Barbara Adolphi

The Route to Functional Graphene Oxide

We report on an easy-to-use, successful, and reproducible route to synthesize functionalized graphite oxide (GO) and its conversion to graphene-like materials through chemical or thermal reduction of GO. Graphite oxide containing hydroxyl, epoxy, carbonyl, and carboxyl groups loses mainly hydroxyl and epoxy groups during reduction, whereas carboxyl species remain untouched. The interaction of functionalized graphene with fluorescent methylene blue (MB) is investigated and compared to graphite, fully oxidized GO, as well as thermally and chemically reduced GO. Optical absorption and emission spectra of the composites indicate a clear preference for MB interaction with the GO derivatives containing a large number of functional groups (GO and chemically reduced GO), whereas graphite and thermally reduced GO only incorporate a few MB molecules. These findings are consistent with thermogravimetric, X-ray photoelectron spectroscopic, and Raman data recorded at every stage of preparation. The optical data also indicate concentration-dependent aggregation of MB on the GO surface leading to stable MB dimers and trimers. The MB dimers are responsible for fluorescence quenching, which can be controlled by varying the pH value.

Passive Wireless Resonant Galfenol Sensor for Osteosynthesis Plate Bending Measurement

The healing process of bone fractures can be monitored by a measurement of the osteosynthesis plate bending. For this purpose a wireless magnetostrictive bending sensor is proposed. A planar rectangular coil on top of a magnetostrictive Galfenol ( alloy) layer forms an electrical resonant circuit. The sensor is manufactured in thin film technology. Coil turns were electrodeposited by pattern plating. Sensors with overall dimensions of (13 2 0.5) mm were manufactured with varied turn numbers showing self-resonance frequencies from 5 to 50 MHz. Examined sensors possess linear frequency-force characteristic up to 6 N with frequency shifts of 6 kHz . In order to obtain the sensor resonance frequency wirelessly, several measurement techniques were employed using inductively coupled coils. Frequency domain measurements have been carried out by employing a network analyzer with a single detection coil and a lock-in amplifier with separate coils for excitation and detection. In time domain measurements, two coils for transmission and reception are used. In the transmit case a short sine pulse excites the sensor and afterwards its decaying response signal is received. To determine the resonance frequency, a frequency counting, Fourier or wavelet technique can be used. By integrating additional cores of high permeability into sensor and detection coil, measurement ranges can be increased.

Improvement of sputtered Galfenol thin films for sensor applications

Galfenol Fe83Ga17 films are sputtered on Si wafers without, and with Ti or Ti/Cu metallic seed layers in order to obtain a magnetoelastic layer which is sensitive to bending deformations of the compound structure. The layer thicknesses range from 100?nm to 5? ?m. Layer morphology, texture, and the Villari effect are examined. The texture of the Galfenol films is strongly influenced by the seed layer. No low-index texture components are found for films directly deposited on Si and SiO2. On Ti, a (111) texture is formed on layers with more than 1000?nm thickness. A favorable (110) fiber texture is formed on Ti/Cu. Deforming the bimorphs (Si + layer system) by 0.012%, the Villari effect is detected due to the change in relative permeability. The maximum change occurs for Galfenol films with a thickness of 1? ?m on a Ti/Cu buffer layer. The films open a route to the incorporation of magnetoelastic films into integrated magnetoelastic sensor devices.

Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions

Germanium is a promising material for future very large scale integration transistors, due to its superior hole mobility. However, germanium-based devices typically suffer from high reverse junction leakage due to the low band-gap energy of 0.66 eV and therefore are characterized by high static power dissipation. In this paper, we experimentally demonstrate a solution to suppress the off-state leakage in germanium nanowire Schottky barrier transistors. Thereto, a device layout with two independent gates is used to induce an additional energy barrier to the channel that blocks the undesired carrier type. In addition, the polarity of the same doping-free device can be dynamically switched between p- and n-type. The shown germanium nanowire approach is able to outperform previous polarity-controllable device concepts on other material systems in terms of threshold voltages and normalized on-currents. The dielectric and Schottky barrier interface properties of the device are analyzed in detail. Finite-element drift-diffusion simulations reveal that both leakage current suppression and polarity control can also be achieved at highly scaled geometries, providing solutions for future energy-efficient systems.

Investigations on Ru-Mn films as plateable Cu diffusion barriers

In this study Ru-Mn alloys are discussed in terms of some of the major questions that are typically associated with the development of new types of barriers. First, the Cu diffusion barrier performance after annealing at high temperatures and under subsequent bias temperature stress is investigated, on SiO2 and on low-k dielectrics. Second, the origin of the barrier performance - either a self forming barrier caused by segregation of an alloyed element, or the stuffing of grain boundaries - is investigated, since this is of importance with regard to an electromigration barrier at the bottom of a via. Third, Cu plating and Cu adhesion behavior are addressed, since they are also important with regard to electromigration, specifically along the side walls of trenches. Fourth, the blocking of oxygen diffusion is investigated. Furthermore, down-scaling of the Mn content to a lowest possible level is pursued in order to reduce line and via resistances.

