Doped Silicon Wafers Research Articles

Blue-white electroluminescence of diamond/WS2 quantum dot composite films

Two kinds of diamond films with completely different morphologies were prepared on N-type heavily doped silicon wafers by microwave plasma chemical vapor deposition (MPCVD) method, namely, micron-scale large grain polycrystalline diamond film dominated by (220) crystal plane (220DF) and nano-scale small grain polycrystalline diamond film dominated by (111) crystal plane (111DF). And WS2 quantum dot powder was obtained by aqueous liquid phase ultrasonic method. Then, the 111DF/WS2 quantum dot composite structure film (111DWSF) and 220DF/WS2 quantum dot composite structure film (220DWSF) were prepared by applying WS2 quantum dot powder uniformly on diamond film substrate. The results of electroluminescence (EL) detection show that the 220DWSF device emits visible blue light, and the main peak of EL spectrum is located at 443 nm in the blue region. The 111DWSF device emits white light, and the corresponding EL spectra show strong emission peaks in the blue region (454 nm), green region (536 nm) and red region (632 nm) respectively, meanwhile, the luminous intensity of 111DWSF device is much higher than that of 220DWSF device. In addition, it is also found that the 220DWSF EL device does not show obvious rectification characteristics, while the 111DWSF EL device has obvious rectification characteristics. After FN fitting of the IV characteristic curve of 111DWSF EL device, the tunneling characteristics of electrons are found in the region of high electric field intensity.

Optical Characterisation of Doped Silicon Wafers Using THz Time-Domain Ellipsometry

Terahertz (THz) time-domain spectroscopic ellipsometry (TDSE) is a powerful, self-referenced, and non-destructive technique for characterizing the electrical and optical properties of a wide range of materials including semiconductors such as doped silicon wafers. By analysing the polarization changes of THz pulses reflected off the silicon samples, TDSE provides detailed information on carrier concentration, mobility, complex conductivity, and complex dielectric response. This method leverages the unique sensitivity of THz radiation to free carrier dynamics in semiconductors, enabling precise measurements of doping levels, conductivity, and hence resistivity at once. Here we show the capability of THz TDSE in distinguishing between different doping types (n-type and p-type) and concentration level, providing critical insights for semiconductor research and fast quality control in silicon wafer production.

Porous Silicon and Silicon Nanotubes with Embedded FePt Nanoparticles Investigated by High Temperature Magnetic Measurements

Porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures. The difference of the magnetic characteristics between the two systems is figured out. Furthermore, the FePt filled templates are compared with the same template materials filled with Ni/Co by electrodeposition.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution. The produced morphology offers separated pores of about 50 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure and a wall of about 10 nm are used (1). FePt nanoparticles (NPs) are deposited electroless inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied. For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.The varying magnetic response of the different composite systems, porous silicon and silicon nanotubes is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.The influence of high temperatures on the nanocomposite samples is of interest, as well as the high temperature magnetic behavior. Therefore, beside low temperature and room temperature magnetic measurements, the magnetic behavior of the samples is investigated at high temperatures up to 1273 K.(1) K. Rumpf, et.al, ECS Transactions 98 (2020) 37

Integrating Conjugated Polymers with Bacteriorhodopsin to Realize Quasi Dual‐Gate Organic Field‐Effect Transistors

AbstractFour conjugated polymers are integrated with a bacteriorhodopsin D94N‐HmBRI in organic field‐effect transistors (OFETs) with the device architecture of doped Si bottom gate/SiO2 bottom electric/semiconducting polymer/Au electrodes/D94N‐HmBRI top dielectric. Photosensitivity of D94N‐HmBRI in the devices is validated. It is proposed that light activates the conformational change of all‐trans retinal to 13‐cis retinal in D94N‐HmBRI. The D94N‐HmBRI layer then applies momentary dipoles to the semiconductors, affecting threshold voltage, resulting in photosensitivity. Film‐thickness variation, capacitance determination, and grazing‐incidence X‐ray scattering are performed to support the proposed working principle. Quasi dual‐gate OFETs with a highly doped silicon wafer as the bottom gate and light as the top gate are thus realized by combining conjugated polymers with D94N‐HmBRI.

