Bare Silicon Surface Research Articles

Enhancement in the Stability of Porous Silicon Using Electrochemical Grafting of Polymer 2,6 Dihydroxy Naphthalene

While there have been many advancements related to porous silicon, the reactivity of silicon with the ambient (particularly in environments with oxygen and humidity) has limited its use and integration in a wide variety of applications. Therefore, it is important to passivate the surface of nanostructured/porous silicon. To this end, there have been many reports in literature where passivation of bare (or unpassivated) porous silicon (UPSi) surface has been performed using gas phase techniques (thermal carbonization) and solution-based methods. In this work, we have studied the influence of the electrochemical deposition of polymer 2,6 dihydroxynaphthalene (2,6 DHN), in enhancing the stability of porous silicon surfaces.Porous silicon was synthesized by the electrochemical etching of pre-cleaned p-type silicon substrates with resistivity of about 0.001 Ω-cm to 0.005 Ω-cm, in a PTFE cell that we have fabricated, with 48% HF and ethanol mixture (7:3) as the electrolyte solution, at a current density of about 1.08 A/cm². The polymer solution used for electrodeposition was prepared as a solution of 1 mM 2,6-dihydroxy naphthalene (2,6-DHN) in 100 mL of 1x phosphate buffer solution, which was vacuum infiltrated in the synthesized porous silicon and electrodeposited on the same with the standard three electrodes chronopotentiometry method, at a constant current density of about 2 mA/cm² for 120 seconds. Electrodeposited porous silicon was kept on the hot plate for 10 min at 220℃, followed by a thermal treatment at 600℃, for 180 min, in the presence of N2 flow (1 L/min).The surface morphology of the unpassivated porous silicon (UPSi) and passivated porous silicon (PPSi) are shown in the insets of Fig. 1(a) and (b), respectively. This suggests the presence of an incredibly thin coating of the polymer on the pore walls. The pores in, both, unpassivated and passivated porous silicon samples (UPSi and PPSi) remained open and unobstructed, offering a uniform distribution of pores with sizes ranging between 5 nm and 20 nm.To perform a corrosion test of the UPSi and PPSi, we look at these layers after they have been exposed to 1 M NaOH aqueous solution, for different time durations. We have seen the formation of a spontaneous bubble on the surface of the UPSi sample during the test. To this end, we have observed visible and morphological changes of both UPSi and PPSi samples after the corrosion stability test for 5 seconds and 120 minutes, respectively, as seen in Fig. 1(a) to (h). Due to the very high internal area and the hydrogen-terminated surface, in an aqueous solution, UPSi is oxidized by water at room temperature and degrades. In comparison, the PPSi sample is stable for more than 120 minutes.Electrochemical characterisation of UPSi and PPSi was performed in a 10 mM NaCl aqueous electrolyte with a three-electrode cyclic voltammetry (C-V) setup. C-V measurements of the UPSi sample show strong redox reaction in the potential window of 0 V to 1 V, whereas, the PPSi sample shows a nearly constant charging current response in the potential window of -1 V to 1 V, as shown in Fig. 1(i). These results emphasize that the passivation of porous silicon using 2,6 DHN polymer makes it more stable and less reactive in an aqueous medium. Figure 1

Analysis of CeO2/SiO2 double-layer thin film stack with antireflection effect for silicon solar cells

This study introduces CeO2/SiO2 double-layer film stacks and its antireflection coating effect. Optical properties were analyzed by spectrophotometer measurements; surface morphology and cross-sections were observed by Scanning Electron Microscopy (SEM); elemental distributions and crystallographic properties were determined by Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) measurements. Average reflectance of single-layer 0.3MSiO2, 0.6MSiO2, and 0.3MCeO2 thin films were 30.54%, 20.12%, and 14.23%, respectively. Average reflectance was decreased significantly down to 5.9% by 0.3MCeO2/0.6MSiO2 double-layer thin films comparing to those of the results of single-layer films and bare silicon surface reflection (~40%). Antireflective effect of the films on solar cells was estimated by simulation using the measured reflection data. Simulated solar cells indicate that 0.3MCeO2/0.6MSiO2 double-layer antireflective coatings are capable to increase the efficiency significantly and conversion efficiency of 21.7% could be achieved.

Optoelectronic Readout of Single Er Adatom's Electronic States Adsorbed on the Si(100) Surface at Low Temperature (9 K).

