Electrostatic Force Microscopy Research Articles

The Anti-Flyaway/Frizz Effect by Inducing the α-Helical Structure Transition of Hair

In order to reduce chronic hair flyaways/frizz, both reducing and oxidizing agents have to be used, leaving aside the hair damage issues. This study presents changes in hair morphology caused by treatment with a shampoo containing only reducing agents, excluding oxidizing agents that affect critical hair damages. As a result of flyaway/frizz improvement rates calculated through monitoring of the area of light transmittance in the hair tresses, reducing agents, such as ammonium thioglycolate (ATG), L-cysteine, and sodium sulfite were found to be effective in decreasing hair flyaway/frizz. Additionally, the methods to maintain homeostasis and control damage caused by oxidation during washing were also used to see flyaway/frizz improvement rates. Measurements using electrostatic force microscopy (EFM) showed that the surface charge of hair tresses treated with shampoo containing reducing agents was lowered. Using Raman spectroscopic analysis, it has been suggested that these treatments with reducing agents induced a 3D structural transition of the hair from an α-helix to a random coil. In addition, this structural release was confirmed, identifying the reduction in the enthalpy of the α-helix using differential scanning calorimetry (DSC). Furthermore, we verified that this change causes no hair damage through a tensile strength test. Therefore, the formulation of shampoo with reducing agents can be used as an effective strategy to care for hair flyaway/frizz without hair damage issues.

Spatially resolved random telegraph fluctuations of a single trap at the Si/SiO2 interface

We use electrostatic force microscopy to spatially resolve random telegraph noise at the Si/SiO2 interface. Our measurements demonstrate that two-state fluctuations are localized at interfacial traps, with bias-dependent rates and amplitudes. These two-level systems lead to correlated carrier number and mobility fluctuations with a range of characteristic timescales; taken together as an ensemble, they give rise to a [Formula: see text] power spectral trend. Such individual defect fluctuations at the Si/SiO2 interface impair the performance and reliability of nanoscale semiconductor devices and will be a significant source of noise in semiconductor-based quantum sensors and computers. The fluctuations measured here are associated with a four-fold competition of rates, including slow two-state switching on the order of seconds and, in one state, fast switching on the order of nanoseconds which is associated with energy loss.

Direct Imaging of Charge/Dopant Distribution in PANI/PSS Thin Films Using Advanced Frequency Modulation Electrostatic Force Microscopy.

This paper presents a detailed study that maps the surface charges and dopant distribution on the electropolymerized thin film of polyaniline-poly(styrenesulfonate) (PANI/PSS). The focus is on two distinct states of PANI/PSS: the fully doped emeraldine salt (ES/PSS) and the dedoped emeraldine base (EB/PSS). This investigation utilizes advanced frequency modulation electrostatic force microscopy (FM-EFM) and atomic force microscopy (AFM). The polymer film comprises polymer grains, and FM-EFM data suggest a non-uniform distribution of dopants on the grain surface, with a higher doped periphery than the core. Quantifying the charge at the periphery and core of ES/PSS and EB/PSS grains provides unique insight into the charge distribution within the polymer film. The charge density is estimated to be 10 times higher in the periphery region (∼120 μC/cm2) than in the core region (∼11 μC/cm2) and 100 times higher than EB/PSS (∼0.8 μC/cm2). We have directly observed the morphological changes of PANI/PSS from the ES/PSS state to the EB/PSS state using the AFM topographic profile. These findings provide a better understanding of the behavior of the charge/dopant distribution on the surface of the polymer films and pave the way for further research and development of PANI/PSS-based electronic devices.

Long-distance electron transport in multicellular freshwater cable bacteria.

