Imaging and strain analysis of nano-scale SiGe structures by tip-enhanced Raman spectroscopy

The spatial resolution and high sensitivity of tip-enhanced Raman spectroscopy allows the characterization of surface features on a nano-scale. This technique is used to visualize silicon-based structures, which are similar in width to the transistor channels in present leading-edge CMOS devices. The reduction of the intensive far-field background signal is crucial for detecting the weak near-field contributions and requires beside a careful alignment of laser polarization and tip axis also the consideration of the crystalline sample orientation. Despite the chemical identity of the investigated sample surface, the structures can be visualized by the shift of the Raman peak positions due to the patterning induced change of the stress distribution within lines and substrate layer. From the measured peak positions the intrinsic stress within the lines is calculated and compared with results obtained by finite element modeling. The results demonstrate the capability of the tip-enhanced Raman technique for strain analysis on a sub-50 nm scale.     

表面增强拉曼光谱的研究进展

本文从提高表面拉曼光谱检测灵敏度和空间分辨率两个方面的发展叙述表面增强拉曼光谱和针尖增强拉曼光谱的原理、方法、特点以及最新进展。对利用表面增强拉曼光谱和针尖增强拉曼光谱研究金属表面上分子吸附等方面的应用进行总结 ,并对他们的应用前景做了预测     

Tip-enhanced near-field Raman spectroscopy with a scanning tunneling microscope and side-illumination optics

Conventional Raman spectroscopy (RS) suffers from low spatial resolution and low detection sensitivity due to the optical diffraction limit and small interaction cross sections. It has been reported that a highly localized and significantly enhanced electromagnetic field could be generated in the proximity of a metallic tip illuminated by a laser beam. In this study, a tip-enhanced RS system was developed to both improve the resolution and enhance the detection sensitivity using the tip-enhanced near-field effects. This instrument, by combining RS with a scanning tunneling microscope and side-illumination optics, demonstrated significant enhancement on both optical sensitivity and spatial resolution using either silver (Ag)-coated tungsten (W) tips or gold (Au) tips. The sensitivity improvement was verified by observing the enhancement effects on silicon (Si) substrates. Lateral resolution was verified to be below 100 nm by mapping Ag nanostructures. By deploying the depolarization technique, an apparent enhancement of 175% on Si substrates was achieved. Furthermore, the developed instrument features fast and reliable optical alignment, versatile sample adaptability, and effective suppression of far-field signals.     

High-resolution microscope for tip-enhanced optical processes in ultrahigh vacuum

An optical microscope based on tip-enhanced optical processes that can be used for studies on adsorbates as well as thin layers and nanostructures is presented. The microscope provides chemical and topographic informations with a resolution of a few nanometers and can be employed in ultrahigh vacuum as well as gas phase. The construction involves a number of improvements compared to conventional instruments. The central idea is to mount, within an UHV system, an optical platform with all necessary optical elements to a rigid frame that also carries the scanning tunneling microscope unit and to integrate a high numerical aperture parabolic mirror between the scanning probe microscope head and the sample. The parabolic mirror serves to focus the incident light and to collect a large fraction of the scattered light. The first experimental results of Raman measurements on silicon samples as well as brilliant cresyl blue layers on single crystalline gold and platinum surfaces in ultrahigh vacuum are presented. For dye adsorbates a Raman enhancement of approximately 10(6) and a net signal gain of up to 4000 was observed. The focus diameter ( approximately lambda2) was measured by Raman imaging the focal region on a Si surface. The requirements of the parabolic mirror in terms of alignment accuracy were experimentally determined as well.     

