Importance of trimethylaluminum diffusion in three-step ABC molecular layer deposition using trimethylaluminum, ethanolamine, and maleic anhydride

Hybrid organic-inorganic films were grown by molecular layer deposition (MLD) with a three-step ABC reaction sequence using (A) trimethylaluminum (TMA), (B) ethanolamine (EA), and (C) maleic anhydride (MA) at 90 °C. Very large steady state mass gains of 1854-4220 ng/(cm(2) cycle) were measured depending on reaction conditions. These mass gains are much larger than typical mass gains for surface reactions. The quartz crystal microbalance (QCM) mass profiles during the TMA reaction were consistent with TMA diffusion into and out of the ABC films. The ABC mass gains per cycle also displayed a strong dependence on the TMA dose and purge times that was consistent with the effects of TMA diffusion. Multiple dose experiments conducted at 130 °C revealed that the ABC reactions were self-limiting for thin ABC films. For thicker ABC films, increased TMA diffusion into the ABC film led to non-self-limiting behavior. Numerical modeling assuming Fickian diffusion for TMA diffusing into and out of the ABC film could fit the QCM mass profiles. The results all indicate that TMA diffusion into the ABC MLD film plays a key role in the thin film growth. In addition, X-ray reflectivity (XRR) measurements revealed that the ABC films were exceptionally smooth.     

Molecular layer deposition of poly(p-phenylene terephthalamide) films using terephthaloyl chloride and p-phenylenediamine

Ultrathin polymer films can be fabricated using the gas-phase method known as molecular layer deposition. This process typically uses bifunctional monomers in a sequential, self-limiting reaction sequence to grow conformal polymer films with molecular layer control. In this study, terephthaloyl chloride (TC) and p-phenylenediamine (PD) were used as the bifunctional monomers to deposit poly(p-phenylene terephthalamide) (PPTA) thin films. 3-Aminopropyl trimethoxysilane or ethanolamine was used to prepare amine-terminated surfaces prior to the PPTA MLD. The surface chemistry and growth rate during PPTA MLD at 145 degrees C were studied using in situ transmission Fourier transform infrared (FTIR) spectroscopy experiments on high surface area powders of SiO2 particles. PPTA MLD thin film growth at 145 degrees C was also examined using in situ transmission FTIR experiments on flat KBr substrates with an amine-terminated Al2O3 ALD overlayer. The integrated absorbances of the N-H and amide I stretching vibrations were measured and used to estimate the thin film thickness. X-ray reflectivity (XRR) experiments were also employed to measure the film thickness after PPTA MLD at 145 degrees C and 180 degrees C. The experiments revealed that the TC and PD reactions displayed self-limiting surface chemistry. The surface species alternated with sequential TC and PD exposures and the PPTA MLD films grew continuously. However, the growth rates per MLD cycle at 145 degrees C were less than expectations based on the size of the molecules involved in the reaction chemistry and were variable between 0.5 and 4.0 A per TC/PD reaction cycle. The lower growth rates are explained by the growth of a limited number of polymer chains on the substrate. The variability in the growth rate is attributed to the difficulties with the bifunctional monomer precursors. Alternative surface chemistries for polymer MLD are proposed that would avoid the use of bifunctional monomers.     

Layer-by-layer-assembled multilayer films of polyelectrolyte-stabilized surfactant micelles for the incorporation of noncharged organic dyes

Noncharged pyrene molecules were incorporated into multilayer films by first loading pyrene into poly(acrylic acid) (PAA)-stabilized cetyltrimethylammonium bromide (CTAB) micelles (noted as PAA&(Py@CTAB)) and then layer-by-layer (LbL) assembled with poly(diallyldimethylammonium chloride) (PDDA). The stable incorporation of pyrene into multilayer films was confirmed by quartz crystal microbalance (QCM) measurements and UV-vis absorption spectroscopy. The resultant PAA&(Py@CTAB)/PDDA multilayer films show an exponential growth behavior because of the increased surface roughness with increasing number of film deposition cycles. The present study will open a general and cost-effective avenue for the incorporation of noncharged species, such as organic molecules, nanoparticles, and so forth, into LbL-assembled multilayer films by using polyelectrolyte-stabilized surfactant micelles as carriers.     

