Porous Silicon Template Research Articles

Growth mechanism of bismuth-filled nanoporous silicon with improved structural stability and low thermal conductivity

Nano porous silicon (PS) is a strong candidate for thermoelectric application, but it shows low structural stability and is prone to collapse. To enhance the structural stability of PS and offer a new way to improve its electrical conductivity, PS was prepared by electrochemical etching and Bi nanowires were fabricated in the pores of PS by electrodeposition. In addition, for studying the effect of structures on the properties of Bi-filled PS composites, aperiodic single-layer (SL) structure, and periodic rugate (Rgt) structure and Bragg structure PS samples were prepared by changing the etching current waveform and etching time. The results show that the initial Bi deposition position and filling fraction of Bi nanowires in PS templates can be precisely controlled. Since Bi nanowires have significantly different continuity in Rgt and Bragg structures compared with SL structures, we proposed two growth mechanisms of Bi nanowires, including the axis-growth mechanism and transverse-axis-growth mechanism, with the supports of the experimental results of XRD, SEM, and EDS.The room temperature thermal conductivities of pristine and Bi-filled PS layers are in the ranges of 4.5 ∼ 5.0 and 4.2 ∼ 6.0 W･m−1K−1, respectively, about 1/10 of the original unetched silicon wafer. No apparent increase of thermal conductivity was observed in any Bi-filled composites. In addition, the thermal conductivities of PS layers with Bragg structure, including pristine and Bi-filled PS composites, are significantly lower than those of the other two structures.SEM images also demonstrates that Bi greatly improved the mechanical property of PS composites, especially the periodic structures composites. This study firmly demonstrates that Bi-filling in PS with periodic Bragg structure is practical to obtain nanocomposites with low thermal conductivity and improved structural stability. It offers a new dimension to optimize the property of PS for thermoelectric application by pore configuration design and controllable nanowire Bi filling.

Porous silicon - A versatile platform for mass-production of ultrasensitive SERS-active substrates

Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most prospective methods combining state-of-the-art nanomaterials and optical techniques for highly sensitive express-analysis and detection of organic and bioorganic objects in liquids and gases. Special programs have been recently started all over the world to bring the SERS-spectroscopy closer to wide implementation in medical diagnostics, forensics, security, monitoring sanitary conditions, etc. Despite outstanding features of SERS-spectroscopy, its effective practical use has been particularly slowed down by moderate reproducibility, non-versatility, and restrictions imposed by commercially available SERS-active substrates to measurement and storage regimes. The present review reports SERS-active substrates constituted by noble metals' nanoparticles (NPs) and porous silicon (PS), which potentially can be a tool to overcome the above-mentioned limitations. The PS template acts as a highly ordered host nanomaterial for the formation of a variety of metallic nanostructures, which morphological and optical properties can be easily tuned for the best performance to meet the customer requirements via managing PS synthesis regimes. An indubitable advantage of PS is the compatibility of its fabrication process with basic microelectronics operations and micro-electromechanical systems (MEMS) that make it possible to integrate SERS-active areas in a silicon chip. In contrast to the previously published reviews in the field, this one covers the most recent results on formation, characterization, and application of PS-based substrates demonstrating prominent SERS-activity that have been achieved for the last decade including modifications with graphene or Bragg structures, detection of molecules at amount down to attomolar concentration, bacteria recognition, etc.

Mechanism of vertically arrays of carbon nanotubes by camphor based catalysed in-situ growth

In this study, a growth mechanism of vertically aligned carbon nanotubes (VACNT) on a nanostructured porous silicon template (NPSiT) was proposed based on the experimental observations obtained. Camphor oil and ferrocene (Fe) were used as a carbon source and a catalyst, respectively. The NPSiT was optimised and used as a template to synthesise VACNT. The VACNT was synthesised on NPSiT by using a double thermal chemical vapour deposition (DTCVD) method. The synthesis was also performed via a floated method in a DTCVD reactor by using an in-situ catalyst in the absence of any catalysts pre-treatment. Each of the growth mechanisms was proposed based on the TEM images obtained at different synthesis conditions. From the results, a mixed top and bottom growth model was proposed for the growth mechanism of VACNT at the pores and pillars. On the contrary, the tip growth model was proposed for the growth inside the pores, while the valley growth model was proposed for the growth within the pillars of NPSiT. Furthermore, a mixed tip and valley growth model was proposed based on the location of Fe particles.

