Electrical properties of surface functionalized silicon nanoparticles

The present study relates to the applicability of silicon nanoparticles as basic component in printing inks for the fabrication of printable electronic devices. It is systematically investigated, how the surface functionalization of silicon nanoparticles with 1-alkenes affects the electrical properties of thin films made of them. Therefore, films of as-prepared silicon nanoparticles with a size of 42 nm as well as freshly etched ones, both terminated with hydrogen, are compared with films of silicon nanoparticles functionalized with n-octene, n-dodecene, allylmercaptan, and allylamine, respectively. It is found, that the activation energy of the electron transport through the films is in the range of 0.5 eV and scales with the polarity of the functionalization.     

Chemical vapor functionalization: a continuous production process for functionalized ZnO nanoparticles

The continuous functionalization of nanoparticles in the gas-phase directly after their generation, chemical vapor functionalization, is studied with ZnO and 1-hexanol as a model system using two reactors in series. In the first reactor ZnO nanoparticles are synthesized in the gas-phase from diethylzinc and oxygen at 1,073 K with grain sizes of 13 nm as determined by Rietveld refinement of X-ray diffractograms. The second reactor, connected at the exit of the first reactor and kept at lower temperatures (573, 673, and 773 K), is used as a functionalization chamber. At the connection point of the two reactors, the vapor of 1-hexanol is injected to react with the surface of ZnO nanoparticles in the gas phase. The process has been analyzed by quadrupole mass spectrometry to obtain information about optimal conditions for functionalization. Dynamic light scattering data show that the functionalized particles have substantially improved colloidal dispersibility with hydrodynamic diameters of 60 nm. Diffuse reflectance fourier transform infrared spectra and ¹H nuclear magnetic resonance spectra are consistent with 1-hexanol adsorbed at the particle surface acting as a functionalizing agent. The agglomerate size is substantially reduced owing to chemical vapor functionalization.     

The transformation of <Emphasis Type="Italic">n</Emphasis>-alkanes on H-forms of zeolites under supercritical conditions

The skeleton isomerization of n-butane, n-hexane, and n-heptane was studied under supercritical conditions on H-forms of zeolites mordenite, beta, and ZSM-5 over the temperature and pressure ranges 260–450°C and 80–130 atm. The isomerization of n-hexane and n-heptane was accompanied by side processes such as oligomerization and cracking. The selectivity of formation of branched isomers of these hydrocarbons did not exceed 70 and 30%, respectively. The catalyst with the most stable operation was pentasil ZSM-5, but the selectivity of formation of branched isomers on it did not exceed 30% even at 260–280°C and decreased to 3% as the reaction temperature increased to 400–450°C. The fraction of aromatization products was then more than 15%. A study of the influence of C₆–C₇ n-alkane additives on the isomerization of n-pentane on mordenite in the H-form under supercritical conditions at 260°C and 120 atm showed that a gradual decrease in the activity of this catalyst in the isomerization of n-pentane was related to the formation of heavier hydrocarbons.     

Patterned laser annealing of silicon oxide films

UV-absorbing silicon monoxide (SiO _x , x≈1) thin films on fused silica substrates are irradiated by an ArF excimer laser (wavelength 193 nm) in the sub-ablation threshold regime. Multi-pulse irradiation of films with ∼200-nm thickness at a fluence of about 100 mJ/cm² leads to a significant increase of the UV transmission, indicating the oxidation of SiO _x to SiO₂. The quality of the obtained films after this laser annealing process depends on the oxygen content of the environment. Irradiation in air at atmospheric pressure leads to the formation of sub-micron-sized oxide particles on top of the film. Structured illumination is applied either to form areas of the film with changed transmission and refractive index, or for the formation of regular particle patterns with sub-micron periods. These processes can be utilized for the fabrication of phase masks or for various types of surface functionalization.     

