This article concentrates on our recent results on several classes of photo- and electro-active organic materials that permit thin film formation and discusses their synthesis, properties, functions and potential applications for electronic and optoelectronic devices. The materials studied include amorphous molecular materials, titanyl phthalocyanine, oligothiophenes with well-defined structures, and non-conjugated polymers containing pendant oligothiophenes or other π-electron systems. The thin films of these materials find potential applications for use in organic electroluminescent, photovoltaic, electrochromic, and other devices.

Organic materials for electronic and optoelectronic devices

Publisher Summary A refractive index can be increased by ion implantation by changes in density and structure, by the addition of high-polarizability impurity ions, by a reduction of the plasma effect that increases the index and that is most important in the wavelength region far from the energy gap, and by absorption changing in the index in the region of the gap, that is, via the Kramers–Kronig relation. This chapter discusses the optical properties of implanted semiconductors, electrooptic components formed by ion implantation, general principles that determine most luminescent systems, effects of implantation temperature, luminescence centers in LiF-Mg-Ti radiation dosimeters, and use of line spectra in defect studies. In the LiF system, the luminescence bands are broad, and if alternative versions of the same complex exist, they cannot be resolved from the spectra. The addition, by implantation, of ions with incomplete inner electron shells opens up new possibilities as the lattice distortions of the free-ion energy levels are strongly perturbed by the defects in the neighborhood of the ion.

Optical Effects of Ion Implantation

Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.

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Gas-assisted focused electron beam and ion beam processing and fabrication

Laser ablation in liquids : Applications in the synthesis of nanocrystals

A new field of organic materials science that deals with amorphous molecular glasses has been opened up. In addition, amorphous molecular materials have constituted a new class of functional organic materials for use in various applications. This article is focused on the recent progress of studies on photo- and electroactive amorphous molecular materials, highlighting photochromic amorphous molecular materials, amorphous molecular resists, and amorphous molecular materials for use in devices such as organic EL devices. The molecular design concepts, syntheses, reactions, molecular and solid-state properties, functions, and device fabrication and performance are described.

Photo- and electroactive amorphous molecular materials—molecular design, syntheses, reactions, properties, and applications

A novel class of low molecular‐weight organic resist materials for nanometer lithography, 1,3,5‐tris[4‐(4‐toluenesulfonyloxy)phenyl]benzene (TsOTPB) and 4,4′,4″‐tris(allylsuccinimido) triphenylamine (ASITPA), was designed and synthesized. TsOTPB with a glass‐transition temperature (Tg) of 64 °C and ASITPA with a Tg of 80 °C were found to function as positive and negative resists, respectively, enabling the fabrication of 150 and 70 nm line patterns on exposure to an electron beam at 50 keV.

Novel class of low molecular‐weight organic resists for nanometer lithography

The surface-cleaning effect of metals was investigated using KrF-excimer-laser irradiation of metal surfaces in air. The laser-induced cleaning of copper, stainless steel and aluminum surfaces was studied. It is found that laser cleaning is an effective cleaning process for metals even if the metal surfaces are heavily contaminated. It is also found that short wavelength and pulse duration are necessary for laser surface-cleaning. The energy density of the laser pulse is an important parameter in the cleaning process. Low energy density results in a cleaner surface but a larger pulse number is required, whereas high energy density can achieve higher cleaning efficiency but the temperature rise can cause surface oxidation and secondary contamination. In contrast to the KrF-excimer-laser, the pulsed CO2 laser is not effective in surface-cleaning. The mechanisms of laser cleaning may include laser photodecomposition, laser ablation and surface vibration due to the impact of the laser pulse. Laser cleaning provides a new dry process to clean different substrate surfaces and can replace the conventional wet cleaning processes such as ultrasonic cleaning with CFC and other organic solvents.

Surface cleaning of metals by pulsed-laser irradiation in air

CNTs (carbon nano tubes) have drawn much attention as a field emitter material because of the high chemical stability, superior mechanical strength, and very high aspect ratio. One can use the well-aligned CNTs produced by CVD method to fabricate the electron emitters, or can also fabricate the electron emitters by a screen-printing method, which is very easy for mass production. In this study, CNTs were screen-printed on the ITO/glass substrate, and were irradiated by an UV (ultra-violet) laser in order to improve the emission behavior of the emitter by cleaning the top surface of screen-printed CNTs or by inducing defect sites, i.e., electron emission sites.

http://iopscience.iop.org/article/10.1143/JJAP.41.4314/pdf

Field emission characteristics of screen-printed carbon nano tube after laser irradiation

Carbon nanotube (CNT) cathode surfaces have been exposed to Ar plasma and the emission characteristics were measured. When a CNT cathode was exposed to Ar plasma for 3 min, the emission characteristics were improved. The emission current increased after an Ar plasma treatment for 3 min by three orders of magnitude from 9.0×10−5 to 3.3×10−1 mA/cm2 at 4.0 V/μm with a decrease in turn-on voltage from 3.3 to 1.7 V/μm. According to scanning electron microscopy images, entangled CNT bundles were raveled out by Ar plasma treatment.

Improvement in electron emission from carbon nanotube cathodes after Ar plasma treatment

Surface contaminations are removed by laser irradiation with pulse output and short wavelength in ambient air. It is a dry cleaning process to remove surface contaminations without using ultrasonic cleaning requiring carbon fluorochloride and other organic solvents. The mechanisms of laser cleaning may include laser photodecomposition, laser ablation and surface vibration due to the impact of the laser pulse. Examples of cleaning metal surfaces and magnetic head sliders show that this cleaning process could be widely used in various industrial applications.

http://iopscience.iop.org/article/10.1143/JJAP.33.7138/pdf

Mikio Takai

Papers

Novel class of low molecular‐weight organic resists for nanometer lithography

Surface cleaning of metals by pulsed-laser irradiation in air

Field emission characteristics of screen-printed carbon nano tube after laser irradiation

Improvement in electron emission from carbon nanotube cathodes after Ar plasma treatment

Laser Surface Cleaning in Air: Mechanisms and Applications.