Nanosilver-embedded silicon nanowires as a SERS-active substrate for the ultrasensitive detection of monoamine neurotransmitters

The trace detection of neurotransmitters is very useful in the diagnosis of severe neuropsychiatric diseases such as Parkinson's, Schizophrenia, and Depression. Surface enhanced Raman scattering (SERS) is a prospective technique for the sensitive detection of analyte with molecular information. Herein, a porous silicon (pSi) template (so-called silicon nanowires) was prepared using a metal-assisted chemical etching process, and the pSi template was successfully embedded with plenty of nanosilvers. The nanosilver-embedded pSi (pSi@Ag) was employed as a SERS-active substrate to detect dopamine (DA) and serotonin (ST) neurotransmitters at ultralow concentrations. The optimized pSi@Ag substrate produced an excellent dynamic linear range over six orders of magnitude (from 10−6 to 10−12 M), as well as showing the picomolar detection limit of ~10−13 M. The substrate exhibited the comparable performance to the current state-of-the-art researches, probably because the SERS signals were generated from larger number of analyte molecules adsorbed on the internal silver nanostructures with porous layer. Furthermore, the pSi@Ag substrate distinguished the individual component in the mixture (DA and ST at 10−8 M) without any labelling, corroborating the reliable pSi@Ag substrate for the application to the actual biological fluid.

(Invited) Metal Oxide Decorated Porous Silicon Interfaces for Sensor Applications: The Question of Water Interaction, Stability, Platform Diversity, Sensitivity, and Selectivity

Key parameters of a metal oxide nanostructure modified porous silicon (PSi) template that can affect the development and performance of PSi-based sensors are considered1. The importance of pore selection and direct in-situ nitrogen functionalization are discussed. Metal oxide (MOx , MxO, x≥1) nanostructured island sites, deposited to select, well defined and reproducible micron sized p and n-type silicon pores (0.7–1.5 µ diameter) provide sensitivity and selectivity as they facilitate rapid “Fickian” analyte diffusion to these highly active sites. The metal oxide nanoparticles are trapped by a thin nanopored wall covering preventing their sintering at elevated temperatures. Variable sensitivities of the metal oxide nanostructured sites are well predicted within the recently developed Inverse Hard/Soft-Acid/Base (IHSAB) model. Ready nitrogen functionalization can further provide the conversion of the decorating metal oxides and an oxidized PSi interface from hydrophilic to hydrophobic character. The decrease in water interaction provides enhanced stability. Selectivity in the measurement of multiple gases is possible with a combination of nanostructure based detection matrices, p and n-type charge carrier variation, time dependent diffusion response, and pore structure influenced sensitivity as the range of variable responses is dominated by the molecular electronic structure of the nanostructured island sites as evaluated using the IHSAB concept. Fast Fourier Transfer techniques (pulsed mode operation) can facilitate low analyte consumption and higher analyte selectivity, and provide the ability to assess false positive signals. A new Fermi distribution–based adsorption isotherm is superior to other isotherms in modeling the PSi system. AIMS Electronics and Electrical Engineering, 4(1): 87-113,2020 DOI: 10.3934/ElectrEng.2020.1.87

Nanostructured metal oxide modification of a porous silicon interface for sensor applications: the question of water interaction, stability, platform diversity and sensitivity, and selectivity