Microwave-assisted fractional precipitation of magnetite nanoparticles using designed experiments

In this study, highly pure magnetite nanoparticle dispersed in water and an organic solvent (n-hexane) and its powder form were prepared in laboratory scale by the fractional precipitation using ammonium hydroxide and microwave heating in the presence of linoleic acid as capping agent. In order to overcome the oxidation of Fe²⁺ during magnetite formation ferrous ammonium sulfate, sodium azide, and fractional precipitation technique were used. The Fe₃O₄ products were investigated by XRD, LLS, EDX, TEM, viscosity measurements, and chemical analysis. The effects of seven main factors on the average diameter of magnetite particles were studied by a screening design. The analysis of the samples showed that this new modified method is able to produce pure magnetite particles in the range of 1–15 nm. The most important factors on the particle size reduction of magnetite were found to be the capping agent used and the pH of solution at the end of precipitation process. Data analysis was performed using Qualitek-4 and Minitab softwares.     

On the enzymatic formation of platinum nanoparticles

A dimeric hydrogenase enzyme (44.5 and 39.4 kDa sub units) was isolated in a 39.5% yield from the fungus Fusarium oxysporum and purified 4.64-fold by ion exchange chromatography on Sephacryl S-200. Characterisation of the enzyme afforded pH and temperature optima of 7.5 and 38 °C, respectively, a half-life stability of 36 min and a V _max and K _m of 3.57 nmol min⁻¹ mL⁻¹ and 2.25 mM, respectively. This enzyme was inhibited (non-competitively) by hydrogen hexachloroplatinic acid (H₂PtCl₆) at 1 or 2 mM with a K _i value of 118 μM. Incubation of the platinum salt with the pure enzyme under an atmosphere of hydrogen and optimum enzyme conditions (pH 7.5, 38 °C) afforded <10% bioreduction after 8 h while at conditions suitable for platinum nanoparticle formation (pH 9, 65 °C) over 90% reduction took place after the same length of time. Cell-free extract from the fungal isolates produced nearly 90% bioreduction of the platinum salt under both pH and temperature conditions. The bioreduction of the platinum salt by a hydrogenase enzyme takes place by a passive process and not an active one as previously understood.     

Laser-induced local dehydroxylation on surface-oxidized silicon substrates: mechanistic aspects and prospects in nanofabrication

Processing of silicon oxide surfaces with a focused laser beam at a wavelength of 514 nm has been investigated. Laser processing of native silicon samples (d _ox=1–2 nm) allows the fabrication of reactive templates with laterally varying hydroxyl group density. Very similar results were also obtained on thermally oxidized silicon samples (d _ox≈100 nm), whereas respective experiments on quartz plates have failed. These results support a photothermal mechanism where laser irradiation causes a local temperature rise and initiates dehydroxylation. In agreement with a photothermally induced dehydroxylation reaction, a thermokinetic analysis of the experimental data points to a highly activated process. In conjunction with site-selective functionalization routines this opens up an avenue towards functional surface structures with lateral dimensions significantly below the optical diffraction limit.     

Surface functionalization of titanium dioxide nanoparticles with alkanephosphonic acids for transparent nanocomposites

The surface functionalization of rutile titanium dioxide nanoparticles with 1-decylphosphonic acid and diethyl undec-10-enyl phosphonate in a two-stage process, involving a change in reaction medium, is described. Similarly, 1-decylphosphonic acid and diethyl 1-decylphosphonate were employed as surface modifiers. The nanoparticles coated in two successive steps formed stable, transparent dispersions in toluene. Surface functionalization was monitored using thermogravimetric analysis (TGA), which showed enhanced surface coverage after the second capping step. Incorporation of C=C-terminal surface coupling molecules in the second stage was directly proved using FTIR. Dynamic light scattering measurements showed that the dual-functionalized particles possessed a uniform size of around 13 nm. Particle dimensions were further analyzed using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Transparent nanocomposites were formed by introducing the functionalized nanoparticles into a poly(benzyl acrylate) matrix. The refractive index of poly(benzyl acrylate) composites, measured by spectroscopic ellipsometry, increased from 1.57 for the pure polymer to 1.63 for 14.0 vol.% TiO₂ at λ = 586 nm. Nanocomposite films with particle weight percentages of up to 30% (9.5 vol.%) showed a high light transmittance of around 90% at wavelengths above λ = 400 nm.     

