In this study, the effects of tetraethyl orthosilicate (TEOS) plasma parameters on the silicon dioxide deposition mechanisms are studied. The films are deposited by the organometallic based plasma ...enhanced chemical vapour deposition method. The plasma generator is capacitively coupled radio frequency power source. The plasma is the mixture of organometallic TEOS vapour, oxygen and argon. The effects of the TEOS/O2 pressure ratio (0.05–1.5), the applied power (100–400W) and the argon gas percentage into the plasma (0–20) on the quality of the film are investigated. The film properties such as structure and chemical composition, surface topography are analysed by Fourier transform infrared spectroscopy and atomic force microscopy. In addition, the relation between the mechanism of deposition phenomenon and the process parameters is studied. It is found that in the deposition process the oxidation and the electron impact mechanisms determine the film characteristics as they can be controlled by adjusting the TEOS/O2 pressure ratio, applied power and argon gas percentage.
•SiO2 film was deposited at low temperature by TEOS based plasma enhanced CVD method.•The correlation of the parameters and the deposition mechanisms was investigated.•We found a good agreement in AFM and FTIR results through full series of parameters.•Finally some proofs were recommended to describe the structural and chemical results.
The Planck theory of blackbody radiation imposes a limit on the maximum radiative transfer between two objects at given temperatures. When the two objects are close enough, near-field effects due to ...tunneling of evanescent waves lead to enhancement of radiative transfer above the Planck limit. When the objects can support electromagnetic surface polaritons, the enhancement can be a few orders-of-magnitude larger than the blackbody limit. In this paper, we summarize our recent measurements of radiative transfer between two parallel silica surfaces and between a silica microsphere and a flat silica surface that show unambiguous evidence of enhancement of radiative transfer due to near-field effects above the Planck limit.
We have investigated the crystallization process of silicon quantum dots (QDs) imbedded in hydrogenated amorphous Si-rich silicon carbide (a-SiC:H) films. Analysis reveals that crystallization of ...silicon QDs upon thermal annealing of the samples can be explained in terms of bonding configuration and evolution of microstructure. The precursor gases were dissociated via electron impact reactions in the plasma-enhanced chemical vapor deposition, where the hydrogenated silicon radicals and reactive SiHn species lead to the formation of primary Si nuclei. With increasing annealing temperature, the breaking of SiHn bonds and decomposition of Si-rich SiC were progressively enhanced, allowing the formation of crystalline silicon QDs inside the a-SiC:H matrix. The results help clarify a probable mechanism for the growth of silicon QDs and provide the possibility to optimize the microstructure of silicon QDs in a-SiC:H films.
•Si-rich SiC samples are grown by plasma-enhanced chemical vapor deposition.•Silicon radicals and reactive SiHn (n=1,2,3) exist in the as-grown samples.•Annealing temperature induces the growth of crystalline silicon quantum dots.•Carbon atoms are incorporated in the formation of SiC and CH bonds in the matrix.
The UV photooxidation of 2-butanone on TiO2(110) was studied using pump–probe laser methods and time-of-flight (TOF) mass spectrometry to identify the gas-phase photoproducts and probe the dynamics ...of the photofragmentation process. A unique aspect of this work is the use of coherent VUV radiation for single-photon ionization detection of gas-phase products, which significantly reduces the amount of parent ion fragmentation as compared to electron impact used in previous studies. The pump–probe product mass spectra showed ions at mass 15 (CH3 +) and mass 29 (C2H5 +), which are associated with the primary α-carbon bond cleavage of the adsorbed butanone–oxygen complex, as well other C2H x + (x = 2–4) fragments, which could originate from ethyl radical secondary surface chemistry or dissociative ionization. Using two different VUV probe energies, it was possible to show that the fragment ions at mass 27 (C2H3 +) and mass 28 (C2H3 +) are not due to secondary reactions of ethyl radicals on the surface, but rather from dissociative ionization of the ethyl radical parent ion (mass 29). Another photoproduct at mass 26 (C2H2 +) peak is also observed, but its pump–probe delay dependence indicates that it is not associated with nascent ethyl radicals. Pump-delayed-probe measurements were also used to obtain translational energy distributions for the methyl and ethyl radical products, both which can be empirically fit to “fast” and “slow” components. The ethyl radical energy distribution is dominated by the “slow” channel, whereas the methyl radical has a much larger contribution from “fast” fragments. The assignment of the C2H x (x = 3, 4) fragments to ethyl (C2H5) dissociative ionization was also confirmed by showing that all three products have the same translational energy distributions. The origin of the “fast” and “slow” fragmentation channels for both methyl and ethyl ejection is discussed in terms of analogous neutral and ionic fragmentation processes in the gas phase. Finally, we consider the possible energetic and dynamical origins of the higher yield of ethyl radical products as compared to that for methyl radicals.
► The surface integrity changes induced by LEHCPEBTs were investigated. ► The hardness was determined by nanoindention method. ► The modification mechanism for LEHCPEBTs was proposed. ► There is no ...new phase but dislocation and fine grains in modified surface layer.
Surface integrity changes of TA2 pure titanium including surface topography, microstructure and nanohardness distribution along surface layer were investigated by different techniques of low energy high current pulsed electron beam treatments (LEHCPEBTs). The surface topography was characterized by SEM. Moreover, the TEM observation and X-ray diffraction analysis were performed to reveal the surface modification mechanism of TA2 pure titanium by LEHCPEBTs. The surface roughness was modified by electron beam treatment and the polishing mechanism was analyzed by studying the cross section microstructure of electron beam treated specimens by SEM and TEM. The results show that the surface finish obtains good polishing quality and there is no phase transformation but the dislocations by LEHCPEBT. Furthermore, the nanohardness in the surface modified layer is improved. The remelt and fine-grain microstructure of surface layer caused by LEHCPEBTs are the main polishing mechanism and the reason of modification of surface topography and the increment in nanohardness is mainly due to the dislocations and fine grains in the modified layer induced by LEHCPEBT.
An analytical expression is derived for the electron thermionic current from heated metals by using a non equilibrium, modified Kappa energy distribution for electrons. This isotropic distribution ...characterizes the long high energy tails in the electron energy spectrum for low values of the index
κ
and also accounts for the Fermi energy for the metal electrons. The limit for large
κ
recovers the classical equilibrium Fermi-Dirac distribution. The predicted electron thermionic current for low
κ
increases between four and five orders of magnitude with respect to the predictions of the equilibrium Richardson-Dushmann current. The observed departures from this classical expression, also recovered for large
κ
, would correspond to moderate values of this index. The strong increments predicted by the thermionic emission currents suggest that, under appropriate conditions, materials with non equilibrium electron populations would become more efficient electron emitters at low temperatures.
Cobaltic protoporphyrin IX (CoPP) was grafted on GaAs(100), Si(111), and highly oriented pyrolytic graphite, HOPG(0001), surfaces using different preparation conditions. Modified surfaces were ...characterized by X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS) recorded in vibrational and electronic domains. XPS confirms the adsorption of the porphyrin on all of the substrates through its main fingerprint, the photoelectron Co 2p region. HREELS spectra also attest to the presence of CoPP on the substrates. The presence of oxides is also clearly detected. Analysis of the corresponding cross sections confirms that vibration excitations are mostly produced via an electron impact mechanism. Analysis of the electronic domain allowed observation of the Q, Soret, N, and C bands present in UV/vis spectra. Quantitative results for relative differential cross sections of vibrational and electronic excitations suggest that negative-ion resonances may play a role in the excitation.
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