Effects of Hydrogen Coverage on Silicon Surface Reactivity

1992 ◽  
Vol 259 ◽  
Author(s):  
A.C. Dillon ◽  
M.B. Robinson ◽  
S.M. George ◽  
P. Gupta
Keyword(s):  
Porous Silicon ◽  
Silicon Surface ◽  
High Surface ◽  
Surface Cleaning ◽  
Surface Reactivity ◽  
Silicon Surfaces ◽  
Initial Surface ◽  
Hydrogen Passivation ◽  
Surface Species ◽  
Oxidation Rates

ABSTRACTHydrogen passivation of silicon surfaces plays an important role in silicon surface cleaning and preparation. To measure the effect of hydrogen passivation on silicon surface reactivity, Fourier transform infrared (FTIR) transmission spectroscopy was used to monitor the oxidation of silicon surfaces versus hydrogen coverage. Experiments were performed insitu in an ultrahigh vacuum (UHV) chamber using high surface area poroussilicon samples. Si-H stretching and bending vibrations and Si-O-Si stretching vibrations were employed to monitor the silicon surface species. Oxidation studies with O2 conducted versus various initial hydrogen coverages revealed that oxidation rates and apparent oxygen saturation levels on porous silicon decreased as a function of initial surface hydrogen coverage. Exceptional surface stability was observed when the porous silicon surface was passivated by both monohydride and dihydride surface species. In addition, new blue-shifted Si-H stretching and bending features were observed following the oxidation of partially hydrogen-passivated porous silicon which indicated the presence of Ox SiH species. Thermal annealing studies revealed that the thermal stability of these OxSiH species increased with increasing oxidation of the silicon surface. These results have important implications for silicon growth and surface cleaning because they indicate that hydrogen removal is more difficult when the silicon surface is contaminated with oxygen. These FTIR results have also been compared with earlier results of oxidation versus hydrogen coverage on Si(111) 7×7.

Decomposition of Alkylsilanes on Silicon Surfaces Using Transmission Ftir Spectroscopy

1991 ◽  
Vol 222 ◽  
Author(s):  
A. C. Dillon ◽  
M. B. Robinson ◽  
M. Y. Han ◽  
S. M. George
Keyword(s):  
Porous Silicon ◽  
Silicon Surface ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Layer ◽  
Silicon Surfaces ◽  
Surface Species ◽  
Reaction Products ◽  
Molecular Precursors ◽  
Hydride Elimination

ABSTRACTFourier transform infrared (FTIR) transmission spectroscopy was used to monitor the decomposition of alkylsilanes such as diethylsilane (DES) [(CH3 CH2)2SiH2], di-t-butylsilane (DTBS) [((CH3)3C)2SiH2] and ethylsilane (ES) [CH3CH2SiH3 on high-surface-area porous silicon samples. The FTIR spectra revealed that tKe akylsilanes dissociatively adsorb on porous silicon at 300 K to form SiH and Si-alkyl species. As the silicon surface was progressively annealed, the Si-alkyl species decomposed and produced gas phase ethylene (DES,ES) or isobutylene (DTBS). The decomposition of the alkyl group was accompanied by the growth of additional SiH surface species. These reaction products were consistent with a [β-hydride elimination reaction. Above 700 K, the SiH surface species decreased concurrently with the desorption of H2 from the porous silicon surface. The uptake of surface species was also monitored at various adsorption temperatures to determine the optimal exposure temperatures for carbon-free silicon deposition. Carbon contamination was not detected at adsorption temperatures below 640 K prior to H2 desorption. Because the alkylsilane adsorption process is self-limiting at temperatures below 640 K, alkylsilanes may be useful molecular precursors for the atomic layer epitaxy (ALE) of silicon.