Integrating nanoscale optoelectronic functions is vital for applications such as optical emitters, detectors, and quantum information. Lanthanide atoms show great potential in this endeavor due to their intrinsic transitions. Here, we investigate Er adatoms on Si(100)-2×1 at 9 K using a scanning tunneling microscope (STM) coupled to a tunable laser. Er adatoms display two main adsorption configurations that are optically excited between 800 and 1200 nm while the STM reads the resulting photocurrents. Our spectroscopic method reveals that various photocurrent signals stem from the bare silicon surface or Er adatoms. Additional photocurrent peaks appear as the signature of the Er adatom relaxation, triggering efficient dissociation of nearby trapped excitons. Calculations using density functional theory with spin-orbit coupling correction highlight the origin of the observed photocurrent peaks as specific 4f→4f or 4f→5d transitions. This spectroscopic technique can facilitate optoelectronic analysis of atomic and molecular assemblies by offering insight into their intrinsic quantum properties.

Design of a Highly Efficient Subwavelength Antireflective Structure for Solar Cells

An efficient optical antireflective (AR) structure plays a vital role in high-performance thin-film solar cells. Here, we design a surface relief AR structure consisting of a two-dimensional (2D) array of a subwavelength ring and pillar-shaped feature, capable of suppressing optical reflection over a wide spectral window of the solar spectrum. Our simulations show that the weighted average reflectance of the subwavelength AR structure is as low as 4.2% in the 400–1100 nm spectral range in the normal incidence condition and almost 10-fold reduction compared with a bare silicon surface. When placed on the front side of a simple Si thin-film photovoltaic solar cell, this subwavelength AR structure leads to an improved light absorption with simulated results showing an increase of 53% short-circuit current compared to a flat solar cell. Besides, our simulations show that this AR structure could, in principle, perform well against reasonable fabrication errors.

Influence of nanofiber coating thickness and drop volume on spreading, imbibition, and evaporation

It is known that heat transfer resulting from the drop impact onto a hot substrate can be enhanced with the use of nanostructured coatings, such as nanofiber mats, on the substrate surface. One heat transfer enhancement mechanism is related to liquid imbibition into the porous structure and subsequent evaporation. The detailed mechanisms of liquid spreading, imbibition into the porous structure, and evaporation are still not understood. In this work, the influence of nanofiber coating thickness and drop volume on the kinetics of ethanol drop spreading, liquid imbibition and evaporation on a substrate without additional heating are studied. The initial phase of drop spreading as well as the overall processes are studied simultaneously which allows a direct comparison of influencing factors on the different wetting stages or subprocesses. Four different mat thicknesses in the range of 4−42 μm were investigated, and the results for the drop spreading and evaporation were compared with the bare silicon surface. The results show that, for a mat thickness of 14 μm and higher, the maximal imbibed area as well as the drying time depend only on the drop volume and are nearly independent of mat thickness. However, for the thinnest mat tested, the imbibed area was significantly smaller and the drying time was longer than for thicker coatings.

Dissolution suppression of self-assembled GaSb quantum dots on silicon by proper surface preparation

The temperature stability of high-density GaSb quantum dots grown on a Si(111) surface using solid-phase epitaxy is investigated during annealing at 450 °C. It is found that the bare silicon surface plays a critical role in the GaSb decomposition through the destruction of Sb–Ga bonds with the simultaneous formation of Sb–Si bonds. GaSb decomposition can be significantly suppressed if saturated monolayer coverage in the form of the Si(111)-(√3 × √3)-R30°-Sb surface reconstruction is preliminarily formed. This allows GaSb quantum dots to be embedded in the silicon matrix using molecular beam epitaxy at high temperature.

Transport dynamics of droplet impact on the wedge-patterned biphilic surface

Droplet impact on biphilic surfaces with a wettability contrast has been intensively studied in recent years. In this work the effects of tilting and apex angles on droplet transport dynamics after impacting on a wedge-patterned biphilic surface at low Weber numbers were investigated experimentally. The biphilic surface was fabricated by applying a hydrophobic polymer coating on a bare silicon surface. According to the experimental results, a larger apex angle below 67.4° can accelerate the droplet effectively at first. Then the friction force controls the droplet movement and reduces the speed. The tilting angle along the hydrophilic direction activates the droplet. If the gravity component is opposite to the hydrophilic direction and the tilting angle is over 15°, the droplet can hardly move toward the hydrophilic area. By modeling the hydrodynamics of the droplet movement after impact on a biphilic surface with assumptions of no evaporation, no Marangoni effect, negligible dynamic contact angle variation and negligible rotation effect, the surface tension values versus the position at different apex angles are derived. The predicted position versus time trends agree well with the experimental data. This study aims to provide a better understanding of the mechanisms of droplet hydrodynamics on wedge-patterned biphilic surfaces at low Weber numbers.