Key parameters of a nanostructure modified porous silicon (PSi) template that can affect the development and performance of PSi-based sensors are considered. The importance of pore selection and direct in-situ nitrogen functionalization are emphasized. Metal oxide nanostructured island sites deposited to select, well defined, and reproducible nano-pore walled, micron sized p and n-type silicon pores (0.7–1.5 μ diameter) provide enhanced selectivity. The micron-sized pores facilitate rapid Fickian analyte diffusion to these highly active sites. The metal oxide nanoparticles are trapped by a thin nanopored wall covering preventing their sintering at elevated temperatures. The varying sensitivities of the highly active metal oxide nanostructured sites are well predicted within the recently developed Inverse Hard/Soft Acid/Base (IHSAB) model. Nitrogen functionalization of the nanostructure decorated surfaces provides the conversion of these PSi interfaces from hydrophilic to hydrophobic character. The decrease of water interaction provides greatly enhanced stability. Selectivity can be extended to the measurement of multiple gases using a combination of nanostructured island site determined detection matrices, p and n-type charge carrier variation, time dependent diffusion response, and pore structure influenced sensitivity. The range of variable responses is dominated by the molecular electronic structure of the nanostructured island sites as evaluated using the IHSAB concept. Pulsed mode operation can facilitate low analyte consumption and high analyte selectivity and further provide the ability to assess false positive signals using Fast Fourier Transfer techniques. The modeling of the PSi sensor response with a new Fermi energy distribution –based response isotherm is found to be superior to other isotherms. The rate of sensor response, linearity of measurement, and hysteresis of response are also considered within the framework of the decorated micron sized pore structure.

Assessment of Arrays of Permanent Nanomagnets Produced By Bi-Metal Deposits within Porous Silicon

This work presents the investigation of the magnetic behavior of bi-metal nanostructures within nanostructured silicon with the aim to exploit the magnetic properties of both metals and gain control of the exchange coupling between the two metals especially with respect to their volume ratio. Furthermore a variation of the structure size and the proximity of the metal deposits modify the exchange coupling and thus the energy product. Finally nanocomposite systems with an energy product as high as possible should be achieved to give rise to on-chip applications using permanent nanomagnets, especially arranged in arrays. Magnetic nanostructures of two different metals are deposited within nanostructured silicon to control the magnetic switching behavior of the silicon/metal nanocomposite. Two different templates, porous silicon and porous silicon nanotubes are utilized to achieve such nanocomposites. The morphology (pore diameter, tube diameter) of the two systems is comparable. In the case of the utilization of porous silicon templates a mesoporous morphology with average pore diameters of 50 nm is used and these oriented and separated pores are filled with two different metals, namely Ni and Co. The two metals are deposited alternatingly by electrodeposition. A further approach is the chemical growth of Co nanoparticles within porous silicon nanotubes (SiNTs) and the additional deposition of a Ni layer on the outer surface of the tubes. The inner diameter of the silicon tubes is around 50 nm and the wall thickness is about 10 nm. Since the silicon wall of the tubes offers a porous structure the Co particles, which are localized near the pore surface on the wall of a given nanotube, can touch the Ni layer. An alternative structure involves the deposition of an additional Si layer, after the growth of Co particles inside the tubes, as a spacer before the Ni deposition. The morphology of the deposited bi-metal Ni/Co structures is figured out by SEM and EDX, magnetic measurements are performed by SQUID magnetometry. In the presented work the dependence of the magnetic properties of a nanostructured silicon/bi-metal nanocomposite on the volume ratio of the metals, on the proximity of the nanostructures and also on the size of the metal deposits is figured out. If the distance between the deposited bi-metal structures is small enough magnetic exchange coupling between them [1] is present which can be explained by the obtained magnetic data. By tuning the bi-metal deposition an optimized energy product [2] is achieved which gives rise to self-assembled nanocomposite systems containing permanent nanomagnets and arrays of them, respectively for on-chip applications. [1] R. Skomski, J.M.D. Coey, Permanent Magnetism, 1st Edition, CRC Press, Taylor and Francis Group, 1999. [2] R. Skomski, P. Manchanda, P.Kumar, B. Balamurugan, A. Kashyap, D.J. Sellmyer, IEEE Trans. Mag. 49, 3215, (2013).

