Triazene Polymer Research Articles

Ferrocene pixels by laser-induced forward transfer: towards flexible microelectrode printing

The aim of this work is to demonstrate the potential of laser-induced forward transfer (LIFT) as a printing technology, alternative to standard microfabrication techniques, in the area of flexible micro-electrode fabrication.First, ferrocene thin films are deposited onto fused silica and fused silica substrates previously coated with a photodegradable polymer film (triazene polymer) by matrix assisted pulsed laser evaporation (MAPLE). The morphology and chemical structure of the ferrocene thin films deposited by MAPLE has been investigated by atomic force microscopy and Fourier transformed infrared spectroscopy, and no structural damage occurs as a result of the laser deposition.Second, LIFT is applied to print for the first time ferrocene pixels and lines onto flexible polydimethylsiloxane (PDMS) substrates. The ferrocene pixels and lines are flawlessly transferred onto the PDMS substrates in air at room temperature, without the need of additional conventional photolithography processes.We believe that these results are very promising for a variety of applications ranging from flexible electronics to lab-on-a-chip devices, MEMS, and medical implants.

A study of photothermal laser ablation of various polymers on microsecond time scales.

To analyze the photothermal ablation of polymers, we designed a temperature measurement setup based on spectral pyrometry. The setup allows to acquire 2D temperature distributions with 1 μm size and 1 μs time resolution and therefore the determination of the center temperature of a laser heating process. Finite element simulations were used to verify and understand the heat conversion and heat flow in the process. With this setup, the photothermal ablation of polystyrene, poly(α-methylstyrene), a polyimide and a triazene polymer was investigated. The thermal stability, the glass transition temperature Tg and the viscosity above Tg were governing the ablation process. Thermal decomposition for the applied laser pulse of about 10 μs started at temperatures similar to the start of decomposition in thermogravimetry. Furthermore, for polystyrene and poly(α-methylstyrene), both with a Tg in the range between room and decomposition temperature, ablation already occurred at temperatures well below the decomposition temperature, only at 30–40 K above Tg. The mechanism was photomechanical, i.e. a stress due to the thermal expansion of the polymer was responsible for ablation. Low molecular weight polymers showed differences in photomechanical ablation, corresponding to their lower Tg and lower viscosity above the glass transition. However, the difference in ablated volume was only significant at higher temperatures in the temperature regime for thermal decomposition at quasi-equilibrium time scales.

Comparison of 193 nm and 308 nm laser liquid printing by shadowgraphy imaging

Over the last years laser-induced forward transfer has emerged as a versatile and powerful tool for engineering surfaces with active compounds. Soft, easily damageable materials can be transferred using a triazene polymer as a sacrificial layer which acts as a pressure generator and at the same time protects the material from direct laser irradiation. To understand and optimize the transfer process of biomolecules in liquid solution by using an intermediate triazene polymer photosensitive layer, shadowgraphy imaging is carried out. Two laser systems i.e. an ArF laser operating at 193nm and a XeCl laser operating at 308nm are applied for the transfer. Solutions with 50% v/v glycerol concentration are prepared and the influence of the triazene polymer sacrificial layer thickness (60nm) on the deposits is studied. The shadowgraphy images reveal a pronounced difference between laser-induced forward transfer using 193nm or 308nm, i.e. very different shapes of the ejected liquid.

Shadowgraphic investigations into the laser-induced forward transfer of different SnO2 precursor films

Laser-induced forward transfer of different SnO2 precursor films for sensor applications were investigated using time resolved imaging, from 0 to 2μs after the onset of the ablation process. Transfers of SnCl2(acac)2 and SnO2 nano-particles, both with and without a triazene polymer dynamic release layer (DRL), were investigated and compared to transfers of aluminum films with a triazene polymer DRL. Shockwave speed and flyer speeds at high laser fluences of Φ=650 mJ/cm2 and at the lower fluences, suitable for the transfer of functional and well defined pixels were analyzed.No influence of the use of a triazene polymer DRL on shockwave and flyer speed was observed. Material ejected under transfer condition showed a velocity of around 200m/s with a weak shockwave.

