RESEARCH ACCOUNT CURRENT SCIENCE, VOL. 91, NO. 2, 25 JULY 2006 175 *For correspondence. (e-mail: subbi@igcar.gov.in) Development of laser-heated diamond anvil cell facility for synthesis of novel materials N. Subramanian*, N. V. Chandra Shekar, N. R. Sanjay Kumar and P. Ch. Sahu Advanced Materials Section, Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India Investigation of material behaviour under extremely high pressures and temperatures using IR laser-heated diamond anvil cells (DACs) has emerged in the recent years as an important area of research, both basic and applied. This article presents details of a laser-heated DAC facility that we have recently set up at our labo- ratory. The facility consists of a suitable arrangement of a CO 2 laser, motorized translation stages, a Mao– Bell-type DAC, IR and visible optical assembly, CCD- based monochromator, etc. Also, the facility has the capability of pressure measurement using Ruby fluo- rescence method and temperature measurement using spectroradiometric technique. With this facility, materials can be subjected simultaneously to high pressures and temperatures (P max ~ 100 GPa; T max ≥ 5000 K). Results on successful synthesis of InSb by direct elemental re- action and on a preliminary experiment wherein di- rect conversion of graphite to a transparent phase has been attempted with this facility are also presented. Keywords: Diamond anvil cell, high-pressure, laser- heating, novel materials. THE diamond anvil cell (DAC) is a unique device to gen- erate high static pressures on matter 1 . With the DAC it is possible nowadays to investigate materials at pressures up to a few megabars 2,3 . High strength of the diamonds coupled with their excellent transmittance to almost the entire electromagnetic spectrum has led to extensive in situ studies on a myriad of pressure-induced phenomena in materials using techniques such as the X-ray diffraction, Raman and Brillouin spectroscopy, luminescence spectro- scopy, Mössbauer spectroscopy, etc. up to several mega- bars 2 . The work done in compressing the system of interest to such high pressures is typically of a few electron volts, and is comparable to the chemical bond energies 4 . This can induce large changes in the behaviour of electronic orbitals and as a result increase the reactivity of the species under study. In addition, heating of the sample squeezed inside the DAC can provide the kinetics necessary to induce novel reactions between the reactant species by overcom- ing activation barriers that are otherwise impossible to do so at ambient conditions 4,5 . This paves the way for synthesis of novel materials which may have exotic mechanical, optical or electronic properties. Samples inside a DAC can be heated either by internal or external methods. The internal heating method involves resistive heating of the sample by passing an electric current through a miniature heating assembly or by directly passing the current through the sample, if it is conducting 6,7 . This poses diffi- culties like sample contamination and frequent breaking of the electrical leads which are taken into the DAC sam- ple chamber that can limit the pressure capability. Tem- peratures of ~2000–3500 K have been achieved by this method 7 . In the external heating method, either the DAC as a whole is heated by placing it in a furnace or the cavity just around the diamond anvils is heated with a heater coil. Either way, limitations arise in terms of weakening of the structural materials constituting the DAC in this external heating method, thereby limiting experiments 7 to temperatures ~1700 K. Another way of externally heating the sample is by means of focusing an infrared (IR) laser beam directly onto the sample. The wide-range transmittance of diamonds to al- most the entire electromagnetic spectrum allows focusing of high-power IR lasers onto the sample squeezed in the DAC, thereby subjecting it simultaneously to high tem- peratures 8 of over 7000 K and pressures of over many megabars. Typically these kinds of pressures and tempera- tures exist in planetary interiors. This technique, called the laser-heated diamond anvil cell (LHDAC) technique, first attempted successfully by Bassett and Ming 9,10 in the early 1970s, has been emerging in recent years as a pre- ferred route for investigating materials and synthesizing novel phases in the hitherto unexplored P–T region. Some of the advantages in using this technique are: (i) extremely localized direct heating of the sample alone; (ii) contami- nation-free sample chamber while using inert gas as pres- sure medium; (iii) amenability of the DAC for a variety of in situ characterization methods like X-ray diffraction, spectroscopy (Raman, IR, UV, visible); (iii) large pressure and temperature ranges that simulate intra-planetary condi- tions, (iv) high quenching rates, etc. Small sample quanti- ties (μg), and P–T-dependent absorption of heating IR laser wavelengths by the samples, pose some of the limi- tations of this technique. Chandra Shekar et al. 11 discuss the recent exciting de- velopments in the LHDAC field. Synthesis of nitrides of C, B, Si and Ge that are expected to rival diamond in terms of hardness, is currently one of the frontline prob-