Growth behavior of Cu, Ni and Cu/Ni electrodeposited microwires within porous Si

In this paper, a systematic growth behavior of Cu, Ni and Cu/Ni microwire arrays in porous silicon (PSi) templates is presented. After preparation of PSi templates via anodizing in HF solution, such microwires are successfully grown into PSi templates by electrodeposition method. Systematic scanning electron microscopy (SEM) imaging reveals that Cu seed nucleation occurs at the bottom and Ni seed nucleation starts on the wall of the silicon pores. The different growth models are explained according to the observed diffusion coefficients of ionic elements in electrodeposition baths. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) were used to further observe the structural characteristics of the grown microwires. We believe that this work can be used in developing microwires with desired structural characteristics.

Arrays of Permanent Nanomagnets Produced By Bi-Metal Deposits within Nanostructured Silicon

This work presents the investigation of the magnetic behavior of bi-metal nanostructures within nanostructured silicon with the aim to exploit the magnetic properties of both metals and gain control of the exchange coupling between the two metals especially with respect to their volume ratio. Furthermore a variation of the structure size and the proximity of the metal deposits modify the exchange coupling and thus the energy product. Finally nanocomposite systems with an energy product as high as possible are achieved to give rise to on-chip applications using permanent nanomagnets, especially arranged in arrays. Magnetic nanostructures of two different metals are deposited within nanostructured silicon to control the magnetic switching behavior of the silicon/metal nanocomposite. Two different templates, porous silicon and porous silicon nanotubes are utilized to achieve such nanocomposites. The morphology (pore diameter, tube diameter) of the two systems is comparable. In the case of the utilization of porous silicon templates a mesoporous morphology with average pore diameters of 50 nm is used and these oriented and separated pores are filled with two different metals, namely Ni and Co. The two metals are deposited alternatingly by electrodeposition. A further approach is the chemical growth of Co nanoparticles within porous silicon nanotubes (SiNTs) and the additional deposition of a Ni layer on the outer surface of the tubes. The inner diameter of the silicon tubes is around 50 nm and the wall thickness is about 10 nm. Since the silicon wall of the tubes offers a porous structure the Co particles, which are localized near the pore surface on the wall of a given nanotube, can touch the Ni layer. An alternative structure involves the deposition of an additional Si layer (after the growth of Co particles inside the tubes) as a spacer before the Ni deposition. The morphology of the deposited bi-metal Ni/Co structures is figured out by SEM and EDX. In the presented work the dependence of the magnetic properties of a nanostructured silicon/bi-metal nanocomposite on the volume ratio of the metals, on the proximity of the nanostructures and also on the size of the metal deposits has been figured out. If the distance between the deposited bi-metal structures is small enough magnetic exchange coupling between them is present which could be observed. By tuning the bi-metal deposition an optimized energy product is achieved which gives rise to self-assembled nanocomposite systems containing permanent nanomagnets and arrays of them, respectively for on-chip applications.

Optical Properties of Nanoporous Silicon in the Presence of Magnetic Nanostructures

