Application of organic monolayers formed on Si(1 1 1): possibilities for nanometer-scale patterning (2023)

Monolayers of organic adsorbates formed on Si wafers are prospective materials for nanometer-scale fabrication, chemical functionalization and biochemical analysis. We have been studying the methods of preparing organic monolayers by activating hydrogen-terminated H:Si(111). In this report, the method of photo-assisted adsorption of allylamine (CH₂CH–CH₂–NH₂) and 1-butene (CH₂CH–CH₂–CH₃) onto H:Si(111) is described. The adsorbates were identified by high-resolution electron energy loss spectroscopy and Auger electron spectroscopy. The functional group, NH₂ in allylamine, was observed reserved in the adlayer. Mixed adlayers of allylamine and 1-butene, which is practically favorable, were also prepared.

The covalent attachment of alkyl groups to silicon surfaces, via carbon–silicon bond formation, has been attempted using gas-surface reactions starting from Cl-terminated Si(111) or H:Si(111) under ultraviolet light irradiation. The formation of Cl-terminated Si(111) and its resulting stability were examined prior to deposition of organic molecules. High-resolution electron energy loss spectroscopy (HREELS) was utilized for detecting surface-bound adsorbates. The detection of photo-deposited organic species on Cl:Si(111) from gas-phase CH₄ or CH₂CH₂ was not significant. On H:Si(111), it was evident that after the photoreaction with gas-phase C₂H₅Cl, C₂H₅ groups were chemically bonded to the surface Si atoms through single covalent bonds. The C₂H₅ groups were thermally stable at temperatures below 600K. Alkyl monolayers prepared on silicon surfaces by dry process will lead to a new prospective technology of nanoscale fabrication and biochemical applications.

The recent topics of our researches concerned with the electrochemical fabrication process of highly functionalized metal thin films and minute structures are reviewed. We present three topics; the soft magnetic materials of Co alloys by electro- and electroless-plating, the micro-dot formation by Ni electroless deposition, and fabrication of barrier layer on SiO₂ by electroless deposition for ULSI technology. The magnetic property of electrodeposited CoNiFe film was deteriorated by the co-deposition of a small amount of sulfur, whereas the carbon co-deposition improved resistivity of the film. The electroless soft magnetic materials were also proposed for future extremely high-density recording system. As the fine dot formation, the electroless deposition processes for producing fine metal structures were demonstrated. For advanced nano-scale patterning technology, an organic monolayer directly grafted to the Si surface was applied to a novel process of selective metal deposition. Another type of organic monolayer, a self-assembled monolayer of organosilane, was also utilized as an adhesive/catalytic layer for fabrication of a diffusion barrier layer on SiO₂ for future ULSI technology.

Angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) of a Si(111) surface regularly terminated by methyl groups is reported. The electrochemical methylation was performed in inert atmosphere. The cleanliness and 1×1 ordering of the surface were confirmed by Auger electron spectroscopy and reflection high-energy electron diffraction, respectively. The energy band diagram has been obtained from ARUPS and each energy level was assigned from the comparison with the results of hydrogen-terminated Si(111) and quantum chemical cluster calculation.

A process of electron-beam patterning of the surface of a Si(111) wafer was developed by utilizing alkyl monolayers as ultrathin patterning media. We performed chemical benchmark tests of the electron-beam patterning of alkyl monolayers on Si(111) in ambient oxygen, followed by the deposition of a metal on bombarded areas by immersion into an aqueous solution containing metal ions of the metal to be deposited. We investigated practically important issues related to this process, such as the robustness of organic monolayers against oxidation in aqueous media, the contrast enhancement of the bombarded areas by metal deposition, and the detectability of electron-bombarded areas of the monolayers by scanning tunneling microscopy (STM). The alkyl-covered Si(111) surface was significantly resistant to the oxidation by dissolved O₂ in pure water, compared to hydrogen-terminated Si(111). By immersion into a solution containing CuSO₄+HF+NH₄F, electron-bombarded areas were visualized by the presence of the deposit of Cu. Electron-bombarded areas were also distinguishable from intact areas in terms of height contrast or roughness measured by STM. These results indicate the usefulness of alkyl monolayers for nano-scale patterning on silicon wafers.

Fluid Phase Equilibria, Volume 388, 2015, pp. 50-58

The first public version of TernAPI (ternary diagrams assessment programming interface) software package for ternary phase diagrams calculation by the convex hull method has been developed. Its reliability and efficiency have been proved on a large set of systems of different kind: organic liquids and fluids mixtures, water solutions, salts, oxides, metallic alloys. A remarkable advantage of TernAPI is a stable work in the case of isolated miscibility gaps (“islands”) described by a uniform Gibbs energy surface equation. It also contains several improvements of phase diagram calculation algorithm, a new module for x–T diagrams polythermal sections calculation and possibility of optimization of thermodynamic models parameters. NRTL model parameters for the acetic acid–N,N-dimethylformamide–cyclohexene ternary system have been optimized in this work. The specialized language based on Ruby and YAML is used for the description of thermodynamic models of phases.

