Connectivity of features in microlens array reduction photolithography: generation of various patterns with a single photomask

Microlens array photolithography (MAP) is a technique in which arrays of microlenses positioned close to photoresist reduce cm-sized figures on photomasks and form mum-scale images in the photoresist. This work demonstrates that MAP, using a single photomask, can generate patterns having different symmetries and periodicities from that of the lens array. This capability of MAP depends on (i) the connectivity between the images produced by individual microlenses and (ii) the orientation of the photomask relative to the lens array prior to exposure. By changing this orientation, MAP, using a single mask and a single array of microlenses, could be used to generate patterns that (i) are separated from each other, (ii) overlap with each other, (iii) are 2D chiral, and thus different from both the lens array and the mask in symmetry, (iv) have a symmetry reduced from that of the lens array, or (v) have a smaller unit cell and smaller pitch than that of the lens array.     

Electronically excited products in multiphoton dissociation: a computational study

Branching fractions for the MPD into electronically excited species, both neutral and ionic, are computed in the statistical limit. Extensive population of excited states is found, particularly so for the smaller fragments. Examples include the formation of excited states of C₂ and CH from ethylene or benzene and of Fe(I) and Fe(II) from Fe(CO)₅.     

Novel hydrofluorocarbon polymers for use as pellicles in 157 nm semiconductor photolithography: fundamentals of transparency

With the advent of 157 nm as the next photolithographic wavelength, there has been a need to find transparent and radiation durable polymers for use as soft pellicles. Pellicles are ∼1 μm thick polymer membranes used in the photolithographic reproduction of semiconductor integrated circuits to prevent dust particles on the surface of the photomask from imaging into the photoresist coated wafer. Practical pellicle films must transmit at least 98% of incident light and have sufficient radiation durability to withstand kilojoules of optical irradiation at the lithographic wavelength. As exposure wavelengths have become shorter the electronics industry has been able to achieve adequate transparency only by moving from nitrocellulose polymers to perfluorinated polymers as, for example, Teflon^® AF 1600 and Cytop™ for use in 193 nm photolithography. Unfortunately, the transparency advantages of perfluorinated polymers fail spectacularly at 157 nm; 1 μm thick films of Teflon^® AF 1600 and Cytop™ have 157 nm transparency of no more than 38 and 2%, respectively, with 157 nm pellicle lifetimes measured in millijoules.Polymers such as [(CH₂CHF)_xC(CF₃)₂CH₂]_y, or (CH₂CF₂)_x[2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole]_y with chains that alternate fluorocarbon segments with either oxygen or hydrocarbon segments frequently show >98% transparency at 157 nm, if amorphous. These polymers are made from monomers, such as vinylidene fluoride (VF₂) and hexafluoroisobutylene, which themselves exhibit good alternation of CH₂ and CF₂ in their structures. In addition, we find that ether linkages also can serve to force alternation. In addition, we find that fluorocarbon segments shorter than six carbons, and hydrocarbon segments less than two carbons or less than three carbons if partially fluorinated also promote 157 nm transparency. We also find that even with these design principles, it is advantageous to avoid small rings, as arise in the cyclobutanes. These results suggest a steric component to transparency in addition to the importance of alternation.Upon irradiation these polymers undergo photochemical darkening and therefore none has demonstrated the kilojoule radiation durability lifetimes required to be commercially attractive. This is likely because these exposure lifetimes require every bond to absorb ∼10 photons, each photon having an energy roughly twice common bond energies. We have studied intrinsic (composition, molecular weight) and extrinsic (trace metals, impurities, environmental contaminants, oxygen, water) contributions to optical absorption and photochemical darkening in these polymers. Studies of photochemical darkening in model molecules illustrate the dynamics of photochemical darkening and that appreciable lifetimes can be achieved in fluorocarbons. To a first approximation the polymers that have lower 157 nm optical absorbance also tend to show the longest lifetimes. These results imply that quantum yield, or the extent to which the polymer structure can harmlessly dissipate the energy, can be important as well.     

Designing a non-volatile imaging switch for mass-persistent,chemically amplified photolithography: a model study

An acid catalysed rearrangement that transforms a bicyclic lactone into a phenolic carboxylic acid has been tested for potential use in chemically amplified microlithographic imaging.     