Dissolution and mineralization behavior of metallic impurity content in diamond wire saw silicon powder during acid leaching

Metallic impurity removal is essential for the recovery and purification of silicon from diamond wire saw silicon powder during acid leaching process. However, the related dissolution and mineralization behavior are unclear, which are the two main factors governing the capacity of metallic impurity removal during the acid leaching process for silicon recovery from diamond wire saw silicon powder. Metallic impurities have different characteristics in diamond wire saw silicon powder, especially the mineralization hindering the deep removal of impurities. In this study, the dissolution behavior in out-field and mixed lixiviant assisted intensification acid leaching were investigated, respectively. Further, it is of interest in this study to search the root cause of the dissolution behavior from impurity sources with a unique insight, where related theory was used to explain both the mineralization behavior and dissolution behavior. Results revealed that the acid leaching dissolution occurred from the surface inwards, as well as the root cause, which is caused by mineralization behavior. Owing to the fact that the bare silicon surface developed on the amorphous SiO2 layer, the retention of metallic impurity was the result of the SiO2 layer obstacle. The dissolution behavior could be explained as the disintegrating corrosion of SiO2. For this reason, the 4 M HCl + 0.5 M HF mixture with a total removal efficiency of 99.28% outperformed out-field assisted leaching. This study can provide a suitable foundation for understanding the dissolution behavior and mineralization behavior for impurity removal, as well as contribute a roadmap for further silicon purification from diamond wire saw silicon powder.

Controlled Electroless Deposition of Noble Metals on Silicon Substrates Using Self-Assembled Monolayers as Molecular Resists To Generate Nanopatterned Surfaces for Electronics and Plasmonics

Electroless deposition of noble metals on silicon has applications in a wide range of fields including electronic circuitry, metal plating industry, lithography, and other fabrication techniques. In addition, studies using self-assembled monolayers (SAMs) as resists for electroless deposition for controlled deposition have significant potential for aiding advancement in the fields of nanoelectronics, sensing applications, and fundamental studies. Herein, we discuss the development of appropriate plating solutions for controlled deposition of metallic gold and silver on Si(111) surfaces in the presence of an organic silane monolayer acting as a resist film for directed metal deposition to produce metal-monolayer hybrid surfaces while investigating microscopic plating trends. For this, plating solutions were optimized to deposit metal on bare silicon surfaces while avoiding deposition on the SAM protected areas. Trends in the electroless deposition of gold and silver on a Si(111) surface as a function of concentration of metal ions, NH4F, citric acid, sodium citrate, polyvinylpyrrolidone (PVP), and deposition time have been monitored under ambient conditions. The resulting surfaces were characterized using atomic force microscopy (AFM), and the stability of plating solutions was investigated by UV–vis spectroscopy. For both gold and silver, we observed an increase in metal deposition when the concentration of NH4F, citric acid, and deposition time increased. The addition of PVP and the pH of the solution were also shown to have a significant effect on the metal deposition. The octadecyltrichlorosilane (OTS) SAM films act as effective nanoscale resists when the NH4F concentration is reduced from typical plating conditions. In particular, NH4F concentrations from 0.02 to 0.50 M and metal ions concentrations from 0.001 to 0.020 M were found to allow deposition of metal nanostructures on a bare Si surface while preserving OTS protected areas.

