We present electrode assemblies of Si nanowires (NW) partially coated with a highly conductive nano-graphitic carbon layer. The surface modifications and overall electrode performance of these electrodes are investigated at high charge and discharge rates. The possibility to directly compare carbon-coated with uncoated SiNW electrodes allows to systematically separate the influences of Si and C on the battery performance and stability from a typically mixed system in electrodes. Consequently, a nanometer thin carbon layer is found to be efficient in withstanding mechanical stress and cracking during battery cycling. Moreover, the protective layer reduces the surface reactivity towards the electrolyte and enhances the electrode conductivity. On the other hand, we conclude that thicker carbon coatings reduce the performance of the Si nanowire network at high currents by introducing an additional diffusion barrier for Li ions.

Silicon anodes offer a very promising approach to boost the energy density of lithium-ion batteries. While silicon anodes show a high capacity and, depending on the system, a good cycle stability in half-cells vs lithium, their integration in industrially applicable lithium-ion full-cells is still challenging. Balancing described as the capacity ratio of negative and positive electrode (n/p ratio) is a crucial necessity for the successful design of lithium-ion batteries. In this work, three different silicon based anode systems, namely carbon coated silicon nanowires, columnar silicon thin films and silicon-carbon void structures are compared in LIB full cells containing NMC111 cathodes. By varying the areal capacity of the NMC111 cathode, the influence of the balancing was investigated over a broad n/p range of 0.8−3.2. The aim was to find an ideal compromise between lithium plating suppression, high cycling stability and maximized energy density. To underline the high volumetric energy density, the columnar silicon thin films are additionally analyzed in multilayered pouch cells with NMC622 and NMC811 cathodes resulting in 605 Wh L−1 and 135 Wh kg−1 and even 806 Wh L−1 and 183 Wh kg−1 as demonstrated on stack level.

Rapid decay of silicon anodes during lithiation poses a significant challenge in application of silicon as an anode material in lithium ion batteries. In situ Raman spectroscopy is a powerful method to study the relationship between structural and electrochemical data during electrode cycling and to allow the observation of amorphous as well as liquid and transient species in a battery cell. Herein, we present in situ Raman spectroscopy on high capacity electrode using uncoated and carbon-coated silicon nanowires during first lithiation and delithiation cycle in an optimized lithium ion battery setup and complement the results with operando X-ray reflection diffraction measurements. During lithiation, we were able to detect a new Raman signal at 1859 cm(-1) especially on uncoated silicon nanowires. The detailed in situ Raman measurement of the first lithiation/delithiation cycle allowed to differentiate between morphology changes of the electrode as well as interphase formation from electrolyte components. (C) The Author(s) 2019. Published by ECS.

Gold nanoparticles were electrodeposited on carbon non-woven substrates from an acidic, alkaline free HAuCl4 electrolyte. The electrochemical behavior of the electrolyte was characterized by potentiostatic experiments. The deposition of the gold nanoparticles was performed by pulse plating, where the particles size distribution and surface coverage are adjusted by variation of the pulse parameters. A homogeneous surface coverage of 2.3% with a mean diameter of the gold nanoparticles of about 54 nm is obtained. The electroplating process is scaled up to a substrate size of 150 cm(2). The gold nanoparticles are used as catalytic nuclei for the growth of Si nanowires by vapor liquid solid mechanism. Finally, the basic applicability of these Si nanowire arrays as highly loaded anode for lithium ion batteries is demonstrated. The various reactions during (de)lithiation and their contribution to the anode capacity are identified, and performance features are exemplarily determined by half-cell tests of such a typical anode.

