Adsorption of alkyltriphenylphosphonium amphiphiles on nafion membranes. X-ray photoelectron spectroscopy and static secondary ion mass spectrometry analysis

Conductivity, UV, and attenuated total reflectance IR measurements show that n-alkyltriphenylphosphonium amphiphiles adsorb on a Ndion 117 membrane. Approximately 20% of the Ndion protons are exchanged for a cationic amphiphile (n-hexadecyltriphenylphoephonium). Diffusion of amphiphile through the membrane was not observed. Once adsorbed, the amphiphiles did not leach from the membrane. Surface-sensitive techniques (x-ray photoelectrion spectroscopy, static secondary ion mass spectrometry) were used to investigate the presence, concentration, and distribution of the amphiphile in the Ndion membrane. Our experiments point to an incomplete monolayer coverage of the membrane, the molar ratio of amphiphile to sulfonate groups being only slightly less than 1 in the uppermost 2-5 nm. The amphiphile is bonded to the membrane, most likely via an ionic bond with the sulfonate groups. X-ray fluorescence measurements show that the amphiphile is also present in the bulk of the membrane, at least in the uppermost micrometer. However, in the bulk the concentration of amphiphile is significantly lower than the sulfonate groups. These results show that thin and stable amphiphilic layers can be made on a solid support material using adsorption of an amphiphile and coupling via an ionic bond

Si-C Linked Organic Monolayers on Crystalline Silicon Surfaces as Alternative Gate Insulators

Herein, the influence of silicon surface modification via Si-CnH2n+1 (n=10,12,16,22) monolayer-based devices on p-type (100) and n-type (100) silicon is studied by forming MIS (metal–insulator–semiconductor) diodes using a mercury probe. From current density–voltage (J–V) and capacitance–voltage (C–V) measurements, the relevant parameters describing the electrical behavior of these diodes are derived, such as the diode ideality factor, the effective barrier height, the flatband voltage, the barrier height, the monolayer dielectric constant, the tunneling attenuation factor, and the fixed charge density (Nf). It is shown that the J–V behavior of our MIS structures could be precisely tuned via the monolayer thickness. The use of n-type silicon resulted in lower diode ideality factors as compared to p-type silicon. A similar flatband voltage, independent of monolayer thickness, was found, indicating similar properties for all silicon–monolayer interfaces. An exception was the C10-based monolayer device on p-type silicon. Furthermore, low values of Nf were\ud found for monolayers on p-type silicon (=6A1011 cm-2). These results suggest that SiClinked monolayers on flat silicon may be a viable material for future electronic devices

Impedance spectroscopy and surface study of potassium-selective silicone rubber membranes

Impedance spectroscopy measurements of silicone rubber membranes containing potassium-selective neutral carriers are reported. Two types of silicone rubbers are studied viz. the commercially available Siloprene and a novel copolymer, that was synthesized for application on Ion-Sensitive Field Effect Transistors (ISFETs). Three different potassium-selective ionophores have been studied, the natural ionophore, valinomycin, and two hemispherand type ionophores. One of the hemispherands can be covalently bonded to the polysiloxane copolymer matrix. The bulk resistance of the valinomycin containing membranes was found to be dependent on the contacting electrolyte solution. The K+/Na+ selectivity of the membrane is reflected in the behavior of the bulk resistance. The presence of a surface film on Siloprene membranes reported in the literature is confirmed. A surface study revealed the presence of small droplets exuded by the Siloprene membrane. The copolymer seems not to suffer from the presence of a surface film

New membrane materials for potassium-selective ion-sensitive field-effect transistors

Several polymeric materials were studied as membrane materials for potassium-selective ion-sensitive field-effect transistors (ISFETs) to overcome the problems related with the use of conventional plasticized poly(vinyl chloride) membranes casted on ISFET gate surfaces. Several acrylate materials, such as ACE, Epocryl and derivatives, showed no reproducible results. Three room-temperature vulcanizing (RTV)-type silicone rubbers were tested. The addition-type RTV-2 silicone rubber was not suitable as a membrane material, but the condensation-type RTV-1 and especially the RTV-2 silicone rubber showed good results. ISFETs with a Silopren membrane showed a durability of at least 2 months

Modification of ISFESTs by covalent anchoring of poly(hydroxyethyl methacrylate) hydrogel. Introduction of a thermodynamically defined semiconductor-sensing membrane interface

Silicon dioxide ion-sensitive field effect transistors were modified by silylation with methacryloxypropyltrimethoxysilane (MPTS) and with in situ photopolymerized poly(hydroxyethyl methacrylate). Subsequently, the covalently linked methacrylate was swollen with a buffered potassium chloride solution, prior to the introduction of a hydrophobic sensing membrane. The introduced hydrogel layer effects a significant reduction in the peak-to-peak noise levels and eliminates completely interference from carbon dioxide. The method is compatible with integrated circuit photolithographic techniques and improves the development of potentiometric biosensors and chemical sensors.\ud \u

Reference field effect transistor based on chemically modified ISFETs

Different hydrophobic polymers were used for chemical modification of ion-sensitive field effect transistors (ISFETs) in order to prepare a reference FET (REFET). Chemical attachment of the polymer to the ISFET gate results in a long lifetime of the device. Properties of polyacrylate (polyACE) REFETs are described in detail. The polyACE-REFET is superior to other polymer modified REFETs, showing an excellent pH insensitivity (1 mV pH−1), a long lifetime and an electrically identical behaviour as an unmodified pH ISFET or a cation-selective PVC-MEMFET (membrane FET). The cation permeselectivity of the polymer can be significantly reduced by addition of immobile cations. The applicability of a polyACE-REFET in differential measurements with a pH ISFET and a K+ MEMFET is demonstrated.\ud \u