N. Moldovan - Academia.edu (original) (raw)

Papers by N. Moldovan

Ultrananocrystalline diamond (UNCD) with grain sizes in the range of 2 - 5 nm is produced using a... more Ultrananocrystalline diamond (UNCD) with grain sizes in the range of 2 - 5 nm is produced using a microwave plasma chemical vapor deposition process with argon-rich C60 or CH4 plasmas. This material has excellent mechanical properties: high hardness and Young modulus, and an extremely low friction coefficient (approximately 0.01). It is resistant to chemical attack, and is potentially biocompatible. These

Materials and Device Characterization in Micromachining II, 1999

The availability of high-energy, high-flux, collimated synchrotrons radiation has extended the ap... more The availability of high-energy, high-flux, collimated synchrotrons radiation has extended the application of deep X-ray lithography (DXRL) to thickness values of the PMMA resist of several millimeters. Some of the most severe limitations come from plastic deformation, stress, and cracks induced in PMMA during exposure and development. We have observed and characterized these phenomena quantitatively. Protilometry measurements revealed that the PMMA is subjected either to local shrinkage or to expansion, while compression and expansion evolve over time. Due to material loss and crosslinking, the material undergoes a shrinkage, while the radiation-induced decomposition generates gases expanding the polymer matrix, The overall dynamics of the material microrelief and stress during and after the exposure depend on the balance between compaction and outgassing. These depend in turn on the exposure conditions (spectrum; dose, dose rate, seaming, temperature), post-exposure storage conditions, PMMA material properties and thickness, and also on t @@ size and geometry of the exposed patterns.

Materials and Device Characterization in Micromachining, 1998

The adhesion of PMMA layers on silicon wafer has been studied in order to protect the front side ... more The adhesion of PMMA layers on silicon wafer has been studied in order to protect the front side of the silicon wafer while etching the backside in KOH aqueous solution. Pre and post-bake treatment have been performed, different primers have been used to optimise the superficial and interfacial tension of both mask layer and substrate. An adherent layer has been obtained and its behaviour has been explained based on the polar and nonpolar interactions across the interface. Keywords: PMMA, silicon, KOH, work of adhesion, surface energy, interfacial tension, superficial tension, contact angle.

Journal of Applied Physics, 2001

ABSTRACT The results of room-temperature wet etching of GaAs using synchrotron-radiation x rays a... more ABSTRACT The results of room-temperature wet etching of GaAs using synchrotron-radiation x rays are described. Under x-ray illumination, etching occurs on the n-GaAs surface in contact with an acid or base solution or even deionized water. The etching process is studied as functions of the electrolytes, their concentration, semiconductor doping level, and x-ray intensity and energy. The etching mechanism is determined to be primarily electrochemical in nature, but the x-ray radiation chemistry plays a role in the etching. Smoothly etched surfaces are achievable with a root-mean-square surface roughness of 0.7–2.0 nm. We also found that the etching rate increases substantially with the ratio of the sample size to the x-ray exposure size. This is accounted for by the rate-limiting effect on the charge transfer across the semiconductor-electrolyte junction. The chemistry of etched surfaces is studied using x-ray photoelectron spectroscopy and compared to that of as-received surfaces. © 2001 American Institute of Physics.

Microsystem Technologies, 2003

A prototype freestanding copper antiscatter grid with parallel lamellar walls has been fabricated... more A prototype freestanding copper antiscatter grid with parallel lamellar walls has been fabricated using deep X-ray lithography and electroforming. The freestanding copper grid has square shaped lamellar walls that are 25 lm thick and 1 mm tall with a 550 lm period. For mammography applications, the lamellar walls have to be aligned to a point X-ray source of the X-ray system. To achieve this goal, we investigated a dynamic doubleexposure technique. Our progress in using stacked exposures and use of the photoresist SU-8, both to reduce fabrication cost, is also presented.

