Silicon-based Surfaces Research Articles

Modeling and optimizing of laser-assisted waterjet process parameters for near-damage-free micromachining of monocrystalline silicon

Monocrystalline silicon-based microstructure functional surfaces are widely used in the field of photoelectricity. However, the traditional process is prone to damage due to the hardness and brittleness of monocrystalline silicon. In this study, the depth, width, and depth-width ratio of the micro-V-groove on the surface of monocrystalline silicon were studied using laser-assisted waterjet technology. Firstly, the nanosecond laser pulse width was optimized to minimize processing damage. Then, the response surface method (RSM) was employed to optimize the V-groove’s depth-width ratio and show the process parameters’ interactive effects. The results show that the heated affected zone (HAZ) and lattice disorder at 10 ns are significantly smaller than those at other pulse widths, and there is almost no amorphous phase on the surface of V-grooves. Single process parameter usually has different effects on the size of the V-groove, and the process parameters have significant interactive effects, which are discussed in detail in the study. According to the prediction model, the highest depth-width ratio of a V-groove is 1.39. Near-damage-free V-groove with a high depth-width ratio helps to lower the reflectivity and increase the hydrophobicity of monocrystalline silicon.

Automated Scanning Probe Tip State Classification without Machine Learning.

The manual identification and in situ correction of the state of the scanning probe tip is one of the most time-consuming and tedious processes in atomic-resolution scanning probe microscopy. This is due to the random nature of the probe tip on the atomic level, and the requirement for a human operator to compare the probe quality via manual inspection of the topographical images after any change in the probe. Previous attempts to automate the classification of the scanning probe state have focused on the use of machine learning techniques, but the training of these models relies on large, labeled data sets for each surface being studied. These data sets are extremely time-consuming to create and are not always available, especially when considering a new substrate or adsorbate system. In this paper, we show that the problem of tip classification from a topographical image can be solved by using only a single image of the surface along with a small amount of prior knowledge of the appearance of the system in question with a method utilizing template matching (TM). We find that by using these TM methods, comparable accuracy and precision can be achieved to values obtained with the use of machine learning. We demonstrate the efficacy of this technique by training a machine learning-based classifier and comparing the classifications with the TM classifier for two prototypical silicon-based surfaces. We also apply the TM classifier to a number of other systems where supervised machine learning-based training was not possible due to the nature of the training data sets. Finally, the applicability of the TM method to surfaces used in the literature, which have been classified using machine learning-based methods, is considered.

Luminescence of Macrocyclic Mononuclear DyIII Complexes and Their Immobilization on Functionalized Silicon-Based Surfaces.

Two mononuclear DyIII complexes, [Dy(L1)(NCS)3] (Dy-EDA) and [Dy(L2)(NCS)3] (Dy-DAP), where Ln (n = 1-2) corresponds to a macrocyclic ligand derived from 2,6-pyridinedicarboxaldehyde and ethylenediamine (L1) and 1,3-diaminepropane (L2) were immobilized on functionalized silicon-based surfaces. This was achieved by the microcontact printing (μCP) technique, generating patterns on a functionalized surface via covalent bond formation through the auxiliary -NCS ligands present in the macrocyclic complex species. With this strategy, it was possible to control the position of the immobilized molecules on the surface. Water contact angle measurements, X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectra (IRRAS), and atomic force microscopy (AFM) confirmed that the surfaces were successfully functionalized. Furthermore, the optical properties in a broad temperature range were investigated for the as-prepared compounds. At room temperature, Dy-EDA was shown to emit in the deep blue region (Commission Internationald'Eclairage (CIE): (0.175, 0.128)), while Dy-DAP in the white region (CIE: (0.252, 0.312)). The different CIE values were due to the contribution of the strong emission of the ligand in the case of Dy-EDA. Besides, surface photoluminescence measurements showed that the immobilized complexes retained their bulk emissive properties.

The Modulation of Electrokinetic Streaming Potentials of Silicon-Based Surfaces through Plasma-Based Surface Processing.

