Surface properties and dissociative chemisorption of water on titanium-oxide surfaces are of particular interest for the biocompatibility of this material. Scanning force microscopy images of electropolished titanium samples and of thin films of titanium evaporated under vacuum show a similar topography with a grain size of 30 nm. Mass spectrometer thermal desorption spectroscopy displays two peaks for e/m = 18, at 380 and 520 K corresponding to adsorbed water molecules and hydroxyl groups, respectively. Auger spectra show the segregation toward the surface of chlorine from the metal-oxide interface upon heating at 720 K and of sulphur from the bulk after annealing at 950 K. The oxygen diffusion from the surface toward the bulk during the heating process induces a metallic behaviour of the surface layer which is revealed by tunneling spectroscopy: the semiconducting gap present in dI/dV curves for the air-exposed sample vanishes upon annealing. STM images of the annealed surface show the presence of tiny crystallites of a few nm in size.

The scanning probe microscopies applied to the sequencing of DNA is a challenging goal attempted by several groups. But one limitant parameter has been the sample preparation of DNA molecules. Here we report how to hold DNA molecules fixed on mica substrate and we show the three-dimensional configuration of double-stranded DNA obtained with our scanning force microscope. We can image DNA under negative supercoiling, a feature of general importance controlling the activities of DNA. We compared the electron micrographs of a carbon replica of the same DNA specimen with scanning force images which demonstrates well the feasibility and accuracy of our scanning probe measurements.

In this study, tobacco mosaic virus (TMV) provides a resolution criterion for specimen preparation methods as well as for imaging parameters of the scanning force microscope (SFM). We present scanning force microscopic images of the virus embedded in 0.5% buffered phosphotungstic acid solution adsorbed on a freshly cleaved mica surface, and imaged under atmospheric conditions. Individual TMV particles were clearly identified with a characteristic shape of long rods of about 300 nm long and 60-70 nm in apparent width due to the geometric parameters of the tip. The structure of the virus was compared with cryo-electron microscopic data of vitrified suspensions observed to a resolution of 1.15 nm. Uncoated TMV particles were also deposited on evaporated titanium thin films and imaged by SFM.

We have imaged with scanning force microscopy in air fibronectin (Fn) molecules sprayed on mica and on polymethylmetacrylate (PMMA), the latter being extensively used as biomaterial for implants. On mica we can observe small aggregates as well as individual molecules whose shape is influenced by the tip interaction during the scanning process, most of the isolated molecules showing a V-shape oriented in the scan direction. This indicates that the arms of the molecules are relatively free to move and the binding to the mica substrate is located near the disulfide bridge between the two subunits of the molecule. On the other side, when Fn molecules are sprayed on PMMA under the same conditions as for mica, we observe a thin network which we interpret as Fn molecules bound to each other. We relate our observation to the fact that mica is known to be strongly hydrophilic, which could reduce the Fn binding properties by interacting relatively strongly with molecules. On the other side, PMMA being hydrophobic, would interact less with molecules, leaving more binding sites for inter-molecular attachment.

Atomic level structural and electronic analysis of titanium passivated by an oxide film is crucial for understanding the biocompatible properties of this transition metal. Scanning tunneling microscope (STM) images of electropolished titanium samples show a rather smooth surface in the nanometer range with structure attributed to surface defects induced by the electropolishing technique. I–V spectra were performed with the STM using W, PtIr, and Au tips. These spectra completed by normalized conductivities spectra are compared and discussed in order to determine surface electronic properties of the oxide film and to estimate the influence of the STM tip. The surface band gap of this amorphous thin film mainly composed of TiO2 is shifted to positive tip voltage and is similar to the one of an n-type semiconductor with band bending bringing the valence band closer to the Fermi level. The surface band gap extends from −0.5 to +0.8 eV for a Au tip and from −0.1 to 0.7 eV for a W tip, which shows that W induces states in the band gap. Reproducible peaks in the local density of states of our Ti oxide surface appear both for Au and W tips at the same energies and are clearly apparent in the normalized conductivity curves.

