Investigation of the Effect of Thermal Annealing on Poly(3‐hexylthiophene) Nanofibers by Scanning Probe Microscopy: From Single‐Chain Conformation and Assembly Behavior to the Interfacial Interactions with Graphene Oxide

Poly(3‐hexylthiophene) (P3HT) has been widely used in devices owing to its excellent properties and structural features. However, devices based on pure P3HT have not exhibited high performance. Strategies, such as thermal annealing and surface doping, have been used to improve the electrical properties of P3HT. In this work, different from previous studies, the effect of thermal annealing on P3HT nanofibers are examined, ranging from the single polymer chain conformation to chain packing, and the interfacial interactions with graphene oxide (GO) at nanoscale dimensions, by using scanning tunneling microscopy (STM), atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). High‐resolution STM images directly show the conformational changes of single polymer chains after thermal annealing. The morphology of P3HT nanofibers and the surface potential changes of the P3HT nanofibers and GO is further investigated by AFM and KPFM at the nanoscale, which demonstrate that the surface potentials of P3HT decrease, whereas that of GO increases after thermal annealing. All of the results demonstrate the stronger interfacial interactions between P3HT and GO occur after thermal treatments due to the changes in P3HT chain conformation and packing order.     

Nanoscale Chemical Imaging Using Tip‐Enhanced Raman Spectroscopy: A Critical Review

Methods for chemical analysis at the nanometer scale are crucial for understanding and characterizing nanostructures of modern materials and biological systems. Tip‐enhanced Raman spectroscopy (TERS) combines the chemical information provided by Raman spectroscopy with the signal enhancement known from surface‐enhanced Raman scattering (SERS) and the high spatial resolution of atomic force microscopy (AFM) or scanning tunneling microscopy (STM). A metallic or metallized tip is illuminated by a focused laser beam and the resulting strongly enhanced electromagnetic field at the tip apex acts as a highly confined light source for Raman spectroscopic measurements. This Review focuses on the prerequisites for the efficient coupling of light to the tip as well as the shortcomings and pitfalls that have to be considered for TERS imaging, a fascinating but still challenging way to look at the nanoworld. Finally, examples from recent publications have been selected to demonstrate the potential of this technique for chemical imaging with a spatial resolution of approximately 10 nm and sensitivity down to the single‐molecule level for applications ranging from materials sciences to life sciences.     

Simultaneous pit generation and visualization of pit topography using combined atomic force–scanning electrochemical microscopy

Combined atomic force microscopy–scanning electrochemical microscopy (AFM–SECM) is for the first time used to generate single corrosion pits on passivating iron surfaces in the micrometer range. The AFM–SECM probe locally generates nitric acid during the oxidation of nitrite ions with the release of protons at selected sites on the surface of the otherwise passive metal. High confinement of passive film breakdown is achieved from the combination of a small probe size and the inhibiting properties of non-reacted nitrite ions on the surrounding passivated surface. Simultaneous visualization of pit nucleation and propagation can be obtained in the same solution without changing the probe by AFM.     

Adsorption and desorption processes of self-assembled monolayers studied by surface-sensitive microscopy and spectroscopy

Adsorption and desorption processes of self-assembled monolayers (SAMs) have been studied on an Au(111) surface by scanning tunnelling microscopy (STM), atomic force microscopy (AFM), X-ray photo-electron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). At the initial growth stage, the ordered nucleation of SAM located at the herringbone turns of the Au(111) − (22 × √3) surface reconstruction and diffusion-controlled domain formation have been imaged by STM and AFM. Details of the oxidation process in UV desorption were also investigated by XPS. In addition, the dimerization reaction during desorption was confirmed by TDS for the first time in the alkanethiol SAM system.     

AFM and STM investigations of hydrogenated amorphous silicon: topography and barrier heights

As-grown films of hydrogenated amorphous silicon (a-Si?:?H, highly phosphorous-doped) were investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Hills up to 10 nm in height and 10 to 20 nm in diameter have been observed by AFM. By using STM in a new high-sensitivity mode, (1) atomically smooth areas (roughness about 0.3 Å rms) which occur at the top of the hills, (2) subnanometer structures several Å in height which cover large parts of the surface have been identified. Simultaneous measurements of the local apparent barrier heights (LABH) show a clear correlation to the topography. Areas showing subnanometer structures have always low LABHs while the highest values of the LABH occur on the smooth areas.     