Performance Investigation of a Proposed Flipped npn Microstructure Silicon Solar Cell Using TCAD Simulation

This work aims at inspecting the device operation and performance of a novel flipped npn microstructure solar cell based on low-cost heavily doped silicon wafers. The flipped structure was designed to eliminate the shadowing effect as applied in the conventional silicon-based interdigitated back-contact cell (IBC). Due to the disappearance of the shadowing impact, the optical performance and short-circuit current density of the structure have been improved. Accordingly, the cell power conversion efficiency (PCE) has been improved in comparison to the conventional npn solar cell microstructure. A detailed analysis of the flipped npn structure was carried out in which we performed TCAD simulations for the electrical and optical performance of the flipped cell. Additionally, a comparison between the presented flipped microstructure and the conventional npn solar cell was accomplished. The PCE of the conventional npn structure was found to be 14.5%, while it was about 15% for the flipped structure when using the same cell physical parameters. Furthermore, the surface recombination velocity and base bulk lifetime, which are the most important recombination parameters, were studied to investigate their influence on the flipped microstructure performance. An efficiency of up to 16% could be reached when some design parameters were properly fine-tuned. Moreover, the impact of the different physical models on the performance of the proposed cell was studied, and it was revealed that band gap narrowing effect was the most significant factor limiting the open-circuit voltage. All the simulations accomplished in this analysis were carried out using the SILVACO TCAD process and device simulators.

Efficient Neutron Irradiation Procedure for Uniform Dopant Distributions in Silicon Doping

Abstract Neutron transmutation doping (NTD) is one of the several techniques used for n-type doping with good homogeneity. NTD performances were investigated in this work within a project funded by the Academy of Scientific Research and Technology (ASRT), Egypt, for the “production of doped Silicon Wafers for Solar Panels and Basic Electronics,” 2015–2018. The Egypt second research reactor (ETRR-2) has two irradiation positions for silicon doping using NTD. The two positions can accommodate silicon ingots with large diameters up to six inches. One crucial parameter that affects the quality of the product is the distribution of the dopant in the irradiated ingot. The irradiation facility provides the option of rotating the sample during irradiation for flattening the radial distribution of the dopant. Since the neutron flux is not flat along the irradiation position due to leakage and the effect of control rods, the generated dopant will be not flat along the axial direction. To overcome this problem, this paper proposed an irradiation procedure to smooth the dopant distribution along the axial direction. Such procedure can be applied for NTD facilities that has not an acceptable axial neutron flux distribution in silicon doping process. The procedure is based on loading the irradiation position by two ingots staked end to end and, at the middle of the irradiation duration, the two ingots swap their places. This strategy was verified by MCNP5 calculations and experimentally.

Assessment of Novel Magnetic/Semiconducting Composites - FePt Nanoparticles Grown within Porous Silicon and Silicon Nanotubes

Porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures offering a hard magnetic behavior and resulting in novel magnetic/semiconducting composite systems. The difference of the magnetic characteristics between the two systems is figured out. Furthermore the FePt filled templates are compared with the same template materials filled with Ni/Co by electrodeposition.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution [1]. The morphology of the porous structure is achieved by the doping density of the silicon wafer and the choice of the electrochemical parameters such as electrolyte concentration, applied current density and temperature. In this case the morphology offers separated pores of about 60 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure and a wall of about 10 nm are used [2]. FePt nanoparticles (NPs) are deposited electroless inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6). For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.Ni and Co, both metals are electrodeposited within the nanostructured silicon. In the case of depositing Ni and Co from separate electrolytes, aqueous NiSO4 and CoSO4 solutions are used. The composition of the Ni-salt solution is 170g/l NiSO4 and 40 g/l H3BO3. For the Co deposition the electrolyte contains 120 g/l CoSO4 and 30 g/l H3BO3. An applied current density of 15 mA/cm2 and a frequency of 0.1 Hz are applied for 15 min. In the case of depositing Ni and Co from a single electrolyte, a solution in the ratio 1:1 of the Ni-salt to Co-salt is employed. Ni is deposited by applying a potential of 1.1 V and Co is deposited by changing to 1.8 V; the necessary deposition time of Co was three times longer than for Ni.Magnetic characterization of the samples is performed by VSM (Vibrating Sample Magnetometer), the structure is analyzed by SEM, TEM and EDX.The varying magnetic response of the different composite systems, porous silicon and silicon nanotubes is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.Porous silicon loaded with Ni/Co offers a different magnetic behavior, especially in the case of stacked deposition from two separate electrolytes. The achieved composite shows a two-slope hysteresis, which will be discussed in contrast to the single electrolyte deposition.By enabling an accurate control of the size and of the volume ratio of different metal structures such materials are promising for the fabrication of three-dimensional arrays of permanent nanomagnets.[1] K. Rumpf, P. Granitzer, H. Michor, NRL 11, 398 (2016).[2] K. Rumpf, P. Granitzer, R. Gonzalez-Rodriguez, J. Coffer, M. Reisser, Phys. Stat. Sol. A 217, 1901040 (2020). Figure 1

