Wyniki wyszukiwania - Biblioteka Nauki

1

Morphology of silicon (111) during electrochemical etching in NH4F electrolytes

100%

Jakubowicz J.

Advances in Materials Science

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2005

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tom Vol. 5, nr 1-3

49-54

EN

The n-type silicon with (111) orientation and resistivity of 8-12 .źcm was electrochemically etched. The results obtained by electrochemical etching of silicon in 0.1M NH4F (pH4.5), 0.1M NH4F (pH4.0) and 0.2M NH4F (pH4.0) electrolytes, indicates that slight increase of the NH4F concentration by 0.1M results in faster silicon dissolution. In slightly reactive 0.1M NH4F (pH4.5), we can observe initial stage of silicon dissolution on the inside edges of atomic terraces. Flat atomic terrace under electrochemical etching undergoes to mesa-type structures surrounded by strongly corrugated areas. The diameter and heights of the mesas are 150-200 nm and 5-7 nm, respectively. The mesa-type structures are the remnants of the atomic terraces and theirs formation proceed independently on the electrolyte concentration. The mesas appear faster at higher concentration and faster disappear by pits formation. During increase of etching time, increase of pore size, more in the case of diameter than depth, because pits coagulation appears.

2

Effect of macroporous silicon layer on opto-electrical parameters of multicrystalline silicon solar cells

100%

Panek P.

Opto-Electronics Review

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2004

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tom Vol. 12, No. 1

45--48

EN

The feasibility of improvement in multicrystalline silicon (mc-Si) solar cells is considered by applying porous silicon (PSi) layers obtained and modified with chemical double-step method. PSi layers have a different diameter of pores which determines electrical and optical characteristics of solar cells. Structural properties of these layers were investigated by means of scanning electron microscopy. The reflectance, internal quantum efficiency, and current-voltage characteristics of the silicon solar cells with porous layers are reported. The PC1D computer program was applied to calculate the correlation between texture slope angle and electrical parameters of the solar cell. The diffusion results are also demonstrated using POCl3 as a donors source in an emitter with a sheet resistance in the range 30–80 Ω) which depends on a structure of the porous layer prepared before a diffusion process. Some technological problems using PSi in a solar cell structure and correlation between porous layer morphology and opto-electrical parameters are discussed. As a result, the mc-Si solar cell with 12.74% efficiency was obtained. We think that macroporous silicon formation process can be applied in industry technology that allows for exceeding efficiency limit of the mc-Si solar cells with TiOx, at the level of 13% at present.

3

A study of the gas specificity of porous silicon sensors for organic vapours

80%

Choi S. H. , Cheng H. , Park S. H. , Kim H. J. , Kim Y. Y. , Lee K. W.

Materials Science Poland

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2009

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tom Vol. 27, No. 2

603--610

EN

A porous silicon sensor was investigated as a means to determine the response specificity for organic vapours. Porous silicon layers were fabricated by electrochemical anodization of p-type crystalline silicon in an HF ethanol solution under various conditions. The porous silicon sensors were placed in a gas chamber with various organic vapours, and the changes in electrical resistance under constant voltage of each sensor were used as detection signals. The sensors recorded various changes in resistivity for various organic vapours.

4

Application of stain etched porous silicon in c-Si solar cells

80%

Dimova-Malinovska D.

Opto-Electronics Review

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2000

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tom Vol. 8, No. 4

353-355

EN

In this work application of porous silicon (PS) to c-Si solar cells is presented. The PS layer is formed between the fingers of the Al grid contact by the method of stain etching. The short circuit current, Isc, of the solar cells with PS between the grid contacts increases of 30-40% comparing with the solar cell without PS. The open circuit voltage decreases a little probably due to decreasing doping concentration of P in n+ - diffused layer, after stain etching, when 80 nm of it is converted to PS. The value of a fill factor does not change significantly. The spectral dependence of Isc demonstrates that it increases in the whole spectral region. This could be related to a decrease in reflectivity and partially to an increase in transparency of the emitter after PS formation.Tthe efficiency of solar cells increases of about 25-30%.

5

Photosensitive macroporous silicon based structures

80%

Pačebutas V. , Grigoras K. , Jasutis V. , Kačiulis S. , Mickevičius S. , Sabataityte J. , Snitka V. , Šimkiene I.

