Near-field Microwave Microprobe Research Articles

Noncontact evaluation of the conductivity of CuPc thin films by near-field microwave microprobe method

AbstractThe conductivity of copper II phthalocyanine (CuPc) thin films with different crystal structures andmorphologies was evaluated by using a near-field microwave microprobe (NFMM) technique in thefrequency range of 4-4.5 GHz. CuPc thin films annealed at 200 °C and 350 °C showed the a- and yS-phasecrystal structures, respectively. Crystal phase structure and morphology of CuPc thin films werecharacterized by optical absorption spectra measurement, X-ray diffraction, and scanning electronmicroscopy methods. Conductivity measurements of CuPc thin films were done in the temperatures rangeof25-160 °C.

Application of a sensitive near‐field microwave microprobe to the nondestructive characterization of microbial rhodopsin

We study the opto-electrical properties of Natronomonas pharaonis sensory rhodopsin II (NpSRII) by using a near-field microwave microprobe (NFMM) under external light illumination. To investigate the possibility of application of NFMM to biological macromolecules, we used time dependent properties of NPSRII before/after light activation which has three distinct states - ground-state, M-state, and O-state. The diagnostic ability of NFMM is demonstrated by measuring the microwave reflection coefficient (S(11)) spectrum of NpSRII under steady-state illumination in the wavelength range of 350-650 nm. Moreover, we present microwave reflection coefficient S(11) spectra in the same wavelength range for two fast-photocycling rhodopsins: green light-absorbing proteorhodopsin (GPR) and Gloeobacter rhodopsin (GR). In addition the frequency sweep shift can be detected completely even for tiny amounts of sample (∼10(-3) OD of rhodopsin). Based on these results NFMM shows both very high sensitivity for detecting conformational changes and produces a good time-resolved spectrum.

Characterization of rubrene polycrystalline thin film transistors fabricated using various heat-treatment conditions

We observed the crystal structure changes of rubrene (5,6,11,12-tetraphenylnaphthacene) polycrystal thin films on SiO2/Si(100) substrates at various heat-treatment temperatures by X-ray diffraction, and a near-field microwave microprobe technique. An amorphous rubrene thin film was initially observed at heat-treatment temperature of 35°C. After the treatment with in-situ vacuum post-annealing at 80°C for 22h, the rubrene thin film was transformed from the amorphous phase into a crystalline phase of orthorhombic structure. We could obtain a higher field effect mobility of 0.047cm2/V·s and lower threshold voltage of −4V for the following heat-treatment process: pre-annealing at 80°C, cooling at 40°C, and post-annealing at 80°C for 22h.

Glucose aqueous solution sensing by a near-field microwave microprobe

We observed the glucose concentration of solutions using a near-field microwave microprobe (NFMM). Instead of the usual technique, we take advantage of the noncontact and label-free evaluation capabilities of a NFMM. A NFMM with a high Q dielectric resonator allows observation of small variations of the relative permittivity due to changes in the glucose concentration. By measuring the reflection coefficient S 11 at an operating frequency near 4.5 GHz, we could observe the concentration of glucose with a detectable resolution of 0.5 mg/ml (0.05%). A glucose biosensor using a NFMM provides a unique approach to monitor glucose concentration.

Investigation of CdS thin films by a near-field microwave microprobe

Cadmium sulphide (CdS) thin films with different microstructures and morphologies were measured by using a near-field microwave microprobe (NFMM). The NFMM system was coupled to a dielectric resonator with a distance regulation system at an operating frequency f=4.1 GHz. The changes in dielectric permittivity of CdS thin films due to different annealing temperatures were investigated by measuring the reflection coefficient S 11. CdS thin films with different microstructures and morphology were characterized by X-ray diffraction, atomic force microscopy and NFMM.

Characterization of Alq3 thin films by a near-field microwave microprobe

We observed tris-8-hydroxyquinoline aluminum (Alq3) thin films dependence on substrate heating temperatures by using a near-field microwave microprobe (NFMM) and by optical absorption at wavelengths between 200 and 900 nm. The changes of absorption intensity at different substrate heating temperatures are correlated to the changes in the sheet resistance of Alq3 thin films.

Characterization of magnetic materials using a scanning microwave microprobe

We investigated the electromagnetic properties of metals of iron, nickel, cobalt, aluminum, gold, copper, silver, and permalloy thin films on SiO 2 substrates using a near-field microwave microprobe. The electromagnetic properties of metal sheets were estimated by measuring the microwave reflection coefficient S 11 and compared with the theoretical values. We observed the hysteresis behavior of permalloy thin films on SiO 2 substrates using a near-field scanning microwave microprobes (NSMM) system. Experimental results are in good agreement with the theoretical model of transmission theory. In order to better characterize the electromagnetic properties of metals and magnetic metals instead of the usual method, we take advantage of the noncontact microprobing evaluation capabilities using a near-field microwave.