Synthesis and optical properties research of gold nanoparticles with different morphologies

本文制备了不同形貌的金纳米颗粒,并对其形貌对光学性能的影响进行了研究。本文用还原法制备了不同粒径的金纳米颗粒,采用晶种生长法成功地制备出了星形、梭形和棒状的金纳米颗粒。颗粒的形貌和大小并采用投射电子显微镜(TEM)进行了表征,结果说明,本文成功制备出了不同形貌大小的金纳米颗粒。UV-Vis光谱和拉曼光谱仪对制备的颗粒的表征测试说明,不同形貌大小对颗粒有着不同的光学性能。拉曼光谱的结果说明,不同形貌大小的金纳米颗粒可以用作不同浓度分子的探针,对物质进行检测。     

Note: tip enhanced Raman spectroscopy with objective scanner on opaque samples

We report on 14 nm lateral resolution in tip-enhanced Raman spectroscopy mapping of carbon nanotubes with an experimental setup that has been designed for the analysis of opaque samples in confocal side-access through a novel piezo-driven objective scanner. The objective scanner allows for fast and stable laser-to-tip alignment and for the adjustment of the focus position with sub-wavelength precision to optimize the excitation of surface plasmons. It also offers the additional benefit of imaging the near-field generated Raman scattering at the gap between tip and sample as direct control of the tip enhancement.     

Probing confined fields with single molecules and vice versa

Single dye molecules are used as local probes to map the spatial distribution of the squared electric field components in the focus of a high numerical aperture lens. Simulated field distributions are quantitatively verified by experimentally obtained fluorescence excitation maps. We show that annular illumination can be used to engineer the field distribution in the focus at a dielectric/air interface such that electric field components in all directions acquire comparable magnitudes. The 3D orientation of molecular absorption dipoles can be determined by comparing measured to simulated image patterns. The presence of longitudinal electric field components in a focus is of particular interest in tip-enhanced scanning near-field optical microscopy.     

Candle Soot as Particular Lubricant Additives

An onion-like carbon material was prepared from candle soot, and its tribological properties as an additive were investigated in water. The material assumed a spherical shape with a layered nanostructure based on high-resolution transmission electron microscopic analysis and had considerable sp² hybrid carbon as revealed by Raman spectroscopy. The tribological properties were determined on an optimal SRV-IV oscillating reciprocating friction and wear tester. The results indicate that these candle soots as additives are able to effectively reduce both the friction and wear of sliding pairs in water. In addition, the chemical reactivity, physical stability, surface charge, and size of candle soot had a key impact on their lubrication properties. Based on our characterization of the wear scars by scanning electron microscopy and in situ Raman spectroscopy, we suggest a rolling and sliding lubrication mechanism.     

Characterization of human ovarian teratoma hair by using AFM, FT-IR, and Raman spectroscopy

The structural, physical, and chemical properties of hair taken from an ovarian teratoma (teratoma hair) was first examined by atomic force microscopy (AFM), Fourier transform infrared (FT-IR), and Raman spectroscopy. The similarities and differences between the teratoma hair and scalp hair were also investigated. Teratoma hair showed a similar morphology and chemical composition to scalp hair. Teratoma hair was covered with a cuticle in the same manner as scalp hair and showed the same amide bonding modes as scalp hair according to FT-IR and Raman spectroscopy. On the other hand, teratoma hair showed different physical properties and cysteic acid bands from scalp hair: the surface was rougher and the adhesive force was lower than the scalp hair. The cystine oxides modes did not change with the position unlike scalp hair. These differences can be understood by environmental effects not by the intrinsic properties of the teratoma hair.     

Strength in numbers: probing and understanding intermolecular bonding with chemical force microscopy

Scanning probe microscopy (SPM) provided researchers with a simple, intuitive, and versatile tool for probing intermolecular interactions using SPM probes functionalized with distinct chemical species. Chemical force microscopy (CFM) was developed as a way to probe and map these interactions in a rational and systematic way. But does the rupture strength of a bond measured in these experiments provide the definitive and useful information about the interaction? The answer to this question is closely linked to understanding the fundamental physics of bond rupture under an external loading force. Even a simple model shows that bond rupture can proceed in a variety of different regimes. I discuss the approaches for extracting quantitative information about the interaction from these experiments and show that even though the measured rupture force is almost never unique for a given bond, force spectroscopy measurements can still determine the essential interaction parameters.     

