bluuebunny/crossref_metadata_2025 huggingface dataset:
Two‐steps functionalization process to extend the novel in situ porous silicon formation‐functionalization method
Authors: Valentini V. , Mattei G. , Cattaruzza F. , Flamini A.
Published: May 2007

Recently, we have presented a novel in situ simultaneous formation‐functionalization (FORFUN) method of porous silicon (PS) layers in which the molecules to be chemisorbed are present in the HF ethanoic solution used for the electrochemical preparation of the PS. In this work we demonstrate that is possible to extend this method to a wider group of organic molecules, in principle even to molecules not compatible with the preparation solution. First a PS single layer functionalized with methyl‐6‐heptynoate was prepared by the FORFUN method (I step) and then, after a second ex situ chemical process (II step), we obtained the correspondent tertiary alcohol bonded to the surface, as proved by the IR reflection spectra. This two‐steps process maintains all the features of the FORFUN method: simplicity, effectiveness and the possibility of confining the chemisorbed species in selected layers in a PS stack (“spatially selective functionalization”). These findings can be relevant for many applications based on PS systems and devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Chemical vapour infiltration of nano‐structured carbon in porous silicon
Authors: Mattei G. , Valentini V. , Polini R.
Published: May 2007

For the first time the results of the chemical vapor infiltration (CVI) of nanostructured sp2 carbon in meso‐porous silicon layers under process conditions normally used to grow diamond films by Hot Filament Chemical Vapour Deposition (HFCVD) are presented. The combined use of micro‐Raman spectroscopy and Field Emission Gun Scanning Electron Microscopy (FEG‐SEM) clearly demonstrated that disordered graphitic carbon was infiltrated in the PS pores, thus permeating completely the PS layer. Such a nanostructured carbon infiltration provided new properties to the PS material, which are potentially of great relevance for opto‐electronics and sensors applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New type of dual macro and nano fractal structure of reaction induced vapor phase stain etched porous silicon
Authors: Stolyarova S. , Weiss S. , Levy M. , Nemirovsky Y.
Published: May 2007

A comprehensive study of morphology of Reaction‐Induced Vapor Phase Stain Etched porous silicon was performed in order to inspect samples for fractal structure and to estimate their potential for sensing applications. A new dual fractal structure is found in porous silicon layer obtained by Reaction‐Induced Vapor Phase Stain Etch. The layer consists of two superposed fractal macro‐ and nanostructures. The macrostructure is formed due to the condensation of drops while the nanostructure is caused by the chemical reactions of the vapor molecules with the silicon surface. A comparison with morphology of porous silicon prepared by Liquid Phase Stain Etch is also presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Room temperature gas sensor based on porous silicon/metal oxide structure
Authors: Arakelyan V. M. , Martirosyan Kh. S. , Galstyan V. E. , Shahnazaryan G. E. , Aroutiounian V. M.
Published: May 2007

N‐type TiO2–x and In2O3 · SnO2 thin films were deposited onto p‐type porous silicon layer which was formed by common electrochemical anodization. The current‐voltage characteristics of obtained structures and sensitivity to different concentrations of hydrogen in air were studied. Measurements were carried out at room temperature. As shown results of measurements, an exponential growth of the current in forward branch of the current‐voltage characteristics of the device made of TiO2–x layer was detected. Higher sensitivity to hydrogen of the TiO2–x ‐porous silicon sensor in comparison to structure made of In2O3 · SnO2 film was detected at room temperature (without preheating of work body of the sensor). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐frequency noise in structures with porous silicon in different gas media
Authors: Mkhitaryan Z. H. , Shatveryan A. A. , Aroutiounian V. M. , Ghulinyan M. , Pavesi L.
Published: May 2007

Noise properties of porous silicon/single‐crystalline silicon structures under exposure to active gases are investigated for the first time. Current‐voltage and noise characteristics of samples are measured. The Al/porous silicon/single‐crystalline Si/Al sandwich‐structures were placed in a special chamber and the influence of adsorption of various gases on low‐frequency noise of the samples was revealed. The adsorption changes the dynamics of the interaction of charge carriers with traps, i.e. the noise characteristics of the samples. The results are encouraging for practical applications of porous silicon structures as gas sensors using measurements of low‐frequency noise characteristics. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gas sensitive porous silicon sensor using rapid thermal annealing screen printing contacts
Authors: Mahmoudi Be. , Gabouze N. , Haddadi M. , Cheraga H. , Belhousse S.
Published: May 2007

The development of sensitive porous silicon (PS) gas sensor which utilizes screen printing for the front and back contacts metallization has been reported. Application of the thick‐film technology results in highly reproducible and economic fabrication of the contacts. We present the design, fabrication, characterization and results when devices were submitted to different gases as opposed to a controlled environment such as vacuum. The C‐V and I‐V measurements performed on metal/CHx/porous silicon/silicon structure showed that the electrical properties of the device are extraordinary sensitive to various gases, oxygen, propane, carbon dioxide at disproportionate level. The response of this device, which operates at bias voltages of 10–100 mV, is rapid and reversible. The electrically operated sensor is more sensitive to oxygen and shows an opposite behaviour if exposed to a reducing environment. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensing of chemical vapor using a porous multilayer prepared from lightly doped silicon
Authors: Salem M. S. , Sailor M. J. , Harraz F. A. , Sakka T. , Ogata Y. H.
Published: May 2007

