Jay Son
Park Systems Corp., South Korea

Introduction

Atomic Force Microscopy (AFM) has become an essential tool for nanoscale surface characterization, enabling high-resolution analysis of surface morphology, mechanical response, and functional properties across a broad range of materials. Its ability to image both conductive and insulating samples makes AFM especially valuable for studying crystalline surfaces, two-dimensional materials, and other nanoscale structures where localized surface information is critical.

Among AFM applications, atomic lattice imaging remains one of the most technically demanding measurements. Resolving periodic structures at the atomic scale requires not only a sharp probe and optimized imaging conditions, but also exceptional mechanical stability, low noise, and minimal thermal drift. These challenges become even more significant under ambient conditions, where environmental vibration, thermal fluctuation, and instability in the tip–sample interaction can obscure atomic-scale contrast.

To achieve stable atomic lattice imaging, the AFM platform must suppress mechanical noise while maintaining stable tip–sample geometry during small-scan measurements. A rigid low-noise mechanical structure, minimized mechanical loop, and low-drift scanner architecture are therefore essential for reproducible high-resolution imaging.

Park Systems developed the NX1 to address these requirements by combining a low-noise mechanical architecture with an AFM workflow for high-resolution imaging under ambient conditions.

Please also refer to the NX1 introduction video available at: https://bcove.video/4tIgI8M

Overview of NX1

The NX1 is Park Systems’ compact high-resolution AFM designed for stable atomic lattice imaging under ambient conditions. Developed in collaboration with Prof. Franz J. Giessibl at the University of Regensburg, the NX1 builds on the Orpheus II concept for ambient AFM operation while integrating Park Systems’ beam-bounce sensing and measurement workflow.

Its low-noise mechanical design, minimized mechanical loop, Kovarbased AFM core body, and precision XYZ tube scanner provide the stability required for small-scan high-resolution measurements.

The system also supports both standard AFM probes and optional qPlus sensor configurations for high-resolution AFM measurements. Figure 1 shows the NX1 with the SmartScan™ operating interface, where atomic-scale imaging results and real-time measurement signals are displayed during AFM operation.

AFM Architecture for Atomic-Scale Imaging

Atomic lattice imaging requires the AFM system to maintain highly stable tip–sample geometry during small-scan measurements. To support this requirement, the NX1 is designed with a rigid AFM architecture featuring a shortened mechanical loop between the probe and sample. By shortening and stiffening this mechanical path, the system reduces mechanical noise and improves high-resolution imaging stability.

The NX1 incorporates a Kovar-based AFM core body, a precision XYZ tube scanner, and a tungsten carbide stick–slip stage. Kovar, a nickel– cobalt ferrous alloy with a low thermal expansion coefficient, helps minimize thermal drift in the AFM core body. The XYZ tube scanner supports small-scan high-resolution imaging, while the stick–slip stage provides reliable positioning for approach and sample navigation. Together, these components establish the mechanical foundation for stable atomic-scale AFM measurements.

Figure 1. The full shot of NX1 with the SmartScanTM operating interface. The monitor displays atomic-scale imaging results and real-time measurement signals during AFM operation.

Figure 2. The AFM architecture of NX1. The compact Kovar-based AFM core body, XYZ tube scanner, and tungsten carbide stick–slip stage are designed to support stable atomic-scale imaging. *Kovar: nickel–cobalt ferrous alloy, Thermal Expansion Coefficient: 6 × 10⁻⁶ K⁻¹

Figure 3. Noise floor comparison between NX1 and a typical AFM. NX1 shows reduced vertical and lateral noise for stable high-resolution imaging.

Low Noise Floor and Reduced Thermal Drift

The stability of the AFM platform directly influences the quality and reproducibility of atomic lattice imaging. Even small vertical or lateral noise can obscure the periodic contrast of atomic structures, particularly when imaging over scan sizes of only a few nanometers. For this reason, the NX1 was designed to reduce mechanical noise and thermal drift through its low-noise mechanical architecture.

As shown in Figure 3, the NX1 demonstrates an order-of-magnitude reduction in both vertical and lateral noise compared with a typical AFM. The zero-scan vertical noise is reduced from 0.24 Å to 0.02 Å, while the zero-scan lateral noise is reduced from 1.40 Å to 0.04 Å. This low noise floor enables highly stable and repeatable atomic-resolution imaging under ambient conditions.

Intuitive Optical Access and Laser Beam Alignment

While the NX1 is optimized for high-resolution imaging, practical usability remains an important part of the system design. The beam-bounce detection module is separated from the AFM core body so that optical access and cantilever deflection detection can be provided without compromising the mechanical stability of the AFM core.

The NX1 uses beam-bounce deflection sensing to detect cantilever motion with high sensitivity. A superluminescent diode (SLD) provides low-coherence illumination to reduce optical interference, while laser alignment knobs allow the laser beam to be positioned on the cantilever. The reflected beam is then centered on the PSPD using steering mirror alignment knobs, simplifying the alignment process during setup.