Journal of Microelectromechanical Systems, 2012

A common method for producing sharp tips used in scanning probe microscopy (SPM) and other applic... more A common method for producing sharp tips used in scanning probe microscopy (SPM) and other applications involving nanoscale tips is to deposit thin-film materials, such as metals, silicon nitride, or diamond-based films, into four-faceted pyramidal molds that are formed by anisotropic etching into a (100) silicon substrate. This well-established method is capable of producing tips with radii as small as a few nanometers. However, the shape of the tip apex is difficult to control with this method, and wedge-shaped tips that are elongated in one dimension are often obtained. This limitation arises due to the practical difficulty of having four planes intersecting at a single point. Here, a new method for producing three-sided molds for SPM tips is demonstrated through the use of etching in (311) silicon wafers. It is shown that silicon nitride and ultrananocrystalline diamond tips fabricated with this new method are wedge free and sharp (< 10 nm radius), thereby restoring tip molding as a well-controlled manufacturing process for producing ultrasharp SPM tips. [2011-0209] Index Terms-Atomic force microscopy (AFM), crystallographic etching, molding, scanning probe microscopy (SPM), silicon, tips. I. INTRODUCTION T IP MOLDING is a well-known nanofabrication method for producing ultrasharp tips, such as those used in scanning probe microscopy (SPM) [1]-[3], field emitters [4], [5], vacuum electronics [6], [7], or tunneling-based devices [8]. Tip molding consists of etching a pyramid-shaped pit into a Manuscript

Introduction Deep x-ray lithography and electroforming allow the production of tall, high-aspect-... more Introduction Deep x-ray lithography and electroforming allow the production of tall, high-aspect-ratio structures with a high degree of precision. One of the important applications for high-aspect-ratio microformed metal structures is mammography. In mammography, an ideal diagnostic image is produced by local reduction in the x-ray intensity as a result of attenuation without scattering by the breast tissue. Because of the large amount of scattered radiation, image contrast is lowered, making diagnosis of diseased tissue subjective and difficult. The quality of mammogram images can be significantly improved by using an antiscatter grid that is transparent for primary radiation and opaque to scattered radiation from all directions [1-4]. In this report, we summarize our results in developing an antiscatter grid for mammography by using deep x-ray lithography and electroforming. The results were presented at international conferences HARMST 2001 [5, 7] and MEMS 2002 [6] and have been ...

Optics Express, 2021

Three (3) items of errata are submitted for our recently published paper [Opt. Express28, 36505 (... more Three (3) items of errata are submitted for our recently published paper [Opt. Express28, 36505 (2020)10.1364/OE.405566]. One is a clarifying extension to the Fig. 3 caption. Two are typographical corrections. The scientific results and conclusions are unaffected.

Optics Express, 2021

Three (3) items of errata are submitted for our recently published paper [Opt. Express28, 36505 (... more Three (3) items of errata are submitted for our recently published paper [Opt. Express28, 36505 (2020)10.1364/OE.405566]. One is a clarifying extension to the Fig. 3 caption. Two are typographical corrections. The scientific results and conclusions are unaffected.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2001

Alkali metals have extremely low-work functions and are therefore expected to result in significa... more Alkali metals have extremely low-work functions and are therefore expected to result in significant enhancement of the electron emission if they are used as coatings on Mo or Si microtip field emission arrays ͑FEAs͒. However, the alkali metals are physically and chemically unstable in layers exceeding a few nanometers in thickness. Maximum enhancement of electron emission occurs for alkali metal layers 0.5-1 monolayer thick, but it is extremely difficult to fabricate and maintain such a thin alkali metal coating. We review here our work of the last three years focused on developing Cu-Li alloy coatings for application to field emitter Spindt-type tip arrays and fabrication of edge emitters with low-voltage high electron emission characteristics for field emission devices. The Cu-Li alloy coatings provide a chemically and thermally stable, self-replenishing, segregated lithium monolayer on the surface of the host Cu layer, resulting in a substantial reduction of the work function of the alloy, compared to that of a thick Li layer or a pure Cu surface. We present results that show a 13-fold reduction in the threshold voltage for electron emission, compared with uncoated Si FEAs. The Cu-Li alloy coatings yielded tip and edge emitters with threshold voltages of 2-10 V/m, depending of the coating thickness and Li concentration in the alloy. New results are presented that show that we can now coat gated Si tip arrays with Cu-Li alloy films, which results in very low emission voltage.

