Alexander X. Gray, Copyright, 2018

Funding by:

Journal Articles and Book Chapters
(in reverse chronological order)

57.

Depth-resolved charge reconstruction at the LaNiO3/CaMnO3 interface,
R. U. Chandrasena, C. L. Flint, W. Yang, A. Arab, S. Nemšák, M. Gehlmann, V. B. Özdöl, F. Bisti, K. D. Wijesekara, J. Meyer-Ilse, E. Gullikson, E. Arenholz, J. Ciston, C. M. Schneider, V. N. Strocov, Y. Suzuki, and A. X. Gray, Phys. Rev. B 98, 155103 (2018). [PDF]

56.

The core-shell engineering of energy product of magnetic nanometals,
W. Zhang, W. Yang, R. U. Chandrasena, B. Ozdol, J. Ciston, M. Kornecki, S. V. Raju, R. Brennan,
A. X. Gray, and S. Ren, Chem. Commun. 54, 11005 (2018). [PDF]

55.

Review Combining Hard and Soft X-ray Photoemission with Standing-Wave Excitation, Resonant Excitation, and Angular Resolution,

A. X. Gray, S. Nemsak, and C. S. Fadley, Synchrotron Rad. News 31, 42 (2018). [PDF]

54.

Ultrafast Terahertz Field Control of Electronic and Structural Interactions in Vanadium Dioxide,

A. X. Gray, M. C. Hoffmann, J. Jeong, N. P. Aetukuri, D. Zhu, H. Y. Hwang, N. C. Brandt, H. Wen, A. J. Sternbach, S. Bonetti, A. H. Reid, R. Kukreja, C. Graves, T. Wang, P. Granitzka, Z. Chen, D. J. Higley, T. Chase, E. Jal, E. Abreu, M. K. Liu, T.-C. Weng, D. Sokaras, D. Nordlund, M. Chollet, H. Lemke, J. Glownia, M. Trigo, Y. Zhu, H. Ohldag, J. W. Freeland, M. G. Samant, J. Berakdar, R. D. Averitt, K. A. Nelson, S. S. P. Parkin, H. A. Dürr, Phys. Rev. B 98, 045104 (2018). [PDF] Editor’s Suggestion

53.

Nature of the Metal-Insulator Transition in Few-Unit-Cells-Thick LaNiO3 Films,

M. Golalikhani, Q. Lei, R. U. Chandrasena, L. Kasaei, H. Park, J. Bai, P. Orgiani, J. Ciston, G. E. Sterbinsky, D. A. Arena, P. Shafer, E. Arenholz, B. Davidson, A. J. Millis, A. X. Gray, and X. X. Xi, Nature Comm. 9, 2206 (2018). [PDF] Editors' Highlight

52.

Electronic Structure of the Dilute Magnetic Semiconductor Ga(1−x)Mn(x)P from Hard X-ray Photoelectron Spectroscopy and Hard X-ray Angle-Resolved Photoemission,
A. Keqi, M. Gehlmann, G. Conti, S. Nemsak, A. Rattanachata, J. Minar, L. Plucinski, J. E. Rault, J.-P. Rueff, M. Scarpulla, M. Hategan, G. K. Palsson, C. Conlon, D. Eiteneer, A. Y. Saw,
A. X. Gray, K. Kobayashi, S. Ueda, O. D. Dubon, C. M. Schneider, and C. S. Fadley, Phys. Rev. B. 97, 155149 (2018). [PDF]

51.

Book Standing-Wave and Resonant Soft- and Hard- X-Ray Photoelectron Spectroscopy of Oxide Interfaces,
S. Nemsak,
A. X. Gray, and C. S. Fadley, invited chapter for the book Spectroscopy of Transition-Metal Oxide Interfaces, C. Cancellieri and V. N. Strocov, Eds. (Springer, 2018) [Official Site]

50.

The electronic structure of negative charge transfer CaFeO3 across the metal-insulator transition,
P. C. Rogge, R. U. Chandrasena, A. Cammarata, R. J. Green, P. Shafer, B. M. Lefler, A. Huon, A. Arab, E. Arenholz, H. N. Lee, T.-L. Lee, S. Nemsak, J. M. Rondinelli,
A. X. Gray, and S. J. May, Phys. Rev. Mater. 2, 015002 (2018). [PDF]

49.