A porous silicon rugate filter was prepared and investigated for its ability to sense ethanol vapors of different concentrations. The structure shows sensitivity to concentrations above 1% in volume up to saturation at room temperature. This sensitivity is in the form of a red shift of the characteristic peak of the filter due to capillary condensation phenomenon. Exposing the structure to saturated ethanol vapor produces partial filling of the pores with liquid. Theoretical calculations using the Bruggeman effective medium approximation and characteristic matrix method were employed to estimate the average volume fraction of ethanol molecules condensed into the pores. Electrochemical oxidation of the filter was performed. Furthermore, the oxidized structure was found to improve the durability of the filter and increase the adsorbed amount of ethanol molecules into the pores. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Chemical sensing by simultaneous measurement of photoluminescence intensity and photoluminescence decay time of porous silicon
Authors: Dian J. , Vrkoslav V. , Jelínek I.
Published: May 2007

Simultaneous measurement of photoluminescence intensity and photoluminescence decay time of porous silicon was used for optical detection of chemical species in gas phase. For the studied set of analytes we observed that quenching of photoluminescence intensity and shortening of photoluminescence decay time scale with the analyte concentration. Simultaneous acquisition of photoluminescence intensity and photoluminescence decay time enabled to improve reliability of the sensor response measurements. Different sensor sensitivity of photoluminescence intensity and decay time to the presence of chemical species makes possible to discriminate between various classes of organic molecules. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Host‐guest interactions in gas phase chemical sensing of permethyl‐6I‐alkenoylamino‐6I‐deoxy‐β‐cyclodextrin derivatized porous silicon
Authors: Jelínek I. , Vrkoslav V. , Trojan T. , Jindřich J. , Dian J.
Published: May 2007

Porous silicon surface was modified by photochemically activated hydrosilylation reaction with permethyl‐6I‐alkenoylamino‐6I‐deoxy‐β‐cyclodextrins. In the presence of controlled amounts of various organic molecules in gas phase photoluminescence response from this derivatized porous silicon revealed formation of host‐guest complexes between β‐cyclodextrin and detected molecules. The strongest modification of photoluminescence response was observed for aromatic compounds that have optimal molecular size for strong interaction with β‐cyclodextrin cavity. For low concentrations of aromatic molecules we observed PL enhancement most probably due to electron transfer from β‐cyclodextrin‐analyte complex to porous silicon. For higher concentrations – after saturation of the β‐cyclodextrin sites – a combined response with dominant PL quenching was observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensing with porous silicon double layers: A general approach for background suppression
Authors: Pacholski Claudia , Sailor Michael J.
Published: May 2007

One‐dimensional porous silicon photonic crystals can be considered as optical double layers. The reflectivity spectrum of the structure displays a strong peak corresponding to the stop band of the photonic crystal (rugate filter) and Etalon fringes due to Fabry‐Pérot interference in the porous silicon film. The intensity (reflectivity) of the rugate peak and of the peak in the Fourier transform of the Fabry‐Pérot interference spectrum changes differently upon adsorption or binding of biomolecules to the solution/porous silicon interface. Whereas the intensity of the rugate peak only tracks lamp fluctuations, bubbles, and other sources of experimental errors, the intensity of the peak in the FFT spectrum detects in addition adsorption/binding of biomolecules to the surface of the biosensor. The intensity ratio between the rugate peak (reference channel) and the peak in the FFT spectrum (sensing channel) efficiently suppresses background and improves the signal to noise ratio for the detection of biomolecules. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of a new microfluidic analysis system based on porous silicon as sensitive element
Authors: Miu Mihaela , Angelescu Anca , Kleps Irina , Craciunoiu Florea , Simion Monica , Bragaru Adina , Ignat Teodora
Published: May 2007

In this paper, a bio‐laboratory on a chip is presented, representing a new miniaturized device on silicon, utilized to monitor a variety of cellular responses. It is equipped with a glass cover wafer which contains cavities for microreservoir feeding and fluid extraction, and for optical detection. The microfluidic system contains a reaction chamber and a channel network laid‐out radially, fabricated by silicon etching process. In order to improve the cell adhesion and the detection sensitivity, the internal bottom of the reaction chamber is nanostructured by silicon porosification. Porous silicon is a biocompatible material, and the cells cultivated on its modified surface, represent a biochemical system which could be the receptor component of a biosensor. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical study of microfluidic channels isolated with chemically modified porous silicon
Authors: Méry E. , Malhaire C. , Remaki B. , Barbier D.
Published: May 2007

This paper deals with On‐Chip‐Electrophoresis separation systems micromachined on porous silicon. The electrical insulation properties of the porous substrates were analyzed and related to physical and chemical treatments such as thermal oxidation and silanisation. From this preliminary study, microfluidic devices including silanized porous silicon layers were realized. Finally, ANSYS 3D‐Finite Element Modelling of a microfluidic device was performed using experimental data from the electrical measurements. The geometrical and electrical limitations were then discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calculation of reflectance of porous silicon double‐layer antireflection coating for silicon solar cells
Authors: Martirosyan Kh. S. , Hovhannisyan A. S. , Aroutiounian V. M.
Published: May 2007