Laser induced forward transfer of SnO2 for sensing applications using different precursors systems

This paper presents the transfer of SnO2 by laser induced forward transfer (LIFT) for gas sensor applications. Different donor substrates of SnO2 with and without triazene polymer (TP) as a dynamic release layer were prepared. Transferring these films under different conditions were evaluated by optical microscopy and functionality. Transfers of sputtered SnO2 films do not lead to satisfactory results and transfers of SnO2 nanoparticles are difficult. Transfers of SnO2 nanoparticles can only be achieved when applying a second laser pulse to the already transferred material, which improves the adhesion resulting in a complete pixel. A new approach of decomposing the transfer material during LIFT transfer was developed. Donor films based on UV absorbing metal complex precursors namely, SnCl2(acac)2 were prepared and transferred using the LIFT technique. Transfer conditions were optimized for the different systems, which were deposited onto sensor-like microstructures. The conductivity of the transferred material at temperatures of about 400 ∘C are in a range usable for SnO2 gas sensors. First sensing tests were carried out and the transferred material proved to change conductivity when exposed to ethanol, acetone, and methane.

The optimisation of the laser-induced forward transfer process for fabrication of polyfluorene-based organic light-emitting diode pixels

Laser-induced forward transfer (LIFT) has already been used to fabricate various types of organic light-emitting diodes (OLEDs), and the process itself has been optimised and refined considerably since OLED pixels were first demonstrated. In particular, a dynamic release layer (DRL) of triazene polymer has been used, the environmental pressure has been reduced down to a medium vacuum, and the donor receiver gap has been controlled with the use of spacers. Insight into the LIFT process's effect upon OLED pixel performance is presented here, obtained through optimisation of three-colour polyfluorene-based OLEDs. A marked dependence of the pixel morphology quality on the cathode metal is observed, and the laser transfer fluence dependence is also analysed. The pixel device performances are compared to conventionally fabricated devices, and cathode effects have been looked at in detail. The silver cathode pixels show more heterogeneous pixel morphologies, and a correspondingly poorer efficiency characteristics. The aluminium cathode pixels have greater green electroluminescent emission than both the silver cathode pixels and the conventionally fabricated aluminium devices, and the green emission has a fluence dependence for silver cathode pixels.

Sequential Printing by Laser-Induced Forward Transfer To Fabricate a Polymer Light-Emitting Diode Pixel

Patterned deposition of polymer light-emitting diode (PLED) pixels is a challenge for electronic display applications. PLEDs have additional problems requiring solvent orthogonality of different materials in adjacent layers. We present the fabrication of a PLED pixel by the sequential deposition of two different layers with laser-induced forward transfer (LIFT), a "dry" deposition technique. This novel use of LIFT has been compared to "normal" LIFT, where all the layers are transferred in a single step, and a conventional PLED fabrication process. For the sequential LIFT, a 50-nm film of an alcohol-soluble polyfluorene (PFN) is transferred onto a receiver with a transparent anode, before an aluminum cathode is transferred on top. Both steps use a triazene polymer dynamic release layer and are performed in a medium vacuum (1 mbar) across a 15 μm gap. The rough morphologies of the single-layer PFN pixels and the PLED device characteristics have been investigated and compared to both bilayer Al/PFN pixels fabricated by normal LIFT and conventionally fabricated devices. The functionality of the sequential LIFT pixels (0.003 cd/A, up to 200 mA/cm(2), at 30-40 V) demonstrates the suitability of LIFT for sequential patterned printing of different thin-film layers.

