We present an overview of the different processes that can result from focusing an ultrafast laser light in the femtosecond–nanosecond time regime on a host of materials, e.g., metals, semiconductors, and insulators. We summarize the physical processes and surface and bulk applications and highlight how femtosecond lasers can be used to process various materials. Throughout this paper, we will show the advantages and disadvantages of using ultrafast lasers compared with lasers that operate in other regimes and demonstrate their potential for the ultrafast processing of materials and structures.

Ultrafast laser processing of materials: a review

This review article aims to provide an updated and comprehensive description on the development of atomic force microscopy (AFM) nanolithography for structuring and fabrication at the nanometer scale. The many AFM nanolithographic techniques are classified into two general groups of force-assisted and bias-assisted nanolithography on the basis of their mechanistic and operational principles. Force-assisted AFM nanolithography includes mechanical indentation and plowing, thermomechanical writing, manipulation and dip-pen nanolithography. Bias-assisted AFM nanolithography encompasses probe anodic oxidation, field evaporation, electrochemical deposition and modification, electrical cutting and nicking, electrostatic deformation and electrohydrodynamic nanofluidic motion, nanoexplosion and shock wave generation, and charge deposition and manipulation. The experimental procedures, pattern formation mechanisms, characteristics, and functionality of nanostructures and nanodevices fabricated by AFM nanolithography are reviewed. The capabilities of AFM nanolithography in patterning a large family of materials ranging from single atoms and molecules to large biological networks are presented. Emphasis is given to AFM nanolithographic techniques such as dip-pen nanolithography, probe anodic oxidation, etc. due to the rapid progress and wide applications of these techniques.

Nanoscale materials patterning and engineering by atomic force microscopy nanolithography

Laser Beam MicroMachining (LBMM) – A review

In thermomechanical data writing, a resistively-heated atomic force microscope (AFM) cantilever tip forms indentations in a thin polymer film. The same cantilever operates as a thermal proximity sensor to detect the presence of previously written data bits. This paper uses recent progress in thermal analysis of the writing and reading modes to develop new cantilever designs for increased speed, sensitivity, and reduced power consumption in both writing and reading operation. Measurements of cantilever electrical resistance during heating reveals physical limits of cantilever writing and reading, and verifies a finite-difference thermal and electrical simulation of cantilever operation. This work proposes two new cantilever designs that correspond to fabrication technology benchmarks. Simulations predict that the proposed cantilevers have a higher data rate and are more sensitive than the present cantilever. The various cantilever designs offer single-bit writing times of 0.2 /spl mu/s-25 /spl mu/s for driving voltages of 2-25 V. The thermal reading /spl Delta/R/R sensitivity is as high as 4/spl times/10/sup -4/ per vertical nm in near steady-state operation.

https://nanoheat.stanford.edu/sites/default/files/publications/A61.pdf

Design of atomic force microscope cantilevers for combined thermomechanical writing and thermal reading in array operation

We describe an analytical method for element-specific in situ investigations of biological samples with high spatial resolution, using laser-induced-breakdown spectroscopy (LIBS). The prerequisites for spatially highly resolved LIBS are an appropriate analytical performance in combination with precise micro-ablation conditions, both laterally and axially. In order to identify the best suitable laser source, the analytical performance and the ablation process were studied for ns-LIBS and fs-LIBS. The analytical performance was studied on an aqueous solution of CaCl2, where water served as a first substitute for biological material. The ablation process was investigated in the outer epidermal wall of a sunflower seedling stem. Besides direct measurements, the physiology of the sunflower seedling can be used in order to estimate the ablation depth. Our results show that analytical measurements with high spatial resolution can be performed on biological samples using fs-LIBS. This was demonstrated by in situ measurements of wall-associated calcium ion (Ca2+) distributions within the peripheral cell wall of the sunflower seedling (Helianthus annuus L.) stem. In this biological sample an axial resolution of about 100 nm was achieved.

Femtosecond laser-induced-breakdown spectrometry for Ca2+ analysis of biological samples with high spatial resolution

We present dynamic plowing nanolithography on polymethylmethacrylate films, performed with a scan-linearized atomic force microscope able to scan up to 250 μm with high resolution. Modifications of the surface are obtained by plastically indenting the film surface with a vibrating tip. By changing the oscillation amplitude of the cantilever, i.e., the indentation depth, surfaces can be either imaged or modified. A program devoted to the control of the scanning process is also presented. The software basically converts the gray scale of pixel images into voltages used to control the dither piezo driving cantilever oscillations. The advantages of our experimental setup and the dependence of lithography efficiency on scanning parameters are discussed. Some insights into the process of surface modifications are presented.

Dynamic plowing nanolithography on polymethylmethacrylate using an atomic force microscope

Ti:sapphire laser pulses of 130 fs and 800 nm were focused on 3.2-μm-thick TiN films by a 60-mm focal length lens in air. The morphology of the ablated areas generated by laser pulses at a fluence slightly above the ablation threshold was characterized in dependence on the pulse number by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The cavity profiles, depths, diameters, and volumes were quantitatively evaluated by AFM. The polarization state of the laser light is discussed as a further parameter, in addition to fluence and pulse number, that influences and controls the ablation precision of these materials. It was observed that circularly polarized radiation enhances the average ablation rates and reduces the roughness in the cavities by a factor of 2–3 as compared to linearly polarized radiation of the same incident laser fluence. Special attention was paid to the interfacial region between the coating and substrate. Ultrashort-pulse laser drilling into the Si substrate revealed the generation of columnar features which even may surmount the original coating under laser conditions.

M. Geuss

Papers

Dynamic plowing nanolithography on polymethylmethacrylate using an atomic force microscope

The precision of the femtosecond-pulse laser ablation of TiN films on silicon