Calculations of the reflectance spectrum of the double‐layer porous silicon antireflection coating for silicon solar cells were carried out using optical matrix approach method. Comparison of obtained reflectance spectrum of double‐layer porous silicon with the spectra obtained experimentally without optimization of parameters of layers and for the SiO2/TiO2 antireflection coating was shown lower reflectance value for this new construction proposed by us. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reflectance spectrum of diamond‐like carbon/porous silicon double‐layer antireflection coatings designed for silicon solar cells
Authors: Aroutiounian V. M. , Martirosyan Kh. S. , Soukiassian P. G.
Published: May 2007

In this study, our purpose was to investigate the possibility of using a diamond‐like carbon/porous silicon double‐layer antireflection coating which is characteriazed by low reflectance, in order to enhance the performance of silicon solar cells and to protect them from various external influences. Experimental results obtained from reflectance measurements showed the possibility of achieving low reflectance value. Theoretical simulations of the reflectance spectra were carried out. The comparison of the reflectance spectrum of such diamond‐like carbon/porous silicon double layer antireflection coating with spectra obtained from other types of coating layers showed a much lower reflectance within larger energy range including the UV, visible and infrared regions of the solar spectrum. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conductivity of free‐standing porous silicon layers using Terahertz differential time‐domain spectroscopy
Authors: Ramani S. , Cheville Alan , Escorcia Garcia J. , Agarwal V.
Published: May 2007

In this paper, we report preliminary experimental results obtained by measuring the conductivity of free‐standing porous silicon with porosities ranging between 35% and 70%, using Terahertz Differential Time‐Domain spectroscopy (THz‐DTDS). The measured conductivity response follows sub‐linear and the super‐linear power laws in the terahertz frequency region. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Peculiarities of ozone adsorption on a porous silicon surface at low temperature
Authors: Pikulev V. B. , Tsyganenko A. A. , Kuznetsov S. N. , Saren A. A. , Gurtov V. A.
Published: May 2007

Interaction between ozone molecules and silicon nanocrystallites in porous silicon (por‐Si) results in effective luminescence similar to optically excited emission but the mechanism still is not quite understood. To study the process the kinetics of both adsorption and oxidation of highly porous silicon surface under exposure to ozone (16O3 and 18O3) at low temperatures were measured using FTIR‐ and luminescence spectroscopy. It is shown that ozone chemisorption on por‐Si surface takes place yet at liquid oxygen temperature. The oxide coat formed instantly after ozone admission inhibits further oxidation and results in the predominance of ozone physisorption. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of iodine molecule adsorption on electronic properties of porous silicon studied by FTIR and EPR spectroscopy
Authors: Osminkina L. A. , Vorontsov A. S. , Kutergin S. A. , Tkachenko A. E. , Mamichev D. A. , Pavlikov A. V. , Konstantinova E. A. , Timoshenko V. Yu. , Kashkarov P. K.
Published: May 2007

The infrared absorption and electron paramagnetic resonance spectroscopy are used for studying the effect of adsorption of iodine (I2) molecules, strong acceptors of electrons, on the electronic properties of silicon nanocrystals in micro‐ and mesoporous silicon layers with different types of doping impurities. It is found that the concentration of free charge carries (holes) in silicon nanocrystals, obtained by electrochemical etching of p‐type and n‐type silicon wafers, sharply increases in the presence of I2 molecules. At the same time the decrease of the dangling silicon bonds (Pb‐centers) concentration is observed. A microscopic model proposed for explaining this effects presumes the formation of donor‐acceptor pairs (Pb1+‐I2–), and shallow acceptor states on the porous silicon surface which, together with the initial dopant and surface defect states, specify the charge carrier type and concentration in the silicon nanocrystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of ammonia adsorption on charge carriers in mesoporous silicon of n‐ and p‐type conductivity
Authors: Pavlikov Alexander V. , Osminkina Liubov A. , Vorontsov Alexander S. , Timoshenko Victor Yu. , Kashkarov Pavel K.
Published: May 2007

Infrared spectroscopy is used to investigate the effect of ammonia adsorption on the concentration of equilibrium charge carriers in porous‐silicon layers with various initial types of dopants at different concentrations. It is found that ammonia adsorption from aqueous solution results in an increase in the concentration of free electrons in n ‐type samples up to a level exceeding 1018 cm–3. In p ‐type samples, a nonmonotonic dependence of the charge‐carrier concentration on ammonia pressure is observed. The obtained results are explained by the appearance of adsorption‐induced shallow donor states that, along with the initial‐dopant and surface‐defect states, determine the charge‐carrier type and concentration in the silicon nanocrystals of the porous layer after ammonia adsorption. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Detection of different states of water and oxide layer in porous silicon by IR spectroscopy
Authors: Korniyenko M. Ye. , Makara V. A. , Shevchenko V. B. , Korniyenko A. M. , Veblaya T. S. , Makhno M. M.
Published: May 2007

