Carbide-derived carbon (CDC) based actuators have been typically formulated as trilayer systems and applied in bending displacement. In this work, we want to demonstrate that CDC deposited on glass fiber fabric (CDC-TL) with an additional poly-3.4-ethylenedioxythiophene (PEDOT) layer electropolymerized on top forming a polylayer (expressed as CDC-PEDOT-TL) can be used as a linear actuator. Isotonic and isometric electro-chemo-mechanical deformation (ECMD) measurements in lithium bis(trifluoromethane) sulfonamide propylene carbonate (LiTFSI-PC) were performed, revealing that the CDC expansion at discharging can be found in CDC-PEDOT-TL (main expansion at oxidation of 0.5% strain) in same extent of 0.24 %. The stress found in similar values of 30 kPa for both system. Besides the nearly 5times better conductivity of CDC-PEDOT-TL, the charge density reduce nearly half in comparison to CDC-TL.
For actuator applications, conducting polymers are typically deposited at lower temperatures e.g. -20°C, in order to obtain more regular, smooth and ordered films with fewer defects. Clearly, standard aqueous electrolyte solutions cannot be used at these temperatures, and some organic solvents cannot be used, as not all salts are soluble in these. A wellknown approach is to use ethylene glycol: water mixtures (often 50:50 wt%, PPy/CDC(EG:W). The goal of this work is to analyze the role of water in the solution: to compare the linear actuation properties of conducting polymer hybrid films PPy/CDC(EG) polymerized from just ethylene glycol solution and that with 50% water, both at -20°C. Cyclic voltammetry and chronoamperometric electro-chemo-mechanical-deformation (ECMD) measurements were performed to study the linear actuation properties in lithium bis(trifluoromethylsulfonyl)imide in aqueous solution (LiTFSI-aq). Both conductivity and linear actuation strain were found dependent on the solvent in the polymerization solution with ethylene glycol: water the clearly superior solvent choice.
Embedding polyethylene oxide (PEO) in polypyrrole doped with dodecylbenzenesulfonate (PPy/PEO-DBS) leads to increase linear actuation due to improved ionic conductivity. In this research our goal is to investigate the effect of solvent exchange from aqueous (aq) to propylene carbonate (PC) using same concentration of electrolyte bis(trifluoromethane) sulfonamide lithium (LiTFSI). As previously observed for the case of PPy/DBS films, the actuation direction of PPy/PEO-DBS changed from purely cation-driven in (aqueous) LiTFSI-aq to purely anion driven in (propylene carbonate) LiTFSI-PC. Cyclic voltammetry driven electro-chemo-mechanical-deformation (ECMD) measurements showed that the strain in LiTFSI-PC was more than double than that of aqueous electrolyte consuming only half of the charge density. The diffusion coefficients were determined from the chronoamperometric measurements with higher values found in LiTFSI-PC. Energy dispersive X-Ray spectroscopy and scanning electronic microscopy measurements were performed to characterize the PPy/PEO-DBS films.
Conducting polymer linear actuators, for example sodium dodecylbenzenesulfonate (NaDBS) doped polypyrrole (PPy/DBS), have shown moderate strain and stress. The goal of this work was to increase the obtainable strain and stress by adding additional active material to PPy/DBS. In recent year’s carbide-derived carbon (CDC)-based materials have been applied in actuators; however, the obtained displacement and actuation speed has been low comparing to conducting polymer based actuators. In the present work, a CDC-PPy hybrid was synthesized electrochemically and polyoxometalate (POM) – phosphotungstic acid – was used to attach charge to CDC particles. The CDC-POM served in the presence of NaDBS as an additional electrolyte. Cyclic voltammetry and chronopotentiometric electrochemomechanical deformation (ECMD) measurements were performed in Lithium bis(trifluoromethanesulfonyl)- imide (LiTFSI) aqueous electrolyte. The ECMD measurements revealed that the hybrid CDC-PPy material exhibited higher force and strain in comparison to PPy/DBS films. The new material was investigated by scanning electron microscopy (SEM) to evaluate CDC particle embedding in the polymer network.
Today most of applications have a small camera such as cell phones, tablets and medical devices. A micro lens is required in order to reduce the size of the devices. In this paper an auto focus system is used in order to find the best position of a liquid lens without any active components such as ultrasonic or infrared. In fact a passive auto focus system by using standard deviation of the images on a liquid lens which consist of a Dielectric Elastomer Actuator (DEA) membrane between oil and water is proposed.