Ethylene and phenylene bridged polysilsesquioxanes functionalized by amine and thiol groups as adsorbents of volatile organic compounds

Ethylene and phenylene bridged polysilsesquioxane xerogels having amine and thiol groups attached to the surface have been obtained by the sol-gel method from 1,2-bis(triethoxysilyl)ethane or 1,4-bis(triethoxysilyl)benzene and functionalized silanes in the presence of an ammonium fluoride catalyst in an ethanol solution. The synthesized samples have a porous structure (700-850 m²/g) and a high content of functional groups (1.4-1.9 mmol/g). The obtained porous bridged polysilsesquioxanes exhibit a considerable affinity for adsorbing several organic compounds (n-hexane, n-heptane, benzene, cyclohexane, acetonitrile and triethylamine) from the gas phase. The sample with an ethylene bridge and amino groups in the surface layer has the highest uptake of all compounds. Data from adsorption measurements show that functionalized organosilicon materials can be used as effective adsorbents of organic contaminants from the gas phase.     

Ar ion milling of InSb for manufacturing single electron devices

Ar⁺ ion milling of InSb for manufacturing single electron devices was studied. It is shown that pyramidal structures (porous) are created on the (1 1 1) surface of InSb wafers by anisotropic etching. Also it was shown the axis of the pyramidal structure is a function of the angle of the Ar⁺ incident beam and does not depend on the energy of the beam. EDX measurement results show In_xO_y and Sb_xO_y were not created on the surface after milling process. FTIR measurement results show that the surface reflection was decreased and less than 0.3 V flat band voltage was seen in capacitance voltage measurement results. SEM images show that the etching has approximately vertical profile. Therefore the Ar⁺ milling technique can be used as a dry etching technique for manufacturing mesa and/or porous structures of InSb. Since the surface is porous and of near-pyramidal morphology, one can simulate the surface by a set of needles each of which is a nanometer-size capacitance (i.e. single electron device). We showed, the threshold voltage of this single electron device is 0.3 V approximately, and therefore it can be used for studying single-electron or Coulomb blockade effects.     

Formation of binary clusters by molecular ion irradiation

In the present study, we have observed silicon–carbon cluster ions (Si_nC_m⁺) emitted from a Si(1 0 0) surface under irradiation of reactive molecular ions, such as C₆F₅⁺, at 4 keV, 1 μA/cm². The cluster Si_n up to n=8 and “binary” cluster Si_nC up to n=6 are clearly detected for the C₆F₅⁺ irradiation. Stoichiometric clusters (Si_nC_m n=m) except SiC⁺ and other binary clusters which contain more than two carbon atoms (m≥2) were scarcely observed. The observed clusters show a yield alternation between odd and even n. The intensities of Si₄, Si₆ and Si₅C clusters are relatively higher than those of the neighboring clusters. In the case of Si₅C, it is considered that doped carbon atom acts as silicon atom. These results imply that the recombination through the nascent cluster emission and subsequent decomposition takes place during the cluster formation.     

A versatile method for the preparation of end-functional polymers onto SiO2 nanoparticles by a combination of surface-initiated ATRP and Huisgen [3 + 2] cycloaddition

A versatile method was developed for the chain-end functionalization of the grafted polymer chains for surface modification of nanoparticles with functionalized groups through a combination of surface-initiated atom-transfer radical polymerization (ATRP) and Huisgen [3 + 2] cycloaddition. First, the surface of SiO₂ nanoparticles was modified with poly(methyl methacrylate) (PMMA) brushes via the “grafting from” approach. The terminal bromides of PMMA-grafted SiO₂ nanoparticles were then transformed into an azide function by nucleophilic substitution. These azido-terminated PMMA brushes on the nanoparticle surface were reacted with alkyne-terminated functional end group via Huisgen [3 + 2] cycloaddition. FTIR and ¹H NMR spectra indicated quantitative transformation of the chain ends of PMMA brushes onto SiO₂ nanoparticles into the desired functional group. And, the dispersibility of the end-functional polymer-grafted SiO₂ nanoparticles was investigated with a transmission electron microscope (TEM).     

