Search for: All records

Electric field-assisted atomic force microscopy (E-AFM)-based nanopatterning is a versatile and cost-effective nanomanufacturing technique for fabricating nanoscale features with high spatial resolutions. Here, we investigate the E-AFM-based nanopatterning of poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) thin films by combining systematic experimental measurements, finite-element simulations, and mechanistic modeling. A key finding of this study is the direct observation and mechanistic explanation of nanoscale protrusion formation under an applied electric field, arising from the coupled action of localized Joule heating and dielectrophoretic (DEP) forces at the AFM tip-film interface. Specifically, the localized Joule heating generates a confined softened zone beneath the biased tip, within which the DEP forces redistribute and attract PEDOT-rich domains toward the tip, leading to upward material transport and protrusion growth. Based on these coupled mechanisms, we developed a mathematical model that predicts protrusion formation as a function of applied bias and dwell time while incorporating relevant material parameters. The model captures feature-height evolution. The model captures the interaction between temperature-dependent viscosity and DEP-driven flow, yielding a scaling relation for feature-height evolution, while an empirical correction accounting for lateral microstructural reorientation improves the width prediction. Experiments over a range of voltage-dwell time combinations produced protrusion features with heights from approximately 8 to 37 nm and widths from approximately 232 to 378 nm, showing strong agreement with the model predictions. This framework achieves a coefficient of determination (R2 value) of 94.5% for feature height and 93.9% for empirically adjusted feature width. Overall, this combined experimental and theoretical framework provides both predictive capability and mechanistic insight into E-AFM-based nanopatterning. The identification of protrusion formation as a coupled thermo-electromechanical process, where Joule-induced softening and DEP-driven polymer redistribution act synergistically, offers a new physical understanding of feature formation in electrically assisted nanofabrication. The findings support the advancement of E-AFM as a controllable technique for fabricating nanoscale structures for various applications, such as advanced nanoelectronics, optoelectronics, and sensing devices. 

PEDOT: PSS is a widely used conductive polymer whose electrical performance depends strongly on doping level, microstructure, and domain connectivity. Although its bulk conductivity is well characterized, it is challenging to achieve controlled nanoscale modulation of conductivity on a continuous film. In this work, we demonstrate that electric-field-assisted atomic force microscopy (E-AFM) enables selective, localized modification of the electrical properties of PEDOT: PSS, allowing the formation of nanoscale regions of suppressed conductivity with and without measurable morphological changes. Direct-write patterning at 17.5 V, a scan speed of 0.5 µm/s, and a contact force of 2 nN produces protruding features with average heights of ~8 nm and widths of ~280 nm, while patterning at a lower voltage of 12.25 V results in only minor morphological changes (~2–3 nm). Despite these differences in surface morphology, conductive atomic force microscope (C-AFM) current mapping reveals a pronounced reduction in local conductivity within the patterned regions relative to the surrounding film. Furthermore, repeated C-AFM scanning at 3 V leads to conductivity reduction without measurable morphological modification, indicating that cumulative electrical stress alone can modify transport pathways. These observations are consistent with electrically driven processes such as localized Joule heating and partial de-doping that may alter percolative transport within the film. Together, the results demonstrate a resist-free, AFM-based direct-write approach for spatially controlling conductivity in PEDOT: PSS thin films, providing a foundation for nanoscale electrical patterning in conductive polymer systems. 

Crucial to plant development, ambient temperature triggers intricate mechanisms enabling adaptive responses to temperature variations. The precise coordination of chromatin modifications in shaping cell developmental fate under diverse temperatures remains elusive. Our study, integrating comprehensive transcriptome, epigenome profiling, and genetics, demonstrates that lower ambient temperature (16°C) partially restores developmental defects caused by H3K27me3 loss in prc2 mutants by specifically depositing H2A.Zub at ectopically expressed embryonic genes in Arabidopsis, such as ABA INSENSITIVE 3 (ABI3) and LEAFY COTYLEDON 1 (LEC1). This deposition leads to downregulation of these genes and compensates for H3K27me3 depletion. Polycomb-repressive complex 1 (PRC1)-catalyzed H2A.Zub and PRC2-catalyzed H3K27me3 play roles in silencing transcription of embryonic genes for post-germination development. Low-temperature-induced reduction of TOE1 protein level decelerates H2A.Z turnover at specific loci, sustaining repression of embryonic genes and alleviating requirement for PRC2-H3K27me3 at post-germination stage. Our findings offer mechanistic insights into the cooperative epigenetic layers, facilitating plant adaptation to varying environmental temperatures. 