Opto-Electronics Review

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2000

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tom Vol. 8, No. 4

388-392

EN

Macroporous silicon prepared in n-type silicon have been used for a photosensitive device formation. Boron-doped spun-on layer was applied for p+ emitter formation of the devices. The obtained structures were investigated by AFM and electron microscopy, photosensitivity and the photocurrent spectra were measured to evaluate the influence of porous layer and boron diffusion conditions. Unusually fast boron diffusion through the porous emitter was investigated, stipulating the p+ -n junction to be positioned 2.5 µm deeper the pores bottom. This effect was explained by a presence of local electric fields, caused by tensions present at the border between PS layer and crystalline substrate and by possible deeper nanoporous structure, what was partially proofed by AFM.

6

Influence of porous silicon on parameters of silicon solar cells

80%

Lipiński M. , Panek P. , Bielańska E. , Węgłowska J. , Czternastek H.

Opto-Electronics Review

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2000

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tom Vol. 8, No. 4

418-420

EN

The silicon solar cells with PS /n+/ p-Si structure (PS - porous Si) have been realised. Porous silicon obtained by stain etching or by electrochemical etching on standard alkaline textured surface has reduced effective reflectance coefficient to about 3% in a wavelength range of 400-1000 nm. Improved performance of solar cells due to formation of PS layer on the top surface between grid fingers has been demonstrated. Increases in efficiency of more than 25% have been achieved. In one chemical process antireflection coating as well as the selective emitter could be simultaneously obtained.

7

Porous silicon in solar cell structures

80%

Yerokhov V. , Melnyk I. , Tsisaruk A. , Semochko I.

Opto-Electronics Review

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2000

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tom Vol. 8, No. 4

414-417

EN

The purpose of the present paper was technology development of generation of efficient and cost - effective porous silicon (PS) based antireflection coating (ARC), which would be the best adapted to the silicon solar cell (SC) processing sequence. Owing to optimisation of anodisation process conditions an average reflection coefficient of PS in the range of 400-1000 nm was decreased to 7.59% for porous layers, grown on a polished surface, and to 1.72% for layers that were grown on textured surface. Minimisation of optical losses allowed improving short circuit current by over than 50% for mono- and multicrystalline SC that had PS based ARC formed on the frontal surface. Under this, the increment of efficiency of these SCs was 31% and 22%, correspondingly. However, the revealed decrease in the SC open-circuit voltage with PS layer by 2.5% gives the evidence on insufficient improvement and stabilisation of passivating properties of the porous layer.

8

Porous silicon layer as antireflection coating in solar cells

80%

Panek P. , Lipiński M. , Czternastek H.

Opto-Electronics Review

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2000

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tom Vol. 8, No. 1

57-59

EN

The purpose of work is to improve the performance of standard screen - printed silicon solar cells by incorporating a method by forming a porous silicon (PS) layer on the top surface of large area n+/p monocrystalline, multicrystalline and textured silicon solar cells by electrochemical etching in a fluorohydric solution. The photovoltaic properties of three solar cells groups with and without PS layer are compared. Reflectivity measurements are presented in order to evaluate the effectiveness of PS layer as antireflection coating.

9

On the mechanism of electroluminescence emission by porous silicon layers

80%

Velasco J.

Open Chemistry

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2005

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tom 3

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nr 3

470-481

EN

The analytical treatment of a model considering the electrooxidation of p-porous silicon layers under galvanostatic conditions is able to give account of experimental facts such as the shape and location of the electroluminescence peak as well as of the spectral shift of the electroluminescence peak produced by oxidation. The proposed model considers electroluminescence to be the result of electron injection into the conduction band by an adsorbed intermediate produced by electrooxidation of the surface coverage with hydrogen or siloxene of the silicon nanocrystallites. The access of holes to the surface is made possible by low accumulation layer conditions and is the rate determining step in the electroluminescence mechanism. In this way it is possible to give a satisfactory explanation to the shift towards the blue experimented by the electroluminiscence emission maximum as a consequence of electrooxidation.