Optical diagnostics will be critical for the operation and performance assessment of burning plas... more Optical diagnostics will be critical for the operation and performance assessment of burning plasma experiments, such as ITER. At the same time, extracting light for these diagnostics with reflective mirrors becomes difficult in the burning plasma environment, due to prolonged exposure to plasma and nuclear radiation. As an alternative, we explore free-standing diffractive optical elements, such as transmission gratings and zone plates. Since in the case of diffractive extractors the light is deflected by periodic slits rather than a surface, they may withstand plasma exposure with less degradation of their optical properties. To investigate this possibility we developed free-standing transmission gratings for the visible range and exposed them in to conditions resembling or exceeding those expected for the ITER `first mirrors'. The results of this study indicate that the gratings can withstand high heat fluxes and plasma and energetic radiation bombardment. In addition, in cont...

MRS Proceedings, 1992

ABSTRACTStress in thin films is one of the mayor technological problems of silicon micromachining... more ABSTRACTStress in thin films is one of the mayor technological problems of silicon micromachining. Therefore stress reduction by a compensation method increases the technological use of a material. Three methods to obtain stress free films are investigated:1. Stress in SiO2 and Si3N4 can be compensated by ion implantation.2. Sandwich layers of SiO2 and Si3N4 can be made internally stress compensated by variation of the thickness ratio.3. Polysilicon is stress reduced by appropriate doping and annealing.The film stress is evaluated by the measurement of the bending of the substrate. Examples of processed membranes, bridges and cantilevers made of stress compensated films are given.

MRS Proceedings, 1992

ABSTRACTStress in thin films is one of the mayor technological problems of silicon micromachining... more ABSTRACTStress in thin films is one of the mayor technological problems of silicon micromachining. Therefore stress reduction by a compensation method increases the technological use of a material. Three methods to obtain stress free films are investigated:1. Stress in SiO2 and Si3N4 can be compensated by ion implantation.2. Sandwich layers of SiO2 and Si3N4 can be made internally stress compensated by variation of the thickness ratio.3. Polysilicon is stress reduced by appropriate doping and annealing.The film stress is evaluated by the measurement of the bending of the substrate. Examples of processed membranes, bridges and cantilevers made of stress compensated films are given.

Materials Science and Engineering: B, 1996

A Monte Carlo program and a program based on the formula of the evolution of atom disappearance p... more A Monte Carlo program and a program based on the formula of the evolution of atom disappearance probabilities were used for the simulation of anisotropic etching of silicon-like crystal dots containing several thousands of atoms. An additional program extracts the local values of the etching rates and represents them in polar diagrams. The obtained figures respect the symmetry of the

Microsystem Technologies, 2004

A method to fabricating two-dimensional antiscatter grids with septa walls oriented toward the fo... more A method to fabricating two-dimensional antiscatter grids with septa walls oriented toward the focal point using deep X-ray lithography and copper electroforming is described. These focused grids can be used in mammography to eliminate scattered X-rays, and result in contrast improvement and significantly better image quality in comparison with the conventional one-dimensional antiscatter grids. Freestanding copper antiscatter grids, up to 2 mm thick, 60 mm • 60 mm in size, and focused to one point have been fabricated. This method can be used for fabrication of various other structures with gradually inclined walls.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2010

Nanoporous membranes have a wide range of applications in many fields, including medical diagnost... more Nanoporous membranes have a wide range of applications in many fields, including medical diagnostics, drug delivery, and hemodialysis. Ultrananocrystalline diamond (UNCD ®) coatings are becoming more and more significant in medical applications because of the highest degree of biocompatibility, unmatched by other materials. The 100-nm-and 200-nm-diameter pores have been fabricated in 1-μm-thick UNCD film on silicon wafers using e-beam lithography, reactive ion etching and laser writing.

