Porous Silicon Structures Research Articles

Hard Magnetic Composite: FePt Nanoparticles Grown within Nanostructured Silicon

In this work porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures which offer a hard magnetic behavior. The difference of the magnetic characteristics between the two systems is figured out.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution [1]. The morphology offers separated pores of about 60 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO [2]. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure are used. FePt nanoparticles (NPs) are chemically grown inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6). For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.Magnetic characterization of the samples is performed by VSM (Vibrating Sample Magnetometer), the structure is analyzed by SEM, TEM and EDX.The magnetic response of the two different composite systems is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.Hard magnetic materials within nanostructured silicon give rise for on-chip applications using 3 dimensional arrays of nanomagnets.[1] K. Rumpf, P. Granitzer, H. Michor, NRL 11, 398 (2016).[2] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Comm. 49, 5760 (2013). Figure 1

Pore-size dependence of the heat conduction in porous silicon and phonon spectral energy density analysis

Semiconductor devices made of silicon material have been widely used due to its excellent thermoelectrical properties. Here, the silicon material with aligned distributed rectangular-shaped holes is proposed for the manufacture of semiconductor device. Comprehensive understanding the heat conduction is of great significance to improve the efficiency of the thermoelectrical materials. This letter investigates the thermal conductivity of nanoscale porous silicon structures by adopting the nonequilibrium molecular dynamics method. The results demonstrate that the temperature is sensitive to the sizes of the rectangular-shaped holes. Additionally, it is found that the effective thermal conductivity significantly decreases with the increase of the dimensions of the holes. Our work reveals that the key to reduce the effective thermal conductivity is to disturb the distribution of heat flux. Furthermore, the phonon spectral energy density method is used to obtain the phonon dispersion and phonon energy in the frequency domain.

Low temperature growth of graphitic carbon on porous silicon for high-capacity lithium energy storage

With highly yield and low-cost micrometer-sized polycrystalline silicon powders, a hierarchical porous silicon (PS) structure is fabricated. As a novel passivated layer, graphitic carbon (GC) is in-situ growth on the three-dimensional surfaces of PS. The GC is synthesized with 1 nm Al2O3 catalyst, and the thickness can be controlled to 2 nm at a relatively low temperature 700 °C. With this unique GC layer coated PS, the structure integrity and solid electrolyte interphase stability substantially improved. As a result, the PS/GC shows a high capacity retention of 91% after 100 cycles at 0.2 A g−1. During a long-life test at 1 A g−1, the PS/GC electrode delivers 1024 mAh g−1 after 600 cycles. In addition, an accumulated areal capacity of 492 mAh cm−2 is achieved, further demonstrates the high mass loading of micrometer-sized PS as well as the electrochemical stability of highly-stacking GC coating layer. Our work invents a new approach of the GC growth and its application on large volume change electrode materials, which is enabled by a low temperature Al2O3 catalyzed method.

Fabrication, structural and optical properties of a virtual GeSi template by Ge filling the porous Si prepared by EC etching

In this paper, a virtual GeSi template has been successfully fabricated by Ge filling the porous silicon (PSi) prepared by electrochemical etching (EC etching). The microstructure quality measured with cross-sectional scanning electron microscopy and photoluminescence spectra reveal that the PSi structure is fully filled with uniformly distributed Ge. Furthermore, Raman and X-ray diffraction results also show that the template has a typical GeSi feature, which originates from Ge interdiffusion with PSi during the Ge deposition. This design and structure can be expected to be useful as a template for Ge-related materials growth and device fabrication.

