摘要:

Acoustic techniques are used to monitor the temperature of silicon wafers during rapid thermal processing from room temperature to 1000 °C with ±5 °C accuracy. Acoustic transducers are mounted at the bases of the quartz pins that hold up the silicon wafer during rapid thermal processing. An electrical pulse applied across a transducer generates an extensional mode acoustic wave guided by the quartz pins. The extensional mode is converted into Lamb waves in the silicon wafer which acts as a plate waveguide. The Lamb waves propagate across the length of the silicon wafer and are converted back into an extensional mode in the opposite pin. The time of flight of the extensional mode in the quartz pins is measured using pulse echo techniques and is subtracted from the total time of flight to obtain the Lamb wave time of flight across the wafer. Because the velocity of Lamb waves in the silicon wafer is systematically affected by temperature, the measurement of the time of flight of the Lamb wave provides the accurate temperature of the silicon wafer.

ISSN:0034-6748    

DOI:10.1063/1.1144929

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A compact heater, designed for the deposition of thin films at high temperatures in an oxidizing atmosphere or in vacuum, is described. The heater, including an oxygen‐resistant case and the attached substrate, can be loaded into a vacuum deposition chamber through a small‐diameter load‐lock port, and will operate in 0–1 atm of oxygen at temperatures up to at least 800 °C. Heat is generated resistively, and the substrates are heated directly by thermal conduction. The heater was built specifically to heat substrates during the growth of high‐temperature superconducting thin films.  

ISSN:0034-6748    

DOI:10.1063/1.1144930

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The principles of the zero‐balance heat‐flux meter (HFM) technique are studied with two steady‐state finite difference computer models developed to simulate the responses of a sensor mounted either on the cold face or on the warm face of a wall. Computations show that a particular Biot number (defined by the authors), the dimensionless wall width, and the dimensionless wall thickness are the parameters affecting the HFM accuracy. The authors present outputs of their models that show the influence of these parameters, and propose three empirical expressions that allow corrections of the operational errors. It can be affirmed that the flux meter should be mounted on the cold face in the case of a small Biot number (it assures an accuracy of at least 5% if the Biot number value is smaller than 0.2). And it should be mounted on the warm face when the Biot number is large (in the case of building insulators in normal environment conditions it assures an accuracy of at least 10%). In other cases, the flux meter should be used as a gradient flux meter switching off the internal heater.

ISSN:0034-6748    

DOI:10.1063/1.1144876

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A method of measuring the critical current of polycrystalline high temperature superconductors is described at various temperatures between 65 K and the transition temperature with the sample immersed in liquid nitrogen (LN2). The temperature of LN2is varied following its phase diagram above the triple point (63.15 K). To increase the temperature of the nitrogen bath above 77 K, one increases the container gas pressure above 1 atm and pumps on the liquid to obtain temperatures below 77 K.

ISSN:0034-6748    

DOI:10.1063/1.1144877

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Substantial improvements have been made in the sensitivity of an ac susceptibility measurement system which determines the pressure dependence of the superconducting transition temperature,Tc(P). The pressure,P, is determined nearTcfrom the position of theR1andR2fluorescence peaks from ruby chips. The system was used to determineTc(P) for several highTcsingle crystals, but was not sufficiently sensitive to determineTc(P) of polycrystalline samples for HgBa2CuO4+&dgr;. This motivated us to improve the sensitivity of our system. Other parts of the system and the data analysis procedures also have been improved. As a demonstration,Tc(P) of HgBa2CuO4+&dgr;polycrystal to 4 GPa is presented. The improvement of the system using the diamond anvil cell opens the possibility of measuringTcabove 10 GPa and on smaller samples.

ISSN:0034-6748    

DOI:10.1063/1.1144878

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A sensitive density meter for measuring the density of small amounts of solid, solution, or dispersed materials, e.g., biological systems in the liquid environment, is presented. The chamber for the measured sample is in the lower part of a glass buoy. It is closed by the glass stopper containing the permanent magnet. The buoy is immersed in the carrying liquid with the known density and is balanced by the magnetic force. The device enables the measurement at constant temperature as well as in the temperature scanning regime. The accuracy of measuring the liquid density is 1 mg/lin a 1.5 ml chamber; the sensitivity of measuring the temperature is 1 mK. The volume of solids or dispersed systems of known weight is measured with an accuracy of 1.5 nl.

ISSN:0034-6748    

DOI:10.1063/1.1144879

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A technique to distinguish between materials that can and cannot shield microwaves in liquid nitrogen was developed. The samples are placed in a modifiedX‐band waveguide, which operates by the same ‘‘insertion loss’’ principle as a coaxial device used to measure shielding effectiveness from 300 to 1000 MHz. Verification of the waveguide fixture was accomplished by measuring the shielding effectiveness of a good conductor, coppper; a nonconductor, Teflon; and two intermediate conductors, steel and a carbon‐filled elastomer. After verification, the waveguide fixture was used at liquid nitrogen temperatures to compare the shielding effectiveness of YBa2Cu3O7−x, a high temperature superconductor, with copper, a known shielding material.

ISSN:0034-6748    

DOI:10.1063/1.1145103

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A new robot‐performance calibration system based on tracking multilaser trilateration has been developed. To realize 1 &mgr;m coordinate accuracy, a beam‐deflecting tracking mechanism with both a ball‐seated bearing and a spherically shaped cat’s eye retroreflector whose refractive index is 2.0 has been developed. The coordinate error and the repeatability of a commercial industrial robot have been verified by the system we developed in a two‐dimensional plane.

ISSN:0034-6748    

DOI:10.1063/1.1145104

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An autocollimator based optical system has been developed which allows the relative angular positions of separate reflecting targets to be measured with high accuracy over a relatively large area. Misalignments suffered by the autocollimator head during translation between different measuring points are accounted for by utilizing a large plane reference mirror. Accuracies better than ±2 arcsec have been obtained over a 0.5 m diameter circular exploring area.

ISSN:0034-6748    

DOI:10.1063/1.1145105

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A method for sealing a semirigid solid dielectric radio frequency quality coaxial cable against ultrahigh vacuum is described. It was developed for the output cable of a hydrogen maser frequency standard that operates at the single spot frequency of 1420.4 MHz. The cable is squeezed in two places a quarter of a wavelength apart so that the two impedance mismatches introduced cancel to the first order at the spot working frequency. The length of solid dielectric trapped between the two ‘‘tourniquets’’ forms an excellent and enduring vacuum seal.  

ISSN:0034-6748    

DOI:10.1063/1.1145106

出版商:AIP    

年代:1994

数据来源: AIP