A Laser Source with High Spectral Purity for Simple Tunable Laser Raman Instrument

The authors present an external cavity diode laser with high spectral purity for tunable laser Raman spectroscopy. To achieve high spectral purity required for Raman spectroscopy, a laser cavity utilizing a volume phase holographic grating, which has very low stray light, is developed and the first-order diffracted beam from the grating is taken as the output. Raman signals can be obtained from common samples with only a commercial laser rejection filter, greatly simplifying a tunable Raman instrument.     

用同步辐射源建立紫外及真空紫外光谱区光谱辐射度基准的研究

叙述了中国科学技术大学国家同步辐射实验室800 MeV电子储存环同步辐射的特性及作为光谱辐射亮度基准的原理和方法,精确计算出同步辐射光源光谱功率空间分布,并在计量学上将同步辐射“经典”理论与标定氘灯光谱辐射亮度结合起来,对“同步辐射作为标准源进行光谱辐射功率计量”进行深入的研究。介绍了国家同步辐射实验室计量光束线站的装置,该装置利用同步辐射波长范围宽、亮度高、辐射特性可精确计算等特点,可用于标定传递标准氘灯的光谱辐射亮度(115~350 nm),并进行了不确定度分析。并与德国技术物理研究院(PTB)标定的氘灯光谱辐射亮度进行比较,两者符合。     

Ultrasensitive PbS‐Quantum‐Dot Photodetectors for Visible–Near‐Infrared Light Through Surface Atomic‐Ligand Exchange

A surface atomic‐ligand exchange method is applied the first time in the construction of photodetectors (PDs) based on PbS quantum dots (QDs) for ultrasensitivity. The device thus produces a high photosensitivity to visible and near‐infrared light with a photoresponsivity up to 7.5 × 10³ A W^?1 and a high stability in air. In particular, these PbS‐QD‐based PDs show the capability of following a pulse light with a frequency up to 100 kHz well at a relatively fast response time/recovery time of ≈4/40 μs, much faster than most previous QD‐based PDs. The short response time is attributed to modification for the surface of the PbS‐QDs by cetyltrimethylammonium bromide treatment, which effectively improves the contact between the QDs and the Au electrodes, leading to extracting a high carrier mobility (≈0.142 cm² V^?1 s^?1). These findings show the great potential of PbS‐QDs as high‐speed nano‐photodetectors, and, more importantly, demonstrate the importance of the surface atomic‐ligand exchange method in the construction of QD‐based devices.     

High‐Responsivity Photodetectors Based on Formamidinium Lead Halide Perovskite Quantum Dot–Graphene Hybrid

Highly performance photodetector requires a wide range of responses of the incident photons and converts them to electrical signals efficiently. Here, a photodetector based on formamidinium lead halide perovskite quantum dots (e.g., FAPbBr₃ QDs)–graphene hybrid, aiming to take the both advantages of the two constituents. The FAPbBr₃ QD–graphene layer not only benefits from the high mobility and wide spectral absorption of the graphene material but also from the long charge carrier lifetime and low dark carrier concentration of the FAPbBr₃ QDs. The photodetector based on FAPbBr₃ QD–graphene hybrid exhibits a broad spectral photoresponse ranging from 405 to 980 nm. A photoresponsivity of 1.15 × 10⁵AW⁻¹ and an external quantum efficiency as high as 3.42 × 10⁷% are obtained under an illumination power of 3 µW at 520 nm wavelength. In detail, a high responsivity is achieved in 405–538 nm, while a relatively low but fast response is observed in 538–980 nm. The photoelectric conversion mechanism of this hybrid photodetector is investigated in the view of built‐in electric field from the QD–graphene contact which improves the photoconductive gain.     