Magnetic Switching in Granular FePt Layers Promoted by Near-Field Laser Enhancement,

P. W. Granitzka, E. Jal, L. Le Guyader, M. Savoini, D. J. Higley, T. Liu, Z. Chen, T. Chase, H. Ohldag, G. L. Dakovski, W. F. Schlotter, S. Carron, M. C. Hoffman, A. X. Gray, P. Shafer, E. Arenholz, O. Hellwig, V. Mehta, Y. K. Takahashi, J. Wang, E. E. Fullerton, J. Stohr, A. H. Reid, and H. A. Dürr, Nano Letters 17, 2426 (2017). [PDF]

48.

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy,
Q. Lei, M. Golalikhani, B. A. Davidson, G. Liu, D. G. Schlom, Qiao Qiao, Y. Zhu, R. U. Chandrasena, W. Yang,
A. X. Gray, E. Arenholz, A. K. Farrar, D. A. Tenne, M. Hu, J. Guo, R. K. Singh, X. X. Xi, npj Quantum Materials 2, 10 (2017). [PDF]

47.

Strain-Engineered Oxygen Vacancies in CaMnO3 Thin Films,
R. U. Chandrasena, W. Yang, Q. Y. Lei, M. U. Delgado-Jaime, K. Wijesekara, M. Golalikhani, B. A. Davidson, E. Arenholz, K. Kobayashi, M. Kobata, F. M. F. de Groot, U. Aschauer, N. A. Spaldin, X. X. Xi, and
A. X. Gray, Nano Letters 17, 794 (2017). [PDF]

46.

Inter-Layer Coupling Induced Valence Band Edge Shift in Mono-to-Few Layer MoS2,
D. J. Trainer, A. V. Putilov, C. Di Giorgio, T. Saari, B. Wang, M. Wolak, R. U. Chandrasena, C. Lane, T.-R. Chang, H.-T. Jeng, H. Lin, F. Kronast,
A. X. Gray, X. X. Xi, J. Nieminen, A. Bansil, and M. Iavarone, Scientific Reports 7, 40559 (2017). [PDF]

45.

Effects of Spin Excitons on the Surface States of SmB6: a Photoemission Study,
A. Arab,
A. X. Gray, S. Nemsak, D. V. Evtushinsky, C. M. Schneider, D.-J. Kim, Z. Fisk, P. F. S. Rosa, T. Durakiewicz, and P. S. Riseborough, Phys. Rev B 94, 235125 (2016). [PDF]

44.

Measurement of Collective Excitations in VO2 by Resonant Inelastic X-ray Scattering,

Haowei He, A. X. Gray, P. Granitzka, J. W. Jeong, N. P. Aetukuri, R. Kukreja, Lin Miao, Y. B. Huang, P. Olalde-Velasco, J. Pelliciari, W. F. Schlotter, E. Arenholz, T. Schmitt, M. G. Samant, S. S. P. Parkin, H. A. Dürr, L. Andrew Wray, Phys. Rev. B 94, 161119(R) (2016). [PDF]

43.

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures,
B. A. Gray, S. Middey, G. Conti,
A. X. Gray, C.-T. Kuo, A. M. Kaiser, S. Ueda, K. Kobayashi, D. Meyers, M. Kareev, I. C. Tung, Jian Liu, C. S. Fadley, J. Chakhalian, and J. W. Freeland, Scientific Reports 6, 33184 (2016). [PDF]

42.

Depth-Resolved Composition and Electronic Structure of Buried Layers and Interfaces in a LaNiO3/SrTiO3 Superlattice from Soft- and Hard- X-ray Standing-Wave Angle-Resolved Photoemission,

D. Eiteneer, G. K. Palsson, S. Nemsak, A. X. Gray, A. M. Kaiser, J. Son, J. LeBeau, G. Conti, A. A. Greer, A. Keqi, A. Rattanachata, A. Y. Saw, A. Bostwick, E. Rotenberg, E. M. Gullikson, S. Ueda, K. Kobayashi, A. Janotti, C. G. Van de Walle, A. Blanca-Romero, R. Pentcheva, C. M. Schneider, S. Stemmer, and C. S. Fadley, J. Electron Spectrosc. Rel. Phenom. 211, 70 (2016). [PDF]

41.

