μCP Method Research Articles

Tuning interfacial interactions for bottom‐up assembly of surface‐anchored metal‐organic frameworks to tailor film morphology and pattern surface features

AbstractSurface‐anchored metal‐organic frameworks (surMOFs) integrate nanoporous supramolecular MOF materials directly into architectures for applications such as gas storage, chemical sensing, and energy storage. Layer‐by‐layer solution‐phase deposition of the MOF‐14 components (1,3,5‐tris(4‐carboxyphenyl)benzene and copper (II) dimers, respectively) produces a porous and conformal film on carboxyl‐terminated self‐assembled monolayers (SAMs). In this research, the formation of ultrathin (less than 25 nm) surMOF films on codeposited bicomponent SAMs and microcontact printed SAMs is investigated by atomic force microscopy, ellipsometry, infrared spectroscopy, and contact angle goniometry. SAMs composed of methyl‐terminated alkanethiols assembled on gold substrates inhibit surMOF formation, whereas carboxyl‐terminated alkanethiols promote MOF‐14‐based film growth. To tune the density of carboxyl groups that anchor the film, methyl‐ and carboxyl‐terminated alkanethiols of varying concentrations are codeposited on gold. This systematic study demonstrates how surMOF film formation and morphology are impacted by these SAMs with mixed surface functionalities. Chemical patterning methods for SAMs, such as microcontact printing (μCP), commonly have mixed chemical functionalities within certain regions of the pattern. Insights gained regarding how mixed surface functionalities affect surMOF film formation are applied herein to optimize the μCP method to produce chemically patterned SAMs that selectively direct surMOF assembly to produce high‐quality surMOF film features.

Selective Cu Electrodeposition for Sub-Micrometer Redistribution Layers

The density of integrated circuit (IC) was doubled by shrinking the feature size in semiconductor industry. An improvement in density of standard interconnection and the packaging technology is much slower than the IC trends. To overcome the increasing I/O interconnect gap, the semiconductor packaging technology has been driven by many researchers and companies over the many years. The redistribution layers (RDL), one of the important parts for the package process, play a role to rearrange I/O connections from the die to substrate. For fine line pitch below 10μm, the damascene RDL process was proposed. The flow of damascene RDL process was composed of photoresist patterning, a metal layer deposition, Cu electrodeposition and chemical-mechanical planarization (CMP). During the Cu electrodeposition for the damascene RDL process, Cu overburdens were formed on top surfaces of sub-micrometer trenches. Typically the CMP process has been used to remove these overburdens in semiconductor industry, however, this surface planarization process caused an increase in process cost. For prevent the Cu overburden at low cost, the selective Cu electrodeposition which is process filling only trench is required. The selective Cu electrodeposition can be achieved by μCP with various additives. The microcontact printing (μCP) process which transfers the self-assembled monolayers (SAMs) on the top surface of trenches can be one of the solutions preventing the Cu deposition on these top surfaces.[1-2] SAMs are organic molecules that formed spontaneously on the solid surface by chemisorption and organization of alkanethiol, silane, and so forth.[3] In this research, flat polydimethylsiloxane (PDMS) stamp is used for providing on the top surface of patterned substrate. Selective Cu electrodeposition was proceeded on trench in CuSO4 1 M/H2SO4 0.58M electrolyte with various additives. In this study, electrochemical behavior of additives was studied by cyclic voltammetry and selective electrodeposition process was investigated with various additives, applied potential, charge density. The µCP process show the effective suppression of Cu growth on the top surface of trenches so that Cu overburden thickness was significantly reduced. This result reveals the feasibility of Cu trench-selective deposition below 10 μm. The μCP method with various additives shows the possibility of replacing surface planarization process which removes overburden of Cu for the RDL process.. [1]Y.Xia and G. Whitesides, "Soft lithography", Annu. Rev. Mater. Sci., vol. 28, no. 1, pp. 153-184, 1998. [2]S.Alom Ruiz and C. Chen, "Microcontact printing: A tool to pattern", Soft Matter, vol. 3, no. 2, pp. 168-177, 2007. [3]P.Laibinis, G. Whitesides, D. Allara, Y. Tao, A. Parikh and R. Nuzzo, "Comparison of the structures and wetting properties of self-assembled monolayers of n-alkanethiols on the coinage metal surfaces, copper, silver, and gold", J. Am. Chem. Soc., vol. 113, no. 19, pp. 7152-7167, 1991.

