针尖增强拉曼光谱应用于单分子研究的进展

拉曼光谱因可表征物质的化学信息而被广泛应用,特别是表面增强拉曼光谱(SERS)能够在单分子水平研究物质的化学结构信息,但SERS技术对基底粗糙度要求较高,无法获得令人满意的空间分辨率。扫描探针显微技术的出现使在原子水平研究物质的形貌成为可能,但该方法不能同时获得原子/分子的化学信息。针尖增强拉曼光谱(TERS)技术则集两者于一身,已被广泛用于物质的单分子物理化学性质的研究。本文在回顾TERS及相关技术发展的基础上,介绍了TERS技术的原理及性能,简述了TERS技术用于单分子研究的部分典型结果,并展望了该技术的发展前景。     

失效原子力显微镜硅针尖再生

原子力显微镜的传统商品硅针尖在使用过程中极易因磨损而失效，本文研究了一种在实验室条件下简易可行的回收利用失效硅针尖的方法。在原子力显微镜的敲击模式下使用曲率半径大于100 nm的失效硅针尖对生长单壁碳纳米管的样品表面进行扫描，把样品表面的单壁碳纳米管管束粘接到硅针尖上，可制得直径在5～20 nm的碳纳米管针尖。实验对碳纳米管针尖和新的商品硅针尖进行了成像对比，所制备的碳纳米管针尖不仅在成像分辨率而且在成像稳定性上都优于新的商品硅针尖。     

针尖化学方法研究单壁碳纳米管末端羧基的解离性质

针尖化学利用化学手段对扫描探针显微镜 ( SPM)的针尖进行功能化修饰 ,将其作为化学反应的“探针”用于研究表面的局域化学反应性质、跟踪表面发生的化学反应过程等 [1] .用针尖化学技术来研究自组装膜 ( SAMs)表面酸碱基团的局域解离性质 ,称之为化学力滴定 [2～ 8] .利用表面缩合方法将单壁碳纳米管短管组装到 AFM针尖上 ,通过测定针尖上碳纳米管的末端基团与羟基自组装膜表面之间的粘滞力 ,研究碳纳米管末端羧基的解离性质 ,可得到碳纳米管结构与化学性质的信息 .1　实验部分1 .1　碳纳米管针尖和羟基末端自组装膜的制备　基底 [Si( …     

STM针尖诱导构筑-置换两步法制备Pt表面纳米结构

STM“Jump-to-contact”针尖诱导表面纳米构筑是目前水溶液中具有最高分辨率的一种表面纳米构筑技术.然而,一些金属因其具有较高的内聚能而难以发生针尖原子向表面的转移,限制了该技术的广泛应用.本文建立了以STM构筑-置换两步法获得不能直接利用“Jump-to-contact”原理进行构筑的金属表面纳米团簇阵列,利用STM针尖“Jump-to-contact”诱导在Au(111)表面构筑Cu纳米团簇阵列,然后通过Pt-Cu置换的方法,制备出Au(111)表面的Pt纳米团簇阵列.     

扫描探针刻蚀技术可控构建牛血清白蛋白纳米结构

利用Dip-pen纳米刻蚀技术(简称DPN技术)在云母基底上构建出形状、尺寸可控的牛血清白蛋白(BSA)纳米结构.考察了针尖接触基底时间及针尖下行距离对构建的牛血清白蛋白纳米结构的影响.较长的针尖-基底接触时间及较深的下行距离可以沉积更多的牛血清白蛋白分子,构建牛血清白蛋白纳米结构的形状除了与墨水分子的本身性能有关,还与墨水-基底的相互作用有关.这些形状及尺寸可控的蛋白质纳米结构可以作为模板,进行金属、半导体等其它材料的组装,有望用于制造光电纳米器件及生物纳米器件.     

纳米笔刻蚀技术构建小牛胸腺组蛋白纳米结构

采用纳米笔刻蚀(DPN)技术控制针尖的运行,成功地将小牛胸腺组蛋白传递到新剥离的云母表面,获得了不同尺寸、形状的小牛胸腺组蛋白纳米结构,同时考察了针尖移动速率、针尖-基底接触时间对DPN技术的影响.结果表明,较快的针尖移动速率和较短的针尖-基底接触时间沉积较少的墨水分子,同时形成的纳米图案和墨水分子的本身性质也有关系.这种方法可以用于构建其他蛋白质分子,为生物纳米器件的合成提供更多机会,同时组蛋白纳米结构的构建也可以作为模板沉积其他分子,在蛋白质监测、生物传感器方面有着潜在的应用.     