Apertureless near-field scanning Raman microscopy using reflection scattering geometry

The combination of near-field scanning optical microscopy and Raman spectroscopy provides chemical/structural specific information with nanometer spatial resolution, which are critically important for a wide range of applications, including the study of Si devices, nanodevices, quantum dots, single molecules of biological samples. In this paper, we describe our near-field Raman study using apertureless probes. Our system has two important features, critical to practical applications. (1) The near-field Raman enhancement was achieved by Ag coating of the metal probes, without any preparation of the sample, and (2) while all other apertureless near-field Raman systems were constructed in transmission mode, our system works in the reflection mode, making near-field Raman study a reality for any samples. We have obtained the first 1D Raman mapping of a real Si device with 1s exposure time. This is a very significant development in near-field scanning Raman microscopy as it is the first demonstration that this technique can be used for imaging purpose because of the short integration time. In addition, the metal tips used in our set-up can be utilized to make simultaneous AFM and electrical mappings such as resistance and capacitance that are critical parameters for device applications.     

AFM characterization of biomolecules in physiological environment by an advanced nanofabricated probe

Many relevant questions in biology and medicine require both topography and chemical information with high spatial resolution. Several biological events that occur at the nanometer scale level need to be investigated in physiological conditions. In this regard Atomic Force Microscopy (AFM) is one of the most powerful tools for label‐free nanoscale characterization of biological samples in liquid environment. Recently, the coupling of Raman spectroscopy to scanning probe microscopies has opened new perspectives on this subject; however, the coupling of quality AFM spectroscopy with Raman spectroscopy in the same probe is not trivial. In this work we report about the AFM capabilities of an advanced high‐resolution probe that has been previously nanofabricated by our group for coupling with Raman spectroscopy applications. We investigate its use for liquid AFM measurements on biological model samples like lipid bilayers, amyloid fibrils, and titin proteins. We demonstrate topography resolution down to nanometer level, force measurement and stable imaging capability. We also discuss about its potential as nanoscale chemical probe in liquid phase. Microsc. Res. Tech., 2012. © 2012 Wiley Periodicals, Inc.     

Application of scanning probe microscopy to the characterization and fabrication of hybrid nanomaterials

Scanning probe microscopy (SPM) is a widely used experimental technique for characterizing and fabricating nanostructures on surfaces. In particular, due to its ability to spatially map variations in materials properties with nanometer spatial resolution, SPM is particularly well suited to probe the subcomponents and interfaces of hybrid nanomaterials, i.e., materials that are made up of distinct nanometer scale components with distinguishable properties. In addition, the interaction of the SPM tip with materials can be intentionally tuned such that local surface modification is achieved. In this manner, hybrid nanostructures can also be fabricated on solid substrates using SPM. This report reviews recent developments in the characterization and fabrication of hybrid nanomaterials with SPM. Specific attention is given to nanomaterials that consist of both organic and inorganic components including individual biomolecules mounted on inorganic substrates. SPM techniques that are particularly well suited for characterizing the mechanical and electrical properties of such hybrid systems in atmospheric pressure environments are highlighted, and specific illustrative examples are provided. This review concludes with a brief discussion of the remaining challenges and promising future prospects for this field.     