Different states of water and oxide layer in porous silicon (PS) have been studied by IR spectroscopy method. The water states have been shown to depend on contact conditions between PS and condensed or vaporous forms of water and to determine all the variety of oxidation scenarios. Weakly‐ and strongly‐bonded water states are characterized by different frequencies of stretching bands νOH. Fine structure of absorption bands of oxygen‐silicon complexes (Si‐O‐Si, SiSiXO4–X) has been observed in the IR spectra. We associate it with fractal structure for thin oxide layers. Transition of fractal structure into nearly bulk SiO2 structure (where LO‐TO splitting is observed) with oxide layer thickness growth is considered. The oxide layer states are characterised by the intensity ratio of stretching to deformation bands for considered silicon‐oxygen complexes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of porous silicon oxidation on its behaviour in simulated body fluid
Authors: Pastor E. , Matveeva E. , Parkhutik† V. , Curiel‐Esparza J. , Millan M. C.
Published: May 2007

This work aims at studying of electrochemical oxidation of porous silicon (PSi) and its behaviour in simulated body fluid (SBF). Continuing electrochemical oxidation of PSi introduces gradual changes in morphology of the porous structure and composition of PSi. As a result, interaction between this material and SBF is changed. As more oxidized is the PSi sample, slower is the dissolution process (biodegradability) and more easily it becomes covered by the calcium‐phosphorous deposits from SBF (bioactivity). We observed that crystalline hydroxyapatite HA phase could be deposited in a very homogeneous manner onto OxPSi layers immersed in SBF at 36.5 °C during 30 days. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stabilization of nano‐crystalline porous silicon electroluminescence by high pressure water vapor annealing
Authors: Gelloz B. , Shibata T. , Koshida N.
Published: May 2007

Stabilization of electroluminescence (EL) from nanocrystalline porous silicon diodes has been achieved by using high pressure water vapor annealing (HWA) of nanocrystalline porous silicon (PS). HWA is performed at 260 °C and a pressure of 1.3 MPa. Devices treated by HWA show no degradation in EL intensity and diode current density under dc operation at constant voltage. The high stability is attributed to the high quality of the oxide surrounding the Si nanocrystals after HWA. This oxide is mostly unstrained and consists of a very uniform network. Furthermore, the Si/SiO2 interfacial defect density is very much reduced by HWA in comparison to that of conventional as‐prepared PS. The electrical characteristics of the diodes are also improved by HWA by reduced charge carrier trapping and charging. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical gain in oxidized porous silicon waveguides impregnated with a laser dye
Authors: Oton C. J. , Navarro‐Urrios D. , Ghulinyan M. , Capuj N. E. , González‐Pérez S. , Lahoz F. , Martín I. R. , Pavesi L.
Published: May 2007

We report positive optical gain under pulsed excitation in oxidized porous silicon planar waveguides impregnated with Nile Blue (LC 6900). Guided photoluminescence measurements show a dramatic line narrowing and a strong superlinear behaviour of the red emission when the pump power is increased. Variable stripe length (VSL) measurements show a clear transition from losses to gain, with a threshold of ∼3 mJ/cm2 at 700 nm. A maximum gain coefficient of 8.7 cm–1 is reported. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Role of hydrogen in the photoinduced evolution of porous silicon luminescence
Authors: Koropecki R. R. , Arce R. , Spies C. , Gennaro A. M. , Schmidt J.
Published: May 2007

Photo‐induced post preparation evolution effects in porous silicon were studied by IR, EPR, photoluminescence, and hydrogen effusion spectroscopies. The results show that two independent mechanisms are present during the photo‐induced evolution. We also show that hydrogen photo‐effusion takes place, in agreement with our previously proposed model. Photo‐effusion experiments performed in vacuum, combined with IR and photoluminescence spectroscopies allow to discriminate the competing mechanisms present in the evolution of the photoluminescence. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence from porous layers produced by Ag‐assisted electroless etching
Authors: Hadjersi T. , Gabouze N.
Published: May 2007

Porous layers were formed on highly resistive p‐type silicon by an Ag‐ assisted electroless etching method using a chemical solution of HF and K2Cr2O7. The porous silicon (PS) layer formed by this method as a function of etching time was investigated by scanning electron microscopy (SEM) and backscattering spectrometry (BS) in random and channelling mode. Channelling spectra show that the porous layer remains crystalline after etching. On the other hand, random and channelling spectra show that the deposited silver diffuses into the pore. Luminescence from Ag‐assisted chemically etched layers was measured. It was found that the photoluminescence spectra strongly depend on etching time. Indeed, for etching time lower than 60 min, the PL emission is in the blue region with a peak located at 450 nm. In addition, for an etching time of 60 min or higher, the PL peak is centred at about 630 nm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence from porous layers formed on phosphorus‐implanted silicon by Ag‐assisted chemical etching
Authors: Gabouze N. , Hadjersi T. , Guerbous L.
Published: May 2007

