Mohammad S M Saifullah

Mohammad S M Saifullah
Paul Scherrer Institut | PSI · Laboratory of Micro- and Nanotechnology

Ph. D. (Cambridge)

About

72
Publications
11,959
Reads
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1,807
Citations
Additional affiliations
March 2013 - March 2016
Agency for Science, Technology and Research (A*STAR)
Position
  • Senior Scientist I
August 2006 - March 2013
Agency for Science, Technology and Research (A*STAR)
Position
  • Scientist III
January 2003 - July 2006
University of Cambridge
Position
  • Project Leader in Nanofabrication & IRC Research Fellow
Education
October 1994 - December 1997
University of Cambridge
Field of study
  • Nanolithography
July 1992 - January 1994
Indian Institute of Science
Field of study
  • Metallurgy
May 1988 - June 1992

Publications

Publications (72)
Article
Full-text available
Background: Metal-containing resists entered the mainstream semiconductor industry process flow to mitigate the low absorbance of extreme ultraviolet (EUV) radiation by thin films of organic resists that lead to poor sensitivity and their inability to handle rigors of development and etching conditions. Aim: The long and rich history of using met...
Article
Full-text available
Increasing the surface area-to-volume ratio of materials through size reduction is a desired approach to access maximum possible surface sites in applications such as catalysis. However, increase in the surface energy with the decrease in dimension warrants strong ligands to stabilize nanosystems, which mask the accessibility of the active surface...
Article
Carbon nanotube (CNT)–silicon (Si) heterojunctions show exceptional electrical behavior and hence are promising for electronic and optoelectronic applications. In particular, single wall CNTs (SWCNTs)–Si heterojunctions have been widely studied for these applications. Since multiwall CNTs (MWCNTs) have higher electrical conductivity than SWCNTs, en...
Article
Direct patterning of thermoelectric metal chalcogenides can be challenging and is normally constrained to certain geometries and sizes. Here we report the synthesis, characterization, and direct writing of sub-10 nm wide bismuth sulfide (Bi2S3) using a single source, spin coatable, and electron beam sensitive bismuth(III) ethylxanthate precursor. I...
Article
Molybdenum disulfide (MoS2) is traditionally grown at a high temperature and subsequently patterned to study its electronic properties or make devices. This method imposes severe limitations on shape and size of MoS2 crystals that can be patterned precisely at required positions. Here we describe a method of direct nanoscale patterning of MoS2 at r...
Article
Full-text available
Friction and wear remain the primary cause of mechanical energy dissipation and system failure. Recent studies reveal graphene as a powerful solid lubricant to combat friction and wear. Most of these studies have focused on nanoscale tribology and have been limited to a few specific surfaces. Here, we uncover many unknown aspects of graphene's cont...
Article
This work presents a procedure for large-area patterning of designed plasmon resonators that are much smaller than possible with conventional lithography techniques. Fused Colloidal Nanopatterning combines directed self-assembly and controlled fusing of spherical colloidal nanoparticles. The two-step approach first patterns a surface covered with h...
Conference Paper
Full-text available
This work explores the possibility of using ultrathin silicon nitride (SiNx) films with high positive fixed charge in a SiNx/poly-Si passivating contact. The factors including (i) film thickness, (ii) annealing condition (time, temp and ambient) and (iii) surface pre-treatment were optimized to boost the passivation performance of ultrathin LPCVD S...
Article
Current induced spin orbit torques (SOTs) offer an efficient pathway to manipulate the magnetization of a ferromagnet for future magnetic memories and logic devices. Among the various non-magnets utilized, the topological insulators, such as Bi 2 Se 3 , have proven to be one of most efficient spin current generators for SOTs. So far, the preferred...
Article
Full-text available
Friction and wear cause energy wastage and system failure. Usually, thicker overcoats serve to combat such tribological concerns, but in many contact sliding systems, their large thickness hinders active components of the systems, degrades functionality, and constitutes a major barrier for technological developments. While sub-10-nm overcoats are o...
Article
Full-text available
The alloy Co−Fe−B finds extensive application in spintronics, and in particular the perpendicular magnetic anisotropy characteristic of Co−Fe−B−MgO systems is of great interest. While some efforts have been made to examine the effect of composition on magnetic properties of Co−Fe−B materials, the magnetic-property–composition relationship for the C...
Article
Full-text available
L10 FePtC granular media are being studied as potential future magnetic recording media and are set to be used in conjunction with heat assisted magnetic recording (HAMR) to enable recording at write fields within the range of current day recording heads. Media structures based on a FePtC storage layer and a capping layer can alleviate the switchin...