Many MEMS devices are based on polysilicon because of the current availability of surface microma... more Many MEMS devices are based on polysilicon because of the current availability of surface micromachining technology. However, polysilicon is not the best choice for devices where extensive sliding and/or thermal fields are applied due to its chemical, mechanical and tribological properties. In this work, we investigated the mechanical properties of three new materials for MEMS/NEMS devices: silicon carbide (SiC) from Case Western Reserve University (CWRU), ultrananocrystalline diamond (UNCD) from Argonne National Laboratory (ANL), and hydrogen-free tetrahedral amorphous carbon (ta-C) from Sandia National Laboratories (SNL). Young’s modulus, characteristic strength, fracture toughness, and theoretical strength were measured for these three materials using only one testing methodology – the Membrane Deflection Experiment (MDE) developed at Northwestern University. The measured values of Young’s modulus were 430GPa, 960GPa, and 800GPa for SiC, UNCD, and ta-C, repectively. Fracture toug...

Arrays of atomic force microscope (AFM) probes were developed for applications of dip-pen nanolit... more Arrays of atomic force microscope (AFM) probes were developed for applications of dip-pen nanolithography (DPN), which is capable of surface patterning with functionalized bio-molecules and can be used to construct biological and chemical sensors. Microchannels were embedded in AFM probes to transport ink or bio-molecules from reservoirs to substrates, realizing continuous writing at the nanoscale. This so-called “fountain-pen nanolithography ” (FPN) device was developed using surface and bulk micromachining. A volcano tip, which is a completely novel design for microfluidics, was built at the end of the AFM probe as a dispensing mechanism. Numerical simulations were performed to evaluate flow characteristics and the optimal materials for the volcano-tip probes. The results determined the selection of appropriate materials and the design of microfabrication steps. Multilayer films and thermal oxidation were used to integrate volcano tips and microchannels into AFM probes. The propos...

Ultrananocrystalline diamond (UNCD) with grain sizes in the range of 2 - 5 nm is produced using a... more Ultrananocrystalline diamond (UNCD) with grain sizes in the range of 2 - 5 nm is produced using a microwave plasma chemical vapor deposition process with argon-rich C60 or CH4 plasmas. This material has excellent mechanical properties: high hardness and Young modulus, and an extremely low friction coefficient (approximately 0.01). It is resistant to chemical attack, and is potentially biocompatible. These

Materials and Device Characterization in Micromachining II, 1999

The availability of high-energy, high-flux, collimated synchrotrons radiation has extended the ap... more The availability of high-energy, high-flux, collimated synchrotrons radiation has extended the application of deep X-ray lithography (DXRL) to thickness values of the PMMA resist of several millimeters. Some of the most severe limitations come from plastic deformation, stress, and cracks induced in PMMA during exposure and development. We have observed and characterized these phenomena quantitatively. Protilometry measurements revealed that the PMMA is subjected either to local shrinkage or to expansion, while compression and expansion evolve over time. Due to material loss and crosslinking, the material undergoes a shrinkage, while the radiation-induced decomposition generates gases expanding the polymer matrix, The overall dynamics of the material microrelief and stress during and after the exposure depend on the balance between compaction and outgassing. These depend in turn on the exposure conditions (spectrum; dose, dose rate, seaming, temperature), post-exposure storage conditions, PMMA material properties and thickness, and also on t @@ size and geometry of the exposed patterns.

Materials and Device Characterization in Micromachining, 1998

The adhesion of PMMA layers on silicon wafer has been studied in order to protect the front side ... more The adhesion of PMMA layers on silicon wafer has been studied in order to protect the front side of the silicon wafer while etching the backside in KOH aqueous solution. Pre and post-bake treatment have been performed, different primers have been used to optimise the superficial and interfacial tension of both mask layer and substrate. An adherent layer has been obtained and its behaviour has been explained based on the polar and nonpolar interactions across the interface. Keywords: PMMA, silicon, KOH, work of adhesion, surface energy, interfacial tension, superficial tension, contact angle.

