Article
Nanoscience & Nanotechnology
Jianwei Xiao, Chuang Deng
Summary: By introducing amorphous intergranular films into nanotwinned copper, the dominant plastic deformation mechanisms shift from dislocation-mediated deformation to interfacial activities in the AIFs, reducing dislocation nucleation and slowing down the Hall-Petch breakdown prevalent in regular nanotwinned metals. This work provides new insights into designing ultrastrong and tough materials beyond the conventional limits of nanotwinned metals.
SCRIPTA MATERIALIA
(2021)
Article
Chemistry, Multidisciplinary
Hsiang-Hou Tseng, Hung-Che Liu, Min-Hsun Yu, Jia-Juen Ong, Dinh-Phuc Tran, Chih Chen
Summary: Copper joints have replaced solder interconnects in integrated circuits due to their great electrical properties and lower-temperature processing. To isolate Cu from oxidizing during bonding processes, a (111)-oriented nanotwinned Ag (NT-Ag) thin layer was electroless-deposited on a (111)-oriented NT-Cu film. The microstructures of the Ag films were then analyzed, showing that columnar NT-Ag grains epitaxially grew along the columnar NT-Cu grains. Additionally, the bonding strength of the Cu-Ag joints was found to be higher than that of the Ag-Ag joints, possibly due to the greater diffusion rate of Ag atoms in Cu than the self-diffusion of Ag.
CRYSTAL GROWTH & DESIGN
(2023)
Article
Nanoscience & Nanotechnology
Linfeng Bu, Zhao Cheng, Yin Zhang, HengAn Wu, Ting Zhu, Lei Lu
Summary: The strength-controlling dislocation mechanism in nanotwinned metals is illuminated by partitioning the flow stress into effective stress and back stress components. Recent experiments show a nearly constant saturated effective stress of about 100 MPa in nanotwinned Cu with nanotwin thicknesses less than 100 nm. This surprising result suggests that trans-twin dislocations spanning multiple nanotwin lamellae, rather than threading dislocations within individual lamellae, control the effective stress.
SCRIPTA MATERIALIA
(2023)
Article
Physics, Applied
Han Wang, Julian J. Rimoli, Penghui Cao
Summary: By using atomistic simulations, we investigated a range of nanotwinned materials with different stacking fault energies (SFEs) to understand the limit of twin boundary (TB) strengthening. In contrast to Cu and Al, nanotwinned materials with ultra-low SFEs (Co, NiCoCr, and NiCoCrFeMn) exhibited continuous strengthening down to a twin thickness of 0.63 nm. Our study revealed that even at the nanometer scale, hard dislocation modes persisted while the soft dislocation mode, which caused detwinning in Cu and Al, resulted in phase transformation and lamellar structure formation in Co, NiCoCr, and NiCoCrFeMn. This enhanced understanding of dislocation mechanisms in nanotwinned materials showcases the potential for controlling mechanical behavior and ultimate strength through tunable composition and SFE, particularly in multi-principal element alloys.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Chemistry, Physical
Yao Chen, Aiqin Wang, Jingpei Xie, Yanchuang Guo
Summary: In this study, the plastic deformation mechanisms and the variables affecting the properties of Cu/Al layered composites were investigated, along with the interface characteristics and plastic deformation mechanisms under compressive loading in Al/Al2Cu/Cu multilayer materials. Results showed that temperature and strain rate have significant effects on the compressive deformation of the system.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Chemistry, Multidisciplinary
Zailin Yang, Xiaoyang Ding, Yong Yang, Shihao Cao
Summary: By using molecular dynamics method, the influence of temperature on the compressive loading behavior of nanotwinned Cu was analyzed. The plastic deformation mechanism of nanotwinned Cu depends on the temperature, with detwinning behavior dominating at temperatures below 220 K and twin boundaries' migration behavior controlling the plastic deformation process between 250 and 400 K. At temperatures below 150 K, twin boundaries hinder dislocations, while the hindrance becomes less apparent above 200 K. In general, low temperatures are more conducive to detwinning behavior. This research provides guidance for controlling detwinning behavior in nanotwinned materials.