More than ever, there are increasing requirements for rechargeable energy storage in today’s mobile society, which are accompanied by a high demand in flexibility. This reflects in a large field of applications ranging from low power consumption devices like portable electronics up to high power draining systems like electrical powered vehicles. Li-Ion batteries are more and more dominating the market for these applications. Especially, the high power sector including electromobile applications shows a tremendous growth. In this sector, new materials are needed, which result in battery systems with high energy, high power densities and increased lifetime. One promising candidate is silicon because of its enormous theoretical capacity of nearly 4000 mAh/g­Si [1]. Unfortunately, a large volume expansion of 400% accompanies the charging of this anode material with Li ions [2], which leads to a disintegration of the electrode after cycling. Using nanostructures is one way of relaxing stress induced by the expansion. For example, amorphous Si films in the nanometer range show promising long term performance during slow cycling. Unfortunately, they are uninteresting for rapid charging/discharging in electrical vehicles [3]. Another disadvantage is the low capacity and low energy density due to the small amount of active material. Si Nanowires (SiNWs) are able to circumvent the drawbacks of thin films. Their inherent geometry possesses the ability to accommodate for the volume expansion stress [4, 5], (fig. 1, left) and deliver sufficient active material for a reasonable area capacity. A process was developed to integrate SiNWs and its advantages on various different current collectors [4]. The electrochemical investigation of the anode showed an increased lifetime at a high capacity approaching values with relevance for commercial application (fig. 1, right). The anode has a starting capacity of about 4000 mAh/g with respect to Si which is close to the theoretical value. The capacity still remains at more than 2000 mAh/g(Si) after more than 200 cycles. The change of morphology before and after cycling of these structures has been investigated with various methods. Those experiments point to a strong SEI formation, which is mainly responsible for the decrease of capacity. Furthermore, they show a remaining SiNW mesh after various cycles, no immanent degradation was seen. Additionally, the performance of the anode will be shown in a full cell setup, which unfolds insides related to real world battery operation. [1] W.J. Weydanz et al, Journal of Power Sources 81, 237 (1999). [2] B. A. Boukamp et al, J. Electrochem. Soc., 128, 752 (1981). [3] J.R. Szczech, S. Jin, Energy & Environmental Science, 4, 56-72 (2011). [4] A. Krause et al, MRS Proceedings, 1751, (2015). [5] T. Mikolajick et al, Phys. Status Solidi RRL, 7, 793 (2013). [6] U. Kasavajjula, Journal of Power Sources 163, 1003 (2007). Fig. 1: Charging and discharging of Si-Anodes. Left: Sketch of the volume expansion and contraction during lithiation and delithiation of Si-Nanowires. Right [4]: The integration of Si-Nanowires as anode material leads to starting capacity of almost the theoretical value, after more than 200 cyles the capacity remains at 2000 mAh/g, which is still 5 times higher than the standard carbon electrode [6]. Figure 1

The optical excitation energies of organic dye molecules are often said to depend sensitively on the polarizability of the utilized substrate. To this end, we employ differential reflectance spectroscopy (DRS) to analyze the S-0 -> S-1 fundamental transition energies observed for 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) as a function of coverage on various surfaces, such as sp(2)-bonded insulating layers [graphene and hexagonal boron nitride (h-BN)], and noblemetals pre-covered by a molecular wetting layer which prevents hybridization of the second-layer molecules with the metal states. We elucidate the optical absorbance behavior of PTCDA layers grown on h-BN/Rh(111) and on h-BN/Pt(111) and characterize their structures by means of scanning tunneling microscopy. Surprisingly, although the dielectric properties of the employed substrates differ substantially, only two main transition energies are observed: (i) PTCDA(HE) essentially mimics the behavior of isolated monomers on surfaces (particularly at submonolayer coverage), while (ii) PTCDA(LE), red-shifted by approximate to 70 meV (approximate to 560 cm(-1)), is attributed to two-dimensional densely packed aggregates. This red-shift is in remarkable accordance with previous investigations for PTCDA on NaCl(100) and, therefore, likely arises from the same physical effects, namely the formation of two-dimensional excitonic bands and the polarizability of neighboring molecules within the monolayer. In distinction from earlier studies, we conclude that the polarizabilities of the employed substrates do not constitute the dominant contribution to the molecular S-0 -> S-1 transition energies observed here.

Radio frequency (RF) biasing induced by a second plasma source at the substrate is applied to low-temperature sputtering processes for indium tin oxide (ITO) and titanium nitride (TiN) thin films. Investigations on crystal structure and surface morphology show that RF-biased substrate plasma processes result in a changed growth regime with different grain sizes and orientations than those produced by processes without a substrate bias. The influence of the RF bias is shown comparatively for reactive RF-sputtered ITO and reactive direct-current-sputtered TiN. The ITO layers exhibit an improved electrical resistivity of 0.5 mΩ cm and an optical absorption coefficient of 0.5 × 104 cm−1 without substrate heating. Room-temperature sputtered TiN layers are deposited that possess a resistivity (0.1 mΩ cm) of 3 orders of magnitude lower than, and a density (5.4 g/cm3) up to 45% greater than, those obtained from layers grown using the standard process without a substrate plasma.

We show full Li/S cells with the use of balanced and high capacity electrodes to address high power electro-mobile applications. The anode is made of an assembly comprising of silicon nanowires as active material densely and conformally grown on a 3D carbon mesh as a light-weight current collector, offering extremely high areal capacity for reversible Li storage of up to 9 mAh/cm 2 . The dense growth is guaranteed by a versatile Au precursor developed for homogenous Au layer deposition on 3D substrates. In contrast to metallic Li, the presented system exhibits superior characteristics as an anode in Li/S batteries such as safe operation, long cycle life and easy handling. These anodes are combined with high area density S/C composite cathodes into a Li/S full-cell with an ether- and lithium triflate-based electrolyte for high ionic conductivity. The result is a highly cyclable full-cell with an areal capacity of 2.3 mAh/cm 2 , a cyclability surpassing 450 cycles and capacity retention of 80% after 150 cycles (capacity loss <0.4% per cycle). A detailed physical and electrochemical investigation of the SiNW Li/S full-cell including in-operando synchrotron X-ray diffraction measurements reveals that the lower degradation is due to a lower self-reduction of polysulfides after continuous charging/discharging.

