Diethylsilane Research Articles

Synthesis of ultra-high molecular weight poly(methyl methacrylate) with hydrosilane as initiator

Hydrosilanes, including diethylsilane (DES), triethylsilane (TES), phenylsilane (PSH), and diphenylsilane (DPS), have in the present study been used as initiators for the preparation of poly(methyl methacrylate) (PMMA) in the presence of Pd nanoparticles (Pd NPs). DPS initiated the polymerization of MMA in the production of PMMA, with a number average molecular weight ( M n ) of 2.00×10 6 Da and a dispersity (PDI) of 1.81 in the presence of 18.9 ppm of Pd NPs. The kinetic of the polymerization was investigated and the reaction orders, with regard to the MMA, DPS, and Pd NPs, were calculated as 0.85, 0.58, and 0.80, respectively. The molecular weight of the PMMA was measured using gel permeation chromatography (GPC) and the structure was characterized using proton nuclear magnetic resonance ( 1 H NMR). The transmission electron microscopy (TEM) and electron spin resonance (ESR) results revealed that the polymerization took place at the surface of the Pd NPs through a radical mechanism. • A novel route for preparing ultra-high molecular weight poly(methyl methacrylate) with hydrosilane as initiator had been proposed. • An ultrahigh molecular weight poly(methyl methacrylate) with number-average molecular weight of 2.00×10 6 Da was synthesized at mild conditions. • Kinetic of the polymerization of MMA initiated by DPS was investigated. • The mechanism study reveals that the polymerization was conducted via a radical mechanism.

SYNTHESIS OF ORGANOSILICON COMPOUNDS FOR DRESSING OF NANOCOMPOSITES ON BASIS OF QUARTZ AND HIGH DENSITY POLYETHYLENE

The method of synthesis of epoxy compounds containing silicon on basis of hydrosilylation reaction of allyl derivatives of glycidyl ethers with methyl diethyl silane in the presence of platinum-hydrochloric acid was developed. It was determined that these silanes enter into the reaction with various agents bound with oxirane ring by forming corresponding derivatives of organosilicon compounds. Twelve synthesized organosilicon compounds were used as coupling agents for quartz nanoparticles. It was determined that synthesized organosilicon compounds have good coupling agents promoting improvement of compatibility of mineral filler with polymeric matrix. Quartz nanoparticles (up to 100 nanometers) were used as mineral filler. Nanoparticles quartz received on analytical mill А-11 at speed of rotation of a rotor of 28000 turn/min. The dimension of nanoparticles was defined on the device of model STA PT1600 Linseiz Germany and compounded 20-100 nm. For research of physical-mechanical properties of the polymerous nano composites they subjected to pressing at temperature of 190-200 °С. From the pressed plates samples for definition of breaking stress, specific elongation, flexural strength of the filled composites cut down. Research results of influence of type and concentration of coupling agent and filler upon main physical-mechanical properties of nanocomposites are given. Dressing nanoparticles carried out in 0.5 - 2.0 % water solution of the silicoorganic compound acidified by acetic acid to рН = 3.5, at temperature of 55 °С in flow during 60 min. Optimal concentrations of coupling agents and filler, which provide maximal values of composites physical-mechanical properties, were determined. Main reasons providing improvement of strength properties of finished nanocomposites were revealed. The comparative analysis of the data obtained shows that rather high physical-mechanical properties possess nanocomposites in which as dressing 2-metil-5-metildietylsilil-2- (methylenoxy-1,3-dioxosolano) – pentane was used.Forcitation:Gurbanova R.V., Kakhramanov N.T., Shatirova М.I., Мuzafarov А.М., Kahramanly Yu.N., Mammadli U.M. Synthesis of organosilicon compounds for dressing of nanocomposites on basis of quartz and high density polyethylene. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 2. P. 65-72

First example of noncatalytic C2–H functionalization of imidazole ring with an alkoxy enone system

