Carbon Nanotubes were synthesized on passive scanning probes and silicon nitride membranes using Chemical Vapor
Deposition (CVD) techniques. The catalysts precursors were deposited using a "wet" technique. The synthesized CNT
were subsequently characterized using Scanning Electron Microscopy (SEM).
Carbon Nanotubes (CNT) were synthesized on heated scanning probes and under ambient conditions without requiring
Chemical Vapor Deposition (CVD) apparatus. Dip pen techniques were utilized for deposition of catalyst precursors on
the probe tips in the form of aqueous solution of metal salts. A layer of Fullerene (C60) was deposited on the probe tip
using a microfluidics apparatus and the probes were heated individually using a microheater. The temperature of the
heated probes reached ~350 °C during the synthesis of CNT. The synthesized CNTs were subsequently characterized
using scanning electron microscopy (SEM) and Raman Spectroscopy. The Raman spectroscopy showed peaks in the
Radial Breathing Mode (RBM) mode, as well as the Graphitic band. The RBM peaks indicate that the synthesized
SWCNT has a diameter of ~1 nm. The single peak in the Raman spectra in RBM mode is indicative of SWCNT of a
single chirality. Hence this process can be optimized to synthesize SWCNT of a specific chirality.
In the dip pen nanolithography (DPN) process, ultra-sharp scanning probe tips ("pens") are coated with chemical compounds (or "ink") and contacted with a surface to produce submicron-sized features. This work describes the design, fabrication, and testing of a microfluidic ink delivery device for delivering multiple species of inks to an array of multiple pens, as well as for maximizing the number of inks for simultaneous patterning by DPN. The microfluidic device (called "Centiwell") consists of a 2-D array of 96 microwells that are obtained by silicon bulk micromachining process. A thermoelectric module is attached to the bottom of the substrate. Microbeads of a hygroscopic material (e.g., polyethylene glycol or PEG) are dispensed into the microwells. The thermoelectric module cools the substrate to below the dew point for condensing water droplets on the microbeads and to create PEG solutions that serve as the ink for DPN. An array of pens is then coated with the ink. Subsequently, nanolithography is performed with the coated pens. Multiple PEG nanopatterns obtained by this method are presented as proof-of-concept. This demonstrates the functionality of the Centiwell microfluidic ink delivery device for nanolithography of multiple inks. Also, fractal nanopatterns are observed in the nanolithography experiments.
Nano-patterning of metals on gold film and silicon nitride membrane using Dip Pen Nanolithography (DPNTM)
is reported in this study. Using this technique, nano-particles can be delivered or nano-scale features of metals can
be deposited precisely at specific locations using the unique registration capabilities of DPN. Monolayers of metal
salts (FeCl2, FeCl3, PdCl2, etc.) are deposited with nano-scale precision using DPN. These metal salts can be
subsequerntly reduced to pure metals in a reducing environment for various applications (e.g., magnetic memory
storage, nano-catalysis, molecular electronics, brand protection, nano-sensors, etc.). Square nano-patterns of
Palladium and Iron salts were successfully deposited using this technique with thickness of the deposited materials
being less than 1 nm.
This paper describes the fabrication and testing of a microfluidic ink delivery device for Dip Pen Nanolithography (DPNTM). The purpose of this microfluidic device is to maximize the number of chemical species (inks) for nanofabrication that can be simultaneously patterned by DPN. The device (called 'Centiwells') consists of a two-dimensional array of 96micro-wells micro-machined on a silicon substrate and a thermoelectric module attached to the
bottom of the substrate. Microbeads of a hygroscopic material (Poly-Ethylene Glycol) are dispensed into the microwells.
By reducing the temperature of the substrate to below the dew point water droplets are condensed on the PEG
microbeads, dissolving the beads and creating PEG solutions. Following the formation of the PEG solutions, an AFM
tip (pen) is lowered into the micro-wells for loading ink ('dipping' or 'inking' step) and subsequently nanolithography
The objective of this study is to develop a portable micro-sensor platform for real-time detection of energetic materials (e.g., explosives) over a wide range of vapor pressures. The bending response of an electrically heated microcantilever thermal bi-morph array is used for specific detection of combustible substances using their calorimetric properties. Chemical reactions on the surface induce stress on a micro-cantilever which affects the bending and is
measured in real-time using an optical apparatus. The threshold value of actuation current is found to provide a unique signature for identifying equilibrium concentration of iso-propyl alcohol, acetone and gasoline vapors at room temperature. The threshold current is found to scale with the vapor pressure of the volatile species and the ignition temperature. This shows that the sensors can be used for specific detection of different types of combustible materials.
The sensor array can be used to detect, identify and monitor volatile combustible species in real time (response time in milliseconds) with the capability for redundancy checks and the ability to eliminate false positive/ false-negative results. The sensor is capable of remote monitoring on a continuous basis for indoor and outdoor applications - which protects the operator of the sensor instrument from explosive effects. The sensor design permits detection at a nominal distance away from the source without coming in contact with the contaminated surface. The sensor capability can be enhanced by specifically coating the micro-cantilever surfaces (e.g. using Dip Pen Nanolithography techniques) and can be integrated into a portable detection platform or instrument.
In Dip Pen NanolithographyTM (DPNTM) ultrasharp tips coated with chemical compounds (or "ink") are in contact with a surface to produce submicron sized features. There is a need to deliver multiple inks to an array of closely spaced tips (or "pens"). This work demonstrates the design optimization, fabrication process development, process optimization, and testing of a microfluidic ink delivery apparatus (called "inkwells") for simultaneously coating an array of DPN pens with single or multiple inks. The objective of this work is to deliver between four and ten different inks from reservoirs into an appropriately spaced microwell array. The tips of the multipen array are coated with the same or different inks by dipping them into the microwell array. The reservoirs, microwells, and their connecting microchannels were etched in silicon wafers using deep reactive ion etching. Fluid actuation was achieved by capillary flow (wicking). The optimum layouts for different applications were selected with respect to the volume requirement of different inks, the efficacy of ink-well filling, prevention of bubble formation, and the ease of operation (such as dipping and writing) with a parallel array of pens.
Dip Pen Nanolithography (DPNTM) is a scanning probe technique for nanoscale lithography: A sharp tip is coated with a functional molecule (the “ink”) and then brought into contact with a surface where it deposits ink via a water meniscus. The DPN process is a direct-write pattern transfer technique with nanometer resolution and is inherently general with respect to usable inks and substrates including biomolecules such as proteins and oligonucleotides. We present functional extensions of the basic DPN process by showing actuated multi-probes as well as microfluidic ink delivery. We present the fabrication process and characterization of such active probes that use the bimorph effect to induce deflection of individual cantilevers as well as the integration of these probes. We also developed the capability to write with multiple inks on the probe array permitting the fabrication of multi-component nanodevices in one writing session. For this purpose, we fabricate passive microfluidic devices and present microfluidic behavior and ink loading performance of these components.
This work demonstrates the design optimization, fabrication process development, process optimization and testing of a microfluidic ink delivery apparatus (called "Inkwells") for simultaneously coating an array of DPN pens with different inks. The objective of this work is to deliver between 4 and 10 different inks from reservoirs into appropriately spacd microwell array. A tips of the multi-pen array are coated with different inks by dipping them into the microwell array. The reservoirs, microwells and their connecting micro-channels were etched in silicon wafers using Deep Reactive Ion Etching (DRIE). Fluid actuation was achieved by capillary wicking. The optimum layouts for different applications were selected with respect to the volume requirement of inks, the efficacy of ink-well filling, to obviate the problem of bubble formation, and to test the operations of dipping and writing with a parallel array of pens.