Ftir Studies of Water and Ammonia Decomposition on Silicon Surfaces

1990 ◽  
Vol 204 ◽  
Author(s):  
A.C. Dillon ◽  
P. Gupta ◽  
M.B. Robinson ◽  
A.S. Bracker ◽  
S.M. George
Keyword(s):  
Silicon Surface ◽  
Silicon Oxide ◽  
High Surface ◽  
High Vacuum ◽  
High Surface Area ◽  
Ftir Spectra ◽  
Ultra High Vacuum ◽  
Silicon Surfaces ◽  
Surface Species ◽  
Surface Hydrogen

ABSTRACTFourier transform infrared (FTIR) transmission spectroscopy. was used to monitor the decomposition of H2O (D2O) and NH3(ND3) on silicon surfaces. Experiments were performed in-situ in an ultra-high vacuum (UHV) chamber using high surface area poroussilicon samples. The FTIR spectra revealed that H2O dissociates upon adsorption at 300K to form SiH and SiNH2 surface species. NH3 also issociates upon adsorption at 300 K to form SiH and SiOH2 species. Silicon samples with saturation exposures of H2O and NH3 were progressively annealed from 300 K to 860 K. The FTIR spectra of an H2O-saturated silicon surface revealed that the SiOH species decomposed to form a silicon oxide species and additional surface hydrogen between 460 K and 580 K. Likewise, the SiNH2 species decomposed between 540 K and 660 K to produce silicon nitride and additional surface hydrogen. In both cases, the Sill surface species decreased as H2 desorption from the silicon surface was observed above 700 K.

Comparison of Trichlorosilane and Trichlorogermane Decomposition on Silicon Surfaces Using FTIR Spectroscopy

1992 ◽  
Vol 282 ◽  
Author(s):  
A. C. Dillon ◽  
M. B. Robinson ◽  
S. M. George
Keyword(s):  
Porous Silicon ◽  
High Surface ◽  
High Vacuum ◽  
Atomic Layer ◽  
Layer Growth ◽  
Ultra High Vacuum ◽  
Silicon Surfaces ◽  
Absorption Feature ◽  
Surface Species ◽  
Thermal Stabilities

ABSTRACTFourier transform infrared (FTIR) transmission spectroscopy was used to compare the decomposition of trichlorosilane (SiHCl3) and trichlorogermane (GeHCl3) on silicon surfaces. Chlorosilanes, such as SiHCl3 are employed in silicon chemical vapor deposition (CVD). Chlorosilanes and chlorogermanes are also possible molecular precursors for the controlled atomic layer growth of silicon and germanium. GeHCl3 may be useful for the deposition of germanium on silicon surfaces and the growth of Si1−xGex heterostructures. The FTIR studies were performed in-situ in an ultra-high vacuum chamber on high surface area, porous silicon samples. The FTIR spectra revealed that SiHCl3 dissociatively adsorbs at 200 K to form SiH, SiClx, ClSiH and Cl2SiH surface species. The presence of ClxSiH species is revealed by ClxSiH stretching (2196 cm−1) and bending (775, 744 cm−1) vibrations. The presence of these modes indicates that there is incomplete decomposition of SiHCl3 upon adsorption at 200 K. GeHCl3 also dissociatively adsorbs at 200 K to form SiH and SiClx species. An infrared absorption feature in the Ge-H stretching region (1970–1995 cm−1) was not detected in the FTIR spectrum. The absence of a Ge-H absorption feature argues that there is a complete transfer of hydrogen from germanium to surface silicon atoms at 200 K. The thermal stabilities of the surface species were studied with annealing experiments. The Clx SiH formed upon initial SiHCl3 exposures at 200 K were observed to decompose between 200–590 K and form additional surface SiH and SiCl species. For both GeHCl3 and SiHCl3 dissociative adsorption on porous silicon, the SiCL. (x = 2 or 3) surface species were converted to silicon monochloride surface species between 200–600 K. In addition, SiH surface species were lost upon annealing between 680–780 K as H2 desorbed from the surface. The adsorption kinetics of SiHCl3 and GeHCl3 were also monitored on porous silicon at various isothermal temperatures. These experiments provide insight into the surface chemistry of chlorosilanes and chlorogermanes during CVD and atomic layer controlled growth.