JOURNAL OF NANOPARTICLE RESEARCH
(2022)
Article
Materials Science, Multidisciplinary
Feng Zhang, Youran Zhi, Guo Li, Chao Xun, Dasheng Zhu
Summary: The study found that there is an optimal grain size at which both strength and failure strain are improved in bimodal nanotwinned microstructures. The fracture mechanisms of this microstructure involve various interactions such as TB migration, deformation twinning, and void generation.
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING
(2021)
Article
Materials Science, Multidisciplinary
Cheng-Da Wu, Kai-Wei Liu
Summary: This study investigates the effects of voids and temperature on the fracture behavior of Cu/Cu3Sn bilayers during tensile tests using molecular dynamics simulations. The simulation results reveal that the failure of non-voided bilayers is caused by the collapse of the layer interface, while the failure of voided bilayers is influenced by both the interface collapse and the growth of the pre-existing void. The Young's modulus of the bilayers decreases significantly with increasing temperature.
MATERIALS TODAY COMMUNICATIONS
(2022)
Article
Materials Science, Multidisciplinary
Qiongjiali Fang, Frederic Sansoz
Summary: This study investigates the effects of grain boundary (GB) strain accommodation on plastic deformation in columnar-grained nanocrystalline nanotwinned (nt) face-centered cubic metals. The research findings show that CTB strengthening effects are increasingly more pronounced in columnar-grained nt metals as their shear modulus increases.
Article
Materials Science, Multidisciplinary
Zhao Cheng, Linfeng Bu, Yin Zhang, HengAn Wu, Ting Zhu, Lei Lu
Summary: This study aims to reveal the distribution of plastic strain gradients in gradient nanotwinned copper (GNT Cu). Full-field strain mapping reveals the gradient distributions of lateral strains in GNT Cu samples undergoing uniaxial tensile deformation. The results show that with an increasing structural gradient, the lateral strain gradient increases while the maximum lateral strain difference decreases. This gradient distribution of local extra strengths is due to the combined effects of plastic strain gradient and grain size.
Article
Nanoscience & Nanotechnology
Tao Wan, Zhao Cheng, Linfeng Bu, Lei Lu
Summary: Sandwiched gradient nanotwinned (GNT) Cu with different soft and hard components in the central layer and surface, respectively, exhibit improved strength-ductility synergy due to enhanced strain delocalization, prolonged elastic-plastic transition, and increased strain gradient, resulting in more geometrically necessary dislocations (GNDs) at the interfaces.
SCRIPTA MATERIALIA
(2021)
Article
Multidisciplinary Sciences
Shiteng Zhao, Ruopeng Zhang, Qin Yu, Jon Ell, Robert O. Ritchie, Andrew M. Minor
Summary: Nanostructured metals are usually strong due to high internal boundary density, limiting dislocation mean free path, but also more brittle. Nanotwinned materials can overcome this trade-off. A new nanostructuring method enhances the strength and ductility of titanium.
Article
Nanoscience & Nanotechnology
Ting-Chun Lin, Chien-Lung Liang, Shan-Bo Wang, Yung-Sheng Lin, Chin-Li Kao, David Tarng, Kwang-Lung Lin
Summary: The introduction of highly (111)-oriented nanotwinned Cu effectively inhibits detrimental Cu protrusion in TSV technology, reducing protrusion height during thermal annealing and strengthening TSV by impeding dislocation glide. The electrodeposited nanotwinned Cu TSV shows great thermal stability and slight micro-hardness loss under thermal annealing.
SCRIPTA MATERIALIA
(2021)
Article
Engineering, Mechanical
Yongpan Zeng, Xiaoyan Li
Summary: This study conducted large-scale atomistic simulations to investigate the high-temperature creep mechanisms of nanocrystalline and nanotwinned TiAl alloys, revealing the influences of applied stress, grain size, and temperature on creep behaviors and mechanisms. Particularly, a critical twin thickness was identified for nanotwinned samples under high stress, leading to a transition in creep mechanism from dislocation nucleation and slip to detwinning.