Preparation and in vivo evaluation of red blood cell membrane coated porous silicon nanoparticles implanted with 155Tb

IntroductionPorous silicon (PSi) nanoparticles are capable of delivering therapeutic payloads providing targeted delivery and sustained release of the payloads. In this work we describe the development and proof-of-concept in vivo evaluation of thermally hydrocarbonized porous silicon (PSi) nanoparticles that are implanted with radioactive 155Tb atoms and coated with red blood cell (RBC) membrane (155Tb-THCPSi). The developed nanocomposites can be utilized as an intravenous delivery platform for theranostic radionuclides. MethodsTHCPSi thin films were implanted with 155Dy ions that decay to 155Tb at the ISOLDE radioactive ion-beam (RIB) facility at CERN. The films were processed to nanoparticles by ball-milling and sonication, and subsequently coated with either a solid lipid and RBC membrane or solely with RBC membrane. The nanocomposites were evaluated in vitro for stability and in vivo for circulation half-life and ex vivo for biodistribution in Balb/c mice. ResultsNanoporous THCPSi films were successfully implanted with 155Tb and processed to coated nanoparticles. The in vitro stability of the particles in plasma and buffer solutions was not significantly different between the particle types, and therefore the RBC membrane coated particles with less laborious processing method were chosen for the biological evaluation. The RBC membrane coating enhanced significantly the blood half-life compared to bare THCPSi particles. In the ex vivo biodistribution study a pronounced accumulation to the spleen was found, with lower uptake in the liver and a minor uptake in the lung, gall bladder and bone marrow. ConclusionsWe have demonstrated, using 155Tb RIB-implanted PSi nanoparticles coated with mouse RBC membranes, the feasibility of using such a theranostic nanosystem for the delivery of RIB based radionuclides with prolonged circulation time. Advances in knowledge and implications for patient careFor the first time, the RIB implantation technique has been utilized to produce PSi nanoparticle with a surface modified for better persistence in circulation. When optimized, these particles could be used in targeted radionuclide therapy with a combination of chemotherapeutic payload within the PSi structure.

Investigation of Sensitive Structures of Nanostructured Silicon – Melanin

The goal of this work is to study the current-voltage characteristics of structures of porous silicon – melanin and sensitivity of structures to glucose, to compare the characteristics between the samples obtained by different techniques. Object of study – structures of porous silicon – melanin. The subject of the study is the change of electrophysical parameters depending on the change in the analyte concentration. Organic-inorganic structures have recently attracted considerable interest in electronics due to the ability to create cheaper and simpler devices than traditional inorganic semiconductors. Melanin is an organic pigment that is present in many living organisms and has semiconductor properties. Melanin interacts with most biological substances, making it a promising material in the field of biosensors. Measuring glucose levels in the world today is very popular in the health and food sectors, so there is a constant need for easy-to-use and low-cost sensors. The purpose of this work was to investigate the heterojunction of melanin-porous silicon and the possibility of creating glucose sensors on such structures. For sample preparation metal-assisted chemical etching with three different types of metal nanoparticles (silver, copper, gold) was used. This technique allow formation of arrays of silicon nanowires with high aspect ratio. After porous silicon etching metal residuals were removed and thin layer of water-solube melanin was deposited at the surface and polymerized. Silver-based dot contacts was used for measurements. The I-V curves of the studied samples were measured in the work, such parameters as: resistance of structure, coefficient of rectification at contact of porous silicon – melanin, coefficient of rectification at contact of substrate – melanin, sensitivity to glucose were calculated. It was shown that I-V curves of both melanin/porous silicon and melanin/porous silicon/bulk silicon structures are diode-like with rectification factor at 5 V up to 80 for melanin/porous silicon heterojunction and up to 800 for melanin/porous silicon/bulk silicon structure. Resistor-like sencitive structures of melanin – nanostructured silicon are sensitive to glucose with a sensitivity coefficient of up to 1.83 mA /%. It was noticed that samples prepared with copper nanoparticles have opposite dependence (decreasing of current with increase of glucose concentration). No clear correlation was observed between the sensitivity, the rectifying properties and the technology of sample preparation, but the most stable results were obtained for structures made with silver nanoparticles.

