Subwavelength Nanostructuring of Gold Films by Apertureless Scanning Probe Lithography Assisted by a Femtosecond Fiber Laser Oscillator

Optical methods in nanolithography have been traditionally limited by Abbe’s diffraction limit. One method able to overcome this barrier is apertureless scanning probe lithography assisted by laser. This technique has demonstrated surface nanostructuring below the diffraction limit. In this study, we demonstrate how a femtosecond Yb-doped fiber laser oscillator running at high repetition rate of 46 MHz and a pulse duration of 150 fs can serve as the laser source for near-field nanolithography. Subwavelength features were generated on the surface of gold films down to a linewidth of 10 nm. The near-field enhancement in this apertureless scanning probe lithography setup could be determined experimentally for the first time. Simulations were in good agreement with the experiments. This result supports near-field tip-enhancement as the major physical mechanisms responsible for the nanostructuring.© 2018 by the author

Highly Photosensitive Daguerreotypes and their Reproduction: Physico‐chemical Elucidation of Innovative Processes in Photography Developed around 1840 in Vienna

A physico‐chemical elucidation of the first photographic technology that allowed manifold reproduction is presented. An etched daguerreotype manufactured around 1840 in Vienna, preserved by the Technisches Museum Wien, served as a case study. Surface analysis showed that the photographic process involved the formation of colloidal Ag nanoparticles with sizes of 30–120 nm with shell layers consisting of Ag2O, Ag2S, and some AgCl. This breakthrough photographic technique provided a hitherto unachieved high sensitivity because of various halogenide mixtures without the use of Hg. The image development consisted of the reduction of the Ag halides by H2SO3 created by the hydrolysis of S2Cl2 leading to the formation of Ag nanoparticles adjacent to the Ag nuclei of the latent image. The fixing of the image was performed either by KCN or by Na2S2O3. The investigated plate exhibits etched areas with Ag2O conversion layers and no Cl or S. The gum arabic use for etching preferentially wetted the exposed Ag nanoparticle regions so that unexposed areas could be etched by HNO3.© 2019 The Author

Investigation of the wavelength dependence of laser stratigraphy on Cu and Ni coatings using LIBS compared to a pure thermal ablation model

In this study, galvanic coatings of Cu and Ni, typically applied in industrial standard routines, were investigated. Ablation experiments were carried out using the first two harmonic wavelengths of a pulsed Nd:YAG laser and the resulting plasma spectra were analysed using a linear Pearson correlation method. For both wavelengths the absorption/ablation behaviour as well as laser-induced breakdown spectroscopy (LIBS) depth profiles were studied varying laser fluences between 4.3–17.2 J/cm2 at 532 nm and 2.9–11.7 J/cm2 at 1064 nm. The LIBS-stratigrams were compared with energy-dispersive X-ray spectroscopy of cross-sections. The ablation rates were calculated and compared to theoretical values originating from a thermal ablation model. Generally, higher ablation rates were obtained with 532 nm light for both materials. The light–plasma interaction is suggested as possible cause of the lower ablation rates in the infrared regime. Neither clear evidence of the pure thermal ablation, nor correlation with optical properties of investigated materials was obtained.© The Author(s) 201

Femtosecond laser generation of microbumps and nanojets on single and bilayer Cu/Ag thin films

