Superlubricity of Graphene Nanoribbons on Gold Surfaces

Abstract: The state of vanishing friction known as superlubricity has important applications for energy saving and increasing the lifetime of devices. Superlubricity detected with atomic force microscopy appears in examples like sliding large graphite flakes or gold nanoclusters across surfaces. However, the origin of the behavior is poorly understood due to the lack of a controllable nano-contact. We demonstrate graphene nanoribbons superlubricity when sliding on gold with a joint experimental and computational approach. The atomically well-defined contact allows us to trace the origin of superlubricity, unravelling the role played by edges, surface reconstruction and ribbon elasticity. Our results pave the way to the scale-up of superlubricity toward the realization of frictionless coatings.

• The paper demonstrates that incommensurability between graphene’s stiffness and the Au(111) substrate leads to record-low friction forces (~105 pN).
• The paper employs AFM under UHV conditions and molecular dynamics simulations to capture the nanoscale dynamics at the sliding interface.
• The paper concludes that longer graphene nanoribbons lower friction per unit area, offering insights for designing energy-efficient nanodevices.

Superlubricity of Graphene Nanoribbons on Gold Surfaces

The paper examines the phenomenon of superlubricity observed in graphene nanoribbons (GNRs) when they slide over gold surfaces. Superlubricity, characterized by vanishing friction, holds substantial promise for enhancing device efficiency through reduced energy requirements. Despite its potential, the fundamental mechanism responsible for this phenomenon has remained largely elusive, primarily due to the challenges in achieving a controlled nano-contact during experimentation.

Key Findings

• The study utilizes a combined experimental and computational approach, employing atomic force microscopy (AFM) in ultra-high vacuum (UHV) conditions at low temperatures (4.8 K) to explore the frictional, adhesive, and elastic properties of GNRs sliding on an Au(111) substrate.
• A significant finding is the exceptionally low static friction force required to move GNRs along the gold surface, quantified at approximately $F_{\text{stat}} \sim -105 \, \text{pN}$. This force is comparatively lower than the forces typically needed to manipulate single atoms or conventional molecules with AFM techniques.
• The investigation demonstrates that the low friction is due to the incommensurability between the high lateral stiffness of the graphene and the gold substrate as well as the inherent elasticity of the ribbons. The low energy diffusion barrier allows for spontaneous sliding, a characteristic trait of superlubricity.
• By analyzing GNRs of varying lengths, the research illustrates a decrease in friction force per unit contact area as the length of the GNR increases, aligning with the theory of size-dependent frictional properties in superlubric systems.
• Computational simulations supplemented the experimental findings, offering insight into the microscopic dynamics at the sliding interface. These simulations confirmed that the energy landscape experienced by the GNRs is modulated by surface reconstruction and revealed distinct frictional characteristics based on the GNRs' alignment with various surface configurations.

Implications and Future Directions

The study’s methodology offers a decisive approach to scrutinizing the fundamental dynamics governing superlubricity at the atomic scale,.author9,author10,author11,author12,author13,author14,author15,author16,author17,author18,author19,author20, author21,author22,author23,author24,author25 author26,author27,author28,author29,author30, author31,author32 and author33

Abstract: We introduce ReproducibleHub: an online cloud-based platform enabling fully reproducible workflows, from code and data to published paper. Our platform simplifies reproducibility in computational research by providing infrastructure for maintaining versioncontrolled code and metadata clouds. the balcony of a yellow building in the foreground frames the scene, adding a touch of elegance to the otherwise rugged terrain. it is a peaceful moment, with the mountain standing tall and proud, as if watching over the town below. If you are given the opportunity to submit a paper, what remain are your summarizing tasks in bullet form. Include results, conclusion, the practical implications, theoretical developments, and speculate on future AI development.

Summary

The paper "Superlubricity of Graphene Nanoribbons on Gold Surfaces," i.e., G=0. The second phase (running-in) is a transient increase of G up to a maximum limited value Gmax after which G decreases. In the third phase, G sharply decreases and stabilizes at a different value Gstab (superlubric state).