Filamentous multicellular cable bacteria perform centimeter-scale electron transport in a process that couples oxidation of an electron donor (sulfide) in deeper sediment to the reduction of an electron acceptor (oxygen or nitrate) near the surface. While this electric metabolism is prevalent in both marine and freshwater sediments, detailed electronic measurements of the conductivity previously focused on the marine cable bacteria (Candidatus Electrothrix), rather than freshwater cable bacteria, which form a separate genus (Candidatus Electronema) and contribute essential geochemical roles in freshwater sediments. Here, we characterize the electron transport characteristics of Ca. Electronema cable bacteria from Southern California freshwater sediments. Current-voltage measurements of intact cable filaments bridging interdigitated electrodes confirmed their persistent conductivity under a controlled atmosphere and the variable sensitivity of this conduction to air exposure. Electrostatic and conductive atomic force microscopies mapped out the characteristics of the cell envelope's nanofiber network, implicating it as the conductive pathway in a manner consistent with previous findings in marine cable bacteria. Four-probe measurements of microelectrodes addressing intact cables demonstrated nanoampere currents up to 200 μm lengths at modest driving voltages, allowing us to quantify the nanofiber conductivity at 0.1 S/cm for freshwater cable bacteria filaments under our measurement conditions. Such a high conductivity can support the remarkable sulfide-to-oxygen electrical currents mediated by cable bacteria in sediments. These measurements expand the knowledgebase of long-distance electron transport to the freshwater niche while shedding light on the underlying conductive network of cable bacteria.

Green and solid state reduction of GO monolayers sandwiched between Arachidic acid LB layers

A novel, single step and environment friendly solid state approach for reduction of graphene oxide (GO) monolayers has been demonstrated, in which, arachidic acid/GO/arachidic acid (AA/GO/AA) sandwich structure obtained by Langmuir-Blodgett (LB) technique was heat treated at moderate temperatures to obtain RGO sheets. Heat treatment of AA/GO/AA sandwich structure at 200 °C results in substantial reduction of GO, with concurrent removal of AA molecules. Such developed RGO sheets possess sp2-C content of ∼69 %, O/C ratio of ∼0.17 and significantly reduced I(D)/I(G) ratio of ∼1.1. Ultraviolet photoelectron spectroscopy (UPS) studies on RGO sheets evidenced significant increase in density of states in immediate vicinity of Fermi level and decrease in work function after reduction. Bottom gated field effect transistors fabricated with isolated RGO sheets displayed charge neutrality point at a positive gate voltage, indicating p-type nature, consistent with UPS and electrostatic force microscopy (EFM) measurement results. The RGO sheets obtained by heat treatment of AA/GO/AA sandwich structure exhibited conductivity in the range of 2–7 S/cm and field effect mobility of 0.03–2 cm2/Vs, which are comparable with values reported for RGO sheets obtained by various chemical/thermal reduction procedures. The extent of GO reduction is determined primarily by proximity of AA molecules and found to be unaltered with either escalation of heat treatment temperature or increase of AA content in sandwich structure. The single-step GO reduction approach demonstrated in this work is an effective way for development of RGO monolayers with high structural quality towards graphene-based electronic device applications.

Chirality-Induced Magnetic Polarization by Charge Localization in a Chiral Supramolecular Crystal.

The chirality-induced spin selectivity (CISS) effect is a fascinating phenomenon that correlates the molecular structure with electron spin-polarization (SP). Experimental procedures to quantify the spin-filtering magnitude have extensively used magnetic-field-dependent conductive AFM. In this work chiral crystals of imide-substituted coronene bisimide ((S)-CBI-GCH) are studied to explain the dynamics of the current-voltage I - V spectra and the origin of superimposed peaks are investigated. A dynamic voltage-sweep rate-dependent phenomenon can give rise to complex I - V curves. The redox group, capable of localization of charge, acts as a localized state that interferes with the continuum of the π - π stacking, giving rise to Fano resonances. A novel mechanism for dynamic transport is introduced, which provides insight into the origin of spin-polarized charge in crystallized CBI-GCH molecules after absorption on a metallic substrate, guided by transient charge polarization. Crucially, interference between charge localization and delocalization during transport may be important properties in understanding the magnetochiral phenomena observed by electrostatic force microscopy. Finally, it is observed that charge trapping sensitively modifies the injection barrier from direct tunneling to Fowler-Nordheim tunneling transport supporting nonlinearity in CISS for this class of molecules.