EXTREME MECHANICS LETTERS
(2021)
Article
Chemistry, Multidisciplinary
Jin Cai, Qing Zhao, Wei-You Hsu, Chungseok Choi, Yang Liu, John Mark P. Martirez, Chih Chen, Jin Huang, Emily A. Carter, Yu Huang
Summary: A highly (111)-oriented Cu foil electrocatalyst with dense twin boundaries (tw-Cu) is demonstrated to exhibit high selectivity towards CH4 in the electrochemical carbon dioxide reduction reaction. The tw-Cu catalyst achieves a high Faradaic efficiency of 86.1 +/- 5.3% for CH4 production. Theoretical studies suggest that tw-Cu reduces the reduction barrier for the rate-determining hydrogenation of CO compared to planar Cu(111), leading to the observed high CH4 selectivity.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
(2023)
Article
Chemistry, Physical
Long Wang, Anh Kiet Tieu, Guojuan Hai, Jiaqing Li, Hongtao Zhu, The Pham Sang, Jun Yang
Summary: The study demonstrates an improved load-carrying capability of a composite of sodium carbonate and graphene in lubricated contacts under heavier loads, reducing friction and wear significantly. The enhanced lubricating property is attributed to stronger adhesion of the composite on the steel surface and the formation of a sliding-induced soft tribofilm.
Article
Engineering, Mechanical
Shaogang Cui, Yangzhen Liu, Tong Wang, Kiet Tieu, Long Wang, Dahai Zeng, Zhou Li, Wei Li
Summary: The study investigates the effects of different counterfaces on the tribological behavior of stainless steel and mild steel, finding that Si3N4 and SiC provide better wear resistance and the friction coefficients depend on the type of ceramic. Furthermore, forming a thick tribo-oxide layer on stainless steel can prevent sticking issues but comes with severe pull-out and fracture wear.
Article
Engineering, Mechanical
Long Wang, Anh Kiet Tieu, Huong T. Thi Ta, Germanas Peleckis, Guojuan Hai, Hongtao Zhu
Summary: This study investigated the high temperature lubrication effect of different alkaline carbonates (high-temperature ionic liquid) and found that the lubrication properties are alkaline species dependent, with potassium carbonate showing better lubrication than sodium and lithium carbonate. At high temperatures, alkaline carbonates decompose and react with iron oxide to form alkali ferrites with promising anti-wear properties. Li2Fe3O4 exhibits better lubricity compared to NaFeO2 and KFeO2.
TRIBOLOGY INTERNATIONAL
(2022)
Article
Engineering, Mechanical
Guanyu Deng, Yan Chong, Lihong Su, Lihua Zhan, Peitang Wei, Xing Zhao, Liang Zhang, Yanzhong Tian, Hongtao Zhu, Nobuhiro Tsuji
Summary: The study found that the powder nano-grained Ti6Al4V alloy has lower friction coefficient and higher wear resistance compared to its coarse-grained counterpart, and that sliding wear can alter its nanomechanical properties and microstructure evolution, which depends on the initial microstructural features.
TRIBOLOGY INTERNATIONAL
(2022)
Article
Materials Science, Multidisciplinary
Rui Wang, Cheng Lu, Kiet A. Tieu, Azdiar A. Gazder
Summary: The heterogeneous evolution of intragranular strain within polycrystalline copper grains during uniaxial tension was evaluated using in-situ electron back-scattering diffraction. Deformation heterogeneity between grains led to a proliferation of slip bands within grains and lattice rotation. The development of intragranular orientation gradient caused by lattice rotation depended on the initial grain orientation and grain interactions with its local neighborhood.
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T
(2022)
Article
Chemistry, Physical
Jiaqing Li, Ziyue Wu, Fang Wang, Liang Zhang, Chilou Zhou, Cheng Lu, Lin Teng, Qifeng Lin
Summary: This study reveals the H segregation and hydrogen embrittlement mechanisms in nanograined materials through classical molecular dynamics simulations. The results show that the H segregation ratio increases as the grain size decreases, while the local H concentration at the grain boundaries decreases. Additionally, it is found that smaller grain sizes lead to lower local H concentration at the grain boundaries and enhanced grain boundary-mediated intergranular deformation, resulting in increased resistance to hydrogen embrittlement.
Article
Materials Science, Multidisciplinary
Ruxin Zheng, Liuqing Yang, Liang Zhang
Summary: This study investigates the dynamic interaction between grain boundaries and voids in tungsten at high temperatures using molecular dynamics simulations. The results show that the dynamic migration of grain boundaries can absorb voids, and high-angle grain boundaries have higher absorption efficiency. This study reveals a grain boundary migration-induced self-healing mechanism of tungsten at high temperatures.