Subcooled flow boiling on hydrophilic and super-hydrophilic surfaces in microchannel under different orientations

An experimental investigation of subcooled flow boiling in the rectangular microchannel with hydraulic diameter of 0.94 mm (5.01 mm × 0.52 mm) for different orientations on hydrophilic and super-hydrophilic surfaces is conducted utilizing deionized water as the working fluid. The contact angles of the bare silicon surface and the nano-silica surface prepared through the plasma enhanced chemical vapor deposition method are 65° ± 3° and less than 5° respectively. With an inlet subcooling temperature of 10 °C, the mass fluxes and heat fluxes are tested in the range of 200–500 kg/(m2 s) and 4–25 W/cm2 respectively, while the orientation angles are 0° (bottom-heated horizontal flow), 90° (vertical upflow), 180° (top-heated horizontal flow) and 270° (vertical downflow). Significant appearances at the onset of nucleate boiling (ONB) accompanied with bubble nucleation are observed in the boiling curves. An earlier occurrence of critical heat flux (CHF) is presented for vertical downflow. With the direction of buoyancy opposite to the fluid inflow, the buoyancy force impedes the departure and movement of bubbles against the inertia, causing easier bubble coalescence and elongation as well as prolonged dry-out, which deteriorates heat transfer. At low mass fluxes the pressure drop for the case of vertical downflow is the highest among others, whereas at high mass fluxes the bottom-heated horizontal flow exhibits the maximum pressure drop. Most intense pressure drop fluctuation is obtained for vertical downflow, indicating the most severe flow instability under this orientation. The effect of orientation is weakened with the increment of mass flux due to the dominance of inertia force. At the mass flux of 200 kg/(m2 s), the super-hydrophilic surface delays CHF without increased pressure drop penalty in the vertical orientation, while in the horizontal orientation the effect of surface wettability seems more significant.

Self-assembly of cysteine-functionalized silver nanoparticles at solid/liquid interfaces

Cysteine-functionalized silver nanoparticles (AgNPs) of an average size of 20 ± 5 nm, applied in the studies, were synthesized in a chemical reduction method. Dynamic light scattering (DLS) measurements showed that the nanoparticles were stable for ionic strength lower than 3 × 10−2 M and at pH 4.0 and 9.0. The electrophoretic mobility measurements enabled to determine that the nanoparticles were positively charged with the zeta potential equal to + 51 mV at pH 4.0 and ionic strength 10−2 M. Under the same ionic strength and at pH 9.0, the zeta potential of AgNPs was negative attaining value of −52 mV. The self-assembly of the nanoparticles on bare and polyelectrolyte-modified surfaces of silicon was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The influence of ionic strength and pH on the coverage and structure of the monolayers was studied in detail. It was found that the diffusion-controlled deposition of the nanoparticles on bare silicon surface, under acidic conditions, allows to obtain silver monolayers of coverage up to 0.25. The monolayers of coverage up to 0.26 were formed also under alkaline conditions on poly(diallyldimethylammonium chloride) (PDDA)-modified surfaces. The density and structure of the monolayers were tuned by ionic strength. The experimental results were interpreted in terms of the random sequential model (RSA) which allowed to confirmed that the electrostatic interactions play a dominant role in the self-assembly of the nanoparticles at solid/ liquid interfaces. The characteristics of optical properties of the monolayers revealed that the monolayers deposited under acidic conditions reduce reflection properties of silicon wafers. The decrease in specular reflectance was explained in terms of the plasmonic properties of the nanoparticles. It was shown that the changes in the reflectance strongly depend on the coverage of the AgNP monolayers and on the presence of supporting layer of PDDA. It was conclude that stable cysteine-capped AgNPs can be used for the construction of antireflection materials and in the biology as mimics of such proteins as human serum albumin (HSA).

On-Surface Synthesis of Highly Oriented Thin Metal-Organic Framework Films through Vapor-Assisted Conversion.

Controlled on-surface film growth of porous and crystalline frameworks is a central prerequisite for incorporating these materials into functional platforms and operational devices. Here, we present the synthesis of thin zirconium-based metal-organic framework (MOF) films by vapor-assisted conversion (VAC). We established protocols adequate for the growth of UiO-66, UiO-66(NH2), UiO-67, and UiO-68(NH2) as well as the porous interpenetrated Zr-organic framework, PPPP-PIZOF-1, as highly oriented thin films. Through the VAC approach, precursors in a cast solution layer on a bare gold surface are reacting to form a porous continuous MOF film, oriented along the [111] crystal axis, by exposure to a solvent vapor at elevated temperature of 100 °C and 3 h reaction time. It was found that the concentration of dicarboxylic acid, the modulator, the droplet volume, and the reaction time are vital parameters to be controlled for obtaining oriented MOF films. Using VAC for the MOF film growth on gold surfaces modified with thiol SAMs and on a bare silicon surface yielded oriented MOF films, rendering the VAC process robust toward chemical surface variations. Ethanol sorption experiments show that a substantial part of the material pores is accessible. Thereby, the practical VAC method is an important addition to the toolbox of synthesis methods for thin MOF films. We expect that the VAC approach will open new horizons in the formation of highly defined functional thin MOF films for numerous applications.