Use of atomic layer deposition to improve the stability of silver substrates for in situ,high‐temperature SERS measurements

A method to stabilize silver surface‐enhanced Raman spectroscopy (SERS) substrates for in situ, high‐temperature applications is demonstrated. Silver island films grown by thermal evaporation were coated with a thin layer (from 2.5 to 5 nm) of alumina by atomic layer deposition (ALD), which protects and stabilizes the SERS‐active substrate without eliminating the Raman enhancement. The temporal stability of the alumina‐coated silver island films was examined by measurement of the Raman intensity of rhodamine 6G molecules deposited onto bare and alumina‐coated silver substrates over the course of 34 days. The coated substrates showed almost no change in SERS enhancement, while the uncoated substrates exhibited a significant decrease in Raman intensity. To demonstrate the feasibility of the alumina‐coated silver substrate as a probe of adsorbates and reactions at elevated temperatures, an in situ SERS measurement of calcium nitrate tetrahydrate on bare and alumina‐coated silver was performed at temperatures ranging from 25 to 400 °C. ALD deposition of an ultrathin alumina layer significantly improved the thermal stability of the SERS substrate, thus enabling in situ detection of the dehydration of the calcium nitrate tetrahydrate at an elevated temperature. Despite some loss of Raman signal, the coated substrate exhibited greater thermal stability compared to the uncoated substrate. These experiments show that ALD can be used to synthesize stable SERS substrates capable of measuring adsorbates and processes at high temperature. Copyright © 2009 John Wiley & Sons, Ltd.     

Atomic layer deposition of TiO2 and Al‐doped TiO2 films on Ir substrates for ultralow leakage currents

TiO₂ and Al‐doped TiO₂ (ATO) films were grown on Ir substrates by atomic layer deposition using O₃ as the oxygen source. With increasing O₃ feeding time, the crystalline structure of the TiO₂ films was transformed from anatase to rutile. Above an O₃ feeding time of 35 s, the films crystallized as only rutile due to the formation of IrO₂ layer at the interface. The TiO₂ and ATO films showed higher dielectric constants of 78 and 51, respectively. The films on Ir showed superior leakage properties compared to the films on Ru due to the high work‐function of Ir. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contact passivation in silicon solar cells using atomic‐layer‐deposited aluminum oxide layers

Atomic‐layer‐deposited aluminum oxide (AlO_x) layers are implemented between the phosphorous‐diffused n⁺‐emitter and the Al contact of passivated emitter and rear silicon solar cells. The increase in open‐circuit voltage V_oc of 12 mV for solar cells with the Al/AlO_x/n⁺‐Si tunnel contact compared to contacts without AlO_x layer indicates contact passivation by the implemented AlO_x. For the optimal AlO_x layer thickness of 0.24 nm we achieve an independently confirmed energy conversion efficiency of 21.7% and a V_oc of 673 mV. For AlO_x thicknesses larger than 0.24 nm the tunnel probability decreases, resulting in a larger series resistance. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

用伪同色光谱图像检测色觉正常观察者的锥细胞光谱响应

为了能够快速、准确的检测色觉正常观察者的辨色差异,从而对其红、绿、蓝三通道的锥细胞光谱响应进行研究,设计并制作了由背景层（或和明度层）以及数字层组成的伪同色光谱图像,其中背景层和数字层具有不同的光谱反射曲线,经过照明光源以及人眼锥细胞光谱响应的共同作用,使色觉正常的观察者产生不同的颜色感知差异。实验首先基于不同光谱原色的输出设备,在不同的照明光源下,制作出能够放大观察者差异的近同色异谱色样对。要求用不同颜色匹配函数计算近同色异谱色样对的CIEDE2000色差值,有的色差在人眼辨色阈值之内,有的色差人眼可明显识别。通过优化计算,将放大观察者色觉差异的近同色异谱色样对应用于伪同色光谱图像的数字层和背景层,并利用Epson Stylus Pro7908喷墨打印机和OKI C9600激光打印机分别输出伪同色光谱图像的背景层和数字层。同时组织了72名色觉正常的观察者（包含55名18～25岁的年轻观察者和17名62～74岁的老年观察者）分别在D65和LED-5000K两种光源下,对伪同色光谱图像进行识读检验。识读结果表明,伪同色光谱图像可以较为准确的判定年轻和老年观察者的视网膜锥细胞光谱响应是否老化。同种照明光源下,年轻观察者可以识读出数字的伪同色光谱图像（②/④）老年观察者不能识读,老年观察者可以识读的伪同色光谱图像（①/③）大多年轻观察者不能识读,且55名年轻观察者中有4名观察者的目视结果与老年人相同。另外,年轻观察者的锥细胞光谱响应与CIE1964和CIE2006（age=25 y）颜色匹配函数较为一致,而老年观察者的锥细胞光谱响应与CIE1931和CIE2006（age=75 y）颜色匹配函数更为一致。对比颜色匹配函数的分布,发现老年观察者的锥细胞光谱响应向长波段偏移,同时由于屈光系统光学密度增加导致其锥细胞光谱响应有所降低。     