Generation mechanism of terahertz coherent acoustic phonons in Fe,
T. Henighan, M. Trigo, S. Bonetti, P. Granitzka, D. Higley, Z. Chen, M. P. Jiang, R. Kukreja,
A. X. Gray, A. H. Reid, E. Jal, M. C. Hoffmann, M. Kozina, S. Song, M. Chollet, D. Zhu, P. F. Xu, J. Jeong, K. Carva, P. Maldonado, P. M. Oppeneer, M. G. Samant, S. S. P. Parkin, D. A. Reis, H. A. Dürr, Phys. Rev. B 93, 220301(R) (2016). [PDF]

40.

Energetic, spatial and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides,

S. Nemsak, G. Conti, A. X. Gray, G. K. Palsson, C. Conlon, D. Eiteneer, A. Keqi, A. Rattanachata, A. Y. Saw,  A. Bostwick, L. Moreschini, V. Strocov, M. Kobayashi, W. Stolte, A. Gloskovskii, W. Drube, C. Jackson, P. Moetakef, A. Janotti, L. Bjaalie, B. Himmetoglu, C. G. Van de Walle, J. Minar, J. Braun, H. Ebert, L. Plucinski, J. B. Kortright, C. M. Schneider, L. Balents, S. Stemmer, and C. S. Fadley, Phys. Rev. B 93, 245103 (2016). [PDF]

39.

Correlation-Driven Insulator-Metal Transition in Near-Ideal Vanadium Dioxide Films,
A. X. Gray, J. Jeong, N. P. Aetukuri, P. Granitzka, Z. Chen, R. Kukreja, D. Higley, T. Chase, A. H. Reid, H. Ohldag, M. A. Marcus, A. Scholl, A. T. Young, A. Doran, C. A. Jenkins, P. Shafer, E. Arenholz, M. G. Samant, S. S. P. Parkin, H. A. Dürr, Phys. Rev. Lett. 116, 116403 (2016). [PDF]

38.

Book Hard X-ray Angle-Resolved Photoelectron Spectroscopy (HARPES),
A. X. Gray, invited chapter in the book HAXPES, J. Woicik, Ed. (Springer, 2016). [Official Site]

37.

Interface Fe magnetic moment enhancement in MgO/Fe/MgO trilayers,
E. Jal, J. B. Kortright, T. Chase, T. M. Liu,
A. X. Gray, P. Shafer, E. Arenholz, P. Xu, J. Jeong, M. G. Samant, S. S. P. Parkin, and H. A. Dürr, Appl. Phys. Lett. 107, 092404 (2015). [PDF]

36.

Incomplete Protection of the Surface Weyl Cones of the Kondo Insulator SmB6: Spin Exciton Scattering,

G. A. Kapilevich, P. S. Riseborough, A. X. Gray, M. Gulacsi, T. Durakiewicz, and J. L. Smith, Phys. Rev. B 92, 085133 (2015). [PDF]

35.

Self Referencing Heterodyne Transient Grating Spectroscopy with Short Wavelength,

E. Sistrunk, J. Grilj, J. Jeong, M. G. Samant, A. X. Gray, H. A. Dürr, S. S. P. Parkin, M. Gühr, Photonics 2, 3092 (2015). [PDF]

34.

Broadband Extreme Ultraviolet Probing of Transient Gratings in Vanadium Dioxide,

E. Sistrunk, J. Grilj, J. Jeong, M. G. Samant, A. X. Gray, H. A. Dürr, S. S. P. Parkin, M. Gühr, Optics Express 23, 4340 (2015). [PDF]

33.

Extreme Ultraviolet Transient Grating Measurement of Insulator-Metal Transition Dynamics in VO2,

E. Sistrunk, J. Grilj, J. Jeong, M. G. Samant, A. X. Gray, H. A. Dürr, S. S. P. Parkin, and M. Gühr, Ultrafast Phenomena XIX, Springer Proc. in Phys. 162, 64 (2015). [PDF]

32.

Review Future Directions in Standing-Wave Photoemission,

A. X. Gray, invited review article for a special issue of Journal of Electron Spectroscopy and Related Phenomena entitled Structure Determination and Wave function Analysis, J. Electron Spectrosc. Relat. Phenom. 195, 399 (2014). [PDF]

31.