The effects of surface modification on the electrical properties of p–n+ junction silicon nanowires grown by an aqueous electroless etching method

Although the aqueous electroless etching (AEE) method has received significant attention for the fabrication of silicon nanowires (SiNWs) due to its simplicity and effectiveness, SiNWs grown via the AEE method have a drawback in that their surface roughness is considerably high. Thus, we fabricated surface-modified p–n ⁺ junction SiNWs grown by AEE, wherein the surface roughness was reduced by a sequential processes of oxide growth using the rapid thermal oxidation (RTO) cycling process and oxide removal with a hydrofluoric acid solution. High-resolution transmission electron microscopy analysis confirmed that the surface roughness of the modified SiNWs was significantly decreased compared with that of the as-fabricated SiNWs. After RTO treatment, the wettability of the SiNWs had dramatically changed from superhydrophilic to superhydrophobic, which can be attributed to the formation of siloxane groups on the native oxide/SiNW surfaces and the effect of the nanoscale structure. Due to the enhancement in surface carrier mobility, the current density of the surface-modified p–n ⁺ junction SiNWs was approximately 6.3-fold greater than that of the as-fabricated sample at a forward bias of 4 V. Meanwhile, the photocurrent density of the surface-modified p–n ⁺ junction SiNWs was considerably decreased as a result of the decreases in the light absorption area, light absorption volume, and light scattering.     

Structural analysis of PVA-based proton conducting membranes

We have synthesized and characterized a new family of proton conducting membranes based on cross-linked poly(vinyl alcohol), PVA, and functionalized silica filler. Glutaraldehyde, GLA, was used as the cross-linking agent in order to improve chemical and thermal stabilities. The functionalization of the silica particles is such that terminal –SO₃H groups are formed during membrane preparation, thus possibly providing additional mobile protons. We find that the crystallinity of the PVA-based membranes is enhanced by the presence of the functionalized silica particles, whereas it is reduced by means of cross-linking. The thermal stability of the ternary system PVA:GLA:silica is improved due to the additive contribution of GLA and silica. The conductivity of membranes swelled in a sulfuric acid solution was found to be of the order of 10^− 1 S cm^− 1.     

Controlled surface functionalization of silica-coated magnetic nanoparticles with terminal amino and carboxyl groups

General and versatile methods for the functionalization of superparamagnetic, silica-coated, maghemite nanoparticles by surface amino and/or carboxyl groups have been established. The nanoparticles were synthesized using co-precipitation from aqueous solutions and coated with a thin layer of silica using the hydrolysis and condensation of tetraethoxysilane (TEOS). For the amino functionalization, 3-(2-aminoethylamino)propylmethyldimethoxysilane (APMS) was grafted onto the nanoparticle surfaces in their aqueous suspensions. The grafting process was followed by measurements of the ζ-potential and a determination of the concentration of the surface amino groups with conductometric titrations. The surface concentration of the amino groups could be varied by increasing the amount of APMS in the grafting process up to approximately 2.3 –NH₂ groups per nm². The carboxyl functionalization was obtained in two ways: (i) by a ring-opening linker elongation reaction of the surface amines at the functionalized nanoparticles with succinic anhydride (SA) in non-aqueous medium, and (ii) by reacting the APMS and SA first, followed by grafting of the carboxyl-terminated reagent onto the nanoparticle surfaces. Using the first method, the SA only reacted with the terminal primary amino groups (–NH₂) of the surface-grafted APMS molecules. Infra-red spectroscopy (ATR FTIR) and mass spectrometry (HRMS) showed that the second method enables the bonding of up to two SA molecules per one APMS molecule, since the SA reacted with both the primary (–NH₂) and secondary amino (–NH–) groups of the APMS molecule. When using both methods, the ratio between the surface amino and carboxyl groups can be controlled.     

Investigation of rapid thermal oxide/ silicon nitride passivation stack of n+ emitter

To anticipate the initial phosphorus diffusion parameters of silicon solar cells process fabrication, we report in this paper an overview of our experiments on silicon n⁺-emitters passivation by means of rapid thermal silicon oxide/silicon nitride stack. The process-induced changes have been evaluated and explained. We found that 900 °C and 80 s were the appropriate process parameters to grow 10 nm silicon oxide. Investigation of the effect of this oxidation on n⁺ multicrystalline silicon emitters revealed a large decrease (more than 25%) of the sheet resistance and around 12% increase of the junction depth. The experiments also revealed that the passivation effect of the optimal silicon oxide/silicon nitride stack is efficient only for higher emitter quality. In addition, we found that this stack reduces the surface reflection more than the optimal single silicon nitride layer.     