Semiconductor nanowire transistors are considered potential successors of finFETs providing the ultimate miniaturization capabilities of MOS transistors targeting an even higher circuit complexity and performance. A promising perspective for further advancement beyond classical CMOS scaling is to exploit functionality enhancement of the elementary computing units. Several nanowire based multi-gated device concepts known as reconfigurable field effect transistors (RFETs) [1,2] and polarity control (PC) FETs [3] that combine multifunctionality with the inherent advantages of silicon nanowires are being currently evaluated. These four-terminal devices merge unipolar nand pFET switching characteristics from the same device as selected simply by an electric signal and without the need for doping enabling complementary CMOS operation with a single kind of transistor. RFETs make use of two sharp metal-NiSi2 / intrinsic-silicon interfaces with individual gates for the selective injection of electrons and holes into the channel region [4]. In order to allow complementary circuit operation symmetry in the pand n-type I-V characteristics is mandatory. To this end, the application of radially compressive strain to <110> oriented silicon nanowires is able to align the injection efficiency of electrons and holes [5]. Full swing complementary operating circuits are shown with symmetric RFETs [6]. Multi-functionality is used to synthesize logic circuits with lower transistor count reducing critical pathes and power consumption as compared to conventional CMOS [7,8]. We will further analyze the prospects of Ge based RFETs for performance enhancement.

Silicon nanowires have emerged as a cheap and efficient technology for nanostructured Si necessary for electronic devices as well as anode material in Li battery technology. They are typically grown via the vapor-liquid-solid mechanism and gold nanoparticles used as catalyst. Here we compare the CVD growth of those silicon nanowires on different substrates, namely Si with 130 nm SiO2 as well as on a carbon surface. The presence of carbon does change the typical characteristics of single crystalline growth to more amorphous or polycrystalline growth regardless of different process conditions typically varied to get optimal nanowire growth.

Simulations and experimental results of ultrathin layers of the model perovskite CaTiO3' prove its suitability for integration as a novel dielectric in industrial applications due to an excellent compromise between band gap and permittivity. The computational approach relies on density functional theory in the local density approximation for CaTiO3 and comparable perovskites. With low-energy EELS measurements, the band gap of 3.8-4.38 eV for CaTiO3 was determined with exceptional precision, using a monochromatic electron beam (80 kV acceleration voltage, 0.18 eV FWHM) in a high resolution scanning transmission electron microscopy setup. Results of capacitance voltage measurements of ultrathin CaTiO3 capacitors show an excellent permittivity of 102.3 for 17.8 nm layer thickness. DUV-VIS ellipsometric measurements are carried out to complete the picture of band gap and permittivity of CaTiO3 as a competing perovskite to SrTiO3 or others for possible integration in ultrathin capacitor stacks.

Medical imaging is an important tool for the post-operative checkup of an accurate position of an implant as well as for monitoring the integration in the adjacent tissue that may influence the success of a medical device. Unfortunately, the possibility to use imaging methods is associated with the implant material and all the established metallic materials for surgery do not show a proper "imaging compatibility". The present study is a combined investigation of the in vitro response to human mesenchymal stromal cells (hMSC) and magnetic resonance imaging (MRI) compatibility of the potential material combination polyetheretherketone/titanium (PEEK/Ti) for medical devices. Because of the advantageous imaging properties and the mechanical and chemical stability, PEEK becomes more and more an alternative to common metallic implant materials like titanium or cobalt-chrome. However, PEEK is a bioinert material having a limited ability for direct bone incorporation. Due to its excellent biocompatibility, Ti was chosen as coating material to enhance the cellular response. The result is a combination with advantageous properties: the magnetic susceptibility and elastic modulus close to bone, corrosion resistance and mechanical flexibility of PEEK and the excellent biocompatibility of titanium. The appearance of metal-related artifact was discussed in electrical resistivity and magnetic susceptibility. Therefore, two titanium coatings have been investigated: a complete coating and a structured surface avoiding surface conductivity. To determine the in vitro biocompatibility, the cell responses were assessed in terms of the overall morphology of the hMSC and their cell area distribution, proliferation, osteogenic differentiation and mineral deposition. The cellular stress was evaluated by the prostaglandin E-2 level. The bonded materials both produced no disturbing artifacts in magnetic resonance imaging. Compared to the pure PEEK material, the titanium coated specimens showed an enhanced biocompatibility, which is indicated by a higher cell number, larger activity of the enzyme tissue non-specific alkaline phosphatase and therefore a greater amount of deposited calcium and phosphate. The results on bare PEEK are accompanied with a higher cellular stress level, which is indicated by prostaglandin E-2. Copyright (C) 2015, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited. All rights reserved.

