Measurement Of Sample Temperature Research Articles

Temperature measurement for scanning tunnel microscope samples using a detachable thermocouple

A detachable thermocouple contact for the measurement of sample temperature in ultrahigh vacuum was constructed and tested. The thermocouple was demonstrated to be accurate to within 1.2 K from 77 to 373 K. The thermocouple was also compared against a reference thermocouple of conventional design up to 1300 K (during ohmic heating) and the agreement was within 20 K throughout this temperature range.

In situ TEM studies of the effect of misfit strain on the kinetics of sil-xgex solid phase epitaxy: temperature calibration & surface effects

While in situ TEM studies have proven useful for the direct observation of solid-state reaction mechanisms, such studies rarely provide quantitative kinetic data. This limitation is due to problems associated with the accurate measurement of local sample temperature, assessment of beam heating and damage, and minimization of thin-film effects. Sinclair et al. have proposed a technique for establishing the temperature of a sample during in situ TEM annealing experiments in which the wellcharacterized Si <001> solid phase epitaxy amorphous-crystalline (a/c) transformation rate is used to estimate the temperature in an adjacent (but not contiguous) region of the specimen. We have used this in situ technique to determine the activation energy for strained solid phase epitaxy of Sil-xGex (x=5.4, 11.6, and 17 at.%). The alloys were grown by CVD on <001> Si substrates to a thickness of approximately 200 nm. The entire alloy layer, and 180 nm of the underlying substrate, were amorphized with 100, followed by 200 keV 29Si implantation.

TGA experimental data-analysis provided by transpiration theory

Thermogravimetric analysis (measurement of sample mass vs. temperature) is a frequently used laboratory technique in the analysis of materials, and commercial computerautomated equipment is available. The TGA experiment is designed in much the same way as a transpiration experiment; the transpiration experiment was theoretically analyzed using a transport mechanism coupling diffusion and viscous flow. This coupled flow analysis as applied to the TGA experiment will be discussed. The analysis allows one to calculate equilibrium vapor pressures and related thermodynamic properties. As an example, data for the vaporization of Tl 2O 3(s) will be discussed.

The superheat phenomenon in the combustion of magnesium particles

Magnesium is known to be a likely fuel for engines that could work in the CO 2 atmospheres of Mars and Venus. The present paper reports temperature measurements of magnesium samples during combustion in CO 2. The burning sample temperature increases with the decrease in the initial size. The temperature of the 1-mm samples is 300–400 K higher than the boiling point of magnesium. The stability of the superheated drop is explained by the presence of a porous shell on the surface. An attempt has been made to describe vaporization on the superheated drop by the Knudsen-Langmuir equation. During combustion at high-pressure fragment ejection of the flame is observed in high-speed motion pictures. This phenomenon is shown to be connected with the drop superheat. The repeated fracture of the outer shell formed in the flame ensures the complete burnout of metal particles at high pressure.

Defect Penetration During the Plasma Etching of Semiconductors

ABSTRACTDry etching can introduce defects into the material being etched. Simple expressions for both sidewall and top surface defect distributions may be obtained by assuming that the defects are introduced according to a phenomenological source function. Calculations of conductance based on these expressions are found to describe very well measurements on dry-etched wires and epilayers. Mechanisms by which defects can penetrate into the sample are discussed. The role of sample heating and defect diffusion is examined. In-situ measurements of sample temperature during a dry-etch run indicate that simple diffusion is insufficient to account entirely for the observed damage. Instead, dry-etch damage may arise from other mechanisms such as by knock-on replacement collisions, or via a channeling effect. A more complex form of diffusion may also affect the final damage distribution.

A gas-flow furnace for X-ray crystallography

A gas-flow furnace has been built for high-temperature single-crystal X-ray diffraction measurements using a Huber 512 four-circle goniometer. The furnace assembly is mounted on an XYZ stage which is fixed to the ϕ-axis counterbearing and the sample is mounted on the ϕ circle. The XYZ stage allows a determination of the temperature profile around the sample and a selection of the optimum furnace position. The sample temperature is measured with a thermocouple placed 0.5 mm from the center of the crystal. Thermocouple temperature was calibrated up to 991 K using the thermal expansion of a single-crystal of NaCl. The accuracy of the sample temperature measurements and the fluctuations of the sample temperature are both better than ± 2 K. The furnace has been successfully used to study the crystal structures and the thermal expansion of β-Mg2SiO4 up to 1100 K and the phase transitions in ilvaite, Ca(Fe2+ Fe3+) Fe2+Si2O7O(OH), and anorthite, CaAl2Si2O8, at 346 and 516 K, respectively.