Fabrication of detachable hydrogel microplates for separably patterned cell culture

The well plates allow the reduced consumption of culture media in the conventional cell culture. Combined with microtechnology, microengineered templates allowed a precise control of the size, shape and location of the cultured cell into micropatterns. The localized, and micropatterned culture provides many number of cell samples for the subsequent analysis which are cultured at the same condition. However the patterned cells are immobilized on the surface, therefore the limitation still exists that there are difficulties on the cell analysis of the separated cell patterns. In this study, we propose a fabrication method of separable type Poly ethylene glycol diacrylate (PEGDA) microplates and its application onto a micropatterned culture of NIH/3T3 cells. PEGDA microplates were fabricated by single process of photholithography of hydrogel. Collagen layer was transferred onto PEGDA microplates to improve cell-microplate adhesion using µCP method. The 400 µm dot patterns were used in the test. The fabrication process is very simple, low-cost, and does not require expensive MEMS facilities. Because the fabricated microplates are detachable, it provides efficient way for further studies of cell biology by allowing separated analysis of many number of cell samples which are cultured at the same environment with small amount of cell media.

Cool Microcontact Printing To Fabricate Thermosensitive Microgel Patterns

A facile method, cool microcontact printing (cool μCP), of fabricating microgel patterns under ambient conditions is developed. By using spontaneously condensed water on the surface of cold items and the phase transition of polymer microgels below the lower critical solution temperature (LCST), a cool poly(dimethylsiloxane) (PDMS) stamp can be easily decorated with a thin layer of water ink and its pattern can substantially transfer to a substrate that is assembled with microgels. As a proof of concept, one kind of thermosensitive microgel (i.e., poly(N-isopropylacrylamide) (pNIPAM)) is selected to demonstrate our method. A series of pNIPAM microgel patterns with various geometries can be easily generated by featured PDMS stamps through a cool μCP method. The results of control experiment using room-temperature PDMS stamps or patterning the pNIPAM microgel-incorporated fluorescent probe reveal that condensed cold water on a cool PDMS stamp plays an important role when microgel particles are lifted off. In addition, it is also observed that both humidity and contact pressure have effects on the shapes of the pattern fabricated by cool μCP, and more precise or sophisticate patterns can be obtained by adjusting the conditions. It is envisioned that this practically available method, as a good extension to μCP, can facilitate the design of complex patterns, affording great convenience for many inherent applications ranging from photonics to chemical sensing to biotechnology.

Positive‐/Negative‐, Erasable‐/Immobilized‐, Mono‐/Multi‐Color Fluorescence Image Patterning of Molecular‐Scale Porous Polymer Film via a Microcontact Printing Method Using Various Chemical Inks

Fluorescent image patterns of a substituted acetylene polymer film with a large FFV were successfully obtained by a µCP method using several kinds of chemical ink compounds. PO and SCA generated positive-type fluorescent image patterns. On the other hand, an ethanolic solution of DNT generated a negative-type fluorescent image pattern due to a significant quenching effect. An NMP solution of NR gave a two-color image pattern due to an intermolecular energy transfer from PTMSDPA to NR.

A method of printing uniform protein lines by using flat PDMS stamps

In this paper, we report a method of printing uniform protein lines on glass slides by using UV-treated flat PDMS stamps. Unlike traditional microcontact printing (μCP) which requires microstructured PDMS stamps, this μCP method only requires a flat PDMS stamp, an UV lamp and a number of straight needles. Our results show that lines of bovine serum albumin (BSA), immunoglobin (IgG), anti-biotin, anti-human IgG and anti-mouse IgG can be printed evenly on glass slides by using this μCP method. We also demonstrate that the printed protein lines are suitable for applications such as microfluidic immunoassays.

Field-effect transistor characteristics and microstructure of regioregular poly(3-hexylthiophene) on alkylsilane self-assembled monolayers prepared by microcontact printing

Molecular orientation of regioregular poly(3-hexylthiopene) (P3HT) on self-assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS) prepared by microcontact printing (μCP) are investigated using grazing-incidence X-ray diffraction and field-effect measurements. Spin-coated P3HT films on OTS SAMs fabricated by the μCP method are less oriented and exhibit lower diffraction intensity than those prepared by conventional liquid phase deposition (LPD). In spite of the lower crystallinity, the field-effect mobility in P3HT film on μCP-OTS is almost the same as that on LPD-OTS. This result is attributed to the lower density of trapping centers in P3HT films on μCP-OTS, which is manifested by the lower subthreshold swing of transistor characteristics of P3HT films on μCP-OTS.

Study of selective deposition of TaN thin films on OTS patterned Si(100) substrates

Cubic TaN thin films have been selectively deposited on Si(100) substrates in the temperature range of 400 - 500 °C by combination of micro-contact printing (μCP) and metalorganic chemical vapour deposition (MOCVD) methods. The patterned Si(100) substrates were initially fabricated with the self-assembled monolayers (SAMs) using an organic molecule of octadecyltrichlorosilane (OTS) by μCP method. Ta(N(MeEt))3(NtBu) and NH3 were used for the growth of TaN thin film. For a selective growth study, we characterized the as-grown films with optical microscopy (OM), micro-Raman spectrometer and atomic force microscopy (AFM). In the beginning of film deposition TaN thin film preferred to grow on silicon surface area rather than OTS printed area due to hydrophilicity of silicon surface, however, the selectivity of TaN thin film deposition was depended on the deposition time in the deposition temperature range.