Functionalized imidazoles are well known due to their pharmaceutical importance. It is not occasional that many popular medications such as metronidazole (antibiotic) [1], dacarbazine (antitumor drug) [2], cimetidine (histamine H2 receptor antagonist) [3], as well as best sold losartan and olmesartan (anti-hypertensive agents) and ondanserton (anti-vomiting drug), are imidazole derivatives [4]. Therefore, search for new methods for functionalization of imidazole ring remains one of the priority problems of modern organic synthesis. It is related to the general problem of C–H functionalization, which now attracts increasing attention of synthetic chemists [5]. In most cases such functionalization is achieved by reactions catalyzed by transition metal compounds which often have fairly complicated structure. For example, aryl substituents are introduced into the 2-position of imidazole ring via cross-coupling reactions catalyzed by palladium and copper complexes [6–9]. 1-Methylimidazole was converted into 2-{1-[diethyl(methyl)silyloxy]methyl}1-methylimidazoles in 32–92% yield in the presence of Ir4(CO)12, carbonyl compounds, and diethyl(methyl)silane [10]. However, even traces of transition metals (sometimes very toxic) in substances for pharmaceutical purposes are strongly undesirable [11]. In this communication we report the first example of noncatalytic regioselective C–H functionalization of imidazole ring with an alkoxy enone system via three-component condensation of 1-methylimidazole (1) with 1,3-diphenylprop-2-yn-1-one (2) and isobutyraldehyde (3). The product of this reaction was 3-[2-methyl-1-(1-methyl-1H-imidazol-2-yl)propoxy]1,3-diphenylprop-2-en-1-one (4) which was isolated in 69% yield as a 3 : 2 mixture of E and Z isomers (Scheme 1). The reaction was complete in 10 days at room temperature under solvent-free conditions. The progress of the reaction was monitored by IR spectroscopy, following the disappearance of the C≡C stretching band at 2198 cm. Raising the temperature to 55– 60°C shortened the reaction time to 21 h, but the yield of 4 decreased to 32%, and the isomer ratio essentially changed in favor of the E isomer (E/Z 9 : 1). It may be presumed that the Z isomer is the kinetically controlled product which is converted into more thermodynamically stable E isomer at elevated temperature. Thus, the reaction time may be shortened by more than an order of magnitude, and the E isomer can be obtained with high selectivity at the expense of the yield. The structure of 4 was proved by IR and H, C, and N NMR spectra. The H NMR spectrum of 4 ISSN 1070-4280, Russian Journal of Organic Chemistry, 2016, Vol. 52, No. 4, pp. 602–604. © Pleiades Publishing, Ltd., 2016. Original Russian Text © B.A. Trofimov, L.P. Nikitina, L.V. Andriyankova, K.V. Belyaeva, A.V. Afonin, A.G. Mal’kina, 2016, published in Zhurnal Organicheskoi Khimii, 2016, Vol. 52, No. 4, pp. 614–616.

Easy Access to L‐Mannosides and L‐Galactosides by Using CH Activation of the Corresponding 6‐Deoxysugars

Rare sugars by CH activation: The title compounds have been prepared from the corresponding 6-deoxysugars by an intramolecular CH activation in high yields. Diethyl silane is attached to the 4-OH group followed by formation of a SiC bond; both transformations are catalyzed by iridium in a one-pot fashion. The subsequent Fleming–Tamao oxidation provided the L-sugars.

Evidence of an electron-induced channel for desorption of ethylene from diethylsilane-covered Si(100)

The effects of electron irradiation on the diethylsilane (DES) dosed Si(100) surface were studied using temperature programmed desorption and high-resolution electron energy loss spectroscopy (HREELS). Previous research has shown that without electron irradiation, carbon is thermally removed from the DES/Si(100) surface via a β-hydride elimination process that is characterized by desorption of ethylene at 725 K followed by desorption of hydrogen at 810 K. After irradiating the surface with electrons, HREELS data showed that the electrons dissociated ethyl groups and deposited CH x groups on the surface. Furthermore, electron irradiation of DES/Si(100) resulted in thermal desorption of ethylene at 810 K, with only trace amounts desorbing at 725 K. Hydrogen desorbs at 810 K but also exhibits a high temperature shoulder due to desorption of hydrogen from surface carbon deposited by electrons. This is indicative of an unexplored electron-induced channel for desorption of ethylene from DES/Si(100).

