The authors would like to thank the Ministry of Science and Technology of Taiwan, for their financial support of this research under Contract Nos. MOST-102-2923-E-492- 001-MY3 (W. J. Lee) and NSC-102- 2112-M-005-003-MY3 (M. S. Ho). Support from the High-performance Computing of Taiwan in providing huge computing resources to facilitate this research is also gratefully acknowledged.

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The authors have nothing to disclose.

In this study, we demonstrate the fabrication of a self-assembled monolayer of C84 on a Si substrate through a novel annealing process (Figure 1). This process can also be used to prepare other kinds of nanoparticle-embedded semiconductor substrates. The C84-embedded Si substrate was characterized at the atomic scale using UHV-STM (Figure 2), field emission spectrometer, photo-luminescence spectroscopy, MFM and SQUID (Figure 3).
The adhesion strength corresponding to nanomechanical properties (i.e., stress) of the C84-embedded Si substrates can be measured using AFM (Figure 4). Our results demonstrate that the hardness of the proposed C84-embedded Si substrate is comparable to that of SiC and Si surfaces, making it applicable as an abrasive material for cutting tools as well as a film in MEMS devices.
In the simulation section, the von Mises strain (&#949;vM) analysis is capable to detect the local deformation of atomic structure, which is very difficult to be observed in experiment. However, it is not possible to characterize the phase transformation. Here, we suggest some useful indices such as coordination number and HA index23 to examine the phase transformation. In the setting of the indentation model, we have to point out that the size of the substrate in plan direction must be at least three times larger than diameter of the probe for eliminating the size effect and the boundary condition limitation, which would affect the dynamics and force flow of atoms.
In addition, due to the time limit of MD simulation, to study the indentation process, the probe should exert the specimen with a very fast speed compared to that in experiment. We note that such a loading speed is too high to come out the long-time atomic diffusion and migration behavior, but it is still suitable to observe and describe the plastic deformation behavior and material properties under mechanical loading24 because the results can be recognized as approximately quasi-static in nature25. An alternative theory, named Parallel Replica dynamics (PRD)26, has been developed to substantially accelerate the simulation time, but it requires heavy computing resources.
The data obtained from the MD simulation study is in agreement with the AFM indentation experiment (Figure 8); additionally, the hardness and reduced modulus of the C84-embedded Si substrate are comparable to other Si substrates. These data suggest that C84-embedded Si substrates can have significant impacts in optoelectronic and dilute magnetic semiconductor (DMS) nanodevices.

Fullerene molecules and the composite materials they comprise are distinctive among nanomaterials due to their excellent structural characteristics, electronic conductivity, mechanical strength, and chemical properties1-4. These materials have proven highly beneficial in a range of fields, such as electronics, computers, fuel cell technology, solar cells, and field emission technology5,6.
Among these materials, silicon carbide (SiC) nanoparticle composites have received particular attention thanks to their wide band gap, high thermal conductivity and stability, high electrical breakdown ability, and chemical inertness. These benefits are particularly obvious in optoelectronic devices, metal-oxide-semiconductor field-effect transistors (MOSFET), light-emitting diodes (LEDs), and high-power, high-frequency, and high-temperature applications. However, high density defects commonly observed on the surface of conventional silicon carbide can have detrimental effects on the electronic structure, even leading to device failure7,8. Despite the fact that the application of SiC has been studied since 1960, this particular unresolved problem remains.
The aim of this study was the fabrication of a C84-embedded Si substrate heterojunction and subsequent analysis to obtain a comprehensive understanding of the electronic, optoelectronic, mechanical, magnetic, and field emission properties of the resulting materials. We also addressed the issue of using numerical simulation to predict the characteristics of nanomaterials, through the novel application of molecular dynamics calculations.