Influence of precursors chemistry on ALD growth of cobalt-molybdenum oxide films

Cobalt molybdenum compounds are important catalytic materials in many processes, e.g. in splitting of ammonia to form CO free hydrogen fuel. We here report on deposition of such cobalt molybdenum oxides by atomic layer deposition (ALD) using different types of metal precursors CoCp(2) (Cp = cyclopentadienyl), Co(thd)(2) (Hthd = 2,2,6,6-tetramethylheptan-3,5-dione), Mo(CO)(6) and oxygen precursors O(3), H(2)O, and (O(3) + H(2)O). The growth dynamics have been investigated using quartz crystal microbalance (QCM) methods. It is evident that mixing of the different precursor chemistries affect the growth patterns. When water is introduced to the reactions, a surface controlled mechanism takes place which guides the deposited stoichiometry towards the CoMoO(4) phase over a wide range of cobalt rich pulsed compositions. This is a rare example of how surface chemistry can control stoichiometry of depositions in ALD. The deposited films have been investigated by X-ray diffraction, Raman spectroscopy and atomic force microscopy. The catalytic activity of selected films have been characterized by temperature programmed ammonia decomposition, proving the films to be catalytically active and lowering the decomposition temperature by some 200 °C.     

Organic vapor detection by quartz crystal microbalance modified with mixed multilayer Langmuir-Blodgett Films

Mixed chloroform solution of Polysiloxane PS-264 and stearic acid was made into multilayer Langmuir-Blodgett (LB) films on the surface of quartz crystal microbalance (QCM). The condition for forming mixed multilayer LB films is discussed in this paper. In addition, PS-264, stearic acid and their mixture (molar ratio 1:1) were coated on the surface of QCM sensors by a spin coating method. The above modified crystals were exposed to different concentrations of various organic vapors, including related chlorinated hydrocarbons and alcohol vapors. The results of frequency changes corresponding to concentration change of the above vapors were compared. The linear regression coefficients of the QCM with LB film had better values (0.9881相似文献   

Detecting cells on the surface of a silver electrode quartz crystal microbalance using plasma treatment and graft polymerization

This paper utilizes a silver electrode quartz crystal microbalance (QCM) mass sensor to detect the physiology of cells. This study also investigates the plasma surface modification of silver electrode QCMs through deposition of hexamethyldisilazane (HMDSZ) films as a protection film. To improve the cell growth, this paper also performs post-treatments by surface-grafting acrylic acid (AAc), acrylamide (AAm), and oxygen plasma treatment onto the QCM electrodes. Experimental results indicate that plasma deposition is a useful technique to protect the surface of silver electrodes. This technique extends the unpeeling time of silver electrodes from 1 to 7 days. The hydrophilic silver electrode QCM surface modified by AAm exhibited a better storage time effect than other post-treatments.     

A novel quartz crystal microbalance gas sensor based on porous film coatings. A high sensitivity porous poly(methylmethacrylate) water vapor sensor

We describe a novel and generally applicable approach for creating voids in films deposited on the surface of solid substrates. Such films are advantageous when a quartz crystal microbalance (QCM) is the basis of a sensor. We show that films with large void volumes produce more sensitive sensors than with the original film. Poly(methylmethacrylate) (PMMA) was used as the polymer layer deposited on a quartz crystal microbalance (QCM) to demonstrate our technique for the model system of water vapor analysis in flowing nitrogen gas. A film of pure PMMA on a QCM is a sensor for water vapor in a gas phase. A more sensitive sensor was created by dip coating QCM crystals into solutions containing mixtures of PMMA and poly(d,l-lactide) (PDLL) and then evaporating the solution films on the QCM crystals to form mixed polymer films of varying PDLL content. The PDLL was then removed from the mixed polymer films by exposure to a NaOH solution to form pure PMMA films having various void volumes. A leached PMMA film that originally contained 50% by weight PDLL had a 3.7 times larger QCM sensitivity for water vapor than a pure PMMA film.     