Extraordinarily High Minority Charge Carrier Lifetime Observed in Crystalline Silicon

Recent progress in surface passivation technology and wafer pretreatment already resulted in significant improvements in the achievable minority charge carrier lifetime of crystalline silicon. Herein, this is further exemplified by studying the lifetime on lowly doped crystalline silicon wafers passivated by poly‐Si. To ensure credible lifetime measurements multiple measurement techniques are compared and good agreement between the investigated approaches is found. The resulting lifetime curves are analyzed in detail and the main limitation is very likely caused by silicon bulk recombination—most likely due to impurities. This analysis indicates that even very low impurity concentrations can be a limiting factor at the extraordinary high level of charge carrier lifetime observed in this study. Despite these limitations, lifetimes of 0.18 s on p‐type and 0.5 s on n‐type crystalline silicon wafers are measured, which to our knowledge exceed previously reported lifetimes. In both cases, these measured lifetimes correspond to an effective minority charge carrier diffusion length of ≈2.5 cm.

Doping profiling of beveled Si wafers via UV-micro Raman spectroscopy

Doping profiling methods are required to provide doping monitoring of heavy doped Silicon wafers, widely used in electronic devices, with high concentration sensitivity and spatial resolution. Herein, we demonstrate that ultraviolet (UV) micro-Raman spectroscopy implemented on small-angle beveled surfaces is able to produce a Raman-based doping profile without any further measurements. The reliability of the approach is verified on ion-implanted p-type B-doped single-crystalline Si (100) wafers with shallow (100 nm) doping profile, directly comparing the Raman-based doping profiling results with independent secondary ion mass spectrometry (SIMS) and spreading resistance profiling (SRP) measurements. The Raman-based technique is capable to fully reproduce the doping profile down to 100 nm with excellent doping sensitivity (10 ppm) in the 1018–1020 cm−3 doping concentration range providing high lateral (vertical) resolution of 1μm (10 nm). The technique is comparable to SIMS in terms of resolution and sensitivity down to 1018 cm−3 concentration but requires the beveling process. Instead, it is a better alternative to SRP on bevel due to its higher spatial resolution and avoiding probe contact. The Raman-based doping profiling technique is, therefore, suitable for heavy doped Si with typical shallow doping profiles of state-of-the-art Si-based nanoelectronics.

Hard Magnetic Composite: FePt Nanoparticles Grown within Nanostructured Silicon

In this work porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures which offer a hard magnetic behavior. The difference of the magnetic characteristics between the two systems is figured out.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution [1]. The morphology offers separated pores of about 60 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO [2]. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure are used. FePt nanoparticles (NPs) are chemically grown inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6). For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.Magnetic characterization of the samples is performed by VSM (Vibrating Sample Magnetometer), the structure is analyzed by SEM, TEM and EDX.The magnetic response of the two different composite systems is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.Hard magnetic materials within nanostructured silicon give rise for on-chip applications using 3 dimensional arrays of nanomagnets.Figure 1: Field dependent magnetization measurements of PSi and SiNTs filled with FePt NPs, respectively showing a higher coercivity in the case of PSi.[1] K. Rumpf, P. Granitzer, H. Michor, NRL 11, 398 (2016).[2] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Comm. 49, 5760 (2013). Figure 1