The atomic force microscopy (AFM) technology is a promising method for nanofabrication due to the high tunability of this affordable platform. The quality inspection and control significantly impact the manufacturing effectiveness for realizing the functionality of the achieved nanochannel. Particularly, the surface characteristics of nanochannel sidewalls, which play a significant role in determining the quality of the nanomachined products, can not be accurately captured using conventional surface integrity metrics (e.g., surface roughness). Therefore, it is necessary to propose a method to quantitatively characterize the surface morphology and detect the abnormal parts/regions of the nanochannel sidewall. This paper presents a statistical process control approach derived from the self-affine fractal model to detect the sidewall surface anomalies. It evaluates changes in the self-affine fractal model parameters (standard deviation, correlation length, and roughness exponent), which can be used to signify the changes on the sidewall surface; the statistical distributions of these parameters are derived and used to develop control charts to allow inspection of the sidewall morphology. The approach was tested on the AFM-based nanomachined samples. The results suggest that the presented approach can effectively reflect the abnormal regions on the machined parts, which opens up a new avenue toward guiding the quality control and rework for process improvement for AFM-based nanomachining. 

Atomic force microscope (AFM)-based nanomanufacturing offers an affordable and easily deployable method for fabricating high-resolution nanopatterns. This study employs a comprehensive design of experiment (DOE) approach to investigate the effects of various parameters, such as voltage, speed, and vibration axis, on the width and depth of lithography patterns using electrical field and vibration-assisted lithography on PEDOT: PSS films. The DOE explores the effect of voltage and speed on the process of electrical field and vibration-assisted AFM-based nanopatterning in two vibration trajectories: a circular trajectory employing X and Y axis vibration and a reciprocating trajectory employing Y axis vibration. The results indicate that using circular XY-vibration with a low stiffness contact probe and optimized speed and voltage factors results in higher depth and width of the lithography patterns compared to Y-vibration alone at the same parameters as expected. In both cases, pattern width was dominantly controlled by the voltage. Regarding depth, in XY-vibration, the speed of the tip is the most significant factor, while for Y-vibration, voltage plays the most significant role. It is noteworthy that there is a minimum threshold of speed that can produce a pattern; for example, the high-speed level that produced patterns in the circular trajectory (XY-vibration) did not produce patterns in reciprocating motion (Y-vibration). In conclusion, the study demonstrates the significant impact of voltage, speed, and axis on the width and depth of the lithography patterns. These findings can be instrumental in developing and understanding AFM-based high-resolution nanofabrication techniques. 

Understanding the kinetics of nanobubbles encapsulated by ultrathin two-dimensional (2D) layered van der Waals crystal membranes on atomically flat substrates is important to the applications of 2D materials and the pursuit of 2D nanobubble technologies. Here, we investigate the controlled motion of monolayer molybdenum disulfide (MoS2)-encapsulated nanobubbles on flat hexagonal boron nitride substrates using atomic force microscopy (AFM). Our study reveals a distinct transition from standstill bubble deformations to stable, stepwise bubble translations on flat substrates. The membrane tension-dominated 2D nanobubble behaves like an elastic soft body in its collision interaction with the AFM tip. This delicate motion-control technique enables neighboring 2D nanobubbles to move closer and eventually coalesce into larger nanobubbles. These findings pave the way for high-precision manipulation of nanobubbles and facilitate the exploration of their emerging applications.