Influence of surface temperature on the mechanism of atomic layer deposition of aluminum oxide using an oxygen plasma and ozone

We have examined the role of substrate temperature on the surface reaction mechanisms during the atomic layer deposition (ALD) of Al(2)O(3) from trimethyl aluminum (TMA) in combination with an O(2) plasma and O(3) over a substrate temperature range of 70-200 °C. The ligand-exchange reactions were investigated using in situ attenuated total reflection Fourier transform infrared spectroscopy. Consistent with our previous work on ALD of Al(2)O(3) from an O(2) plasma and O(3) [Rai, V. R.; Vandalon, V.; Agarwal, S. Langmuir 2010, 26, 13732], both -OH groups and carbonates were the chemisorption sites for TMA over the entire temperature range explored. The concentration of surface -CH(3) groups after the TMA cycle was, however, strongly dependent on the surface temperature and the type of oxidizer, which in turn influenced the corresponding growth per cycle. The combustion of surface -CH(3) ligands was not complete at 70 °C during O(3) exposure, indicating that an O(2) plasma is a relatively stronger oxidizing agent. Further, in O(3)-assisted ALD, the ratio of mono- and bidentate carbonates on the surface after O(3) exposure was dependent on the substrate temperature.     

Rapid vapor-phase fabrication of organic-inorganic hybrid superlattices with monolayer precision

We report a new layer-by-layer growth method of self-assembled organic multilayer thin films based on gas-phase reactions. In the present molecular layer deposition (MLD) process, alkylsiloxane self-assembled multilayers (SAMs) were grown under vacuum by repeated sequential adsorptions of C=C-terminated alkylsilane and titanium hydroxide. The MLD method is a self- limiting layer-by-layer growth process, and is perfectly compatible with the atomic layer deposition (ALD) method. The SAMs films prepared exhibited good thermal and mechanical stability, and various unique electrical properties. The MLD method, combined with ALD, was applied to the preparation of organic-inorganic hybrid nanolaminate films in the ALD chamber. The organic-inorganic hybrid superlattices were then used as active mediums for two-terminal electrical bistable devices. The advantages of the MLD method with ALD include accurate control of film thickness, large-scale uniformity, highly conformal layering, sharp interfaces, and a vast library of possible materials. The MLD method with ALD is an ideal fabrication technique for various organic-inorganic hybrid superlattices.     

Film thickness studies for the chemically synthesized conducting polyaniline

The chemical oxidation of aniline with ammonium persulphate (APS) in aqueous acidic medium to form polyaniline (PANI) films has been studied using the quartz crystal microbalance (QCM) technique. PANI films can also grow onto glass supports immersed in the reaction mixture during the polymerization. The optical absorption for these films was measured. Multilayer deposition of polymer films onto the gold electrode of QCM and onto the glass supports from consecutive repetitive treatments by the reaction mixture containing aniline and APS, were studied. The induction period, the yield and the growth rate of the polymer films during the multilayer deposition were discussed. A relation between the thickness of the films determined, from QCM technique and the optical absorption of the films was established. The electrical conductivity of the PANI films was also measured.     

Buildup mechanism of carboxymethyl cellulose and chitosan self-assembled films

Films with different numbers of layers have been built by alternating the adsorption of carboxymethyl cellulose (CMC) and chitosan (CHI) at different pH levels. The adsorption process was recorded by quartz crystal microbalance (QCM). The results showed that under all pH conditions considered, the growth of the films is nonlinear. The film construction performed at pH 4.0 (preferred assembly pH) with different numbers of bilayers (CMC/CHI as one bilayer) was also observed step by step by atomic force microscopy (AFM). Comparing the growth process from QCM with the surface morphological changes from AFM shows the existence of an inhomogeneous structure for the first nine bilayers, and, after a coalescence of islands, an increase in the number of bilayers was demonstrated. The possible growth mechanism was also evaluated.     