Growth experiments show significant differences in the crystallization of ultrathin CaTiO3 layers on polycrystalline Pt surfaces. While the deposition of ultrathin layers below crystallization temperature inhibits the full layer crystallization, local epitaxial growth of CaTiO3 crystals on top of specific oriented Pt crystals occurs. The result is a formation of crystals embedded in an amorphous matrix. An epitaxial alignment of the cubic CaTiO3 ⟨111⟩ direction on top of the underlying Pt {111} surface has been observed. A reduced forming energy is attributed to an interplay of surface energies at the {111} interface of both materials and CaTiO3 nanocrystallites facets. The preferential texturing of CaTiO3 layers on top of Pt has been used in the preparation of ultrathin metal-insulator-metal capacitors with 5-30 nm oxide thickness. The effective CaTiO3 permittivity in the capacitor stack increases to 55 compared to capacitors with amorphous layers and a permittivity of 28. The isolated CaTiO3 crystals exhibit a passivation of the CaTiO3 grain surfaces by the surrounding amorphous matrix, which keeps the capacitor leakage current at ideally low values comparable for those of amorphous thin film capacitors.

Thin film capacitors were fabricated by sputtering TiN-Y doped HfO2-TiN stacks on silicon substrates. Yttrium was incorporated into the HfO2 layers by simultaneously sputtering from Y2O3 and HfO2 sources. Electric polarization and relative permittivity measurements yield distinct ferroelectric properties as a result of low yttrium dopant concentrations in the range of 0.9-1.9 mol. %. Grazing incidence x-ray diffraction measurements show the formation of an orthorhombic phase in this range. Compared to atomic layer deposition films, the highest remanent polarization and the highest relative permittivity were obtained at significantly lower doping concentrations in these sputtered films.

Using radio frequency sputtering, CaTiO3 layers with varying thicknesses and deposition temperatures are deposited on different bottom electrodes. On elevated temperatures, the CaTiO3 layer growth and therefore the properties like crystallinity and leakage current depend strongly on the morphology and lattice constant of the bottom layer. With the use of temperature stable bottom electrodes, which are deposited prior to the oxide deposition without any vacuum break, like Pt on PVD TiN and Pt on RuO2, an improvement to the k-value as well as the leakage current is achieved compared to CVD -TiN/ Pt stacks. In addition, a pyrolytic C electrode is used the first time in a metal-insulator-metal capacitor for DRAM applications. Keywords—Dielectrics, High-k, CaTiO3, MIM capacitor

CaTiO3 layers with varying thicknesses in metal-insulator-metal capacitor stacks were deposited at 550 degrees C using radio-frequency magnetron sputtering. The combination of electrical and transmission electron microscopy measurements allows a correlation of k-value and leakage current to the degree of crystallinity. Experiments show that higher crystallinity and, therefore, higher k-values lead to increasing leakage currents and change of conduction mechanisms. However, leakage currents are significantly reduced when crystallites are embedded in an amorphous matrix. Selective growth of these crystallites is owed to cube-on-cube nucleation of CaTiO3 on {011} Pt. (C) 2011 American Institute of Physics. [doi:10.1063/1.3664395]

Thin calcium titanate (CaTiO3) films are investigated as promising insulator materials with very high-k values for future microelectronic devices such as metal-insulator-metal (MIM) capacitors and field-effect transistor gate stacks. MIM stacks were deposited by sputtering under UHV conditions without breaking vacuum. A capacitance equivalent thickness of 1.3 nm with a leakage current density of 1×10−7 A/cm2 at 1 V was achieved with deposition temperatures of 550 °C on Pt as bottom electrode. The effect of different electrode materials was studied, resulting in leakage densities correlating directly to the different work function values. grazing incidence x-ray diffraction and high-resolution transmission electron microscopy images are analyzed to study the crystallization behavior. As grown CaTiO3 at 550 °C exhibits crystallites in an amorphous matrix. A dielectric constant of k≈93 was obtained for crystallized films.

Doping-induced absorption changes of organic molecules on an insulating solid are reported. The charge transfer between alkali metal atoms and individual molecules on a surface leads to new electronic transitions identified with optical absorption spectroscopy. Progressive doping allows the discrimination of neutral, monoanionic, and dianionic molecules in the solid state through examination of the spectra and rate equation modeling.