A new ultra-high-vacuum variable temperature and high-magnetic-field X-ray magnetic circular dichroism facility at LNLS

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOX-ray magnetic circular dichroism (XMCD) is one of the most powerful tools for investigating the magnetic properties of different types of materials that display ferromagnetic behavior. Compared with other magnetic-sensitive techniques, XMCD has the advantage of being element specific and is capable of separating the spin and magnetic moment contributions associated with each element in the sample. In samples involving, for example, buried atoms, clusters on surfaces or at interfaces, ultrathin films, nanoparticles and nanostructures, three experimental conditions must be present to perform state-of-the-art XMCD measurements: high magnetic fields, low temperatures and an ultra-high-vacuum environment. This paper describes a new apparatus that can be easily installed at different X-ray and UV beamlines at the Brazilian Synchrotron Light Laboratory (LNLS). The apparatus combines the three characteristics described above and different methods to measure the absorption signal. It also permits in situ sample preparation and transfer to another chamber for measurement by conventional surface science techniques such as low-energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD). Examples are given of XMCD measurements performed with this set-up on different materials.X-ray magnetic circular dichroism (XMCD) is one of the most powerful tools for investigating the magnetic properties of different types of materials that display ferromagnetic behavior. Compared with other magnetic-sensitive techniques, XMCD has the advantage of being element specific and is capable of separating the spin and magnetic moment contributions associated with each element in the sample. In samples involving, for example, buried atoms, clusters on surfaces or at interfaces, ultrathin films, nanoparticles and nanostructures, three experimental conditions must be present to perform state-of-the-art XMCD measurements: high magnetic fields, low temperatures and an ultra-high-vacuum environment. This paper describes a new apparatus that can be easily installed at different X-ray and UV beamlines at the Brazilian Synchrotron Light Laboratory (LNLS). The apparatus combines the three characteristics described above and different methods to measure the absorption signal. It also permits in situ sample preparation and transfer to another chamber for measurement by conventional surface science techniques such as low-energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD). Examples are given of XMCD measurements performed with this set-up on different materials.163346351FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP [2007/08244-5]2007/08244-5Sem informaçãoThe authors would like to thank the LNLS staff, particularly the magnets, project and vacuum groups for their help during the construction of the XMCD UHV chamber. P. T. Fonseca and Dr F. Vicentin are acknowledged for their excellent technical support at the SGM and SXS beamlines. Furthermore, the authors would like to thank Dr A. Gobbi and M. M. Soares for their help in the preparation of the multilayer samples. JJSF would like to thank FAPESP for the studentship support. This project was supported financially by FAPESP (grant No. 2007/08244-5), CNPq and LNLS of Brazil

Electronic and structural study of Pt-modified Au vicinal surfaces: a model system for Pt–Au catalysts