An automated dosimetry system for microwave and thermal exposure of biological samples in vitro.

A waveguide exposure system with automated sample temperature measurement is described. This system provides on-line determination of the temperature profile over time of biological samples in vitro. It allows automated computation of the specific absorption rate determined from heating/cooling curves, uses minimally-perturbing thermometry, is biocompatible and can be used for measurements of both microwave and conventional heating.

Simple improvements to the varian 35 GHz EPR liquid nitrogen insertion Dewar

Low-temperature EPR measurements are generally performed by one of two methods; either the whole cavity/sample assembly is inserted in or just above a cryogenic fluid, or a cold finger Dewar is inserted into the cavity. At 35 GHz the preferred cavities, using low-order cylindrical or rectangular modes, are too small to accommodate a cold finger without serious perturbation of mode patterns and degradation of cavity Q. Immersion Dewars are the preferred alternative at this frequency. Our Varian device (Dewar Model No. V-45671) consists of a cylindrical TE,,, 1 cavity (part number 909925 ), coupled to the spectrometer source via a short section of stainless steel waveguide to provide thermal isolation, and tuned by a rotatable, threaded bottom plunger which is made of aluminum and carries a long extension immersed in the liquid nitrogen. The cavity is positioned in the neck of the storage Dewar. The idea is elegantly simple but has some disadvantages: sample temperature measurement is not straightforward since the sample is not in the gas flow and the aluminum base of the cavity is eddy-current heated by the modulation field, the base temperature is 110 K unless the Dewar neck is filled, and there is no temperature control. The modifications described here permit tuning the cavity without having to remove it from the Dewar (a modification with the same purpose has been described before ( 1))) provide a lower base temperature which is controllable independently of cryogen level, and permit temperature measurement which is essentially that of the sample. The addition of a heating element and closed-loop controller would permit stable variable temperature operation if desired. A fixed temperature (77 K) arrangement has been described (2). In our device, the cold gas flows through the cavity, not outside it. The essential features of the unmodified device are shown schematically on the left of Fig. 1, dashed lines indicating modifications for gas flow and thermocouple access. Additional parts needed are shown transposed to the right of the figure in the interests of clarity. The main modification to the commercial device is extending the hole (H)

Modifications of a Diffuse Reflectance Cell to Allow the Characterization of Carbon-Supported Metals by DRIFTS

Carbon-supported metal catalysts have been investigated with the use of Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) for the first time. In order to successfully pretreat such catalysts, obtain IR spectra, and characterize these highly opaque materials, one must make extensive modifications of DRIFTS cells, commercial or otherwise. These modifications include the arrangements for capability and ease of sample height adjustment from outside the spectrometer chamber, the improvement of the thermal performance of the cell to provide high temperatures in flowing H2, the accurate measurement of sample temperature, and the guarantee of adequate gas flows through the catalyst bed. These capabilities are essential for proper in situ investigations of catalysts. This improved DRIFTS cell was used to follow the thermal decomposition of carbon-supported Os3(CO)12 for the first time. The cluster transformed rapidly in flowing H2 to a more stable H4Os4(CO)12 terra-nuclear cluster, similar to the reaction in solution, which then further decomposed at higher temperatures. The spectrum of CO adsorbed on carbon-supported Os crystallites after complete decomposition was also obtained, and it showed the presence of only reduced metallic Os. These findings provide the first IR evidence for the relative inertness of oxygen-free carbon, compared to oxide supports, towards the formation of stable, positive-valent Os species. In order to facilitate the effective use of DRIFTS for characterization of opaque materials in general, our modifications to a commercial DRIFTS cell are described and representative spectra are shown.

A Study of Diffusion, Clustering and Defects in As+ And Bf2+ Implanted Silicon During Scanning Electron Beam Annealing.