Article
Full-text available
UV-nanoimprint lithography (UV-NIL) is a promising technique for direct fabrication of functional oxide nanostructures. Since it is mostly carried out in aerobic conditions, the free radical polymerization during imprinting is retarded due to the radical scavenging ability of oxygen. Therefore, it is highly desirable to have an oxygen-insensitive p...
Article
Full-text available
Nano-patterning on the order of sub-10 nm is integral to achieve high-density nano-scale devices for various data storage and data processing applications. However, the additional requirement of plana-rization and unwanted side-effects of physical or chemical etching have so far limited the patterning of sub-10 nm devices. In this work, we have dem...
Article
Nanostructures of metal sulfides are conventionally prepared via chemical techniques and patterned using self-assembly. This poses a considerable amount of challenge when arbitrary shapes and sizes of nanostructures are desired to be placed at precise locations. Here we describe an alternative approach of nanoscale patterning of zinc sulfide (ZnS)...
Article
Satisfying the mutually conflicting requirements of easy switchability and high thermal stability still remains a hindrance to achieving ultra-high areal densities in hard disk drives. Exchange coupled composite media used with proper exchange control layers (ECLs) presents a potential solution to circumvent this hindrance. In this work, we have st...
Article
Directed self-assembly of nanoparticles using topographical templates has demonstrated great capabilities of ordering particles at their maximum packing fraction resulting from template confinement effects and free energy minimization. However, to self-assemble nanostructures at a lower packing fraction with a precise control over particle's positi...
Article
Direct imprinting of metals is predominantly achieved by using polydimethylsiloxane (PDMS) molds to pattern metal nanoparticles and subsequently melting them to form continuous structures. Although such a combination can successfully imprint metals, the yield and reproducibility are usually low when sub-100 nm features over large areas are desired....
Article
Full-text available
Assessment of the microbial safety of water resources is among the most critical issues in global water safety. As the current detection methods have limitations such as high cost and long process time, new detection techniques have transpired among which microfluidics is the most attractive alternative. Here, we show a novel hybrid dielectrophoret...
Article
The photocatalytic self-cleaning characteristics of titania facilitate the fabrication of re-useable templates for protein nanopatterning. Titania nanostructures were fabricated over square centimeter areas by interferometric lithography (IL) and nanoimprint lithography (NIL). Using a Lloyd's mirror two-beam interferometer, self-assembled monolayer...
Article
Moth's eye inspired multi-scale ommatidial arrays offer multi-functional properties of great significance in optoelectronic devices. However, a major challenge remains in fabricating these arrays on large-area substrates using a simple and scalable technique. Here we present the fabrication of these multi-scale ommatidial arrays over large-areas by...
Article
Full-text available
After the cost of ownership of tool, the next significant cost involved in nanoimprint lithography is that of mold fabrication. The cost of mold fabrication is proportional to the area of pattern and follows an inverse relationship with the pattern resolution. In this work, the authors demonstrate proof-of-concept fabrication of Si and SiO 2 gratin...
Article
Full-text available
Previous studies have shown that fundamental cell functions such as adhesion, proliferation, and morphology are regulated by the interaction of cells with basement membrane nano- and micron- scale surface topography. By taking the basement membrane as a guiding principle, the surface can be designed with biophysical cues in the form of surface topo...
Article
Full-text available
Shallow embedding of C+ ions (<2 nm) into commercial CoCrPt-based magnetic media using the filtered cathodic vacuum arc technique improves its anti-oxidation and anti-wear properties which are comparable to the conventionally used thicker carbon overcoats of <3 nm. The next generation L10 FePt media subjected to low energy embedment of C+ ions have...
Article
UV- and E-beam direct patterning processes using photosensitive precursor films are reviewed in this chapter. For the UV patterning process, discussed in the first part, reaction processes of precursors, such as metal alkoxides modified with β-diketones and metal complexes of carboxylic acids, with UV-irradiation are reported. The discussion of mul...
Article
Step-and-flash imprint lithography (S-FIL) is a wafer-scale, high-resolution nanoimprint technique capable of expansion of nanoscale patterns via serial patterning of imprint fields. While S-FIL patterning of organic resins is well known, patterning of metal-organic resins, followed by calcination to form structured oxide films remains relatively u...
Article
Flexible palladium-based H2 sensors have a great potential in advanced sensing applications as they offer advantages such as light weight, space conservation and mechanical durability. Despite these advantages, the paucity of such sensors is due to the fact that they are difficult to fabricate whilst maintaining excellent sensing performance. Here,...