The system also integrates an on-axis optical microscope that provides a direct view of the sample surface and AFM probe. This optical access helps users locate the region of interest and position the probe before high-resolution AFM measurement. Software-controlled LED illumination further improves visibility across different sample types, supporting efficient sample navigation and measurement preparation.

Figure 4. Laser beam alignment and optical vision of NX1. The laser beam alignment pathway enables cantilever deflection detection, while the on-axis optics provide a direct view of the sample surface.

Easy Probe Exchange and Measurement Versatility

Probe handling is an important part of practical AFM operation, particularly for high-resolution measurements where consistent probe positioning is required. Park Systems’ probe holder design incorporates prealigned probe chip carriers and kinematic mounting points to support consistent probe positioning and simplify probe handling.

The NX1 supports both standard AFM probes and optional qPlus sensor holder configurations, allowing users to select the appropriate sensor setup depending on the measurement purpose. The optional qPlus sensor holder provides compatibility with high-stiffness quartz tuning fork sensors for measurements requiring enhanced sensitivity to shortrange forces.

Figure 5. AFM probe holder and qPlus sensor holder for NX1. The system supports both standard AFM probes and optional qPlus sensors for high-resolution AFM measurements.

Atomic Lattice and Moiré Imaging on Two-Dimensional Materials

Atomic lattice imaging is a critical capability for evaluating crystalline surfaces and two-dimensional material systems, where local lattice periodicity, crystalline order, and moiré superlattice structures provide important information about the sample.

To demonstrate NX1 performance for these applications, four representative samples were selected: MoS₂ single crystal for LFM-based atomic lattice imaging on a layered two-dimensional semiconductor, Highly Oriented Pyrolytic Graphite (HOPG) as a reference material for FMM-based lattice imaging, and twisted bilayer graphene and WSe₂ on graphene for multi-scale FMM imaging of moiré structures.

Figure 6. Atomic lattice imaging of MoS₂ single crystal using NX1. Height and lateral signals measured by LFM clearly resolve the atomic lattice structure at a 3 nm scan size. The corresponding LFM measurement conditions were as follows: 256 × 256 pixels, scan rate of 16 Hz, and scan size at 3 × 3 nm².

Figure 6 shows atomic lattice imaging of MoS₂ single crystal, a layered two-dimensional semiconductor with a hexagonal lattice structure. MoS₂ was selected to evaluate atomic periodicity on a representative 2D crystal beyond graphite-based reference materials.

The sample was measured by Lateral Force Microscopy (LFM) at a 3 nm scan size, and the atomic lattice was clearly observed in both height and lateral signals. The measured lattice spacing of 3.164 Å agrees with the reference lattice constant of MoS₂, confirming consistent atomic-scale measurement.

Figure 7. Atomic lattice imaging of HOPG using NX1. FMM amplitude imaging resolves the periodic lattice structure of graphite at a 5 nm scan size. The corresponding FMM measurement conditions were as follows: 512 × 512 pixels, scan rate of 12 Hz, and scan size at 5 × 5 nm².

HOPG is widely used as a reference material for atomic-scale AFM imaging because of its well-defined layered graphite structure and known lattice spacing. As shown in Figure 7, Force Modulation Microscopy (FMM) amplitude imaging of HOPG at a 5 nm scan size resolves the periodic lattice structure of graphite.

The measured lattice spacing is consistent with the reference value of graphite, demonstrating the ability of NX1 to acquire stable atomic lattice images using FMM.

Beyond direct atomic lattice imaging, the NX1 also enables multi-scale imaging of moiré structures in two-dimensional material systems. Twisted bilayer graphene and WSe₂ on graphene were selected as representative moiré systems because they contain periodic structures across different length scales.

Figure 8. Multi-scale FMM imaging of twisted bilayer graphene and WSe₂ on graphene using NX1. Moiré patterns are observed at larger scan sizes, while atomic lattice features are resolved at smaller scan sizes. The corresponding FMM measurement conditions were as follows: 512 × 512 pixels, and scan rates of 12 Hz for twisted bilayer graphene and 8 Hz for WSe₂ on graphene. Scan sizes are indicated in each image.

Twisted bilayer graphene forms a moiré superlattice due to rotational misalignment between graphene layers, while WSe₂ on graphene forms moiré patterns due to lattice mismatch between the two materials. As shown in Figure 8, moiré patterns are observed at larger scan sizes, while atomic lattice features are resolved as the scan size is reduced, demonstrating the capability of NX1 for nanoscale-to-atomic-scale imaging of 2D material systems.

Conclusions

Advancements in AFM technology continue to expand the ability to characterize surfaces at increasingly smaller length scales, making stable atomic-scale imaging an important capability for modern materials research.

Park NX1 was developed to provide a practical high-resolution AFM platform for researchers pursuing atomic lattice imaging under ambient conditions. With its rigid low-noise mechanical architecture, minimized mechanical loop, Kovar-based AFM core body, precision XYZ tube scanner, and refined optical and probe workflow, the NX1 is designed to support stable and repeatable high-resolution measurements.

The atomic lattice and moiré imaging results presented in this note demonstrate the capability of NX1 for crystalline surfaces and two-dimensional material systems, supporting stable atomic-scale imaging under ambient conditions.