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOTwo single crystalline surfaces of Au vicinal to the (111) plane were modified with Pt and studied using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in ultra-high vacuum environment. The vicinal surfaces studied are Au(332) and Au(887) and different Pt coverage (θPt) were deposited on each surface. From STM images we determine that Pt deposits on both surfaces as nanoislands with heights ranging from 1 ML to 3 ML depending on θPt. On both surfaces the early growth of Pt ad-islands occurs at the lower part of the step edge, with Pt ad-atoms being incorporated into the steps in some cases. XPS results indicate that partial alloying of Pt occurs at the interface at room temperature and at all coverage, as suggested by the negative chemical shift of Pt 4f core line, indicating an upward shift of the d-band center of the alloyed Pt. Also, the existence of a segregated Pt phase especially at higher coverage is detected by XPS. Sample annealing indicates that the temperature rise promotes a further incorporation of Pt atoms into the Au substrate as supported by STM and XPS results. Additionally, the catalytic activity of different PtAu systems reported in the literature for some electrochemical reactions is discussed considering our findings. © 2014 The Owner Societies.Two single crystalline surfaces of Au vicinal to the (111) plane were modified with Pt and studied using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in ultra-high vacuum environment. The vicinal surfaces studied are Au(332) and Au(887) and different Pt coverage (yPt) were deposited on each surface. From STM images we determine that Pt deposits on both surfaces as nanoislands with heights ranging from 1 ML to 3 ML depending on yPt. On both surfaces the early growth of Pt ad-islands occurs at the lower part of the step edge, with Pt ad-atoms being incorporated into the steps in some cases. XPS results indicate that partial alloying of Pt occurs at the interface at room temperature and at all coverage, as suggested by the negative chemical shift of Pt 4f core line, indicating an upward shift of the d-band center of the alloyed Pt. Also, the existence of a segregated Pt phase especially at higher coverage is detected by XPS. Sample annealing indicates that the temperature rise promotes a further incorporation of Pt atoms into the Au substrate as supported by STM and XPS results. Additionally, the catalytic activity of different PtAu systems reported in the literature for some electrochemical reactions is discussed considering our findings.Two single crystalline surfaces of Au vicinal to the (111) plane were modified with Pt and studied using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in ultra-high vacuum environment. The vicinal surfaces studied are Au(332) and Au(887) and different Pt coverage (yPt) were deposited on each surface. From STM images we determine that Pt deposits on both surfaces as nanoislands with heights ranging from 1 ML to 3 ML depending on yPt. On both surfaces the early growth of Pt ad-islands occurs at the lower part of the step edge, with Pt ad-atoms being incorporated into the steps in some cases. XPS results indicate that partial alloying of Pt occurs at the interface at room temperature and at all coverage, as suggested by the negative chemical shift of Pt 4f core line, indicating an upward shift of the d-band center of the alloyed Pt. Also, the existence of a segregated Pt phase especially at higher coverage is detected by XPS. Sample annealing indicates that the temperature rise promotes a further incorporation of Pt atoms into the Au substrate as supported by STM and XPS results. Additionally, the catalytic activity of different PtAu systems reported in the literature for some electrochemical reactions is discussed considering our findings.16261332913339FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO07/54829-5; 2011/12.566-3; 2012/16860-6160172/2011-0Greeley, J., Stephens, I.E.L., Bondarenko, A.S., Johansson, T.P., Hansen, H.A., Jaramillo, T.F., Rossmeisl, J., Nørskov, J.K., (2009) Nat. Chem., 1, pp. 552-556Wu, G., More, K.L., Johnston, C.M., Zelenay, P., (2011) Science, 332, pp. 443-447Chu, Y.H., Shul, Y.G., (2010) Int. J. Hydrogen Energy, 35, pp. 11261-11270Kowal, A., Li, M., Shao, M., Sasaki, K., Vukmirovic, M.B., Zhang, J., Marinkovic, N.S., Adzic, R.R., (2009) Nat. Mater., 8, pp. 325-330Xu, C.W., Su, Y.Z., Tan, L.L., Liu, Z.L., Zhang, J.H., Chen, S.A., Jiang, S.P., (2009) Electrochim. Acta, 54, pp. 6322-6326Colmati, F., Antolini, E., Gonzalez, E.R., (2008) J. Alloys Compd., 456, pp. 264-270Antolini, E., (2007) J. Power Sources, 170, pp. 1-12Colmati, F., Antolini, E., Gonzalez, E.R., (2006) J. Power Sources, 157, pp. 98-103Stamenkovic, V.R., Mun, B.S., Mayrhofer, K.J.J., Ross, P.N., Markovic, N.M., (2006) J. Am. Chem. Soc., 128, pp. 8813-8819Freund, H.-J., Pacchioni, G., (2008) Chem. Soc. Rev., 37, pp. 2224-2242Kim, Y., Kim, H.J., Kim, Y.S., Choi, S.M., Seo, M.H., Kim, W.B., (2012) J. Phys. Chem. C, 116, pp. 18093-18100Kwon, Y., Birdja, Y., Spanos, I., Rodriguez, P., Koper, M.T.M., (2012) ACS Catal., 2, pp. 759-764Freitas, R.G., Pereira, E.C., (2010) Electrochim. Acta, 55, pp. 7622-7627Colmati, F., Tremiliosi, G., Gonzalez, E.R., Berna, A., Herrero, E., Feliu, J.M., (2009) Phys. Chem. Chem. 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Chem., 607, pp. 47-53Kobiela, T., Moors, M., Linhart, W., Cebula, I., Krupski, A., Becker, C., Wandelt, K., (2010) Thin Solid Films, 518, pp. 3650-3657Petkov, V., Wanjala, B.N., Loukrakpam, R., Luo, J., Yang, L., Zhong, C.-J., Shastri, S., (2012) Nano Lett., 12, pp. 4289-4299Authors thank Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP-07/54829-5) and Conselho Nacional de Pesquisa (CNPq) for financial support. Specially thank to L. H. Lima for experimental assistance with STM measurements and Prof. G. Tremiliosi-Filho for lending the Au(332) crystal. MJP, SF and EAC thank FAPESP and CNPq for the fellowships granted (Procs. FAPESP 2011/12.566-3 and 2012/16860-6; Proc. CNPq 160172/2011-0)