Article
Full-text available
Polymer-based anti-reflective coatings (ARCs) on glass pose major challenges for outdoor photovoltaic applications due to their incompatible mechanical and thermal properties. Here we demonstrate a durable, chemically and thermally stable polyhedral oligomeric silsesquioxane-based (POSS) anti-reflective moth's eye nanostructures on glass fabricated...
Article
Direct patterning of oxides using thermal nanoimprint lithography is performed using either the sol-gel or methacrylate route. The sol-gel method results in resists with long shelf-life, but with high surface energy and a considerable amount of solvent that affects the quality of imprinting. The methacrylate route, which is limited to certain oxide...
Article
Full-text available
Three-dimensional hierarchical patterning of metals is of paramount importance in diverse fields involving photonics, controlling surface wettability and wearable electronics. Conventionally, this type of structuring is tedious and usually involves layer-by-layer lithographic patterning. Here, we describe a simple process of direct nanoimprint lith...
Article
Full-text available
Spacer materials are often used to fabricate granular L1{sub 0} FePt media and reduce the grain size, however, at the expense of reduced out-of-plane coercivity. Here, we demonstrate a spacer-less method in which adding 1% helium to argon sputtering gas leads to a substantial improvement in the chemical ordering, as well as the magnetic and microst...
Article
Full-text available
Self-assembly of block copolymers has been identified as a potential candidate for high density fabrication of nanostructures. However, the factors affecting its reliability and reproducibility as a patterning technique on various kinds of surfaces are not well-established. Studies pertaining to block copolymer self-assembly have been confined to u...
Article
Full-text available
Nanostructuring of Al₂O₃ is predominantly achieved by the anodization of aluminum film and is limited to obtaining porous anodized aluminum oxide (AAO). One of the main restrictions in developing approaches for direct fabrication of various types of Al₂O₃ patterns, such as lines, pillars, holes, etc, is the lack of a processable aluminum-containing...
Article
Although step-and-flash imprint lithography, or S-FIL, has brought about tremendous advancement in wafer-scale fabrication of sub-100 nm features of photopolymerizable organic and organo-silicon-based resists, it has not been successful in direct patterning of inorganic materials such as oxides because of the difficulties associated with resist for...
Article
Full-text available
The use of polymerization to solidify, strengthen and imprint liquid organic materials is the basis of ultraviolet (UV) nanoimprint lithography. In spite of these advantages, the use of polymerization to pattern materials in thermal nanoimprint lithography is almost non-existent. In this study, we demonstrate a facile and general method to directly...
Article
The fabrication of very narrow metal lines by the lift-off technique, especially below sub-10 nm, is challenging due to thinner resist requirements in order to achieve the lithographic resolution. At such small length scales, when the grain size becomes comparable with the line-width, the built-in stress in the metal film can cause a break to occur...
Article
Full-text available
We demonstrate a different approach to direct nanoimprint lithography of oxides, in particular TiO(2), using the metal methacrylate route which not only gives very high resolution ( approximately 20 nm) but also provides yields of approximately 100% over areas > 1 cm x 1 cm. TiO(2) was imprinted using a polymerizable liquid 'TiO(2) resin' consistin...
Article
Full-text available
Conventional patterning of HfO(2) as a gate dielectric is a multistep complicated process that involves deposition of oxide, photolithography, and hard mask etching. In order to simplify the process of HfO(2) patterning, the authors have developed photo- and electron beam-sensitive spin-coatable HfO(2) resists for direct writing. They were prepared...
Article
Full-text available
We have studied the response of a sol-gel based TiO(2), high k dielectric field effect transistor structure to microwave radiation. Under fixed bias conditions the transistor shows frequency dependent current fluctuations when exposed to continuous wave microwave radiation. Some of these fluctuations take the form of high Q resonances. The time dep...
Article
Full-text available
This article reviews the progress made in the sub-10 nm electron beam patterning of metal oxides over the last thirty years. The patterning of inorganic resists began with metal halides, they were soon taken over by metal oxides due to their excellent environmental stability. However, these inorganic materials, both halides and oxides, suffered fro...
Article
Full-text available
The transient behavior of a trapped electron in the TiO2 sol-gel based gate dielectric layer of a silicon-on-insulator metal-oxide-semiconductor field effect transistor is investigated. Defects in this dielectric layer give rise to microwave resonances that are electrically detected via the channel current. The lifetime of the excited state is infe...
Article
Full-text available
A silicon on insulator field effect transistor for cryogenic operation has been fabricated using a sol-gel derived TiO2 electron beam resist as a high-k gate dielectric and characterized over a range of temperatures. The TiO2 dielectric layer allows too large a gate leakage current for good device operation at room temperature, but the leakage curr...