<table><tbody><tr><td>Silicon wafer</td><td></td><td></td><td>Si(111). Type/Dopant: P/Boron; Resistivity: 0.05-0.1 Ohm&amp;#183;cm</td></tr><tr><td>Carbon, C&lt;sub&gt;84&lt;/sub&gt;</td><td>Legend Star</td><td></td><td>C&lt;sub&gt;84&lt;/sub&gt; powder, 98%</td></tr><tr><td>Hydrochloric acid</td><td>Sigma-Aldrich</td><td>84422</td><td>RCA, 37%</td></tr><tr><td>Ammonium</td><td>Choneye Pure Chemical</td><td></td><td>RCA, 25%</td></tr><tr><td>Hydrogen peroxide</td><td>Choneye Pure Chemical</td><td></td><td>RCA, 35%</td></tr><tr><td>Nitrogen</td><td>Ni Ni Air</td><td></td><td>high-pressure bottle, 95%</td></tr><tr><td>Tungsten</td><td>Nilaco</td><td>461327</td><td>wire, diameter 0.3 mm, tip</td></tr><tr><td>Sodium hydroxide</td><td>UCW</td><td>85765</td><td>etching Tungsten wire for tip</td></tr><tr><td>Acetone</td><td>Marcon Fine Chemicals</td><td>99920</td><td>suitable for liquid chromatography and UV-spectrophotometry</td></tr><tr><td>Methanol</td><td>Marcon Fine Chemicals</td><td>64837</td><td>suitable for liquid chromatography and UV-spectrophotometry</td></tr><tr><td>UHV-SPM</td><td>JEOL Ltd</td><td>JSPM-4500A</td><td>Ultrahigh Vacuum Scanning Tunneling Microscope and Ultrahigh Vacuum Atomic Force Microscope</td></tr><tr><td>Power supply</td><td>Keithley</td><td>237</td><td>High-Voltage Source-Measure Unit</td></tr><tr><td>SQUID</td><td>Quantum desigh</td><td>MPMS-7</td><td>Magnetic field strength: &amp;plusmn;7.0 Tesla, Temperature range: 2&amp;#8211;400 K, Magnetic-dipole range: 5&amp;nbsp;&amp;times;&amp;nbsp;10&lt;sup&gt;-7&lt;/sup&gt; &amp;#8211; 300 emu</td></tr><tr><td>ALPS</td><td>National Center for High-performance Computing, Taiwan</td><td></td><td>Advanced Large-scale Parallel Supercluster, 177Tflops; 25,600 CPU cores; 73,728 GB RAM; 1,074 TB storage</td></tr></tbody></table>

probing c84-embedded si substrate using scanning probe microscopy and molecular dynamics

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The characteristics of the C84-embedded Si surface, such as atomic resolution topography, local electronic density of states, band gap energy, field emission properties, nanomechanical stiffness, and surface magnetism, were examined using a variety of surface analysis techniques under ultra, high vacuum (UHV) conditions as well as in an atmospheric system. Experimental results demonstrate the high uniformity of the C84-embedded Si surface fabricated using a controlled self-assembly nanotechnology mechanism, represents an important development in the application of field emission display (FED), optoelectronic device fabrication, MEMS cutting tools, and in efforts to find a suitable replacement for carbide semiconductors. Molecular dynamics (MD) method with semi-empirical potential can be used to study the nanoindentation of C84-embedded Si substrate. A detailed description for performing MD simulation is presented here. Details for a comprehensive study on mechanical analysis of MD simulation such as indentation force, Young&#39;s modulus, surface stiffness, atomic stress, and atomic strain are included. The atomic stress and von-Mises strain distributions of the indentation model can be calculated to monitor deformation mechanism with time evaluation in atomistic level.