10

Adsorption properties of porous silicon

80%

Domański K. , Grabiec P. , Gotszalk T. , Beck R. B. , Dębski T. , Rangelow I. W.

Journal of Telecommunications and Information Technology

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2001

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tom nr 1

53-56

EN

Porous silicon shows some interesting features for micromechanical applications. Some applications make use of its high surface-to-volume ratio. A capacitive gas or humidity sensor using the adsorption of gases on the porous surface can be easily fabricated. However an opportunity for more sensitive device is given by micromechanical structure. In this paper we report on the piezoresistive cantilever beam structure with porous silicon adsorbing spot as a gas sensor.

11

Novel gas sensor based on porous silicon measured by photovoltage, photoluminescence, and admittance spectroscopy

80%

Bratkowski A. , Korcala A. , Łukasiak Z. , Borowski P. , Bała W.

Opto-Electronics Review

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2005

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tom Vol. 13, No. 1

35--38

EN

Porous silicon (PSi) layer as gas sensor, based on the change in photoconductivity, photoluminescence and admittance has been presented. PSi layer was prepared by electrochemical dissolution of p-type silicon wafer in HF. Photovoltage curves, photoluminescence spectra (PL) and admittance spectra have been measured in different gas concentrations. Photoconductivity (PC) spectra in vacuum and different gas atmosphere have been compared. Changes of photovoltage intensity curves and change of PC spectra versus concentration of vapour have been observed.

12

Temperature measurement using a Chx/porous silicon/Si structure encapsulated in a CO2 rich environment

80%

Chiali A. , Ghellai N. , Gabouze N. , Sari N.

Advances in Materials Science

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2010

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tom Vol. 10, nr 2(24)

4-10

EN

This work reports on the possible use of microporous silicon as a temperature sensor. This work is based on previous published works [7, 8, and 9]. The device is based on hydrocarbon group (CHx) / porous silicon (PS) /Si structure. The porous sample was coated with hydrocarbons groups deposited by the plasma of methane /argon mixture. Current–voltage characteristics have been investigated as a function of temperature in the range 200C-70°C.The results show that for a constant voltage in the range 0.7-1V, the current increases linearly with the environment temperature reaches a maximum at 70°C and then stabilizes. This result suggests that the developed structure can be used for sensing temperatures not exceeding 70°C.

13

Sensors on the Basis of PorSi for MEMS

70%

Lobur M. , Kosobutskyy P. , Naperalski A. , Monastyrski L.

Machine Dynamics Research

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2013

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tom Vol. 37, No. 2

60-64

EN

We propose to use technology of electrochemical formation of low-dimensional porous silicon(porSi), which is compatible with the standard technologies of silicon VLSI, for creation of sensor part of MEMS "Lab-on-chip" type.

14

Optical and microstructural properties of granded porous silicon layer

70%

Lipiński M. , Czternastek H. , Sokołowski M. , Panek P.

Archives of Metallurgy and Materials

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2005

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tom Vol. 50, iss. 2

387-393

EN

In this work we present the results of investigations of porous silicon (PS) layers for solar cells application. The PS was formed by chemical etching (stain etching) of n+-p Si substrate in a solution of HF, HNO3 and H2O. The dielectric response of a PS layer was modeled using a Bruggeman effective-medium approximation. It was shown that PS layer could be described by a model of graded layer with effective optical constants n(eff) and k(ef f) changing from these of bulk material (silicon) to these of surrounding (air). The porosity of the PS layer changed from 10% near the bulk silicon region to nearly 85% at the silicon-air interface. The effective reflectance of Cz-Si surface decreased to about 5% after PS layer formation.

PL

Przedstawiono wyniki badań własności optycznych i mikrostrukturalnych gradientowej warstwy z porowatego krzemu naniesionej metodą chamicznego trawienia. Podłożem były płytki polerowanego krzemu typu p z uformowanym złaczem n+-p. Do symulacji własności wynikających z istniejącego gradientu założono wielowarstwową strukturę porowatego krzemu stosując przybliżenie Bruggeman’a efektywnego ośrodka. Określono wartości współczynnika załamania i ekstynkcji (neff i keff) w warstwie porowatego krzemu w funkcji długosci fali światła oraz odległoćci od powierzchni krzemowego podłoża. Porowatość zmieniała się w granicach od 10% w pobliżu granicy podłoże-krzem porowaty do około 85% na granicy krzem porowaty-powietrze. Efektywny współczynnik odbicia dle krzemu z naniesiona warstwa porowatego krzemu wynosił tylko 5% w porównaniu z 25% wartoscią współczynnika odbicia od steksturyzowanej w KOH powierzchni multikrystalicznego krzemu.