(Invited) Gallium Doped Silicon for High Efficiency Solar Cells

In the past year or so, gallium doped silicon wafers have become a mainstream substrate for solar cell production in China [1], and hence for the world. They offer intrinsically better carrier lifetime stability than boron doped substrates [2] without requiring post-cell production stabilisation processes while requiring only minimal changes to established cell lines. Gallium doped monocrystalline silicon is likely to account for the majority of passivated emitter and rear cell (PERC) production in the coming years.High purity gallium doped silicon has been the subject of much less study than some other silicon material types, and the limits of its performance are not yet well established. In terms of effective carrier lifetime – one of the most important properties for solar cells – the highest reported values are typically around 1 ms. We have conducted a study to evaluate the performance limit of modern Ga doped silicon materials with high quality surface passivation. We find effective lifetime to vary with resistivity and measure effective lifetimes > 9 ms in 11.2 Ωcm material, which is much higher than reported previously. Furthermore, the injection dependence is less strong than in the boron case which may result in a higher fill factor and favourable cell performance in operation.One of Ga doped silicon’s perceived advantages is its stability under illumination relative to B doped silicon which suffers heavily from boron-oxygen light induced degradation if not mitigated. We have monitored the stability of commercial gallium doped PERC cells under illumination (> 3000 h in some cases) using a photoluminescence imaging proxy method. We have shown however that dark annealed Ga doped PERC cells can degrade when exposed to light, albeit on a much smaller scale than B doped PERC, and this degradation occurs due to a reduction in bulk lifetime [3]. We will now present our latest results which show inconsistencies in degradation behaviour between solar cell batches. Surprisingly, cells from one ingot exhibit degradation, then recovery behaviour when annealed at 300 °C, but near stability when not annealed, but, for another ingot, the opposite is observed. We have also investigated the effect of stabilisation processes of the kind typically used to mitigate boron-oxygen degradation. We find these processes make essentially no difference to the degradation behaviour in Ga doped PERC cells. Our investigations using secondary ion mass spectrometry (SIMS) find that commercial Ga doped PERC cells contain detectable levels of boron, and this could play a role in the degradation processes observed.In summary, our work generally confirms the positive effects of a transition from B to Ga doping for solar cells. Any degradation in cell performance under illumination is fairly small, but understanding the reasons for this is one of the most important questions in high purity silicon research at present. We will highlight urgent research in this area necessary to mitigate instability issues which may arise in newly manufactured modules featuring Ga doped silicon solar cells.

X-ray scattering profiles: revealing the porosity gradient in porous silicon

Porous silicon layers with different porosities were prepared by adjusting the anodization current density of the electrochemical etching process, starting from highly doped p-type crystalline silicon wafers. The microstructural parameters of the porous layers were assessed by high-resolution X-ray diffraction, total external reflection, scanning electron microscopy and nitrogen adsorption–desorption analysis. Furthermore, both the surface porosity and the mean porosity for the entire volume of the samples were estimated by employing total external reflection measurements and X-ray reciprocal-space mapping, respectively. The results clearly indicate that the surface porosity is different from the mean porosity, and the presence of a depth porosity gradient is suggested. To evaluate the porosity gradient in a nondestructive way, a new laboratory method using the grazing-incidence X-ray diffraction technique is reported. It is based on the analysis of the X-ray scattering profiles of the porous layers to obtain the static Debye–Waller factors. In this way, a description of the porosity gradient in a quantitative framework becomes possible, and, as a result, it was shown that the porosity increases exponentially with the X-ray penetration depth. Moreover, a strong dependence between the porosity gradient and the anodization current was demonstrated. Thus, in the case of the lowest anodization current (e.g.50 mA cm−2) a variation of only 15% of the porosity from the surface to the interface is found, but when applying a high anodization current of 110 mA cm−2the porosity close to the bulk interface is almost three times higher than at the surface.

From Crystalline to Low-cost Silicon-based Solar Cells: a Review

Renewable energy has become an auspicious alternative to fossil fuel resources due to its sustainability and renewability. In this respect, Photovoltaics (PV) technology is one of the essential technologies. Today, more than 90 % of the global PV market relies on crystalline silicon (c-Si)-based solar cells. This article reviews the dynamic field of Si-based solar cells from high-cost crystalline to low-cost cells and investigates how to preserve high possible efficiencies while decreasing the cost. First, we discuss the various types of c-Si solar cells with different device architectures and report recent developments. Next, thin-film solar cells with their recent advancements are given. Then, Si nanowires solar cells and their recent results are discussed. Finally, we present the most encouraging tendencies in achieving low-cost solar cells utilizing cheap materials like heavily doped silicon wafers.

Heat-assisted μ-electrical discharge machining of silicon

Micro-electrical discharge machining (μEDM) is an unconventional machining method that is suitable for machining of conductive materials including highly doped silicon (Si) wafers. This paper reports a novel method of heat-assisted μEDM machining of Si wafers by varying the temperature to increase the electrical conductivity of Si. In order to achieve this condition, a ceramic heater is used to heat the Si wafers within the temperature range of 30–250 °C. In this study, the machining performances in terms of the material removal rate, tool wear rate, surface quality, and materials characterization have been investigated accordingly. The machining performance of p-type (1–10 Ω cm) Si wafers was investigated to machine a cavity based on different temperatures with a constant discharge energy of 50 μJ and a feed rate of 50 μm/min. The results indicated that increasing the machining temperature allowed achieving a higher material removal rate, lower tool wear rate, and lower surface roughness. The highest material removal rate of 1.43 × 10−5 mm3/s and a surface roughness of 1.487 μm were achieved at 250 °C. In addition, the material removal rate increased by a factor of ~16 times compared to the results obtained at the lowest temperature, 30 °C, and the Raman spectroscopy analysis revealed that no significant changes occurred in the Si structure before and after machining.

