Measured Step Heights Research Articles

Perspective: imaging atomic step geometry to determine surface terminations of kagome materials and beyond

Here we review scanning tunneling microscopy research on the surface determination for various types of kagome materials, including 11-type (CoSn, FeSn, FeGe), 32-type (Fe3Sn2), 13-type (Mn3Sn), 135-type (AV3Sb5, A = K, Rb, Cs), 166-type (TbMn6Sn6, YMn6Sn6 and ScV6Sn6), and 322-type (Co3Sn2S2 and Ni3In2Se2). We first demonstrate that the measured step height between different surfaces typically deviates from the expected value of ±0.4 ∼0.8Å, which is owing to the tunneling convolution effect with electronic states and becomes a serious issue for Co3Sn2S2 where the expected Sn-S interlayer distance is 0.6Å. Hence, we put forward a general methodology for surface determination as atomic step geometry imaging, which is fundamental but also experimentally challenging to locate the step and to image with atomic precision. We discuss how this method can be used to resolve the surface termination puzzle in Co3Sn2S2. This method provides a natural explanation for the existence of adatoms and vacancies, and beyond using unknown impurity states, we propose and use designer layer-selective substitutional chemical markers to confirm the validity of this method. Finally, we apply this method to determine the surface of a new kagome material Ni3In2Se2, as a cousin of Co3Sn2S2, and we image the underlying kagome geometry on the determined Se surface above the kagome layer, which directly visualizes the p-d hybridization physics. We emphasize that this general method does not rely on theory, but the determined surface identity can provide guidelines for first-principles calculations with adjustable parameters on the surface-dependent local density of states and quasi-particle interference patterns.

Chromatic confocal coherence scanning interferometry with speed-variable scanning method to measure large-depth step

Coherence scanning interferometry (CSI) is a crucial measurement technique for achieving non-contact, rapid, and high-precision measurements. However, when applied to large-depth steps, CSI encounters challenges related to prolonged measurement times and suboptimal signal utilization. This paper introduces a hybrid CSI system that integrates the chromatic confocal technique (CC-CSI). The confocal spectral signal peak facilitates the rapid determination of the coherence area, allowing the scanning process to be divided into two phases. The signal collection is limited within the coherence area at a lower scanning speed, while in other positions, the scanning speed is increased. This speed-variable scanning technique significantly augments measurement efficiency. The CC-CSI system with the speed-variable scanning method demonstrated a significant enhancement in measurement time compared to conventional CSI under identical experimental conditions. The measured step heights were 100 μm, 200 μm, and 300 μm. Standard deviations of less than 0.3 μm were observed in 10 consecutive measurements. In addition, the proposed CC-CSI system demonstrated the capability to profile the groove structure.

The threshold of an intra oral scanner to measure lesion depth on natural unpolished teeth

ObjectivesTo investigate the threshold and accuracy of intraoral scanning in measuring freeform human enamel surfaces. MethodsSoftware softgauges, ranging between 20 and 160 µm depth, were used to compare four workflow analysis techniques to measure step height on a freeform surface; with or without reference areas and in combination with surface-subtraction to establish which combination produced the most accurate outcome. Having established the optimum combination, 1.5 mm diameter, individual depths ranging from 11 to 81 µm were created separately on 14 unpolished human enamel samples and then scanned with gold standard laboratory optical profilometry (NCLP, TaiCaan Technologies™, XYRIS2000CL, UK) and a clinical intraoral scanner (TrueDefinition™, Midmark Corp., USA). The sequence of surface registration and subtraction determined from the softgauges was used to measure step height on natural human enamel surfaces. Step heights (μm) were compared using two-way ANOVA with post-hoc Bonferroni (p < 0.05) and Bland-Altman analyses. ResultsSoftware differences were significantly reduced from − 29.7 to − 32.5% without, to − 2.4 to − 3.6% with reference areas (p < 0.0001) and the addition of surface-subtraction after registration reduced this further to 0.0 to − 0.3% (p < 0.0001). The intraoral scanner had a depth discrimination threshold of 73 µm on unpolished natural enamel and significant differences (p < 0.05) were observed compared to NCLP below this level. SignificanceThe workflow of combining surface-registration and subtraction of surface profiles taken from intraoral scans of freeform unpolished enamel enabled confident measurement of step height above 73 µm. The limits of the scanner is related to data capture and these results provide opportunities for clinical measurement.