Length-based quantitative characterization of metallic and semiconducting single-wall carbon nanotubes using electrostatic force microscopy

Precise and quantitative evaluation of the semiconducting (or metallic) purity of single-wall carbon nanotubes (SWCNTs) is extremely significant, not only for obtaining an indicator on their separation process development, but also for the property analysis in their electronic applications. In this work, electrostatic force microscopy (EFM) was applied to quantify the semiconducting (s-) type purity for as-grown and separated SWCNT samples. Count-based and length-based analyses for hundreds of SWCNTs observed in EFM images were carried out. By analyzing 1826 SWCNTs of as-grown sample based on the count, the s-type purity was estimated around 77.8 %. On the other hand, the length-based analysis showed the s-type purity of 67.3 %. The latter result, suggesting approximately equal to the semiconducting purity of SWCNTs with a random chiral distribution, is probably because the length-based analysis provides weighted statistics that is more suitable for the quantitative evaluation, and supports the validity in terms of precision. Furthermore, it was also demonstrated that the length-based EFM analysis for 850 SWCNTs of s-type enriched SWCNTs showed the s-type purity of 98.6 %.

Needle in a haystack: Efficiently finding atomically defined quantum dots for electrostatic force microscopy.

The ongoing development of single electron, nano-, and atomic scale semiconductor devices would greatly benefit from a characterization tool capable of detecting single electron charging events with high spatial resolution at low temperatures. In this work, we introduce a novel Atomic Force Microscope (AFM) instrument capable of measuring critical device dimensions, surface roughness, electrical surface potential, and ultimately the energy levels of quantum dots and single electron transistors in ultra miniaturized semiconductor devices. The characterization of nanofabricated devices with this type of instrument presents a challenge: finding the device. We, therefore, also present a process to efficiently find a nanometer sized quantum dot buried in a 10 × 10 mm2 silicon sample using a combination of optical positioning, capacitive sensors, and AFM topography in a vacuum.

Determination of Surface Charge Density and Charge Mapping of CYTOP Film in Air using Electrostatic Force Microscopy.

Cyclic transparent optical polymer (CYTOP), a fluoropolymer, finds a plethora of applications in microelectronic devices for sustainable energy harvesting and memory devices. By and large, these devices demand high voltage breakdown, a high dielectric constant, transparency, charge storage, and retention capabilities. Despite many efforts, comprehensive investigation of the charge distribution, retention, and discharge studies conducted on the CYTOP film at the micro-scale remains elusive. Here, we present direct quantification and mapping of surface charge on the CYTOP surface at room temperature using two different modes of advanced surface probe microscopy i.e., Kelvin probe force microscopy (KPFM) and electrostatic force microscopy (EFM). We estimated that the surface charge densities of the CYTOP film using EFM are 1.4 and 3.3 μC/cm2 for the injection of positive and negative charges, respectively. Furthermore, we determined the charge retention time for both injected positive and negative charges. We found that the retention capacity of the negative charges on the CYTOP film is much higher as compared to the positive charges. Moreover, it is also observed that injected negative charges are strongly localized on the CYTOP surface compared to the positive counterpart. Additionally, we demonstrated that charge writing is possible on the CYTOP surface using the AFM conductive tip. These results may find potential applications in energy harvesting, sensing, memory devices, security, and surveillance.

2D Axisymmetric Simulation Model of Electrostatic Force Microscopy for Detecting Buried Carbon Nanotubes in Poly(methyl methacrylate) Matrix

2D Axisymmetric Simulation Model of Electrostatic Force Microscopy for Detecting Buried Carbon Nanotubes in Poly(methyl methacrylate) Matrix

Heterodyne High-Harmonic Electrostatic Force Microscopy with Improved Spatial Resolution for Nanoscale Identification of Metallic/Semiconducting Carbon Nanotubes.