A monolayer of C84 molecules on a disordered Si(111) surface was fabricated using a controlled self-assembly process in a UHV chamber. Figure 1 shows a series of topographic images measured by UHV-STM with various degrees of coverage: (a) 0.01 ML, (b) 0.2 ML, (c) 0.7 ML, and (d) 0.9 ML. The electronic and optical properties of the C84 embedded Si substrate were also investigated using a variety of surface analysis techniques, such as STM and PL (Figure 2). The excellent material properties of the resulting samples demonstrate how nanotechnology can be used for the control of matter at the atomic- and nano-scales. The MFM and SQUID results in Figure 3 show the surface magnetism of C84 embedded substrate. Figure 4 presents the UHV-AFM results that refer to the nanomechanics of proposed substrate. Our experimental results demonstrate the potential of the C84 embedded silicon substrate as an alternative to semiconductor carbide in nanoelectronic devices for high-temperature, high-power, high-frequency applications as well as in magnetic and MEMS devices (in Figure 4).
In the simulation section, all the procedures are completed by using LAMMPS to perform the MD simulations. The mechanical properties (indentation force and contact stress) of the fullerene embedded substrate is calculated and shown in Figure 6. The von-Mises strain analysis of atoms at different time step are used to characterize the local deformation. The corresponding snapshots as a function of indentation depth can be seen in the inserts of Figure 6, which were calculated and visualized by OVITO. The results of indentation force as a function of indentation depth are used to calculate the hardness H (Figure 7a), reduced modulus Er (Figure 7b), and loading stiffness S (Figure 8) of the C84 monolayer. The results can be compare with that determined by experiment and provides a more detail point of view to interpret the variation of the mechanical property.
<img alt="Figure 1" src="/files/ftp_upload/54235/54235fig1.jpg" /> 
Figure 1: C84 Embedded Si substrate with different coverage. Series of STM topographic images (40 x 40 nm2) showing C84 molecules adsorbed on Si(111) surface at a negative sample bias of 2 V, as measured by UHV-STM with various degrees of coverage: (a) 0.01 ML, (b) 0.2 ML, (c) 0.7 ML, and (d) 0.9 ML.
<img alt="Figure 2" src="/files/ftp_upload/54235/54235fig2.jpg" /> 
Figure 2: Electronic properties measurements on C84 Embedded Si substrate. (a) I-V curves and differential derivative conductance (dI/dV) vs the voltage curve of a single self-assembled layer of C84, as determined by UHV-STM; (b) Field emission current density vs electric field curve; (c) Corresponding F-N plot of surface with embedded C84, as measured using a source-measure unit; (d) Photoluminescence spectrum of single self-assembled layer of C84. Re-print with permission from reference12. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54235/54235fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/54235/54235fig3.jpg" /> 
Figure 3: Surface magnetism on C84 Embedded Si substrate. (a) MFM image of Si Substrate embedded with C84; (b) Magnetization loop plotted against external magnetic field <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54235/54235fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/54235/54235fig4.jpg" /> 
Figure 4: Nanomechanical investigation on C84 Embedded Si substrate. Force-distance analysis of disordered Si surface, 7 x 7 surface, single self-assembled layer of C84 embedded within Si surface, and Si surface, as determined using UHV-AFM. Re-print with permission from reference11. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54235/54235fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/54235/54235fig5.jpg" /> 
Figure 5: Flow chart for establishing simulation model. The dramatic illustrate the setting in MD simulation from a single layer C84 and Si(111) 7 x 7 surface to a C84 monolayer embed into Si(111) 7 x 7 model. The detail procedures can be seen in the section 5 of protocol. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54235/54235fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/54235/54235fig6.jpg" /> 
Figure 6: Indentation force and Contact stress analysis. Indentation force (black) and Contact stress (blue) of C84 as a function of indentation depth. Inserts show the corresponding snapshots, where the different color indicates the corresponding von Mises strain (&#949;vM) of all atoms. To clear display the strain localization, only the atoms with &#949;vM &#62; 0.08 are shown in the snapshot. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54235/54235fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/54235/54235fig7.jpg" /> 
Figure 7: Hardness and reduced modulus analysis. (a) Hardness and (b) reduced modulus variation as a function of indentation depth for the C84 monolayer on Si surface. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54235/54235fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" src="/files/ftp_upload/54235/54235fig8.jpg" /> 
Figure 8: Loading stiffness analysis. Loading stiffness as a function of distance determined by MD simulations compared with that by AFM experiments for C84/Si. Modified from reference16. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54235/54235fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics at JoVE.com

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports the nanomaterial fabrication of a fullerene Si substrate inspected and verified by nanomeasurements and molecular dynamic simulation.

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The ...

probing-c84-embedded-si-substrate-using-scanning-probe-microscopy

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11.7K Views.  National Chung Hsing University. This paper reports the nanomaterial fabrication of a fullerene Si substrate inspected and verified by nanomeasurements and molecular dynamic simulation.

Video: Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Scanning-probe Single-electron Capacitance Spectroscopy

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the electronic quantum structure of small systems - including individual atomic dopants in semiconductors. Here we present a capacitance-based method, known as Subsurface Charge Accumulation (SCA) imaging, which is capable of resolving single-electron charging while achieving sufficient spatial resolution to image individual atomic dopants. The use of a capacitance technique enables observation of subsurface features, such as dopants buried many nanometers beneath the surface of a semiconductor material1,2,3. In principle, this technique can be applied to any system to resolve electron motion below an insulating surface.
As in other electric-field-sensitive scanned-probe techniques4, the lateral spatial resolution of the measurement depends in part on the radius of curvature of the probe tip. Using tips with a small radius of curvature can enable spatial resolution of a few tens of nanometers. This fine spatial resolution allows investigations of small numbers (down to one) of subsurface dopants1,2. The charge resolution depends greatly on the sensitivity of the charge detection circuitry; using high electron mobility transistors (HEMT) in such circuits at cryogenic temperatures enables a sensitivity of approximately 0.01 electrons/Hz&frac12; at 0.3 K 5.