Influence of H2O2 concentration on the structural and photoluminescent properties of porous silicon nanowires fabricated by metal-assisted chemical etching

Porous silicon nanowires (PSi NWs) are a promising material for applications in sensorics, photovoltaics, and biomedicine. However, the structural and optical properties of PSi NWs are extremely sensitive to the concentrations of chemical solutions used in their manufacture. In this study, PSi NWs were fabricated by a two step metal-assisted chemical etching method from highly doped crystalline silicon wafers with a resistivity of <0.005 Ω cm. It was shown that the structural and optical properties of the obtained samples depend on the concentration of hydrogen peroxide (H2O2), which in our experiments varied from 5 to 30%. As a result of etching, a layer of NWs with a diameter of 50–200 nm is obtained from above, and a thin layer of porous silicon is obtained from below. The ratio of the thicknesses of these two layers can be tuned by choosing the required concentration of H2O2. The porosity of the samples, calculated in the approximation of the effective Bruggeman medium from the IR reflection spectra, was 40–50%. Electron microscopy demonstrated the presence of a large amount of silicon nanocrystals in the volume of PSi NWs, which exhibited efficient visible photoluminescence due to quantum confinement effect. It was shown that the size of the nanocrystals can be also tunable on the used concentration of H2O2.

Electrochemical Actuation in Porous Silicon

We show large and reversible electrochemical actuation in a material based on self-organised nanoporosity in silicon (pSi) in combination with the electrically conductive polymer polypyrrole (PPy), which is introduced inside the pore space. On a single-pore scale the electrochemical actuation can be traced to the high porosity of 50 % and to potential-dependent pressures of up to 15 MPa acting at the single-pore scale. These pressures originate in charging or discharging and the related counter-ion movements. The exceptionally small operation voltages (0.4-0.9V) and the simple synthesis enable a silicon based actor. INTRODUCTION Self-organized nano-porosity in silicon has been attracting interest from a fundamental point of view and for applications due to its special thermal, electrical and optical properties and its bio compatibility [1]. However, the absence of the piezo-electric effect in silicon makes applications in the field of electro-mechanics for this widely used semiconductor difficult. The aim of this work is to study the sensor and actuator characteristics of bare pSi and pSi filled with PPy. An electrochemical change in the oxidation state of PPy can increase or decrease the number of delocalised charges in the polymer. Immersed in an electrolyte this is also accompanied by a reversible counter-ion uptake or expulsion and thus with a marcroscopic contraction or swelling under electrical potential control, making PPy one of the most employed artificial muscle materials [2]. The material is immersed in an electrolyte solution and studied by different techniques as in-situ dilatometry and in-situ X-ray diffraction. EXPERIMENTAL RESULTS AND DISCUSSIONS Porous silicon is prepared by an electrochemical anodization process in a solution of hydrofluoric acid and ethanol by applying a constant current between a platinum cathode and a highly doped silicon wafer. The resulting pores are characteristically straight and orthogonally aligned to the silicon surface. The pore diameter amounts to 7.6 nm and is determined via nitrogen sorption isotherm as is the porosity of 50 %. In a second step PPy is incorporated inside the pores via an electro-polymerisation in galvanostatic mode.Dilatometry measurements in an in-situ electrochemical setup are performed in order to characterize the actuating properties of the resulting pSi-PPy hybrid material. The sample is therefore immersed in perchloric acid (HClO4) and positioned in the setup, so that the pores are pointing in a horizontal direction, i.e. the sample is standing upright.Measuring the sample length change while recording Cyclovoltammograms (CVs) allows a detailed characterisation of the electrochemical actuation. The potential E is reversibly changed from 0.4 V to 0.9 V versus the normal hydrogen electrode potential. An increasing potential leads to an increased insertion of chlorate-anions in the PP. Vice versa, decreasing the potential expells anions from the PPy. It is found, that the repetitive change in sample length coincides linearly with E. So, the incorporation of anions leads to an expansion of the sample and the release of the anions lets the sample contract.For obtaining a further understanding of the electrochemical actuation mechanism of the PPy filled pSi membranes, the micromechanical properties are modelled based on the microstructure as recorded by electron transmission micrographs.REFERENCES[1] M. J. Sailor, Porous Silicon in Practice - Preparation, Characterization and Applications, Wiley-VCH, 2011.[2] E. Smela, Adv. Mater., 2003, 15, 481–494.