The growth of CeOx(111) thin films on Ru(0001)

Ceria has attracted great attention in recent years in the catalysis community. Metal catalysts supported on ceria exhibit a promising catalytic activity due to the ceria’s unique redox properties and oxygen storage capacity. The purpose of this paper is to look at the fundamental aspect of CeOx(111) thin films on Ru(0001). The investigation presented in this paper utilizes the surface science method to understand the properties of CeOx(111). In one component, through a series of XPS studies, it is shown that the deposition of Ce in the presence of oxygen on Ru(0001) can produce ceria thin films. Fully oxidized CeO2 can be obtained with an oxygen pressure of 2 x 10−7 Torr. With the decrease in the oxygen pressure, partially reduced CeOx films can be prepared. Moreover, STM images are collected from the CeO2 growth in the presence of 2×10−7 Torr of oxygen and partially reduced ceria with oxygen pressures of 8×10−8 Torr. These films can completely cover the Ru(0001) substrate. The measured step height is about 0.3 nm, which is consistent with the 0.313 nm spacing of O-Ce-O tri-layers in the CeO2(111) fluorite bulk structure.

Estimation of an uncertainty budget and performance measurement for a dual-wavelength Twyman-Green interferometer.

In this paper, the uncertainty budget from 10 sources we claim they have direct impact on measurement is estimated. The measurement has been applied to nominal step heights of 1.34 and 1.50 μm using a dual-wavelength Twyman-Green interferometer. Experimental results show that the measured step heights match with their nominal values with expanded uncertainty in the range of 5% from the object being measured. The performance of the measurement process over time has been estimated at different confidence levels and the obtained results show that the process is maintained in a state of statistical control. To the best of our knowledge, this is the first report for estimation of uncertainty budget from a synthetic wavelength.

Synthesis of BiFeO3 thin films on single-terminated Nb : SrTiO3 (111) substrates by intermittent microwave assisted hydrothermal method

We report on a simple and fast procedure to create arrays of atomically flat terraces on single crystal SrTiO3 (111) substrates and the deposition of ferroelectric BiFeO3 thin films on such single-terminated surfaces. A microwave-assisted hydrothermal method in deionized water and ammonia solution selectively removes either (SrO3)4− or Ti4+ layers to ensure the same chemical termination on all terraces. Measured step heights of 0.225 nm (d111) and uniform contrast in the phase image of the terraces confirm the single termination in pure and Nb doped SrTiO3 single crystal substrates. Multiferroic BiFeO3 thin films were then deposited by the same microwave assisted hydrothermal process on Nb : SrTiO3 (111) substrates. Bi(NO3)3 and Fe(NO3)3 along with KOH served as the precursors solution. Ferroelectric behavior of the BiFeO3 films on Nb : SrTiO3 (100) substrates was verified by piezoresponse force microscopy.

Atomic force microscopy of novel zeolitic materials prepared by top-down synthesis and ADOR mechanism.