Free standing conducting polymer films based on polypyrrole doped with dodecylbenzoesulfate (PPyDBS) are investigated in TBACF3SO3 (tetrabutylammonium trifluoromethanesulfonate) propylene carbonate (PC-Tf) followed in aqueous TMACl tetramethylammonium chloride (Aq-TM) with the aim to investigate actuation properties (anion or cation-driven actuation). Under isometric (constant force) conditions ECMD (electro-chemo-mechanical deformation) measurements are performed during cyclic voltammetric and chronoamperometric experiments. Electrolyte and solvent effects revealing that the actuation direction in propylene carbonate electrolyte changed from expansion at anodic potential to expansion at cathodic potentials during square wave potential steps. Finally if the PPyDBS film immersed in aqueous electrolyte the anion-driven actuation properties are maintenance. SEM measurements are implemented to reefer changes in film morphology and ion content (EDX, energy dispersive X-Ray) before and after actuation.
An investigation is reported into the electrochemomechanical deformation (ECMD) of polypyrrole (PPy) doped with
dodecylbenzenesulfonate (DBS) in the form of freestanding films and deposited onto conductive substrates (chemically
fixed poly-3,4-(ethylenedioxythiophene, PEDOT) based on PVdF (poly(vinylidenefluoride)). Linear actuation has been
achieved starting from a trilayer bending actuator design with a stretchable middle layer. To allow evaluation of the
proposed design, commercially available PVdF membranes were chosen as model material. For bending trilayer
functionality, electronic separation of both electrode layers is essential, but in order to obtain linear actuation, the CP
layers on either side are connected to form a single working electrode. The PPyDBS free standing films and PPyDBS
deposited on PEDOT-PVdF-PEDOT were investigated by electrochemical methods (cyclic voltammetry, square wave
potentials) in a 4-methyl-1,3-dioxolan-2-one (propylene carbonate, PC) solution of tetrabutylammonium
trifluoromethanesulfonate (TBACF3SO3). This study also presents a novel method of utilizing scanning ion-conductance
microscopy (SICM) to accurately examine the electrochemical redox behavior of the surface layer of the linear actuator
using a micropipette tip.
The autofocus fluid lens device, as developed by Philips, is based on water/oil interfaces forming a spherical lens where
the meniscus of the liquid can be switched by applying a high voltage to change from a convex to a concave divergent lens. In this work we construct a device to evaluate the performance of membrane actuators based on electro active
polymers, in a design applicable for autofocus fluid lens applications. The membrane with a hole in the middle separates
the oil phase from the electrolyte phase, forming a meniscus in the middle of the membrane between the oil and
electrolyte. If the membrane actuator shows a certain force and displacement, the meniscus between oil and electrolyte changes form between concave and convex, applicable as a fluid lens. Ionic polymer metal composites (IPMCs) are applied in this work to investigate how the performance of the membrane actuator takes place in Milli-Q, certain
electrolytes and in combination with an electrochemically deposited conducting polymer. The goal of this work is to
investigate the extent of membrane displacement of IPMC actuators operating at a low voltage (±0.7 V), and the back relaxation phenomena of IPMC actuators.
Carbide–derived Carbon (CDC) material is applied for super capacitors due to their nanoporous structure and their high
charging/discharging capability. In this work we report for the first time CDC linear actuators and CDC combined with
polypyrrole (CDC-PPy) in ECMD (Electrochemomechanical deformation) under isotonic (constant force) and isometric
(constant length) measurements in aqueous electrolyte. CDC-PPy actuators showing nearly double strain under cyclic
voltammetric and square wave potential measurements in comparison to CDC linear actuators. The new material is
investigated by SEM (scanning electron microscopy) and EDX (energy dispersive X-ray analysis) to reveal how the
conducting polymer layer and the CDC layer interfere together.
Comparative measurements of carbon-polymer composite micro-actuators based on room temperature ionic
liquid electrolyte were carried out in situ (1) in vacuum using a state-of-the-art scanning electron microscope, (2)
in an oxygen-free atmosphere under ambient pressure, and (3) under ambient environment. The fabricated
micro-actuators sustained their actuation performance in all three environments, revealing important implications
regarding their humidity-dependence. SEM observations demonstrate high stroke actuation of a device with submillimeter
length, which is the typical size range of actuators desirable for medical or lab-on-chip applications.