An etching technique to reveal the supermolecular structure of crystalline polymers

Highly polished surfaces of nylon 6, nylon 66, polychlorotrifluoroethylene and polypropylene were etched by aromatic and chlorinated hydrocarbons at temperatures between 25 and 75°C to reveal surface morphology. Comparison with micrographs obtained with microtomed sections shows the absence of etching artifacts which are known to accompany the use of oxidizing etching agents.     

Fragmentation patterns in multiphoton ionization: a statistical interpretation

The simplest statistical theory wherein the mass spectral fragmentation pattern is governed by the mean energy is derived and compared with the observed results for resonance-enhanced multiphoton ionization of benzene. By varying the mean energy absorbed it is possible to span the range of different patterns up to the dominance of C⁺₁ions above 37 eV/molecule.     

Star-branched polymers in an adsorbing slit: a Monte Carlo study

A coarse-grained model of star-branched polymer chains confined in a slit was studied. The slit was formed by two parallel impenetrable surfaces, which were attractive for polymer beads. The polymer chains were flexible homopolymers built of identical united atoms whose positions in space were restricted to the vertices of a simple cubic lattice. The chains were regular star polymers consisted of f = 3 branches of equal length. The chains were modeled in good solvent conditions and, thus, there were no long-range specific interactions between the polymer beads-only the excluded volume was present. Monte Carlo simulations were carried out using the algorithm based on a chain's local changes of conformation. The influence of the chain length, the distances between the confining surfaces, and the strength of the adsorption on the properties of the star-branched polymers was studied. It was shown that the universal behavior found previously for the dimension of chains was not valid for some dynamic properties. The strongly adsorbed chains can change their position so that they swap between both surfaces with frequency depending on the size of the slit and on the temperature only.     

Synthetic polymer nanoparticle-polysaccharide interactions: a systematic study

The interaction between synthetic polymer nanoparticles (NPs) and biomacromolecules (e.g., proteins, lipids, and polysaccharides) can profoundly influence the NPs fate and function. Polysaccharides (e.g., heparin/heparin sulfate) are a key component of cell surfaces and the extracelluar matrix and play critical roles in many biological processes. We report a systematic investigation of the interaction between synthetic polymer nanoparticles and polysaccharides by ITC, SPR, and an anticoagulant assay to provide guidelines to engineer nanoparticles for biomedical applications. The interaction between acrylamide nanoparticles (~30 nm) and heparin is mainly enthalpy driven with submicromolar affinity. Hydrogen bonding, ionic interactions, and dehydration of polar groups are identified to be key contributions to the affinity. It has been found that high charge density and cross-linking of the NP can contribute to high affinity. The affinity and binding capacity of heparin can be significantly diminished by an increase in salt concentration while only slightly decreased with an increase of temperature. A striking difference in binding thermodynamics has been observed when the main component of a polymer nanoparticle is changed from acrylamide (enthalpy driven) to N-isopropylacryalmide (entropy driven). This change in thermodynamics leads to different responses of these two types of polymer NPs to salt concentration and temperature. Select synthetic polymer nanoparticles have also been shown to inhibit protein-heparin interactions and thus offer the potential for therapeutic applications.     

Modeling the phase behavior of commercial biodegradable polymers and copolymer in supercritical fluids

Biodegradable polymers have received much attention as materials for reducing environmental problems caused by conventional plastic wastes. In this work, the thermodynamic behavior of binary and ternary systems composed by commercial biodegradable polymers and high-pressure fluids [poly(d,l-lactide) + dimethyl ether, poly(d,l-lactide) + carbon dioxide, poly(d,l-lactide) + chlorodifluoromethane, poly(d,l-lactide) + difluoromethane, poly(d,l-lactide) + trifluoromethane, poly(d,l-lactide) + 1,1,1,2-tetrafluoroethane, poly(butylene succinate) + carbon dioxide and poly(d,l-lactide) + dimethyl ether + carbon dioxide] and binary systems formed by commercial biodegradable copolymers and supercritical fluids [poly(butylene succinate-co-butylene adipate) + carbon dioxide] were studied. The Perturbed Chain-SAFT (PC-SAFT) and the Sanchez–Lacombe (SL) non-cubic EoS were used to model the liquid–fluid equilibrium (LFE) for these binary systems, by fitting one temperature-dependent binary interaction parameter. For comparison, the same data were also modeled by using the traditional Peng–Robinson (PR) cubic EoS. The three pure-component parameters of PC-SAFT and SL EoS and two pure-component of PR EoS were regressed by fitting pure-component data (liquid pressure–volume–temperature data for polymers and copolymer and vapor pressure and saturated liquid molar volume for fluids). The estimation of pure-component and binary interaction parameters was performed by using the modified maximum likelihood method with an objective function that includes the cloud point pressure. An excellent agreement was obtained with the PC-SAFT EoS, while the performance of the SL and PR EoS was less satisfactory.     