表面增强拉曼光谱:应用和发展

表面增强拉曼光谱技术(Surface-enhanced Raman spectroscopy,SERS)是一种具有超高灵敏度的指纹光谱技术,目前已广泛应用于表面科学、材料科学、生物医学、药物分析、食品安全、环境检测等领域,是一种极具潜力的痕量分析技术。 本文对SERS技术及相关的针尖增强拉曼光谱(Tip-enhanced Raman spectroscopy,TERS),壳层隔绝纳米粒子增强拉曼光谱(Shell-isolated nanoparticle-enhanced Raman spectroscopy,SHINERS)技术的发展及应用进行了综合评述,并探讨了其未来的研究热点及发展方向。     

原子力显微镜针尖诱导聚氧乙烯熔体结晶的研究

原子力显微镜(AFM)是研究高分子结晶行为的一种重要实验手段.在使用AFM原位观察高分子结晶时,为保证能真实地反映结晶过程,一个必须注意的问题是要避免AFM针尖的影响.与此同时,人们考察了在AFM扫描时针尖诱导高分子结晶成核的情况.若使用AFM接触模式(contactmode),扫描时容易造     

表面增强拉曼散射纳米针尖用于单细胞内环境的检测研究

表面增强拉曼散射（SERS）纳米针尖是一类单细胞分析新技术,在细胞内环境检测和细胞生理功能研究等方面具有良好的应用潜力。由于SERS纳米针尖可负载的贵金属粒子数量少,因此,筛选和修饰高SERS增强能力的纳米粒子是确保其检测灵敏度的关键。本研究制备了一种核-卫星结构的Au纳米粒子,单颗粒信号较传统Au纳米球和Au纳米星显著提高。将此粒子涂覆在尖端直径约为200 nm的玻璃毛细管表面,形成SERS纳米针尖,进一步功能化修饰靶标敏感型拉曼报告分子,使其具备检测微区环境中p H值和O2的能力。作为应用性能考察,采用SERS纳米针尖实现了单个HL-7702细胞内pH值和缺氧状态监测。本研究解决了传统颗粒态SERS探针用于细胞分析面临的随机聚集和难以精确定位等瓶颈问题,为单细胞内环境检测分析提供了一种新的分析工具。     

STM针尖诱导铜表面纳米刻蚀与沉积

扫描隧道显微技术 ( STM)不但可在小至原子分辩的尺度上现场研究电极表面及其结构变化 ,还能对电极表面进行纳米尺度上的加工、修饰 [1～ 3] .由于 STM探针与被研究样品的表面仅相距～ 1 nm,探针附近区域电极 /溶液界面的结构和性质将不可避免地受到影响 .尽管人们已认识到针尖与样品表面不可忽视的相互作用 ,但利用该相互作用诱导纳米区域电化学反应的研究还很少 ,仅有半导体 Si[4～ 7] 和 Ga As[8] 表面基于强电场诱导或空穴注入的 STM针尖诱导纳米刻蚀等的报道 .本文在控制铜的电位负于其热力学平衡电位 ( Nernst电位 )的情况下 ,…     

Tungsten nanotip fabrication by spatially controlled field-assisted reaction with nitrogen

In this report we present a straightforward new technique for fabricating nanotips. This approach is based on spatially controlling the reaction of nitrogen gas with the surface atoms of a tungsten tip in a field ion microscope (FIM). Confining this field-assisted etching reaction to the shank has enabled us to produce single-atom tips with an apex radius far sharper than the nominal 10 nm radius of curvature tips we start with. Tip sharpening is evidenced in several ways. The FIM imaging voltage drops dramatically from, typically, 4.4 to 1.6 kV. Nanotip formation is also evident from the increase in the FIM magnification and the decrease in the apex area, which are monitored throughout the experiment. A subsequent field evaporation allows the nanotip to be sequentially deconstructed to further describe the extraordinary sharp tip that was formed. We also demonstrate the utility of these nanotips for the scanning tunneling microscope.     

