charles wilker - Academia.edu (original) (raw)

Papers by charles wilker

Organometallics, Jul 1, 1984

In this paper we study the reactivity of butterfly and square-pyramidal transition-metal cluster ... more In this paper we study the reactivity of butterfly and square-pyramidal transition-metal cluster carbides, compounds which are interesting because they have a sterically exposed carbon atom. First we discuss the stability of these compounds which have such an unusual coordination for carbon. Next we use perturbation theory arguments to discuss the relative reactivities of different sites on the butterfly cluster and of the carbon site on the square-pyramidal cluster. The results parallel the experimentally obtained products; in particular the carbon atom is not electronically the most favored site of attack. The orbital explanation of these trends gives us further insight into bonding in the cluster. We also discuss electron counting and ?r-bonding in the product of attack on the cluster and consider some relevant data on transition-metal and transition-metal-carbide surfaces.

Inorganic Chemistry, Oct 1, 1986

Organometallic reactivity patterns of the rhodium tetraphenylporphyrin derivatives Rh(TPP)(H), Rh... more Organometallic reactivity patterns of the rhodium tetraphenylporphyrin derivatives Rh(TPP)(H), Rh(TPP)-, and (Rh(TPP)), are found to closely parallel those of the corresponding rhodium octaethylporphyrin species. Preparation and physical properties of the formyl, hydroxymethyl, and alkyl complexes of Rh(TPP) are described along with the photoinduced insertion of carbon monoxide into the Rh-CH, bond. Thermodynamic values for the reaction Rh(TPP)(H) + CO F? Rh(TPP)(CHO) in C6D6 are AHo =-42 kJ/mol and ASo =-89 f 15 J/(K mol).

Chemischer Informationsdienst, May 4, 1982

Chemischer Informationsdienst, Apr 19, 1983

Chemischer Informationsdienst, 1983

Advances in Superconductivity IV, 1992

Low-noise oscillators operating as pure microwave frequency sources have many critical real world... more Low-noise oscillators operating as pure microwave frequency sources have many critical real world uses in modern radar, communications, and information processing applications. One such application would be as a local oscillator in an advanced microwave front-end receiver. Hybrid oscillators consisting of III-V FETs and high temperature superconducting (HTS) passive microwave devices have been fabricated and tested at cryogenic temperatures at Du Pont. Initial devices operating in the C-band at 4.7 GHz have utilized commercially available High Electron Mobility Transistor (HEMT) unpackaged chips. Wide band amplifiers with bandwidth from 2 to 8 GHz were fabricated and tested at 77 K show 17 dB gain. This is 3 dB higher than amplifiers operating at room temperature. Hybrid oscillators were fabricated using these wide-band amplifiers with feed back provided by a Tl2Ba2CaCu2O8 microstrip resonators. Resonators were fabricated from two-side coated HTS films on LaAlO3 substrates and had loaded Qs of 5000 with insertion loss of -6 dB. Oscillators show phase noise of less than -106 dBc (1 Hz) at 10 KHz offset from operating frequency of 4.7 GHz.

This paper is a summary of the high Tc superconducting (HTS) device development program a1 Du Pon... more This paper is a summary of the high Tc superconducting (HTS) device development program a1 Du Pont over the past two years. We have designed, fabricated and tested a number of HTS devices such as a 5 GHz microstrip line rcsonator: 3-pole. 5-pole and 7pole microstrip line bandpass filters: an 11-nanosecond coplanar delay line: a 0.5-4.5 GHz 7-section Chebyshev microstrip line power splitter/combiner: a 5.55 GHz HTS-sapphire resonator with extremely high Q-value: and a 111-V semiconductor-HTS hybrid amplifier and oscillator, etc. The thin film HTS materials used for fabricating these devices were: YBaCuO(123). TIBaCaCuO(2212) and TlPbSrCaCuO(lZ12). These films have very low surface resistance and high power handling ability.

Includes bibliographical references. Honors thesis--Swarthmore College.

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Journal of Superconductivity

The surface resistance R[sub s] of Tl[sub 2]Ba[sub 2]CaCu[sub 2]O[sub 8] films fabricated on LaAl... more The surface resistance R[sub s] of Tl[sub 2]Ba[sub 2]CaCu[sub 2]O[sub 8] films fabricated on LaAlO[sub 3] wafers up to 3 inches (7.6 cm) in diameter through a post-deposition anneal process was measured over the frequency range 5.55-94.1 GHz by the following techniques: 5.55 and 27.5 GHz high-temperature superconductor (HTS)-sapphire resonators, 10 GHz parallel plate resonator, and 94.1 GHz scanning confocal resonator. R[sub s] was found to exhibit a quadratic dependence on frequency f at 77 K: R[sub s] oc f[sup 2.0][+-](0.1). The highest-quality films The highest-quality films yield R[sub s] = 145 [+-] 15 [mu][Omega] at 10 GHz and 77 K. Scanning confocal resonator mapping of R[sub s] across a 2-inch (5.1 cm) diameter wafer yielded a base value for R[sub s] of 16 [+-] 1 m[Omega] at 77 K and 94.1 GHz (equivalent to 180 [+-] 10 [mu][Omega] at 10 GHz) and good uniformity in R[sub s] across the wafer. HTS-sapphire resonator measurements of R[sub s] for fifteen 1.2 cm square parts cut fr...

Advances in Superconductivity V, 1993

Application of high temperature superconductor (HTS) thin films in microwave systems may require ... more Application of high temperature superconductor (HTS) thin films in microwave systems may require a range of microwave devices and the hybrid integration of these devices with III-V semiconductors. To demonstrate the utility of HTS microwave technology, we have developed several prototype HTS/III-V hybrid devices including wide band amplifiers, narow band amplifiers, and very low phase noise oscillators. C-band amplifiers designed to function at cryogenic temperatures show a 3 dB gain over those at room temperature. Low phase noise oscillators stabilized by HTS half wavelength resonators with loaded Q value of 3 × 103 or a sapphire loaded HTS resonator cavity with a loaded Q value of 1.2 × 106 at 80 K have been fabricated and tested. The phase noise at 70 K of the sapphire loaded HTS resonator cavity was below -125 dBc/Hz at 10 kHz off-set and limited by the test equipment This is the lowest phase noise yet reported for such an HTS stabilized oscillator.

50th ARFTG Conference Digest, 1997

The same intrinsic nonlinear property that produces intermodulation distortion from two or more e... more The same intrinsic nonlinear property that produces intermodulation distortion from two or more excitation tones, also produces harmonic generation from a single excitation tone. The measurement of one of these distortions, therefore, can be used to derive the results of the other. We have configured, tested and qualified an experimental setup to measure the nonlinear properties by harmonic generation using a broadband 50 Q transmission line as the test device. This setup has a 50 dB dynamic range enhancement over the intermodulation measurement setup. The harmonic generation technique was used to characterize a high temperature superconducting (HTS) coplanar transmission line. The input power at 1.5 GHz versus the output power for a 3 0 p by 5mm Tl,Ba,CaCu,O, coplanar transmission line was measured at 50, 70,77 and 85 K. At 77 K, the 2"d order intercept (SOI) was +136 dBm, the 3d order intercept (TOI) was +75 dBm. At the maximum input power that this HTS device can handle, +43 dBm, the 3'd harmonic was-65 dBc, just within the 75dB dynamic range for the two tone intermodulation measurement. The unexpected nonlinear performance of this HTS device would have been missed by an intermodulation measurement.