Article
High temperature nanoimprinting of viscous polymers which are glassy at room temperature is usually performed using brittle and expensive molds made of inorganic materials. As a replacement, soft molds made of plastics or elastomers have been used because of their low cost and ease of fabrication. However, the deformation of polymer molds under pre...
Article
To explore the full capabilities of proton beam writing (PBW) as a lithographic tool it is important to investigate potential new resist materials. In PBW the interactions of the protons with the resist are comparable to the electron interactions with the resist in electron beam writing. In both techniques the induced secondary electrons will modif...
Article
A photosensitive sol-gel based spin-coatable TiO2 resist has been used for the direct 3D patterning of TiO2 structures, using femtosecond laser pulses. The TiO2 resist is transparent to the femtosecond laser radiation of 780 nm wavelength, and thus allows focusing of laser pulses tightly into the material volume. In the focal area, where the intens...
Article
We demonstrate the uniaxial alignment of a liquid-crystalline conjugated polymer, poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) by means of nanoconfinement during nanoimprinting. The orientation of the conjugated backbones was parallel to the nanolines imprinted into the polymer film. Polarized UV-vis absorption and photoluminescence spectra...
Article
Full-text available
An increasing number of technologies require the fabrication of micro- and nanostructures over large areas. Soft lithographic methods are gaining in popularity for the manufacture of low-cost micrometre and sub-micrometre structures. Increasingly, these methods developed to structure organic resists can also be used to pattern inorganic materials....
Article
Full-text available
We demonstrate the fabrication of sub-10-nm high aspect ratio electron beam patterning of ZnO at the center as well as corners of the 500 μm square main deflection field using a negative tone zinc naphthenate resist. After electron beam exposure, the resist was developed in toluene, resulting in high-resolution patterns as small as 7 nm with an asp...
Article
The fabrication of sub-10 nm high-aspect-ratio structures, as small as ∼5 nm, of ZnO using zinc naphthenate resist was reported. It was observed that zinc naphthenate resist has an electron-beam sensitivity and contrast of ∼15 mCcm-2 and ∼3.3, respectively. A Digital Instruments Nanoscope AFM was used to measure the heights of exposed areas after d...
Article
Full-text available
Electron beam-sensitive spin-coatable Al2O3 resists were prepared by chemically modifying aluminium tri-sec-butoxide with various -ketoesters (R-acetoacetates, R = methyl, ethyl, isopropyl, isobutyl, isoamyl, heptyl, benzyl and 2-[methacryloyloxy] ethyl) in isopropyl alcohol. The reaction product was a chelated complex. With increasing molecular we...
Article
Full-text available
We describe a direct write technique using an electron beam to pattern ZrO 2 on a sub-10 nm scale that bypasses the conventional method of sputtering and lift-off. This technique utilizes spin-coatable ZrO 2 resist prepared by chemically reacting zirconium n-butoxide with benzoyl acetone in ethanol. The patterned resist has a sensitivity and contra...
Article
Conventional methods for electron beam patterning of TiO2 are based on sputtering and lift-off. This poses significant problems in producing high aspect ratio and stoichiometric structures, especially in the sub-100 nm size range. We describe an alternative approach of preparing spin-coatable TiO2 resists by chemically reacting titanium n-butoxide...
Conference Paper
Full-text available
Titanium dioxide has shown its potential application in solar cells, optical waveguides, gas sensors and photochromic devices. One of the hindrances for miniaturization of these devices is the lack of an easy and reliable way of patterning TiO2. In this paper, we describe a simple process of electron beam patterning of TiO2 using a spin-coatable Ti...
Article
Full-text available
We demonstrate a high yield production scheme to fabricate sub-5 nm co-planar metal–insulator–metal junctions. This involves determining the relationship between the actual gap between the metallic junctions for a given designed gap, and the use of weak developers with ultrasonic agitation to process the exposed resist. This results in an improved...
Article
Full-text available
We describe measurements of the stiffness and Young’s modulus, Y of single crystals of molybdenum-based compounds. Atomic force microscopy is used first to image, and then to perform stiffness measurements on crystals which are growing up out of a substrate. Y is extracted by comparing the measured stiffness with that calculated from a continuum el...
Article
Full-text available
We report the self-assembly of single crystals of single-walled carbon nanotubes (SWCNTs) using thermolysis of nano-patterned precursors. The synthesis of these perfectly ordered, single crystals of SWCNTs results in extended structures with dimension on the micrometer scale. Each crystal is composed of an ordered array of tubes with identical diam...