Top-down synthesis of 2D materials from a parent 3D zeolite with subsequent post-synthetic modification is an interesting method for synthesis of new materials. Assembly, disassembly, organisation, reassembly (ADOR) processes towards novel materials based on the zeolite UTL are now established. Herein, we present the first study of these materials by atomic force microscopy (AFM). AFM was used to monitor the ADOR process through observation of the changes in crystal surface and step height of the products. UTL surfaces were generally complex and contained grain boundaries and low-angle intergrowths, in addition to regular terraces. Hydrolysis of UTL to IPC-1P did not have adverse effects on the surfaces as compared to UTL. The layers remained intact after intercalation and calcination forming novel materials IPC-2 and IPC-4. Measured step heights gave good correlation with the X-ray diffraction determined d200 -spacing in these materials. However, swelling gave rise to significant changes to the surface topography, with significantly less regular terrace shapes. The pillared material yielded the roughest surface with ill-defined surface features. The results support a mechanism for the majority of these materials in which the UTL layers remain intact during the ADOR process as opposed to dissolving and recrystallising during each step.

Frequency-comb-referenced multi-wavelength profilometry for largely stepped surfaces

3-D profiles of discontinuous surfaces patterned with high step structures are measured using four wavelengths generated by phase-locking to the frequency comb of an Er-doped fiber femtosecond laser stabilized to the Rb atomic clock. This frequency-comb-referenced method of multi-wavelength interferometry permits extending the phase non-ambiguity range by a factor of 64,500 while maintaining the sub-wavelength measurement precision of single-wavelength interferometry. Experimental results show a repeatability of 3.13 nm (one-sigma) in measuring step heights of 1800, 500, and 70 μm. The proposed method is accurate enough for the standard calibration of gauge blocks and also fast to be suited for the industrial inspection of microelectronics products.

A new phase unwrapping algorithm based on Three Wavelength Phase Shift Profilometry method

Phase Shift Profilometry (PSP) method is widely used in 3D shape measurement. The advantage of the PSP method is that it is less sensitive to the surface reflectivity variations and the object can be measured point by point. But if only a single wavelength λ1 is used, the step height cannot be larger than λ1/4. In order to measure step height object, Gray Code (GC) and Multi-Wavelength Phase Shift Profilometry (MWPSP) method are used. But the GC method cannot solve the problem of the objects with a variety of colors under different illumination. The shortcoming of MWPSP method is that its speed is too slow because a lot of images with multi-wavelengths should be captured by the system. In order to solve the problem of measurement speed and measurement range, a new phase unwrapping algorithm based on Three Wavelength Phase Shift Profilometry (TWPSP) is proposed in this paper. A series of fringe images only with three wavelengths λ1, λ2 and λ3, are captured by the 3D measurement system. Three equivalent wavelengths λ12, λ23and λ123 based on the original three wavelengths are calculated to perform the phase unwrapping algorithm. Compared with the GC method, the proposed method can measure the objects with different colors under different illuminations. Compared with the MWPSP method, the proposed method is faster and high precision. Experiments demonstrate that the proposed method is robust, high precision, low noise and suit to measure the object with variety colors under different illumination. It can be used to measure arbitrary step height and multiple objects together.

Structure of the (010) surface of the orthorhombic complex metallic alloyT-Al3(Mn,Pd)

The atomic and electronic structures of the (010) surface of the $\mathrm{T}{\text{-Al}}_{3}$(Mn,Pd) complex metallic alloy is investigated by means of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), x-ray photoelectron diffraction (XPD), and ab initio calculations. While structural imperfections are observed at the surface and out of the various possible terminations, the puckered P2 layer is identified as the only surface termination, thus pointing out the existence of a well-defined minimum in the surface energy landscape. The measured step heights correspond to distances between identical planes along the [010] direction in the bulk model, i.e., $b/2$. A bias dependency of the STM topography is found. The XPD and LEED patterns confirm the pseudotenfold symmetry of the sample. XPS and UPS show a more metallic signature of the $\mathrm{T}$ phase compared to Al-based quasicrystalline phases.