Self-assembly Of Nitpp On Cu(111): A Transition From Disordered 1d Wires To 2d Chiral Domains.

The growth and self-assembling properties of nickel-tetraphenyl porphyrins (NiTPP) on the Cu(111) surface are analysed via scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). For low coverage, STM results show that NiTPP molecules diffuse on the terrace until they reach the step edge of the copper surface forming a 1D system with disordered orientation along the step edges. The nucleation process into a 2D superstructure was observed to occur via the interaction of molecules attached to the already nucleated 1D structure, reorienting molecules. For monolayer range coverage a 2D nearly squared self-assembled array with the emergence of chiral domains was observed. The XPS results of the Ni 2p(3/2) core levels exhibit a 2.6 eV chemical shift between the mono- and multilayer configuration of NiTPP. DFT calculations show that the observed chemical shifts of Ni 2p(3/2) occur due to the interaction of 3d orbitals of Ni with the Cu(111) substrate.1718344-1835

Magnetic moment of Fe3O4 films with thicknesses near the unit-cell size

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORWe perform a systematic study on the evolution of the magnetic spin moment (ms) of epitaxial [100]- and [111]-magnetite films of increasing thickness. The ultrathin films are characterized by low-energy electron diffraction, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). By employing sum rules on the XMCD spectra we obtain ms=3.6 μB/f.u. for samples of around 35 Å. This is considered a bulk value and has been reported only for films more than 10 times thicker. Moreover, we show that even 10-Å-thick magnetite already presents a significant magnetic moment. For both grown directions the moment increases similarly with the thickness. The ferromagnetic behavior for each iron ion site (Feocta2+, Feocta3+, Fetetra3+) of Fe3O4 is measured by monitoring XMCD peaks. The deduced hysteresis curves (per ion, per site) exhibit a coercive field of 300 Oe. Our results show that both the ferrimagnetic order and the bulk moment value are preserved at room temperature around the thickness of 2 unit cells.We perform a systematic study on the evolution of the magnetic spin moment (ms) of epitaxial [100]- and [111]-magnetite films of increasing thickness. The ultrathin films are characterized by low-energy electron diffraction, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). By employing sum rules on the XMCD spectra we obtain ms=3.6 μB/f.u. for samples of around 35 Å. This is considered a bulk value and has been reported only for films more than 10 times thicker. Moreover, we show that even 10-Å-thick magnetite already presents a significant magnetic moment. For both grown directions the moment increases similarly with the thickness. The ferromagnetic behavior for each iron ion site (Feocta2+, Feocta3+, Fetetra3+) of Fe3O4 is measured by monitoring XMCD peaks. The deduced hysteresis curves (per ion, per site) exhibit a coercive field of 300 Oe. Our results show that both the ferrimagnetic order and the bulk moment value are preserved at room temperature around the thickness of 2 unit cells.We perform a systematic study on the evolution of the magnetic spin moment (ms) of epitaxial [100]- and [111]-magnetite films of increasing thickness. The ultrathin films are characterized by low-energy electron diffraction, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). By