This work aims to combine luminescent microporous silicon with a ferromagnetic metal to create a nanocomposite system with modifiable photoluminescence due to the presence of metal deposits as well as to influence the optical properties by an external magnetic field. Due to the metal filling of the porous silicon (PSi) the peak of the photoluminescence is blue-shifted and furthermore an increase of the intensity is observed. The influence of the magnetic metal filling on the optical properties is discussed and the magnetic characterization of the samples is presented. The microporous silicon is fabricated by anodization of a moderately doped p-silicon wafer. The electrolyte consists of HF, distilled water and ethanol in the ratio 1:1:2. The deposition of the magnetic metal has been performed by pulsed electrodeposition in using in the case of Ni the so called Watts electrolyte (NiCl2 and NiSO4). First the optical properties of the luminescent PSi are investigated, second the magnetic metal is electrochemically deposited within the porous silicon and subsequently the nanocomposite specimens are characterized optically and magnetically. The samples are structurally characterized by SEM, EDX and TEM. The optical properties are investigated with respect to the shift of the photoluminescence peak due to the metal filling. Photoluminescence spectra of bare PSi show a maximum around 620 nm whereas in the case of Ni filled samples the peak is blue-shifted to around 580 nm depending on the metal deposition time and furthermore the luminescence intensity is increased. The deposition of the metal is crucial since the metal has to be incorporated within the nanopores but has to be avoided on the sample surface to still enable the luminescence. Furthermore the oxide layer between PSi and metal is essential to guarantee a photoluminescence of the specimens. Concerning the magnetic properties of the nanocomposites the embedded Ni structures offer the same branched morphology as the porous silicon template and thus these interconnected Ni-structures do not offer a superparamagnetic behavior which is confirmed by temperature dependent magnetization measurements. Generally superparamagnetic behavior is possible due to the pore diameters in the nanometer range. Field dependent magnetization measurements have been performed with a magnetic field applied perpendicular and parallel to the sample surface showing a high magnetic anisotropy. Due to the interconnected Ni-structures the samples offer a film-like behavior with the easy axis parallel to the surface. Figure 1 shows the film-like behavior of a Ni-filled sample. In the frame of this work the optical characterization of luminescent PSi with respect to the peak position of the photoluminescence compared with Ni filled samples is discussed in detail as well as the corresponding magnetic properties of the nanocomposites. Furthermore the influence of an external magnetic field on the optical properties is elucidated. The presented systems give not only rise to optoelectronic applications but also to magneto optical integrated devices. Figure 1: Field dependent magnetization measurements performed in two directions, showing a high magnetic anisotropy with the easy axis for an applied field parallel to the surface. Figure 1

Bi-Metal Deposits within Nanostructured Silicon with Respect to Permanent Nanomagnets

The purpose of this work is to fabricate nanostructured silicon with two different materials of embedded magnetic nanostructures to exploit the magnetic properties of both metals and gain control of the exchange coupling between the two metals especially with respect to their volume ratio. Furthermore a variation of the structure size and the proximity of the metal deposits modifies the exchange coupling and thus the energy product. Finally nanocomposits with an energy product as high as possible are achieved to give rise to on-chip applications using permanent nanomagnets, especially arranged in arrays. In this work magnetic nanostructures of two different metals are deposited within nanostructured silicon to control the magnetic switching behavior of the silicon/metal nanocomposite. Two different templates, porous silicon and porous silicon nanotubes are utilized to achieve such nanocomposites. The morphology (pore diameter, tube diameter) of the two systems is comparable. In the case of the utilization of porous silicon templates a mesoporous morphology with average pore diameters of 50 nm are used and these oriented and separated pores are filled with two different metals, namely Ni and Co. The two metals are deposited alternatingly by electrodeposition. A further approach is the chemical growth of Co nanoparticles within porous silicon nanotubes (SiNTs) and the additional deposition of a Ni layer on the outer surface of the tubes. The inner diameter of the silicon tubes is around 50 nm and the wall thickness is about 10 nm. Since the silicon wall of the tubes offers a porous structure the Co particles, which are localized near the pore surface on the wall of a given nanotube, can touch the Ni layer. An alternative structure involves the deposition of an additional Si layer (after the growth of Co particles inside the tubes) as a spacer before the Ni deposition. The morphology of the deposited bi-metal Ni/Co structures is figured out by SEM and EDX. Figure 1 shows an EDX-map of a cross-section of a porous silicon sample filled with Ni and Co. In the presented work the dependence of the magnetic properties of a nanostructured silicon/bi-metal nanocomposite on the volume ratio of the metals, on the proximity of the nanostructures and also on the size of the metal deposits has been figured out. If the distance between the deposited bi-metal structures is small enough magnetic exchange coupling between them is present which could be observed. By tuning the bi-metal deposition an optimized energy product is achieved which gives rise to self-assembled nanocomposite systems containing permanent nanomagnets and arrays of them, respectively for on-chip applications. Figure 1: EDX mapping of a cross-section of a porous silicon sample with deposited Ni-Co structures showing the ratio between Ni and Co (Ni …yellow, Co … Red). Figure 1