Description of oxygen permeability in various high polymers using a graph theoretical approach

Graph theory methods are shown to complement group additivity methods of predicting oxygen permeability in certain types of polymers. Graph theory is a topological approach that assigns a set of indices to a molecule to describe its structure. Since many physical properties of molecules depend upon their structure, graph theory indices can be used to describe important properties of molecules. In this work a set of graph theory indices are used to describe the property of a polymer based on a modified representation of the monomer unit. More specifically, Randic indices are used to describe the log of the oxygen permeability with 3.2% average relative error. Polymers comprising the basis set contain backbones of sp², sp³, or aromatic carbons, oxygen, or silicon and have substituents that contain chloride, fluoride, alkyl groups, hydrogen, oxygen, aromatic carbons, or chloro and/or fluoro substituted alkyl groups. The correlation coefficient (R²) (0 ≤ R² ≤ 1) of a nonlinear model is 0.91. The graph theory method for describing the oxygen permeability of these selected groups of polymers is in good agreement with that predicted by the permachor model. The permachor method makes oxygen permeability predictions based upon group additivity and distinguishes the degree of crystallinity of a polymer by empirically assigning different permachor (π) values to identical groups based upon the polymer crystallinity. The inability of graph theory to explain the remaining 9% of the scatter in the data is probably due to failure to incorporate into the graph theory model terms which quantify crystallinity.     

Feasibility study of a commercial irradiation plant in Morocco

On the basis of a market survey, Centre National de l’Energie, des Sciences et des Techniques Nucléaires carried out a feasibility study of a commercial irradiation facility, identified the principal products which will be retained for the industrial applications and evaluated the projection of their volumes for the next five years. The site implementation of the irradiation plant is defined according to the national nuclear regulation and respecting the end users requirements. The costs of the irradiation services and the transport have been discussed and accepted by the industrials. This study shows that all the conditions are regrouped now in Morocco to introduce the irradiation technology to the industrial scale.     

Helix formation in linear achiral dendronized polymers: a computer simulation study

We present a molecular simulation study of the structure of linear dendronized polymers. We use excluded volume interactions in the context of a generic coarse grained molecular model whose geometrical parameters are tuned to represent a poly(paraphenylene) backbone with benzyl ether, Frechet-type dendrons. We apply Monte Carlo sampling in order to investigate the formation of packing-induced chiral structures along the polymer backbone of these chemically achiral systems. We find that helical structures can be formed, usually with defects consisting of domains with reversed helical handedness. Clear signs of helical arrangements of the dendrons begin to appear for dendritic generation g=4, while for g=5 these arrangements dominate and perfect helices can be observed as equilibrium structures obtained from certain types of starting configurations.     

Properties of polythiophene and related conjugated polymers: a density-functional study

Using a parameter-free, density-functional method that has been developed explicitly for the theoretical treatment of infinite, periodic, isolated, helical polymers we study various polymers related to polythiophene. In particular we discuss how the electronic properties of polythiophene are changed when replacing some of the H atoms by CH3 group, by incorporating vinylene bridges into the backbone, or when replacing some or all the CH units of the backbone by N atoms. We observe the weakest effects for the methyl-substitution and the strongest for the N-incorporation. The latter leads to an overall downward shift of all bands, but in contrast to the case for polyacetylene, the unrelaxed compound with N atoms does not have N lone-pair orbitals as the highest occupied ones. Instead these occur at somewhat deeper energies. When comparing the aromatic and quinoid forms we found for the pure compound as well as for the methyl-containing one that the gap closes when passing from the one to the other form which was not found for any of the other materials of the present study. Moreover, the energy of the HOMO was found to depend stronger on the bond-length alternation than the energy of the LUMO, ultimately giving that polarons will induce two asymmetrically placed gap states with the energetically lower one appearing deeper in the gap than the other one.     

A systematic study for the structures and properties of phosphorylated pulp fibers prepared under various conditions

Cellulose - A bleached softwood kraft pulp was phosphorylated with (NH4)2HPO4 and urea at 150 ℃ for 0‒40 min, and the structures and properties of the resulting...     