The discovery of luminescence from porous silicon has stimulated intense and still increasing research activity. A great deal of effort has been devoted to study the photoluminescence from anodized ion‐implanted silicon. In the present work, we propose the metal‐assisted chemical etching method, using Na2S2O8 as oxidizing agent, to form photoluminescent porous layers on phosphorus implanted silicon. The properties of porous layers formed on implanted silicon as a function of doses and energies were investigated by scanning electron microscopy (SEM) and photoluminescence. The result shows that the PL spectra exhibit two principals emission bands centred at about 410 nm and 625 nm. In addition, it was shown that PL intensity corresponding to the red emission increases with increasing dose and energy. Finally, the changes in the PL spectrum are attributed to structural changes caused by both etching and ion implantation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Light‐emission characteristics of silicon nanocrystals formed by anodization of bulk crystalline silicon in the transition regime
Authors: Gardelis S. , Nassiopoulou A. G.
Published: May 2007

In this study we report on the light‐emission characteristics of Si nanocrystals formed at the initial stages of anodization of bulk crystalline Si in the transition regime using extremely short pulses of anodic current. A considerable enhancement and a red‐shift of the photoluminescence (PL) peak of the as‐grown films under prolonged laser illumination in atmosphere was observed. Ageing or thermal oxidation in atmosphere at 300 °C caused similar red‐shift and significant enhancement of PL relative to the as‐grown films. In all cases the enhancement and the red‐shift of the PL coincided with the appearance of O2‐Si‐H2 and O2‐Si‐H(OH) stretching modes in the Fourier‐Transform‐Infra‐Red (FTIR) absorption spectra. Oxidation in dry oxygen at 900 °C caused red‐shift of PL without enhancement. Finally removal of the oxide caused blue shift of PL. All these observations are discussed in the context of the quantum confinement model. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient luminescence from rhodamine 6G absorbed by porous alumina: Excitation mechanisms
Authors: Moadhen A. , Elhouichet H. , Nosova L. , Oueslati M.
Published: May 2007

Porous alumina (PA) samples are impregnated in rhodamine 6G (Rh6G) solution in order to form Rh6G/PA nanocomposites. The Fourier Transformer Infrared (FTIR) measurements show dispersion of dye molecules into the PA matrix. The investigations are focused on the photoluminescence (PL) properties and PL mechanisms in Rh6G/PA. We have discussed the effect of excitation beam wavelength on the PL spectrum of Rh6G/PA nanocomposite. It was found that the efficient luminescence of Rh6G/PA nanocomposite is governed by direct excitation and by dipolar interactions between Rh6G molecules with chemical species in alumina crystallites, as has been proved by FTIR measurements. An anti‐Stokes photoluminescence (APL) has been observed using a He‐Ne laser excitation. We show that its origin is related to a second order phenomenon where phonon absorption plays a key role. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Innovative electrochemical deep etching technique involving aluminum thermomigration
Authors: Kouassi S. , Gautier G. , Ventura L. , Semai J. , Boulmer‐Leborgne C. , Morillon B. , Roy M.
Published: May 2007

A novel micro‐machining technique for silicon deep anisotropic etching and isolating porous silicon structure formation is developed in this paper. This method combines aluminum thermomigration through a N type silicon wafer and silicon electrochemical etching in a HF‐based solution. Using this technique, high aspect ratio trenches (1:5) and porous silicon isolating regions have been achieved through the entire thickness of the silicon wafers. Etch rate measurements have been performed varying the anodization current density. A maximum value of 22 µm.min–1 has been obtained. Moreover, the porosity behavior with the current density increase is also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations on porous silicon as electrode material in electrochemical capacitors
Authors: Desplobain S. , Gautier G. , Semai J. , Ventura L. , Roy M.
Published: May 2007

In this study, we have demonstrated the possibility of using macroporous silicon electrodes in electrochemical capacitors. Macroporous silicon was used to increase the surface exchange between pore surface and electrolyte. The inherent resistivity of the porous silicon can be reduced through the use of subsequent doping and metallization processes of the macropore surface. A systematic study of the electrolyte concentration and the porous silicon depth influences was also performed. A unit cell capacitance value of 320 µF/cm2 was obtained with doped and metallized p‐type macroporous silicon electrodes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Porous silicon surfaces for metabonomics: Detection and identification of nucleotides without matrix interference
Authors: Gómez D. , Fernández José Andrés , Astigarraga Egoitz , Marcaide Arrate , Azcárate Sabino
Published: May 2007

In present work, porous silicon surfaces (PSS) have been developed for time of flight mass spectrometric experiments (TOF‐MS) in the monitoring of nucleotides, commonly found as metabolites in the cell. The mass range of the studied molecules (∼ 400 amu) is common to several important messengers and other metabolites. Different porosified surfaces have been developed by means of electrochemical etching and different degree of porosity and pore size achieved as function of silicon dopant concentration, silicon resistivity, current density and the presence or absence of illumination along the process. As main conclusion, it can be said that an interesting commercial nucleotide (Cyclic adenosine monophosphate, c‐AMP) has been detected on low concentrations (∼hundreds of femtomols) for some of the fabricated porous surfaces. Taking into account that these concentrations are similar to the ones found in real samples, this result opens the possibility to the fabrication of DIOS (Desorption Ionization On Silicon) chips for the detection of nucleotides in biological fluids. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bruggeman effective medium approach for modelling optical properties of porous silicon: comparison with experiment
Authors: Khardani M. , Bouaïcha M. , Bessaïs B.
Published: May 2007