Nerve agent simulant detection by solidly mounted resonators (SMRs) polymer coated using laser induced forward transfer (LIFT) technique

Abstract Novel chemical sensor based on film bulk acoustic resonators (FBARs), in the solidly mounted resonator (SMR) configuration, exploiting three polymer sensitive layers deposited by laser-induced forward transfer (LIFT) are reported. The resonators operate at a frequency of 2 GHz and consist of a piezoelectric aluminium nitride film “sandwiched” between two metal electrodes deposited on a silicon substrate with an acoustic Bragg reflector at the interface to ensure the acoustic insulation. Chemically sensitive polymers, i.e. polyepichlorohydrin (PECH), polyethyleneimine (PEI), and polyisobutylene (PIB), are applied by LIFT onto the SMRs. In order to improve the process efficiency, and to protect the polymer materials from the energetic laser pulses, a triazene polymer, acting as a dynamic release layer (DRL) was used. Upon exposure to different concentrations of dimethyl methyl phosphonate (DMMP) vapour, the polymer coated sensors show fast and reversible responses, with a sensitivity between 239 and 405 Hz/ppm. Our findings, i.e. the use of LIFT in conjunction with highly sensitive, robust, and reliable SMR transducers show that this approach is well-suited to implement chemical sensor arrays.

Improved laser-induced forward transfer of organic semiconductor thin films by reducing the environmental pressure and controlling the substrate–substrate gap width

Laser-induced forward transfer (LIFT) has been investigated for bilayer transfer material systems: silver/organic film (Alq3 or PFO). The LIFT process uses an intermediate dynamic release layer of a triazene polymer. This study focuses on the effect of introducing a controlled donor–receiver substrate gap distance and the effect of doing the transfer at reduced air pressures, whilst varying the fluence up to ∼200 mJ/cm2. The gap between ‘in-contact’ substrates has been measured to be a minimum of 2–3 μm. A linear variation in the gap width from ‘in contact’ to 40 μm has been achieved by adding a spacer at one side of the substrate–substrate sandwich. At atmospheric pressure, very little transfer is achieved for Alq3, although PFO shows some signs of successful doughnut transfer (with a large hole in the middle) in a narrow fluence range, at gaps greater than 20 μm. For the transfer of Ag/PFO bilayers at atmospheric pressure, the addition of a PFO layer onto the receiver substrate improved the transfer enormously at smaller gaps and higher fluences. However, the best transfer results were obtained at reduced pressures where a 100% transfer success rate is obtained within a certain fluence window. The quality of the pixel morphology at less than 100 mbar is much higher than at atmospheric pressure, particularly when the gap width is less than 20 μm. These results show the promise of LIFT for industrial deposition processes where a gap between the substrates will improve the throughput.

Laser induced forward transfer aluminum layers: Process investigation by time resolved imaging

Laser induced forward transfer of an aluminum thin film on a triazene polymer as a sacrificial layer has been studied with time resolved imaging. Both side- and front-on imaging of the process give a more detailed understanding of the stability of the ejected material during flight. For high fluence ablation (800mJ/cm2) the flyer is stable for 400ns and gets decomposed completely when interacting with the shockwave after 1μs. Material detachments on the edges of the flyer are observed at an early stage of the ablation process (<200ns) which leads to a pixel smaller than its ablation cross section.For low laser fluence (200mJ/cm2) the flyer has the size of the ablation spot and keeps its shape for nearly 1μs. The back pressure of the decomposed triazene polymer bends the flyer towards the direction of flight and indications for folding are observed.

Laser-induced ablation dynamics and flight of thin polymer films

We investigated the ejection dynamics of triazene polymer layers in the thickness range of 40 nm to 600 nm upon nanosecond laser ablation at a wavelength of 532 nm. The ablation is due to laser-induced thermal degradation of a small part of the polymer in contact with the silicon substrate. The subsequent dynamics of the flying polymer layer are measured with sub-nanosecond time resolution. The evaluation of the initial velocity for different film thicknesses gives insight into the energy transfer process during the acceleration of the films.