Structural behavior of hyperbranched polymers in solvents of various qualities: Brownian dynamics simulation

Structural characteristics of third- and fourth-generation dendrimers and irregular hyperbranched polymers of various topologies equal to regular dendrimers in terms of molecular mass in solutions of various topologies are studied via Brownian dynamics simulation. Terminal and inner groups of the studied molecules feature different sensitivities to the quality of a solvent. The mean-square of the radius of gyration, <R _g²>; hydrodynamic radius <R _hyd>; and the radial density distribution functions of monomer units, ρ(r), are calculated. A change in the structural characteristics of molecules induced by worsening in the quality of the solvent is affected by molecular mass, the amount of terminal groups, the ratio between the amount of terminal groups and the total amount of monomer units, and the topology of hyperbranched macromolecules. A comparison of simulation results with the available experimental data makes it possible to use the computersimulation data for determination of the topology of polymers.     

Slow release from gels in various solvents: a fluorescence study

A novel in situ steady state fluorescence experiment was performed for studying slow release processes in gels formed by free radical cross-linking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate. Gels were prepared at 75 °C with pyrene (P_y) as a fluorescence probe. After drying these gels, slow release experiments were performed in various solvent with different molar-volume, V and solubility parameters, δ at room temperature by real-time monitoring of the P_y fluorescence intensity. Slow release diffusion coefficients (D) were measured and found to be in between 0.23×10⁻⁶ and 2.06×10⁻⁶ cm² s⁻¹ depending on the solvent used.     

VOCs在吸附剂上吸附性能的热力学研究

采用色谱法与热重(TG)法,测量了正己烷、甲苯和乙酸乙酯在活性炭、5A、NaY、13X、ZSM-5 (SiO_2/Al_2O_3=27、300)、Hβ以及M CM-41等吸附剂上不同温度下的吸脱附行为,并基于反相气相色谱法测得的数据,计算了其吸附热力学参数ΔH、ΔS和ΔG,分析了上述VOCs分子与吸附剂之间的作用机制,并借助FT-IR验证了吸附质在分子筛表面的吸附机制。结果表明,上述吸附过程存在物理吸附和化学吸附两种方式,其中,物理吸附的作用力大小与吸附剂的孔径分布和分子直径相关,而化学吸附的作用力大小依赖于分子筛硅铝比和Ca~(2+)、Na~+、H~+等阳离子及吸附质分子的偶极矩,且强的化学吸附使得部分吸附质分子的脱附温度高于200℃。     

Interactions between polymers and carbon nanotubes: a molecular dynamics study

We used force-field-based molecular dynamics to study the interaction between polymers and carbon nanotubes (CNTs). The intermolecular interaction energy between single-walled carbon nanotubes and polymers was computed, and the morphology of polymers adsorbed to the surface of nanotubes was investigated. Furthermore, the "wrapping" of nanotubes by polymer chains was examined. It was found that the specific monomer structure plays a very important role in determining the strength of interaction between nanotubes and polymers. The results of our study suggest that polymers with a backbone containing aromatic rings are promising candidates for the noncovalent binding of carbon nanotubes into composite structures. Such polymers can be used as building blocks in amphiphilic copolymers to promote increased interfacial binding between the CNT and a polymeric matrix.     

Fibrous membranes electrospinning from acrylonitrile-based polymers: specific absorption behaviors and states of water

Fibrous membranes with a fiber diameter ranging from 80 to 800 nm are prepared from polyacrylonitrile and poly[acrylonitrile-co-(N-vinyl-2-pyrrolidone)] by the electrospinning process. The parameters can be controlled to fabricate fibrous membranes with similar fiber diameters (between 600 and 800 nm) for further studies on the swelling behaviors and water states. Water swelling experiments indicate that the fibrous membrane has a great capacity for water sorption, which reaches a maximum in a few minutes because of its extremely high porosity. Furthermore, a remarkable overshoot occurs as a result of polymer chain relaxation and the non-compact structure of the fibrous membranes. Contrary to the dense membrane, the equilibrium water content in the fibrous membrane decreases with the content of hydrophilic NVP though the maximum is almost the same. Results from DSC experiments demonstrate that only non-freezable bound water and free water can be distinguished in the fibrous membrane. On the basis of the results of water swelling and DSC experiments, it is concluded that the specific behaviors of the fibrous membranes are induced by the non-compact and pore-fiber discontinuous structure, which is different from either dense membranes or hydrogels. [GRAPHS: SEE TEXT] DSC curves of fully swollen electrospun fibrous membranes and of fully swollen dense membranes with different NVP contents.