employing sum rules on the XMCD spectra we obtain ms=3.6 μB/f.u. for samples of around 35 Å. This is considered a bulk value and has been reported only for films more than 10 times thicker. Moreover, we show that even 10-Å-thick magnetite already presents a significant magnetic moment. For both grown directions the moment increases similarly with the thickness. The ferromagnetic behavior for each iron ion site (Feocta2+, Feocta3+, Fetetra3+) of Fe3O4 is measured by monitoring XMCD peaks. The deduced hysteresis curves (per ion, per site) exhibit a coercive field of 300 Oe. Our results show that both the ferrimagnetic order and the bulk moment value are preserved at room temperature around the thickness of 2 unit cells.901316CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORSem informaçãoSem informaçãoSem informaçãoSem informaçãoOrna, J., Algarabel, P.A., Morellón, L., Pardo, J.A., De Teresa, J.M., López Antón, R., Bartolomé, F., Wildes, A., (2010) Phys. Rev. B, 81, p. 144420. , PRBMDO 1098-0121Hari Babu, V., Govind, R.K., Schindler, K.-M., Welke, M., Denecke, R., (2013) J. Appl. Phys., 114, p. 113901. , JAPIAU 0021-8979Moussy, J.-B., Gota, S., Bataille, A., Guittet, M.-J., Gautier-Soyer, M., Delille, F., Dieny, B., Snoeck, E., (2004) Phys. Rev. B, 70, p. 174448. , PRBMDO 1098-0121Morrall, P., Schedin, F., Langridge, S., Bland, J., Thomas, M.F., Thornton, G., (2003) J. Appl. Phys., 93, p. 7960. , JAPIAU 0021-8979Liu, W.Q., Xu, Y.B., Wong, P.K.J., Maltby, N.J., Li, S.P., Wang, X.F., Du, J., Zhang, R., (2014) Appl. Phys. Lett., 104, p. 142407. , APPLAB 0003-6951Lu, Y.X., Claydon, J.S., Xu, Y.B., Schofield, D.M., Thompson, S.M., (2004) J. Appl. Phys., 95, p. 7228. , JAPIAU 0021-8979Eerenstein, W., Hibma, T., Celotto, S., (2004) Phys. Rev. B, 70, p. 184404. , PRBMDO 1098-0121Voogt, F.C., Palstra, T.T.M., Niesen, L., Rogojanu, O.C., James, M.A., Hibma, T., (1998) Phys. Rev. B, 57, p. R8107. , PRBMDO 0163-1829Monti, M., Santos, B., Mascaraque, A., Rodríguez De La Fuente, O., Niño, M.A., Mentes, T.O., Locatelli, A., De La Figuera, J., (2012) Phys. Rev. B, 85, p. 020404. , PRBMDO 1098-0121Lu, Y.X., Claydon, J.S., Xu, Y.B., Thompson, S.M., Wilson, K., Van Der Laan, G., (2004) Phys. Rev. B, 70, p. 233304. , PRBMDO 1098-0121Lu, Y.X., Claydon, J.S., Ahmad, E., Xu, Y.B., Ali, M., Hickey, B.J., Thompson, S.M., Wilson, K., (2005) J. Appl. Phys., 97, p. 10C313Schedin, F., Hewitt, L., Morrall, P., Petrov, V.N., Thornton, G., Case, S., Thomas, M.F., Uzdin, V.M., (1998) Phys. Rev. B, 58, p. R11861. , PRBMDO 0163-1829Wong, P.K.J., Zhang, W., Cui, X.G., Xu, Y.B., Wu, J., Tao, Z.K., Li, X., Van Der Laan, G., (2010) Phys. Rev. B, 81, p. 035419. , PRBMDO 1098-0121Goering, E., Gold, S., Lafkioti, M., Schütz, G., (2006) Europhys. Lett., 73, p. 97. , EULEEJ 0295-5075Chen, C.T., Idzerda, Y.U., Lin, H.-J., Smith, N.V., Meigs, G., Chaban, E., Ho, G.H., Sette, F., (1995) Phys. Rev. Lett., 75, p. 152. , PRLTAO 0031-9007Goering, E.J., Lafkioti, M., Gold, S., Schuetz, G., (2007) J. Magn. Magn. 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Sci., 371, p. 245. , SUSCAS 0039-6028Ritter, M., Ranke, W., Weiss, W., (1998) Phys. Rev. B, 57, p. 7240. , PRBMDO 0163-1829Weiss, W., Ritter, M., (1999) Phys. Rev. B, 59, p. 5201. , PRBMDO 0163-1829The authors thank CNPq, FAPEMIG, FAPESP, and CAPES, Brazilian research agencies, for financial support and the Laboratorio Nacional de Luz Sincrotron for beam time (SGM-10986 and SGM-12716)

