Ultrasmooth Organic Films Via Efficient Aggregation Suppression by a Low-Vacuum Physical Vapor Deposition

Organic thin films with smooth surfaces are mandated for high-performance organic electronic devices. Abrupt nucleation and aggregation during film formation are two main factors that forbid smooth surfaces. Here, we report a simple fast cooling (FC) adapted physical vapor deposition (FCPVD) method to produce ultrasmooth organic thin films through effectively suppressing the aggregation of adsorbed molecules. We have found that thermal energy control is essential for the spread of molecules on a substrate by diffusion and it prohibits the unwanted nucleation of adsorbed molecules. FCPVD is employed for cooling the horizontal tube-type organic vapor deposition setup to effectively remove thermal energy applied to adsorbed molecules on a substrate. The organic thin films prepared using the FCPVD method have remarkably ultrasmooth surfaces with less than 0.4 nm root mean square (RMS) roughness on various substrates, even in a low vacuum, which is highly comparable to the ones prepared using conventional high-vacuum deposition methods. Our results provide a deeper understanding of the role of thermal energy employed to substrates during organic film growth using the PVD process and pave the way for cost-effective and high-performance organic devices.

Isotope Exchange Kinetics in Clay-Water System

<p>Knowledge of reactions at solid/liquid and solid/gas interfaces is of great importance in the study of all adsorption phenomena. Techniques that enable a study of molecules (liquid or gaseous) adsorbed onto a surface may be divided into two categories: (a) those that upset the equilibrium between molecules in the gaseous (or liquid) phase above the solid surface and molecules actually adsorbed onto it, and (b) those that do not. Those techniques that do not disturb this equilibrium will give results that would be expected to have greater reliability than those obtained from techniques that upset this equilibrium (for example by heating or by affecting one component of the equilibrium by titration, precipitation etc.) In an endeavour to study the properties of water adsorbed onto various substances such as clay, wool and textile fibres without affecting the equilibrium the technique of isotopic exchange has been developed. Essentially the procedure is to take a closed adsorber system in equilibrium with a gas (or liquid), part of which is in the sensitive region of a geiger counter, and to add a very small amount of radioactively labelled gas (or liquid) to the system. The adsorber is placed in the bottom of a geiger counter out of the sensitive volume and a known fraction of gas (or liquid) is in the sensitive volume. As the system is at equilibrium there is continuous exchange between the adsorbed molecules on the sample and the molecules in the gaseous (or liquid) state. Thus, when a very small amount, by weight, of the radioactively labelled gas (or liquid) is added to the system, exchange will take place with the non-radioactive molecules adsorbed on the surface of the material under study. Thus radioactivity will be removed from the sensitive volume of the geiger counter and adsorbed onto the surface of the material, and so the specific activity (count rate), as measured with the geiger counter, will drop. The advantage of this technique is that the equilibrium between the adsorbed molecules and the free gas (or liquid) is not disturbed. The actual amount of radioactive material added is so minute that there is no effective change in the concentration of the free gas (or liquid).</p>

Isotope Exchange Kinetics in Clay-Water System

<p>Knowledge of reactions at solid/liquid and solid/gas interfaces is of great importance in the study of all adsorption phenomena. Techniques that enable a study of molecules (liquid or gaseous) adsorbed onto a surface may be divided into two categories: (a) those that upset the equilibrium between molecules in the gaseous (or liquid) phase above the solid surface and molecules actually adsorbed onto it, and (b) those that do not. Those techniques that do not disturb this equilibrium will give results that would be expected to have greater reliability than those obtained from techniques that upset this equilibrium (for example by heating or by affecting one component of the equilibrium by titration, precipitation etc.) In an endeavour to study the properties of water adsorbed onto various substances such as clay, wool and textile fibres without affecting the equilibrium the technique of isotopic exchange has been developed. Essentially the procedure is to take a closed adsorber system in equilibrium with a gas (or liquid), part of which is in the sensitive region of a geiger counter, and to add a very small amount of radioactively labelled gas (or liquid) to the system. The adsorber is placed in the bottom of a geiger counter out of the sensitive volume and a known fraction of gas (or liquid) is in the sensitive volume. As the system is at equilibrium there is continuous exchange between the adsorbed molecules on the sample and the molecules in the gaseous (or liquid) state. Thus, when a very small amount, by weight, of the radioactively labelled gas (or liquid) is added to the system, exchange will take place with the non-radioactive molecules adsorbed on the surface of the material under study. Thus radioactivity will be removed from the sensitive volume of the geiger counter and adsorbed onto the surface of the material, and so the specific activity (count rate), as measured with the geiger counter, will drop. The advantage of this technique is that the equilibrium between the adsorbed molecules and the free gas (or liquid) is not disturbed. The actual amount of radioactive material added is so minute that there is no effective change in the concentration of the free gas (or liquid).</p>

Polarization-dependent vibrational shifts on dielectric substrates

On dielectrics, infrared spectra of adsorbed molecules recorded in reflection can depend strongly on the polarization of the incident light.

IR Studies of the Cu Ions in Cu-Faujasites

The properties of Cu ions in dealuminated faujasite-type zeolites (Si/Al = 31) containing 1, 2, and 5 wt.% of Cu were investigated by IR spectroscopy with CO and NO as probe molecules. Cu was introduced by impregnation into zeolites in both protonic (HFAU) and sodium (NaFAU) forms of zeolite. Four kinds of Cu species were found: Cu+exch., Cu+oxide, Cu2+exch. (square, planar, and square pyramidal), and Cu2+oxide (CuO). The proportions between these four kinds of Cu depended on the amount of Cu and on the form of zeolite to which Cu was introduced (HFAU or NaFAU). Zeolites with 1 wt.% of Cu introduced to HFAU (denoted as Cu(1)HFAU) contained only Cu+exch., whereas other forms of Cu were present in zeolites of higher Cu contents. The concentration of Cu+exch. was determined by quantitative IR studies of CO adsorption. According to the IR results, some Cu ions were situated inside hexagonal prisms and/or cuboctahedra, and were inaccessible to adsorbed molecules. IR studies also evidenced that Cu ions in oxide forms—Cu+oxide and Cu2+oxide (CuO)—were better electron donors than Cu in exchange positions (Cu+exch. and Cu2+exch).