Wear characteristics of diamond-coated atomic force microscope probe

In atomic force microscope (AFM) applications, the wear of the probe is undoubtedly a serious concern since it affects the integrity of the measurements. In this work, wear tests were performed using an AFM with lateral force monitoring capability with the aim to better understand the wear characteristics of diamond-coated probes. For the assessment of the probe wear, a transmission electron microscope (TEM) as well as a scanning electron microscope were utilized. The degree of the probe wear was quantified using the Archard's wear equation. The structure of the diamond-coated probe was analyzed by using the TEM and Raman spectroscopy. From the experimental results, two different wear characteristics, the gradual wear and the abrupt fracture of the diamond coating, were observed. In the case of gradual wear, the wear coefficient of the diamond-coated probe slid against a silicon nitride specimen was about 10(-5)-10(-6). It was also found that the wear rate significantly decreased with increase in the sliding distance. Raman spectroscopy analysis showed that the difference in the chemical structure of the diamond coating may induce the different wear phenomena. These results may be effectively utilized for fundamental understanding of nano-wear characteristics of AFM probes.     

Unique laser-scanning optical microscope for low-temperature imaging and spectroscopy

Low-temperature optical characterization of single quantum nanostructures can reveal detailed information on structure-dependent properties of these materials. We describe the development of a unique laser-scanning optical microscope capable of low-temperature single molecule/particle imaging and spectroscopy. Making use of the magnification of a microscope objective, the laser- scanning scheme of the present microscope allows for high-repeatability imaging over large sample areas. The microscope is utilized to measure the low-temperature Raman scattering spectra of individual single-walled carbon nanotubes and single molecule fluorescence spectra of conjugated polymers. The developed low-temperature microscope can be applied to study a wide array of nanomaterials at a single particle level.     

拉曼光谱技术在石油化工领域应用进展

拉曼散射是物质一种分子光谱,可以获取物质结构和官能团信息,已经用于物质的定性分析。本文就拉曼光谱技术在石油化工行业的应用进行简述。结合化学计量学,拉曼光谱技术已经用于石油产品组成分析、燃料（汽油、柴油、航煤和生物柴油）质量指标测定、输油管线油品监控以及化工产品和石油产品在线监控等领域。拉曼光谱技术具有结果准确、分析速度快、操作简单、不破坏样品、多参数、便携以及可现场分析等优点,将在石油化工领域得到进一步推广应用。     

Optical complexities of living cytoplasm--implications for live cell imaging and photo-micromanipulation techniques

The ability to manipulate the intracellular environment within living cells and to monitor the cytosolic chemical changes which occur during cell stimulation has lead to major advances in our understanding of how cells read and respond to their environment. Perhaps the most powerful suite of techniques for achieving these dual objectives is based on the use of light (photons). Because cells are 'transparent', light has been used to both interrogate and manipulate the chemistry inside living cells, exploiting technical advances in both the physical and biochemical sciences. However, cells are neither transparent nor homogeneous with respect to their optical properties. The interface between light and the living cell cytoplasm thus represent an important, yet largely ignored, interface. There has been no review of the optical properties of cytoplasm and little discussion about how the optical properties of living cytoplasm influence the outcome of such measurements and manipulations. In this short review, we discuss the importance of understanding the optical properties of cytoplasm for such techniques and how imperfections in experimental interpretation can arise.     

State-of-the-art of non-destructive measurement of sub-surface material properties and damages

The possibilities of common non-destructive measuring techniques are reviewed in this paper for their applications in precision engineering. The grazing X-ray technique is believed to be a powerful improvement of the conventional X-ray techniques under both the diffraction mode and the fluorescent mode. Information of the crystallographic structure and chemical composition can be obtained to a nanometre resolution. Ultrasound can be used in scanning acoustic microscopy to give information on the physical or even chemical nature of superficial layers. Raman spectroscopy has now become an important tool for studying superficial structures, chemical composition and stresses in cyrstalline and amorphous materials: it is recommended to use this method especially for the investigation of monocrystalline silicon and germanium. The instrumented microindentation technique is a quasi- non-destructive technique for evaluating mechanical material properties like hardness and Young's modulus in a nanometre range. It can be used on any material that does not require special surroundings like a vacuum. Photothermal microscopy has been developed recently for the non-destructive testing of the local thermal properties of materials. By using the Mirage effect and its local measurement above the surface, a non-destructive depth profiling of surface damages can be obtained.