Epitaxial growth of ultrathin palladium films on Re{0001}

Ultrathin bimetallic layers create unusual magnetic and surface chemical effects through the modification of electronic structure brought on by low dimensionality, polymorphism, reduced screening, and epitaxial strain. Previous studies have related valence and core-level shifts to surface reactivity through the d-band model of Hammer and Nørskov, and in heteroepitaxial films this band position is determined by competing effects of coordination, strain, and hybridization of substrate and overlayer states. In this study we employ the epitaxially matched Pd on Re{0001} system to grow films with no lateral strain. We use a recent advancement in low-energy electron diffraction to expand the data range sufficiently for a reliable determination of the growth sequence and out-of-plane surface relaxation as a function of film thickness. The results are supported by scanning tunneling microscopy and X-ray photoemission spectroscopy, which show that the growth is layer-by-layer with significant core-level shifts due to changes in film structure, morphology, and bonding

Moderate energy restriction with high protein diet results in healthier outcome in women

BACKGROUND: The present study compares two different weight reduction regimens both with a moderately high protein intake on body composition, serum hormone concentration and strength performance in non-competitive female athletes. METHODS: Fifteen normal weighted women involved in recreational resistance training and aerobic training were recruited for the study (age 28.5 ± 6.3 yr, height 167.0 ± 7.0 cm, body mass 66.3 ± 4.2 kg, body mass index 23.8 ± 1.8, mean ± SD). They were randomized into two groups. The 1 KG group (n = 8; energy deficit 1100 kcal/day) was supervised to reduce body weight by 1 kg per week and the 0.5 KG group (n = 7; energy deficit 550 kcal/day) by 0.5 kg per week, respectively. In both groups protein intake was kept at least 1.4 g/kg body weight/day and the weight reduction lasted four weeks. At the beginning of the study the energy need was calculated using food and training diaries. The same measurements were done before and after the 4-week weight reduction period including total body composition (DXA), serum hormone concentrations, jumping ability and strength measurements RESULTS: During the 4-week weight reduction period there were no changes in lean body mass and bone mass, but total body mass, fat mass and fat percentage decreased significantly in both groups. The changes were greater in the 1 KG group than in the 0.5 KG group in total body mass (p < 0.001), fat mass (p < 0.001) and fat percentage (p < 0.01). Serum testosterone concentration decreased significantly from 1.8 ± 1.0 to 1.4 ± 0.9 nmol/l (p < 0.01) in 1 KG and the change was greater in 1 KG (30%, p < 0.001) than in 0.5 KG (3%). On the other hand, SHBG increased significantly in 1 KG from 63.4 ± 17.7 to 82.4 ± 33.0 nmol/l (p < 0.05) during the weight reducing regimen. After the 4-week period there were no changes in strength performance in 0.5 KG group, however in 1 KG maximal strength in bench press decreased (p < 0.05) while endurance strength in squat and counter movement jump improved (p < 0.05) CONCLUSION: It is concluded that a weight reduction by 0.5 kg per week with ~1.4 g protein/kg body weight/day can be recommended to normal weighted, physically active women instead of a larger (e.g. 1 kg per week) weight reduction because the latter may lead to a catabolic state. Vertical jumping performance is improved when fat mass and body weight decrease. Thus a moderate weight reduction prior to a major event could be considered beneficial for normal built athletes in jumping events.peerReviewe