ABSTRACTScanning electron beam annealing techniques have been applied to the study of diffusion of implanted arsenic and boron difluoride. Electron beam anneals over the time range 0-180s (at Tmax), with peak temperatures in the range 1100-1200°C have been performed on uniformly implanted samples. Controlled slow cooling has been performed for some samples. Direct sample temperature measurements were made using a dual-colour pyrometer under control of a microcomputer, which provided data-logging and feedback control of temperature. The accurate temperature control achieved using this system is important for realistic diffusion modelling.Measurement of the resulting chemical and electrical dopant profiles, using SIMS, RBS and spreading resistance methodshas shown the presence of non-equilibrium diffusion at short times [6]. Channelling RBS studies used to investigate the activation and clustering behaviour of arsenic during the first stages of these very rapid anneals is reported.Modelling of the arsenic diffusion occuring for a range of implant doses subjected to these anneals has been performed,applying avariety of models, including a dynamic clustering model. This dynamic clustering model, based upon an equilibrium cluster model and a measured de-clustering rate, has been shown previously to give good agreementwith experiment. Forthese experiments, a modified de-clustering coefficient was needed to model the diffusion occuring for a wider range of arsenic implants. A solution of the Poisson equation for the internal electric field has also been incorporated.DLTS techniques have been used to study the defects remaining in diodes fabricated using these implagts andanneals. Trap densities of <5×1010cm−3 and leakages of <2×10−9 A.cm2 at −5V have been measured for the best devices, similar tothose observed for control furnace anneals.

High-temperature oven for vibrating sample magnetometers

The construction and operation of a high-temperature oven, particularly designed for use in conventional vibrating sample magnetometers (VSM), is described. The oven may be used in the temperature range 300-1150K. The location of the temperature sensor enables a fast and accurate measurement of the sample temperature. The oven can be heated from room temperature to 1050K in less than fifteen minutes with a temperature difference between temperature sensor and sample of less than one kelvin at the final temperature. The fast cooling rate of the oven permits a quick interchange of samples.

Precision manipulator heating and cooling assembly compatible with sample transfer

A technique is described for the transfer of a UHV sample system to a precision manipulator. It allows direct sample temperature measurement in a broad range of sample temperatures (150-1750 K) and simultaneously retains the benefit of the additional degree of freedom provided by the precision manipulator flip mechanism. The technique is similar to that reported by Crider (1976) but with several modifications. The pump is mounted at the extreme end of the magnetically coupled linear motion feedthrough (to maximize the separation). Samples are mounted on a threaded circular sample holder, transferred to the flip mechanism of the manipulator. The flip mechanism contains a rear electrode assembly and thermocouple, in direct contact with the sample, and a copper plate and a flexible strap are attached to the receiving block (to facilitate sample cooling).

Measurement of the oxidative stability of polyethylene by differential thermal analysis

An evaluation has been made of the experimental features critical to the evaluation of the oxidative stability of polyethylene using constant temperature DTA, with particular reference to the control and measurement of the sample temperature.

Sample temperature measurement in the PAR vibrating sample magnetometer oven

A method is described which allows direct measurement of sample temperature in the high−temperature oven accessory of a Princeton Applied Research vibrating sample magnetometer.

Apparatus for Production, Measurement and Reaction Studies of Dissociated Gases at Elevated Temperatures

An apparatus is described which is used for the controlled production, characterization, and study of dissociated gases in a microwave discharge at elevated temperatures. A unique feature is the ability to produce and study a microwave discharge plasma in the heated zone. This allows elevated temperature reactions to be studied in high concentrations of dissociated gases. Further, the system permits weight change measurements of specimens in the plasma, thus facilitating reaction rate determinations. Included is a description of a cavity for use on a 50-mm diameter cylindrical reactor. The effects of flow rate, pressure, temperature, power, metal sample, and sampling position on dissociation percentage of oxygen in the apparatus are described as well as a technique for sample temperature measurements in the plasma which permits determination of high temperature recombination coefficients and reaction rates.

