W的响应率,响应时间为1.67 μs,噪声等效功率为0.81 nW/Hz^1/2。在0.29 THz波段辐射下仍达到了0.12 A/W的响应率,且噪声等效功率为1.78 nW/Hz^1/2。该工作展示了二维铁电异质结构在太赫兹波段中的巨大应用前景。     

Double modulated differential THz-TDS for thin film dielectric characterization

Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz radiation to characterize the optical properties of thin dielectric films. Characterizing thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonic systems and micro-electro-mechanical systems. There are potential applications for gene and protein chips. This paper shows how DTDS can be combined with double modulation in the pump-probe system to improve sensitivity by an order of magnitude. An iterative algorithm is presented to estimate the optical properties of a given thin film. The technique is experimentally verified using 1-μm-thick samples of silicon dioxide on silicon.     

The measurement of the dielectric and optical properties of nano thin films by THz differential time-domain spectroscopy

As feature sizes of circuits and devices approach 100 nm and chip frequencies climb into the upper GHz to THz range, it becomes increasingly important to have a convenient method of characterizing properties of thin dielectric films in the GHz to THz frequency range. THz time-domain spectroscopy provides a non-contact, non-destructive and highly sensitive optical tool to characterize the dielectric and optical properties of micron to nanometer scaled thin films at GHz and THz frequencies. The measurement of the dielectric and the optical properties of nanometer scaled dielectric films is performed using the THz differential time-domain spectroscopy. The real and imaginary parts of the complex dielectric constants and the optical constants of a variety of nano thin films are measured at GHz and THz frequencies.     

Tera Tool [terahertz time-domain spectroscopy]

The terahertz differential time-domain spectroscopic method is applied to characterize the dielectric and optical properties of a variety of thin films at terahertz frequency. The results of several samples including silicon dioxide, parylene-n polymer film, tantalum oxide film, and protein thin layer samples were presented. The dielectric property of silicon dioxide thin film is well fitted to that of a bulk. The dielectric properties of parylene-n thin films show good agreement with the result measured by the goniometric terahertz time-domain spectroscopy. The dielectric and optical properties of the tantalum oxide show reasonable data with previously available data. Some properties in thin films are slightly different from the bulk materials. The origin of this discrepancy is considered due to fine grain formation, mechanical stresses, formation of interfacial layers, or rough interfaces during thin-film deposition process. The terahertz differential time-domain spectroscopy may be applied to the measurement of the dielectric and optical properties of thin films (nanometer to micrometer) of several materials, which cannot be done by any other method.     

Strain-Induced Ferroelectricity of a SrTiO3 Thin Film on a MgAl2O4 Substrate Observed by Terahertz Time-Domain Spectroscopy

A SrTiO₃ thin film was deposited on a MgAl₂O₄(100) substrate with a 3.5 % larger lattice constant than that of the SrTiO₃. The temperature dependence of the dielectric dispersion of the SrTiO₃ thin film was measured by terahertz time-domain spectroscopy, and the dielectric strength and soft-mode frequency showed positive and negative peaks at around 170 K, respectively. In addition, a deviation of the dielectric constant from the theoretical fitting curve in the gigahertz range and an increase in the value of the damping factor were observed below the ferroelectric transition temperature. These phenomena strongly indicate the emergence of ferroelectricity at around 170 K.     

Tunable,Grating-Gated,Graphene-On-Polyimide Terahertz Modulators

An electrically switchable graphene terahertz (THz) modulator with a tunable-by-design optical bandwidth is presented and it is exploited to compensate the cavity dispersion of a quantum cascade laser (QCL). Electrostatic gating is achieved by a metal grating used as a gate electrode, with an HfO₂/AlO_x gate dielectric on top. This is patterned on a polyimide layer, which acts as a quarter wave resonance cavity, coupled with an Au reflector underneath. The authors achieve 90% modulation depth of the intensity, combined with a 20 kHz electrical bandwidth in the 1.9–2.7 THz range. The modulator is then integrated with a multimode THz QCL. By adjusting the modulator operational bandwidth, the authors demonstrate that the graphene modulator can partially compensate the QCL cavity dispersion, resulting in an integrated laser behaving as a stable frequency comb over 35% of the operational range, with 98 equidistant optical modes and a spectral coverage ~1.2 THz. This paves the way for applications in the terahertz, such as tunable transformation-optics devices, active photonic components, adaptive and quantum optics, and metrological tools for spectroscopy at THz frequencies.     

A thermally tunable terahertz bandpass filter with insulator-metal phase transition of VO2 thin film

A terahertz bandpass filter with the sandwich structure consisting of thermally tunable vanadium dioxide （VO2） thin film, silica substrate and subwavelength rectangular Cu hole arrays is designed and theoretically analyzed. The results show that the transmittance of the filter can be actively tuned by controlling the temperature of VO2, the narrow band terahertz （THz） waves with the transmittance from 85.2% to 10.5% can be well selected at the frequency of 1.25 THz when the temperature changes from 50 ℃ to 80 ℃, and the maximum modulation depth of this terahertz bandpass fil- ter can achieve 74.7%.     

基于二氧化钒薄膜的太赫兹开关器件

二氧化钒(VO2)作为一种优质的光电功能材料一直备受人们的关注,在信息存储、光调制器、太阳能电池、光电探测器等方面有着重要应用。采用磁控溅射及原位退火氧化的"两步法"制备了VO2薄膜,并对其进行晶态、形貌表征。设计并搭建VO2薄膜热致相变实验系统,研究了VO2薄膜在变温条件下对2.52 THz辐射的开关特性。结果表明,VO2薄膜样品为多晶态,具有明显的太赫兹调制效果,可以实现对2.52 THz波的调制,并可作为太赫兹开关/调制器件的功能材料。     

Calculation and Study of Graphene Conductivity Based on Terahertz Spectroscopy

Based on terahertz time-domain spectroscopy system and two-dimensional scanning control system, terahertz transmission and reflection intensity mapping images on a graphene film are obtained, respectively. Then, graphene conductivity mapping images in the frequency range 0.5 to 2.5 THz are acquired according to the calculation formula. The conductivity of graphene at some typical regions is fitted by Drude-Smith formula to quantitatively compare the transmission and reflection measurements. The results show that terahertz reflection spectroscopy has a higher signal-to-noise ratio with less interference of impurities on the back of substrates. The effect of a red laser excitation on the graphene conductivity by terahertz time-domain transmission spectroscopy is also studied. The results show that the graphene conductivity in the excitation region is enhanced while that in the adjacent area is weakened which indicates carriers transport in graphene under laser excitation. This paper can make great contribution to the study on graphene electrical and optical properties in the terahertz regime and help design graphene terahertz devices.