Structure Of PMMA Research Articles

Effects of inorganic components on the structure and thermo-oxidative degradation of PMMA modified metal alkoxide–EAA complex

Abstract Poly(methyl methacrylate) (PMMA) modified titanium and zirconium n-butoxide–ethyl acetoacetate (EAA) complex [M5-Ti(OBun)2(EAA)2 and M5-Zr(OBun)2(EAA)2] were obtained from trialkoxysilane-functional PMMA and EAA modified titanium and zirconium alkoxide via the sol–gel method. Infrared (IR), 13 C nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) were used to analyze the structures and properties of the hybrids with various proportions of metal oxide species. The effect of the complex of metal oxides and EAA ligands on structure and thermo-oxidative degradation of the M5-Ti(OBun)2(EAA)2 and M5-Zr(OBun)2(EAA)2 hybrids were investigated in this study. The 1 H spin–diffusion path length of the hybrids was in a nanometer scale as estimated from the spin–lattice relaxation time in a rotating frame (T1ρH). The apparent activation energies (Ea), evaluated by van Krevelen’s method, for random scission of PMMA segments in hybrids decreased with increasing metal oxide content.

Surface modification of PMMA by DC glow discharge and microwave plasma treatment for the improvement of coating adhesion

PMMA shows poor adhesion for evaporated inorganic coatings. The DC and microwave plasma treatments can considerably increase free surface energy but an improvement of coating adhesion is, according to our results, only possible by the DC process. ATR spectroscopy has been applied to investigate the changed chemical structure of DC plasma-treated PMMA. Samples treated by microwave plasma did not show ATR alteration while XPS analysis indicated surface oxygen enrichment.

Adsorption of heavy‐metal ions on poly(ethylene imine)‐immobilized poly(methyl methacrylate) microspheres

AbstractPoly(methyl methacrylate) (PMMA) microspheres carrying poly(ethylene imine) (PEI) were prepared for the removal of heavy‐metal ions (copper, cadmium, and lead) from aqueous solutions with different amounts of these ions (50–600 mg/L) and different pH values (3.0–7.0). Ester groups in the PMMA structures were converted to imine groups in a reaction with PEI as a metal‐chelating ligand in the presence of NaH. The adsorption of heavy‐metal ions on the unmodified PMMA microspheres was very low [3.6 μmol/g for Cu(II), 4.6 μmol/g for Cd(II), and 4.2 μmol/g for Pb(II)]. PEI immobilization significantly increased the heavy‐metal adsorption [0.224 mmol/g for Cu(II), 0.276 mmol/g for Cd(II), and 0.126 mmol/g for Pb(II)]. The affinity order of adsorption (in moles) was Cd(II) > Cu(II) > Pb(II). The adsorption of heavy‐metal ions increased with increasing pH and reached a plateau value around pH 5.5. Their adsorption behavior was approximately described with the Langmuir equation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 197–205, 2001

Surface structure of amorphous PMMA from SPM: auto-correlation function and fractal analysis

The surface topography of amorphous poly(methyl methacrylate) has been investigated by scanning probe microscopy technique and analysed using an auto-correlation function approach. Spatial correlations in the arrangement of sub-macromolecular fragments on the surface are studied depending on preparation conditions (whether the surface was free, i.e. in contact with air, or confined with the silicon substrate). The correlation length of the roughness distribution on the surface of amorphous polymers corresponds to the internal dimensions of unperturbed polymer chains (the radius of gyration). The scaling behaviour of the roughness is analysed with the Hurst approach, and found to be different for the free surface and for the confined one. As a result of annealing at a temperature above the glass transition temperature of the bulk polymer, both surfaces converge to similar fractal dimensionalities and correlation lengths.

A Study on the Sub-Micron LIGA Process

Microstructures with sub-micron widths and gaps (lines and spaces) can be applied to practical and high performance MEMS devices. In the sub-micron LIGA process, one of the most crucial considerations is the fabrication of an X-ray mask with thick X-ray absorbers having sub-micron width. An X-ray mask, which is composed of 1μm-thick Au with a 0.6μm line width and a 0.2μm space as absorbers, 2μm-thick SiC with 240MPa of tensile stress as a membrane and 625μm-thick Si as a frame, was fabricated. As a result of the sub-micron LIGA process, a sub-micron PMMA structure with a maximum aspect ratio of 85, corresponding to 0.2μm minimum width, 6μm length and 17μm height, and sub-micron Ni structures with a maximum aspect ratio of 75, corresponding to 0.2μm minimum width and 15μm height, were fabricated.