Degradation of Perfluorotrichlorosilane Antisticking Layers: The Impact on Mold Cleaning, Ultraviolet-Nanoimprinting, and Bonded Ultraviolet-Nanoimprint Molds

A reduction of the adhesion between imprint resist and mold is crucial for defect free imprints and is commonly achieved by silane based antisticking layers. Highly stable antisticking layers are required for high throughputs and long imprint mold lifetimes. Hybrid nanoimprint molds avoid the imprint inherent residual polymer layer in UV-assisted nanoimprinting. Such hybrid molds have chemically heterogeneous surfaces of silica and, e.g., chromium oxide regions. The chemical stability of vapor-coated 1H,1H,2H,2H-perfluorodecyltrichlorosilane antisticking layers against acetone, acidic piranha, reactive ion etching and UV-assisted nanoimprinting was investigated. To evaluate the behavior of hybrid mold surfaces, flat silica and antireflective chromium-oxynitride surfaces were used. The antisticking layer on both surfaces was highly chemical resistant against acetone. A continuous antisticking layer degradation with a surface free energy increase of 0.9mN/m per 10min piranha treatment and 1.2mN/m per 10 subsequent UV-assisted imprints was found for silica surfaces. On the chromium surfaces, the antisticking layer quality was much lower than on fused silica and degraded much faster. The surface free energy of silane coated chromium surfaces was increased by 2.3mN/m after 10 imprints and the antisticking layer was completely degraded after a single 10min piranha cleaning step. The lower antisticking layer quality on antireflective chromium was attributed to the surface itself. Additionally, the high chemical resistance of the vapor coated silane was used to successfully protect the adhesive joints of cost-efficient, adhesively bonded nanoimprint molds from being degraded by acidic piranha during mold cleaning. This can significantly increase the life-time of such bonded molds. # 2011 The Japan Society of Applied Physics

Molecular beam deposited zirconium dioxide as a high-κ dielectric for future GaN based power devices

Molecular beam deposited zirconium dioxide (ZrO2) was assessed as high-κ gate dielectric for future GaN based devices. To compare and study electrical and structural properties, thin ZrO2 films were deposited on three different substrates, n++-c-plane GaN, p-(100) Si, and TiN. The films were fabricated by electron beam evaporation from a single stoichiometric ZrO2 target. A substrate-independent phase transition from amorphous ZrO2 to the tetragonal/cubic phase was identified by gracing incidence x-ray diffractometry. Finally, monoclinic ZrO2 emerged with increasing film thickness. As found by x-ray photoelectron spectroscopy, ZrO2 formed an abrupt interface to both GaN and TiN without intermixture. Dielectric constants in the range of 14–25 were extracted from capacitance versus voltage measurements for as-deposited ZrO2 films. The leakage currents of ZrO2 on GaN resembled their counterparts on Si as well as on TiN.

Galfenol resonant sensor for indirect wireless osteosynthesis plate bending measurements

The healing process of bone fractures can be monitored by a measurement of the osteosynthesis plate bending. An electrical resonant circuit consisting of a coil with a magnetostrictive Galfenol core and a capacitance enables an indirect wireless measurement of the plate bending. The Galfenol core is manufactured with a thin film technology using a Galfenol Fe83Ga17 alloy. The sensor has a quit good linear resonant frequency-force characteristic. Both, time and frequency domain measurement techniques for the sensor, use an external measurement coil. In the frequency domain the transformed sensor impedance is evaluated and the resonance frequency is determined by a local extremum. In the time domain a short energizing sinus pulse is transmitted, the sensor response is received and a frequency counting, Fourier or Wavelet technique is used for resonance frequency detection.

Hafnium oxide for optical applications deposited by different CMOS compatible methods

Hafnium oxide is a promising candidate for electronic applications. It also offers interesting properties for a wide variety of optical applications as antireflective coatings, dielectric mirrors or protective coatings. Besides favorable optical properties, the mechanical stability and chemical inertness of hafnium oxide offers further advantages. Microelectronics require ultra thin layers in the 3-5nm range for gate dielectrics. For optical applications a wider range is necessary. As optical coatings should be capable to be integrated in a CMOS or MEMS technology, only compatible deposition processes can be used. In this presentation we report on atomic layer deposition (ALD) for thicknesses in the 2-30nm range and r.f. sputtering from 30 to above 150nm. Thus almost every wavelength from EUV to NIR can be covered for λ/4 applications, keeping in mind, that the refractive index is 2.1 at 586nm. Deposition took place on 2x2 cm2 silicon substrates for ALD and on 150mm silicon wafers for sputtering each either HF etched of thermally oxidized. The layers have been analyzed by AFM, XPS, XRD, TEM to gather information about morphology, composition, bonding and structural properties. Optical properties have been evaluated by ellipsometry. The different deposition methods are compared as well as the effects of thermal annealing after deposition. All layers are very smooth and reveal optical properties close to bulk HfO2. As deposited the layers are predominately amorphous, thermal annealing leads to crystallization.

Copper Pthalocyanine by XPS

Copper pthalocyanine (CuPc) is an important technological material, being used for both dyes and chemical sensors. Our interest is focused on the sensors. The thin films were deposited by a sublimation technique on polycrystalline SiO2 layers (1.65 μm) on a silicon wafer from a commercial CuPc powder. Films were deposited at a substrate temperature of 293 K and with a deposition rate of 0.3 nm/s forming an α-form with a preferential orientation in the [200] direction. After deposition the thin films were heated to investigate the α→β phase transformation in a separate chamber. X-ray diffraction analysis indicated that annealing at 300 °C for 3 h in nitrogen resulted in a complete α→β transformation. The crystals of β phase forming the film have preferential growth orientation in the [100] and [011] direction to the surface of the SiO2 layer. Surface analysis by XPS was used in order to clarify the molecular structure and chemical compositions of the thin films. The measurements from the core level peaks, ...