While numerous works deal with the properties and applications of porous silicon (PS), some of the related topics are not complete or could be investigated from different aspects. The main objective of this paper is to provide novel information associated with the optical properties of nano‐ and meso‐PS by studying the variation of the effective refractive index (neff) and the relative dielectric constant (εr,eff) as a function of porosity. For this purpose various PS samples were prepared by electrochemical etching of p and p+‐type silicon wafers in order to form silicon supported nano‐PS and free‐standing meso‐PS layers, respectively. The experimental effective optical parameters (neff, εr,eff) of the meso‐PS films, were determined from the transmission spectra and the Bragg law. While, in the case of nano‐PS layers, we applied the Goodman method, and deduced the values of neff and εr,eff from the Bruggeman's effective medium approximation (EMA). In the EMA calculation, the PS structure was considered as being a physical combination of three distinct phases formed by silicon, silicon dioxide and voids with a convenient volume fraction. A good agreement between theory and experiment was found in the case of silicon‐supported nano‐PS for all porosities. However, for free‐standing meso‐PS, the theory does not well fit the experimental results for porosities lower than 50% and higher than 70%. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Role of surface in light induced degradation of porous silicon
Authors: Mandal N. P. , Kumar Abhishek , Agarwal S. C.
Published: May 2007

Exposure of porous silicon (PS) to moisture is found to increase its photoluminescence (PL) intensity, whereas it decreases drastically upon light soaking. On the other hand, coating by a thin layer of polystyrene protects PS against light induced degradation without changing PL significantly. Further, polystyrene coating protects the PS from humidity also. FTIR shows appearance of new bonding configurations at the PS/polymer interface, whcih may account for the improved stability. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of surface roughness for ARXPS
Authors: Oswald S. , Oswald F.
Published: May 2007

Angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) is a method for non‐destructive depth profiling in the nm thickness range. For the quantification of the data, usually model calculations are used which approximate the surface structures by smooth layers. Using ARXPS data from a computer simulation, in this paper we study the influence of overlayer roughness on the quantification results. It can be followed, that rough overlayers modeled by means of small‐sized islands are identified nearly as smooth layers. The effective thickness, however, can be evaluated always satisfactorily. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth studies of Ta‐based films on Si with STM and XPS
Authors: Zahn W. , Oswald S. , Fülle A. , Hildebrand D. , Zier M. , Wetzig K.
Published: May 2007

The aim of the experiments was the characterization of the first stages of film growth on silicon substrates with scanning tunneling microscopy (STM) and angle‐resolved X‐ray photoelectron spectroscopy (ARXPS). Thin Ta films were deposited in situ by magnetron sputtering onto Si in the thickness range from less than one monolayer up to 10 nm. The results of the experiments show a formation of tantalum silicide at the interface to the substrate. The local current‐voltage characteristics obtained by scanning tunneling spectroscopy (STS) measurements show that the first stages of tantalum silicide growth are characterized by island formation. The in situ STM results are in good agreement with those of the ARXPS investigations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of FeO films on SrTiO3(100)
Authors: Heinrich B. , Demund A. , Szargan R.
Published: May 2007

Depending on different annealing steps (100 °C to 800 °C) and the pretreatment of the substrate, we investigated the chemical and morphological state of ultra thin FeO films on SrTiO3(100) by XPS and LEED. Two types of pretreated substrates were used: (A) SrTiO3, annealed at 600 °C and (B) SrTiO3, annealed at 800 °C. While (A) showed no change in colour, (B) became blue due to oxygen vacancies in the bulk. We found, that annealing of SrTiO3 in UHV influences the reactivity of the contact FeO/SrTiO3. Depending on the pretreatment, approximately 50% of FeO were reduced to Fe at different temperatures ((A): T = 300 °C; (B): T = 200 °C). During annealing reduced Ti(IV) species, such as Ti(III, II and 0), occurred only in the case of preannealing at 800 °C (B). LEED investigations showed the rearrangement of the deposited films starting from 600 °C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gas phase and bulk photoemission spectra of highest occupied molecular orbitals of pi‐conjugated organic molecules
Authors: Sauther J. , Wüsten J. , Lach S. , Ziegler Ch.
Published: May 2007

The highest occupied molecular orbital (HOMO) of the pi‐conjugated organic molecule 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) was investigated via bulk and gas phase ultraviolet photoemission spectroscopy. As a result of the absence of various photoemission linewidth broadening effects which occur in the case of condensed matter, the measurements on single molecules allow an estimate of the contributions of these effects to the total linewidth. Distinctive peaks resulting from vibrational excitations can be recognized and thus a comparison with other spectroscopy methods is possible. Furthermore, spectra of the HOMOs of 1,4,5,8‐naphthalene‐tetracarboxylic dianhydride (NTCDA) and 1,8‐naphthalene‐dicarboxylic anhydride (NDCA) were also recorded and compared to the results for PTCDA, showing a decrease in linewidth with decreasing molecule size. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Use of focused ion beam sample preparation for Auger analysis
Authors: Scheithauer U.
Published: May 2007