Recent progress in probing atomic and molecular quantum coherence with scanning tunneling microscopy

Quantum coherent physics and chemistry concern the creation and manipulation of an excited-state manifold that contains the superposition and entanglement of multiple quantum levels. Electromagnetic waves such as light and microwave can be used to generate and probe different quantum coherent phenomena. The recent advances in scanning tunneling microscopy (STM) techniques including ultrafast laser coupled STM and electron spin resonance STM combine electromagnetic excitation with tunneling electron detection, bringing the investigation of quantum coherence down to the atomic and molecular level. Here, we survey the latest STM studies of different quantum coherent phenomena covering molecular vibration, electron transfer, surface plasmon resonance, phonon, spin oscillation, and electronic transition, and discuss the state and promise of characterizing and manipulating quantum coherence at the atomic or molecular scale.     

Enhanced feature analysis using wavelets for scanning probe microscopy images of surfaces

In this work we develop wavelet theory for the analysis of surface topography images obtained by scanning probe microscopy (SPM) such as atomic force microscopy (AFM). Wavelet transformation is localized in space and frequency, which can offer an advantage for analyzing information on surface morphology and topography. Wavelet transformation is an ideal tool to detect trends, discontinuities, and short periodicities on a surface. Additionally, wavelets can be used to remove artifacts and noise from scanning microscopy images. In terms of 3-D image analysis, discrete wavelet transform can capture patterns at all relevant frequency scales, thus providing a level of image analysis that is not possible otherwise. It is also possible to use the methodology for analyzing surface structures at the molecular level. The results demonstrate superior capabilities of wavelet approach to scanning probe microscopy image analysis compared to traditional analysis techniques.     

Solvent- and Temperature-Dependent Assembly in Monolayer Films of a Ferrocene-Naphthyridine Hybrid on HOPG

The formation of a monolayer film of bis-naphthyridyl ferrocene on highly oriented pyrolytic graphite (HOPG) at ambient conditions is demonstrated. The films are prepared by drop casting from different solvents. The microscopic structure of the films is understood using atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). The analysis reveals two different types of Phases (I and II) in the films and the relative percentage of these phases depends on the nature of the solvents used for the preparation and the thermodynamical condition. Solvents like methanol, acetonitrile and DMF exclusively select Phase-I, whereas acetone and ethanol show a mix of both phases at room temperature. The different phases are formed by different conformers of the molecule. We also show that the selectivity of one of the phases over the other is related to the difference in the energetics for the formation of these phases.     

STM studies on porphyrins

Porphyrins are promising components to be used in molecular electronics due to their rich electronic/photonic properties. Preparation of supramolecular architectures of porphyrins on solid surfaces would constitute a basis for further development toward molecular circuitry or other constructs for molecular electronics applications. Assemblies on surfaces can be probed with scanning tunneling microscopy (STM) at submolecular resolutions to reveal the arrangements and conformations of molecules on an individual molecule basis. The electronic characteristics within a single porphyrin molecule can also be probed by means of the same technique. This review summarizes the status quo of STM studies on porphyrins on surfaces with regard to their assemblies, structures, and electronic properties at the single molecule level.     

Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by dip pen nanolithography

We report on DNA arrays produced by dip pen nanolithography (DPN) on a novel Au-Ag micropatterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting multi-instrument and multitechnique local detection and analysis. Moreover the smooth surface of the Au squares ( approximately 5-10 A roughness) allows AFM/STM to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label-free detection methods for DNA nanoarrays based on the use of scanning probes.     

基于扫描探针显微镜（SPM）的高密度信息存储

随着信息技术的飞速发展,高密度信息存储的研究成为国际上备受关注的研究领域。扫描探针显微技术（SPM）通过改变材料的光、电、磁等局域特性可以实现纳米尺度的信息存储,成为提高信息存储密度的最有效手段之一。本文从信息存储材料和技术角度综述了基于SPM的高密度信息存储最近的研究进展,并讨论了其将来的研究和发展方向。     

扫描探针显微镜在纳米加工中的应用

扫描探针显微镜不仅能对材料表面形貌进行原子级观测，还能够对单个的分子、原子及纳米粒子进行操纵。本文综述了扫描探针显微镜在纳米加工中对自组装单层膜的扫描探针刻蚀以及“蘸写笔”两方面的应用情况。     