Laser ablation sample preparation for atom probe tomography and transmission electron microscopy

Laser ablation is capable of removing large volumes of material with micron scale precision at very high speeds. This makes it an ideal tool for the initial stage of preparation of samples for atom probe and electron microscopy studies. However, the thermal nature of the laser ablation process is such that thermal and mechanical damage is induced in the samples in the form of zones of recrystallisation and stress induced deformation. For the analysis of nanometer-sized samples, such as those required for atom probe tomography and transmission electron microscopy, it is necessary to ensure that any damage induced during sample preparation will not introduce artefacts and that specimens are representative of the microstructure of the bulk sample. Here we have undertaken an analysis of the damage caused during sample preparation through a study of pure aluminium and phosphorous doped silicon wafers. Our findings indicate that recrystallisation and stress induced misorientations occur in pure aluminium at the micron scale, however, no detectable damage is observed in the silicon sample.

Solution processed all-carbon transistors via directed assembly and transfer printing of CNT channel and electrodes

Carbon nanotube (CNT) field effect transistors (FETs) have shown great promise for flexible device applications, but a method to selectively print each layer with high fidelity and low cost on flexible substrates remains elusive. To address this gap, we combine the simplicity of directed assembly with the high resolution and pattern fidelity of transfer printing to print all-carbon transistors on a flexible polyimide substrate. For the presented device, the channel and electrodes consist of semiconducting single-walled CNTs and multi-walled CNTs, respectively. We demonstrate an approach to selectively assemble multi-walled CNTs on a chemically heterogenous surface of a highly doped silicon wafer using electrophoresis, while single-walled CNTs are assembled on a photoresist templated substrate using meniscus driven fluidic assembly. Both layers are sequentially transfer printed on a stack of polyurethane and SU-8, which serves as the gate dielectric. This approach utilizes lithographically patterned silicon wafers as reusable templates, which significantly lowers the manufacturing cost and provides greater resolution than other printing techniques. The printed transistors exhibit on/off ratio as high as 106 with mobility approaching 10 cm2 V−1 s−1, which is highly promising for fully printed flexible FETs.

Design and modeling of a highly sensitive microelectromechanical system capacitive microphone

A single-chip microelectromechanical system (MEMS) capacitive microphone is designed and modeled. The mechanical model of the structure is extracted and the mathematical equations for a description of the microphone behavior are obtained. Then the proposed microphone characteristics are considered. In this structure, by adding Z-shape arms around the diaphragm, diaphragm hardness is decreased and diaphragm displacement becomes uniform. The sensitivity and the pull-in voltage are improved despite the decreasing size. The perforated diaphragm of this microphone is supported by Z-shape arms at its four corners. These arms around the diaphragm decrease the stiffness and air damping of the microphone. The behavior of this microphone is also analyzed by the finite element method. The structure has a diaphragm thickness of 2 μm, a diaphragm size of 0.32 × 0.32 mm2, an air gap of 2 μm, and a highly doped monocrystalline silicon wafer as a backplate. The proposed microphone is simulated with IntelliSuite software. According to the results, the new microphone has a sensitivity of 14.245 mV / Pa and a pull-in voltage of 5.83 V. The results show that the proposed MEMS capacitive microphone is one of the best structures in performance. The obtained mathematical equations for description of the microphone’s behavior have good agreement with the simulation results.

Hard Magnetic Composite: FePt Nanoparticles Grown within Nanostructured Silicon

In this work porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures which offer a hard magnetic behavior. The difference of the magnetic characteristics between the two systems is figured out.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution [1]. The morphology offers separated pores of about 60 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO [2]. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure are used. FePt nanoparticles (NPs) are chemically grown inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6). For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.Magnetic characterization of the samples is performed by VSM (Vibrating Sample Magnetometer), the structure is analyzed by SEM, TEM and EDX.The magnetic response of the two different composite systems is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.Hard magnetic materials within nanostructured silicon give rise for on-chip applications using 3 dimensional arrays of nanomagnets.[1] K. Rumpf, P. Granitzer, H. Michor, NRL 11, 398 (2016).[2] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Comm. 49, 5760 (2013). Figure 1