Fabrication of three-dimensional photonic structures with submicrometer resolution by x-ray lithography

We report on the fabrication of diamond-like photonic structures in PMMA resist and their use as porous templates for transferring three-dimensional patterns to metals or dielectrics. Following the original “three drilling holes” approach first proposed by Yablonovitch, we used three consecutive exposures of PMMA resist to an x-ray beam through a triangular lattice of holes. A submicronic patterning was thus obtained in thick PMMA layers (>6 μm). Optical characterizations of 1.3 μm period templates showed a well-defined photonic gap in the midinfrared. The pattern transfers from the PMMA templates to a metal (copper) and a high refractive index dielectric (titania) were achieved by the electrodeposition and sol–gel filling techniques, respectively. Three-dimensional metallic structures of 1.3 μm lattice constant were obtained with extreme regularity over a thickness of ∼6 μm, thereby providing a way to build submicrometer photonic band gap materials for optical wavelengths.

Interchain ion formation in secondary ion mass spectrometry resulting from the double-helical structure of isotactic poly(methyl methacrylate) in adsorbed monolayers

Results from time-of-flight secondary ion mass spectra (TOF-SIMS) of Langmuir-Blodgett monolayers of various isomers (isotactic and syndiotactic) of poly(methyl methacrylate) (PMMA) are reported. A detailed analysis of the repeating pattern of fragment ion clusters yields very different patterns for isotactic PMMA LB layers than for the syndiotactic and atactic forms. This is attributed to the resulting double-helical tertiary structure of isotactic PMMA, a structure that does not form for the syndiotactic and atactic PMMA polymer monolayers. The double-helical structure of isotactic PMMA monolayers is verified using reflection absorption Fourier transform infrared spectroscopy. The repeating patterns of cluster ions in syndiotactic and atactic PMMA monolayers can be explained using statistical chain-breaking models for fragmentation of single isolated polymer chains. The repeating ion patterns from the TOF-SIMS of the isotactic PMMA monolayers are analyzed by considering bond breaking and ion formation between adjacent polymer chains, resulting in a newly proposed ion formation model due to the tertiary structure of the double-helical form. A rearrangement mechanism consistent with all ions that are formed is proposed.

Fabrication of Sub-Micron Structures with High Aspect Ratio for Practical MEMS

It is necessary for practical and high performance MEMS to be fabricated microstructures with sub-micron widths and gaps (lines and spaces). In sub-micron deep X-ray lithography, one of the most crucial considerations is the fabrication of an X-ray mask with thick X-ray absorbers having sub-micron width. An X-ray mask, which was composed of 1μm thick Au with a 0.6μm line width and a 0.2μm space as absorbers, 2μm thick SiC with 240MPa of tensile stress as a membrane and 625μm thick Si as a frame, was fabricated. In order to reduce the influence of Fresnel diffraction, a PMMA resist was polymerized without residual stress, which had been the main cause of a warp in the substrate, by controlling of the polymerization process. As a result, a sub-micron PMMA structure with a maximum aspect ratio of 85, corresponding to 0.2μm minimum width, 6μm length and 17μm height, was fabricated by deep X-ray lithography.

Toughening of polystyrene by natural rubber-based composite particles: Part II Influence of the internal structure of PMMA and PS-grafted core-shell particles

This work was focused on the influence of the internal structure of natural rubber (NR)-based core-shell particles on the toughness of polystyrene (PS). Several emulsion polymerization processes were used to control the degree of grafting of the NR phase and the site of polymerization, which determines the final morphology of the prepared composite NR-based particles. PS subinclusions were introduced into the NR core in order to determine their influence on the deformation behaviour of PS. A continuous extrusion process was adapted for the direct feeding of the wet NR-based latexes into the molten PS matrix. Impact testing indicated that core-shell particles based on NR containing a large number of small crosslinked PS subinclusions toughened PS most effectively. A very effective toughening agent is obtained if a hard shell of 25 wt% crosslinked PMMA surrounds the composite rubber particle. Grafting of NR chains during the subinclusion synthesis has to be avoided since a high rubber particle modulus is detrimental for craze nucleation in PS. From the fracture surface morphology the craze nucleating and stabilizing efficiency of composite NR particles having different morphologies or grafting degrees could be deduced.

