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Materialien zu einem Handbuche des Mecklenburg-Schwerinschen Particular-Civil-Processes, 1

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The morphological, rheological and electrical properties of nanocomposites based on multi-walled carbon nanotubes (MWNTs) and high density polyethylene (HDPE), prepared by melt mixing, have been investigated. The effects of temperature, MWNT concentration and nanotube surface treatment have been analyzed. A good dispersion of oxidized nanotubes in the HDPE matrix was found using electron microscopy investigations, as has also been found in the case of related nonfunctionalized MWNTs. The rheological oscillatory shear tests in the melt state have been carried out with strain amplitude values within the linear viscoelastic region. The rheological measurements on the nonfunctionalized MWNT/HDPEs revealed that the percolation threshold was temperature dependent with lower values at higher temperatures. At low frequencies, the oxidized MWNTs/HDPE composites showed storage modulus and complex viscosity values lower than the corresponding values measured for nanocomposites prepared with nonfunctionalized MWNTs. The conductivity decrease is more than 2 orders of magnitude for the sample with 2.5 wt% oxidized MWNTs, compared to the un-oxidized comparator materials. A constant voltage, long-term stability test allowed to estimate the average number of electrically active percolation paths and showed that stepwise conductivity loss is preceded by a strong increase in the noise amplitude related to the electrical current. POLYM. ENG. SCI., 57:665–673, 2017. © 2017 Society of Plastics Engineers

The concentrating photovoltaic system represents one of the most promising solar technologies because it allows a more efficient energy conversion. When a CPV system is designed, the main parameter which has to be considered is the concentration factor that affects both the system energy performances and its configuration. An experimental characterization of a CPV system previously realized at the University of Salerno, is presented in this paper considering several aspects related to the optical configuration, the concentration factor and the solar cell used. In particular, the parameters of an Indium Gallium Phosphide/Gallium Arsenide/Germanium triple-junction solar cell are investigated as function of the concentration factor determined by means of an experimental procedure that uses different optical configurations. The maximum concentration factor reached by the CPV system is 310 suns. The cell parameters dependence on the concentration is reported together with an electroluminescence analysis of the Indium Gallium Phosphide/Gallium Arsenide/Germanium cell. A monitoring of the electrical power provided by the system during its working is also presented corresponding to different direct irradiance values. A mean power of 2.95 W with an average efficiency of 32.8% is obtained referring to a mean irradiance of 930 W/m 2 ; lower values are obtained when the irradiance is highly fluctuating. The concentrating photovoltaic system electric energy output is estimated considering different concentration levels; the maximal obtained value is 23.5 W h on a sunny day at 310×. Finally, the temperature of the triple-junction solar cell is evaluated for different months in order to evaluate the potential annual thermal energy production of the concentrating photovoltaic system.

Low-frequency noise spectroscopy has been used to monitor electronic properties of solar cells under temperature or radiation stress. For all the investigated polymer:fullerene, silicon and perovskite solar cells this technique evidences a clear correlation of the recombination and the transport processes with the device performances.

The wet anisotropic etching process is generally used in the field of micromachining (MEMS), particularly for commercial products such as accelerometers. Hard masks like oxide or nitride play a key role in the transfer of patterns to the substrate during the lithography process. This work reports on the use of polycrystalline graphenic carbon as an etch mask for wet chemical processing and outlines a simple method to create patterned structures on (100) silicon wafers. Graphenic carbon (GC) was deposited on the silicon substrate by chemical vapor deposition (CVD) using C2H4 as precursor. The desired pattern was written in the spin-coated negative photoresist using UV laser lithography. Different geometrical shapes were printed on the substrate with dimensions ranging from 10 to 50 micrometers. In the next stage, the O2 plasma etched away the carbon from the area not covered by the photoresist, acting as an additional mask for this and the subsequent processing steps. Finally, the sample was immersed in the KOH bath saturated with isopropanol and the etching rate was evaluated for each crystal plane. Compared to the use of a sacrificial oxide mask, this technique is simpler and produces more reliable results.

The hole mobility of a semiconducting film with a new type of small molecule has been determined by electrical characterization with two different device geometries. The small molecule, namely Zn(OC)2, consists of oxadiazole groups (O), that act as electron conductor and blue emitter, and carbazole groups (C), that are hole conductors, which are arranged around a central Zn-atom. This disordered organic material has in principal ambipolar conduction properties. In both the organic devices investigated, that is, a vertical diode and a bottom-gate organic field effect transistor, the transport is dominated by holes. In the diode structure, the charge carrier transport shows a dependence from the electric field with a space charge limited current characteristic. The hole mobility value is several orders of magnitude higher as compared to the one extracted from the characteristics of the organic transistor. This large difference in the charge carrier transport properties for the two different device configurations is due to the strong influence of the dielectric/semiconductor interface which degrades the hole transport in the organic field effect transistor.