Scanning white-light interferometry with a supercontinuum source

A supercontinuum light source was incorporated into a custom-built scanning white-light interferometer. This light source based on a Nd:YAG pumped microstructured optical fiber exhibits 1.21+/-0.10 microm temporal coherence length. The device operation was validated by characterizing the step height on a microelectromechanical system component. The measured step height- 7.027+/-0.020 microm-agreed with results obtained by employing traditional light sources: a halogen lamp and a white light-emitting diode. The new light source features high output intensity of 20-35 mW, which is beneficial when measuring low-reflectivity samples. As the supercontinuum light source may be modulated at frequencies exceeding 10 MHz, it holds potential for stroboscopic dynamic measurements.

High Precision Measurement of 3D Profile Using Confocal Differential Heterodyne Interferometer

The differential heterodyne interferometer (DHI) is suitable for precise measurement of step height and line width, since its differential configuration can significantly reduce disturbances from the environment [1,2]. Like most phase measuring interferometers, however, the DHI is limited, in that it can obtain only the phase from 0 to 2π, because of the sinusoidal nature of the optical interference involved. Thus, the measurable step height is limited to one quarter of the wavelength of the light source. This study describes a confocal differential heterodyne interferometer (CDHI) for measuring step heights of several micrometers, with a high resolution and line width with high repeatability. The CDHI has a simple structure and rapid measurement speed.

Morphological and surface analysis of titanosilicate ETS-4 synthesized hydrothermally with organic precursors

Morphological and surface analysis was performed on titanosilicate ETS-4 crystals using atomic force microscopy (AFM) and field emission scanning electron microscopy. Crystals were synthesized hydrothermally at 175 °C in Teflon-lined stainless steel autoclaves using organic precursors. Rectangular and plate shaped crystals were formed with the largest crystals being 2 × 20 × 5 μm and 2 × 10 × 10 μm, respectively. EDX analysis revealed a disparity between the Si/Ti ratio in crystals characterized by different morphologies (2.5 for rectangular vs. 2.8 for plates). Growth occurred on the slowest growing and the largest crystal via a layer mechanism. Spiral hillocks were found on {1 0 0} surfaces of rectangular shaped crystals and on the largest faces of intergrown plate crystallites. Steps on these surfaces were observed to emanate from spiral hillocks and had a step height of 1.10 ± 0.15 nm. The crystallographic d-spacing of the (2 0 0) plane, as measured by powder X-ray diffraction, correlated with the AFM measured step height.

Surface step structure of Ag13OsO6, experimental evidence for Ag13 cluster building blocks.

The surface of single crystal Ag(13)OsO(6) has been investigated using atomic force microscopy. Growth spirals with very large flat terraces, separated by steps of equal height, have been observed. The measured step height of approximately 6.7 Angstrom corresponds to the diameter of one Ag13-icosahedron and identifies the cluster as the key structural building block.

Comparison on Nanometrology: Nano 2—Step height

The ability to measure step height and to calibrate step height artefacts is of vital interest in nanometrology. On that score the WGDM7 decided in 1998 to include measurements of step heights in a series of comparisons on the field of nanometrology.The comparison about step height (NANO2) started in September 2000 with the Physikalisch-Technische Bundesanstalt (PTB) as pilot laboratory. Fourteen national metrology institutes worldwide participated in this comparison. A set of five step height standards in the range from 7 nm to 800 nm was used for the comparison. The lateral size of the structures of the step height standards was chosen so that the height could be measured by different types of instruments, for example, interference microscopes, stylus instruments and scanning probe microscopes (SPM). The reference values were calculated as the weighted mean of all measurements that fulfilled the En < 1 criteria.Most of the results were in good agreement with the reference values. It is noticeable that the results obtained by different types of instruments are quite compatible. Also this comparison is the first comprehensive test of the reliability of SPM and their suitability for traceable measurements of step heights. Further it was shown that today step heights on samples can be measured with uncertainties in the sub-nanometre range. Differences in the calculation of the uncertainty depend on the types of instruments and on the users. For each class of instrument, e.g. SPM, it would be meaningful to homogenise these models. Hence the results of this comparison are of great importance in many respects.Main text.To reach the main text of this paper, click on Final Report.Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to theprovisions of the Mutual Recognition Arrangement (MRA).