Ferromagnetic Resonance of Y3Fe5O12 Nanowires

In this letter, yttrium-iron-garnet (YIG) nanowires are synthesized in a porous silicon template via a sol-gel method; ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques are then utilized to investigate the magnetic properties of the YIG nanowires. Moreover, the effects of the annealing temperature on the saturation magnetization ${\text{4}\pi}M_{S}$ and the crystal phase of the ceramic wires are assessed. For annealing temperatures above the crystallization temperature (∼710 °C), ${\text{4}\pi}M_{S}$ is dramatically increased. Therefore, the ceramic wires are then routinely annealed at 800 °C for 2 hours. Based on the VSM measurements, the net saturation magnetization and the loading factor of the nanowires are found to be 85 G and 35% respectively. Using the FMR technique, a DC magnetic field is applied either perpendicular or parallel to the wire axis to obtain the anisotropy field from the FMR resonance conditions. It is confirmed that the anisotropy field is uniaxial and is equal to 398 Oe.

NbN superconducting nanonetwork fabricated using porous silicon templates and high-resolution electron beam lithography

Superconducting NbN nanonetworks with a very small number of interconnected nanowires, with diameter of the order of 4 nm, are fabricated combining a bottom-up (use of porous silicon nanotemplates) with a top-down technique (high-resolution electron beam lithography). The method is easy to control and allows the fabrication of devices, on a robust support, with electrical properties close to a one-dimensional superconductor that can be used fruitfully for novel applications.

Porous silicon ZnO/SnO2 structures for CO2 detection

In this work, we report the CO2 sensing properties of tin oxide (SnO2) and zinc oxide (ZnO) thin films deposited onto the macro porous silicon (PS) substrates. PS was synthesized by electrochemical etching of p-type monocrystalline silicon along with the metal oxide (MO) thin film deposition using precipitation method. X-ray diffraction (XRD) confirms the presence of tetragonal and wurtzite phases of SnO2 and ZnO respectively. Scanning electron microscopy (SEM) reveals the formation of substrate porosity dependent porous metal oxide nanostructures. CO2 sensing properties of SnO2/PS and ZnO/PS were studied as a function of deposition time, gas concentration and operation temperature (up to 300 °C). Sensing response of approximately 19 was obtained with SnO2/PS, whereas, ZnO/PS reveals a relatively faster response time (∼65s). Porous silicon templates improve the gas-sensing properties of both SnO2 and ZnO films by a factor of 2 with respect to the films over cSi substrates due to increase in specific surface area. Irrespective of substrate type, the SnO2 films showed higher sensing response than ZnO films due to the association and dissociation reactions of SnO2 with adsorbed atmospheric oxygen. An increased conductivity of ZnO films synthesized with zinc carbonate precursor and subsequently their sensing response (∼4) at lower temperatures (100 °C), has been attributed to an additional interface and new nano passages created due to Zn2SiO4 formation. As compared to the c-Si substrate, the faster response time was achieved for all films using PS substrates.

(Invited) Silicon-Based Hydrogel Nanocomposites for the Treatment and Diagnosis of Pulmonary Diseases

Lung cancer is the most frequent cause of cancer worldwide for men, and second only to breast cancer for women. Lung cancer is the leading cause of cancer death worldwide. Yet, if cancer is detected in the earliest stages it is a treatable, if not curable disease. However, we lack the tools to detect early stages of this disease in a non-invasive manner. To overcome this challenge we have developed a simple non-invasive urine-based test for the early detection of lung cancer using a silicon-hydrogel composite microparticles. Hydrogel-based microparticles are particularly attractive for pulmonary delivery. Their size can be engineered for efficient delivery into the bronchi, where they subsequently swell, avoiding macrophage uptake. Here, I will present our work in developing enzyme-responsive peptide functionalized hydrogel microparticles via emulsion synthesis. Additionally, these hydrogels will include silicon nanocrystals as a reporter particle. We will present a top-down approach to fabricate silicon nanocrystals with diameters smaller than 6 nm from a porous silicon template. The viability of these composite hydrogel microparticles to serve as drug delivery vectors and as diagnostic agents will be reported.

