This review on magnetic force microscopy does not provide an exhaustive overview of the past accomplishments of the method but rather discusses the present state of the art. Magnetic force microscopy is a special mode of noncontact operation of the scanning force microscope. This mode is realized by employing suitable probes and utilizing their specific dynamic properties. The particular material composition of the probes and the dynamic mode of their operation are discussed in detail. The interpretation of images acquired by magnetic force microscopy requires some basic knowledge about the specific near-field magnetostatic interaction between probe and sample. The general magnetostatics as well as convenient simplifications of the general theory, which often can be used in practice, are summarized. Applications of magnetic force microscopy in the magnetic recording industry and in the fundamental research on magnetic materials are discussed in terms of representative examples. An important aspect for any kind of microscopy is the ultimately achievable spatial resolution and inherent restrictions in the application of the method. Both aspects are considered, and resulting prospects for future methodical improvements are given.

A special method, which is a combination of macroscopic “modified molecular combing” and microscopic “molecular cutting”, is proposed in this paper. DNA strands are first aligned on a solid substrate to form a matrix of 2D networks. Atomic force microscopy is then used to cut the DNA network in order to fabricate fairly complex artificial patterns. Curved and wavy structures are constituted by a manipulation process based on the elastic behavior of DNA strands. A new phenomenon of physical “folding” of DNA induced by the AFM probe has been found. DNA strands can be converted into spherical nanoparticles and nanorods by the special process of “pushing” during which DNA molecules fold up into ordered structures in air.

Iron(III) tert-butoxide, [Fe(O t Bu) 3 ] 2 , was used as a single source for iron and oxygen to obtain nanocrystalline hematite (Fe 2 O 3 ) or magnetite (Fe 3 O 4 ) films by low-pressure (LP) CVD. The decomposition profile of the molecular precursor and the crystallization temperature of iron oxide were derived from thermogravimetry/differential thermal analysis (TG/DTA). The substrate temperature was found to markedly influence the morphology and Fe/O stoichiometry in the deposited films. The morphological features and phase identification of the grown films were obtained by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The compositional identity of the phases was determined by the X-ray photoelectron spectroscopy (XPS) of the CVD deposits. Annealing the films ex-situ under reducing or oxidizing conditions allows selective interconversion (Fe 2 O 3 « Fe 3 O 4 ) among the deposited phases with no particle size variation. The interplay between the rate of precursor delivery and substrate temperature controlled the mean particle size in the films. Magnetite film with a mean particle size of 10 nm was obtained on silicon at 450 C. Formation of larger grains and grain clusters was observed at higher temperatures. High coercivity (4000 Oe) and small saturation magnetization (0.3 emu g ±1 ) of the Fe 3 O 4 film confirmed superparamagnetic behavior due to small particle size. Absorption spectra of magnetite and hematite films deposited on glass show them to be transparent to the visible light. The sheet resistance of nanocrystalline Fe 3 O 4 and Fe 2 O 3 films was found to be 2.4 kX and 2 MX, respectively.

No abstract