A Versatile Method for the Distance-Dependent Structural Characterization of Interacting Soft Interfaces by Neutron Reflectometry.

Interactions between soft interfaces govern the behavior of emulsions and foams and crucially influence the functions of biological entities like membranes. To understand the character of these interactions, detailed insight into the interfaces' structural response in terms of molecular arrangements and conformations is often essential. This requires the realization of controlled interaction conditions and surface-sensitive techniques capable of resolving the structure of buried interfaces. Here, we present a new approach to determine the distance-dependent structure of interacting soft interfaces by neutron reflectometry. A solid/water interface and a water/oil interface are functionalized independently and initially macroscopically separated. They are then brought into contact and structurally characterized under interacting conditions. The nanometric distance between the two interfaces can be varied via the exertion of osmotic pressures. Our first experiments on lipid-anchored polymer brushes interacting across water with solid-grafted polyelectrolyte brushes and with bare silicon surfaces reveal qualitatively different interaction scenarios depending on the chemical composition of the two involved interfaces.

Pool Boiling Heat Transfer Characteristics of Inclined pHEMA-Coated Surfaces

New requirements for heat exchangers offered pool boiling heat transfer on structured and coated surfaces as one of the promising methods for effective heat removal. In this study, pool boiling experiments were conducted on polyhydroxyethylmethacrylate (pHEMA)-coated surfaces to investigate the effect of surface orientation on bubble dynamics and nucleate boiling heat transfer. pHEMA coatings with thicknesses of 50, 100, and 200 nm were deposited using the initiated chemical deposition (iCVD) method. De-ionized water was used as the working fluid. Experiments were performed on horizontal and inclined surfaces (inclination angles of 10 deg, 30 deg, 50 deg, and 70 deg) under the constant heat flux (ranging from 10 to 80 kW/m2) boundary condition. Obtained results were compared to their plain surface counterparts, and heat transfer enhancements were observed. Accordingly, it was observed that the bubble departure phenomenon was affected by heat flux and wall superheat on bare silicon surfaces, while the supply path of vapor altered the bubble departure process on pHEMA-coated surfaces. Furthermore, the surface orientation played a major role on bubble dynamics and could be considered as a mechanism for fast vapor removal from surfaces. Bubble coalescence and liquid replenishment on coated surfaces had a promising effect on heat transfer coefficient enhancement on coated surfaces. For horizontal surfaces, a maximum enhancement of 25% relative to the bare surface was achieved, while the maximum enhancement was 105% for the inclined coated surface under the optimum condition. iCVD was proven to be a practical method for coating surfaces for boiling heat transfer applications due to the obtained promising results.

Role of water in the tribochemical removal of bare silicon

Nanowear tests of bare silicon against a SiO2 microsphere were conducted in air (relative humidity [RH]=0%–89%) and water using an atomic force microscope. Experimental results revealed that the water played an important role in the tribochemical wear of the bare silicon. A hillock-like wear trace with a height of 0.7nm was generated on the bare silicon surface in dry air. As the RH increased, the wear depth increased and reached the maximum level in water. Analysis of frictional dissipated energy suggested that the wear of the bare silicon was not dominated by mechanical interactions. High-resolution transmission electron microscopy detection demonstrated that the silicon atoms and crystal lattice underneath the worn area maintained integral perfectly and thus further confirmed the tribochemical wear mechanism of the bare silicon. Finally, the role of water in the tribochemical wear of the bare silicon may be explained by the following three aspects: the hydroxylation by hydroxyl ions auto-ionized in water, the hydrolytic reaction of water molecules, and the dissolution of the tribochemical product SiOmHn in liquid water. With increasing RH, a greater water amount would adsorb to the Si/SiO2 interface and induce a more serious tribochemical wear on the bare silicon surface. The results of this paper may provide further insight into the tribochemical removal mechanism of bare monocrystalline silicon and furnish the wider reaction cognition for chemical mechanical polishing.

