Ethanol-mediated metal transfer printing on organic films

Ethanol-mediated metal transfer printing (mTP) is a soft method, which allows to efficiently deposit metals onto various organic surfaces for applications in organic electronics. This simple approach in based on the stronger adhesion of the metals to the organic materials in the presence of thin ethanol layer between the metallized PDMS and the substrate due to the capillary action. Patterns with a resolution of at least 20 μm have been obtained on organic polymeric materials and photoresists without heating or applied pressure. Compared to other methods ethanol mediated mTP is considerably faster and has smaller limitations on the stamp depth. Residual silicone layer detected on the metal surface after the transfer by XPS studies has been mostly removed by UV/ozone treatment. Organic field-effect transistors (OTFTs) based on the metal electrodes deposited by mTP have been successfully fabricated and tested.     

Direct micro/nano metal patterning based on two-step transfer printing of ionic metal nano-ink

We present a direct metal patterning method by a two-step transfer printing process of non-particle, ionic metal nano-ink solution. This fabrication method allows a simple direct patterning of various micro/nanoscale metallic structures. Complex structures such as multilayer line arrays, patterns along non-flat topologies, and micro/nanoscale hybrid patterns can be achieved by using this process. Also, the low temperature and pressure process conditions are compatible with the fabrication of electronic structures and devices on flexible substrates such as polyimide film and photographic papers. As an application of this process, we fabricated ZnO nanowire-based flexible UV sensors, where metal electrodes were fabricated by two-step transfer printing. In the case of ZnO nanowire sensors, highly sensitive and fast responding performances to UV illumination and good mechanical robustness against repeated bending conditions could be verified.     

High-resolution, resistless patterning of indium-tin-oxide thin films using excimer laser projection annealing process

High-resolution, large-area patterning of indium-tin-oxide (ITO) thin film was demonstrated using an excimer laser projection crystallization process. After amorphous ITO (a-ITO) was deposited on a glass substrate, the a-ITO was selectively crystallized using an excimer laser scanning projection exposure system. Following the selective crystallization, the substrate was dipped in an etchant for an optimized time, resulting in formation of high-resolution patterns of polycrystalline ITO (p-ITO) on the substrate because the a-ITO has higher etch rate than the p-ITO. The p-ITO patterns were clean and sharp, and the pattern quality was suitable for production applications in the microelectronics industry.     

Direct patterning of double-layered metal thin films by a pulsed Nd:YAG laser beam

Metal thin-film patterning is of technological significance because modern electronic devices commonly require an electrode or metallization pattern. There are many cases where this pattern consists of two different metallic layers in order to improve the mechanical and electrical contact. We here show that double-layered metal thin films evaporated on glass can be directly patterned by a spatially-modulated pulsed Nd-YAG laser beam incident from the backside of the substrate. This method utilizes a pulsed laser-induced thermo-elastic force exerting on the film which plays a role to detach it from the substrate. Since the film is polycrystalline with nano-sized grains, a spatially-modulated thermo-elastic force may enable selective removal of the material by shearing along the weakly-bonded grain boundary regions. Many different combinations of Al, Ag, and Au layers have been investigated and their pattern fidelity and morphology are discussed, along with the simulation results for double-layered nanocystalline films.     

Heat transfer mechanisms during short-duration laser heating of thin metal films

A perturbation technique is used to simplify the generalized governing equations of the parabolic two-step model. The generalized form of the two-step model contains diffusion terms in both electron and lattice energy equations and assumes that incident laser radiation is absorbed by both electron gas and solid lattice to account for the thermal behavior of semiconducting and impure materials. The simplified perturbation technique is used to eliminate the coupling between the electron and the lattice energy equations when the temperature difference between the electron and the lattice is a small perturbed quantity, which is true in materials exhibiting high coupling factors. A mathematical criterion is derived to determine the conditions under which electron and lattice are in thermal equilibrium. It is found that five dimensionless parameters control the state of thermal equilibrium between the lattice and the electron.     

Direct transfer patterning of gold films with minimal processing steps

We were able to reduce the processing steps of transfer printing of thin gold films through prolonged evaporation times. We suspect the reduced evaporation rate to cause diffusion of small chain molecules (oligomers) in the PDMS (poly(dimethylsiloxane)) stamp to facilitate the transfer. Typical wrinkling of the PDMS surface was avoided by fabricating thin stamps of approximately 50 μm with polymer backing. The transferred films with a thickness of 20 nm showed enhanced edge resolution and a roughness of 1.31 nm root mean square. We were further able to fabricate 3D structures, indicating stability of the transferred films. Adhesion problems remain a limitation for contacting purposes.     