Review
Materials Science, Multidisciplinary
Liang Zhang, Zhihui Zhang, Xuan Zhang, Xiaoxu Huang
Summary: The high strength of nanocrystalline metals is of great interest, but their low ductility and microstructural instability pose challenges. Previous experimental works have shown that grain boundary segregation of solute atoms can overcome these disadvantages. However, the microscopic mechanisms are not well understood yet. Computational simulation has provided insights into the effects of solute atoms on the structure, energy, and mechanical properties of segregated grain boundaries in nanocrystalline metals.
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T
(2022)
Article
Materials Science, Multidisciplinary
Pengfei Wang, Hebin Jiang, Mao Liu, Liang Zhang, Songlin Xu
Summary: Lubricant exhibits abnormal strengthening and toughening effects during high-speed perforation, improving the resistance of laminar aluminum through reducing stress concentration, delaying failure displacement, and increasing dissipated energy. This phenomenon is significant for understanding the friction and fracture evolution in developing membrane-like protective structures.
MATERIALS & DESIGN
(2022)
Article
Chemistry, Physical
Ruxin Zheng, Wujing Xuan, Junjun Xie, Shasha Chen, Liuqing Yang, Liang Zhang
Summary: Tungsten (W) is used in fusion reactors due to its excellent radiation resistance. This study investigates the differences in defect evolution between single-crystal and bicrystal W using molecular dynamics simulations. The results show that the number of defects is more sensitive to the energy of the primary knocked atom (PKA) than temperature, and the presence of the grain boundary affects the recombination of interstitial atoms and vacancies, leading to the formation of large vacancy clusters in bicrystal models. These simulations provide insights into the role of grain boundaries in the evolution of irradiated structural defects.
Editorial Material
Materials Science, Multidisciplinary
Guanyu Deng, Hongtao Zhu, Anh Kiet Tieu
Article
Materials Science, Multidisciplinary
Jiaqing Li, Ziyue Wu, Lijie Zhu, Zhuwu Zhang, Lin Teng, Liang Zhang, Cheng Lu, Rui Wang, Che Zhang
Summary: The influence of temperature on hydrogen diffusion and hydrogen embrittlement of X80 steel was studied. The results showed that the hydrogen diffusion and subsurface hydrogen concentration in the steel increased with increasing temperature. Macro slow strain rate tensile tests and microstructural analysis revealed a temperature threshold THE, max of 315 K for hydrogen-induced embrittlement susceptibility. The determination of THE, max is crucial for determining test temperatures in hydrogen-related engineering material applications.
Article
Materials Science, Multidisciplinary
Xuan Zhang, Liang Zhang, Zhihui Zhang, Xiaoxu Huang
Summary: First-principles calculations were used to study the segregation behavior of Mg and Cu in different Al grain boundaries and their effects on energy and mechanical properties. The results showed that Mg and Cu both segregated at the grain boundaries, with Cu having a stronger segregation tendency. Mg segregation reduced the grain boundary strength, while Cu segregation enhanced it.
MECHANICS OF MATERIALS
(2023)
Review
Engineering, Mechanical
Khai K. Huynh, Sang T. Pham, Kiet A. Tieu, Shanhong Wan
Summary: Carbon-based tribofilms and/or nanomaterials have emerged as potential solutions to the current shortcomings of phosphorus- and sulphur-rich tribofilms and coatings. These tribofilms have the capability to continuously repair/replenish themselves during sliding, making them of significant interest.
Article
Materials Science, Multidisciplinary
Y. Liu, K. Zweiacker, C. Liu, J. T. McKeown, J. M. K. Wiezorek
Summary: The evolution of rapid solidification microstructure and solidification interface velocity of hypereutectic Al-20at.%Cu alloy after laser melting has been studied experimentally. It was found that the formation of microstructure was dominated by eutectic, alpha-cell, and banded morphology grains, and the growth modes changed with increasing interface velocity.