European Journal of Medicinal Chemistry, Volume 152, 2018, pp. 1-9

The synthesis and characterization of two new sets of arylsulfonehydrazone benzenesulfonamides (4a-4i with phenyl tail and 4j-4q with tolyl tail) are reported. The compounds were designed according to a dual-tails approach to modulate the interactions of the ligands portions at the outer rim of both hydrophobic and hydrophilic active site halves of human isoforms of carbonic anhydrase (CA, EC 4.2.1.1). The synthesized sulfonamides were evaluated invitro for their inhibitory activity against the following human (h) isoforms, hCA I, II, IV and IX. With the latter being a validated anticancer drug target and a marker of tumor hypoxia, attractive results arose from the Compounds' inhibitory screening in terms of potency and selectivity. Indeed, whereas the first subset of compounds 4a-4i exhibited great efficacy in inhibiting both the ubiquitous, off-target hCA II (K_Is 9.5–172.0 nM) and hCA IX (K_Is 7.5–131.5 nM), the second subset of tolyl-bearing derivatives 4j-4q were shown to possess a selective hCA IX inhibitory action over isoforms I, II and IV. The most selective compounds 4l and 4n were further screened for their invitro cytotoxic activity against MCF-7 and MDA-MB-231 cancer cell lines under hypoxic conditions. The selective IX/II inhibitory trend of 4j-4q compared to those of compounds 4a-4i was unveiled by docking studies. Further exploration of these molecules could be useful for the development of novel antitumor agents with a selective CA inhibitory mechanism.

Electrochimica Acta, Volume 408, 2022, Article 139934

Electrocatalytic reduction of N₂ to ammonia (NH₃) at ambient conditions has attracted widespread attention, and revealing the mechanism has been a remarkably challenging problem for decades. This work developed a low-cost and efficient multiple heteroatom codoped porous carbon catalyst from municipal sludge (MSB-P), which demonstrated excellent electrochemical stability and selectivity for the electrochemical N₂ reduction reaction (N₂RR). In 0.1mol/L HCl solution, a high NH₃ yield rate of 35.76µg.h⁻¹.mg⁻¹_cat. and an excellent Faraday Efficiency (FE) of 7.79% at -0.7V vs. RHE (reversible hydrogen electrode) were obtained under ambient conditions. Furthermore, the electrocatalytic mechanism of MSB-P for N₂RR was also revealed by in situ Fourier transform infrared spectroscopy (FTIR) data, and an associative route was identified. These findings provide an exciting new method for fabricating inexpensive and efficient carbon-based catalysts for production of NH₃ at ambient conditions.

Food Chemistry, Volume 300, 2019, Article 125188

An effective, simple and sensitive analytical method has been developed employing liquid chromatography coupled with tandem mass spectrometry and validated for estimation of five organophosphate pesticides at trace levels in six fruits and twelve vegetables. Plackett-Burman design and central composite design was used to screen and optimize the significant factors in modified QuEChERS (quick, easy, cheap, effective, rugged and safe) extraction method. The method evaluation was done by matrix-matched calibration with linearity ranging from 5 to 500 µg/L with a correlation coefficient more than 0.990. The detection and quantification limit ranged from 0.1 to 1.0 µg/kg and 0.5 to 5 µg/kg, respectively. The mean recoveries were in the range of 76.89–110.30 % with the relative standard deviation less than 13.26% for all pesticides. Further, the method developed was applied to analyze real samples cultivated in the hill areas of Nilgiris, South India.

Electrochimica Acta, Volume 258, 2017, pp. 353-359

Three nickel (II) complexes of o-phenylenebis(N′-methyloxamidate) (L¹), o-phenylene(N′-methyloxamidate)oxamate (L²) and o-phenylenebis(oxamate) (L³) with tetradentate ligands are synthesized and characterized. These four-coordinate complexes, (Me₄N)₂[NiLⁱ] (i=1–3 for complex 1–3), are investigated for electrocatalytic water oxidation in basic phosphate buffer solution. Experimental results show that (Me₄N)₂[NiL¹] (1) is a homogeneous catalyst for electrochemical water oxidation. However, under the same condition, 2 and 3 decompose into NiO_x nanoparticles, which acts as precatalyst for the electrocatalytic water oxidation. The catalytic mechanism for electrocatalytic water oxidation by 1 is proposed using cyclic voltammetry experiments, kinetic isotope effect and Pourbaix diagram. By constructing the relationship between the molecular structure and stability of these catalysts, nitrogen atom is found to be more beneficial than carboxyl group for the stability of nickel based homogeneous electrochemical water oxidation catalysts.

Food Chemistry, Volume 310, 2020, Article 125928

The objective of this study was to simultaneously obtain protein isolates and lipids from the dried powder of large yellow croaker (Pseudosciaena crocea) roes (pcRs) to achieve high-value utilization. Protein isolates and lipids were extracted simultaneously from pcRs by saline and acidic solutions. The purity of the protein isolates from the pcRs (pcRPIs) was greater than 70%, with vitellogenin, vitellogenin B and vitellogenin C as the main proteins. The lipids from pcRs (pcRLs) were mainly composed of triglycerides with high levels of EPA and DHA. The pcRPIs exhibited a higher surface hydrophobicity, water/oil holding capacity and emulsifying ability than those of the pcRs. Moreover, pcRPIs had a better oil holding capacity and emulsifying ability than soy protein isolate. These results suggest that protein isolates and lipids can be simultaneously extracted by saline and acidic solutions, and pcRPIs and pcRLs can be used as functional materials in the food industry.