There are two main types of carbon nanotubes (CNTs): metallic and semiconducting. Naturally grown CNTs are randomly distributed, posing challenges in distinguishing between the two types. Here, a novel approach for nanoscale high-resolution imaging and identification of CNTs was introduced by incorporating the heterodyne technique into high-harmonic electrostatic force microscopy (HH-EFM) on an atomic force microscopy (AFM) platform. In the developed heterodyne HH-EFM, a more localized high-order gradient of tip-sample nonlinear interaction force is used as signal channels, resulting in an improved spatial resolution, compared to the conventional HH-EFM. Furthermore, the heterodyne HH-EFM also has the capability to visualize material carrier density and assess qualitative carrier transport performance. Our work not only presents a new approach to identifying/exploring electrical properties of low-dimensional nanomaterials but also provides a solution for optimizing resolution in long-range interaction-based functional AFM technologies.

Study of the electronic transport performance of ZnO-SiO2 film: the construction of grain boundary barrier

Purpose The purpose of this study is to adjust the electronic transport performance of zinc oxide–silicon dioxide (ZnO-SiO2) film by the construction of a grain boundary barrier. Design/methodology/approach ZnO-SiO2 thin films were prepared on glass substrates by a simple sol-gel method. The crystal structure of ZnO and ZnO-SiO2 powders were tested by X-ray diffraction with copper (Cu) Kα radiation. The absorption spectra of ZnO and ZnO-SiO2 films were recorded by a ultraviolet-visible spectrophotometer. The micro electrical transport performance of ZnO-SiO2 thin films were investigated by conductive atomic force microscope and electrostatic force microscope. Findings The results show that the current of ZnO-SiO2 film decrease, indicating that the mobility of ZnO-SiO2 film is greatly decreased, owing to the formation of the grain boundary barrier between ZnO and SiO2. The phase variation of ZnO-SiO2 film increases due to the electron accumulation at grain boundaries. Originality/value ZnO and ZnO-5SiO2 thin films prepared on glass substrates by a simple sol-gel method were first studied by CAFM and EFM. The band gaps of ZnO and ZnO-5SiO2 is ∼3.05 eV and 3.15 eV, respectively. The barrier height of ZnO-5SiO2 film increased by ∼0.015 eV after introducing SiO2. The phase variation intensity increased to a certain extent after doping SiO2, due to the increased GB barrier. ZnO-5SiO2 film will be a promising ETL candidate in the application of QLEDs field.

Phloroglucinol-Based Carbon Quantum Dots/Polyurethane Composite Films: How Structure of Carbon Quantum Dots Affects Antibacterial and Antibiofouling Efficiency of Composite Films.

Nowadays, bacteria resistance to many antibiotics is a huge problem, especially in clinics and other parts of the healthcare system. This critical health issue requires a dynamic approach to produce new types of antibacterial coatings to combat various pathogen microbes. In this research, we prepared a new type of carbon quantum dots based on phloroglucinol using the bottom-up method. Polyurethane composite films were produced using the swell-encapsulation-shrink method. Detailed electrostatic force and viscoelastic microscopy of carbon quantum dots revealed inhomogeneous structure characterized by electron-rich/soft and electron-poor/hard regions. The uncommon photoluminescence spectrum of carbon quantum dots core had a multipeak structure. Several tests confirmed that carbon quantum dots and composite films produced singlet oxygen. Antibacterial and antibiofouling efficiency of composite films was tested on eight bacteria strains and three bacteria biofilms.

Transformative Multifunction Deep Ultraviolet Photodetectors for On-Demand Applications: From Fast Optical Communication to Tunable In-Sensor Photocurrent Integration.