Atomic Force Microscopy for Molecular Structure Elucidation

Using scanning probe microscopy techniques, at low temperatures and in ultrahigh vacuum, individual molecules adsorbed on surfaces can be probed with ultrahigh resolution to determine their structure and details of their conformation, configuration, charge states, aromaticity, and the contributions of resonance structures. Functionalizing the tip of an atomic force microscope with a CO molecule enabled atomic‐resolution imaging of single molecules, and measurement of their adsorption geometry and bond‐order relations. In addition, by using scanning tunneling microscopy and Kelvin probe force microscopy, the density of the molecular frontier orbitals and the electric charge distribution within molecules can be mapped. Combining these techniques yields a high‐resolution tool for the identification and characterization of individual molecules. The single‐molecule sensitivity and the possibility of atom manipulation to induce chemical reactions with the tip of the microscope open up unique applications in chemistry, and differentiate scanning probe microscopy from conventional methods for molecular structure elucidation. Besides being an aid for challenging cases in natural product identification, atomic force microscopy has been shown to be a powerful tool for the investigation of on‐surface reactions and the characterization of radicals and molecular mixtures. Herein we review the progress that high‐resolution scanning probe microscopy with functionalized tips has made for molecular structure identification and characterization, and discuss the challenges it will face in the years to come.     

Quantitative Assessment of Tip Effects in Single‐Molecule High‐Speed Atomic Force Microscopy Using DNA Origami Substrates

High‐speed atomic force microscopy (HS‐AFM) is widely employed in the investigation of dynamic biomolecular processes at a single‐molecule level. However, it remains an open and somewhat controversial question, how these processes are affected by the rapidly scanned AFM tip. While tip effects are commonly believed to be of minor importance in strongly binding systems, weaker interactions may significantly be disturbed. Herein, we quantitatively assess the role of tip effects in a strongly binding system using a DNA origami‐based single‐molecule assay. Despite its femtomolar dissociation constant, we find that HS‐AFM imaging can disrupt monodentate binding of streptavidin (SAv) to biotin (Bt) even under gentle scanning conditions. To a lesser extent, this is also observed for the much stronger bidentate SAv–Bt complex. The presented DNA origami‐based assay can be universally employed to quantify tip effects in strongly and weakly binding systems and to optimize the experimental settings for their reliable HS‐AFM imaging.     

Sequential electrochemical oxidation and site-selective growth of nanoparticles onto AFM probes

In this work, we reported an approach for the site-selective growth of nanoparticle onto the tip apex of an atomic force microscopy (AFM) probe. The silicon AFM probe was first coated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) through a chemical vapor deposition (CVD) method. Subsequently, COOH groups were selectively generated at the tip apex of silicon AFM probes by applying an appropriate bias voltage between the tip and a flat gold electrode. The transformation of methyl to carboxylic groups at the tip apex of the AFM probe was investigated through measuring the capillary force before and after electrochemical oxidation. To prepare the nanoparticle terminated AFM probe, the oxidized AFM probe was then immersed in an aqueous solution containing positive metal ions, for example, Ag+, to bind positive metal ions to the oxidized area (COOH terminated area), followed by chemical reduction with aqueous NaBH 4 and further development (if desired) to give a metal nanoparticle-modified AFM probe. The formation of a metal nanoparticle at the tip apex of the AFM probe was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA).     

Structure and Growth of Two-dimensional Ices at the Surfaces Probed by Scanning Probe Microscopy

Scanning probe microscopy(SPM) stands out as one of the most powerful tools for characterizing the solid surface and the adsorbed molecules with ?ngstr?m resolution in real space. In particular, this unique technique provides an unprecedented opportunity for directly probing the low-dimensional ices at surfaces. In this perspective, we first review the recent advances of scanning tunneling microscopy(STM) imaging of various two-dimensional(2 D) ice structures on metal[1-7], insulator[8-12], graphite[13-15] surfaces and under strong confinement[10, 16-19]. We then introduce that noncontact atomic-force microscopy(AFM) with a CO-terminated tip enables atomic imaging of a genuine 2 D ice grown on a hydrophobic Au(111) surface with minimal perturbation[20], paying particular attention to the growth processes at the edges of 2 D ice. In the end, we present an outlook on the future applications of 2 D ice as well as the relation between the 2 D and 3 D ice growth.     