Synthesis of Silicon Carbonitride for the Machining of Resonant Nanomechanical Biosensors

ABSTRACTWe report a study on the plasma-enhanced chemical vapor deposition of silicon carbonitride, as well as the resonant behavior of nanomachined SiCN structures. Films with thicknesses of 1 um, and 200 nm were deposited at varying gas ratios using ammonia (NH3), nitrogen (N2), and diethylsilane (DES) as precursors. X-ray photoelectron spectroscopy revealed high nitrogen and low carbon content in films deposited at high NH3:DES gas flow ratios. Selected samples annealed at varying temperatures experienced shifts in stress towards tensile of Δσ = 235 MPa, 432 MPa, 724 MPa, and 1140 MPa, at annealing temperatures of T = 400 °C, 500 °C, 600 °C, and 700 °C respectively. Infrared spectroscopy reported a loss of incorporated hydrogen as a mechanism of stress modulation. Resonant assaying of cantilevers fabricated from 200 nm-thick SiCN yielded root-modulus-over-density values of √(E/ρ) = 6.95 × 103 m/s and √(E/ρ) = 8.35 × 103 m/s, comparable to those of silicon.

Electron irradiation effects on DES/Ge(1 0 0) at 90 K

The effects of electron irradiation of diethylsilane-covered Ge(100) surfaces at 90K was studied by temperature programmed desorption (TPD), electron stimulated desorption (ESD), and Auger electron spectroscopy (AES). Adsorption of diethylsilane (DES) at 90K on Ge(100) results in thermal desorption of hydrogen at 570K from the substrate and at 635K a β-hydride elimination process which results in the removal of carbon species from the surface. The β-hydride elimination process leads to desorption of ethylene (mass 28) at 635K. A low temperature peak due to desorption of physisorbed DES is observed at 150K. After electron irradiation, two new high temperature hydrogen TPD peaks at 725 and 800K appear. In the case of ethylene, a new TPD peak is observed at 800K following electron irradiation of DES/Ge(100). ESD decay curves and kinetic energy distribution data show that hydrogen desorbs from at least two surface states while ethylene electronically desorbs from one state. Thermal desorption of DES from Ge(100) leads to accumulation of silicon on the surface up to a saturation level of 40% (atomic concentration). This result indicates that it is not possible to epitaxially grow silicon on germanium, due to diffusion of silicon into the germanium substrate. Electron irradiation of DES/Ge(100) leads to increasing amounts of carbon on the surface and no detectable changes in the surface concentration of silicon. This suggests that electron induced removal of ligands from silicon facilitates the migration of silicon into germanium.

Electron beam effects on diethylsilane‐covered Si(100) surfaces investigated by electron stimulated and temperature programmed desorption

AbstractThe effect of low‐energy electron irradiation on adsorbed layers of diethylsilane (DES) on the Si(100) surface at 100 K were studied using temperature programmed desorption (TPD) and electron stimulated desorption (ESD). As has been observed previously, TPD studies of adsorbed DES have shown desorption of both molecular hydrogen and ethylene. Adsorption of DES at 100 K also results in a loosely bound layer that desorbs molecularly at a temperature of ∼140 K. Strong evidence exists for thermal removal of ethylene from the surface during programmed heating via a β‐hydride elimination process. Irradiation of the dosed surface with electrons results in a number of interesting effects. Electron‐induced enhancement of both hydrogen and ethylene desorption from Si(100) is observed. In addition, both neutral and ionic desorption of surface species was observed, induced by electron irradiation. Desorption of neutral species having masses of 2, 15 and 28 indicate electron‐induced removal of hydrogen and ethylene, with a methyl group appearing as a result of ethylene dissociation. Hydrogen removal occurs from two distinct states, as identified by the decay of neutral hydrogen from the surface, characterized by two decay constants. Analysis of the energy of desorbing H+ species suggests two distinct kinetic energy distributions at 1.8 and 4.1 eV, which contribute to the desorption signal. Copyright © 2003 John Wiley & Sons, Ltd.