Synthesis and Magnetic Characterization of Nanostructured Silicon with Bi-Metal Filling

The purpose of this work is to combine magnetic nanostructures of two different metals within nanostructured silicon to influence the magnetic switching behavior of the porous silicon/metal nanocomposite. Two routes are used to achieve such nanocomposites. The porous silicon templates are fabricated with a mesoporous morphology offering average pore diameters of 50 nm and these pores are filled with a bi metal filling, namely Ni and Co. The two metals are deposited alternatingly by electrodeposition. A further approach is the chemical growth of Co nanoparticles within porous silicon nanotubes (SiNTs) and the additional deposition of a Ni layer on the outer surface of the tubes (Figure 1). The inner diameter of the silicon tubes is around 50 nm and the wall thickness is about 10 nm. Since the silicon wall of the tubes offers a porous structure the Co particles, which are localized near the pore surface on the wall of a given nanotube, can touch the Ni layer. An alternative structure involves the deposition of an additional Si layer (after the growth of Co particles inside the tubes) as a spacer before the Ni deposition. These samples have been characterized structurally and magnetically. The magnetic properties of the systems strongly depend on the size and shape of the deposited bi-metal nanostructures and also on the proximity of the Ni and Co structures to each other. If the distance is small enough magnetic exchange coupling between the two metal structures is present. Due to the size of the metal deposits and the coupling of the bi-metal structures the switching behavior of the hysteresis can be tuned. The aim is to achieve self-assembled nanocomposite systems with a high as possible energy product which can be promising for permanent nanomagnets. Figure 1: SEM image of silicon nanotubes (SiNTs) with Co particles deposited inside the tubes and Ni covering the walls of the tubes. Figure 1

Electrodeposition and characterization of one-dimensional CuInSe2 nanostructures in mesoporous silicon templates

Abstract In this work, the electrodeposition and characterization of 1D CuInSe2 (CIS) nanostructures formed by the assistance of porous silicon (PSi) templates is presented. The formation of CIS was found to be potential dependent on the specific substrate being used. The filling process of the pores of PSi template was studied directly by the current transient response during electrodeposition of nanostructured CIS and results were compared with FESEM images. CIS nanostructures were fully characterized by using FE-SEM, FIB, XRD, and Raman spectroscopy, in order to know their physical properties.

Synthesis and Magnetic Characterization of (Porous Silicon/"Hard-Soft" Magnetic) Nanocomposites

The purpose of this work is to combine magnetic nanostructures of two different metals within porous silicon (PS) to influence the magnetic switching behavior of this porous silicon/metal nanocomposite. These “hard/soft” magnetic nanocomposites have been achieved by two different routes. Porous silicon templates in the mesoporous regime have been employed for the electrochemical incorporation of different types of magnetic nanostructures. Two kinds of PS templates have been used, on the one hand double sided porous silicon which has been achieved by etching of an ultrathin wafer in a double tank cell and on the other hand a silicon wafer has been porosified on one side only. The double-sided porous silicon has been filled with Ni on one side and with Co on the other side, also using a double tank cell. In the case of the one-sided sample both metals have been electrochemically deposited alternatingly inside the pores. Magnetic characterization of the samples has been performed by SQUID magnetometry (field range ± 6 T, temperature range 4 – 300 K). Considering the magnetic measurements of the porous silicon containing “hard and soft” magnetic nanostructures, one sees that the magnetization curves show a first term due to the softer magnetic material, Ni, which exhibits a saturation magnetization of 0.6 T (bulk Ni) and a second one due to the harder magnetic material, Co, which exhibits a saturation magnetization of 1.7 T (bulk Co). Thus the hysteresis curves of the investigated nanocomposite systems show two different slopes corresponding to the two different materials. In any case samples offer a clear kink corresponding to the different magnetic switching behavior of Ni and Co, whereas the slope is a little steeper for double sided samples. The gained results indicate that in the case of filling both materials in one porous layer only poor exchange coupling between Co and Ni is present which could be due to the formation of a small amount of NiCo alloy at the interface. The aim is to control the magnetic behavior of the samples by the ratio between the two magnetic materials. The presented two-metal/PS magnetic nanocomposite is fabricated during a low-cost two-step electrochemical process whereas double sided as well as one sides PS acts as template. Because the magnetic properties are determined by the geometry of the deposits and their spatial arrangement the coercivity, remanence and magnetic anisotropy of the samples (both types) can be modified by varying the size and shape of the Ni and Co deposits. Thus the magnetic characteristics of the specimens can be broadly tailored, as desired. Nevertheless the magnetic properties of the resulting nanocomposites are not only correlated with the size, shape and spatial distribution of the deposited metal structures but also strongly depend on the filling ratio between the softer (Ni) and harder (Co) magnetic materials. In fabricating bi-metal nanocomposites which offer specific magnetic characteristics the magnetic coupling between the nanostructures plays an important role, especially exchange coupling between the deposits of two different metals.