Germanium Deposition on Silicon: Surface Chemistry of (CH3CH2)2GeH2 and GeC14

1992 ◽  
Vol 282 ◽  
Author(s):  
P. A. Coon ◽  
M. L. Wise ◽  
A. C. Dillon ◽  
S. M. George
Keyword(s):  
Porous Silicon ◽  
Surface Chemistry ◽  
Silicon Surface ◽  
Atomic Layer ◽  
Silicon Surfaces ◽  
Desorption Kinetics ◽  
Surface Species ◽  
Adsorption And Desorption ◽  
Controlled Deposition ◽  
Sticking Coefficients

ABSTRACTDiethylgermane, (CH3CH2)2GeH2, and germanium tetrachloride, GeCl4 may be useful precursors for chemical vapor deposition (CVD) or atomic layer controlled deposition of germanium. To explore the surface chemistry of these alternative precursors, the adsorption and desorption kinetics of (CH3CH2)2GeH2 (DEG) and GeCl4 on Si(111) 7×7 have been examined using laser-induced thermal desorption (LITD), and temperature programmed desorption (TPD) techniques. Fourier transform infrared (FTIR) spectroscopy has also been employed to monitor the decomposition of DEG on porous silicon surfaces. The FTIR spectra revealed that DEG dissociatively adsorbs on porous silicon surfaces at 200 K to form SiH, GeH, and SiCH2CH3 surface species. No spectral features were observed for GeCH2CH3 surface species. The TPD studies following DEG exposures on Si(111) 7×7 observed CH2=CH2 and H2 desorption products at 700 and 800 K, respectively. The production of CH2=CH2 (ethylene) was consistent with a βhydride elimination mechanism from surface ethyl species, i.e. SiCH2CH3(ad) → SiH(ad) + CH2=CH2 (g). Similar TPD experiments following GeCl4 exposures monitored the desorption of only SiCl2 at approximately 920 K. Desorption of SiCl2 indicates that the chlorine on GeCl4 has transferred to the silicon surface. Atomic Ge was also observed to desorb at 1200 K following both DEG and GeCl4 adsorption. LITD experiments measured initial reactive sticking coefficients of So ∼0.05 for DEG and So ∼1.0 for GeCl4 at 200 K. As expected from a precursor-mediated adsorption model, the sticking coefficients decreased versus increasing surface temperature. The sticking coefficients for these germanium containing precursors were higher than the corresponding sticking coefficients for (CH3CH2)2SiH2 and SiCl4. Possible recipes for the CVD or atomic layer controlled deposition of germanium on silicon can be proposed based on the surface chemistry and adsorption and desorption kinetics for DEG and GeCl4.

Functionalized Porous Silicon in a Simulated Gastrointestinal Tract: Modeling the Biocompatibility of a Monolayer Protected Nanostructured Material

2007 ◽  
Vol 1063 ◽  
Author(s):  
Daniel S. Albrecht ◽  
Jacob T. Lee ◽  
Nick Molby ◽  
Steven D. Rhodes ◽  
Hieu Minh Dam ◽  
...  
Keyword(s):  
Gastrointestinal Tract ◽  
Porous Silicon ◽  
High Surface ◽  
High Surface Area ◽  
Surface Oxidation ◽  
Nanostructured Material ◽  
Synthetic Methods ◽  
Silicon Surfaces ◽  
Ambient Conditions ◽  
Chemical Attack

ABSTRACTOwing to its photoluminescent properties and high surface area, porous silicon (por-Si) has shown great potential toward a myriad of applications including optoelectronics, chemical sensors, biocomposite materials, and medical implants. However, the native hydride-termination is only metastable with respect to surface oxidation under ambient conditions. Por-Si samples oxidize and degrade even more quickly when exposed to saline aqueous environments. Borrowing from solution phase synthetic methods, a selection of hydrosilylation reactions has been recently reported for functionalizing organic groups onto oxide-free, hydride-terminated porous silicon surfaces. Monolayers, bound through direct silicon-carbon bonds, are produced via thermal, microwave, Lewis acid, and carbocation mediated pathways. All of these wet, benchtop methods result in the formation of stable monolayers which protect the underlying silicon surface from ambient oxidation and chemical attack. However, no direct comparison of monolayer stability resulting from these diverse mechanisms has been reported. A variety of alkyl monolayers were prepared on porous silicon using the diverse hydrosilylation routes describe above and then immersed into a sequence of simulated gastric and intestinal fluids to replicate the conditions of potential por-Si biosensors or medicinal delivery systems in the human gastrointestinal tract. Degradation of the organic monolayers and oxidation of the underlying por-Si surfaces were monitored using both qualitative and semiquantitative transmission mode Fourier transform infrared spectroscopy (FTIR). Our initial results indicate that methods employing chemical catalysts often incorporate these species within the monolayer as defects, producing less robust surfaces compared to catalyst-free reactions. Regardless, monolayer protected por-Si samples demonstrated superior durability as opposed to the unfunctionalized controls.