A new plasma processing-based methodology for enhancing the streaming potential (Vs) that may be obtained in electrokinetic flows for a given pressure gradient over a silicon surface-based microchannel is indicated. The dependence of the Vs on both the surface zeta potential and the electrolyte slip length was carefully determined through a series of experiments involving the variation of CF4- and Ar-based plasma parameters, incorporating pressure, exposure time, and power. It was determined through analytical estimates that, while the zeta potential is always increased, the slip length may be diminished under certain conditions. A record value of ∼0.1 mV/Pa was obtained using CF4 plasma at 500 W, 10 mTorr, and 300 s of exposure. The implications of the work extend to the investigation of whether smooth surfaces may be effective for generating large Vs's for new modalities of electrical voltage sources in microfluidics-based applications.

Bifunctional nanomaterials for simultaneously improving cell adhesion and affecting bacterial biofilm formation on silicon-based surfaces

In the biomedical field, silicon-based materials are widely used as implants, biomedical devices, and drug delivery systems. Although these materials show promise for implant technologies and clinical applications, many of them fail to simultaneously possess key properties, such as mechanical stability, biostability, stretchability, cell adhesiveness, biofilm inhibition, and drug delivery ability. Therefore, there is considerable need for the development and improvement of new biomaterials with improved properties. In this context, we describe the synthesis of a new hybrid nanocomposite material that is prepared by incorporating bifunctional nanomaterials onto glass and polydimethylsiloxane surfaces. The results show that our hybrid nanocomposite material is elastic, stretchable, injectable, biostable, has pH-controlled drug delivery ability, and display improved cell adhesion and proliferation and, at the same time, impacted bacterial biofilm formation on the respective surfaces.

The Influence of Electrode Width and Sealing Method on Leakage Pressure of Microfluidic Electrochemical Devices

Polydimethylsiloxane (PDMS) has been one of the most actively developed polymers for microfluidics, which irreversibly seals on silicon-based surfaces (e.g., glass) after it is exposed to air plasma. The problem lies in its use in the fabrication of microfluidic electrochemical cells. The metal electrodes (e.g. gold) are inert to the plasma, which causes leakage in the PDMS-gold interface of the cell, affecting the data obtained in electrochemical detection experiments. In recent years, advances have been made in sealing methods of PDMS-glass and PDMS-gold interfaces, using a peptide bond by the reaction of a carboxylic acid and an amine, for the fabrication of microfluidic devices. In this work we have studied the effect of the variation of the width of gold electrodes in the sealing of the PDMS-gold interfaces of the electrochemical cells. It was observed that, using the plasma method, at a width of 3 μm, the system supported leakage pressures of 105 kPa, decreasing to 19 kPa at a width of 700 μm. The influence of the width of the electrode on the leakage pressure can be due to the fact that around the electrode there is a stronger bonding force and, the smaller the width of the electrode, the greater the pressure needed to deform the PDMS. Leakage pressure measurements on chips sealed with the carboxyl-amine method are planned. It is expected that the carboxyl-amine method will support higher pressures than the plasma method at large electrode widths due to the higher adhesion forces between the PDMS-gold interfaces in this method. At small widths, the plasma method is expected to be superior. Figure 1

Lubrication of Si-Based Tribopairs with a Hydrophobic Ionic Liquid: The Multiscale Influence of Water

This work aims to elucidate the role of water on the tribological behavior of silicon-based surfaces lubricated with a hydrophobic ionic liquid (IL), by means of a multitechnique, multiscale approach. At the nanoscale, the presence of water at the interface was found to promote adhesion between a sharp silicon tip and a silicon substrate, when submerged in the IL. In line with this finding, in the case of samples that had been exposed to humid air, lateral force microscopy at low loads revealed a significant contribution of adhesion to friction. Under dry conditions, a low-to-high friction-regime transition is observed at low loads, which is reminiscent of the behavior already observed at the nanoscale in previous studies on IL-mediated lubrication. The comparison of friction-vs-load curves from tests carried out under both humid and dry conditions suggests that a similar mechanism of energy dissipation, presumably involving solid–solid contact between sliding counterparts, is established when applied loa...

Note: Making tens of centimeter long uniform microfluidic channels using commercial glass pipette.