Quartz crystal microbalance immunoassay for carcinoma antigen 125 based on gold nanowire-functionalized biomimetic interface

Gold nanowires with of designed length on a solid substrate have been proven as an efficiently immobilized affinity support for the detection of carcinoma antigen 125 (CA 125) in this study. The presence of gold nanowires provides a well-defined three-dimensional structure, and greatly amplifies the coverage of the anti-CA 125 protein on the probe surface. Moreover, the amount of anti-CA 125 varied with the change of the morphology of the probe, and achieved an optimal quartz crystal microbalance (QCM) response towards anti-CA 125 adsorption at the number of gold nanolayers of 5. The formed immune-probe exhibits good QCM responses for the detection of CA 125, and allows the detection of CA 125 at concentrations as low as 0.5 U ml(-1). The QCM immunosensor exhibited good precision, high sensitivity, acceptable stability, accuracy and reproducibility. The as-prepared immunosensors were used to analyze CA 125 in human serum specimens. Analytical results suggest that the developed immunoassay method is a promising alternative approach for detecting CA 125 in the clinical diagnosis. Compared with conventional ELISA, the proposed immunoassay system was simple and rapid without multiple labeling and separation steps. Importantly, the route provides an alternative approach to incorporate multiple gold nanolayers onto the solid matrix for biosensing applications.     

Oligomer orientation in vapor-molecular-layer-deposited alkyl-aromatic polyamide films

The surface-limited molecular-layer deposition of alkyl-aromatic polyamide films using sequential doses of 1,4-butane diamine (BDA) and terephthaloyl dichloride (TDC) is characterized using in situ quartz crystal microbalance and ex situ spectroscopy analysis. For the first time, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to offer insight into molecular orientation in films deposited via molecular-layer deposition (MLD). The results show that the oligomer units are lying nearly parallel to the surface, which differs from the linear vertical growth mode often used to illustrate film growth.     

Characterisation of ultra-thin films of oxidised bacterial cellulose for enhanced anchoring and build-up of polyelectrolyte multilayers

The process of catalytic oxidation of bacterial cellulose (BC) ultra-thin films with 2,2,6,6-tetramethyl-1-piperidinyloxy was investigated along with their capability to adsorb oppositely charged polyelectrolytes of chitosan and alginate. The time-dependent oxidation of BC films was analysed by X-ray photoelectron spectroscopy and quartz crystal microbalance (QCM) experiments. A negatively charged surface was achieved by inserting carboxylic groups, which was augmented by prolonged media exposure (17.9 %), compared with a fast oxidation process (9.1 %). Polyelectrolyte deposition was followed by QCM, which indicated that BC oxidation increased the first layer uptake of chitosan 17-fold (?105.0?±?1.5 Hz) in comparison with unoxidised BC (?6.0?±?0.2 Hz), confirming the capability of oxidised BC surfaces to exhibit strong electrostatic interactions and to support the build-up of a thicker multilayer system. These findings indicate that oxidised BC surfaces are capable of immobilising and detecting several charged species.     

Organocatalysts for the controlled "immortal" ring-opening polymerization of six-membered-ring cyclic carbonates: a metal-free, green process

Six-membered cyclic carbonates, namely trimethylene carbonate (TMC), 3,3-dimethoxytrimethylene carbonate (DMTMC) and 3-benzyloxytrimethylene carbonate (BTMC), undergo controlled "immortal" ring-opening polymerization (iROP) under mild conditions (bulk, 60-150 °C), by using organocatalysts, including an amine [4-N,N-dimethylaminopyridine (DMAP)], a guanidine [1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD)], or a phosphazene [2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP)], in the presence of an alcohol [benzyl alcohol (BnOH), 1,3-propanediol (PPD), glycerol (GLY)] that acts as both a co-initiator and a chain-transfer agent. Remarkably, such organocatalysts remain highly active in the iROP of technical-grade, unpurified TMC. Under optimized conditions, as much as 100,000 equivalents of TMC were fully converted by as little as 10 ppm of BEMP with the simultaneous growth of as many as 200 polymer chains, allowing the preparation of high molar mass poly(trimethylene carbonate)s (up to 45,800 g mol(-1)). These catalyst systems enable among the highest activities (TOF=55,800 h(-1)) and productivities (TON=95,000) ever reported for the ROP of TMC.     

