Tip Artifact Research Articles

Tip artifacts in atomic force microscope imaging of ion bombarded nanostructures on germanium surfaces

In this communication, we present a study of tip artifacts in atomic force microscope images of nanometer-scale cellular structures created on germanium surfaces by ion bombardment. It is demonstrated that the appearance of a columnar/granular morphology is due to severe image distortion when the tip size is comparable with the mean cell/hole diameter. These tip artifacts can often be deconvoluted by inverting the image and the lateral extension of the cell/hole can be reproduced with reasonable accuracy.

Self-assembled monolayer film for enhanced imaging of rough surfaces with atomic force microscopy

The significance of the surface chemical state and resulting forces on the imaging fidelity of atomic force microscopy (AFM) was investigated experimentally in ambient air. Adhesion tests were conducted on smooth monocrystalline (100) silicon substrates with sharp silicon tips of 5 nm nominal radius. Surface topography imaging of rough polycrystalline silicon surfaces was performed with similar sharp silicon tips. The substrates were initially subjected to different chemical treatments to obtain either hydrophilic or hydrophobic surface behaviors. The AFM tip treatment involved the deposition of an organized close-packed octadecyltrichlorosilane (OTS) hydrophobic self-assembled monolayer. Statistical results for the surface force at the tip-sample interface versus the separation distance and the various moments of the surface height distribution function demonstrated that imaging artifacts due to sticking of the tip on sidewalls of steep asperities were particularly pronounced when imaging hydrophilic surfaces with uncoated tips. The tip artifacts comprised spurious negative excursions or exaggerated asperity heights depending on the direction of scanning. Significant enhancement of the AFM imaging quality was accomplished with OTS-coated tips, as demonstrated by the markedly reduced magnitude of the adhesive force at the tip-sample interface (about 1 nN for both hydrophilic and hydrophobic smooth silicon surfaces), the consistency of the calculated surface height moments, and the negligibly small effect of the scanning direction on the imaged topographies. The results suggest that the present treatment of the AFM tip surface could provide an effective means for overcoming tip artifacts with other difficult-to-image surfaces.

In situ AFM and STM investigation of electrochemical hydride growth on Ge(110) and Ge(111) surfaces

In situ images of Ge(110) and Ge(111) surfaces under potential control have been obtained with an atomic force microscope (AFM) and a scanning tunneling microscope (STM). Atomic resolution images, using the AFM, of Ge(111) and Ge(110) revealed lattice structures close to that expected for bare Ge even in a potential region where the surface is hydroxylated. Long-range images of the Ge surface revealed the reversible, anisotropic formation and dendritic growth of spikes of a hydride species at the Ge surface upon cathodic polarization. These spikes were manifested as tip artifacts with both the AFM and the STM. The observed density of hydride features on the surface was about 1 × 10 9/cm 2 which is an order of magnitude less than the number of surface states previously predicted from impedance measurements. This indicates that each hydride feature is composed of several surface states. The features appeared ca. 25 nm higher in the STM images relative to the AFM, indicating a high degree of electron density around or associated with each feature. The STM locally enhances the formation of the hydride features. Anodic polarization causes the hydride spikes to disappear and the surface to anneal. The hydride most likely forms at defects in the hydroxide overlayer after the hydroxide overlayer is formed on anodic polarization.

Tip artifacts in atomic force microscope imaging of thin film surfaces

We report a study of tip artifacts in atomic force microscope (AFM) images of thin film surfaces. Specifically, a troublesome artifact that occurs when an AFM tip images surface features with a radius of curvature less than the apex of the tip. These artifacts are not easily detected, since the affected AFM images are similar to those expected for a thin film with a columnar microstructure. In a study of 23 thin films, we found that for a significant fraction, the AFM image was affected by this type of tip artifact. In the worst cases, the AFM images consisted almost entirely of images of the AFM tip. We discuss a simple technique to determine the extent of these tip artifacts.

Parameters controlling contamination tip growth for atomicforce microscopy

An investigation into improving the tip fabrication technique for Atomic Force Microcopy (AFM) tips has been undertaken. The problems addressed here relate to the artifacts that are produced from imaging high aspect ratio (depth/width) features with standard AFM pyramidal tips. Standard tips, while having a regular geometry present a problem: the pyramid's base is 3-5 microns square and the walls are angled at 55°. This tip shape can cause a great deal of “smoothing” to high aspect ratio topological features, whether they are a few nm or a few μm in height. The use of electron beam grown microtips eliminates many of the tip artifacts found when using standard pyramidal tips. Actual growth of tips is quite easy. Once the SEM is set up properly (focused and stigmated) the scan generator for the beam is turned off, placing the microscope in the spot mode. The beam spot is placed at the point where a tip is desired and left for several minutes.

Faceting, reconstruction, and defect microstructure at ceramic surfaces revealed by atomic force microscopy

Atomic force microscopy has been used to directly observe the surface microstructure and morphology of several single crystal ceramics which were either cleaved in air or processed in ultrahigh vacuum. Atomic and/or multiatomic height steps and atomically flat terraces were observed on cleaved Cr2O3 (101̄2) and NiO (100) surfaces and on polished and annealed Al2O3 (101̄2). Examples of faceting, reconstruction, and Ar+ ion induced damage were revealed on the (110), (100), and (001) surfaces of TiO2. Tip degradation and artifacts were evident during imaging of VC0.75 (100) surfaces. The atomic force microscopy results indicate that a wealth of nanometer scale features exists even on carefully prepared single crystal ceramic surfaces.

Tip artifacts of microfabricated force sensors for atomic force microscopy

It is demonstrated that due to inevitable intrinsic imperfections in the microfabrication process of atomic force microscopy (AFM) tips, images of rough surfaces can be totally dominated by tip artifacts. These images reflect the mesoscopic tip shape as concluded from a comparison of AFM and scanning electron microscopy images of the tip and sample. These tip artifacts have been found on a scale of 20–600 nm, showing the necessity of characterizing the tip shape in order to make reliable sample-specific statements.

Tip-related artifacts in scanning tunneling potentiometry.

We show that tip-related artifacts can produce artificially abrupt and/or nonmonotonic behavior in scanning-tunneling-potentiometry (STP) measurements of rough surfaces, and thus considerable care must be used in interpreting actual STP images. Low-noise STP measurements were made on several metal films, and confirm that such artifacts do in some cases exist. These tip artifacts are often more obvious in STP images than in the corresponding topographic images, and hence STP may provide a valuable means to detect the presence of tip artifacts in other scanning-tunneling-microscope experiments.