A new type of tissue, based on the combination of tobacco cells and multi-walled carbon nanotubes exhibited good mechanical stability even after more than 2 years of room temperature storage. The original intermediate value of electrical conductivity in coplanar configuration, decreased strongly after high electric field stress before the storage period. In the visible wavelength range optical transmission values between 0.1% and 1% have been measured for the more than 100 μm thick sample. The bio/nano-composite in the low-conductivity state revealed to be a sensitive photoreceiver in the visible wavelength range, when illuminated with white LED light. A notable decrease of the low-frequency current noise amplitude with LED illumination has been observed.

In this work the preparation of flexible polymeric films with controlled electrical conductivity, light transmission and surface wettability is reported. A drop casted graphene oxide thin film is photo-reduced at different levels by UV light or laser irradiation. Optical microscopy, IR spectroscopy, electrical characterization, Raman spectroscopy and static water contact angle measurements are used in order to characterize the effects of the various reduction methods. Correlations between the optical, electrical and structural properties are reported and compared to previous literature results. These correlations provide a useful tool for independently tuning the properties of these films for specific applications.

In this paper, we investigate the electrical hole transport properties of an organic/inorganic heterostructure consisting of a thin organic film, that combines hole and electron conducting molecules around a bridging Zn-atom, deposited on top of an n-type crystalline silicon substrate. Current-voltage characteristics and capacitance voltage measurements have been used for the determination of the organic layer dielectric and hole conduction parameters.

A Candida albicans/multiwalled carbon nanotube (Ca/MWCNTs) composite material has been produced. It can be used as a temperature-sensing element operative in a wide temperature range (up to 100 °C). The Ca/MWCNTs composite has excellent linear current-voltage characteristics when combined with coplanar gold electrodes. We used growing cells of C. albicans to structure the CNT-based composite. The fungus C. albicans combined with MWCNTs coprecipitated as an aggregate of cells and nanotubes that formed a viscous material. Microscopic analyses showed that Ca/MWCNTs formed a sort of artificial tissue. Slow temperature cycling was performed up to 12 days showing a stabilization of the temperature response of the material.

A theoretical model, combining trapping/detrapping and recombination mechanisms, is formulated to explain the origin of random current fluctuations in silicon-based solar cells. In this framework, the comparison between dark and photo-induced noise allows the determination of important electronic parameters of the defect states. A detailed analysis of the electric noise, at different temperatures and for different illumination levels, is reported for crystalline silicon-based solar cells, in the pristine form and after artificial degradation with high energy protons. The evolution of the dominating defect properties is studied through noise spectroscopy.

The radiation hardness of CH3 NH3 PbI3 -based solar cells is evaluated from in situ measurements during high-energy proton irradiation. These organic-inorganic perovskites exhibit radiation hardness and withstand proton doses that exceed the damage threshold of crystalline silicon by almost 3 orders of magnitude. Moreover, after termination of the proton irradiation, a self-healing process of the solar cells commences.

Some commercially available solar panels with very high efficiencies for terrestrial photovoltaic applications are based on the amorphous silicon on crystalline silicon material system. This type of heterostructure has more than 40 years' old history. The early development of the technology and the results, obtained in the last years with this type of solar cell are reviewed. In particular it is demonstrated why the physical understanding of the interface properties and band-structure was important for the development of high efficiency solar cells.

Organic/inorganic heterojunctions have been fabricated by spin-coating of an oxadiazole based polyether on top of either n-type or p-type crystalline silicon substrates. The prepared heterodiodes showed good rectification. During current-voltage measurements sharp current switching effects have been observed in the reverse bias characteristics for both types of heterodiodes. In particular a very stable hysteresis in the reverse characteristics of the polyether/n-type crystalline silicon has been measured at applied voltages below 1V. The application of this heterodiode as electrical memory with an on/off-ratio of about 2 orders of magnitude has been demonstrated (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of the electrical field on the conductivity of linear low-density polyethylene/carbon nanotubes/ (LLDPE/CNT) composites during temperature cycling has been investigated. Under applied voltage a positive resistivity temperature coefficient was observed during heating already at low (2–3 wt%) CNT content, followed by a large negative temperature coefficient during cooling whose value depends on the applied voltage. The resistivity values after thermal cycling were markedly lower, while they slightly increased in the absence of an electrical field. The effects of thermal cycling on structural and physical properties of the composites have been evaluated by X-ray diffraction and differential scanning calorimetry.

