V. N. Petryakov

Magnetic nanodot arrays produced by direct laser interference lithography

Periodic magnetic nanodot arrays have been produced on an area as large as 1 cm×1 cm by direct nanolithography using interferometric laser radiation. The dots are formed by the local annealing of sputtered amorphous Co–C films in regions where the laser intensity is highest. At room temperature the dots exhibit ferromagnetic order and are embedded in a paramagnetic matrix. The onset of room-temperature ferromagnetism is caused by nanoscale chemical and morphological changes during dot formation and reflects the phase separation of magnetic Co-rich clusters. The present single-step nanolithography is potentially an efficient method for fabrication of patterned magnetic arrays.

Ordered nanostructures written directly by laser interference

We present a simplified method to employ laser interference lithography for the fabrication of ordered nanostructures. Neither resist, nor an elaborate fabrication process was needed. Four-beam interference patterns generated in this work included periodic arrays of holes in GaAs, covered with SiO(2) bubbles, and they were directly written into the sample. The diameters of the smallest holes were less than 30 nm. We propose a model to interpret the results.

Line defects in two-dimensional four-beam interference patterns

We have studied laser interference patterns, which consist of line defects on the surface of a GaAs substrate, generated by four-beam interference lithography. The orientation and periodicity of the defects are shown to depend on the configuration of the incident laser beams, while the widths of the defects are modified by varying the beam intensity. Influences of the phase and polarization on the simulated patterns are discussed.

Ferromagnetic Co-C nanodot arrays produced by direct interferometric laser annealing

Magnetic properties of Co-C nanodot arrays produced by direct interferometric laser annealing are investigated by magnetic force microscopy (MFM) and magnetization measurements. The dots are formed by locally annealing sputtered amorphous Co-C films in regions where the laser intensity is highest. As-sputtered Co-C films do not exhibit ferromagnetic order at room temperature, but MFM shows that the dots become magnetic upon annealing, possibly due to the agglomeration or phase separation of Co-rich clusters. The dots are embedded in either a paramagnetic or weakly magnetic matrix. The magnetic properties of the generated pattern can be changed by varying the laser power. The present results show that direct interferometric lithography may become a useful tool for fabricating future patterned magnetic nanostructures.

Arrays of magnetic wires created in phase-separating Fe-containing alloys by interference laser irradiation

Using the interference of laser beams, we have fabricated the periodic arrays of submicron wires in Fe/C and Fe/Cr thin-film alloys. The array formation is found to arise from iron agglomeration in interference maxima. The dramatic decay of the in-plane magnetic anisotropy was observed in the fabricated arrays with decrease in the interference periodicity down to 170 nm. This decay can rather be explained by transforming the wires into separate granules than a smallness of the temperature modulation at small periodicities. Such an explanation is supported by the electronmicroscopic and ferromagnetic resonance data.

Observation of Laser-Induced Local Modification of Magnetic Order in Transition Metal Layers

Laser-induced local modifications of magnetic order in thin Fe-Cr layers were investigated. Local modification in the layers were induced by interfering laser beams. The results of the study give evidence for the formation of submicron-sized anisotropically shaped ferromagnetic regions with a well-defined direction of the easy magnetic axis in the interference maxima at the modification threshold. It was also found that the magnetic anisotropy of a medium is drastically reduced with changing the shapes of these local regions and distances between them. This may be due to the strengthening of the interaction between the regions through the paramagnetic matrix.

Formation of two-dimensional periodic nanostructures on fused quartz, polyimide, and polycrystalline diamond by pulsed four-wave interference laser modification

Atomic force microscopy is used to examine the topography of submicron periodic structures formed on the surfaces of synthetic polycrystalline diamond and polyimide films. The films are deposited on fused quartz substrates by four-wave interference modification using a pulsed 308-nm UV XeCl excimer laser. It is demonstrated that a two-dimensional periodic relief with a submicron period can be formed on the diamond surface directly by laser evaporation in the absence of a photoresist. Depending on the exposure, two mechanisms of polyimide film modification are observed. At exposures less than 100 mJ/cm2, the relief is formed due to swelling at the positions of interference maxima. At exposures greater than 100 mJ/cm2, holes are formed in the films. A periodic relief on the fused quartz surface is formed by using a UV photoresist exposed to pulsed interference laser radiation and subsequent Ar ion etching.

Formation of magnetic nanosize gratings in the illumination of thin-film Fe-Cr mixtures by interfering laser beams

The conditions for formation of nanosize gratings (∼100 nm) of ferromagnetic stripes in the illumination of thin-film (10–15 nm) paramagnetic Fe-Cr mixtures by interfering beams from an excimer laser are investigated. The ferromagnetic ordering arises as a result of the thermally stimulated clustering of Fe atoms. The gratings are formed in a certain energy interval of the laser radiation. The width of this interval depends substantially on both the interference period and the illumination time τi. For τi=10 ns there exists an energy interval in which gratings with periods as small as 300 nm are formed.

Interference nanolithography with a UV laser

The sensitivity and resolution of a photoresist composed of a two-layer (polymer-metallic indium) film are measured. 2D masks used to create nanodimensional metallic and insulating islands on a silicon substrate are prepared by direct laser action. Conditions are found for preparing submicron periodic structures on TiO2 films that are applied on a glass substrate by the sol-gel technology. Optical properties of these arrays are measured, and it is shown that they can be used for exciting plane electromagnetic waves.

Nanoscale relief on quartz: from phase masks to anti-reflection structures

Nanoscale periodic and quasiperiodic relieves on fused quartz are of interest for the creation of a variety of optical and electronic devices such as phase masks, one- and two-dimensional stamps for nanoimprint and wide-band antireflection structures. The authors of this paper have developed a method of interference lithography to pattern nanoscale relief on quartz with a high-power pulsed XeCl laser with high-quality output radiation at wavelength 308nm. One of the advantages of the proposed technique is the significantly smaller influence of mechanical oscillations in an optical setup on the results of nanoscale modification. The relief on quartz was formed with the use of a complete cycle of lithography. As the mask, a two-layer structure of a copper film of 50nm in thickness and a photoresist of 400nm in thickness were employed. The mask pattern was formed by exposure of a photoresist by two radiation beams of a XeCl laser with energy density ~ 30mJ/cm2, aqueous-alkali development of a photoresist, and copper etching by the ion beam (Ar+). Quartz was etched by the method of ion-beam reactive etching in a flow of CF4 - O2(20%) gas mixture, with etching rate 30nm/min.