Protein patterning on self-assembled polyelectrolyte thin films

This study demonstrated a simple micropatterning method using engineered surface and microcontact printing (μCP). For the selection of appropriate surface, several representative surfaces modified with various functional materials including aldehyde, epoxide, poly- l-lysine, amine, and self-assembled polyelectrolyte multilayers (PEL) were investigated. The PEL coated surface endowing electrostatic interaction force showed most high functionality in point of homogeneous patterning of proteins with high density and preservation of inherent three-dimensional structure of proteins. The printed sizes of protein micropatterns were almost identical to the used microstamp, which proves the μCP method is independent of diffusion of the transferring proteins. At last, the immunoassay as a model system of protein–protein interaction showed good linearity over a range from 100 to 25 μg/ml, indicating the feasibility of a quantitative measurement of the concentration of target proteins in sample. Our proposed approach will be useful for the development of biomedical microdevices because of green chemistry, simple process, and high potential of various applications.

Micropatterning of Electrodes by Microcontact Printing Method and Application to Thin Film Transistor Devices

Electrode micropatterning without etching was successfully achieved by the microcontact printing (µCP) method. We used a conductive polymer poly(3,4-ethylenedioxythiophene)/poly(4-stylenesulfonate) (PEDOT/PSS) as an electrode material. We controlled the surface free energy of poly(dimethylsiloxane) (PDMS) by exposure to vacuum ultraviolet (VUV) light with a wavelength of 172 nm using an excimer lamp. Consequently, we established an inking technique for PEDOT/PSS aqueous dispersion on a PDMS elastomer stamp. The micropatterns of PEDOT/PSS thin films of 1 µm width were fabricated by transferring the PEDOT/PSS aqueous dispersion on the PDMS elastomer stamp to another substrate by the µCP method. Furthermore, we fabricated top contact (TC) organic thin film transistors (OTFTs) with PEDOT/PSS as source and drain electrodes. We demonstrated the successful operation of the fabricated OTFTs with a channel length of 5 µm and an electrode width of 8 µm. Results show that the µCP method is promising for application to various devices that require micropatterning.

Selective growth of iron oxide thin films using the combined method of metal-organic chemical vapor deposition and microcontact printing

The authors have carried out the selective deposition of magnetite iron oxide (Fe3O4) thin films with about 50nm thickness on Si(100) surfaces which were patterned by octadecyltrichlorosilane (OTS) using microcontact printing (μCP) method. The μCP method showed that hydrophobic patterns with microdimension were able to be formed on hydrophilic area such as silicon surface. Iron oxide thin films were deposited on the Si(100) substrates by thermal metal-organic chemical vapor deposition (MOCVD) method using single molecular organometallic precursor of iron pentacarbonly [Fe(CO)5] with high purity (99.999%) oxygen gas. The deposition was performed in the range of 250–350°C substrate temperature for 2–10min under 1×10−2Torr in a homemade MOCVD system. In order to check the selectivity of as-deposited thin films optical microscopy, scanning electron microscopy, and atomic force microscopy analyses were performed. To confirm the crystallinity of deposited thin films, x-ray diffraction patterns and micro-Raman were studied. Also energy dispersive x-ray and x-ray photoelectron spectrometry results showed the composition of the as-grown iron oxide thin films. By means of these results, the authors can suggest the selective deposition mechanisms and tendencies of iron oxide thin films onto the OTS patterned Si(100) surfaces.

Growth of GaN Thin Films on Silicon Using Single Source Precursors and Development of New Patterning Technology by Combination of MOCVD and Micro‐Contact Printing Methods

We have grown the GaN thin films on silicon substrates using the newly developed single source precursors by thermal MOCVD method. Highly oriented GaN thin films in the [002] direction with hexagonal structure were deposited on Si(111) substrates at 800 °C and 1 Torr with Triazido(triphenylphosphine oxide) gallium. XRD pattern and pole-figure analysis proved that the highly oriented GaN film has a single-crystalline nature. PL data of this film show that a strong emission peak but with some large FWHM of 100 meV could be observed at 3.4 eV (365 nm). Patterning of GaN thin films was also successfully performed by MOCVD onto Si(100) substrates of which surface was modified by organic thin film. The organic thin film of SAMs was in first obtained by μCP method. The deposition of GaN thin films has then been carried out onto those modified Si(100) substrates using the single molecular precursor by thermal MOCVD without carrier and bubbler gases. In addition, a buffer layer of thin TiO2 film was applied into the modified Si(100) substrates to understand a possibility of selective deposition of GaN film.