Excess charge carrier transport and relaxation in semiconductor layered structures have been numerically simulated by a finite-difference method.

The synthesis of segmented polyethers (PO) contg. oxadiazole units was carried out in a two-step scheme involving condensation reaction of acid chlorides with diphenoxyalkane dihydrazides; the polyazides were subsequently subjected to cyclization to form the oxadiazole moieties, in the presence of POCl3. Because of the anisotropic shape of oxadiazole-conjugated segments, the copolymers of the series show the monotropic nematic phase to be somewhat different from that obsd. in the case of the low mol. wt. analogous compds. In that case, high ordered liq. cryst. smectic phases are reported while the nematic phase is obsd. just in few cases. According to previous reports on oxadiazole-contg. materials, the POs show high photoluminescence activity in the blue region of the visible spectra. The good soly. in chlorinate solvents allows prepn. of films with homogeneous thickness by spin coating. The glass transition temp. is 100-120„a, which ensures good stability of film morphol. at room temp. For these features, the POs are potential candidate materials for fabrication of blue-light-emitting devices.

In this paper, we discuss the conditions under which we can correctly extract a variety of module parameters of single mode bidirectional optoelectronic duplexer and diplexer modules during relatively slow thermal cycling between -40/spl deg/C and +85/spl deg/C. The obtained values of parameters such as tracking error, optical crosstalk, and the laser diode characteristic temperature have been compared for bidirectional modules from different manufacturers and the impact on these parameters of different interconnect techniques, like microoptic (Mo), silicon optical bench, and planar lightwave circuit technologies is discussed. It is shown that there is a conflict between small threshold currents and good temperature stability for InGaAsP-based Fabry-Perot laser diodes emitting at 1300 and 1550 nm. Then the results of spatially low coherence reflectometry for the different bidirectional module types are presented.

Two types of lignin, alkali lignin and lignosulfonic acid sodium salt, are blended into thermoplastic zein through melt mixing in order to develop biodegradable insulator materials for multifunctional applications in electronics. The effects of lignin type and content on the dielectric properties of the resulting bio-nanocomposites are investigated. The results indicate that, by modifying the structural arrangement of the zein with the use of lignin, it is possible to obtain bio-nanocomposites characterized by tunable dielectric properties. The bio-nanocomposites containing low amounts of lignin derivatives exhibit extensive protein structural changes together with a modification of the dielectric properties compared to the pristine thermoplastic zein. Changes in the dielectric properties of these systems are also observed to change over time, indicating a loss of plasticizer, as is evident by a decrease in the glass-transition temperature. At high frequencies, the resulting values of the dielectric permittivity and of the loss tangent demonstrate that the bio-nanocomposite can be used as biodegradable dielectric material for transient (temporary) electronics.

A HDPE/CNT composite has been fabricated based on a commercial polyethylene loaded with a high concentration of CVD grown multiwalled carbon nanotubes with a high aspect ratio. Exploiting the resulting high conductivity of this composite material, we tested the possibility to use it as absorber of electromagnetic waves at microwave frequencies up to 25 GHz. For this purpose the device under test was placed as substrate of a microstrip transmission line. Measurements of the scattering parameters, done with a vectorial network analyzer, have been used in order to obtain the power absorption at different frequencies. Special attention was paid to the optimization of the microstrip geometry. A comparison of the microwave power absorption spectrum with those of commercial cavity absorbers showed encouraging results, regarding the microwave absorption capability of the HDPE/CNT composite material.

The sensitivity of vertical cavity surface-emitting lasers to electrostatic discharge (ESD) pulses has been investigated under human body model test conditions. Very similar degradation behavior has been found for vertical-cavity surface-emitting lasers (VCSELs) from two different manufacturers, both with proton-implantation for lateral current confinement. For all investigated devices we observed during forward bias stress that the optical degradation precedes the electrical degradation and the forward bias damage threshold pulse amplitudes were only slightly higher than the reverse bias values. At the initial stage of the VCSEL degradation, damage of the upper p-DBR mirror region has been observed without modification of the active layer. During the ESD tests we monitored the electrical and the optical parameters of the VCSELs and measured during forward bias stress additionally the optical emission transients. The optical transients during ESD pulsing enable a fast evaluation of the damage threshold and give also an indication of the time scale of the junction heating during ESD pulses.