Novel bending actuators were made solely from electrochemically polymerized conducting polymer materials. The working principle for these free-standing conducting polymer (CP) films is based on different anion- and cation-dominated actuation for the two layers. Synthesis conditions for the two layers of the same polymer film have been chosen such that the mobility of cations and anions in the considered potential window is different. Polymerization of CP layers of this nature on top of each other results in a sandwich structure with bilayer functionality in a properly chosen electrolyte. The results of a comparative study of various combinations of sandwiched PEDOT films in terms of actuation properties are presented in this study. Free-standing films of PEDOT linear actuators electrodeposited in the same electrolyte at different polymerization potentials were investigated by means of electro-chemo-mechanical deformation measurements. PEDOT-PEDOT bilayer functionality is studied in this work with a view to their bending actuation properties.
Trilayer actuators were constructed using polypyrrole (PPy) films doped with dodecylbenzene sulfonate (DBS). Identical
5-20 μm PPy/DBS films were grown on either side of a 110 μm poly(vinylidene fluoride) (PVDF) membrane to serve as
working and counter electrodes with respect to each other. The performance of the trilayer actuator was tested using
potential step experiments between -0.8 and +0.8 V at different frequencies (0.03 to 10 Hz) and trilayer lengths (1 to 2.5
cm), and the extent of deflection was measured using a CCD camera. Satisfactory deflections in the range of 1-3 mm
were observed for 10 μm thick PPy layers on trilayers 1.5 to 2.5 cm in length when operated at 1-5 Hz for over 40,000
cycles. The trilayer actuators were examined in a fluidics channels, and mathematical modelling using finite element
analysis was used to predict overall fluid movement and flow rates. The trilayers were also used to construct a 'fish-tail'
positioned at the back of a self-driven robotic fish.
The actuation properties of free standing films of poly-3,4-ethylenedioxythiophene (PEDOT) prepared from propylene
carbonate (PC) solutions of tetrabutylammonium trifluromethanesulfonate have been studied in a range of aqueous and
organic (PC) solvent electrolytes. The following electrolyte salts were investigated: TBACF3SO3, LiCF3SO3, TBAPF6,
NaPF6, NaDBS and TMACl. The best actuation performance was achieved in TMACl (aq.) with >4 % strain, 0.18 % s-1
strain rate and a low creep of 2.3 % after 50 cycles using potential step experiments. The PEDOT film morphology was
significantly changed from an open sub-micron pore polymer network to a morphology with fewer and less open pores when the solvent was changed from PC to water.
Investigations of the actuation properties of free standing PPy and PEDOT films in a propylene carbonate-triflate electrolyte (PC/TBACF3SO3) under isotonic (constant load)
conditions are presented in this work. The PPy film showed mixed ion movement during charging and discharging in cyclic voltammetric and chronoamperometric experiments. At a potential of -1.0 V the maximum strain was in the range of 1-2 % whereas at the anodic potential of +1.0 V strains in the range of 3-4 % were observed. Cyclic voltammetry experiments at higher scan rates to 10 mV/s led to a decrease in the anodic strain and an increase in the cathodic strain before it declined at higher scan rates. The free-standing PEDOT films showed mainly cathodic actuation at the potential -1.0 V and the size of actuation was again dependent upon the scan rate. Cation movement is discussed in terms of
the immobilisation of CF3SO3- anions during polymerisation. Extended potential step experiments showed good actuation and low creep in the potential range between 0.0 and
+1.0 V. The surface morphology (SEM) showed an open porous structure for PEDOT in contrast to the smooth morphology of PPy.
To construct practical devices based on the actuating properties of conducting polymers we need to understand the underlying mechanism of the reversible length change and the effect of numerous synthetic and processing parameters on the extent of actuation, reversibility and durability. Here, we have investigated the out-of-plane actuation of polypyrrole (PPy) doped with dodecylbenzenesulfonate (DBS) in an aqueous electrolyte, and the linear actuation of PPy/DBS (aq.) and PPy/ hexafluorophosphate (PF6) in a propylene carbonate (PC) based electrolyte. The out-of-plane actuation was examined by means of AFM, and linear actuation was evaluated by a combination of electrochemomechanical deformation (ECMD) measurements, cycling voltammetry, chronoamperometry and conductivity measurements. The results revealed a very large actuation for PPy/DBS (aq.) in the out- of-plane mode, but a very limited actuation in the linear direction with low reversibility. PPy/PF6 (PC) showed much higher linear actuation than PPy/DBS, with reversible ECMD characteristics.