15

Porous surface silicon layers in silicon solar cells

70%

Panek P. , Dutkiewicz J. , Levy-Clement C. , Lipiński M. , Bielańska E. , Wodnicka K.

Archives of Metallurgy and Materials

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2005

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tom Vol. 50, iss. 2

417-421

EN

The porous silicon (PSi) layers have been studied in the aspect of their application in the multicrystalline silicon (mc-Si) solar cells. The macroporous layers were prepared by double-step chemical etching prior to the donor diffusion. They have been investigated using scanning (SEM) and transmission (TEM) electron microscopy to reveal the morphology of PSi layers. The techniques of spectral response and current-voltage characteristics have been used to determine the opto-electrical parameters of the solar cells. The porosity was measured by the mercury porosimetry and nitrogen sorption method. The porous layers reported here have had a sponge-like homogeneous structure over the whole 25 cm2 surface of each sample and the decreased effective reflectance (Reff) below 10%. As a final result the mc-Si solar cells with PSi layer were obtained with the conversion effciency (Eff) over 13%.

PL

W pracy przedstawiono metodę uzyskania redukcji odbicia fektywnego ( Eeff) poniżej 10% od powierzchni krzemu multikrystalicznego ( mc-Si ) dla promieniowania w zakresie 400÷1100 nm długości fali. Metoda polega na chemicznym trawieniu powierzchni mc-Si w roztworach na bazie HNO3:HF i wytworzeniu powierzchniowej tekstury geometrycznej w formie porów o średnicy od 30÷800 nm i porownywalnej głębokości. Krzem multikrystaliczny z warstwami krzemu porowatego wykorzystano do wytworzenia ogniw słonecznych. W zależnosci od wielkości porów otrzymano ogniwa o sprawności konwersji fotowoltaicznej od 9.8% do 13.0%.

16

Optical properties of porous Si/PECVD SiNx:H reflector on single crystalline Si for solar cells

70%

Remache L. , Nychyporuk T. , Guermit N. , Fourmond E. , Mahdjoub A. , Lemiti M.

Materials Science Poland

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2016

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tom Vol. 34, No. 1

94--100

EN

The improvement of optical confinement on the back crystalline silicon solar cell is one of the factors leading to its better performance. Porous silicon (PS) layer can be used as a back reflector (BR) in solar cells. In this work, single layers of porous silicon were grown by electrodeposition on a single crystalline silicon substrate. The measurement of the total reflectivity (RT) on Si/PS surface showed a significant improvement in optical confinement compared to that measured on Si/standard Al back surface field (BSF). The internal reflectivity (RB) extracted from total reflectivity measurements achieved 86 % for the optimized single PS layer (92 nm thick layer with 60 % porosity) in the wavelength range between 950 and 1200 nm. This improvement was estimated as more than 17 % compared to that measured on the surface of Si/BSF Al contact. To improve the stability and passivation properties of PS layer BR, silicon nitride layer (SiNx) was deposited by PECVD on a PS layer. The maximum measured total reflectivity for PS/SiNx achieved approximately 56 % corresponding to an improved RB of up to 83 %. The PS formation process in combination with the PECVD SiNx, can be applied in the photovoltaic cell technology and offer a promising technique to produce high-efficiency and low-cost c-Si solar cells.

17

Role of surface substances in excitation of porous silicon photoluminescence

70%

Khomenkova L. Y. , Baran N. P. , Dzhumaev B. R. , Korsunskaya N. E. , Torchinskaya T. V. , Goldstein Y. , Savir E. , Many A.

