The effective Q-factor of the cantilever is one of the most important figures-of-merit for a non-contact atomic force microscope (NC-AFM) operated in ultra-high vacuum (UHV). We provide a comprehensive discussion of all effects influencing the Q-factor and compare measured Q-factors to results from simulations based on the dimensions of the cantilevers. We introduce a methodology to investigate in detail how the effective Q-factor depends on the fixation technique of the cantilever. Fixation loss is identified as a most important contribution in addition to the hitherto discussed effects and we describe a strategy for avoiding fixation loss and obtaining high effective Q-factors in the force microscope. We demonstrate for room temperature operation, that an optimum fixation yields an effective Q-factor for the NC-AFM measurement in UHV that is equal to the intrinsic value of the cantilever.

Calcite is a mineral of fundamental importance that plays a crucial role in many fields of research such as biomineralization, biomolecule adsorption, and reactivity as well as industrial and daily life applications. Consequently, the most stable cleavage plane of calcite has been studied extensively using both direct imaging techniques such as atomic force microscopy as well as spectroscopic and diffraction techniques. Several surface structures have been reported for the (1014) cleavage plane of calcite differing from the simple bulk-truncated structure and an ongoing controversy exists in literature whether the cleavage plane exhibits a (2 x 1) reconstruction or not. We study the (1014) cleavage plane using high-resolution noncontact atomic force microscopy (NC-AFM) under ultrahigh vacuum conditions and obtain a clear signature of the (2 x 1) reconstruction. This reconstruction is observed in very narrow tip-surface distance ranges only, explaining why in some experiments the reconstruction has been observed and in others not. Moreover, as all sample preparation is performed in ultrahigh vacuum, the possibility of the (2 x 1) reconstruction being adsorbate-induced appears rather unlikely. Additionally, tip-induced surface changes are ruled out as origin for the observed reconstruction either. In conclusion, our study suggests that the (2 x 1) reconstruction is a true surface property of the (1014) cleavage plane of calcite.

The surface morphology of CeO(2)(111) single crystals and silicon supported ceria films is investigated by non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) for various annealing conditions. Annealing bulk samples at 1100 K results in small terraces with rounded ledges and steps with predominantly one O-Ce-O triple layer height while annealing at 1200 K produces well-ordered straight step edges in a hexagonal motif and step bunching. The morphology and topographic details of films are similar, however, films are destroyed upon heating them above 1100 K. KPFM images exhibit uniform terraces on a single crystal surface when the crystal is slowly cooled down, whereas rapid cooling results in a significant inhomogeneity of the surface potential. For films exhibiting large terraces, significant inhomogeneity in the KPFM signal is found even for best possible preparation conditions. Applying X-ray photoelectron spectroscopy (XPS), we find a significant contamination of the bulk ceria sample with fluorine while a possible fluorine contamination of the ceria film is below the XPS detection threshold. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) reveals an accumulation of fluorine within the first 5 nm below the surface of the bulk sample and a small concentration throughout the crystal.

A key issue for high-resolution frequency-modulation atomic force microscopy imaging in liquids is minimizing the frequency noise, which requires a detailed analysis of the corresponding noise contributions. In this paper, we present a detailed description for modifying a commercial atomic force microscope (Bruker MultiMode V with Nanoscope V controller), aiming at atomic-resolution frequency-modulation imaging in ambient and in liquid environment. Care was taken to maintain the AFMs original stability and ease of operation. The new system builds upon an optimized light source, a new photodiode and an entirely new amplifier. Moreover, we introduce a home-built liquid cell and sample holder as well as a temperature-stabilized isolation chamber dedicated to low-noise imaging in liquids. The success of these modifications is measured by the reduction in the deflection sensor noise density from initially 100 fm/√Hz to around 10 fm/√Hz after modification. The performance of our instrument is demonstrated by atomically resolved images of calcite taken under liquid conditions.

We report on sample holders for crystals to be cleaved for the preparation of surfaces with large atomically flat terraces. The concept for mounting sample crystals is based on a vicelike clamping mechanism to securely hold the crystal in position while reducing the risk of fragmentation. Sample holders based on this concept and made of suitable materials allow preparation and cleavage of crystals in the ultrahigh vacuum at high or low temperatures. To cleave the crystal, we employ a scalpel blade mounted on a wobble stick to generate a highly localized stress field initiating the cleavage process. The sample holders are used for experiments of highest resolution scanning force microscopy, however, the concept can be transferred to any other system where cleavage faces of crystals are of interest. Exemplarily, scanning force microscopy results demonstrate that (111) cleavage faces of CaF2 crystals can be prepared with steps only a few F-Ca-F triple-layers high and atomically flat terraces extending over areas of several microm2.

We report on a modification of a commercial scanning force microscope (Omicron UHV AFM/STM) operated in noncontact mode (NC-AFM) at room temperature in ultrahigh vacuum yielding a decrease in the spectral noise density from 2757 to 272 fm/Hz. The major part of the noise reduction is achieved by an exchange of the originally installed light emitting diode by a laser diode placed outside the vacuum, where the light is coupled into the ultrahigh vacuum chamber via an optical fiber. The setup is further improved by the use of preamplifiers having a bandpass characteristics tailored to the cantilever resonance frequency. The enhanced signal to noise ratio is demonstrated by a comparison of atomic resolution images on CeO(2)(111) obtained before and after the modification.

We present a versatile system for the preparation of oxide crystal surfaces in the ultra-high vacuum (UHV) at temperatures up to 1300 K. Thermal treatment is accomplished by direct current heating of a tantalum foil in contact with the oxide sample. The sample temperature is measured by a thermocouple at a position close to the crystal and its reading is calibrated against the surface temperature determined by a second thermocouple temporarily attached to the surface. The design of the sample holder is based on a transferable plate originally developed for a commercial UHV scanning probe microscope. The system is, however, also suitable for the use with electron spectroscopy or electron diffraction based surface analytical techniques. We present results for the high-temperature preparation of CeO(2)(111) surfaces with atomically flat terraces exhibiting perfect atomic order and cleanliness as revealed by non-contact atomic force microscopy (NC-AFM) imaging. NC-AFM imaging is, furthermore, used to demonstrate the temperature-controlled aggregation of gold atoms on the CeO(2)(111) surface and their evaporation at high temperatures.

Design of surface forces apparatus for tribology studies combined with nonlinear optical spectroscopy Rev.