Hierarchical porous silicon structures with extraordinary mechanical strength as high-performance lithium-ion battery anodes

Porous structured silicon has been regarded as a promising candidate to overcome pulverization of silicon-based anodes. However, poor mechanical strength of these porous particles has limited their volumetric energy density towards practical applications. Here we design and synthesize hierarchical carbon-nanotube@silicon@carbon microspheres with both high porosity and extraordinary mechanical strength (>200 MPa) and a low apparent particle expansion of ~40% upon full lithiation. The composite electrodes of carbon-nanotube@silicon@carbon-graphite with a practical loading (3 mAh cm−2) deliver ~750 mAh g−1 specific capacity, <20% initial swelling at 100% state-of-charge, and ~92% capacity retention over 500 cycles. Calendered electrodes achieve ~980 mAh cm−3 volumetric capacity density and <50% end-of-life swell after 120 cycles. Full cells with LiNi1/3Mn1/3Co1/3O2 cathodes demonstrate >92% capacity retention over 500 cycles. This work is a leap in silicon anode development and provides insights into the design of electrode materials for other batteries.

Effect of Etching Duration on the Morphological and Opto-Electrical Properties of Silicon Nanowires Obtained by Ag-Assisted Chemical Etching

Silicon nanowires (SiNWs) were obtained on p-Si (100) substrate by Ag-assisted chemical etching method in two-step process. The influence of the etching duration on the morphological, optical and electrical properties of SiNWs samples was investigated. SEM images show clearly the presence of nanowires and the existence of porous silicon structure especially for low etching duration. Fourier Transformed Infrared spectroscopy (FTIR) measurements allow identifying several particles on the SiNWs surfaces such as oxygen and hydrogen elements. The optical properties of the SiNWs layer were investigated by Photoluminescence spectroscopy (PL). A strong broad PL band was observed at room temperature for an etching time of 30 s. The PL spectra exhibit multi-band profile in the red-green region. The luminescence of SiNWs is mainly attributed to Si-oxide interface states and oxygen deficient centers. Ag/SiNWs/Si Schottky diodes were analyzed by X-ray diffraction (XRD) and studied by current - voltage (I-V) measurements. Diode parameters such as ideality factor (n), series resistance (Rs), saturation current (Is) and energy barrier (φb) were determined by analyzing the I-V characteristics. Ag/SiNWs/Si diode for an etching duration of 30 s exhibits a rectifying behavior with a factor ideality of 2.8 and a low threshold voltage of about 0.44 V in forward bias. Space charge limited current (SCLC) model is the dominant transport mechanism through Ag/SiNWs/Si diode. The trap states, on the Ag/SiNWs interface, play in important role in the conduction phenomenon through these structures.

Communication—Supercritically-Dried Membranes and Powders of >90% Porosity Silicon with Pore Volumes Exceeding 4 cm3 g−1

Porous silicon structures can display full biodegradability into orthosilicic acid and are under development for medical uses such as drug delivery. Here we demonstrate optimized electrochemical etching and drying conditions to achieve ultrahigh porosity structures (“silicon aerocrystals”), which should enable ultrahigh nanostructured drug payloads. Supercritical drying (SCD) of detached 41 to 210 micron thick films from etched p + wafers generates structures with pore volumes 3.5 to 5.13 cm3 g−1, average pore diameters of 29 nm to 35 nm and surface areas 425 to 549 m2 g−1. For anodized p + wafers, the benefits of SCD vs air drying (AD) are primarily elevated pore volumes.

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Formation of Au Nanoparticles and Features of Etching of a Si Substrate under Irradiation with Atomic and Molecular Ions

The formation of nanoparticles under the irradiation of a thin metallic gold film by accelerated atomic and molecular ions is demonstrated. The obtained structures are used to form porous silicon by the metal-assisted chemical etching. The size of the gold nanoparticles and structure of porous silicon greatly depend on the type of incident particles and their fluence. A local increase in the density of energy released at the target surface under molecular ion bombardment significantly reduces the doses required to form the desired film morphologies and spread of nanoparticles over the surface and simultaneously makes a weaker radiative impact on the substrate. The shape of the fluorescence and fluorescence-excitation spectra of porous silicon obtained from the irradiated structures is independent of the irradiation parameters, but changes with the etching-solution concentration.