Human Body Model ESD tests on two commercially available different types of wavelength division multiplexing bidirectional optoelectronic modules, intended for data transmission over multimode optical fibers at 820 and 1320 nm wavelengths, have been performed. These bidirectional modules incorporated pin diode receivers and light emitting diode in a single package. In particular, the 820 nm light emitting diodes had rather high damage threshold pulse amplitudes of about +10,000 V under forward bias and −5000 V under reverse bias conditions, and no active layer degradation has been observed. In-situ measurements of the optical transients emitted during forward bias ESD pulses enabled a damage pulse threshold detection of a LED without the need of further optoelectronic characterization. The receiver photodiodes, however, were very sensitive to reverse bias ESD pulses. The InGaAs photodiodes degraded during ESD pulses with amplitudes as low as −150 V and in the case of the Silicon photodiodes as low as −175 V.

Here we present new materials obtained using, either fungal or isolated tobacco cells in association with different percentages of carbon nanotubes (CNTs). As a proof of concept, we used eitherCandida albicansor a non-green Tobacco BY-2 cell line combined with multi-walled CNTs. The electrical, mechanical, and conductivity vs temperature properties for some of these materials have been determined.C. albicans-based tissues have high conductivity and are stable at elevated temperatures. By lowering the CNTs content, we obtained a stable, electrically conductive optical transparent film, though with a relatively high sheet resistance. Further, we produced, using tobacco cells, a material that exhibits good electrical as well as mechanical properties.

An overview over typical defects and reliability aspects regarding the operation of InGaAs InP avalanche photodiodes for the use in fiber-optic communication systems is given. Measurements regarding the performance and stability of different types of top illuminated InGaAs InP Separate Absorption Grading Multiplication avalanche photodiodes have been compared with special emphasis on the homogeneity of the photoresponse. High resolution scanning optical microscopy measurements at different wavelengths allowed to identify specific technological problems. Guard ring misalignment resulting in increased responsivity of the junction perimeter have been found on devices from one manufacturer. The responsivity images of the active area of some of the investigated photodiodes showed sharp peaks due to microplasma formation. The impact of these microplasmas on dark current and photocurrent of the devices has been investigated in detail. A step-stress test performed at successively increasing temperatures resulted in the catastrophic failure of the tested devices from one family. An analysis of the dark current-voltage characteristics before and after degradation leads to the conclusion that a modification of the semiconductor-insulator interface properties caused a dramatic increase in the surface leakage currents.

The decay of optically generated excess charge carriers at the heterointerface between crystalline silicon and amorphous silicon has been monitored in situ during plasma deposition of the amorphous layer. A dramatic increase in the interface recombination rate is seen instantly when the silane plasma is ignited. In a later stage of amorphous layer deposition, the recombination rate decreases. This interface passivation depends strongly on the substrate temperature and is more efficient at higher temperature and in the presence of silane plasma. The effect is not due to a change in the band bending at the heterointerface.

The damage induced by hydrogen and helium plasmas at the surface of crystalline silicon has been monitored in situ by time‐resolved microwave conductivity and by spectroscopic ellipsometry measurements. Both plasma treatments increase the decay rate of the optically generated excess charge carriers and decrease the amplitude of the microwave reflection transients. While for the helium plasma a high density of electronic defects is created immediately after plasma ignition, a continuously increasing number of recombination centers is observed in the case of the hydrogen plasma exposure. In support of the transient microwave measurements, the analysis of the spectroscopic ellipsometry measurements reveals the creation of a damaged surface layer, which in the case of the helium plasma exposure has a high and in the case of the hydrogen plasma a low fraction of amorphous silicon. This can be explained by the different nature of the processes involved in the interaction of hydrogen (chemical) and helium (physi...

We report on the application of a self electro-optic effect device in waveguiding configuration for the generation of a wide variety of different nonlinear optical transfer functions. It makes use of the Wannier-Stark effect in an InGaAs/InP short period superlattice and operates at room temperature for TE-polarized light around 1.55 μm. In particular, optical bistability, optical signal-frequency multiplication and the operation as an optical power discriminator are demonstrated.

In this work we describe the influence of the growth parameters on the optical and crystallographic properties of InGaAs/InP short period superlattices (SPSLs). The optimized growth conditions applied for multiquantum wells are no longer appropriate when the period thickness is below 85 A and quasi-continuous growth interruption times are required. The assessment of new growth conditions enabled the realization of SPSL structures with ultimate period of 31 A presenting good optical and structural properties. The electron wave-function coherence length of seven SPSLs was evaluated. Application of these devices enabled the realization of Wannier-Stark modulators operating at 1545 nm with extinction ratio of 22 dB at 2.5 V reverse bias. The electron wave-function was evaluated, for the first time in the InGaAs/InP system, to be at last seven SPSL periods using both transmittance and photocurrent methods. The on state attenuation determined using Wood's method is below 2 dB in the range between 1540 and 1555 nm. SPSL structures are therefore well suited for the realization of guided wave electro-optic modulators based on the Wannier-Stark effect.