F. K. Perkins

1∕f noise in single-walled carbon nanotube devices

We report the scaling behavior of 1∕f noise in single-walled carbon nanotube devices. In this study we use two-dimensional carbon nanotube networks to explore the geometric scaling of 1∕f noise and find that for devices of a given resistance the noise scales inversely with device size. We have established an empirical formula that describes this behavior over a wide range of device parameters that can be used to assess the noise characteristics of carbon nanotube-based electronic devices and sensors.

Low voltage electron beam lithography in self‐assembled ultrathin films with the scanning tunneling microscope

With a scanning tunneling microscope (STM) operating in vacuum, we have studied the lithographic patterning of self‐assembling organosilane monolayer resist films. Where the organic group is benzyl chloride, the resist layer can be patterned with electrons down to 4 eV in energy. The patterned films have been used as templates for the electroless plating of thin Ni films. Linewidths down to ∼20 nm have been observed in scanning electron micrographs of the plated films. Still smaller features are observed in STM images of the exposed organosilane films.

The functionalization of graphene using electron-beam generated plasmas

A plasmas-based, reversible functionalization of graphene is discussed. Using electron-beam produced plasmas, oxygen and fluorine functionalities have been added by changing the processing gas mixtures from Ar/O2 to Ar/SF6, respectively. The reversibility of the functionalization was investigated by annealing the samples. The chemical composition and structural changes were studied by x-ray photoelectron spectroscopy and Raman spectroscopy.

Carbon nanotube networks: Nanomaterial for macroelectronic applications

We describe the properties and potential applications of an electronic material that consists of an interconnected random network of single-walled carbon nanotubes. This material possesses useful electronic properties, and it can be patterned into devices with high yield using conventional microfabrication technology. One unique aspect of this material is that every atom is a surface atom. For this reason nanotube networks form an ideal electronic material to utilize interface phenomena to engineer its properties for specific applications. We discuss two such applications: chemical sensing and macroelectronics.

Design and performance of a simple, room-temperature Ga2O3 nanowire gas sensor

Ga2O3 nanowire gas sensors were fabricated using the vapor-liquid-solid method of nanowire growth over platinum interdigitated electrodes. While cheaply and easily fabricated, the sensors are capable of detecting various analytes at room temperature. As analyte is adsorbed onto the nanowire surfaces, a change in the device capacitance is measured. Fast recovery of the sensing devices, without the use of an external heat source, allows these devices to operate at low power. Capacitance is seen to increase following a Freundlich isotherm in response to increasing concentrations of analyte vapors.

Imaging layers for 50 kV electron beam lithography: Selective displacement of noncovalently bound amine ligands from a siloxane host film

We report the development of an imaging layer technology for 50 kV electron-beam lithography based upon the displacement of noncovalently bound amine ligands from a siloxane host film. The patterned films were used as templates for the selective deposition of an electroless nickel film resulting in a positive tone imaging mechanism. The deposited nickel was sufficiently robust to function as an etch mask for pattern transfer by reactive ion etching. Metallized and etched patterns with linewidths to approximately 40 nm are demonstrated using an exposure dose of 500 μC/cm2.

HIGH SPEED PATTERNING OF A METAL SILICIDE USING SCANNED PROBE LITHOGRAPHY

We describe a simple high-speed process for patterning metal silicides with an atomic force microscope (AFM). The process uses a thin AFM-generated oxide to block Pt diffusion during the formation of Pt silicide. Because the process requires only ∼1 nm of oxide, high write speeds and fine lateral resolution are achieved. We find that by maintaining ambient moisture at the tip–sample interface we can under optimal tip conditions achieve a minimum exposure time of ∼300 ns for a 30 nm size pixel which corresponds to a maximum write speed of ∼10 cm/s.

Modeling of electron elastic and inelastic scattering

The role of the form of the elastic and inelastic cross section in Monte Carlo simulations of electron–solid scattering has been studied to understand the processes whereby energy is deposited by electrons as they traverse thin films. Specifically we are interested in these phenomena as they relate to proximity effects in electron‐beam lithography and the detection of electrons by a Schottky diode with a patterned absorber overlayer. Lithographic point and line spread functions have been measured in three resist materials. We show that the inclusion of discrete inelastic scattering events whereby fast secondaries are generated is essential for matching simulation and experiment. The secondaries are crucial in determining the shape of the spread functions in the 0.1–1 μm regime and must be included to model proximity effects. Further, the fitting of line spread function simulations to experiment allows the accurate prediction of dot spread functions and applied dose thresholds as well as three dimensional ...

Ultrathin PtSi layers patterned by scanned probe lithography

A process for patterning ultrathin layers of PtSi with high spatial resolution is presented. In this process, scanned probe anodic oxidation is used to pattern a surface oxide layer on a H-passivated Si surface. This oxide pattern prevents the reaction of a deposited Pt film with the underlying Si in the formation of PtSi. The unreacted Pt on the oxide is removed by a selective etch before any annealing. This process greatly reduces lateral diffusion and produces a 2-nm-thick PtSi layer with good electrical properties that maintains the fidelity of the patterned oxide mask. Such nanostructured PtSi films are a good candidate for use in constructing lateral Si-based quantum devices.

Simulation of scanning tunneling microscope interaction with resists

Three‐dimensional electron optical simulations were used to model scanning tunneling microscope (STM) lithography in resists under field emission conditions. This work focuses on the effect of resists, as dielectric layers, between the tip and conducting substrate on the operation of the STM. Simulations were performed for resist thicknesses of 1–50 nm and tip‐resist separations of 1–20 nm. For a fixed 10 nm tip‐resist separation, the axial electric field at the tip decreases by a factor of 2.3 over the resist thickness range. The results show that the tip‐resist separation must decrease with increasing resist thickness, to achieve the operating conditions and the energy of electrons entering the resist can be significantly less than the applied tip‐substrate bias.