Producing microchannels with diameters between 10 and 20 μm and with lengths in the tens of centimeters is reported. The method can be modified to obtain diameters as narrow as 350 nm. Length-to-diameter aspect ratios that surpass 104 can be produced for a fraction of current production costs. The controllable channel is produced by applying a flame to the narrow end of a commercial pipette that is made from a soda-lime silicate. In combination with a pulling mechanism, applying heat to the composite material lengthens the pipette in a highly uniform way. Given that the materials and methods in this research are cost-effective when compared to femtosecond laser micromachining on 2D silicon-based surfaces, further research into producing microchannels from soda-lime silicates may revolutionize access to 3D controllable microchannels.

Surface structure and wettability tuning of porous silicon films by capillary-driven surface texturing under different current densities of electrochemical etching

Silicon-based biomimetic surfaces with special wettabilities are difficult to be fabricated without lithographic techniques. In this report, superhydrophobic surfaces of porous silicon (PSi) with adjustable papillary microstructures have been prepared simply by electrochemical etching of n-type silicon, capillary-driven surface texturing (CDST) of PSi films and surface modification. According to the results of FE-SEM and Drop Shape Analyzer, surface morphologies (from 2D pore structures to 3D papillary microstructures) and corresponding wettabilities (Contact angles, CAs: 134.8°-158.9°; Sliding angles, SAs: 180°-1°) of PSi films can be adjusted efficiently by current density (<20 mA cm−2). The sizes and distribution of inverted-pyramid structures (IPSs) at the interfaces and symbiotic macropores in their centers are essential for such an adjustment. Considering the excellent biocompatibility of PSi, Such surfaces will be beneficial to the silicon-based biosensors, microarrays and microfluidics.

Covalent immobilization of dysprosium-based metal–organic chains on silicon-based polymer brush surfaces

We report on a process for immobilizing metal–organic chains constructed of dysprosium and sodium ions based on 5-aminopyridine-2-carboxylic acid, onto silicon-based surfaces coated with poly(acrylic acid) (PAA) polymer brushes.

ADHESIVE CONTACT BETWEEN SILICON-BASED MEMS TOOTH SURFACES MODELLED BY THE MULTISCALE MULTI-BLOCK MODEL

The contact interactions between microgear silicon-based MEMS teeth working in a clean and a vacuum environment are under consideration. A new approach has used to determine the friction force and the coefficient of friction over the whole meshing surfaces of the teeth. In this approach, the dry friction force is calculated through the energy dissipated during sliding contact between two meshed micro-tooth elastic rough surfaces. The energy dissipated may be caused by the different physical and chemical interactions between the counterparts surfaces. Due to the vacuum environment, these mechanisms reduced to the energy lost due to the dissociation of chemical and van der Waals bonds, and the energy lost through the elastic interlocking between the asperities located on the meshing micro-tooth surfaces. There is no plastic deformation of the microgear tooth surface asperities due to their size and the Polonsky-Keer effect. A multiscale hierarchical elastic structure (a multiscale block) is used to model the surface asperities. The tooth block roughness has modelled at two scales specified by the character of interactions: atomic level, where chemical interactions occur, and adhesive subscale, where van der Waals interactions are significant. The adhesion layer is defined similarly to Maugis approximation. The adhesion force of each nanoasperity has assumed to be equal to the pull-off force in the Boussinesq-Kendall model and corrected by the Borodich no-slip coefficient. Atomic Force Microscopy (AFM) techniques have been used to measure the tooth roughness. It is argued that there be a high probability for stiction between the clean silicon surfaces due to very high values of the friction force between the micro-conjunctions. On the other hand, the tooth surfaces having functionalized carbon-based layers are much less prone to stiction. However, due to wear of the functionalized coating the probability of stiction will start to increase. The results of the simulation for both the non-functionalized and functionalized micro-tooth surfaces (silicon-based MEMS surfaces) are presented.