Progress Toward Time-Resolved Molecular Imaging: a Theoretical Study of Optimal Parameters in Static Photoelectron Holography,
S. X-L. Sun, A. P. Kaduwela,
A. X. Gray, and C. S. Fadley, Phys. Rev. A 89, 053415 (2014). [PDF]

30.

Momentum-Resolved Electronic Structure at a Buried Interface from Soft X-ray Standing-Wave Angle-Resolved Photoemission,
A. X. Gray, J. Minar, L. Plucinski, M. Huijben, A. Bostwick, E. Rotenberg, S.-H. Yang, J. Braun, A. Winkelmann, G. Conti, D. Eiteneer, A. Rattanachata, A. A. Greer, J. Ciston, C. Ophus, G. Rijnders, D. H. A. Blank, D. Doennig, R. Pentcheva, C. M. Schneider, H. Ebert, and C. S. Fadley, Europhys. Lett. 104, 17004 (2013). [PDF]

29.

Control of the Metal-Insulator Transition in Vanadium Dioxide by Modifying Orbital Occupancy,
N. B. Aetukuri,
A. X. Gray, M. Drouard, M. Cossale, L. Gao, A. H. Reid, R. Kukreja, H. Ohldag, C. A. Jenkins, E. Arenholz, H. A. Durr, M. Samant, S. S. P. Parkin, Nature Physics 9, 661 (2013). [PDF] [News and Views]

28.

Identifying the Role and the Electronic Character of the Mn-derived States in the Valence Band of (Ga,Mn)As,
J. Fujii, B. R. Salles, M. Sperl, S. Ueda, K. Kobayashi, Y. Yamashita, M. Kobata, P. Torelli, M. Utz, C.S. Fadley,
A. X. Gray, J. Minar, J. Braun, H. Ebert, I. Di Marco, O. Eriksson, P. Thunstrom, C. H. Back, G. van der Laan, and G. Panaccione, Phys. Rev. Lett. 111, 097201 (2013). [PDF]

27.

Band Offsets in Complex-Oxide Thin Films and Heterostructures of SrTiO3/LaNiO3 and SrTiO3/GdTiO3 by Soft and Hard X-ray Photoelectron Spectroscopy,
G. Conti, A. M. Kaiser, A. X. Gray, S. Nemsak, G. K. Palsson, J. Son, P. Moetakef, A. Janotti, L. Bjaalie, C. S. Conlon, D. Eiteneer, A. A. Greer, A. Perona, A. Rattanachata, A. Y. Saw, A. Bostwick, W. Stolte, A. Hloskovsky, W. Drube, S. Ueda, K. Kobayashi, C. G. Van de Walle, S. Stemmer, C. M. Schneider, and C. S. Fadley, J. Appl. Phys. 113, 143704 (2013). [PDF]

26.

Making Use of X-ray Optical Effects in Photoelectron-, Auger Electron-, and X-ray Emission Spectroscopies: Total Reflection, Standing-Wave Excitation and Resonant Effects,
S.-H. Yang,
A. X. Gray, A. M. Kaiser, B. S. Mun, B. C. Sell, J. B. Kortright, and C. S. Fadley, J. Appl. Phys. 113, 073513 (2013). [PDF]

25.

Observation of Boron Diffusion in an Annealed Ta/CoFeB/MgO Magnetic Tunnel Junction with Standing-Wave Hard X-ray Photoemission,
A. A. Greer,
A. X. Gray, S. Kanai, A. M. Kaiser, S. Ueda, Y. Yamashita, C. Bordel, G. Palsson, N. Maejima, S.-H. Yang, G. Conti, K. Kobayashi, S. Ikeda, F. Matsukura, H. Ohno, C. M. Schneider, J. B. Kortright, F. Hellman, and C. S. Fadley, Appl. Phys. Lett. 101, 202402 (2012). [PDF]

24.

Bulk Electronic Structure of the Dilute Ferromagnetic Semiconductor Ga(1-x)Mn(x)As through Hard X-ray Angle-Resolved Photoemission,
A. X. Gray, J. Minar, S. Ueda, P. R. Stone, Y. Yamashita, J. Fujii, J. Braun, L. Plucinski, C. M. Schneider, G. Panaccione, H. Ebert, O. D. Dubon, K. Kobayashi, and C. S. Fadley, Nature Materials 11, 957 (2012). [PDF]

23.