Electron beam effects on diethylsilane‐covered Si(100) surfaces investigated by x‐ray photoelectron spectroscopy

AbstractEthylated silanes and germanes are promising candidates for heterojunction atomic layer epitaxy of SiGe devices. However, thermal dissociation of unwanted ligands in the parent molecules usually is not suitable for device fabrication. Hence, alternative means for dissociation employing low thermal budgets are desirable. In this work, an electron beam was used to irradiate diethylsilane (DES)‐covered Si(100) surfaces at 100 K in order to initiate non‐thermal, electron‐driven dissociation and desorption processes in the adsorbed species. Clean Si(100) surfaces were dosed with gas‐phase DES molecules at 100 K followed by irradiation with 600‐eV electrons (current density 5.4 µAcm−2). The effects of electron irradiation were investigated by obtaining x‐ray photoelectron spectra before and after exposing the DES/Si(100) to the electron beam. Shifts in the binding energy of the C 1s photoelectron peak and a decrease in the total surface carbon concentration are indicative of dehydrogenation and removal of carbon species by electron irradiation. Our results suggest the possibility of electron‐beam‐assisted β‐hydride elimination at 100 K as one channel for surface carbon removal. Copyright © 2003 John Wiley & Sons, Ltd.

A comparative study of plasma enhanced chemically vapor deposited SiOH and SiNCH films using the environmentally benign precursor diethylsilane

The environmentally benign precursor diethylsilane (DES) was used with either N 2O or NH 3 to synthesize SiOH or SiNCH films by plasma enhanced chemical vapor deposition (PECVD). The growth rates were observed to decrease with higher temperature while increasing with total pressure. Oxide films with optimal properties were synthesized at a deposition temperature of 300 °C, total pressure of 0.3 Torr, DES flow rate of 15 sccm, and N 2O/DES flow rate ratio of 16. Comparative values of refractive index, stress, hardness and Young's modulus are presented as a function of processing variables and related to film density and resulting film compositions.

Numerical analysis of LPCVD of SiO2 films from diethylsilane/oxygen

A mathematical model has been developed to explore the low pressure chemical vapor deposition (LPCVD) of silicon dioxide from diethylsilane (DES)/oxygen in a horizontal hot-wall reactor. We propose a new kinetic mechanism that includes realistic gas-phase and surface reactions. The partial differential equations in two-dimensional cylindrical coordinates are solved numerically by a control-volume-based finite difference method. The model successfully describes the behavior of the experimental data. Film growth rate and uniformity are studied over a wide range of operating conditions including deposition temperature, pressure, reactant flow rate, and distance between the inlet and the wafer. The predicted results show that parasitic gas-phase reactions become significant at higher pressures and temperatures resulting in a decrease in deposition rate. It is seen that the deposition rate becomes a maximum at the O2/DES ratio of around 2.5. A temperature of 475‡C a pressure of 0.75 torr, and a total flow rate of 1,000 sccm are found to be desirable for obtaining both high deposition rate and good film uniformity.

Structure and orientation control of organopolysilanes and their application to electronic devices

Molecular structure and packing of various organopolysilanes having symmetrical side-chains of alkyl substituents, such as poly(di-methyl silane), poly(di-ethyl silane), poly(di-propyl silane), poly(di-butyl silane), poly(di-pentyl silane), and poly(di-hexyl silane), are examined, and the method of orientation control of the polysilane thin film is proposed. The application of the evaporated film to the electro-luminescent device is also demonstrated.

Thermochemistry of Gaseous Ethylsilanes and Their Radical Cations

The dissociation behavior of energy-selected tetraethylsilane, triethylsilane, and diethylsilane photocations is studied using the threshold photoelectron–photoion coincidence (TPEPICO) technique. In the 8–12.5 eV photon energy range, 0 K dissociation onsets have been measured from the TPEPICO data. The dissociation channels observed include loss of ethane, hydrogen molecule, ethyl radical and hydrogen atom, depending upon the molecular ion under investigation. The thermochemistry of the molecular ions and dissociation fragments is obtained by an analysis that takes into account the kinetics and internal energy distributions of the ions. The various dissociation onsets permit the reevaluation of both neutral and ionic silane thermochemistry. We observed 298-K ethyl group values of 60 ± 10 and 94 ± 10 kJ mol −1 for neutral and ionic silanes, respectively. These values are considerably smaller than the previously reported values of 86 and 130 kJ mol −1, respectively. Finally, a Δ f H° (298 K) of −141.5 ± 21 kJ/mol for neutral diethyl silane is derived from the dissociative ionization onset of diethylsilane.

