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Jan 2004

Volume 75, Issue 1, pp. 1-286

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back to top THERMOMETRY; THERMAL DIFFUSIVITY; ACOUSTIC; PHOTOTHERMAL and PHOTOACOUSTIC

Ultrasensitive, fast, thin-film differential scanning calorimeter

Mikhail Yu. Efremov, Eric A. Olson, Ming Zhang, François Schiettekatte, Zishu Zhang, and Leslie H. Allen

Rev. Sci. Instrum. 75, 179 (2004); http://dx.doi.org/10.1063/1.1633000 (13 pages) | Cited 36 times

Online Publication Date: 22 December 2003

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The equipment for an ultrasensitive, fast, thin-film differential scanning calorimetry [(TDSC) or nanocalorimetry] technique is described. The calorimetric cell (∼0.30 cm2) operates by applying a short (∼10 ms) dc current pulse (∼10 mA) to a thin (∼50 nm) patterned metal strip, which is supported by a thin (∼50 nm) SiNx membrane. The calorimeter operates at high heating rates (15–200 K/ms) and is very sensitive (30 pJ/K). The design of the calorimeter, the timing/synchronization methods, as well as the choice of key components of the instrument are discussed. Comparisons are made between two dc pulsing circuits that generate the current, a battery powered system and a system based on discharge of an assembly of charged capacitors (recommended). Design concepts for the differential as well as a simplified nondifferential technique are discussed and evaluated via experiments on thin films of indium. The differential design shows an increase in sensitivity, making it suitable for small samples. The custom made electronic circuits are also described, including the design of a preamplifier with low (28×) and high (700×) gain options, which are also compared using experimental data. Noise considerations are critical for the method. Simple models which describe noise levels in the calorimetric data are given and methods for reducing noise are discussed in detail. The sources of noise in the instrument are discussed in terms of both fundamental factors such as Johnson noise of the metal strip, as well as the limiting attributes of the sensing and pulsing circuits and instrumentation. These limiting attributes include spurious signals generated by desorption of ambient gases from the sensor, ground loops, switching regulators, and missing codes in analog-to-digital converter instruments. Examples of the experimental data of heat capacity Cp(T) of various thin films of indium, tin, and polystyrene are presented. A complete data set of raw experimental values is included for a 20 nm sample of Sn which shows the values of current and voltage of both the sample and reference sensors, as well as the differential voltage and the final values of the heat capacity. © 2004 American Institute of Physics.
Show PACS
07.20.Fw Calorimeters
81.70.Pg Thermal analysis, differential thermal analysis (DTA), differential thermogravimetric analysis
84.30.Le Amplifiers
65.40.Ba Heat capacity

Europium beta-diketonate temperature sensors: Effects of ligands, matrix, and concentration

Gamal E. Khalil, Kimberly Lau, Gregory D. Phelan, Brenden Carlson, Martin Gouterman, James B. Callis, and Larry R. Dalton

Rev. Sci. Instrum. 75, 192 (2004); http://dx.doi.org/10.1063/1.1632997 (15 pages) | Cited 35 times

Online Publication Date: 22 December 2003

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Europium beta diketonates are easily synthesized highly luminescent complexes with high temperature sensitivity. We report on the temperature dependence of the luminescence of recently synthesized europium complexes originally prepared for use as light emitting diodes. It has been discovered that when incorporated in a polymer matrix, their decay lifetime can provide accurate measurement of temperature. Their lifetime as a function of temperature depends on three factors: (i) the type and number of ligands in the complex, (ii) the particular polymer used for the matrix, and (iii) the europium chelate to polymer matrix concentration ratio. Various tris and tetrakis europium chelates are used to study ligand effects, while the polymers FIB, polycarbonate, and Teflon© are used to analyze matrix effects. In all cases studied, higher concentrations give rise to shorter lifetimes and higher temperature sensitivities, with sensitivity defined as ΔI/(IrefΔT). We propose to explain this phenomenon by using the following equation: 1/τobs ≡ Ktotal = kr+knr(T)+kc([Eu]). Here Ktotal is the observed decay rate, which is the inverse of the observed lifetime, while kr and knr(T) are the radiative and nonradiative decay rates, respectively. As well as being dependent on temperature, knr(T) for these complexes is very dependent on the environment, i.e., solvent or polymer, and can be considered as ken(T). The rate kc([Eu]) is the quenching term dependent on the concentration of the europium complex. © 2004 American Institute of Physics.
Show PACS
07.20.Dt Thermometers
78.55.Kz Solid organic materials
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