Electronic structure of delta-doped La:SrTiO3 layers by hard x-ray photoelectron spectroscopy,
A. M. Kaiser,
A. X. Gray, G. Conti, B. Jalan, A. P. Kajdos, A. Gloskovskii, S. Ueda, Y. Yamashita, K. Kobayashi, W. Drube, S. Stemmer, and C. S. Fadley, Appl. Phys. Lett. 100, 261603 (2012). [PDF]

22.

Temperature-Driven Nucleation of Ferromagnetic Domains in FeRh Thin Films,
C. Baldasseroni, C. Bordel,
A. X. Gray, A. M. Kaiser, F. Kronast, J. Herrero-Albillos, C. M. Schneider, C. S. Fadley, F. Hellman, Appl. Phys. Lett. 100, 262401 (2012). [PDF]

21.

Electronic Structure Changes across the Metamagnetic Transition in FeRh via Hard X-ray Photoemission,

A. X. Gray, D. W. Cooke, P. Kruger, C. Bordel, A. M. Kaiser, S. Moyerman, E. E. Fullerton, S. Ueda, Y. Yamashita, A. Gloskovskii, C. M. Schneider, W. Drube, K. Kobayashi, F. Hellman, and C. S. Fadley, Phys. Rev. Lett. 108, 257208 (2012). [PDF]

20.

Chemical Stability of the Magnetic Oxide EuO Directly on Silicon Observed by Hard X-ray Photoemission Spectroscopy,
C. Caspers, M. Muller,
A. X. Gray, A. M. Kaiser, A. Gloskovskii, C. S. Fadley, W. Drube, and C. M. Schneider, Phys. Rev. B 84, 205217 (2011). [PDF]

19.

Fabrication of Layered Nanostructures by Successive Electron Beam Induced Deposition with Two Precursors: Protective Capping of Metallic Iron Structures,
M. Schirmer, M.-M. Walz, C. Papp, F. Kronast,
A. X. Gray, B. Balke, S. Cramm, C. S. Fadley, H.-P. Steinruck, and H. Marbach, Nanotechnology 22, 475304 (2011). [PDF]

18.

Identification of Different Electron Screening Behavior between Bulk and Surface of (Ga,Mn)As,

J. Fujii, M. Sperl, S. Ueda, K. Kobayashi, Y. Yamashita, M. Kobata, P. Torelli, F. Borgatti, M. Utz, C. S. Fadley, A. X. Gray, G. Monaco, C. H. Back, G. Van der Laan, and G. Panaccione, Phys. Rev. Lett. 107, 187203 (2011). [PDF]

17.

Electronic Structure of EuO Spin Filter Tunnel Contacts Directly on Silicon,
C. Caspers, M. Muller,
A. X. Gray, A. M. Kaiser, A. Gloskovskii, C. S. Fadley, W. Drube, C. M. Schneider, Phys. Status Solidi RRL 5, 441 (2011). [PDF] [Journal Cover]

16.

Suppression of near-interface electronic states at the Fermi level of LaNiO3/SrTiO3 superlattices,

A. M. Kaiser, A. X. Gray, J. Son, G. Conti, A. Greer, A. Perona, A. Rattanachata, A. Saw, A. Bostwick, S. Stemmer, and C. S. Fadley, Phys. Rev. Lett. 107, 116402 (2011). [PDF]

15.

Probing Bulk Electronic Structure with Hard X-Ray Angle-Resolved Photoemission,
A. X. Gray, C. Papp, S. Ueda, B. Balke, Y. Yamashita, L. Plucinski, J. Minar, J. Braun, E. Ylvisaker, C. M. Schneider, W. E. Pickett, H. Ebert, K. Kobayashi, and C. S. Fadley, Nature Materials 10, 759 (2011). [PDF] [News and Views]

14.

Insulating State of Ultrathin Epitaxial LaNiO3 Thin Films Detected by Hard X-Ray Photoemission,
A. X. Gray, A. Janotti, J. Son, J. LeBeau, S. Ueda, Y. Yamashita, K. Kobayashi, A. M. Kaiser, C. G. Van de Walle, S. Stemmer, and C. S. Fadley, Phys. Rev. B 84, 075104 (2011). [PDF]

13.