Формирование наночастиц Au и особенности травления подложки Si после облучения атомарными и молекулярными ионами

Formation of metal nanoparticles on silicon substrate by thin gold film irradiation with accelerated atomic and molecular ions is shown. Structures obtained were etched by metal-assisted catalytic chemical technique to get porous silicon structure. Size of gold nanoparticles and the structure of porous siliconstrongly depend on kind of incident species and ion dose. A local increase in the energy release density at the target surface that takes place during molecular ion bombardment significantly reduce the doses required for the formation of predetermined film morphology and the distribution of nanoparticles on the surface, while at the same time molecules exhibit lower radiation effect on the substrate. Luminescent properties of porous silicon do not depend on the kind of ion used, and can be tuned by composition of an etching solution

Fabrication of Silicon Nitride Fiber Materials by Organic Foam Impregnation Method

In this paper, porous silicon was prepared by organic foam impregnation, and silicon nitride fibers were prepared by direct in-situ nitridation of porous silicon. The effect of pore structure of porous silicon on material properties was studied. The results show that the silicon nitride fiber material with low density, high strength and low thermal conductivity can be obtained by using organic foam impregnation method. The pore size of template has a certain effect on the growth of silicon nitride fibers. The smaller the pore size of the template, the higher the content of silicon nitride in silicon nitride fiber material. This is due to the concentration of gas phase reactants in pore.

Excitation of Bloch surface wave using silver nanoparticles for sensitivity enhanced biosensor

A silver nanoparticles array is introduced on the top layer of all-porous-silicon refractive index sensor. Bloch surface wave (BSW) resonance is realized at the interface between air and multilayer porous silicon structure, which can be excited by different coupling schemes: the Kretschmann prism and silver nanoparticles array. In addition to sustaining the BSW mode, the silver nanoparticles add an additional degree of freedom to the phase-matching conditions. We demonstrated the sharp BSW reflectivity dip with an ultra-narrow linewidth. The performance of the designed BSW sensor is numerically calculated by the rigorous coupled wave analysis (RCWA) method under s-polarized light. The optimized silver nanoparticles coupled BSW (AgNPs-BSW) sensor has a much higher figure of merit () than conventional prism-coupled BSW sensors. The azimuthal sensitivity can reach about 703°/RIU or even higher. The proposed silver nanoparticles coupled BSW (AgNPs-BSW) sensor exhibits the capacity to eliminate the adverse effects of inhomogeneous penetration of analytes. With such excellent performance, our study demonstrates its potential applications in the field of chemical and biological sensors in the future.

Features of Defect Formation in Nanostructured Silicon under Ion Irradiation

Nanostructured silicon is irradiated by Si+ and He+ ions with energies of 200 and 150 keV, respectively. Destruction of the structure of irradiated samples and the accumulation of defects at different irradiation fluences are investigated by Raman scattering. It is shown that single-crystal silicon films are amorphized under irradiation at 0.7 displacements per atom. However, at 0.5 displacements per atom, porous silicon does not completely amorphize and the Raman spectra contain a weak signal of the amorphous silicon phase along with a pronounced signal of the crystalline silicon phase. The size of nanocrystals in the structure of porous silicon at different irradiation fluences is estimated.

Synaptic and Fast Switching Memristance in Porous Silicon-Based Structures.

Memristors are two terminal electronic components whose conductance depends on the amount of charge that has flown across them over time. This dependence can be gradual, such as in synaptic memristors, or abrupt, as in resistive switching memristors. Either of these memory effects are very promising for the development of a whole new generation of electronic devices. For the successful implementation of practical memristors, however, the development of low cost industry compatible memristive materials is required. Here the memristive properties of differently processed porous silicon structures are presented, which are suitable for different applications. Electrical characterization and SPICE simulations show that laser-carbonized porous silicon shows a strong synaptic memristive behavior influenced by defect diffusion, while wet-oxidized porous silicon has strong resistance switching properties, with switching ratios over 8000. Results show that practical memristors of either type can be achieved with porous silicon whose memristive properties can be adjusted by the proper material processing. Thus, porous silicon may play an important role for the successful realization of practical memristorics with cost-effective materials and processes.