Scanning-probe single-electron capacitance spectroscopy facilitates the study of single-electron motion in localized subsurface regions. A sensitive charge-detection circuit is incorporated into a cryogenic scanning probe microscope to investigate small systems of dopant atoms beneath the surface of semiconductor samples.

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the ...

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

Probing The Structure And Dynamics Of Nucleosomes Using Atomic Force Microscopy Imaging

Chromatin, which is a long chain of nucleosome subunits, is a dynamic system that allows for such critical processes as DNA replication and transcription to take place in eukaryotic cells. The dynamics of nucleosomes provides access to the DNA by replication and transcription machineries, and critically contributes to the molecular mechanisms underlying chromatin functions. Single-molecule studies such as atomic force microscopy (AFM) imaging have contributed significantly to our current understanding of the role of nucleosome structure and dynamics. The current protocol describes the steps enabling high-resolution AFM imaging techniques to study the structural and dynamic properties of nucleosomes. The protocol is illustrated by AFM data obtained for the centromere nucleosomes in which H3 histone is replaced with its counterpart centromere protein A (CENP-A). The protocol starts with the assembly of mono-nucleosomes using a continuous dilution method. The preparation of the mica substrate functionalized with aminopropyl silatrane (APS-mica) that is used for the nucleosome imaging is critical for the AFM visualization of nucleosomes described and the procedure to prepare the substrate is provided. Nucleosomes deposited on the APS-mica surface are first imaged using static AFM, which captures a snapshot of the nucleosome population. From analyses of these images, such parameters as the size of DNA wrapped around the nucleosomes can be measured and this process is also detailed. The time-lapse AFM imaging procedure in the liquid is described for the high-speed time-lapse AFM that can capture several frames of nucleosome dynamics per second. Finally, the analysis of nucleosome dynamics enabling the quantitative characterization of the dynamic processes is described and illustrated.

Here, we present a protocol to characterize nucleosome particles at the single-molecule level using static and time-lapse atomic force microscopy (AFM) imaging techniques. The surface functionalization method described allows for the capture of the structure and dynamics of nucleosomes in high-resolution at the nanoscale.

Chromatin, which is a long chain of nucleosome subunits, is a dynamic system that allows for such critical processes as DNA replication and transcription ...

Biochemistry

Characterizing Individual Protein Aggregates by Infrared Nanospectroscopy and Atomic Force Microscopy

The phenomenon of protein misfolding and aggregation results in the formation of highly heterogeneous protein aggregates, which are associated with neurodegenerative conditions such as Alzheimer&#8217;s and Parkinson&#8217;s diseases. In particular low molecular weight aggregates, amyloid oligomers, have been shown to possess generic cytotoxic properties and are implicated as neurotoxins in many forms of dementia. We illustrate the use of methods based on atomic force microscopy (AFM) to address the challenging task of characterizing the morphological, structural and chemical properties of these aggregates, which are difficult to study using conventional structural methods or bulk biophysical methods because of their heterogeneity and transient nature. Scanning probe microscopy approaches are now capable of investigating the morphology of amyloid aggregates with sub-nanometer resolution. We show here that infrared (IR) nanospectroscopy (AFM-IR), which simultaneously exploits the high resolution of AFM and the chemical recognition power of IR spectroscopy, can go further and enable the characterization of the structural properties of individual protein aggregates, and thus offer insights into the aggregation mechanisms. Since the approach that we describe can be applied also to the investigations of the interactions of protein assemblies with small molecules and antibodies, it can deliver fundamental information to develop new therapeutic compounds to diagnose or treat neurodegenerative disorders.

We describe the application of infrared nanospectroscopy and high-resolution atomic force microscopy to visualize the process of protein self-assembly into oligomeric aggregates and amyloid fibrils, which is closely associated with the onset and development of a wide range of human neurodegenerative disorders.

The phenomenon of protein misfolding and aggregation results in the formation of highly heterogeneous protein aggregates, which are associated with ...