The biological as well as physico-chemical aspects of the interface between metallic implants and living tissue was investigated. The results presented show that the evaluation of staphylococcal adherence is a quite convenient and sensitive assay for measuring the functional state of surface adsorbed fibronectin. For surface analysis, scanning electron microscopy and auger spectroscopy together with a scanning tunneling microscope (STM), especially designed for this purpose, was used and STM images of a titanium coverslip and of fibronectin molecules are presented.

A scanning tunneling microscope (STM) coupled with a high resolution reflective optical microscope has been developed to investigate some aspects of the interface between metallic biomedical implants and living tissue. Initial biological measurements show that fibronectin (Fn), a glycoprotein which plays an important role in the promotion of cell and bacterial attachment, is well adsorbed on Ti and V substrates, but is not biologically active on V. STM images of the Ti oxide layer and of single and multiple Fn molecules deposited on mica and shadowed with a conductive layer are presented. These images demonstrate the capability of the STM for studying clinical implant surfaces with roughness larger than 1 μm as well as interface biochemical processes at the molecular level.

We have used scanning tunneling microscopy to characterize the surface of epitaxial gold on mica in air. We find that these surfaces are simple to prepare, are relatively inert to exposure to air or to water, and have atomically flat terraces extending for up to several hundred angstroms. The observed topography is consistent with the Au(111) surface. It is possible to produce bumps on the surface of less than 100 Å in size in a controlled manner by pulsing the tip voltage while scanning. Self-diffusion of gold is observed in the decay of written features and well as in the movement of existing terrace edges. In some cases, a periodicity in both the geometry of terrace edges and the spatial variation of surface diffusion rates suggest the presence of the 22×1 surface reconstruction.

SUMMARYWe have developed a scanning tunnelling microscope specially designed for biological applications presenting some new features: the scanner tube is mounted parallel to the surface of the sample which enables a high resolution optical microscope to be brought close to the sample when working in air or liquids. The maximum scan range is 5×20 μm with a vertical range of 20 μm and the total size of the system does not exceed 10×40 mm. The piezo‐sensitivity of the scanner tube versus applied voltage was analysed by interferometry measurements and by using scanning tunnelling microscopes. We found a value for the piezoelectric constant d13 of −1·71 Å/V at low voltages (under a few volts) going up to −2 Å/V for higher voltages. Large‐scale images of a carbon grid showed a surprisingly good linearity of the scanner tube.

SUMMARYIn order to characterize the surface of epitaxial gold on mica in air we have used a scanning tunnelling microscope (STM) to image and to modify this surface. It was possible to create controlled features by applying voltage pulses on the tip while scanning. The voltage threshold for writing (about 3 V, 100 ns pulses) was dependent of the tip condition. The lowest pulses were associated with sub‐50 Å feature size. We observed that at ambient temperature the written features disappeared in a time scale of half an hour for the smallest (<30 Å) to a few hours for the bigger features (∼500 Å). We have used the same surface as a substrate for organic imaging. We also present images of a polymer deposited on gold.

SUMMARY The properties of monolayer films of organic materials are important for a variety of technologies. We have employed STM and AFM to study Langmuir‐Blodgett films of a variety of polymers on substrates of graphite, MoS 2 , and Au(111) on mica. The polymers were poly(octadecyl acrylate) (PODA), atactic and syndiotactic poly(methyl methacrylate) (PMMA) and poly(2‐methyl‐1‐pentene sulphone) (PMPS). One striking feature was the degree of order observed; a second was the morphological difference between films of submonolayer thickness (long, thin fibrils) and those of at least monolayer thickness (lumpy structures arranged in domains). By pulsing the STM bias voltage to values in excess of 4V, we were able to bring about local modification of the polymer morphology.

We describe a piezoelectric device which allows continuous movement and high-resolution micropositioning, without distance limitation. Both mechanical construction and the electronics for the device are very simple. The movement is obtained via a stick-slip mechanism, and steps as small as 10 nm are obtained. A displacement speed of 0.4 mm/s has been attained, and the device was capable of carrying several times its own weight, exerting a horizontal force, or climbing a plane inclined by 7°. Due to its compact construction, the device shows prospects for miniaturization.