Solid-Liquid Thermal Transport and Its Relationship with Wettability and the Interfacial Liquid Structure.

Experiments and atomistic simulations have suggested the existence of a direct correlation between the wetting properties of a surface and heat transfer across it. In this investigation, molecular dynamics simulations of surface wettability and solid-liquid thermal transport were conducted in order to better understand the relationship between the surface chemistry and thermal transport. The wettability transparency of graphene-coated surfaces was considered in order to investigate heat transfer across a complex interface with similar wettability as a bare surface. The results indicate that the relationship between the interfacial heat transfer and wettability is not universal. The density depletion length was found to reconcile the thermal boundary conductance calculations for different bare and graphene-coated silicon surfaces.

Atmospheric vapor phase deposition of nanometer-thick anti-stiction fluoropolymer coatings for silicon surfaces

Anti-stiction coatings for silicon surfaces are a key technology to prevent the failure of nanoelectromechanical systems (NEMS) during operation and improve the forming accuracy in nanoimprint technology. In this study, we propose an atmospheric vapor phase deposition method to coat a silicon surface with fluoropolymers such as the perfluoropolyethers Fomblin Zdol 2000 and Zdol 4000. Thickness distributions, surface energies, coverages, and stiction forces for the deposited films were evaluated experimentally. The proposed method resulted in over 90% coverage with a film thickness of about 1 nm. The film thickness uniformity was around 0.1 nm over an area of 5 × 5 mm2. This coating effectively reduced the stiction forces by half compared with a bare silicon surface.

ミニチャネル内における微細構造付き伝熱面の流動沸騰熱伝達

In this study, we investigated the influence of the surface wettability on behavior of thin liquid film in the minichannel boiling and heat transfer characteristics. In the air bubble injection experiment under adiabatic condition, the liquid-repellent-type dry-out, where a thin liquid film on the wall ruptures and then the nucleated dry-patch expands without heating, was observed on the bare silicon surface with the contact angle of 50°. On the other hand, the liquid-repellent-type dry-out was not observed on the superhydrophilic surface. The minichannel boiling experiment using the superhydrophilic surface fabricated by wet-etching and chemical oxidation was conducted, and the superhydrophobic surface was found effective to prevent the liquid-repellent-type dry-out that potentially deteriorate the heat transfer coefficient.

シリコン表面に気相蒸着したナノ厚さフッ素系潤滑膜の耐凝着性能の評価

Anti-stiction coating must be one of the key technologies to ensure reliability of NEMS devices and to improve accuracy in a nanoimprint lithography. Typically, polymer films were coated on a silicon surface for anti-stiction. In this study, we proposed vapor-phase deposition technique to form fluoropolymer film on silicon surfaces. Fluoropolymer used in this study was perfluoropolyether (PFPE) Fomblin Zdol (molecular weight of 2000 amu). As a substrate to coat the Zdol, we used a silicon wafer. Anti-stiction properties were verified by measuring surface energies by a contact angle measurement and also by measuring stiction forces using an atomic force microscope (AFM). As a result, it was revealed that the films thicker than 0.5 nm effectively reduced the adhesion forces down to approximately a half of that of the bare silicon surface.

Enhanced adhesion of electron beam resist by grafted monolayer poly(methylmethacrylate-co-methacrylic acid) brush

In electron beam lithography, poor resist adhesion to a substrate may lead to resist structure detachment upon development. One popular method to promote resist adhesion is to modify the substrate surface. In this study, the authors will show that a poly(methylmethacrylate-co-methacrylic acid) [P(MMA-co-MAA)] monolayer “brush” can be grafted onto a silicon substrate using thermal annealing that leads to chemical bonding of the P(MMA-co-MAA) copolymer to the hydroxyl group-terminated substrate, followed by acetic acid wash to remove the bulk, unbonded copolymer. The monolayer brush has a thickness of 12 nm. The authors will show that it can greatly improve the adhesion of positive resist, the ZEP-520A, and negative resist polystyrene to bare silicon surfaces, which led to high resolution patterning without resist detachment upon development. The improvement was more dramatic when patterning dense sub-100 nm period grating structures. But the improvement was negligible for an aluminum substrate, because, even without the brush layer, resist adhesion to aluminum is found already to be strong enough to prevent resist structure peeling off. The current simple and low cost method could be very useful when resist adhesion to the substrate for a given developer is weak.