Opto-Electronics Review

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1999

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tom Vol. 7, No. 2

135-138

EN

Photoluminescence (PL) and photoluminescence excitation (PLE) spectra studies as well as SIMS and FTIR methods were used for investigation of PL excitation mechanism of porous silicon (PS). It is shown that there are two types of PS PLE spectra, which consist of either two bands (visible and ultraviolet) or only ultraviolet one. The different dependencies of intensity of each PLE band upon anodization regimes as well as during aging and thermal treatment were observed. Two excitation channels have been shown to be present in PS. The visible PLE band at 300 K has been attributed to light absorption of some species on Si wire surface.

18

Celecoxib confinement within mesoporous silicon for enhanced oral bioavailability

70%

Wang F. , Barnes T. J. , Prestidge C. A.

Mesoporous Biomaterials

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2014

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tom 1

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nr 1

EN

We investigate the physicochemical characteristics of celecoxib (CEL) entrapped within particles of an oxidized porous silicon matrix (pSiox); determine the oral dose response of CEL compared to pure drug and innovator formulation; develop in vivo-in vitro correlation (IVIVC). CEL was loaded into a pSiox matrix by solvent partitioning, with the physical state of the CEL characterized by FTIR, DSC, TGA and XRD, and correlated with in vitro dissolution behavior. Single dose pharmacokinetic parameters of orally dosed CEL were determined in fasted rats for aqueous suspensions of pure CEL, Celebrexr and CEL-pSiox microparticles. Physicochemical testing of CEL-pSiox formulation confirmed the entrapment of CEL within porous nanostructure in an amorphous or non-crystalline form. CEL-pSiox demonstrated superior pharmacokinetics compared with CEL particles or Celebrexr, i.e. increased absolute bioavailability (96.2% vs. 65.2% vs. 88.1%), increased Cmax (0.91 ± 0.09 μg/mL vs. 0.50 ± 0.16 μg/mL vs. 0.73 ± 0.23 μg/mL) and reduced Tmax (1.0 ± 0.0 h vs. 2.8 ± 0.8 h vs. 3.4 ± 1.0 h). Single point correlation was established between in vitro dissolution efficiency (% DE) and in vivo absolute bioavailability or Cmax . Porous silicon microparticles can be formulated as an effective orally dosed solid dispersion preparation for celecoxib

19

Kinetics of photoluminescence of porous silicon studied by photo-luminescence excitation spectroscopy and time-resolved spectroscopy

70%

Łukasiak Z. , Dalasiński P. , Bała W.

Opto-Electronics Review

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2003

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tom Vol. 11, No. 2

113-117

EN

Photoluminescence (PL) spectra and excitation spectra (PLE) (under steady-state conditions), time resolved spectra (PL-TRS) and decay curves of photoluminescence (PL-DC) in micro- and nanosecond range (under pulsed operation) at different temperatures (10 K-room) on anodically etched boron–doped silicon are presented. PLE shows that visible PL is excited by light from UV region. PL and PL-TRS exhibit multiband structure and can be decomposed as a sum of few Gaussians. PL-DCs have multiexponential shape. Relaxation times depend on wavelength of the observation. To explain our results we assumed a model in which the multibarrier structure is formed by larger Si crystallites or wires (quantum well) surrounded by Si crystallites with diameters in the nanometer range (barrier region). The visible photoluminescence originates from radiative recombination between discrete energy levels in a quantum well

20

Micro- and nanostructurization of surfaces - techniques and applications

60%

Górecka-Drzazga A.

Optica Applicata

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2007

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tom Vol. 37, nr 4

341-357

EN

In the paper some surface structurization methods are presented. Wet and/or dry etching, and thermal oxidation process have been used to form arrays of gated and non-gated sharp silicon microtips on a silicon wafer. A transfer mold technique (mold) has been applied to produce arrays of silicon carbide (SiC) microtips located on a glass wafer. The surface of the fabricated arrays has been also modificated by thin film metal layers and carbon nanotubes. Current-voltage characteristics of electron sources with a cold cathode build on the base of microtips arrays are presented. A new application of silicon microtips arrays for biochemistry is shown. The process of electrochemical etching of silicon has been used to form porous silicon and porous silicon dioxide layers. Applications of the porous layers for chemical and biochemical analyses are presented. Microstructurized surfaces modificated by carbon nanotubes have been used to improve the field emission characteristics of electron sources, and to obtain a miniature light source.