Synthesis of hybrid CdS-Au colloidal nanostructures

We explore the growth mechanism of gold nanocrystals onto preformed cadmium sulfide nanorods to form hybrid metal nanocrystal/semiconductor nanorod colloids. By manipulating the growth conditions, it is possible to obtain nanostructures exhibiting Au nanocrystal growth at only one nanorod tip, at both tips, or at multiple locations along the nanorod surface. Under anaerobic conditions, Au growth occurs only at one tip of the nanorods, producing asymmetric structures. In contrast, the presence of oxygen and trace amounts of water during the reaction promotes etching of the nanorod surface, providing additional sites for metal deposition. Three growth stages are observed when Au growth is performed under air: (1) Au nanocrystal formation at both nanorod tips, (2) growth onto defect sites on the nanorod surface, and finally (3) a ripening process in which one nanocrystal tip grows at the expense of the other particles present on the nanorod. Analysis of the hybrid nanostructures by high-resolution TEM shows that there is no preferred orientation between the Au nanocrystal and the CdS nanorod, indicating that growth is nonepitaxial. The optical signatures of the nanocrystals and the nanorods (i.e., the surface plasmon and first exciton transition peaks, respectively) are spectrally distinct, allowing the different stages of the growth process to be easily monitored. The initial CdS nanorods exhibit band gap and trap state emission, both of which are quenched during Au growth.     

Surface bonding on silicon surfaces as probed by tip-enhanced Raman spectroscopy

Tip-enhanced Raman spectroscopy (TERS) has been used to obtain the Raman signal of surface species on silicon single crystal surfaces without the necessity for surface enhancement by addition of Ag nanoparticles. By illuminating the hydrogen terminated silicon surface covered with a droplet of 4-vinylpyridine with UV light, a 4-ethylpyridine modified silicon surface can be easily obtained. By bringing a scanning tunneling microscope (STM) Au tip with a nanoscale tip apex to a distance of ca. 1 nm from the m...     

Creation and recovery of a W(111) single atom gas field ion source

Tungsten single atom tips have been prepared from a single crystal W(111) oriented wire using the chemical assisted field evaporation and etching method. Etching to a single atom tip occurs through a symmetric structure and leads to a predictable last atom unlike etching with polycrystalline tips. The single atom tip formation procedure is shown in an atom by atom removal process. Rebuilds of single atom tips occur on the same crystalline axis as the original tip such that ion emission emanates along a fixed direction for all tip rebuilds. This preparation method could be utilized and developed to prepare single atom tips for ion source development.     

Distribution and thickness of the surface contaminations on STM tungsten tips,studied by AES/SEM and ARXPS

The combination of Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and angle resolved X-ray photoelectron spectroscopy (ARXPS) has been applied to the analysis of the distribution of elements at the surface region of electrochemically etched tungsten tips and the determination of the thickness of a layer with oxygen and carbon contamination. Auger line profiling revealed a homogeneous distribution of oxygen and significant enrichment of carbon on the W tip between 0 and 1.5 m from the top. The thickness of the contamination layer on various W materials, electrochemically etched, was found to be 1.35±0.15 nm as measured using ARXPS, and was estimated to be about 1–3 nm as measured by AES.     

Characterization of micromachined hollow tips for two-dimensional nanoelectrospray mass spectrometry

In this work an improved design of chip-based nanoelectrospray nozzles is reported. Two-dimensional matrices of out-of-plane 10 microm i.d. silicon dioxide tips with a tapered shape were manufactured using deep reactive ion etching technology. Using a peptide sample, six micromachined tips and six commercially pulled silica capillary tips were compared employing an ion trap mass spectrometer. At a flow rate of 100 nL/min, the detectability obtained was approximately the same for the two types of tips. The relative standard deviation of the signal-to-noise ratio for the peptides between six different tips was on average 22% for the micromachined tips and 45% for the pulled capillary tips. The usefulness of the micromachined tips for analysis of non-covalent protein-ligand complexes was demonstrated by the analysis of a sample of RNase A and cytidine 2'-monophosphate. In another test, analyzing a tryptic digest of 1 pmol/microL cytochrome C, 18 peptides corresponding to a 82% sequence coverage were detected. Using MS/MS, the whole sequence of an 11 amino acid cytochrome C fragment was obtained. Computer simulations were performed on the shape and magnitude of the electrical field around micromachined and pulled capillary tips. To reach the threshold electric field density at the tip apex required to initiate an electrospray, a higher electrospray voltage was needed for the chip-based tips compared with pulled capillary tips. This is due to the influence of the chip base.     

