We demonstrate a wafer-bonded silica-on-silicon planar waveguide platform with record low total propagation loss of (0.045 ± 0.04) dB/m near the free space wavelength of 1580 nm. Using coherent optical frequency domain reflectometry, we characterize the group index, fiber-to-chip coupling loss, critical bend radius, and propagation loss of these waveguides.
Bottom-up nanotechnology has to start with the precise positioning of molecules. For this purpose we are developing molecular printboards, that is, self-assembled monolayers (SAMs) of molecules that have specific recognition sites, for example, molecular cavities, to which molecules can be anchored through specific and directional supramolecular interactions.[1] Such molecular printboards are prepared by the self-assembly of b-cyclodextrin (b-CD) derivatives on gold and silicon oxide surfaces. Herein we describe how to print or write, by microcontact printing (mCP) and dip-pen nanolithography (DPN), respectively, molecular patterns of guest-functionalized calixarene molecules, dendritic wedges labeled by fluorescent groups, and dendrimers on b-CDterminated printboards. The binding, as well as the desorption of the molecules, can be fine-tuned by chemical design, which allows virtually unlimited flexibility in the chemical functions that can be employed. These structures can be subsequently used to direct the adsorption of different materials, for example, fluorescent dyes.Microcontact printing has been developed by Whitesides for the preparation of patterns of molecules on bare surfaces by, for example, the transfer of thiols to gold substrates in the contact areas between a soft polymeric stamp and the substrate. [2,3] This has recently been extended by Mirkin and co-workers to writing with molecules on such surfaces by using the DPN approach.[4] Various types of molecules were deposited onto different substrates by DPN which led to arrays of, for example, DNA, [5] proteins, [6] and nanoparticles. [7] Registry capabilities have been demonstrated as well, [8] and a multipen nanoplotter able to produce parallel patterns with different ink molecules has been developed.[9]b-CD (1 a, Scheme 1) can act as a host for the binding of a variety of small, organic guest functionalities in water through hydrophobic interactions. We prepared self-assembled monolayers (SAMs) of a b-CD heptathioether adsorbate 1 b (Scheme 1) on gold as described before. [10,11] Such adsorbates form densely packed, well-ordered SAMs with equivalent
The implementation of high‐resolution polymer templates fabricated by capillary force lithography (CFL) is explored both in nanoimprint lithography (NIL) and in the wet‐etching of metals. Several different thermoplastic and UV‐curable polymers and types of substrates are incorporated into the general CFL procedure to meet the diverging requirements of these two applications. The mechanical stability of UV‐curable templates for imprinting in polymers, as examined by atomic force microscopy (AFM), and their anti‐adhesive properties are excellent for application in NIL. The conditions for curing the UV‐curable polymer are optimized in order to obtain high‐stability polymer templates. Gold patterns on silicon with a lateral resolution of 150 nm are fabricated by subsequent lift‐off in acetone. Similar patterns with a lateral resolution of 100 nm are fabricated using templates of thermoplastic polymers on gold layers on silicon as an etch mask. The transfer of stamp residues during CFL with these polymer templates is proven by X‐ray photoelectron spectroscopy (XPS) and AFM friction analysis. For poly(methylmethacrylate) (PMMA), the presence of large amounts of silicon‐containing residues is found to compromise the processability of the resulting template in subsequent O2 reactive‐ion etching (RIE) treatment. The extent of silicon contamination is up to six times less for polystyrene (PS). At this level, the etch performance of the PS etch mask is not affected, as was the case for PMMA. Accurate downscaling of the lateral dimensions of the resulting metal patterns by several factors with respect to the dimensions of the PS etch mask is achieved by over‐etching of the gold. Overall, the results in this paper demonstrate the potential of CFL templates as tools for high‐resolution soft lithography.
The transfer of functional molecules onto self-assembled monolayers (SAMs) by means of soft and scanning-probe lithographic techniques-microcontact printing (muCP) and dip-pen nanolithography (DPN), respectively-and the stability of the molecular patterns during competitive rinsing conditions were examined. A series of guests with different valencies were transferred onto beta-cyclodextrin- (beta-CD-) terminated SAMs and onto reference hydroxy-terminated SAMs. Although physical contact was sufficient to generate patterns on both types of SAMs, only molecular patterns of multivalent guests transferred onto the beta-CD SAMs were stable under the rinsing conditions that caused the removal of the same guests from the reference SAMs. The formation of kinetically stable molecular patterns by supramolecular DPN with a lateral resolution of 60 nm exemplifies the use of beta-CD-terminated SAMs as molecular printboards for the selective immobilization of printboard-compatible guests on the nanometer scale through the use of specific, multivalent supramolecular interactions. Electroless deposition of copper on the printboard was shown to occur selectively on the areas patterned with dendrimer-stabilized gold nanoparticles.
This paper reports on recent developments to increase the performance of biomimetic flow-sensor arrays by means of several technological advancements in the fabrication procedures and corresponding sensor design optimizations. Advancements include fabrication procedures with higher process latitude and geometrical modifications of several parts of the flow sensor. The conclusive measurements in this paper support our sensormodel predictions for a 100-fold increase in acoustic sensitivity (down to oscillating flow amplitudes in the order of 1 mm⋅s-1) translating to substantially higher capacitive outputs in comparison to our first-generation biomimetic flow-sensor arrays.
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