Journal of Applied Physics, 2001

ABSTRACT The results of room-temperature wet etching of GaAs using synchrotron-radiation x rays a... more ABSTRACT The results of room-temperature wet etching of GaAs using synchrotron-radiation x rays are described. Under x-ray illumination, etching occurs on the n-GaAs surface in contact with an acid or base solution or even deionized water. The etching process is studied as functions of the electrolytes, their concentration, semiconductor doping level, and x-ray intensity and energy. The etching mechanism is determined to be primarily electrochemical in nature, but the x-ray radiation chemistry plays a role in the etching. Smoothly etched surfaces are achievable with a root-mean-square surface roughness of 0.7–2.0 nm. We also found that the etching rate increases substantially with the ratio of the sample size to the x-ray exposure size. This is accounted for by the rate-limiting effect on the charge transfer across the semiconductor-electrolyte junction. The chemistry of etched surfaces is studied using x-ray photoelectron spectroscopy and compared to that of as-received surfaces. © 2001 American Institute of Physics.

Microsystem Technologies, 2003

A prototype freestanding copper antiscatter grid with parallel lamellar walls has been fabricated... more A prototype freestanding copper antiscatter grid with parallel lamellar walls has been fabricated using deep X-ray lithography and electroforming. The freestanding copper grid has square shaped lamellar walls that are 25 lm thick and 1 mm tall with a 550 lm period. For mammography applications, the lamellar walls have to be aligned to a point X-ray source of the X-ray system. To achieve this goal, we investigated a dynamic doubleexposure technique. Our progress in using stacked exposures and use of the photoresist SU-8, both to reduce fabrication cost, is also presented.

Journal of Microelectromechanical Systems, 2012

A common method for producing sharp tips used in scanning probe microscopy (SPM) and other applic... more A common method for producing sharp tips used in scanning probe microscopy (SPM) and other applications involving nanoscale tips is to deposit thin-film materials, such as metals, silicon nitride, or diamond-based films, into four-faceted pyramidal molds that are formed by anisotropic etching into a (100) silicon substrate. This well-established method is capable of producing tips with radii as small as a few nanometers. However, the shape of the tip apex is difficult to control with this method, and wedge-shaped tips that are elongated in one dimension are often obtained. This limitation arises due to the practical difficulty of having four planes intersecting at a single point. Here, a new method for producing three-sided molds for SPM tips is demonstrated through the use of etching in (311) silicon wafers. It is shown that silicon nitride and ultrananocrystalline diamond tips fabricated with this new method are wedge free and sharp (< 10 nm radius), thereby restoring tip molding as a well-controlled manufacturing process for producing ultrasharp SPM tips. [2011-0209] Index Terms-Atomic force microscopy (AFM), crystallographic etching, molding, scanning probe microscopy (SPM), silicon, tips. I. INTRODUCTION T IP MOLDING is a well-known nanofabrication method for producing ultrasharp tips, such as those used in scanning probe microscopy (SPM) [1]-[3], field emitters [4], [5], vacuum electronics [6], [7], or tunneling-based devices [8]. Tip molding consists of etching a pyramid-shaped pit into a Manuscript

Introduction Deep x-ray lithography and electroforming allow the production of tall, high-aspect-... more Introduction Deep x-ray lithography and electroforming allow the production of tall, high-aspect-ratio structures with a high degree of precision. One of the important applications for high-aspect-ratio microformed metal structures is mammography. In mammography, an ideal diagnostic image is produced by local reduction in the x-ray intensity as a result of attenuation without scattering by the breast tissue. Because of the large amount of scattered radiation, image contrast is lowered, making diagnosis of diseased tissue subjective and difficult. The quality of mammogram images can be significantly improved by using an antiscatter grid that is transparent for primary radiation and opaque to scattered radiation from all directions [1-4]. In this report, we summarize our results in developing an antiscatter grid for mammography by using deep x-ray lithography and electroforming. The results were presented at international conferences HARMST 2001 [5, 7] and MEMS 2002 [6] and have been ...