Laser-Induced Forward Transfer of Polymer Light-Emitting Diode Pixels with Increased Charge Injection

Laser-induced forward transfer (LIFT) has been used to print 0.6 mm × 0.5 mm polymer light-emitting diode (PLED) pixels with poly[2-methoxy, 5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) as the light-emitting polymer. The donor substrate used in the LIFT process is covered by a sacrificial triazene polymer (TP) release layer on top of which the aluminium cathode and functional MEH-PPV layers are deposited. To enhance electron injection into the MEH-PPV layer, a thin poly(ethylene oxide) (PEO) layer on the Al cathode or a blend of MEH-PPV and PEO was used. These donor substrates have been transferred onto both plain indium tin oxide (ITO) and bilayer ITO/PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) blend) receiver substrates to create the PLED pixels. For comparison, devices were fabricated in a conventional manner on ITO substrates coated with a PEDOT:PSS hole-transporting layer. Compared to multilayer devices without PEO, devices with ITO/PEDOT:PSS/MEH-PPV:PEO blend/Al architecture show a 100 fold increase of luminous efficiency (LE) reaching a maximum of 0.45 cd/A for the blend at a brightness of 400 cd/m(2). A similar increase is obtained for the polymer light-emitting diode (PLED) pixels deposited by the LIFT process, although the maximum luminous efficiency only reaches 0.05 cd/A for MEH-PPV:PEO blend, which we have attributed to the fact that LIFT transfer was carried out in an ambient atmosphere. For all devices, we confirm a strong increase in device performance and stability when using a PEDOT:PSS film on the ITO anode. For PLEDs produced by LIFT, we show that a 25 nm thick PEDOT:PSS layer on the ITO receiver substrate considerably reduces the laser fluence required for pixel transfer from 250 mJ/cm(2) without the layer to only 80 mJ/cm(2) with the layer.

Liposome micropatterning based on laser-induced forward transfer

The numerous properties of liposomes, i.e., non- toxicity, biodegradability, and their ability to encapsulate different biological active substances in aqueous and lipid phase, make them perfect models of biomembranes. Lipo- somes made up of phospholipids may be used to study new applications such as cell targeting or, under specific experi- mental conditions, may be applied in micro and nano-sized biosensors. This study demonstrates the capability of direct laser printing of liposomes in micron-scale patterns for the real- ization of biosensors or drug delivery systems. The transfer experiments were carried out onto ordinary glass substrates, and optical microscopy images reveal that well-defined patterns without splashes can be obtained for a narrow range of laser transfer fluences using 193 nm irra- diation and an intermediate triazene polymer. The triazene polymer with different thicknesses was used as sacrificial layer with the purpose of protecting the liposome solution

Improvement in semiconductor laser printing using a sacrificial protecting layer for organic thin-film transistors fabrication

Laser-induced forward transfer (LIFT) has been used to deposit pixels of an organic semiconductor, distyryl-quaterthiophenes (DS4T). The dynamics of the process have been investigated by shadowgraphic imaging for the nanosecond (ns) and picosecond (ps) regime on a time-scale from the laser iradiation to 1.5 μs. The morphology of the deposit has been studied for different conditions. Intermediate sacrificial layer of gold or triazene polymer has been used to trap the incident radiation. Its role is to protect the layer to be transferred from direct irradiation and to provide a mechanical impulse strong enough to eject the material.

Microfabrication of polystyrene microbead arrays by laser induced forward transfer

In this study we describe a simple method to fabricate microarrays of polystyrene microbeads (PS-μbeads) on Thermanox coverslip surfaces using laser induced forward transfer (LIFT). A triazene polymer layer which acts as a dynamic release layer and propels the closely packed microspheres on the receiving substrate was used for this approach. The deposited features were characterized by optical microscopy, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. Ultrasonication was used to test the adherence of the transferred beads. In addition, the laser ejection of the PS-μbead pixels was investigated by time resolved shadowgraphy. It was found that stable PS-μbeads micropatterns without any specific immobilization process could be realized by LIFT. These results highlight the increasing role of LIFT in the development of biomaterials, drug delivery, and tissue engineering.