FIB cross‐sections are often used to get access to sample features of interest. Due to the inherent surface sensitivity an AES measurement is favourable for small feature compositional analysis on such samples. Even though the primary electron beam diameter of a modern field emission AES instrument is about 30 nm and thereby nearly ten times that of a SEM, the analysis volume of an AES measurement is much smaller than that of SEM/EDX. As AES measurements on small sample features can last for many hours it is mandatory to compensate a likely mechanical drift. In this procedure at regular intervals SE images are compared with an SE image recorded at the beginning of the measurement. Lateral drifts are compensated by an additional electrostatic deflection of the primary beam. For this purpose on low contrast samples or samples with periodically repetitive structures a FIB crater cut into the sample surface can be successfully applied as a marker feature to determine sample drift. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Induction and analysis of cell adhesion and differentiation on inkjet micropatterned substrates
Authors: Blau A. , Ugniwenko T.
Published: May 2007

In the context of interfacing biological entities to technical substrates, proof of principle results on patterning cell culturing substrates by inkjet deposition of the cell adhesion mediator polyethyleneimine are presented. Pattern fidelity, cell adhesion, and cell differentiation of chick neurons and glia cells on such interfaces were evaluated microscopically. The exemplary results demonstrate that piezo inkjet printing of biologically active compounds has the potential of becoming an easy to handle and versatile strategy for applying a wide variety of substances in any combination and concentration with cellular to subcellular resolution onto a wide selection of substrates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elemental imaging mass spectrometry of thin sections of tissues and analysis of brain proteins in gels by laser ablation inductively coupled plasma mass spectrometry
Authors: Becker J. Sa. , Zoriy M. , Becker J. Su. , Dobrowolska J. , Dehnhardt M. , Matusch A.
Published: May 2007

Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) has become established as a very efficient and sensitive trace and surface analytical technique in the life sciences. We applied LA‐ICP‐MS to produce images for investigating the spatial element distribution as well as the layered structures and inhomogeneities in thin tissue sections (e.g., human and rat brain tissues). In order to quantify the analytical data, matrix‐matched laboratory standards were prepared and analyzed by applying the optimized experimental parameters using LA‐ICP‐MS. Furthermore, the possibility of the nanometer‐scale analysis of elements on sample surfaces by near‐field LA‐ICP‐MS on soft matter (e.g., on 2D gels and biological samples) will be discussed briefly. This novel technique opens up a new challenging path for future applications in the quantitative imaging of elements in life sciences and nanotechnologies. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Secondary ion mass spectrometry (SIMS) – a powerful tool for studying mass transport over various length scales
Authors: De Souza Roger A. , Martin Manfred
Published: May 2007

Secondary Ion Mass Spectrometry (SIMS) is a sophisticated analytical technique for determining the elements present in materials, and especially on surfaces, with trace level sensitivity and high spatial resolution. The aim of this article is to give a short introduction to the SIMS technique and to focus then on selected case studies of mass transport in oxides over various length scales. It is shown that SIMS is capable of analysing diffusion profiles on a broad length scale, from some tens of nanometres to several hundred micrometres, which makes it possible to measure diffusion coefficients from about 10–18 cm2 s–1 to 10–6 cm2 s–1. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thin niobium/boron bilayers and multilayers annealed via Rapid Thermal Processing (RTP)
Authors: Mertens R. , Bock W. , Lommel B. , Kolbesen B. O.
Published: May 2007

Nb/B bilayers (thickness: 210 nm) and multilayers (thickness: 306 nm) have been deposited on Si‐(100) wafers with 100 nm thermally grown oxide. The niobium layers were deposited by magnetron sputtering, whereas the boron layers were deposited by electron‐beam‐evaporation. Both types of samples were heated separately via Rapid Thermal Processing (RTP) at varying temperatures, under Ar gas flow to investigate the interdiffusion of niobium and boron, and under NH3 in order to observe the influence of this reactive gas on interdiffusion, as well as to form nitrides. The formation of phases was investigated by X‐Ray Diffraction (XRD). The surface morphology and roughness was studied via Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), resp.. Elemental depth profiles of selected samples were recorded by Secondary Ion Mass Spectrometry (SIMS) to track the position of the phases formed in the film. Under the applied experimental setups the formation of NbB2 was observed only. Although NH3 is a reactive gas no nitride phases were found. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of HOLZ rings in EBSD patterns
Authors: Langer E. , Däbritz S.
Published: May 2007

Higher‐Order Laue Zone (HOLZ) rings and their appearance in Electron Backscattered Diffraction (EBSD) pattern from molybdenum were fundamentally investigated in the Scanning Electron Microscope. HOLZ rings of the type 〈100〉, 〈110〉, 〈111〉, 〈113〉 and 〈133〉 could be unambiguous detected in EBSD pattern of different pure Mo crystals. The [100] HOLZ ring was observed more in detail in dependence on the accelerating energy in the pattern center, and the lattice spacing was determined for all energies. A relatively good accuracy could be obtained for Mo as model sample for problematical high atomic number materials. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural investigation of pristine and annealed nanocrystalline TiO2 thin films by X‐ray diffraction and Raman spectroscopy
Authors: Orendorz A. , Brodyanski A. , Lösch J. , Bai L. H. , Chen Z. H. , Le Y. K. , Ziegler C. , Gnaser H.
Published: May 2007