Adsorption of bovine serum albumin onto poly(methyl methacrylate) stereocomplex films with a molecularly regulated nanostructure

Stereoregular poly(methyl methacrylate)s (PMMAs) were stepwise assembled on a quartz crystal microbalance (QCM) substrate after the immersion of the QCM into alternating acetonitrile solutions at ambient temperature. A quantitative QCM analysis at each step showed stereocomplex formation on the substrate surface. The adsorption of bovine serum albumin (BSA) onto stereocomplex films with a molecularly regulated nanostructure was analyzed quantitatively. The adsorption constant and the maximum adsorption amount, calculated by the assumption of Langmuir‐type adsorption, showed that BSA adsorbed with a relatively weak interaction onto the stereocomplex films. The BSA adsorption onto the stereocomplex films occurred in an end‐on manner, with a smaller adsorption constant than for that onto individual spin‐coated films. The amount of BSA adsorbed was significantly affected by the molecular weight of syndiotactic PMMA. Attenuated total reflection spectra indicated that BSA adsorbed onto the films with or without denaturing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1807–1812, 2003     

Atomic/molecular layer deposited thin-film alloys of Ti-4,4'-oxydianiline hybrid-TiO(2) with tunable properties

By combining atomic layer deposition (ALD) and molecular layer deposition (MLD) thin-film techniques, the latter being a variant of the former in which organic precursors are used, it is possible to deposit thin films containing precisely controlled portions of inorganic and organic constituents. This in turn enables the adjustment of material properties by changing the number of ALD and MLD cycles applied during the deposition. In this work, the properties of such thin-film "alloys" prepared by varying the portions of Ti-4,4'-oxydianiline (Ti-ODA) inorganic-organic hybrid and TiO(2) in the structure were investigated. The films were deposited at 280 °C using TiCl(4) and water as precursors for TiO(2), and TiCl(4) and ODA for the Ti-ODA hybrid. The results demonstrate excellent tunability of the film properties such as degree of crystallinity, roughness, refractive index, and hardness depending on the relative number of TiO(2) and Ti-ODA cycles employed.     

The kinetics and spectral studies of the in situ polyaniline film formation

The chemical oxidation of aniline with ammonium persulfate (APS) in an aqueous acidic solution to form polyaniline (PANI) films has been studied using the quartz crystal microbalance (QCM) technique. The kinetics of the film formation was investigated. The reaction exhibited half-order with respect to APS and first-order to aniline. The effect of temperature on the growth rate of PANI films was studied. The activation energy is 39.79 kJ/mol. This is in agreement with the corresponding one determined for the chemical polymerization of PANI in the bulk. The UV-visible spectra of the PANI films grown onto a glass support immersed into the bulk solution were measured. The absorption of the PANI film with time was also studied and compared to the growth of the PANI film thickness using the QCM technique.     

Synthesis of cross-linked epoxy microparticles: effect of the synthesis parameters

Epoxy crosslinked microparticles were synthesized from the reaction between diglycidyl ether of bisphenol A and a diamino hardener, through precipitation polymerization in a polypropylene glycol solvent. The influence of the monomer concentration, the amine/epoxy stoichiometric ratio, the reaction temperature and the structure of the diamine (aromatic or cycloaliphatic) were investigated, since these parameters may affect the structure and properties of the particles. Morphological analysis revealed that, in all cases, spherical particles were obtained with diameters ranging from 1 to 6 μm. The glass transition temperatures of the particles was found to vary between 130 and 160 °C using the aromatic diamine and between 116 and 141 °C using the cycloaliphatic diamine. It was also found that the effective stoichiometry of the particles was different from the initial stoichiometry in the feed solution.     

Bimodal swelling responses in microgel thin films

A series of studies on microgel thin films is described, wherein quartz crystal microgravimetry (QCM), surface plasmon resonance (SPR), and atomic force microscopy (AFM) have been used to probe the properties of microstructured polymer thin films as a function of film architecture and solution pH. Thin films composed of pNIPAm-co-AAc microgels were constructed by using spin-coating layer-by-layer (scLbL) assembly with poly(allylamine hydrochloride) (PAH) as a polycationic "glue". Our findings suggest that the interaction between the negatively charged microgels and the positively charged PAH has a significant impact on the pH responsivity of the film. These effects are observable in both the optical and mechanical behaviors of the films. The most significant changes in behavior are observed when the motional resistance of a quartz oscillator is monitored via QCM experiments. Slight changes to the film architecture and alternating the pH of the environment significantly changes the QCM and SPR responses, suggesting a pH-dependent swelling that is dependent on both particle swelling and polyelectrolyte de-complexation. Together, these studies allow for a deeper understanding of the morphological changes that take place in environmentally responsive microgel-based thin films.