Polymer pixel enhancement by laser-induced forward transfer for sensor applications

This paper presents polymer pixel printing for applications in chemoselective sensors where nanosecond laser direct transfer methods, with a triazene polymer (TP) acting as a Dynamic Release Layer (DRL), are used. A sys- tematic study of laser fluence, donor film morphology and both single- and multiple-pixel deposition were optimized with the final goal to obtain continuous pixels of sensi- tive polymers, polyethylenimine (PEI) and polyisobutylene (PIB), on SAW surfaces. Morphology characterization after the laser transfer has been performed by Optical Microscopy and Scanning Electron Microscopy (SEM). The responses of the coated transducers were measured after deposition with different laser fluences and it was found that a fluence under 625 mJ/cm 2 was required in order to prevent damage of the interdigital transducers (IDT) of the sensor devices. The sen- sitivity of the polymer coated devices to acetone concentra- tions gives an indication that LIFT can be used for printing sensitive polymer pixels onto transducer devices.

A comparative study of DRL-lift and lift on integrated polyisobutylene polymer matrices

This paper presents a comparative study of polymer pixel on sensors obtained by Laser Induced Forward Transfer (LIFT) assisted by a triazene polymer as Dynamic Release Layer (DRL). Polyisobutylene (PIB) was selected as model for chemoselective polymers which could be used as hydrogen-bond acidic polymer for vapor sensors. PIB films deposited on fused silica, respectively, on triazene polymer coated fused silica substrates were used as targets. Both targets were prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE). The parameters related to a regular, well-defined transfer were analyzed and compared for the substrates with and without the DRL. The morphological characterization of the transferred PIB was performed by Atomic Force Microscopy (AFM), Optical Microscopy, and Scanning Electron Microscopy (SEM). It was found that a minimal thickness of the dynamic release layer, i.e. 100 nm is required to protect the sensitive PIB polymer in a clean laser transfer process.

Laser-Induced Forward Transfer of Organic LED Building Blocks Studied by Time-Resolved Shadowgraphy

The patterned deposition of thin films is essential for many technological applications. One promising material deposition technique is laser-induced forward transfer (LIFT), where a thin layer coated on a transparent substrate is ablated by a laser pulse passing through the substrate. The ablated material is collected on a nearby receiver substrate in a pattern defined by the laser. The technique can be applied to heat and light sensitive materials, provided that they are not directly irradiated by the laser pulse. For this application, a sacrificial layer is introduced between the substrate and the transfer layer so that the laser energy is converted into mechanical propulsion while protecting the sensitive layer from radiation. In this work, the application of a triazene polymer as a sacrificial layer for LIFT has been studied with the final goal of transferring organic light-emitting diode (OLED) pixels. Donor films made of a stack of triazene polymer, metal, and optionally an electroluminescent polym...

Nanometer-nanosecond dynamics in laser-induced expansion/contraction and ablation of polymer films

In this account we have summarized our systematic studies on laser ablation and related phenomena of polymer films by utilizing time-resolved absorption spectroscopy and nanosecond interferometry. Polystyrene, poly(methyl methacrylate), poly(methyl acrylate), azobenzene-substituted urethane-urea copolymer, nitrocellulose, triazene polymer, polyurethane, and polyimide were examined, and their expansion and contraction dynamics were confirmed directly at the laser fluence below the ablation threshold. The molecular species which are formed by intense laser excitation are identified by absorption spectroscopy and correlated to the morphological changes. We proposed the cyclic multiphotonic absorption mechanism and explained well the ablation and related phenomena in terms of photophysics and photochemistry.

Shadowgraphic studies of triazene assisted laser-induced forward transfer of ceramic thin films

The laser-induced forward transfer process of solid ceramic donor materials (gadolinium gallium oxide and ytterbium doped yttrium aluminium oxide) was studied using triazene polymer as a sacrificial layer by means of a time-resolved nanosecond-shadowgraphy technique. The dependence of the ablation dynamics and quality of the ejected donor material on the laser fluence and thickness of the sacrificial and donor layers were investigated and discussed.