Investigation of the adhesive strength of PMMA structures on substrates obtained by deep X-ray lithography

The adhesive strength of PMMA structures obtained by deep X-ray lithography with synchrotron radiation is a decisive factor for effective structure replication in subsequent electroforming processes. The adhesion depends on various factors, in particular on the interaction of radiation and secondary electrons at the boundary resist/substrate. We have determined the adhesion strength of PMMA microcolumns as a function of the dose deposited below the mask absorber by breaking tension measurements applying a new experimental method. Care has been taken to separate degradation effects in the resist due to the primary photon beam from the loss of adhesion at the boundary substrate/resist caused by secondary electrons. This has been studied quantitatively by utilizing different substrate materials like glassy carbon, wet oxidized titanium, copper and gold. Monte Carlo simulations have been carried out to simulate the deposited dose at the surface layer of different substrates. The corresponding results are supplemented by deep lithography experiments, which may be used as a means to directly conclude the deposited resist dose from secondary electrons emitted from the substrate surface. All the irradiation experiments have been performed with specially designed masks for deep X-ray lithography at the storage ring DCI (Orsay/France).

Application of electron beam lithography for downscaling of SOI-bipolar and BiCMOS

A direct-write sub-100-nm electron beam lithography has been used for scaling of a novel lateral bipolar structure. The keyprocess is a lithographic base definition by using small PMMA structures as implantation masks. Downscaling of base widths into the sub-100-nm-regime could be successfully demonstrated. Process simulation is used to estimate the effects of process parameters on device scaling. The physical and technological effects which are responsible for base formation are intensively discussed. A relation for base formation is derived and confirmed by electrical measurements.

Production of buried waveguides in PMMA by high energy ion implantation

Abstract Optical waveguiding structures in PMMA were produced by irradiation with ions in the dose range of 10 12 –10 14 ions/cm 2 . Waveguides buried in various depths of the bulk material were generated using ions with different energies between 100 keV and 180 MeV. Optical devices such as Y-branches, couplers and Mach-Zehnder interferometers were produced using ion irradiation through a mask. The refractive index and profile as well as the attenuation of the waveguides were measured at different wavelengths. These properties of the waveguiding structures at different depths of the bulk material will be discussed.

Microstructures and interdiffusions of Pt/Ti electrodes with respect to annealing in the oxygen ambient

The microstructural variation and the interdiffusion of Pt (80 nm)/Ti (70 nm)/SiO2/Si during annealing in O2 were investigated using Auger electron spectroscopy, x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. While the as-deposited and 400 °C annealed samples showed well-defined layer structures without any significant interfacial reaction, the degree of oxidation remarkably increased with increasing temperature above 500 °C. The PtTi alloy phase with Pmma structure (AuCd type) was observed from the 500 °C annealed sample. Drastic interdiffusion occurring above 600 °C changed the Pt/Ti bilayer into a very entangled structure. Some TiO2 phases were exposed to the ambient between Pt hillocks. In addition, a small amount of Pt-silicide was found near the TiOx/SiO2 interface.

Site specific photochemical reaction by core electron excitation: carbon and oxygen K-edge fine structure of PMMA

Abstract The photon energy dependence of ion desorption from thin films of PMMA was measured in the 250–700 eV photon energy range to investigate the primary steps in radiation induced decomposition using monochromatic pulsed-synchrotron radiation. The desorption of the most intense ions; CH + 3 , H + , CH + 2 and CHO + , depends on the nature of the electronic state created in the primary excitation process. The fragmentation occurs specifically around the site of the atom where the optical excitation took place. The very localized desorption of CH + 3 , and CH + 2 at 288.7 and 535.6 eV, and of CHO + at 539.3 eV can be very useful for lithographic applications or for future molecular electronic devices fabrication.

Fabrication of sub-10 nm structures by lift-off and by etching after electron-beam exposure of poly(methylmethacrylate) resist on solid substrates

Sub-10 nm structures were fabricated by lift-off and by etching following electron-beam exposure of poly(methylmethacrylate) (PMMA) resist on solid semiconductor substrates. Electron beam lithography at 80 kV with a beam diameter smaller than 5 nm was used to expose PMMA resist on either Si or GaAs substrates. The exposed resist was developed with a 3:7 cellosolve:methanol mixture in an ultrasonic bath for 5 s followed by rinsing in IPA and blown dry with pure nitrogen. Ultrasonic agitation during development was found to be essential for forming sub-10 nm structures in PMMA. The patterned PMMA resist was used either as a lift-off mask or an etching mask and successful transfer of the pattern to the substrates was achieved. For lift-off an ionized beam deposition method, which gives smaller grain size and better adhesion of the metal film to the substrate, was used to deposit a layer of AuPd. Metal dots with sub-10 nm diam and metal structures with sub-10 nm gaps were fabricated. For sub-10 nm etched structures reactive ion etching was used to transfer either the PMMA pattern or the lift-off metal pattern to either Si or GaAs substrates. Etched lines and pillars with dimensions smaller than 10 nm were obtained.