The formation mechanisms of microbumps and nanojets on films composed of single and double Cu/Ag layers deposited on a glass substrate and irradiated by a single 60 fs laser pulse are investigated experimentally and in atomistic simulations. The composition of the laser-modified bilayers is probed with the energy dispersive X-ray spectroscopy and used as a marker for processes responsible for the modification of the film morphology. For the bilayer with the top Ag layer facing the laser, the increase in fluence is found to result in a sequential appearance of a Ag microbump, the exposure of the Cu underlayer by removal of the Ag layer, a Cu microbump, and a frozen nanojet. The Cu on Ag bilayer exhibits a partial spallation of the top Cu film, followed by the generation of surface structures that mainly consist of Ag at higher fluences. The experimental observations are explained with atomistic simulations, which reveal that the stronger electron–phonon coupling of Cu results in the confinement of the deposited laser energy in the top Cu layer in the Cu on Ag case and channelling of the energy from the top Ag layer to the underlying Cu layer in the Ag on Cu case. This difference in the energy (re)distribution directly translates into differences in the morphology of the laser-modified bilayers. In all systems, the generation of microbumps and nanojets occurs in the molten state. It is driven by the dynamic relaxation of the laser-induced stresses and, at higher fluences, the release of vapor at the interface with the substrate. The resistance of the colder periphery of the laser spot to the ejection of spalled layers as well as the rapid solidification of the transient molten structures are largely defining the final shapes of the surface structures

Femtosecond laser processing of biopolymers at high repetition rate

The large intensities available with femtosecond (fs) laser pulses allow permanent structural modifications in transparent materials with high spatial resolution. Irradiation of self-standing transparent biopolymer films, such as collagen, pure and curcumin doped gelatine employing a 60-fs high-power 11 MHz Ti-Sapphire oscillator laser system linked to an optical microscope led to modifications and ablation. Swelling modifications consisting in the foaming of the irradiated area and formation of a single layer of bubbles arranged around the narrow ablation crater were investigated by optical, scanning force (SFM) and scanning electron (SEM) microscopy. These modifications occur at fluences below the respective ablation thresholds, i.e. ablation processes take place on modified swelled phases. The results are discussed in terms of local temperature increase, generation of thermoelastic stress, physico-chemical effects, and in terms of an incubation model, i.e. the accumulation of these phenomena upon successive pulse irradiation

Alkoxylated β-Naphthol as an Additive for Tin Plating from Chloride and Methane Sulfonic Acid Electrolytes

β-naphthol was one of the first additives introduced for smooth and homogeneous tin electrodeposition. Although it can be oxidized under the plating conditions, forming either 1,2-napthoquinone or polymeric materials based on naphthioxides, it is still in use. In this work, an investigation of its more stable form, alkoxylated β-naphthol (ABN), on tin plating is undertaken. For this purpose, chloride based (pH ~5) and methane sulfonic acid (MSA, pH ~0.5) electrolytes, including ABN, were prepared. Reaction kinetics were studied by polarization, Tafel measurements, and cyclic voltammetry. Tin electrodeposits were obtained on flat brass substrates. Surface morphology and preferred crystal orientation were studied by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). In both studied electrolytes ABN acts as an inhibitor but in the case of the chloride electrolyte it is more pronounced. In the MSA electrolyte this effect was overlaid by the presence of tin-citrate complexes. In the chloride-based electrolyte, ABN has a grain refining effect, while in the MSA electrolyte an increase of ABN concentration leads to a slight enlargement of the average grain size. X-ray analysis shows a constant decrease of the (101) intensity with increasing concentration of ABN for the sample deposited from both baths.© 2018 by the author

Nanocrystalline Ga2O3 films deposited by spray pyrolysis from water-based solutions on glass and TCO substrates

A low-cost and up-scalable fabrication method for high-quality gallium oxide films using spray pyrolysis from water-based solutions and moderate temperatures is presented. The solution chemistry and spraying process parameters were optimized to obtain homogeneous films on glass and three different transparent conducting oxide substrates. Structural and optical film properties of the deposited nanocrystalline Ga2O3 were evaluated by scanning electron microscopy, grazing-incidence X-ray diffraction, atomic force microscopy and optical spectroscopy. The elemental composition of the surface and the bulk film was analyzed by X-ray photoemission spectroscopy depth profiling. To show the applicability of the deposited Ga2O3 in electronic devices, the electronic valence region of the material was studied by ultraviolet photoemission spectroscopy, resulting in an energy level diagram of the material