Control of the Magnetic Properties of a Magnetic Field Guidable Biocompatible Nanovehicle

Within this work a biocompatible magnetic nanovehicle which is movable in aqueous solutions by a magnetic field is presented. The nanovehicle consists of a porous silicon template and encapsulated iron oxide nanostructures. Both materials employed, porous silicon (PSi) as well as iron oxide are known to be biocompatible (1, 2). Mainly the synthesis of the nanocomposite as well as the magnetic properties of the systems will be discussed. Two routes are employed to produce various iron oxide phases of the embedded nanostructures within PSi. On the one hand, readily synthesized magnetite nanoparticles (NPs) which are superparamagnetic (SPM) due to their size, are infiltrated into the pores. On the other hand chemical deposition of iron oxide inside the PSi templates is used. The loading process of the templates depends not only on the pore-diameter/particle-size ratio but also on the particle-template interactions due to different surface treatments (e.g. as etched or oxidized PSi). Considering the chemically grown iron oxide, it does not form monodisperse particles but mainly clusters of particles. An increase of the temperature during the deposition resulted in a decrease of the coercivity which can be due to an iron oxide phase modification or due to a modification of the shape of the deposits. An adjustability of the magnetic properties of the system is achieved by a variation of the iron oxide loading within the PSi. An investigation of the iron oxide deposition dependent on the template and on the chemical parameters as well as of the magnetic properties in dependence on the particle size and on the template morphology of the nanocomposite will be presented. Temperature dependent magnetization measurements give information about the nature of the particle filling (packing density, spatial distribution), from field dependent magnetization measurements characteristics such as saturation magnetization, coercivity and remanence can be evaluated. For a sample containing a moderate filling with 8 nm Fe3O4 NPs the saturation magnetization has been estimated in using the measured hysteresis curves and considering the 1/H approach to be in the order of 6×10-3 emu/cm2. The amount of iron oxide particles inside the pores of the PSi matrices has been estimated in taking the magnetic moment of an individual iron oxide NP which is about 1.49 × 10-18 emu. In this case this leads to a number of about 1.3 × 1019 particles/cm3. The coercivity HC of the nanocomposite systems below TBdecreases with decreasing particle size which is due to SPM relaxation effects. The fabricated magnetic nanovehicles can be tuned in its magnetic behavior (e.g. coercivity, TB) due to the morphology of the template, the particle size and the filling conditions. The resulting magnetic moment of the samples is high enough to be moved within aqueous surroundings by a magnetic field of 0.1 T. (1) D. Ling, T. Hyeon, Small 9, 2013. (2) L.T. Canham, Adv. Mater. 7, 1033, 1995.

Preparation of Porous Silicon Templates in Two Steps of Au-Assisted Chemical Etching

Preparation of Porous Silicon Templates in Two Steps of Au-Assisted Chemical Etching