Valence electronic structures of organopolysilanes having symmetric alkyl side-chains studied by x-ray photoelectron spectroscopy

The valence electronic structures of organopolysilanes having symmetrical alkyl side-chains, i.e., poly(di-n-alkyl silanes) , have been systematically studied by x-ray photoelectron spectroscopy (XPS) for the first time. The specimens used in this work are poly(di-methyl silane) , poly(di-ethyl silane) , poly(di-pentyl silane) , poly(di-hexyl silane) and poly(di-decyl silane) . By comparing the XPS spectra of the poly(di-n-alkyl silanes) with those of normal alkanes, it is found that the spectral features are strongly affected by two factors, i.e., the carbon 2s and 2p electrons in the side-chains and the silicon 3s and 3p electrons in the backbone. The shape of the spectrum from 0 to 5 eV, which is strongly affected by the structure of the valence band edge, shows no significant change with a change in the number of carbon atoms in the alkyl substituents. On the other hand, the splitting of the carbon 2s orbitals in the side-chains strongly affects the shape of the spectrum in the region from 12 to 20 eV. The results are also discussed on the basis of the theoretical calculations as well as the ultraviolet photoelectron spectrum reported previously.

A structural study of substituted polysilanes in the solid state by 29Si NMR

29Si spin-lock cross-polarization NMR measurements have been performed to characterize the solid structure of different polysilanes in the solid state. The polysilane samples are (1) symmetrically substituted polysilane derivatives, dimethyl (PDMS) and diethyl (PDES) derivatives, and (2) the copolymer formed from two symmetrically substituted monomers, PM-co-ES with dimethyl and diethyl silane units, and (3) the unsymmetric polysilane, poly(ethylmethylsilane) (PEMS). Finite perturbation theory calculations of the 29Si shielding constants within the CNDO/2 MO framework were carried out in order to understand and discuss the observed 29Si NMR chemical shifts. As a result, the conformation of PDMS takes small, statistical deviations from exact trans planarity as an increase of temperature. PDES takes one ordered phase at low temperature, with an increase of temperature takes disordered and ordered phases and then the temperature more increased, a transformation to more disordered (gauche rich conformation) phase occur slowly. For PM-co-ES, the 29Si chemical shift of the PDMS moiety is almost independent of temperature, while that of the PDES moiety gradually shifts downfield. The conformation of Si backbone for PEMS does not change almost during −70 to 120°C.

Microporous SiO2/Vycor membranes for gas separation

In this study, porous Vycor tubes with 40 Å initial pore diameter were modified using low pressure chemical vapor deposition (LPCVD) of SiO2. Diethylsilane (DES) in conjunction with O2 or N2O were used as precursors to synthesize the SiO2 films. Both “single side” (reactants flowing on the same side of porous membrane) and “counterflow” (reactants flowing on both sides of porous membrane) reactant geometries have been investigated. The flow of H2, He, N2, Ar, and toluene (C7H8) was monitored in situ after each deposition period. Membranes modified by the “single side” reactants geometry exhibited good selectivities between small and large molecules. However, cracking in these membranes after prolonged deposition limited the maximum achievable selectivity values. Higher selectivities and better mechanical stability were achieved with membranes produced using the “counterflow” reactants geometry. Pore narrowing rate was observed to increase with oxidant flow (O2 or N2O). For membranes prepared using both oxidants, selectivities on the order of 1000: 1 were readily attained for H2 and He over N2, Ar, and C7H8. As compared to O2, the use of N2O caused improvements in both the pore narrowing rate and N2: C7H8 selectivity. Membranes prepared using the “counterflow” geometry showed no signs of degradation or cracking after thermal cycling.

Adsorption and decomposition of diethylsilane and diethylgermane on Si(100): Surface reactions for an atomic layer epitaxial approach to column IV epitaxy