Probing Surface Electrochemical Activity of Nanomaterials using a Hybrid Atomic Force Microscope-Scanning Electrochemical Microscope (AFM-SECM)

Scanning electrochemical microscopy (SECM) is used to measure the local electrochemical behavior of liquid/solid, liquid/gas and liquid/liquid interfaces. Atomic force microscopy (AFM) is a versatile tool to characterize micro- and nanostructure in terms of topography and mechanical properties. However, conventional SECM or AFM provides limited laterally resolved information on electrical or electrochemical properties at nanoscale. For instance, the activity of a nanomaterial surface at crystal facet levels is difficult to resolve by conventional electrochemistry methods. This paper reports the application of a combination of AFM and SECM, namely, AFM-SECM, to probe nanoscale surface electrochemical activity while acquiring high-resolution topographical data. Such measurements are critical to understanding the relationship between nanostructure and reaction activity, which is relevant to a wide range of applications in material science, life science and chemical processes. The versatility of the combined AFM-SECM is demonstrated by mapping topographical and electrochemical properties of faceted nanoparticles (NPs) and nanobubbles (NBs), respectively. Compared to previously reported SECM imaging of nanostructures, this AFM-SECM enables quantitative assessment of local surface activity or reactivity with higher resolution of surface mapping.

Probing Surface Electrochemical Activity of Nanomaterials using a Hybrid Atomic Force Microscope-Scanning Electrochemical Microscope AFM-SECM

Atomic force microscopy (AFM) combined with scanning electrochemical microscopy (SECM), namely, AFM-SECM, can be used to simultaneously acquire high-resolution topographical and electrochemical information on material surfaces at nanoscale. Such information is critical to understanding heterogeneous properties (e.g., reactivity, defects, and reaction sites) on local surfaces of nanomaterials, electrodes and biomaterials.

Scanning electrochemical microscopy (SECM) is used to measure the local electrochemical behavior of liquid/solid, liquid/gas and liquid/liquid interfaces. ...

Chemistry

Microscopic Visualization of Porous Nanographenes Synthesized through a Combination of Solution and On-Surface Chemistry

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly successful in the synthesis of graphene nanoribbons, nanographenes and intrinsically reactive and instable, yet attractive species. It is based on the combination of solution chemistry aimed at preparation of appropriate molecular precursors for further ultra-high vacuum surface assisted transformations. This approach also owes its success to an incredible development of characterization techniques, such as scanning tunneling/atomic force microscopy and related methods, which allow detailed, local characterization at atomic scale. While the surface-assisted synthesis can provide molecular nanostructures with outstanding precision, down to single atoms, it suffers from basing on metallic surfaces and often limited yield. Therefore, the extension of the approach away from metals and the struggle to increase productivity seem to be significant challenges toward wider applications. Herein, we demonstrate the on-surface synthesis approach for generation of non-planar nanographenes, which are synthesized through a combination of solution chemistry and sequential surface-assisted processes, together with the detailed characterization by scanning probe microscopy methods.

A combination of solution and surface assisted synthesis opens new directions in the atomically precise synthesis of nanostructures. Scanning tunneling microscopy (STM) supplemented by non-contact atomic force microscopy (nc-AFM) enables detailed characterization of newly designed and generated carbon-based nano-objects.

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly ...

Co-localizing Kelvin Probe Force Microscopy with Other Microscopies and Spectroscopies: Selected Applications in Corrosion Characterization of Alloys

Kelvin probe force microscopy (KPFM), sometimes referred to as surface potential microscopy, is the nanoscale version of the venerable scanning Kelvin probe, both of which measure the Volta potential difference (VPD) between an oscillating probe tip and a sample surface by applying a nulling voltage equal in magnitude but opposite in sign to the tip-sample potential difference. By scanning a conductive KPFM probe over a sample surface, nanoscale variations in surface topography and potential can be mapped, identifying likely anodic and cathodic regions, as well as quantifying the inherent material driving force for galvanic corrosion.
Subsequent co-localization of KPFM Volta potential maps with advanced scanning electron microscopy (SEM) techniques, including back scattered electron (BSE) images, energy dispersive spectroscopy (EDS) elemental composition maps, and electron backscattered diffraction (EBSD) inverse pole figures can provide further insight into structure-property-performance relationships. Here, the results of several studies co-localizing KPFM with SEM on a wide variety of alloys of technological interest are presented, demonstrating the utility of combining these techniques at the nanoscale to elucidate corrosion initiation and propagation.
Important points to consider and potential pitfalls to avoid in such investigations are also highlighted: in particular, probe calibration and the potential confounding effects on the measured VPDs of the testing environment and sample surface, including ambient humidity (i.e., adsorbed water), surface reactions/oxidation, and polishing debris or other contaminants. Additionally, an example is provided of co-localizing a third technique, scanning confocal Raman microscopy, to demonstrate the general applicability and utility of the co-localization method to provide further structural insight beyond that afforded by electron microscopy-based techniques.