Investigation of space charge at pentacene/Au interface with UV/ozone treatment by a near-field microwave microprobe

The near-field microwave microprobe (NFMM) and Kelvin-probe measurements were performed to evaluate the conductivity in terms of surface potential of pentacene films on Au electrode. The UV/ozone treated and untreated Au electrodes were prepared to reveal the relationship between the electrical conductivity and interfacial electrostatic charging phenomena. For the pentacene film deposited on the Au electrode with UV/ozone treatment, holes were displaced from Au electrode to pentacene film, resulting the accumulation of apparent positive charges in the interfacial region of pentacene film around Au electrode. The NFMM measurement revealed that the reflection coefficient of microwave, S 11 increased with UV/ozone treatment, indicating the resistance decrease of the surface. Accumulation of positive charge in the interfacial region of Au electrode/pentacene film is one of the essential reasons for the increase of the conductivity of pentacene film.

Sodium chloride sensing by using a near-field microwave microprobe

The authors observed the NaCl concentration of solutions using a near-field microwave microprobe (NFMM). Instead of the usual technique, they take advantage of the noncontact evaluation capabilities of a NFMM. A NFMM with a high Q dielectric resonator allows observation of small variations of the permittivity due to changes in the NaCl concentration. By measuring the reflection coefficient S11, they could observe the concentration of NaCl. The measured signal-to-noise was about 53dB and the minimum detectible signal was about 0.005dB∕(mg∕ml). In order to determine the probe selectivity, they measured a mixture solution of NaCl and glucose.

Nondestructive and Non-Contact Characterization Technique for Metal Thin Films Using a Near-Field Microwave Microprobe

We observed the surface resistance of metal thin films by a nondestructive characterization method using a near-field scanning microwave microprobe (NSMM). The NSMM system was coupled to a dielectric resonator with a distance regulation system. To demonstrate the ability of local microwave characterization, the surface resistance dependence of the metallic thin films has been mapped nondestructively.

Glucose Biosensing Using a Near-Field Microwave Microprobe

We observed the glucose concentration of solutions using a near-field microwave microprobe (NFMM). Instead of the usual invasive technique, we take the advantage of the noncontact and noninvasive evaluation capabilities of an NFMM. The NFMM with a high Q dielectric resonator allows observation of small variations of the permittivity due to changes in the glucose concentration. By measuring the reflection coefficient we could observe the concentration of glucose with a detectable resolution to 0.5 mg/ml (0.05 %). The glucose biosensor using a NFMM provides an unique approach for glucose monitoring for diabetes.

Phase transition of copper(II) phthalocyanine thin films characterized by a near-field microwave microprobe

Metal phthalocyanine is one of the promising organic compounds due to the possibility of applications in electrooptical devices, photoconducting agents, photovoltaic cell elements, nonlinear optics, electrocatalysis, and other photoelectronic devices. Several metal substituted phthalocyanines have been widely investigated. Among the metal substituted phthalocyanines, copper (II) phthalocyanine (Cu-Pc) has been found to have superior properties. Cu-Pc is a p-type semiconductor and mobility changes could be achieved by employing controlled substrate heating temperature during deposition. The crystal phase and the grain orientation of Cu-Pc depend on the heat-treatment temperatures and substrate heating conditions [1]. In order to better characterize the electrical properties of theαand the β-phase of Cu-Pc thin films, we take advantage of the nondestructive evaluation capabilities of a near-field microwave microprobe (NFMM) [2]. NFMM techniques with high sensitivity have been developed for the microwaveand millimeter-wave ranges. An important ability of the NFMM is nondestructive and contactless characterization of thin films, in particular, the characterization of electrical properties of organic thin films. Organic multilayer thin films have attracted considerable interest in regard to various display applications. Nondestructive and contactless characterization techniques are very useful for these applications. NSMM technique, which directly measures the physical properties such as surface resistance of organic thin films shows practical promise. To study the phase transition of Cu-Pc thin films, wemeasured the surface resistance using a NFMM by measuring the microwave reflection coefficient S11. The crystal structure of Cu-Pc thin films transformed from the α-phase of the orthorhombic crystal to the thermally stable β-phase of themonoclinic crystal as the substrate heating temperatures increased. The surface resistance depended on the crystal structures of the Cu-Pc thin films. As the phase changed from the α-phase to the β-phase, the surface resistance of the Cu-Pc thin films decreased.

Noncontact characterization of sheet resistance of indium–tin-oxide thin films by using a near-field microwave microprobe

The sheet resistance of indium–tin-oxide (ITO) thin films with different microstructures and morphologies was measured by using a near-field scanning microwave microprobe (NSMM). The NSMM system was coupled to a dielectric resonator with a distance regulation system at an operating frequency f=5.2–5.5 GHz. ITO thin films with different microstructures and morphology were characterized by X-ray diffraction and atomic force microscopy. As the sheet resistance increased, the intensity ratio of the (222) to the (400) diffraction peak increased and the surface roughness increased.