National Institute Of Materials Physics - Romania

We report on the synthesis of novel ovine and bovine derived hydroxyapatite thin films on titanium substrates by pulsed laser deposition for a new generation of implants. The calcination treatment applied to produce the hydroxyapatite powders from ovine/bovine bones was intended to induce crystallization and to prohibit the transmission of diseases. The deposited films were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy. Pull-off adherence and profilometry measurements were also carried out. X-ray diffraction ascertained the polycrystalline hydroxyapatite nature of the powders and films. Fourier transform infrared spectroscopy evidenced the vibrational bands characteristic to a hydroxyapatite material slightly carbonated. The micrographs of the films showed a uniform distribution of spheroidal particulates with a mean diameter of similar to 2 mu m. Pull-off measurements demonstrated excellent bonding strength values between the hydroxyapatite films and the titanium substrates. Because of their physical-chemical properties and low cost fabrication from renewable resources, we think that these new coating materials could be considered as a prospective competitor to synthetic hydroxyapatite used for implantology applications. (C) 2012 Elsevier B.V. All rights reserved.

Polarized Raman scattering studies on stiff layered structure of surfactant intercalated with trilayer graphene were performed at different intensities and excitation wavelengths. The D and 2D Raman bands reach the highest and lowest intensity when the polarization of laser excitation light is oriented along and perpendicular on the edges. The 2D band discloses two lorentzian components, separated by similar to 40 cm(-1), which result from the action of interplanar forces, of Casimir nature. The value of similar to 40 cm(-1) is close to the energy value associated with E-2g interplanar layer shear mode evidenced so far only by neutron spectrometry. A new result regards the opposite variation of the intensities of D and 2D bands with the increase of the wavelength of the excitation light. This originates in the different origin of the D and 2D bands; the former is dependent on disorder including also the graphene edges while the latter, results from in a double resonant mechanism combined with a Casimir effect. One demonstrates that the magnitude of Casimir force, which activates interlayer vibration modes, depends on the carrier density on the graphene sheets which can be varied both by the intensity and the wavelength of the excitation laser light. (C) 2012 Elsevier Ltd. All rights reserved.

The high intensity and high repetition rate of the XFEL, the European X-ray Free-Electron Laser presently under construction in Hamburg, results in X-ray doses of up to 1 GGy in silicon sensors for 3 years of operation. Within the AGIPD Collaboration the Hamburg group has systematically studied X-ray-radiation damage using test structures and segmented sensors fabricated on high-ohmic n-type silicon. MOS Capacitors and Gate-Controlled Diodes from 4 vendors with different crystal orientations and different technological parameters, as well as strip sensors have been irradiated in the dose range between 10 kGy and 1 GGy. Current-Voltage, Capacitance/Conductance-Voltage and Thermal Dielectric Relaxation Current measurements were used to extract oxide-charge densities, interface-trap densities and surface-current densities as function of dose and annealing conditions. The results have been implemented into TCAD simulations, and the radiation performance of strip sensors and guard-ring structures simulated and compared to experimental results. Finally, with the help of detailed TCAD simulations, the layout and technological parameters of the AGIPD pixel sensor have been optimized. It is found that the optimization for sensors exposed to high X-ray doses is significantly different than for non-irradiated sensors, and that the specifications of the AGIPD sensor can be met. In 2012 sensors have been ordered, the first batch has been delivered recently, and first results on a comparison between simulations and measurements will be presented.

Commercially pure titanium (CP-Ti) offers a good corrosion resistance and tissue tolerance. The interfacial phenomena between biomaterial and biological fluids depend especially on surface chemistry, energy, roughness and topography of the implant Different methods are used to modify CP-Ti surface in order to improve its bonding properties to bone tissue. Besides the mechanical approaches, chemical etching and chemical oxidation, there are also other procedures improving the biocornpatibility. One of the most important involves the deposition of a bioceramic thin layer on the metallic surface. A bioceramics frequently used is hydroxyapatite (HA), the mineral component of the bone. In this paper. the main objective was to study the effects of different surface pretreatments on adherence of hydroxyapatite layer obtained by electrochemical method. The CP-Ti substrate was used in different treated states of the surface. The applicability of the electrochemical technique is relieved by the fact that it is a very rapid method, requires relatively low temperatures, being also very versatile. The obtained coatings were studied by scanning electron microscopy (SEM) associated with EDX (Energy dispersive X-ray spectroscopy, X-ray diffraction method (XRD). The adherence of the layers was evaluated by the "pull-out" test. The quality of the coating (morphology and adhesion properties) is decisively influenced by the electrochemical parameters and also by the surface state.