Anhydrous Hf Processing as an Alternative to Hf/Water Processes

1996 ◽  
Vol 447 ◽  
Author(s):  
J. Staffa ◽  
P. Roman ◽  
K. Chang ◽  
K. Torek ◽  
J. Ruzyllo
Keyword(s):  
Water Treatment ◽  
Gas Phase ◽  
Water Consumption ◽  
Hydrofluoric Acid ◽  
Silicon Surface ◽  
Water Solution ◽  
Surface Cleaning ◽  
Silicon Surfaces ◽  
Ultrapure Water

AbstractThe HF/water treatment of silicon surfaces is among the most frequently applied steps in surface cleaning processes. It is utilized for clearing oxides from the silicon surface. Large amounts of ultrapure water are necessary to carry out this operation, both in the HF/water solution itself and the thorough rinse which must follow HF/water processes. Therefore, a gas‐phase alternative to this process would significantly reduce deionized (DI) water consumption. The focus of this paper is the anhydrous hydrofluoric acid (AHF)/alcoholic solvent process which has shown promise as an alternative to the aqueous HF process. In particular, the AHF/methanol process has been studied extensively. This paper presents a comparison between properties of silicon surfaces prepared through the dilute HF/water (dHF) process and those of surfaces prepared through AHF/alcoholic solvent processes.

FTIR Studies of H2O and D2O Decomposition on Porous Silicon Surfaces

1990 ◽  
Author(s):  
P. Gupta ◽  
A. C. Dillon ◽  
A. S. Bracker ◽  
S. M. George
Keyword(s):  
Porous Silicon ◽  
Silicon Surfaces ◽  
Ftir Studies

Angular Ellipsometry of Porous Silicon Surface Layers

2020 ◽  
Vol 12 (3) ◽  
pp. 03024-1-03024-4
Author(s):  
L. V. Poperenko ◽  
◽  
S. G. Rozouvan ◽  
I. V. Yurgelevych ◽  
P. O. Lishchuk ◽  
...  
Keyword(s):  
Porous Silicon ◽  
Silicon Surface ◽  
Surface Layers ◽  
Porous Silicon Surface

Recent Advances in Application of Azobenzenes Grafted on Mesoporous Silica Nanoparticles in Controlled Drug Delivery Systems Using Light as External Stimulus

2020 ◽  
Vol 20 (11) ◽  
pp. 1001-1016
Author(s):  
Sandra Ramírez-Rave ◽  
María Josefa Bernad-Bernad ◽  
Jesús Gracia-Mora ◽  
Anatoly K. Yatsimirsky
Keyword(s):  
Drug Delivery ◽  
Mesoporous Silica ◽  
Silica Nanoparticles ◽  
Drug Delivery Systems ◽  
Mesoporous Silica Nanoparticles ◽  
High Surface ◽  
Delivery Systems ◽  
Surface Reactivity ◽  
External Stimulus ◽  
Recent Advances

Hybrid materials based on Mesoporous Silica Nanoparticles (MSN) have attracted plentiful attention due to the versatility of their chemistry, and the field of Drug Delivery Systems (DDS) is not an exception. MSN present desirable biocompatibility, high surface area values, and a well-studied surface reactivity for tailoring a vast diversity of chemical moieties. Particularly important for DDS applications is the use of external stimuli for drug release. In this context, light is an exceptional alternative due to its high degree of spatiotemporal precision and non-invasive character, and a large number of promising DDS based on photoswitchable properties of azobenzenes have been recently reported. This review covers the recent advances in design of DDS using light as an external stimulus mostly based on literature published within last years with an emphasis on usually overlooked underlying chemistry, photophysical properties, and supramolecular complexation of azobenzenes.

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