Heat capacity measurements of nuclear materials by laser flash method

An improved method of laser flash calorimetry for the precise measurements of haat capacity of nuclear materials is presented. The main points of the improvements are (1) the use of an ‘absorption disk’ and (2) the use of a digital micro-voltmeter and line printer systems for the measurement of sample temperature. Experimental results obtained on a standard sample of alumina at temperatures from 80 to 700 K by this method have a precision of ± 0.5%, which proves the feasibility of this improved method for both low- and high-temperature heat capacity determination of nuclear materials. The results of heat capacity determination by this method on graphites and UP are also presented. Une amélioration de la méthode calorimétrique par flash de laser est présentée en vue de mesurer de manière précise la capacité calorifique des matériaux nucléaires. Les principaux points d'amélioration sont les suivants: (1) l'emploi d'un ‘disque d'absorption’ et (2) l'emploi d'un microvoltmètre digital et un système d'imprimante pour la mesure de la température des échantillons. Les résultat expérimentaux obtenus sur un échantillon étalon d'alumine entre 80 et 700 K par cette méthode atteignent une précision de ± 0,5%, ce qui démontre les possibilités de cette méthode améliorée pour effectuer des déterminations de la capacité calorifique des matériaux nucléaires à la fois aux températures faibles et élevées. Les résultats de détermination de la capacité calorifique par cette méthode sont présentés dans le cas des graphites et de UP. Eine verbesserte Methode de Laserblitz-Kalorimetrie zur genauen Messung der Wärmekapazität von Kernbrennstoffen wird mitgeteilt. Die Verbesserungen betreffen hauptsächlich die Verwendung einer Absorptionsscheibe sowie eines digitalen Mikrovoltmeters und eines Druckersystems zur Bestimmung der Probentemperatur. Experimentelle Ergebnisse an einer Standardprobe aus Al 2 O 3 führen nach dieser Methode zwischen 80 und 700 K zu einer Genauigkeit von ± 0,5%, aus der folgt, dass diese verbesserte Methode zur Bestimmung der Wärmekapazität von Kernbrennstoffen bei niedrigen und hohen Temperaturen geeignet ist. Die Ergebnisse der nach dieser Methode gewonnen Wärmekapazität von Graphit und UP werden angegeben.

A Furnace System with Versatile Time-Temperature Programming and Electrical Measurement Capability

A furnace and electrical measurement system is described that is capable of a wide range of time-temperature relationships while allowing for the simultaneous measurement of sample temperature and resistance over any 3–4 decades in the range 10−2–107 Ω. The furnace system consists of a servo-controlled push rod moving a sample fixture in a gradient furnace. The servo system is controlled by a cam wheel driven by a stepping motor whose speed can easily be changed during rotation to provide for increased profile versatility. Two- or four-terminal resistance measurements and temperature measurements are possible with four lead wires; each is monitored with a chart recorder. Possible applications and examples of performance are discussed.

Rocker-type DTA Apparatus for Fluid Samples

Abstract A Rocker-type DTA apparatus, with agitation by rocking, has been developed for use in the thermal analysis of various fluid mixture systems. The heater block, with its assembled cells, is continuously rocked at 20 r.p.m. with a rocking of 180° angle. The glass cell has a volume of about 8 ml and is sealed by means of a burner with a sample of about 5 ml. Distilled water is used as the inert reference in the reference holder. Two thermocouples are inserted in each cell, one to determine the temperature difference and the other for sample temperature measurements. The double thermocouple gives a constant transition temperature of the sample over a wide range of heating rates. The apparatus is applied to solid-liquid and starch-water systems. Variables affecting the DTA thermogram of the K2Cr2O7–H2O system are investigated, and a method is established to correlate the DTA curve with the solubility curve for the system.

The Cooling of Heating Grain by Transfer During Cold Weather1

Experiments were carried out to determine the effectiveness of farm practices to cool heating grain during winter. Two 165-bushel loads of wheat were removed from a ground pile, a portion of which was heating to 95°. A portable grain auger was used to transfer the wheat to a truck. The wheat was later unloaded into a commercial grain elevator where it was “turned” and reloaded into the truck. Temperature measurements of samples taken as the wheat was being transferred and “turned” indicated that the wheat was not cooled appreciably during its actual passage through an auger or during the actual “turning.” However, the use of a grain auger and “turning” the grain in the elevator provided an effective means of mixing warm with cool grain, thus reducing the average grain temperature, These procedures were most effective when the initial temperature of the warm grain was high compared with the peripheral portions

X-ray analysis technique for very high temperatures

A new powder-diffraction technique for very high temperatures is described, in which a thermocouple combines the functions of sample support, heating, and temperature measurement. This device is simple, compact and inexpensive, and has proved to be very reliable. The maximum working temperature depends on the thermocouple material, and is normally 1750° C using 5/20 rhodium-platinum, or 1850° C with 20/40 rhodium-platinum couples.