Reconstructive surgery of bone defects in the calvarium makes use of a multitude of biological and artificial materials. Due to the increased number of such medical casuistry in the recent years, a special attention was dedicated to the biocompatibility and osteointegrative properties of various types of biomaterials. Titanium emerged to be a promising cranioplasty material due to its excellent mechanical properties and biocompatibility. However, the way the host calvarial bone reacts to the titanium implant has not been fully understood. Here, we evaluate the influence of cranial bone substrate on the osteoconduction and osseointegration of titanium mesh implants. The pattern of bone tissue reaction in the areas of contact with metallic implant is analyzed by means of bone density measurements on the computer tomography images. Twenty-eight patients underwent cranioplasty with titanium mesh implants for bone cranial defects due to different aetiology. With the aid of visual analogue scales, the patients' status (osteointegration degree, comfort and cosmetics) was evaluated after 3 - 14 months since surgery (implantation).

This paper reports on the experimental realization and characterization of a wireless sensing system for machine-tool condition based monitoring. The system comprises a vibration sensor, an ARDUINO Leonardo development board and an RM 42 Blue tooth module. The sensing principle is based on a vibration sensor which includes a piezoelectric AlN layer deposited by sputtering on a flexible stainless steel foil. The functional testing of the sensor using a test stand for asynchronous engines equipped with frequency convertors is demonstrated.

In this work, anomalous discontinuities observed in Capacitance-Voltage (C-V) characteristics on non-nitridated n-4H-SiC/SiO2 capacitors at low temperature are addressed. The appearance of abrupt capacitance minima, always at the same gate voltages (4V and 8V) and independent on probe frequency, led us to consider a resonant electron tunneling process from neutral donor states present at the SiC/SiO2 interface into two well defined energy levels in the oxide layer. Results of numerical simulations based on this model describe quantitatively the experimentally observed discontinuities at 4V and 8V and provide strong evidence for the presence resonant tunneling.

We report on the synthesis of advanced nanostructured hydroxyapatite (HA) thin films onto 3D titanium (Ti) mesh substrates by Pulsed Laser Deposition method. Morphological and structural investigations as well as pull-out tests proved the stoichiometric transfer of crystalline HA films along with their good adherence. In vivo tests were performed on 12 patients (six with simple Ti mesh, six with Ti mesh biofunctionalized with HA). The tomodensitometry analysis of the cranial control scans evidenced the process of osseogenesis. For four patients with implanted HA/Ti mesh structures, the modification of the value obtained on Hounsfield scale was observed at the level of implant, proving the progress of osseointegration. We conclude that the structures exhibit excellent bonding strength and functionality, and are suitable for neurosurgical applications.

The presence and structure of paramagnetic point defects in C-13 and O-17 implanted ultrapure Si single-crystal material, two impurities which seem to play a major role in the detectors performance degradation and radiation resistance enhancement, respectively, are reported before and after irradiation with 6 MeV electrons. The investigation, performed by Q-band electron spin resonance spectroscopy in the 300 - 10 K temperature range, included also reference ultrapure and O-16 doped single-crystal Si-platelets. It resulted in the observation of points defects associated with lattice defects as dangling bonds and impurities.

Spectroscopic ellipsometry, X-ray diffraction and transmission electron microscopy experiments are employed to characterize aluminum nitride (AlN) thin films obtained by radio-frequency magnetron sputtering at low temperature (approximate to 50 degrees C). To understand the growth mechanism and to get in depth information of such films by using ex situ characterization techniques, the AlN thin film sample series were prepared for different sputtering times, while keeping constant all the other deposition conditions. The diffraction studies reveal a [002] oriented growth of the AlN thin films. The misorientation of this crystallographic axis to the normal to the surface reduces progressively with film growth. A nonmonotonic behavior of the AlN pseudo-refractive index versus deposition time indicates a complex depth profile of the AlN thin films optical properties. The difference in orientation dispersion of the [002] crystallite axis, the variation of defects concentration and each constituent atom density influence the refractive index evolution. Our interpretation validity was verified by producing and characterizing samples obtained at intermediate deposition time. The AlN thin films show also very good pull-out adherence values. (C) 2012 Elsevier B. V. All rights reserved.