Two-wavelength laser diode interferometer with time-sharing sinusoidal phase modulation.

We describe an interferometer system that uses two separate wavelengths to measure step height. The overlapping interference images detected by a CCD camera are easily separated by an ordinary integrating-bucket method and time-sharing sinusoidal phase modulation, in which two laser diodes are alternately modulated with a sinusoidal signal. A phase map is obtained only for the laser diode into which the modulation signal is injected. In this instance, a 1-microm step height was accurately detected.

IN SITU CHARACTERISATION OF CALCITE GROWTH AND INHIBITION USING ATOMIC FORCE MICROSCOPY

Real time in situ monitoring of calcite growth and inhibition on the cleavage plane [Formula: see text] is investigated using atomic force microscopy (AFM). Calcite growth and inhibition were studied using a Molecular Imaging microscope in contact mode, equipped with an in situ fluid cell. As has been reported previously, it is observed that calcite growth from aqueous solution is by motion of mono-molecular steps, and dissolution by a combination of step motion and etch pit expansion. The measured step heights were between 2.7 to 3 Å. Our aim is to study the effects of a range of phosphonate-based crystal growth inhibitors of related structure, in order to provide insight into the mechanism of inhibition as a function of the additive structure. Results of this study demonstrate the effect of inhibitors on the growth steps and terraces on the [Formula: see text] surface of calcite in real time. The organic additives bind to the crystal surface, with selective binding to the step edges particularly evident in some cases. In other cases, it appears that the additive acts by binding to the terraces on the crystal surface, resulting in inhibition by coating the surface. Efforts to correlate the observations made by atomic force microscopy with bulk crystallization experiments have been made.

Morphology of fcc Co(110) films on Cu(110)

The surface morphology of fcc Co(110) films deposited on Cu(110) using oxygen as a surfactant is characterized by He atom scattering. Interference measurements reveal that the thicker Co films are quite flat and that this flatness is preserved after removal of the oxygen with atomic hydrogen. During growth of the first few layers a rough film morphology is observed which is related to the deconstruction of the Cu(110)-(2×1)O interface and the formation of a (1×2) reconstructed CoCuO phase after deposition of the first Co monolayer. With increasing film thickness the measured step height changes from (1.28±0.02)Å characteristic of the Cu(110) surface to (1.21±0.02)Å attributed to the interlayer spacing of pseudomorphic fcc Co(110).

Atomic steps with tuning-fork-based noncontact atomic force microscopy

Tuning forks as tip–sample distance detectors are a promising and versatile alternative to conventional cantilevers with optical beam deflection in noncontact atomic force microscopy (AFM). Both theory and experiments are presented to make a comparison between conventional and tuning-fork-based AFM. Measurements made on a Si(111) sample show that both techniques are capable of detecting monatomic steps. The measured step height of 0.33 nm is in agreement with the accepted value of 0.314 nm. According to a simple model, interaction forces of 30 pN are obtained for the tuning-fork-based setup, indicating that, at the proper experimental conditions, the sensitivity of such an instrument is competitive to conventional lever-based AFM.

Vertical metrology using scanning-probe microscopes: Imaging distortions and measurement repeatability

We report a study of the repeatability as limited by instrumental imaging distortions in scanning-probe microscope (SPM) measurements of the heights of nominal 44 and 88 nm steps in calibration artifacts. By imaging the same series of locations on different days, we are able to distinguish sample variations from variations originating in the imaging process. In particular, the value and repeatability of the measured step heights are found to depend upon the algorithm used to infer the step height from the SPM image. The three general approaches tested are: a manual single-point method, which represents the most commonly used practice in the SPM community; a histogram-based method, which is available in commercially available SPM image-analysis software; and the polynomial step-function fit (PSFF), which explicitly removes image bow and sample tilt. Factors related to variations in the sample measured such as image size and location on the sample cause up to 10% variations in the step-height measurements. ...