We present recent progress achieved in the development of type-I GaInAsSb/AlGaAsSb quantum-well (QW) lasers covering the 1.74-2.34micrometers spectral range. Diode lasers based on the broadened waveguide design comprising 3 Qws have been studied in detail. Laser structures emitting at 2.23 micrometers exhibited a record high internal quantum efficiency of 89%, internal loss of 6.8cm-1, and threshold current density at infinite cavity length as low as 120 A/cm2, indicating the superior quality of these devices. For the 2micrometers lasers a high characteristic temperature of 179K for the threshold current was achieved for temperatures between 250 and 280 K. In order to investigate the heterobarrier leakage associated with thermally activated carriers, laser structures emitting at 2.23micrometers with different Al- concentrations in the barriers and separate confinement regions have been studied. While the structure with 40% Al revealed the highest To of 103K, the laser with 20% Al yielded the best power efficiency, with a maximum value of 30%. 1.7W in cw mode at room temperature has been achieved for broad area single emitters at (lambda) =2 micrometers , with high-reflection/antireflection coated mirror facets, mounted epi-side down. As an application, tunable diode lasers absorption spectroscopy (TDLAS) sensing small concentrations of methane has been demonstrated using our 2.3micrometers diode laser.
Semiconductor lasers with high beam quality and high optical output power are very attractive for a variety of applications such as optical pumping of solid-state lasers, fiber amplifiers and medical treatment. When easy and low- cost fabrication is a further requirement, devices based on tapered gain sections are the most promising candidates. Low modal gain, single quantum well InGaAs/AlGaAs devices emitting at 940 nm were grown by molecular beam epitaxy. The lateral design consists of a tapered gain guided and a ridge-waveguide section having an overall length between 2 mm and 3 mm. Whereas the length of the tapered structure determines the high output power, the high brightness requires a ridge-waveguide structure with sufficient length. Here the length of the ridge section has been chosen to 500 micrometers . We achieved an optical output power of up to 5.3 W at room temperature in continuous wave mode. The threshold current density depends on the tapered length with values between 200 A/cm2 and 650 A/cm2. The slope efficiency is around 0.9 W/A for all devices. The wall plug efficiency reaches 44% at a current of 3 A. The beam quality factor remains nearly constant up to about 2.2 W having an M2-value of 1.3. At higher optical powers M2 increases fast. The lifetime of such devices has been extrapolated to more than 7500 h at room temperature.
Within the last few years, high power laser diodes with remarkable improvements concerning output power, efficiency, and reliability have been investigated in the wavelength range between 780 nm and 1064 nm. A lot of the work has been focused on 980 nm, the pump wavelength of Erbium Doped Fiber Amplifiers (EDFAs). Pumping of EDFAs requires highest performance diode lasers due to extreme demands in reliability and beam quality. Up to now, the only type of diode laser used in this application is a single-stripe or ridge-laser which emits in a diffraction-limited optical mode and can therefore be coupled into a single-mode fiber with high efficiency. The small stripe-width limits the reliable output power of these devices to about 300 mW resulting in a fiber coupled output power of less than 250 mW. In the following we report on high-power 980 nm diode lasers comprising ridge and tapered sections for near diffraction limited output power in the watt regime. The devices are based on MBE grown layer structures in the AlInGaAs material system. They allow for more than 500 mW of optical power coupled into a single mode fiber. First reliability tests show extrapolated lifetimes of more than 7.500 h at an output power of 1.8 W.
InGaAs/AlGaAs large optical cavity (LOC) single quantum well (SQW) lasers emitting at 980nm were grown incorporating an AlGaAs/GaAs short-period superlattice layer next to the quantum well in order to improve the carrier confinement and thus high-temperature operation. Symmetric and asymmetric structures have been realized. High characteristic temperatures T0 above 300K between 20#C and 50#C operating temperature were measured for the symmetric structures without deterioration of the internal quantum efficiencies (> 90%) and low intrinsic losses (about 1cm-1). The improvement in the characteristic temperature is mainly attributed to the reduced thermionic emission of the carriers out of the quantum well due to the large effective barrier height of the short-period superlattice. Caused by the incorporation of the short-period superlattice the devices showed a higher series resistance, which could be lowered by switching to asymmetric structures. These asymmetric devices had unchanged high internal quantum efficiencies and low intrinsic losses but lower characteristic temperatures of about 250K.