Nanocrystalline anatase TiO2 films were prepared from colloidal suspensions using particles with a nominal size of 12 nm. Their structure was examined by Raman spectroscopy and X‐ray diffraction (XRD). The as‐prepared specimens exhibit exclusively features due to the anatase phase of TiO2 (e.g., the Eg, B1g and A1g vibration modes in Raman spectroscopy and the characteristic diffraction peaks in XRD). Isochronal annealing of the films in air at temperatures of up to 1320 K effected clear structural changes, observed both in Raman and XRD: the crystallite size increases from ∼13 nm to ∼125 nm between 470 K and 1220 K, with the crystallites remaining in the anatase phase. A phase transition to the rutile phase of TiO2 occurs gradually in the temperature range 1220 – 1320 K and the average crystallite size increases to ∼160 nm. The Eg vibration in anatase films reveals a blue shift and an asymmetric peak broadening towards higher frequencies for smaller particle size/lower annealing temperatures. A power‐law dependence between the Raman peak width and the inverse of the crystallite size is found. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Annealing of evaporated and sputtered niobium films in oxygen and nitrogen rich atmospheres by Rapid Thermal Processing (RTP)
Authors: Matylitskaya Volha A. , Brunkahl Oliver , Kothleitner Gerald , Bock Wolfgang , Kolbesen Bernd O.
Published: May 2007

Thin films of niobium were deposited on thermally oxidized Si‐(100)‐wafers by two different methods: electron beam evaporation and direct current reactive magnetron sputtering. The thicknesses of as‐deposited niobium films were 200 and 500 nm. 200 nm evaporated niobium films were nitridated in nitrogen and ammonia using rapid thermal processing (RTP). In these investigations the reactivity of N2 and NH3 with Nb‐films was compared. 500 nm sputtered Nb‐films were annealed in several steps. At first niobium films were nitridated under ammonia atmosphere at 1000 °C for 1 min using an RTP. After that nitridated niobium films were oxidized in molecular oxygen at temperatures ranging from 400 to 600 °C. Before and after reactions with ammonia, oxygen and nitrogen evaporated and sputtered samples were characterized by several complementary analytical methods. X‐ray diffraction (XRD) was used for phase analysis after annealing. Determination of the elemental depth profiles of the films was realized by secondary ion mass spectrometry (SIMS). Microstructure and spatial distribution of the elements were imaged by transmission electron microscopy (TEM) and energy‐filtered TEM (EFTEM). Electron energy loss spectra (EELS) were taken at selected positions to discriminate between different nitride, oxynitride and oxide phases. Investigation by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed differences of the film morphology depending on the reactive agent and reaction temperature. Investigations of sputtered films show that surface roughness of the samples after oxidation of niobium films nitridated in ammonia before is lower then after direct oxidation of as deposited films in oxygen, in spite of the same phase of niobium pentoxide formed after annealing in both cases. We explain this due to large expansion of niobium lattice during direct oxidation of Nb‐film in molecular oxygen. By incorporation of oxygen in the crystal lattice of niobium and formation of niobium pentoxide substantial intrinsic stress was built up in the film frequently resulting in delamination of the film from the substrate. The possibility of the formation of niobium oxynitride phase after three steps annealing in ammonia, oxygen and finally in ammonia was investigated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Secondary ion mass spectrometry (SIMS) – a powerful tool for studying mass transport over various length scales
Authors: De Souza Roger A. , Martin Manfred
Published: May 2007

The cover picture of this issue of physica status solidi (c) has been taken from the article [1].
The photodissociation of hydrogen iodide: Is it adiabatic?
Authors: Brown Alex
Published: May 2007

The assumption that the photodissociation of HI proceeds adiabatically is re‐examined in the context of recently calculated alignment parameters, a(⟂), for the ground state halogen atoms resulting from photodissociation of the analogous HCl and HBr molecules. The a(⟂) alignment parameters for HCl, HBr, and HI are determined from time‐dependent quantum mechanical wave packet calculations based on the best available ab initio electronic structure for each molecule. The experimental measurement of the alignment of the I(2P3/2) atoms is proposed as a stringent test of whether the photodissociation is adiabatic or involves non‐adiabatic coupling of the A1Π1 and a3Π1 electronic states. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Donor–acceptor origin of fullerene C60 dimerization
Authors: Sheka Elena F.
Published: May 2007

The fullerene dimerization is considered as a consequence of donor–acceptor interaction between monomer molecules which is significant for C60+C60 binary system. The dimerization is provided by a two‐well structure of the ground state energy term. Analyzing characteristics of the term, proven by quantum–chemical calculations at different starting intermolecular distances, mechanisms of both physically (photoexcitation, thermal, high pressure, plasma, electron beam, and electric field) and chemically (alkali‐metal adducts AC60) stimulated dimerization processes are suggested. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007