High Vacuum Atomic Force Microscope Research Articles

Investigating the effect of interatomic distance on friction force through MEMS-AFM based experiment

Investigations on the influence of the interatomic distance (IAD) on friction are crucial for gaining a better understanding of friction and comprehending the essential nature of graphene friction. We obtained friction force microscopy (FFM) images of strained surfaces to examine how the IAD affects the friction force. First, using microelectromechanical system (MEMS) fabrication techniques, we fabricated a strain-generating microdevice that can generate surface strain on its Si surface by an electrostatic comb actuator. The microdevice was installed in a high vacuum atomic force microscope. Next, FFM measurements were performed on the stress concentration section of the microdevice using a Si cantilever. The driving voltage on the comb actuator was switched on/off for each scan line during a single raster scan. This procedure allowed us to obtain FFM images representing the surface strain (i.e., the IAD variation) by excluding friction/wear-induced disturbances. The FFM images agreed well with the strain distribution calculated by the elastic finite element method analysis. The relative reduction of the friction was approximately 9% against the calculated strain of 1.2%.

Development of a bending-stress-controllable micro-clamp and applications in nanowear study of polyimide terephthalate.

Inner stress that exists in most natural and artificial materials, such as rocks, coatings, glasses, and plastic products, has a significant impact on their tribological properties at any length scale. Here, we designed a bending-stress controllable micro-clamp that can be applied in a high-vacuum atomic force microscope with limited chamber space for the investigation of stress-dependent nanowear behavior. By accurately quantifying the bending degree of the sample in different directions, the mutual transformation and adjustment of tensile or compressive stress could be realized. The stability of the micro-clamp structure was further verified by simulating the bending deformation state of the sample through Ansys calculations. The maximum applied scratch area on the bended sample surface where the variation of bending-induced stress below 5% was defined by the Ansys simulations. The consistency of polyimide terephthalate (PET) wear inside this defined region under both bending-free and bending states verified the stability and reliability of micro-clamp. Finally, the designed micro-clamp was applied to study the effect of bending deformation on friction and wear of PET in the atomic force microscope tests, where the tensile stress generated with bending deformation was found to facilitate the nanowear of PET material sliding against a diamond probe.

TiO2/SiO2 multilayer as an antireflective and protective coating deposited by microwave assisted magnetron sputtering

AbstractIn this paper designing, preparation and characterization of multifunctional coatings based on TiO2/SiO2 has been described. TiO2 was used as a high index material, whereas SiO2 was used as a low index material. Multilayers were deposited on microscope slide substrates by microwave assisted reactive magnetron sputtering process. Multilayer design was optimized for residual reflection of about 3% in visible spectrum (450–800 nm). As a top layer, TiO2 with a fixed thickness of 10 nm as a protective film was deposited. Based on transmittance and reflectance spectra, refractive indexes of TiO2 and SiO2 single layers were calculated. Ultra high vacuum atomic force microscope was used to characterize the surface properties of TiO2/SiO2 multilayer. Surface morphology revealed densely packed structure with grains of about 30 nm in size. Prepared samples were also investigated by nanoindentation to evaluate their protective performance against external hazards. Therefore, the hardness of the thin films was measured and it was equal to 9.34 GPa. Additionally, contact angle of prepared coatings has been measured to assess the wetting properties of the multilayer surface.

Height distribution of atomic force microscopy images as a tool for atomic layer deposition characterization

The authors propose the analysis of surface height histograms as a tool for the atomic layer deposition (ALD) growth characterization in the initial stage of the process. ALD of HfO2 on a Si(100)/SiO2 substrate was investigated in situ by ultra high vacuum atomic force microscope working in noncontact mode. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf and H2O as precursors, were performed at 230 °C. After each ALD cycle, the relation between the film growth and the root mean square surface roughness was studied. Parameters equivalent to HfO2 layer thickness, coverage, and surface roughness of the substrate and deposited material can be calculated in the proposed routine.

In situ studies of the atomic layer deposition of thin HfO 2 dielectrics by ultra high vacuum atomic force microscope

We studied in situ the initial stages of atomic layer deposition (ALD) of HfO 2 by an ultra high vacuum atomic force microscope working in frequency-modulation mode. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf and water as precursors, were performed on the Si(001)/SiO 2 substrate maintained at 230 °C. After each ALD cycle we studied the influence of the HfO 2 growth on the surface height histogram, the root mean square roughness, the surface fractal dimension and the autocorrelation function. This detailed analysis of the surface topography allowed us to confirm the completion of the first HfO 2 layer after four ALD cycles.

Local probing of the field emission stability of vertically aligned multi-walled carbon nanotubes

Metallic cantilever in high vacuum atomic force microscope has been used as anode for field emission experiments from densely packed vertically aligned multi-walled carbon nanotubes. The high spatial resolution provided by the scanning probe technique allowed precise setting of the tip-sample distance in the submicron region. The dimension of the probe (curvature radius below 50 nm) allowed to measure current contribution from sample areas smaller than 1 μm 2. The study of long-term stability evidenced that on these small areas the field emission current remains stable (within 10% fluctuations) several hours (at least up to 72 h) at current intensities between 10 −5 and 10 −8 A. Improvement of the current stability has been observed after performing long-time conditioning process to remove possible adsorbates on the nanotubes.

Development of low-temperature and high vacuum atomic force microscope with freeze–fracture function

A high vacuum low temperature atomic force microscope (AFM) for the direct observation of biological freeze–fracture samples has been developed. This AFM has an integrated vacuum system and a freeze–fracture mechanism inside the vacuum chamber. It is possible to observe the fractured sample surface without exposing the freshly fractured surface to the ambient atmosphere. The design is described in detail. A sample temperature up to −175 °C is achieved, with the temperature fluctuation less than 0.1 °C. Temperature control is possible from −175 to 0 °C for deep etching. An ultimate vacuum pressure of 8.7×10−6 Pa has been achieved. Freeze-fractured human red blood cell has been examined, and fine structure within the cell has been observed. It is demonstrated that this is convenient and useful for the direct observation of a biological freeze–fractured surface.

Instrumentation of the High-Vacuum Atomic Force Microscope

The high-vacuum atomic force microscope (HV-AFM) is a useful tool that is used in various sample environments and achieve good Z axis sensitivity in a noncontact mode operation because the cantilever is free from hydrodynamic damping. The instrument is designed with the aims of minimizing the measuring time, simplifying the operation and achieving high performance. A pumping pressure of about 10-4 Pa is obtainable within 15 min. To achieve easy operation, the optical lever deflection detection head is placed outside the vacuum chamber. The vibration isolation is achieved using an elastic damper and a magnetic-floating-type turbomolecular pump. This vibration isolation method works well enough to obtain the atomic-resolution image of a highly oriented pyrolytic graphite (HOPG) sample. We checked the sensitivity of the instrument using the noncontact mode of operation of a magnetic force microscope (MFM). The Z axis sensitivity in vacuum operation was compared with that in ambient operation. The quality factor increased by more than 25 times and the Z axis sensitivity increased by more than 10 times in vacuum operation (10-4 Pa).