The Experts below are selected from a list of 126 Experts worldwide ranked by ideXlab platform

Matthew Grayson - One of the best experts on this subject based on the ideXlab platform.

  • Four-Point characterization using capacitive and ohmic contacts
    Bulletin of the American Physical Society, 2012
    Co-Authors: Wang Zhou, Brian S. Kim, Yash D. Shah, Chuanle Zhou, Matthew Grayson
    Abstract:

    A Four-Point characterization method is developed for semiconductor samples that have either capacitive or ohmic contacts. When capacitive contacts are used, capacitive current- and voltage-dividers result in a capacitive scaling factor which is not present in Four-Point measurements with only ohmic contacts. Both lock-in amplifier and pre-amplifier are used to measure low-noise response over a wide frequency range from 1 Hz -- 100 kHz. From a circuit equivalent of the complete measurement system after carefully being modeled, both the measurement frequency band and capacitive scaling factor can be determined for various Four-Point characterization configurations. This technique is first demonstrated with a discrete element Four-Point Test device and then with a capacitively and ohmically contacted Hall bar sample using lock-in measurement techniques. In all cases, data fit well to a circuit simulation of the entire measurement system over the whole frequency range of interest, and best results are achieved with large area capacitive contacts and a high input-impedance preamplifier stage. Results of samples (substrates grown by Max Bichler Dieter Schuh, and Frank Fischer of the WSI) measured in the QHE regime in magnetic fields up to 15 T at temperatures down to 1.5 K will also be shown.

  • Generalized Four-Point characterization method using capacitive and ohmic contacts
    The Review of scientific instruments, 2012
    Co-Authors: Brian S. Kim, Wang Zhou, Yash D. Shah, Chuanle Zhou, N. Işık, Matthew Grayson
    Abstract:

    In this paper, a Four-Point characterization method is developed for samples that have either capacitive or ohmic contacts. When capacitive contacts are used, capacitive current- and voltage-dividers result in a capacitive scaling factor not present in Four-Point measurements with only ohmic contacts. From a circuit equivalent of the complete measurement system, one can determine both the measurement frequency band and capacitive scaling factor for various Four-Point characterization configurations. This technique is first demonstrated with a discrete element Four-Point Test device and then with a capacitively and ohmically contacted Hall bar sample over a wide frequency range (1 Hz–100 kHz) using lock-in measurement techniques. In all the cases, data fit well to a circuit simulation of the entire measurement system, and best results are achieved with large area capacitive contacts and a high input-impedance preamplifier stage. An undesirable asymmetry offset in the measurement signal is described which can arise due to asymmetric voltage contacts.

Wang Zhou - One of the best experts on this subject based on the ideXlab platform.

  • Four-Point characterization using capacitive and ohmic contacts
    Bulletin of the American Physical Society, 2012
    Co-Authors: Wang Zhou, Brian S. Kim, Yash D. Shah, Chuanle Zhou, Matthew Grayson
    Abstract:

    A Four-Point characterization method is developed for semiconductor samples that have either capacitive or ohmic contacts. When capacitive contacts are used, capacitive current- and voltage-dividers result in a capacitive scaling factor which is not present in Four-Point measurements with only ohmic contacts. Both lock-in amplifier and pre-amplifier are used to measure low-noise response over a wide frequency range from 1 Hz -- 100 kHz. From a circuit equivalent of the complete measurement system after carefully being modeled, both the measurement frequency band and capacitive scaling factor can be determined for various Four-Point characterization configurations. This technique is first demonstrated with a discrete element Four-Point Test device and then with a capacitively and ohmically contacted Hall bar sample using lock-in measurement techniques. In all cases, data fit well to a circuit simulation of the entire measurement system over the whole frequency range of interest, and best results are achieved with large area capacitive contacts and a high input-impedance preamplifier stage. Results of samples (substrates grown by Max Bichler Dieter Schuh, and Frank Fischer of the WSI) measured in the QHE regime in magnetic fields up to 15 T at temperatures down to 1.5 K will also be shown.

  • Generalized Four-Point characterization method using capacitive and ohmic contacts
    The Review of scientific instruments, 2012
    Co-Authors: Brian S. Kim, Wang Zhou, Yash D. Shah, Chuanle Zhou, N. Işık, Matthew Grayson
    Abstract:

    In this paper, a Four-Point characterization method is developed for samples that have either capacitive or ohmic contacts. When capacitive contacts are used, capacitive current- and voltage-dividers result in a capacitive scaling factor not present in Four-Point measurements with only ohmic contacts. From a circuit equivalent of the complete measurement system, one can determine both the measurement frequency band and capacitive scaling factor for various Four-Point characterization configurations. This technique is first demonstrated with a discrete element Four-Point Test device and then with a capacitively and ohmically contacted Hall bar sample over a wide frequency range (1 Hz–100 kHz) using lock-in measurement techniques. In all the cases, data fit well to a circuit simulation of the entire measurement system, and best results are achieved with large area capacitive contacts and a high input-impedance preamplifier stage. An undesirable asymmetry offset in the measurement signal is described which can arise due to asymmetric voltage contacts.

Russell Owusu Afrifa - One of the best experts on this subject based on the ideXlab platform.