Void growth in thin silver films

A high density of small voids was observed in thin films of silver on examination with a high resolution transmission electron microscope. Void growth was studied in these films by annealing them in a vacuum as well as in the electron microscope using a specimen heating stage. Heating of the films to 700°C led to thermal grooving at the grain boundaries and finally to grain separation. It appears that the void growth occurs essentially as a result of annihilation of excess vacancies trapped in the film. The observed phenomena of thermal grooving and grain separation can be explained in terms of surface diffusion of silver atoms.     

Optical switch from silver nanocomposite thin films

Silver nanoparticles capped with sodium alginate were assembled into thin films by using the layer-by-layer dipping technique. Composite films were built by sequential dipping of a glass slide in either anionic alginate capped nanoparticles or cationic Poly(diallyldimethylammonium chloride) (PDADMAC). The growth of the film was characterized using UV-Vis spectroscopy by monitoring the increase in absorbance at 420 nm which correspond to the silver nanoparticles plasmon band. The final films formed onto glass slides displayed and interesting color shift upon exposure to water or to a less polar solvent such as ethanol. In this research, changes in spectral absorbance of the nanoparticles film were monitored as a function of ethanol content (0, 20, 40, 60, 80 and 100%) in water. The color shift from yellow to red color was explained by the changes in the dielectric constant of the silver nanoparticles surrounding medium which induce a shift in their plasmon band absorbance. These composite thin films displayed fast color change and could therefore be used in sensing application as well as for optical switches.     

Transport properties of thin metal films

The electrical conductivity, thermal conductivity and thermoelectric power of a metal film subjected to the simultaneous action of an electric field and a temperature gradient were calculated. Analytical equations for the electrical and thermal current densities in thin metal films were obtained.     

Thermophysical properties of thin metal films

The article discusses methods and results of comprehensive investigations of the thermal conductivity, thermal diffusivity, heat capacity, and structure of films of metals 10–10² nm in thickness.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 4, pp. 606–613, April, 1980.     

Thermophysical properties of thin metal films

A method is proposed for determining thermophysical properties of thin metallic films, using solutions of converse thermal conductivity problems.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 1, pp. 130–135, January, 1990.     

Selective atomic layer deposition of metal oxide thin films on patterned self-assembled monolayers formed by microcontact printing

We demonstrate a selective atomic layer deposition of TiO2, ZrO2, and ZnO thin films on patterned alkylsiloxane self-assembled monolayers. Microcontact printing was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. The patterned monolayers define and direct the selective deposition of the metal oxide thin films using atomic layer deposition. The selective atomic layer deposition is based on the fact that the metal oxide thin films are selectively deposited only on the regions exposing the silanol groups of the Si substrates because the regions covered with the alkylsiloxane monolayers do not have any functional group to react with precursors.     

The inherent optical nonlinearities of thin silver films

Thin Ag films with the thickness of 80 Å were prepared by pulsed laser deposition technique. The films were grown on MgO(1 0 0) substrates under the nitrogen pressure of 5.0 Pa at room temperature. The surface images of the films were observed by atomic force microscopy. The linear optical properties of the films were studied in the wavelength range of 300–800 nm. The inherent third-order nonlinear optical responses coming from the silver material itself were determined by z-scan method at the wavelength of 532 nm with laser duration of 10 ns. The significant optical nonlinearities of the pure thin Ag films were determined to have the real and imaginary parts of the third-order nonlinear optical susceptibility (χ⁽³⁾) as 2.49 × 10⁻⁸ and 7.16 × 10⁻⁹ esu, respectively. The obtained χ⁽³⁾ value of Ag films was about one order of magnitude larger than that of Ag colloids.     

Photoelectrochemical properties of anodic silver sulphide thin films

We have investigated the semi-conducting properties and photoelectrochemical characterization of Ag₂S thin films electrodeposited galvanostatically onto silver substrate from alkaline S²⁻ bath. Films grown with a low current density not exceeding 20 μA cm⁻² are uniform and well adhered. An optimal thickness of 1.34 μm has been determined. At high current density, oxygen evolution occurs simultaneously and provokes crashing of films. From photoelectrochemical measurements, the band gap was found to be 1.85 eV and the transition is indirectly allowed. The Mott-Schottky plot exhibits a linear behavior, characteristic of n-type conductivity, from which a flat band potential of − 1.20 V_SCE and a donor density of 5.63 × 10¹⁶ cm⁻³ were determined. The conduction band, located at 3.28 eV, is made up of mainly Ag-5s wave function. Ag₂S is long lived and under illumination, it is stabilized by holes consumption reactions involving S_n²⁻/S²⁻ redox couple. A conversion efficiency of 1.1% and a fill factor of 0.27 have been obtained. The electrochemical impedance spectroscopy, measured over a wide frequency range (10⁻²-10⁵ Hz), reveals contribution of the bulk effect. The experimental data are modeled by shifting the centre of the semi−circle down the real axis and interpreted in terms of constant phase element due mainly to the porosity and inhomogeneity of the film.