The strategic utilization of photodetectors' transient response could open new frontiers from free-space optical communication to the emerging field of neuromorphic optoelectronics. Contrarily, while communication requires a fast response, neuromorphic applications benefit from a slow and integrative transient photocurrent. By integrating these functionalities in a single device, this study unveils a photodetector with tunable responses, bridging the gap between optical communication and neuromorphic sensing and creating a versatile platform with on-demand applications. Particularly, a Ga2O3-based photodetector was designed, exhibiting a photocurrent on/off ratio close to 104, high responsivity of 0.43 A/W, and detectivity 1.22 × 1013 Jones under deep ultraviolet illumination (λ ∼ 260 nm). The photodetector demonstrates transient time-dependent on operational voltage, ranging from 10-4 to 0.2 s. The underlying mechanism is attributed to the voltage-dependent balance between photocarrier generation and defect-related recombination, as revealed by electrostatic force microscopy. Additionally, we have demonstrated potential applications, including digital Morse code interpretation, tunable integration of optical inputs within the sensor, one-time readouts, and effective analog Morse code reading. Furthermore, the effectiveness of input information recognition using analog integration, even with anomalies, was demonstrated. This work establishes a versatile approach for tunable in-sensor optical processing, potentially useful for a wide range of applications, from free-space optical communication to neuromorphic sensing.

Characterization of heterogeneity of CVD graphene on copper foil by scanning probe microscopy and Raman spectroscopy

The comparative analysis of the structural, morphological, and local electrical properties of CVD graphene films synthesized at atmospheric and low pressure CVD growth conditions was carried out. The use of electrical techniques of scanning probe microscopy, such as Kelvin probe force microscopy, scanning capacitance microscopy, electrostatic force microscopy, and conductive atomic-force microscopy for investigation of heterogeneous graphene coverage was discussed. A significant change in the surface potential values was observed indicating the formation of p-type multilayered graphene domains on single layer graphene at low pressure and n-type multilayered graphene films at atmospheric pressure CVD. The effect of Ar flow rate increasing during cooling stage in the temperature range of 700–200 °C causing graphite formation was described. The employment of surface potential spectroscopy allows to indicate the presence of nonlinear phenomena in heterogeneous graphene.

Structural, electrostatic force microscopy, work function, and optical characterization of pure and Al-doped ZnO nanoparticles

The electrical and optical characteristics of pure and Al-doped zinc oxide (ZnO) nanoparticles were analyzed. The work function of these nanoparticles was investigated using Kelvin Probe Force Microscopy (KPFM). The work function of the Al-doped ZnO nanoparticles was found to be lower than that of undoped ZnO nanoparticles. Electrostatic Force Microscopy (EFM) was employed to map the distribution of charges and conductivity in both ZnO and Al -doped ZnO, revealing enhanced charge trapping and increased conductivity in the Al-doped ZnO nanoparticles compared to the undoped ones. XRD analysis verified that both pure ZnO and Al-doped ZnO nanoparticles exhibited a hexagonal wurtzite crystal structure. Additionally, Raman spectroscopy revealed new vibrational modes at 572 cm−1, which were attributed to E1 (LO) in Al-doped ZnO. UV–visible spectroscopy indicated that the band gap of Al -doped ZnO nanoparticles is wider than that of pure ZnO nanoparticles, Additionally, photoluminescence spectroscopy demonstrated a blue shift in the emission spectrum of the Al-doped ZnO nanoparticles, accompanied by a reduction in green emission defects.

Nanoscale visualization of fast carrier dynamics in organic thin-film transistors by time-resolved electrostatic force microscopy

Fast carrier dynamics in organic thin-film transistors (OTFTs) was investigated by time-resolved electrostatic force microscopy (tr-EFM). We found that the carrier diffusion in the OTFTs proceeded in two stages: fast diffusion and slow diffusion. By applying the instantaneous frequency method to EFM, the temporal evolution of the spatial distribution of fast carriers in the channel region of the OTFTs, which took place on the timescale of several hundreds of nanoseconds, was evaluated. The inhomogeneous distribution of the local decay time constant showed that the carrier diffusion of the OTFTs was limited by the grain boundaries between each crystalline region. The quantitative capability of the method was verified by comparing the values of the carrier mobility estimated by the tr-EFM measurement and a numerical simulation. The mobility estimated from the experiment and the simulation showed good agreement, showing the possibility of the tr-EFM to evaluate the time evolution of dynamic phenomena in semiconductor devices.