  • investigation on the flexural behaviour of reinforced concrete beams using phyllite aggregates from mining waste
    Materials & Design, 2011
    Co-Authors: Mark Adomasamoah, Russell Owusu Afrifa
    Abstract:

    Abstract This paper investigated the flexural behaviour of 12 reinforced concrete (RC) beams made of phyllite coarse aggregates produced as by-product of underground gold mining activity. The beams were Tested to failure under four point Test. Collapse of the beams which were adequately designed against shear failure occurred mostly through either flexural-shear failure and/or diagonal tension failure. The experimental failure loads averaged approximately 115% of the theoretical failure loads. It was observed that the beams developed early shear cracks and higher flexural crack widths than allowable at service loads. Deflections compared reasonably well with the design code requirement but displacement ductility was low. It is recommended that British Standard (BS) 8110 design concrete shear stress values be multiplied by 0.8 to assure that the predicted shear capacity of phyllite concrete would be low and reasonable as compared to flexural capacity. In that case, BS 8110 can be used to provide adequate load factor against flexural failure for under-reinforced RC beams made of phyllite coarse aggregates.

Nasimul Huq - One of the best experts on this subject based on the ideXlab platform.

  • Fracture toughness measurements on SiC/Al_2O_3 composite
    Journal of Materials Science, 1992
    Co-Authors: Nasimul Huq, A. Haque, Shaik Jeelani
    Abstract:

    Three Test techniques are addressed for the measurements of plane strain critical stress intensity factors, K _IC, on monolithic Al_2O_3 and SiC-whisker/Al_2O_3 composite: a Four-Point Test on chevron-notched bend bars; a Four-Point Test on single edge-notched bend bars; and a fractometric Test on chevron-notched short bars. The Tests were performed on 99.80% Al_2O_3 and 30 vol % SiC whisker-reinforced Al_2O_3. Bend bar Test techniques yielded more realistic stress intensity factors, K _IC, on the SiC-whisker/Al_2O_3 composite than the short-bar Test results. Chevron-notched bend-bar Tests yielded relatively higher critical stress intensity factors, on both Al_2O_3 and SiC/Al_2O_3, possibly due to R -curve effects, suggesting the use of stress intensity factor as a function of crack length instead of using the minimum value. Ambiguous results, K _IC, obtained from short-bar Tests on SiC/Al_2O_3 composite, strongly suggests the need to run compliance calibration Tests on ceramic composites to determine an appropriate K -factor.

  • Fracture toughness measurements on SiC/Al2O3 composite
    Journal of Materials Science, 1992
    Co-Authors: Nasimul Huq, A. Haque, Jeelani
    Abstract:

    Three Test techniques are addressed for the measurements of plane strain critical stress intensity factors,KIC, on monolithic Al2O3 and SiC-whisker/Al2O3 composite: a Four-Point Test on chevron-notched bend bars; a Four-Point Test on single edge-notched bend bars; and a fractometric Test on chevron-notched short bars. The Tests were performed on 99.80% Al2O3 and 30 vol % SiC whisker-reinforced Al2O3. Bend bar Test techniques yielded more realistic stress intensity factors,KIC, on the SiC-whisker/Al2O3 composite than the short-bar Test results. Chevron-notched bend-bar Tests yielded relatively higher critical stress intensity factors, on both Al2O3 and SiC/Al2O3, possibly due toR-curve effects, suggesting the use of stress intensity factor as a function of crack length instead of using the minimum value. Ambiguous results,KIC, obtained from short-bar Tests on SiC/Al2O3 composite, strongly suggests the need to run compliance calibration Tests on ceramic composites to determine an appropriateK-factor.

Brian S. Kim - One of the best experts on this subject based on the ideXlab platform.

  • Four-Point characterization using capacitive and ohmic contacts
    Bulletin of the American Physical Society, 2012
    Co-Authors: Wang Zhou, Brian S. Kim, Yash D. Shah, Chuanle Zhou, Matthew Grayson
    Abstract:

    A Four-Point characterization method is developed for semiconductor samples that have either capacitive or ohmic contacts. When capacitive contacts are used, capacitive current- and voltage-dividers result in a capacitive scaling factor which is not present in Four-Point measurements with only ohmic contacts. Both lock-in amplifier and pre-amplifier are used to measure low-noise response over a wide frequency range from 1 Hz -- 100 kHz. From a circuit equivalent of the complete measurement system after carefully being modeled, both the measurement frequency band and capacitive scaling factor can be determined for various Four-Point characterization configurations. This technique is first demonstrated with a discrete element Four-Point Test device and then with a capacitively and ohmically contacted Hall bar sample using lock-in measurement techniques. In all cases, data fit well to a circuit simulation of the entire measurement system over the whole frequency range of interest, and best results are achieved with large area capacitive contacts and a high input-impedance preamplifier stage. Results of samples (substrates grown by Max Bichler Dieter Schuh, and Frank Fischer of the WSI) measured in the QHE regime in magnetic fields up to 15 T at temperatures down to 1.5 K will also be shown.

  • Generalized Four-Point characterization method using capacitive and ohmic contacts
    The Review of scientific instruments, 2012
    Co-Authors: Brian S. Kim, Wang Zhou, Yash D. Shah, Chuanle Zhou, N. Işık, Matthew Grayson
    Abstract:

    In this paper, a Four-Point characterization method is developed for samples that have either capacitive or ohmic contacts. When capacitive contacts are used, capacitive current- and voltage-dividers result in a capacitive scaling factor not present in Four-Point measurements with only ohmic contacts. From a circuit equivalent of the complete measurement system, one can determine both the measurement frequency band and capacitive scaling factor for various Four-Point characterization configurations. This technique is first demonstrated with a discrete element Four-Point Test device and then with a capacitively and ohmically contacted Hall bar sample over a wide frequency range (1 Hz–100 kHz) using lock-in measurement techniques. In all the cases, data fit well to a circuit simulation of the entire measurement system, and best results are achieved with large area capacitive contacts and a high input-impedance preamplifier stage. An undesirable asymmetry offset in the measurement signal is described which can arise due to asymmetric voltage contacts.