Hard X-ray Photoemission Study of Near-Heusler Fe(x)Si(1-x) Alloys,
A. X. Gray, J. Karel, J. Minar, C. Bordel, J. Braun, H. Ebert, S. Ueda, Y. Yamashita, K. Kobayashi, F. Hellman, C. S. Fadley, Phys. Rev. B 83, 195112 (2011). [PDF]

12.

Interface Properties of Magnetic Tunnel Junction LSMO/STO Superlattices Studied by Standing-Wave Excited Photoemission Spectroscopy,
A. X. Gray, C. Papp, B. Balke, S.-H. Yang, M. Huijben, E. Rotenberg, A. Bostwick, S. Ueda, Y. Yamashita, K. Kobayashi, E. M. Gullikson, J. B. Kortright, F. M. F. DeGroot, G. Rijnders, D. H. A. Blank, R. Ramesh, C. S. Fadley, Phys. Rev. B 82, 205116 (2010). [PDF]

11.

Band Gap and Electronic Structure of an Epitaxial, Semiconducting Cr(0.80)Al(0.20) Thin Film,
Z. Boekelheide,
A. X. Gray, C. Papp, B. Balke, D. A. Stewart, S. Ueda, Y. Yamashita, K. Kobayashi, F. Hellman, C. S. Fadley. Phys. Rev. Lett. 105, 236404 (2010). [PDF]

10.

Standing-Wave Excited Soft X-Ray Photoemission Microscopy: Application to Co Microdot Magnetic Arrays,
A. X. Gray, F. Kronast, C. Papp, S.-H. Yang, S. Cramm, I. P. Krug, F. Salmassi, E. M. Gullikson, D. L. Hilken, E. H. Anderson, P. Fischer, H. A. Durr, C. M. Schneider, and C. S. Fadley, Appl. Phys. Lett. 97, 062503 (2010). [PDF]

9.

Optical Detection and Characterization of Graphene by Broadband Spectrophotometry,
A. Gray, M. Balooch, S. Allegret, S. De Gendt, and W. Wang, J. Appl. Phys. 104, 053109 (2008). [PDF]

8.

Phase Shift Mask Etch Process Development Utilizing a Scatterometry-Based Metrology Tool,
J. Plumhoff and
A. Gray, Proc. SPIE 7028, 702807 (2008). [PDF]

7.

Measuring Contact Hole Corner Rounding Uniformity Using Optical Scatterometry,
J. C. Lam,
A. Gray, S. Chen, and J. Richter, Proc. SPIE 6792, 679212 (2008). [PDF]

6.

Measurements of Corner Rounding in 2D Contact Holes on Phase-Shift Masks Using Broadband Reflectance and Transmittance Spectra in Conjunction with RCWA,
A. Gray, J. C. Lam, S. Chen, and J. Richter, Proc. SPIE 6730, 67303C (2007). [PDF]

5.

Polarized Transmittance-Reflectance Scatterometry Measurements of 2D Trench Dimensions on Phase-Shift Masks,
J. C. Lam,
A. Gray, R. Howell, and S. Chen, Proc. SPIE 6607, 660710 (2007). [PDF]

4.

Innovative Application of the RCWA Method for the Ultra-Sensitive Transmittance-Based CD Measurements on Phase-Shift Masks,
A. Gray, J. C. Lam, and S. Chen, Proc. SPIE 6533, 65330F (2007). [PDF]

3.

Novel Technique for Critical Dimension Measurements of Phase-Shift Masks Using Broadband Transmittance Spectra in Conjunction with RCWA,
A. Gray, J. C. Lam, and S. Chen, Proc. SPIE 6349, 634949 (2006). [PDF]

2.

Fast Non-Destructive Optical Measurements of Critical Dimension Uniformity and Linearity on AEI and ASI Phase-Shift Masks,
A. Gray and J. C. Lam, Proc. SPIE 6349, 63491O (2006). [PDF]

1.

Optical Measurements of Critical Dimensions at Several Stages of the Mask Fabrication Process,
J. C. Lam and
A. Gray, Proc. SPIE 6152, 61523C (2006). [PDF]