Optimization and characterization of a homogeneous carboxylic surface functionalization for silicon-based biosensing

A well-organized immobilization of bio-receptors is a crucial goal in biosensing, especially to achieve high reproducibility, sensitivity and specificity. These requirements are usually attained with a controlled chemical/biochemical functionalization that creates a stable layer on a sensor surface. In this work, a chemical modification protocol for silicon-based surfaces to be applied in biosensing devices is presented. An anhydrous silanization step through 3-aminopropylsilane (APTES), followed by a further derivatization with succinic anhydride (SA), is optimized to generate an ordered flat layer of carboxylic groups. The properties of APTES/SA modified surface were compared with a functionalization in which glutaraldehyde (GA) is used as crosslinker instead of SA, in order to have a comparison with an established and largely applied procedure. Moreover, a functionalization based on the controlled deposition of a plasma polymerized acrylic acid (PPAA) thin film was used as a reference for carboxylic reactivity. Advantages and drawbacks of the considered methods are highlighted, through physico-chemical characterizations (OCA, XPS, and AFM) and by means of a functional Protein G/Antibody immunoassay. These analyses reveal that the most homogeneous, reproducible and active surface is achieved by using the optimized APTES/SA coupling.

Superhydrophobicity of Silicon-Based Microstructured Surfaces

Here, a simple method was presented for fabricating superhydrophobic silicon surfaces. Square-pillar-array samples were fabricated on silicon substrates by using the femtosecond laser micromachining technology. We measured the static and dynamic contact angles for water on these surfaces. The contact angles and the rolling angles on the silicon surfaces were measured through an optical contact angle meter. Wettability studies revealed the films exhibited a superhydrophobic behaviour with a higher contact angle and lower rolling angle-a water droplet moved easily on the surface.

Fabrication of superhydrophobic and highly oleophobic silicon-based surfaces via electroless etching method

This study reports on a simple method for the preparation of superhydrophobic and highly oleophobic nanostructured silicon surfaces. The technique relies on metal-assisted electroless etching of silicon in sodium tetrafluoroborate (NaBF4) aqueous solution. Then, silver particles were deposited on the obtained surfaces, changing their overall physical morphology. Finally, the surfaces were coated by either C4F8, a fluoropolymer deposited by plasma, or by SiOx overlayers chemically modified with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS) through silanization reaction. All these surfaces exhibit a superhydrophobic character (large apparent contact angle and low hysteresis with respect to water). In addition, they present high oleophobic properties, i.e. a high repellency to low surface energy liquids with various contact angle hysteresis, both depending on the morphology and type of coating.

Micro-and nanostructured silicon-based superomniphobic surfaces

We report on the fabrication of silicon nanostructured superhydrophobic and superoleophobic surfaces also called “superomniphobic” surfaces. For this purpose, silicon interfaces with different surface morphologies, single or double scale structuration, were investigated. These structured surfaces were chemically treated with perfluorodecyltrichlorosilane (PFTS), a low surface energy molecule. The morphology of the resulting surfaces was characterized using scanning electron microscopy (SEM). Their wetting properties: static contact angle (CA) and contact angle hysteresis (CAH) were investigated using liquids of various surface tensions. Despite that we found that all the different morphologies display a superhydrophobic character (CA>150° for water) and superoleophobic behavior (CA≈140° for hexadecane), values of hysteresis are strongly dependent on the liquid surface tension and surface morphology. The best surface described in this study was composed of a dual scale texturation i.e. silicon micropillars covered by silicon nanowires. Indeed, this surface displayed high static contact angles and low hysteresis for all tested liquids.

Comparison of structures and hydrophobicity of femtosecond and nanosecond laser-etched surfaces on silicon

The rough micro- and nano- scale hierarchical structures on surfaces of materials render the surfaces superhydrophobic. In this context, we obtain both microscale grating structures and nanoscale induced structures (with some splashes) on silicon-based surfaces by means of laser etching and inducing. Our research focuses on the differences of morphology and hydrophobicity for silicon-based microstructured surfaces fabricated by femtosecond laser and nanosecond laser. The results indicated that the grating microstructures fabricated by femtosecond laser are smoother and with smaller top width of groove. Moreover, better micro-nanoscale hierarchical structures can be obtained by femtosecond laser overlapped etching for many times. On the surface with such structures, the water droplet is at Cassie–Baxter state and the contact angle (CA) is 144.6°, which indicates that the surface is middle hydrophobic. This work may provide an effective approach for fabrication of self-cleaning functional surfaces and devices.