Rapid Visualization of Latent Fingerprints with Color‐Tunable Solid Fluorescent Carbon Dots

Latent fingerprints (LFPs) imaging is the most important approach to identify individuals, and there is a persisting need for the development of simple, rapid, accurate, and universal LFPs recognition methods. The nitrogen‐ and sulfur‐doped solid fluorescent carbon dots (N,S‐SFCD) are synthesized with a simple microwave‐assisted method by using l ‐glutathione and citric acid as precursors. The obtained N,S‐SFCD has a uniform size from 2 to 7 nm with quantum yield over 48%. The presence of heteroatoms and functional groups on the surface endows the N,S‐SFCD with good dispersibility and strong fluorescence emission, and overcomes the typical aggregation‐induced fluorescence quenching, thus allowing the N,S‐SFCD to be used in both solution and their powder forms. Furthermore, the color‐tunable fluorescence, electrostatic interaction with fingerprints, and good stability enable N, S‐SFCD to act as an excellent chemosensor for fluorescence imaging. LFPs are detected with high resolution through powder method, and their second‐ and third‐level substructures are clearly identified. The method is validated for LFPs visualization on various substrates, and aged (7, 15, and 30 d) LFPs can also be successfully stained with N,S‐SFCD. The results demonstrate that the N,S‐SFCD as a developer has great potential in LFPs imaging for forensic investigations.     

Silicon surface passivation by atomic‐layer‐deposited Al2O3 facilitated in situ by the combination of H2O and O3 as reactants

We investigate the effect of O₃ and H₂O oxidant pre‐pulse prior to Al₂O₃ atomic layer deposition for Si surface passivation. Interfacial oxide SiO_x formed by the O₃ pre‐pulse is more beneficial than that by H₂O to a high level of surface passivation. The passivation of thinner H₂O–Al₂O₃ films is more improved by this O₃ pre‐pulse. O₃ pre‐pulse for 10 nm H₂O–Al₂O₃ reduces saturation current density in boron emitter to 18 fA cm^–2 by a factor of 1.7. Capacitance–voltage measurements reveal this interfacial oxide plays a role of decreasing interface trap density without detrimental effect to negative charge density of Al₂O₃. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

An ultra‐black silicon absorber

An ultra‐black (A > 99%) broadband absorber concept on the basis of a needle‐like silicon nanostructure called Black Silicon is proposed. The absorber comprises Black Silicon established by inductively coupled plasma reactive ion etching (ICP‐RIE) on a highly doped, degenerated silicon substrate. Improved absorbers also incorporate an additional oxide capping layer on the nanostructures and reach an absorptance of A > 99.5% in the range of 350 to 2000 nm and A ∼ 99.8% between 1000 and 1250 nm. Fabrication of the absorbers is consistent with CMOS standards and requires no lithography. (Picture: Kasper, Friedrich‐Schiller‐University Jena)