Article
Materials Science, Multidisciplinary
Bharat Gwalani, Julian Escobar, Miao Song, Jonova Thomas, Joshua Silverstein, Andrew Chihpin Chuang, Dileep Singh, Michael P. Brady, Yukinori Yamamoto, Thomas R. Watkins, Arun Devaraj
Summary: Castable alumina forming austenitic alloys exhibit superior creep life and oxidation resistance at high temperatures. This study reveals the mechanism behind the enhanced creep performance of these alloys by suppressing primary carbide formation and offers a promising alloy design strategy for high-temperature applications.
Article
Materials Science, Multidisciplinary
Jian Song, Qi Zhang, Songsong Yao, Kunming Yang, Houyu Ma, Jiamiao Ni, Boan Zhong, Yue Liu, Jian Wang, Tongxiang Fan
Summary: Recent studies have shown that achieving an atomically flat surface for metals can greatly improve their oxidation resistance and enhance their electronic-optical applications. Researchers have explored the use of graphene as a covering layer to achieve atomically flat surfaces. They found that high-temperature deposited graphene on copper surfaces formed mono-atomic steps, while annealed copper and transferred graphene on copper interfaces formed multi-atomic steps.
Article
Materials Science, Multidisciplinary
Jennifer A. Glerum, Jon-Erik Mogonye, David C. Dunand
Summary: Elemental powders of Al, Ti, Sc, and Zr are blended and processed via laser powder-bed fusion to create binary and ternary alloys. The microstructural analysis and mechanical testing show that the addition of Ti results in the formation of primary precipitates, while the addition of Sc and Zr leads to the formation of fine grain bands. The Al-0.25Ti-0.25Zr alloy exhibits comparable strain rates to Al-0.5Zr at low stresses, but significantly higher strain rates at higher stresses during compressive creep testing. Finite element modeling suggests that the connectivity of coarse and fine grain regions is a critical factor affecting the creep resistance of the alloys.
Article
Materials Science, Multidisciplinary
P. Jannotti, B. C. Hornbuckle, J. T. Lloyd, N. Lorenzo, M. Aniska, T. L. Luckenbaugh, A. J. Roberts, A. Giri, K. A. Darling
Summary: This work characterizes the thermo-mechanical behavior of bulk nanocrystalline Cu-Ta alloys under extreme conditions. The experiments reveal that the alloys exhibit unique mechanical properties, behaving differently from conventional nanocrystalline Cu. They do not undergo grain coarsening during extrusion and exhibit behavior similar to coarse-grained Cu.
Article
Materials Science, Multidisciplinary
Yiqing Wei, Jingwei Li, Daliang Zhang, Bin Zhang, Zizhen Zhou, Guang Han, Guoyu Wang, Carmelo Prestipino, Pierric Lemoine, Emmanuel Guilmeau, Xu Lu, Xiaoyuan Zhou
Summary: This study proposes a new strategy to modify microstructure by phase regulation, which can simultaneously enhance carrier mobility and reduce lattice thermal conductivity. The addition of Cu in layered SnSe2 induces a phase transition that leads to increased grain size and reduced stacking fault density, resulting in improved carrier mobility and lower lattice thermal conductivity.
Article
Materials Science, Multidisciplinary
Jia Chen, Zhengyu Zhang, Eitan Hershkovitz, Jonathan Poplawsky, Raja Shekar Bhupal Dandu, Chang-Yu Hung, Wenbo Wang, Yi Yao, Lin Li, Hongliang Xin, Honggyu Kim, Wenjun Cai
Summary: In this study, the structural origin of the pH-dependent repassivation mechanisms in multi-principal element alloys (MPEA) was investigated using surface characterization and computational simulations. It was found that selective oxidation in acidic to neutral solutions leads to enhanced nickel enrichment on the surface, resulting in reduced repassivation capability and corrosion resistance.
Article
Materials Science, Multidisciplinary
X. Y. Xu, C. P. Huang, H. Y. Wang, Y. Z. Li, M. X. Huang
Summary: The limited slip systems of magnesium (Mg) and its alloys hinder their wide applications. By conducting tensile straining experiments, researchers discovered a rate-dependent transition in the dislocation mechanisms of Mg alloys. At high strain rates, glissile dislocations dominate, while easy-glide dislocations dominate at low strain rates. Abundant glissile dislocations do not necessarily improve ductility.