Photon emission from clean and oxygenated Si and SiO2 surfaces bombarded by 5 keV krypton ions

The effect of oxygen on the light emission from a Si (1 0 0) semiconductor bombarded by energetic Kr⁺ ions has been studied in the 200–300 nm wavelength range. The influence of oxygen was verified by studying the optical spectra of SiO₂ bombarded under similar experimental conditions. It has been found that the measured intensities of the emitted photons are always higher in the presence of oxygen, even higher than those obtained for SiO₂. The electron-transfer model can explain our experimental observations. We do believe that in the presence of oxygen, an intermediate structure of silicon sub-oxide SiO_X<2 is formed on silicon surface, which is responsible for the increase of photon emission. In addition, the radiative dissociation process and breaking of chemical bond seems contribute to the enhancement of emitted photons intensity.     

X-ray photoelectron spectroscopic studies of black silicon for solar cell

The black silicon has been produced by plasma immersion ion implantation (PIII) process. The microstructure and optical reflectance are characterized by field emission scanning electron microscope and spectrophotometer. Results show that the black silicon appears porous or needle-like microstructure with the average reflectance of 4.87% and 2.12%, respectively. The surface state is investigated by X-ray photoelectron spectroscopy (XPS) technique. The surface of the black silicon is composed of silicon, carbon, oxygen and fluorine element. The formation of Si_xO_yF_z in the surface of black silicon can be proved clearly by the O 1s, F 1s and Si 2p XPS spectra. The formation mechanism of the black silicon produced by PIII process can be obtained from XPS results. The porous or needle-like structure of the black silicon will be formed under the competition of SF_x⁺ (x ≤ 5) and F⁺ ions etching effect, Si_xO_yF_z passivation and ion bombardment.     

Autoignition of surrogate fuels at elevated temperatures and pressures

Autoignition of Jet-A and mixtures of benzene, hexane, and decane in air has been studied using a heated shock tube at mean post-shock pressures of 8.5 ± 1 atm within the temperature range of 1000–1700 K with the objective of identifying surrogate fuels for aviation kerosene. The influence of each component on ignition delay time and on critical conditions required for strong ignition of the mixture has been deduced from experimental observations. Correlation equation for Jet-A ignition times has been derived from the measurements. It is found that within the scatter of experimental data dilution of n-decane with benzene and n-hexane leads to slight increase in ignition times at low temperatures and does not change critical temperatures required for direct initiation of detonations in comparison with pure n-decane/air mixtures. Ignition times in 20% hexane/80% decane (HD), 20% benzene/80% decane (BD) and 18.2% benzene/9.1% hexane/72.7% decane (BHD) mixtures at temperature range of T  1450–1750 K correlate well with induction time of Jet-A fuel suggesting that these mixtures could serve as surrogates for aviation kerosene. At the same time, HD, BD and BHD surrogate fuels demonstrate a stronger autoignition and peak velocities of reflected shock front in comparison with Jet-A and n-decane/air mixtures.     

Nanofibrous membrane of polyacrylonitrile with efficient adsorption capacity for cadmium ions from aqueous solution: Isotherm and kinetic studies

The nanofibrous membrane of polyacrylonitrile (NMP) was successfully synthesized after NaOH and NaHCO₃ treatment aiming its functionalization using electrospinning for cadmium ion (Cd²⁺) adsorption. Field emission scanning electron microscopy (FE-SEM) revealed that small particles attached to the surface of functionalized PAN nanofibers. Equilibrium was attained after 60 min following a rapid uptake of Cd²⁺ with maximum adsorption capacity and percentage removal at an optimum solution pH of 7.0. The adsorbent dose of 0.3 g and 90 mg L⁻¹ of initial Cd²⁺ concentration yielded the maximum adsorption capacity. The pseudo-second-order kinetic model was the best fitted to the adsorption data, indicating that the chemisorption is the controlling mechanism of adsorption. The physisorption was proposed based on the calculated values of the mean free energy of adsorption from the D–R isotherm (E < 8 kJ mol⁻¹). Furthermore, three-parameter isotherm models indicated the homogeneous and heterogeneous Cd²⁺ adsorption onto NMP adsorbent.