Columnar mesophases based on zinc chlorophyll derivatives functionalized with peripheral dendron wedges

A chlorophyll derivative with a central zinc ion, a methoxy functionality at its 3(1)-position, and functionalized with a second-generation dendron (3,4-3,4,5)12G2-CH(2)OH at its 17(2)-position was synthesized starting from natural chlorophyll a (Chl a). This compound exhibits liquid crystalline (LC) behavior and its mesomorphic properties have been characterized by differential scanning calorimetry (DSC), polarisation optical microscopy (POM), powder X-ray diffraction (XRD), and scanning probe microscopy (SPM). A combination of powder XRD, high resolution scanning tunneling microscopy (STM), and atomic force microscopy (AFM) experiments revealed the formation of nano-segregated well-ordered columnar tubular superstructures consisting of about five molecules in the column stratum. These self-assembled columns are further self-organized into a two-dimensional oblique unit cell lattice. Semiconducting behavior of this compound has been studied by pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) method and charge carrier mobility values of ～10(-2) cm(2) V(-1) s(-1) are observed. Such organized columnar superstructures constructed from semisynthetic zinc chlorins are reminiscent of the tubular organization of the bacteriochlorophyll dyes in the light-harvesting chlorosomal antennae of green sulphur bacteria.     

The dependence of fractal dimension on measuring conditions of scanning probe microscopy

The fractal dimension of sputtered thin film surfaces was determined. Topography was measured using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). It can be shown that measuring conditions have an important influence on the topographic data and the obtained fractal dimension. This influence was investigated systematically. The results of STM- and AFM-measurements have been compared. The results for surfaces imaged with AFM give lower values for the fractal dimension than with STM. Measurements were carried out with a standard cantilever and so the data have been filtered. Dynamic behavior of the measuring system is influenced by scanning speed and loop gain factor. During measurement of topographic signal high scanning speed and low loop gain factor produce a low pass behavior and the fractal dimension will be varied. If there is a disturbance in addition to the topographic signal (e.g. a noise) we found power spectra with more than one linear part. The calculated fractal dimension especially depended on the density of measuring points in the profile. The experimental results were verified by calculated Weierstrass-Mandelbrot functions.     

The nature of alkanethiol self-assembled monolayer adsorption on sputtered gold substrates

A detailed study of the self-assembly and coverage by 1-nonanethiol of sputtered Au surfaces using molecular resolution atomic force microscopy (AFM) and scanning tunneling microscopy (STM) is presented. The monolayer self-assembles on a smooth Au surface composed predominantly of [111] oriented grains. The domains of the alkanethiol monolayer are observed with sizes typically of 5-25 nm, and multiple molecular domains can exist within one Au grain. STM imaging shows that the (4 x 2) superlattice structure is observed as a (3 x 2) structure when imaged under noncontact AFM conditions. The 1-nonanethiol molecules reside in the threefold hollow sites of the Au[111] lattice and aligned along its [112] lattice vectors. The self-assembled monolayer (SAM) contains many nonuniformities such as pinholes, domain boundaries, and monatomic depressions which are present in the Au surface prior to SAM adsorption. The detailed observations demonstrate limitations to the application of 1-nonanethiol as a resist in atomic nanolithography experiments to feature sizes of approximately 20 nm.     

Synthesis and adsorption of shape-persistent macrocycles containing polycyclic aromatic hydrocarbons in the rigid framework

Shape-persistent macrocycles with interiors in the nanometer regime were prepared by the oxidative cyclization of the appropriate bisacetylene precursors under high-dilution conditions. These compounds contain polycyclic aromatic hydrocarbons in the ring backbone and are decorated with extra annular oligoalkyl or silyl side groups. Interestingly, after depositing them on different surfaces and investigating the self-assembled structures by means of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), various nanostructures were observed. STM showed that these macrocycles are organized in two-dimensional (2D) layers, whereas AFM showed, in addition, the formation of 2D crystallites and one-dimensional fibrils. These results reveal the importance of the extra annular substitution of the macrocycles in creating patterned surfaces and nanoscale objects.