0.15μm E-Beam T-shaped gates for GaAs FETs

This paper details multilayer resist techniques currently being used to produce T-shaped gates with Lgs down to 0.15μm. Using a three layer PMMA/P(MMA/MAA)/PMMA structure gates with a 2:7 foot to top ratio have been produced using electron doses as low as 100μC/cm2, a fraction of those needed to produce gates of similar dimensions using standard lithography techniques. High frequency performances of GaAs FETs can be improved by reducing the gate length. However, with current E-beam lithography techniques, using single layer resist systems, as gate lengths decrease, gate resistances increase due to the triangular metal cross section produced. A solution to this problem is the T, or mushroom-gate. Various bi- or trilayer resist systems have been developed for this purpose (1,2,3) but to our knowledge very little has been published on the processing of these structures. In this paper, we describe our work in this area and the results we have obtained.

Highly syndiotactic poly(methyl methacrylate) with narrow molecular weight distribution formed by tert-butyllithium-trialkylaluminium in toluene

Polymerization of MMA with t-C4H9Li in toluene in the presence of trialkylaluminum(alkyl=methyl, ethyl, butyl, isobutyl, and octyl) was examined at various Al/Li ratios. Triethyl-, tributyl and trioctylaluminums worked quite effectively in the polymerization to give highly syndiotactic PMMA with narrow molecular weight distribution (MWD) at the Al/Li ratio of 3 and higher than 3. The highest syndiotacticity of 96% was attained with t-C4H9Li/(n-C8H17)3Al (1/3) at −93°C. The polymerization was initiated by t-C4H9 anion and proceeded in a living manner. The structure of the syndiotactic PMMA is chemically identical to that of isotactic PMMA prepared with t-C4H9MgBr. Consequently, highly isotactic and syndiotactic PMMAs with narrow MWD and with the same chemical structure from α-end to ω-end were obtained.

Microgap x-ray nanolithography

Abstract At linewidths of 0.1μm and below, the time required to expose large-area patterns (∼1cm 2 ) by electron-beam lithography becomes impractically long. Thus, there is a critical need for reliable replication techniques in this linewidth domain. Replication of features as fine as 18nm by x-ray lithography has been demonstrated. However, all sub-0.2μm-linewidth x-ray lithography to date has been done in intimate contact using polyimide-membrane masks. Polyimide is subject to distortion, and contact can cause mask damage. For these reasons we have investigated x-ray nanolithography with inorganic membranes, and mask-sample gaps of ∼4μm. We discuss the resolution-limiting factors of penumbra, diffraction, and photo-electron range, and consider the tradeoffs of gap and wavelength that need to be made to achieve high resolution. With a Cu L source (λ=1.3nm), a linewidth of 0.1μm requires a gap of ∼4μm. We have used stress-controlled SiON 0.5 membranes of 6cm 2 area attached to a narrow rim etched into a Si substrate. The gap was set by small spaces studs. Gaps of 4–6μm were achieved with uniformities of ∼0.5μm. They were measured using an angular fringe counting technique. Microgap nanolithography was used to replicate 100nm lines with the Cu L x-ray. High aspect-ratio PMMA structures were achieved with steep sidewalls, suggesting that 50nm lines could be faithfully printed with the microgap technique.

Aspects of the influence of plasticizers of varied nature on the physicomechanical properties and structure of polymethylmethacrylate

Abstract The authors have investigated the effect of various plasticizers on the physicomechanical properties and structure of PMMA by translucent electron microscopy, low amplitude periodic deformation and a phytochromic kinetic label. With increase in the plasticizer content the system was found to be microheterogeneous to the point of release of plasticizer into a separate phase.

Dimensions of a critical structural defect in polymethylmethacrylate in conditions of impact loading

A technique is proposed for calculating the parameters of a radial critical structural defect based on the concepts of linear elastic mechanics of fracture. The calculations made on PMMA gave the following values: length of defect 44, radius 100μm. The calculated magnitudes agree with the dimensions of the elements of the supramolecular structure of PMMA. A possible scheme of blunting of the critical defect on the basis of the morphological features of bulk PMMA is considered. Change in the form of the critical defect from radial to sharp roughly halves resilience.