Optics Express, 2021

Three (3) items of errata are submitted for our recently published paper [Opt. Express28, 36505 (... more Three (3) items of errata are submitted for our recently published paper [Opt. Express28, 36505 (2020)10.1364/OE.405566]. One is a clarifying extension to the Fig. 3 caption. Two are typographical corrections. The scientific results and conclusions are unaffected.

Optics Express, 2021

Three (3) items of errata are submitted for our recently published paper [Opt. Express28, 36505 (... more Three (3) items of errata are submitted for our recently published paper [Opt. Express28, 36505 (2020)10.1364/OE.405566]. One is a clarifying extension to the Fig. 3 caption. Two are typographical corrections. The scientific results and conclusions are unaffected.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2001

Alkali metals have extremely low-work functions and are therefore expected to result in significa... more Alkali metals have extremely low-work functions and are therefore expected to result in significant enhancement of the electron emission if they are used as coatings on Mo or Si microtip field emission arrays ͑FEAs͒. However, the alkali metals are physically and chemically unstable in layers exceeding a few nanometers in thickness. Maximum enhancement of electron emission occurs for alkali metal layers 0.5-1 monolayer thick, but it is extremely difficult to fabricate and maintain such a thin alkali metal coating. We review here our work of the last three years focused on developing Cu-Li alloy coatings for application to field emitter Spindt-type tip arrays and fabrication of edge emitters with low-voltage high electron emission characteristics for field emission devices. The Cu-Li alloy coatings provide a chemically and thermally stable, self-replenishing, segregated lithium monolayer on the surface of the host Cu layer, resulting in a substantial reduction of the work function of the alloy, compared to that of a thick Li layer or a pure Cu surface. We present results that show a 13-fold reduction in the threshold voltage for electron emission, compared with uncoated Si FEAs. The Cu-Li alloy coatings yielded tip and edge emitters with threshold voltages of 2-10 V/m, depending of the coating thickness and Li concentration in the alloy. New results are presented that show that we can now coat gated Si tip arrays with Cu-Li alloy films, which results in very low emission voltage.

Optical diagnostics will be critical for the operation and performance assessment of burning plas... more Optical diagnostics will be critical for the operation and performance assessment of burning plasma experiments, such as ITER. At the same time, extracting light for these diagnostics with reflective mirrors becomes difficult in the burning plasma environment, due to prolonged exposure to plasma and nuclear radiation. As an alternative, we explore free-standing diffractive optical elements, such as transmission gratings and zone plates. Since in the case of diffractive extractors the light is deflected by periodic slits rather than a surface, they may withstand plasma exposure with less degradation of their optical properties. To investigate this possibility we developed free-standing transmission gratings for the visible range and exposed them in to conditions resembling or exceeding those expected for the ITER `first mirrors'. The results of this study indicate that the gratings can withstand high heat fluxes and plasma and energetic radiation bombardment. In addition, in cont...

MRS Proceedings, 1992

ABSTRACTStress in thin films is one of the mayor technological problems of silicon micromachining... more ABSTRACTStress in thin films is one of the mayor technological problems of silicon micromachining. Therefore stress reduction by a compensation method increases the technological use of a material. Three methods to obtain stress free films are investigated:1. Stress in SiO2 and Si3N4 can be compensated by ion implantation.2. Sandwich layers of SiO2 and Si3N4 can be made internally stress compensated by variation of the thickness ratio.3. Polysilicon is stress reduced by appropriate doping and annealing.The film stress is evaluated by the measurement of the bending of the substrate. Examples of processed membranes, bridges and cantilevers made of stress compensated films are given.