Article
Materials Science, Multidisciplinary
M. S. Szczerba, M. J. Szczerba
Summary: Inverse temperature dependences of the detwinning stress were observed in face-centered cubic deformation twins in Cu-8at.%Al alloy. The detwinning stress increased with temperature when the pi detwinning mode was involved, but decreased when the pi/3 mode was involved. The dual effect of temperature on the detwinning stress was due to the reduction of internal stresses pre-existing within the deformation twins. The complete reduction of internal stresses at about 530 degrees C led to the equivalence of the critical stresses of different detwinning modes and a decrease in the yield stress anisotropy of the twin/matrix structure.
Article
Materials Science, Multidisciplinary
Taowen Dong, Tingting Qin, Wei Zhang, Yaowen Zhang, Zhuoran Feng, Yuxiang Gao, Zhongyu Pan, Zixiang Xia, Yan Wang, Chunming Yang, Peng Wang, Weitao Zheng
Summary: The interaction between the electrode and the electric double layer (EDL) significantly influences the energy storage mechanism. By studying the popular alpha-Fe2O3 electrode and the EDL interaction, we find that the energy storage mechanism of the electrode can be controlled by modulating the EDL.
Article
Materials Science, Multidisciplinary
Matthew R. Barnett, Jun Wang, Sitarama R. Kada, Alban de Vaucorbeil, Andrew Stevenson, Marc Fivel, Peter A. Lynch
Summary: The elastic-plastic transition in magnesium alloy Mg-4.5Zn exhibits bursts of deformation, which are characterized by sudden changes in grain orientation. These bursts occur in a coordinated manner among nearby grains, with the highest burst rate observed at the onset of full plasticity. The most significant burst events are associated with twinning, supported by the observation of twinned structures using electron microscopy. The bursts are often preceded and followed by a stasis in peak movement, indicating a certain "birth size" for twins upon formation and subsequent growth at a later stage.
Article
Materials Science, Multidisciplinary
Vaidehi Menon, Sambit Das, Vikram Gavini, Liang Qi
Summary: Understanding solute segregation thermodynamics is crucial for investigating grain boundary properties. The spectral approach and thermodynamic integration methods can be used to predict solute segregation behavior at grain boundaries and compare with experimental observations, thus aiding in alloy design and performance control.
Article
Materials Science, Multidisciplinary
Feiyu Qin, Lei Hu, Yingcai Zhu, Yuki Sakai, Shogo Kawaguchi, Akihiko Machida, Tetsu Watanuki, Yue-Wen Fang, Jun Sun, Xiangdong Ding, Masaki Azuma
Summary: This study reports on the negative and zero thermal expansion properties of Cd2Re2O7 and Cd1.95Ni0.05Re2O7 materials, along with their ultra-low thermal conductivity. Through investigations of their structures and phonon calculations, the synergistic effect of local structure distortion and soft phonons is revealed as the key to achieving these distinctive properties.
Article
Materials Science, Multidisciplinary
Thomas Beerli, Christian C. Roth, Dirk Mohr
Summary: A novel testing system for miniature specimens is designed to characterize the plastic response of materials for which conventional full-size specimens cannot be extracted. The system has an automated operation process, which reduces the damage to specimens caused by manual handling and improves the stability of the test results. The experiments show that the miniature specimens extracted from stainless steel and aluminum have high reproducibility, and the results are consistent with those of conventional-sized specimens. A correction procedure is provided to consider the influence of surface roughness and heat-affected zone caused by wire EDM.
Article
Materials Science, Multidisciplinary
Rani Mary Joy, Paulius Pobedinskas, Nina Baule, Shengyuan Bai, Daen Jannis, Nicolas Gauquelin, Marie-Amandine Pinault-Thaury, Francois Jomard, Kamatchi Jothiramalingam Sankaran, Rozita Rouzbahani, Fernando Lloret, Derese Desta, Jan D'Haen, Johan Verbeeck, Michael Frank Becker, Ken Haenen
Summary: This study investigates the influence of film microstructure and composition on the Young's modulus and residual stress in nanocrystalline diamond thin films. The results provide insights into the mechanical properties and intrinsic stress sources of these films, and demonstrate the potential for producing high-quality nanocrystalline diamond films under certain conditions.