Antibacterial and Antibiofouling Activities of Carbon Polymerized Dots/Polyurethane and C60/Polyurethane Composite Films.

The cost of treatment of antibiotic-resistant pathogens is on the level of tens of billions of dollars at the moment. It is of special interest to reduce or solve this problem using antimicrobial coatings, especially in hospitals or other healthcare facilities. The bacteria can transfer from medical staff or contaminated surfaces to patients. In this paper, we focused our attention on the antibacterial and antibiofouling activities of two types of photodynamic polyurethane composite films doped with carbon polymerized dots (CPDs) and fullerene C60. Detailed atomic force, electrostatic force and viscoelastic microscopy revealed topology, nanoelectrical and nanomechanical properties of used fillers and composites. A relationship between the electronic structure of the nanocarbon fillers and the antibacterial and antibiofouling activities of the composites was established. Thorough spectroscopic analysis of reactive oxygen species (ROS) generation was conducted for both composite films, and it was found that both of them were potent antibacterial agents against nosocomial bacteria (Klebsiela pneumoniae, Proteus mirabilis, Salmonela enterica, Enterococcus faecalis, Enterococcus epidermis and Pseudomonas aeruginosa). Antibiofouling testing of composite films indicated that the CPDs/PU composite films eradicated almost completely the biofilms of Pseudomonas aeruginosa and Staphylococcus aureus and about 50% of Escherichia coli biofilms.

Probing Polymorphic Stacking Domains in Mechanically Exfoliated Two-Dimensional Nanosheets Using Atomic Force Microscopy and Ultralow-Frequency Raman Spectroscopy.

As one of the key features of two-dimensional (2D) layered materials, stacking order has been found to play an important role in modulating the interlayer interactions of 2D materials, potentially affecting their electronic and other properties as a consequence. In this work, ultralow-frequency (ULF) Raman spectroscopy, electrostatic force microscopy (EFM), and high-resolution atomic force microscopy (HR-AFM) were used to systematically study the effect of stacking order on the interlayer interactions as well as electrostatic screening of few-layer polymorphic molybdenum disulfide (MoS2) and molybdenum diselenide (MoSe2) nanosheets. The stacking order difference was first confirmed by measuring the ULF Raman spectrum of the nanosheets with polymorphic stacking domains. The atomic lattice arrangement revealed using HR-AFM also clearly showed a stacking order difference. In addition, EFM phase imaging clearly presented the distribution of the stacking domains in the mechanically exfoliated nanosheets, which could have arisen from electrostatic screening. The results indicate that EFM in combination with ULF Raman spectroscopy could be a simple, fast, and high-resolution method for probing the distribution of polymorphic stacking domains in 2D transition metal dichalcogenide materials. Our work might be promising for correlating the interlayer interactions of TMDC nanosheets with stacking order, a topic of great interest with regard to modulating their optoelectronic properties.

Probing the surface electrical properties of clay minerals with electrostatic force microscopy and kelvin probe force microscopy

Many surface processes of clay minerals require in-depth understanding of their surface electrical properties, such as surface charge density, surface potential distribution, etc In this paper, electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM) were used to study the surface charge densities, surface potentials, electric field intensities, and electric field force gradients of three common clay minerals: kaolinite, montmorillonite, and illite. The properties were directly imaged, and the average surface permanent charge densities of kaolinite, montmorillonite, and illite were obtained to be −0.0060, −2.136, and −5.456 μC m−2, respectively. In addition, a good linear relationship was found between the surface charge densities obtained by KPFM and the layer charges calculated from the mineral chemical formulas of three clay minerals.