Kelvin probe force microscopy (KPFM) measures surface topography and differences in surface potential, while scanning electron microscopy (SEM) and associated spectroscopies can elucidate surface morphology, composition, crystallinity, and crystallographic orientation. Accordingly, the co-localization of SEM with KPFM can provide insight into the effects of nanoscale composition and surface structure on corrosion.

Kelvin probe force microscopy (KPFM), sometimes referred to as surface potential microscopy, is the nanoscale version of the venerable scanning Kelvin ...

Parallel Active Cantilever Arrays in AFMS to Enable High-Throughput Inspections

Active Probe Atomic Force Microscopy with Quattro-Parallel Cantilever Arrays for High-Throughput Large-Scale Sample Inspection

An Atomic Force Microscope&#160;(AFM) is&#160;a powerful and versatile tool for nanoscale surface studies to capture 3D topography images of samples. However, due to their limited imaging throughput, AFMs have not been widely adopted for large-scale inspection purposes. Researchers have developed high-speed AFM systems to record dynamic process videos in chemical and biological reactions at tens of frames per second, at the cost of a small imaging area of up to several square micrometers. In contrast, inspecting large-scale nanofabricated structures, such as semiconductor wafers, requires nanoscale spatial resolution imaging of a static sample over hundreds of square centimeters with high productivity. Conventional AFMs use a single passive cantilever probe with an optical beam deflection system, which can only collect one pixel at a time during AFM imaging, resulting in low imaging throughput. This work utilizes an array of active cantilevers with embedded piezoresistive sensors and thermomechanical actuators, which allows simultaneous multi-cantilever operation in parallel operation for increased imaging throughput. When combined with large-range nano-positioners and proper control algorithms, each cantilever can be individually controlled to capture multiple AFM images. With data-driven post-processing algorithms, the images can be stitched together, and defect detection can be performed by comparing them to the desired geometry. This paper introduces principles of the custom AFM using the active cantilever arrays, followed by a discussion on practical experiment considerations for inspection applications. Selected example images of silicon calibration grating, highly-oriented pyrolytic graphite, and extreme ultraviolet lithography masks are captured using an array of four active cantilevers (&#34;Quattro&#34;) with a 125 &#181;m tip separation distance. With more engineering integration, this high-throughput, large-scale imaging tool can provide 3D metrological data for extreme ultraviolet (EUV) masks, chemical mechanical planarization (CMP) inspection, failure analysis, displays, thin-film step measurements, roughness measurement dies, and laser-engraved dry gas seal grooves.

Author Spotlight: Introduction to Active Probe Atomic Force Microscopy with Quattro-Parallel Cantilever Arrays

Large-scale sample inspection with nanoscale resolution has a wide range of applications, especially for nanofabricated semiconductor wafers. Atomic force microscopes can be a great tool for this purpose, but are limited by their imaging speed. This work utilizes parallel active cantilever arrays in AFMs to enable high-throughput and large-scale inspections.

An Atomic Force Microscope&#160;(AFM) is&#160;a powerful and versatile tool for nanoscale surface studies to capture 3D topography images of samples. ...

Large-area Scanning Probe Nanolithography Facilitated by Automated Alignment and Its Application to Substrate Fabrication for Cell Culture Studies

Scanning probe microscopy has enabled the creation of a variety of methods for the constructive (&#39;additive&#39;) top-down fabrication of nanometer-scale features. Historically, a major drawback of scanning probe lithography has been the intrinsically low throughput of single probe systems. This has been tackled by the use of arrays of multiple probes to enable increased nanolithography throughput. In order to implement such parallelized nanolithography, the accurate alignment of probe arrays with the substrate surface is vital, so that all probes make contact with the surface simultaneously when lithographic patterning begins. This protocol describes the utilization of polymer pen lithography to produce nanometer-scale features over centimeter-sized areas, facilitated by the use of an algorithm for the rapid, accurate, and automated alignment of probe arrays. Here, nanolithography of thiols on gold substrates demonstrates the generation of features with high uniformity. These patterns are then functionalized with fibronectin for use in the context of surface-directed cell morphology studies.

Here we present a protocol for wide-area scanning probe nanolithography enabled by the iterative alignment of probe arrays, as well as the utilization of lithographic patterns for cell-surface interaction studies.

Probing C₈₄-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

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