arXiv subjects

M. W. Denhoff

Publications and source records attributed to M. W. Denhoff.

4 recordsLinked to original sources

arXiv2023

Epitaxial Y1Ba2Cu3O7 thin films on CeO2 buffer layers on sapphire substrates

Pulsed laser deposition has been used to deposit Y1Ba2Cu3O7 layer on CeO2 buffer layers on (1102) sapphire. Both layers are epitaxial with the (110) direction of the CeO2 layer aligned with the <2021> direction of the sapphire substrate. The c-axis Y1Ba2Cu3O7 layer has its <100> direction aligned with the <110> direction of the CeO2. Cross-sectional transmission electron microscopy shows the epitaxy to be coherent and the interfaces to be abrupt at an atomic level. The best films have a critical current of 9 e6 A/cm2 at 4.2 K and lower microwave surface resistance than copper at 77 K and at a frequency of 31 GHz.

cond-mat.supr-con↗

arXiv2012

Device model of silicon nanowire bioFETs

A device model of biological molecule sensors based on semiconductor nanowires has been developed. This model of a bioFET is based on the concept of the electrolytic absolute electrode potential. From that starting point a semiconductor device model of the nanowire solution biomolecule system was derived. The model includes the Gouy-Chapman-Stern model of the salt solution double layer, site binding charges on the electrode surface, and biological molecules in the form of a membrane layer. A simple method of solving this model is presented using the finite element method. Some examples showing the general properties of the model are given.

physics.chem-ph↗

arXiv2008

Charge carrier induced barrier height reduction at organic heterojunctions

In order to provide an accurate theoretical description of current density voltage (J-V) characteristics of an organic heterojunction device over a wide range of electric fields at various temperatures, it is proposed that an accumulation of charge carriers at the heterojunction will lead to a reduction in the barrier height across the heterojunction. Two well-known hole transporting materials, 4,4,4-Tris(N-3-methylphenyl-N-phenyl-amino) triphenylamine (MTDATA) and N,N-diphenyl-N,N-bis(1-naphthyl)(1,1-biphenyl)-4,4diamine (NPB) were used to fabricate unipolar heterojunction devices. It is found that the J-V characteristics depends strongly on applied bias. The simulated J-V characteristics of the heterojunction device, with the modified injection model, are found to be in excellent agreement with the experimental data.

cond-mat.mtrl-sci↗

arXiv1999

The microwave power handling of a FIB generated weak link in a YBCO film

We have measured the power dependent microwave properties of a weak link in a YBa2Cu3O7 thin film formed by writing a line of damage using a focused ion beam. The measurement was made using a parallel plate resonator at 5.5 GHz with the weak link written across the width of one of the plates. The ion induced damage was characterized using a TRIM computer simulation and the dc properties of similar weak links was measured. Using a 200 eV Si ion dose of 2e13 cm-2, the Tc of the damaged region was reduced by 5.5 K and the normal resistivity was doubled. Surprisingly, the microwave measurements did not show any Josephson junction characteristics. Rather, the ion damaged region exhibited a greatly increased microwave resistivity that was constant as a function of microwave power up to rf fields of 20 mT at 21 K.

cond-mat.supr-con↗