MRS Proceedings, 1992

ABSTRACTStress in thin films is one of the mayor technological problems of silicon micromachining... more ABSTRACTStress in thin films is one of the mayor technological problems of silicon micromachining. Therefore stress reduction by a compensation method increases the technological use of a material. Three methods to obtain stress free films are investigated:1. Stress in SiO2 and Si3N4 can be compensated by ion implantation.2. Sandwich layers of SiO2 and Si3N4 can be made internally stress compensated by variation of the thickness ratio.3. Polysilicon is stress reduced by appropriate doping and annealing.The film stress is evaluated by the measurement of the bending of the substrate. Examples of processed membranes, bridges and cantilevers made of stress compensated films are given.

Materials Science and Engineering: B, 1996

A Monte Carlo program and a program based on the formula of the evolution of atom disappearance p... more A Monte Carlo program and a program based on the formula of the evolution of atom disappearance probabilities were used for the simulation of anisotropic etching of silicon-like crystal dots containing several thousands of atoms. An additional program extracts the local values of the etching rates and represents them in polar diagrams. The obtained figures respect the symmetry of the

Microsystem Technologies, 2004

A method to fabricating two-dimensional antiscatter grids with septa walls oriented toward the fo... more A method to fabricating two-dimensional antiscatter grids with septa walls oriented toward the focal point using deep X-ray lithography and copper electroforming is described. These focused grids can be used in mammography to eliminate scattered X-rays, and result in contrast improvement and significantly better image quality in comparison with the conventional one-dimensional antiscatter grids. Freestanding copper antiscatter grids, up to 2 mm thick, 60 mm • 60 mm in size, and focused to one point have been fabricated. This method can be used for fabrication of various other structures with gradually inclined walls.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2010

Nanoporous membranes have a wide range of applications in many fields, including medical diagnost... more Nanoporous membranes have a wide range of applications in many fields, including medical diagnostics, drug delivery, and hemodialysis. Ultrananocrystalline diamond (UNCD ®) coatings are becoming more and more significant in medical applications because of the highest degree of biocompatibility, unmatched by other materials. The 100-nm-and 200-nm-diameter pores have been fabricated in 1-μm-thick UNCD film on silicon wafers using e-beam lithography, reactive ion etching and laser writing.

Many MEMS devices are based on polysilicon because of the current availability of surface microma... more Many MEMS devices are based on polysilicon because of the current availability of surface micromachining technology. However, polysilicon is not the best choice for devices where extensive sliding and/or thermal fields are applied due to its chemical, mechanical and tribological properties. In this work, we investigated the mechanical properties of three new materials for MEMS/NEMS devices: silicon carbide (SiC) from Case Western Reserve University (CWRU), ultrananocrystalline diamond (UNCD) from Argonne National Laboratory (ANL), and hydrogen-free tetrahedral amorphous carbon (ta-C) from Sandia National Laboratories (SNL). Young’s modulus, characteristic strength, fracture toughness, and theoretical strength were measured for these three materials using only one testing methodology – the Membrane Deflection Experiment (MDE) developed at Northwestern University. The measured values of Young’s modulus were 430GPa, 960GPa, and 800GPa for SiC, UNCD, and ta-C, repectively. Fracture toug...

Arrays of atomic force microscope (AFM) probes were developed for applications of dip-pen nanolit... more Arrays of atomic force microscope (AFM) probes were developed for applications of dip-pen nanolithography (DPN), which is capable of surface patterning with functionalized bio-molecules and can be used to construct biological and chemical sensors. Microchannels were embedded in AFM probes to transport ink or bio-molecules from reservoirs to substrates, realizing continuous writing at the nanoscale. This so-called “fountain-pen nanolithography ” (FPN) device was developed using surface and bulk micromachining. A volcano tip, which is a completely novel design for microfluidics, was built at the end of the AFM probe as a dispensing mechanism. Numerical simulations were performed to evaluate flow characteristics and the optimal materials for the volcano-tip probes. The results determined the selection of appropriate materials and the design of microfabrication steps. Multilayer films and thermal oxidation were used to integrate volcano tips and microchannels into AFM probes. The propos...