Validity of Resting Energy Expenditure Predictive Equations before and after an Energy-Restricted Diet Intervention in Obese Women

Background We investigated the validity of REE predictive equations before and after 12-week energy-restricted diet intervention in Spanish obese (30 kg/m2>BMI<40 kg/m2) women. Methods We measured REE (indirect calorimetry), body weight, height, and fat mass (FM) and fat free mass (FFM, dual X-ray absorptiometry) in 86 obese Caucasian premenopausal women aged 36.7±7.2 y, before and after (n = 78 women) the intervention. We investigated the accuracy of ten REE predictive equations using weight, height, age, FFM and FM. Results At baseline, the most accurate equation was the Mifflin et al. (Am J Clin Nutr 1990; 51: 241–247) when using weight (bias:−0.2%, P = 0.982), 74% of accurate predictions. This level of accuracy was not reached after the diet intervention (24% accurate prediction). After the intervention, the lowest bias was found with the Owen et al. (Am J Clin Nutr 1986; 44: 1–19) equation when using weight (bias:−1.7%, P = 0.044), 81% accurate prediction, yet it provided 53% accurate predictions at baseline. Conclusions There is a wide variation in the accuracy of REE predictive equations before and after weight loss in non-morbid obese women. The results acquire especial relevance in the context of the challenging weight regain phenomenon for the overweight/obese population.The present study was supported by the University of the Basque Country (UPV 05/80), Social Foundation of the Caja Vital- Kutxa and by the Department of Health of the Government of the Basque Country (2008/111062), and by the Spanish Ministry of Science and Innovation (RYC-2010-05957)

‘‘Beet-ing’’ the Mountain: A Review of the Physiological and Performance Effects of Dietary Nitrate Supplementation at Simulated and Terrestrial Altitude

Exposure to altitude results in multiple physiological consequences. These include, but are not limited to, a reduced maximal oxygen consumption, drop in arterial oxygen saturation, and increase in muscle metabolic perturbations at a fixed sub-maximal work rate. Exercise capacity during fixed work rate or incremental exercise and time-trial performance are also impaired at altitude relative to sea-level. Recently, dietary nitrate (NO3-) supplementation has attracted considerable interest as a nutritional aid during altitude exposure. In this review, we summarise and critically evaluate the physiological and performance effects of dietary NO3- supplementation during exposure to simulated and terrestrial altitude. Previous investigations at simulated altitude indicate that NO3- supplementation may reduce the oxygen cost of exercise, elevate arterial and tissue oxygen saturation, improve muscle metabolic function, and enhance exercise capacity/ performance. Conversely, current evidence suggests that NO3- supplementation does not augment the training response at simulated altitude. Few studies have evaluated the effects of NO3- at terrestrial altitude. Current evidence indicates potential improvements in endothelial function at terrestrial altitude following NO3- supplementation. No effects of NO3- supplementation have been observed on oxygen consumption or arterial oxygen saturation at terrestrial altitude, although further research is warranted. Limitations of the present body of literature are discussed, and directions for future research are provided