The optoelectronic properties of short-period InAs/(GaIn)Sb superlattices (SLs) grown by molecular beam epitaxy on GaSb substrates are discussed. We report on the optimization of the SL materials properties with special emphasis on the use for infrared detection devices. The materials quality is evaluated by using high resolution x-ray diffraction, atomic force microscopy, and photoluminescence spectroscopy. In- plane magneto-transport investigations were performed applying mobility spectrum analysis. The SL diodes were analyzed performing standard electro-optical measurements. The observation of resonances in the I-V curves in the regime of Zener-tunneling due to Wannier-Stark localization opens a new tool for the electrical investigation of photodiodes with low band gap energy. The status of the processing technology is reported demonstrating the feasibility for the fabrication of 256 X 256 focal plane arrays operating in the 8-to-12 micrometers atmospheric window. In addition, results are given for mid-infrared SL-diodes, grown with lattice matched AlGaAsSb barriers instead in the binary InAs/GaSb SL system.
A high power semiconductor laser with a novel lateral design using angular filtering by total reflection for increased brightness is demonstrated. In this so called `Z-Laser' two inner surfaces guide the laser beam by total reflection in a Z-shaped path through the laser. Higher order laser modes with larger divergence angles are suppressed because of a smaller reflectivity. This results in a reduced far-field angle. Simulations based on a 2D steady state wave equation solved by using the Pade approximation, an 1D carrier diffusion equation and a logarithmic gain model have been performed to design the device.
KEYWORDS: Semiconductor lasers, High power lasers, Resistance, Sensors, Lab on a chip, Electro optics, Temperature metrology, Continuous wave operation, Copper
High-power 980 nm-diode laser bars have been fabricated in the AlGaAs/GaInAs material system. The bars are 1 cm wide and comprise 25 broad area lasers with 200 micrometer aperture and 2 mm resonator length. Hence, the fill factor is 50%. To reduce the power density at the facet, we used an LOC structure with low modal gain, which also helps to prevent filamentation. The measured threshold current was 14 A and a record output power of 267 W cw was achieved at 333 A with an electro-optical conversion efficiency of 40%. With less thermal load, at 150 W output power the conversion efficiency was as high as 50% and the corresponding slope efficiency was 0.9 W/A. Microchannel copper heat sinks with a thermal resistance of less than 0.29 K/W were used for mounting the bars. The coolant temperature was set for all measurements to 22 degrees Celsius and the flux was 0.9 l/min. Additionally, the top electrode of the p-side down mounted bars was cooled by a second heat sink, which was pressed gently on the top electrode.
Within the last few years, high power laser diodes with remarkable improvements concerning output power, efficiency, and reliability have been investigated in the wavelength range between 780 nm and 1064 nm. The discussion, whether laser diodes fabricated from Al-free material systems can surpass the performance of devices made from the conventional InAlGaAs-material system is still ongoing. In our contribution to this discussion we present 980 nm high-power InAlGaAs-laser diodes and laser diode bars with high conversion efficiencies grown by MBE. Broad area laser diodes with 100 micrometer aperture show an output power as high as 9.2 W cw at room temperature corresponding to a COMD level of 17 MW/cm2. Up to this output power the conversion efficiency remains above 46%. The highest efficiency of nearly 60% is reached at 2.5 W of output power. Reliability tests are ongoing and predict a lifetime of at least 20.000 h at a power level of 1.5 W cw. Laser diode bars of 1 cm width comprising 25 of these oscillators have been fabricated. Similar to single emitters these devices achieve a conversion efficiency of 58% at 62 W of cw output power. In terms of conversion efficiency and output power these results are among the best reported for both, Al-containing and Al-free laser diodes and laser diode bars. They can be attributed to the material quality, the facet coating technology, and the design of our devices. Clearly, they show the competitiveness of the material system used here.
In high-power, high-brightness laser diodes, beam filamentation is one of the main physical effects that limit the device performance. Due to the interaction between the optical power and the carrier density in the active region of broad area devices, spatial hole-burning leads to an inhomogeneous optical index that causes the degradation of the optical beam profile. We show, that epitaxial layer structures with low optical confinement are much more insensitive to beam filamentation because of their reduced differential gain. Experimentally we find, that the beam quality of tapered laser oscillators can be improved by an order of magnitude, when epitaxial layer structures with reduced modal gain are used for the device fabrication. Two mm long tapered devices with a 200 micrometer wide output facet show near diffraction limited farfield profiles up to output powers of more than 2 W cw.
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