Surface Patterning with Chemisorbed Chemical Cues for Advancing Neurochip Applications

We are currently developing multisite planar patch-clamp chips capable of recording high resolution electrophysiological function from individual neurons established in culture. This capability provides a unique opportunity to establish and study communication between synaptically connected neurons on-chip at the level of ion channel function. Critical to realizing this goal for mammalian cell applications are chip surface functionalization strategies that will promote attraction and adhesion of cells to on-chip interrogation features as well as facilitate in the guidance of connectivity between neurons. Here, a chemical strategy is presented that has been adapted to be compatible with standard photolithography techniques for chemical patterning of amine rich cell adhesion promoters on silicon-based surfaces. This chemisorption approach will not only enable electrophysiological studies of neuronal networks but also allow patterning of small peptides such the ones containing the RGD motif, known to induce cell adhesion via molecular recognition of integrin receptors on cell membranes and also stimulate other important biological processes.

Synthesis of a Zwitterionic Silane and Its Application in the Surface Modification of Silicon-Based Material Surfaces for Improved Hemocompatibility

A phosphorylcholine-like silane coupling agent bearing zwitterionic molecular structure was synthesized and studied. The chemical structure of this silane coupling agent was characterized by FTIR, 1H NMR and 31P NMR. The zwitterionic structure was successfully constructed onto the surface of silicon as a self-assembled layer (SAL). Static water contact angle, and atomic force microscopy (AFM) were used to investigate the wettability and surface topography of the modified silicon surfaces. Static water contact angle results indicated that the hydrophilicity of the surfaces could be effectively improved by the modification with this zwitterionic silane coupling agent. The changes of the topography and water contact angle of the modified surfaces with different incubation periods in PBS solution were also measured to evaluate the stability of the SALs. Blood compatibility of the modified surfaces were evaluated by testing the full-blood activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT), as well as by observing the adhered blood platelets onto the surface. The modified surfaces showed prolonged clotting time and fewer adherent platelets, revealing that the blood compatibility was evidently improved by the modification using this zwitterionic silane.

Investigation of Platelet Responses and Clotting Characteristics of in situ Albumin Binding Surfaces

The response of biomaterial surfaces when exposed to blood is in part dependent upon the nature and composition of the adsorbed layer of proteins. Surfaces passivated with albumin have been shown to reduce platelet adhesion and activation. In an attempt to develop surfaces that can selectively and specifically bind albumin, silicon-based surfaces were functionalized with linear peptides and chemical ligands that displayed an affinity for albumin. Peptide functionalized surfaces were observed to preferentially bind albumin when compared to human immunoglobulin and human fibrinogen, which possess low densities of surface adsorbed platelets. The platelet morphology was noted to be discoid on the peptide modified surface. Both the unmodified control and SCL functionalized surfaces had high densities of surface adhered platelets with spread out morphology. The peptide and SCL functionalized surfaces were noted to have no impact on PTT and PT clotting times, indicating that the extrinsic and intrinsic pathways were unperturbed by the surfaces generated.

DESIGN AND FABRICATION OF SUPER-HYDROPHOBIC SURFACES ON SILICON WAFERS AND STUDY OF EFFECTS TO HYDROPHOBICITY

Some superhydrophobic siliconbased surfaces with periodic square pillar array microstructures were designed and fabricated, also their apparent contact angles (CAs) were quantitatively measured. On the basis of the classical Wenzel's theory and Cassie's theory, two generally applicable equations corresponding of the cases of wetted contact and composite contact, which could reflect the relations between geometrical parameters of square pillar mierostructures and apparent CAs, were educed. Then a theoretical prediction of the fabricated siliconbased surfaces was carried out by the equations, which was compatible with the result of experimental measurement, and this showed the rationality of the educed equations. The CAs of the surface prepared by merely plasma etching to create microstructures and by only Teflon treating were compared, and the result indicated that the effect of the former on achieving hydrophobic surfaces was greater than that of the later. Under the premise of synthetically considering transition between the two contact states, the effects of geometrical parameters of the square pillar microstructures to hydrophobicity were analyzcation, thereon a design condition and a design principle for super-hydrophohic surfaces which would be of specific application value were summarized.