The room-temperature adsorption and desorption kinetics of diethylsilane (DES) and diethylgermane (DEG) on the Si(100)-(2×1) surface were investigated under ultrahigh vacuum using temperature programmed desorption, high resolution electron energy loss spectroscopy, and Auger electron spectroscopy. DES and DEG adsorb at room temperature in a self-limiting fashion, reaching saturation (0.4 and 0.3 monolayers, respectively), at exposures above 30 and 350 L, respectively. Temperature programmed desorption of the DES-saturated and DEG-saturated surfaces revealed only two species, hydrogen and ethylene, desorbing from either surface. In both systems, the hydrogen atoms desorbed primarily through the recombinative desorption of monohydride species, while the ethyl groups decomposed via β-hydride elimination and subsequently desorbed as ethylene. The hydrogen desorption peak temperature was 794 K for the DES-saturated surface and 788 K for the DEG-saturated surface. The desorption peak temperature for ethylene was significantly lower in the DEG/Si(100) system (700 K) than in the DES/Si(100) system (730 K) because of a lower activation energy and higher pre-exponential factor for β-hydride elimination from DEG-dosed Si(100). High resolution electron energy loss spectra of the DEG-saturated surface support an adsorption mechanism in which the ethyl groups remain bonded to the incoming germanium atom throughout the adsorption process.

Plasma enhanced chemical vapor deposition of Si-N-C-H films from environmentally benign organosilanes

The environmentally benign precursors diethylsilane (DES) and di-t-butylsilane were used with NH 3 to synthesize hydrogenated silicon carbonitride films by plasma enhanced chemical vapor deposition. The growth kinetics and film properties were examined as a function of deposition temperature, pressure, and NH 3/organosilane ratio. The growth rate was observed to decrease with higher temperature and higher NH 3/organosilane ratio while increasing with higher total pressure. Values of index of refraction, stress, hardness, and Young's modulus were measured as a function of processing variables and related to film density and resulting film compositions. Oxidation of the films was noted to occur at low deposition temperatures, low NH 3/ organosilane ratios, and high pressures. Carbon was present in all deposits and decreased slightly with higher NH 3/organosilane flow ratios.

Surface chemistry of diethylsilane and diethylgermane on Ge(100)

The adsorption and desorption kinetics of diethylsilane (DES) and diethylgermane (DEG) on a Ge(100) (2×1) surface have been studied using temperature-programmed desorption (TPD), Auger electron spectroscopy (AES), and high-resolution electron energy-loss spectroscopy. DES and DEG adsorb at room temperature in a self-limiting fashion. Data indicate that both precursors dissociatively chemisorb, producing a hydrogen- and ethyl-terminated surface. TPD of DES-saturated and DEG-saturated surfaces revealed only two desorbing species, ethylene and hydrogen. The ethylene signal results from the decomposition of the ethyl groups via β-hydride elimination, with a desorption peak temperature of ∼616 K for both precursors. The hydrogen TPD spectra were also similar for both precursors and consisted of two peaks: a low-temperature peak corresponding to hydrogen desorption from the monohydride state and a high-temperature peak corresponding to desorption of hydrogen produced by β-hydride elimination of the ethyl groups. Using the total hydrogen TPD peak area, DES saturation exposure (30 langmuir) led to 0.42 ML Si atom coverage and DEG saturation exposure (30 langmuir) led to 0.35 ML Ge atom coverage, assuming complete β-hydride elimination of the ethyl groups. 0.44 ML of Si was measured by AES following saturation DES exposure. No carbon contamination of the Ge surface was detected by AES for up to four exposure and TPD cycles of either DES or DEG.

Surface chemistry of diethylsilane and diethylgermane on Si(100): An atomic layer epitaxy approach

The surface chemistry of diethylsilane (DES) and diethylgermane (DEG) on the Si(100) surface was studied using high-resolution electron-energy-loss spectroscopy and temperature programmed desorption. High-resolution electron-energy-loss spectra indicate that the precursors chemisorbed dissociatively as (C2H5)2MHx(ad) and (2−x)H(ad) [x=0,1; M=Si or Ge] groups at room temperature and that the ethyl groups remain bonded to the precursor Si or Ge. Thermal annealing of DEG covered surfaces indicated that the ethyl groups remain attached to Ge at least up to the desorption temperature. Ethyl ligands react to form ethylene via a β-hydride elimination pathway. The ethylene desorption peak temperature from DEG dosed surfaces was approximately 40 K lower than that from DES dosed surfaces (733 K). We propose that ethylene desorbs from Ge atoms rather than from Si surface atoms. The hydrogen remaining on the surface after ethylene desorption desorbs from the β1 state, with peak maxima at 810 and 780 K for DES/Si(100) and DEG/Si(100), respectively.