Synthesis of graphene-like passivating carbon layer into nanostructured porous silicon

The paper presents experimental results on the synthesis of graphene-like (Gr) films in gradient porous silicon structures with variable morphology (GPSi-var). Porous GPSi-var layers are characterized by the presence of a nanostructured layer (later nanoporous) on its surface. By increasing the depth of the anodic etching, the nanopores gradually transform into spongy and then into the columnar structure with micron-sized pores. The peculiarities of Gr layers’ synthesis in the walls of the pores throughout the depth of GPSi-var structures are studied. The proposed method of Gr film synthesis in the porous structure allows to form the carbon coating not only on the wall of the through pores in membrane, but also on the inner surface of the closed pores in the GPSi-var layers. It has been established that the composite formation of nanoporous silicon with Gr coating (GPSi-var/Gr) decreases the surface resistance of porous silicon layers by several orders of magnitude. The relatively higher stability of nanoporous composite layers to the impact of aqueous media has been experimentally demonstrated. Besides, it was found that the synthesized Gr layers are formed predominantly on the outer surface of the porous layer and crystal structure of its skeleton.

The Application of Magnesiothermic Reduction of Silica to Produce Porous Silicon for Lithium Ion Batteries

Increasing demand for portable power applications are pushing conventional battery chemistries to their theoretic limit. Silicon has the potential as an anode material to increase lithium-ion cell capacity. The associated volume change of lithiation leads to a decline in capacity during cycling and low lithium diffusion rates within silicon limit high rate discharging. Many silicon morphologies and nanostructures have been studied including porous architectures. Porous morphologies can potentially address the poor cyclability and rate capabilities simultaneously. The template assisted synthesis ‘magnesiothermic reduction’ of silica to silicon offers a facile and scalable synthesis route to porous silicon structures. However, our review of the recent progress of this method indicates a distinct lack of mechanistic understanding of this phenomenon. To better understand the processes, we have systematically studied the process conditions using a model silica system. Further, we performed a complete characterisation of both the reactant and product structures in order to map how reaction conditions affect the properties of the electrode materials. Finally, we will present the battery performance of these porous silicon structures and compile a processing-structure-property-performance relationship. Figure 1

Compensating porosity gradient to produce flat, micromachined porous silicon structures

Abstract Obtaining flat micromachined porous silicon structures is extremely challenging due to the myriad of factors affecting film stress in such structures. In this work, the relationships between the current control during anodization, average porosity, and residual stress within porous silicon thin films and micro-fabricated structures were investigated. Using a combination of electron microscopy, surface profilometry and reflectance spectroscopy, the optimum conditions to produce near zero residual stress in thin films and micro-fabricated structures were determined. The residual stress was adjusted by a continuous variation of the anodization current in order to achieve flat structures. The flattest released porous silicon microbeams were 2.3 μm thick with a peak to valley height variation of only 72 nm over a length of 150 μm. These were achieved by using an initial current density of 20 mA/cm2 that was reduced down to 8 mA/cm2 during anodization. By using this method of reducing the current during anodization, the inherent high porosity at the porous-silicon/silicon interface was reduced, which also enabled a 36% increase in the film thickness before film delamination compared with using a constant current. These results provide a pathway to fabricate thick, optically flat micromachined multi-layer filters using a single base material (silicon) for the structural and released layers.

Effects of Electrochemical Etching Conditions on the Formation and Photoluminescence Properties of P-Type Porous Silicon

Porous silicon has been widely used in sensors, microelectronics and other fields. This material retains the characteristics of the original silicon-based material, while having good optical, electrical and mechanical properties. How to make porous silicon efficient and controllable by means of anodization has become the focus of research. This article mainly studied the influence of different current conditions and eletrolytes on the pore formation and performance of porous silicon in the electrochemical etching process of p-type silicon. It was found that porous silicon structures with controllable morphologies can be prepared by changing the etching current densities. Moreover, adding oxidants (H2O2) and dimethylformamide (DMF) into the electrolytes will significantly enlarge the etching parameter window of porous silicon and improve its photoluminescence properties. This will help to expand the applications of porous silicon in the field of microelectronics such as biosensors.