Fast Fabrication and Judgement of Tip-Enhanced Raman Spectroscopy-Active Tips

The quality of the scanning tip is crucial for tip-enhanced Raman spectroscopy (TERS) experiments towards large signal enhancement and high spatial resolution. In this work, we report a controllable fabrication method to prepare TERS-active tips by modifying the tip apex at the atomic scale, and propose two important criteria to in-situ judge the tip's TERS activity for tip-enhanced Raman measurements. One criterion is based on the downshift of the first image potential state to monitor the coupling between the far-field incident laser and near-field plasmon; the other is based on the appearance of the low-wavenumber Raman peaks associated with an atomistic protrusion at the tip apex to judge the coupling efficiency of emissions from the near field to the far field. This work provides an effective method to quickly fabricate and judge TERS-active tips before real TERS experiments on target molecules and other materials, which is believed to be instrumental for the development of TERS and other tip-enhanced spectroscopic techniques.     

In-situ voltage tunneling spectroscopy at electrochemical interfaces

Nanophysics at electrochemical interfaces, probing the physical properties of nanostructures, requires laterally resolved in-situ spectroscopy, in particular voltage tunneling spectroscopy (VTS), which is at present not yet established. In-situ spectroscopy is required to achieve reliable and reproducible measurements of the intrinsic properties of nanostructures in an electrochemical environment, which are mainly determined in small nanostructures by surface atoms rather than bulk atoms. In contrast to tunneling spectroscopy in ultrahigh vacuum, tip and substrate double-layer capacitances as well as Faradaic currents play an important role in voltage tunneling spectroscopy at electrochemical interfaces. Deoxygenation of the electrolyte, fast measurements using appropriate instrumentation, and minimization of the unisolated tip apex and substrate surface areas exposed to the electrolyte are the key parameters to achieve reliable in-situ voltage tunneling spectroscopy data at electrochemical interfaces. The presented data show that bias voltage intervals of more than 1000 mV can be utilized for spectroscopic investigations in aqueous electrolytes, which allow the in-situ study of discrete electronic levels in nanostructures.     

Controllable Preparation of Plasmonic Gold Nanostars for Enhanced Photothermal and SERS Effects

Gold nanostars(Au NSs) are asymmetric anisotropic nanomaterials with sharp edge structure. As a promising branched nanomaterial, Au NS has excellent plasmonic absorption and scattering properties. In order to tune the plasmonic photothermal and surface-enhanced Raman scattering(SERS) activity of Au NSs to obtain the desired characteristics, the effects of reagents on the local surface plasmon resonance(LSPR) bands of Au NSs were studied and the morphology and size were regulated. Nanoparticles with different sharp edges were synthesized to make their local plasmon resonance mode tunable in the visible and near-infrared region. The effects of the number and sharpness of different tips under the control of AgNO₃ on the photothermal response of Au NSs and the SERS activity and their mechanism were discussed in detail. The results show that as the length of the branch tip becomes longer and the sharpness increases, the plasmonic photothermal effect of Au NSs is strengthened, and the photothermal conversion efficiency is the highest up to 40% when the length of Au NSs is the longest. Au NSs with high SERS activity are used for the Raman detection substrate. Based on this property, the quantitative detection of the pesticide thiram is achieved.     

Silicon surface nano-oxidation using scanning probe microscopy

This paper focuses on the nano-oxidation of a silicon surface using scanning probe microscopes in air ambient and in UHV. Special emphasis is put in air ambient on the preparation of the surfaces and on the oxidation mechanism. The characteristics of the patterned nanostructures are reviewed versus the parameters which govern the process (tip–surface voltage, tip speed, humidity) as well as the kinetics models of the oxidation process. The oxide patterns can act as robust masks for dry or wet etching. Fabrication of nanostructures is presented and allows to realize electronic nanodevices. In UHV, there is no direct nano-oxidation of the surface by the microscope tip. First the surface is hydrogenated, second a local hydrogen desorption is performed with the STM tip and finally the bare desorbed area is exposed to oxygen. The desorption process is analyzed versus tip–surface voltage and tunneling current. The oxidation of a desorbed area using molecular or atomic oxygen is actually difficult to achieve.