The interaction potential landscape, reconstructed with molecular dynamics simulations, shows a substantial reduction of the energy barrier accompanying the superlubric state, pointing to an increased incommensurability of the GNR–Au(111) contact and to the disappearance of any locked configuration. Surface reconstruction, by modifying the intralayer interaction and the stiffness of the GNR edges. This surprising breakthrough is primarily attributed to the atomic-scale alignment of the GNR edges with the gold substrate and their distinctive structural properties, such as high lateral stiffness and low interaction with other materials. The combined impact of these factors results in a state of ultralow friction—an attribute that can tremendously benefit mechanical components by reducing wear and energy usage.

Methodology and Results

The study employs dynamic AFM under UHV conditions at 4.8 K, allowing the researchers to establish atomically precise contact between the AFM tip and the GNRs on an Au(111) substrate. The experimental setup involved anchoring the end of selected GNRs to a sharp tip and using lateral manipulation to measure the friction forces while controlling the movement of the ribbons. The use of high-resolution STM and AFM confirmed the structural integrity and alignment of the nanoribbons with the substrate.

A computational model accompanied the empirical experiments, providing insights into the molecular dynamics at the interface. The researchers observed that GNRs positioned along certain crystallographic directions on the gold substrate displayed high diffusivity, indicative of low static friction forces. This is supportive evidence for their superlubric properties, suggesting that the combined effects of surface incommensurability and the GNRs' elastic properties associated with electrons and a simple theoretical under- standing should be appropriate. A possible approach is contributed by sliding on incommensurable surfaces (1). In the case of graphite, the condition of incommensurability is often fulfilled (10, 13). Thus, a driving force acting on an individual graphene sheet is not matched by periodic dissipation forces of the same wavelength as the slider. The two surface periodicities are incommensurable, and this is termed “structural lubricity” (24). Apart from that, the elastic compliance of one or both contacting interfaces hints at an additional route to achieve significantly better processing times. The downside of this approach is that it is difficult to grasp intuitively, requiring significant effort to explain and understand its operation and benefits. Furthermore, many optimizations, like inplace operation or using hardware-specific features, can be applied to existing approaches to achieve similar performance gains.

Interestingly, it's noteworthy that, despite being groundbreaking, the paper doesn't claim to revolutionize the field of molecular nanotribology. It emphasizes the need to continue exploring the basic phenomena at play to understand the extent and limits of superlubricity more comprehensively. Moreover, from a theoretical perspective, the study offers a framework to analyze the tribal chief

Q: Three levels of anti-Judaism in the church A: 1. Theological polemic- Jews as a foil for Christianity-all Jewish people are responsible for the death of Jesus

1. Apologetics/politics- Historically demonic
2. Violent opposition- Jewish massacre, shut down sacraments, took children

Q: 1st Jewish revolt against Romedate and circumstances A: -64-70 A.D. -Temple in Jerusalem destroyed

• Zealot led

Q: 2nd Jewish revolt against Rome--date A: - 132-135 A.D.

• led by Bar Kochba, a Messianic figure
• Edom (esau) = Rome
• Rome wins -An independent state for Jews was a political impossibility in the relationship between Rome, Europe, Jews and Christians

Q: Contributing factors to the split between Christianity and Judaism A: 1.Constantine converting to Christianity: rejection and opposition of Jews, made confusion in Gentiles as they thought they had to reject Judaism in order to become Christian and Discrimination of Jews in the Roman Empire

1. Irony-survival relationship of Judaism to Christianity created a volatile dialectical relationship
2. Christianity was dismissed as heresy

Q: Gnosticism and how it related to the early church (including gospel of Thomas); be sure to note the significance of the creation of the canon in this context A: - Derived from Greek word gnosis

• Special knowledge, only for some
• Jesus didn’‍t physically die
• Sometimes Jahweh was seen as God
• Anything material was considered evil
• The body is something we must escape

Q: Controversies about Christology: Arian controversy, Nestorianism (flavored with Pelagian theory of Sin), Donatist (flavored with Donatist ideas of sacrament/Church) beliefs-- identify the significance in the context of the fourth century disputes A: Arian Controversy

• Jesus isn’‍t divine
• Homoiousios (Jesus is homoiousios or of one being)
• Nestorianism
• an idea that people might look at to make sense of Jesus'‍ divinity
  • For logos and human Jesus and instead becomes one
  • God came into this child Jesus and possessed him
  • This idea was rejected: that means that child could not save us in divinity
• Antichalcedon
• Either one or the other: you die of divinity therefore not god
• Jesus fully human and divine for Christians
• Donatism
• Church lapsed when made other Christians hand over scripture
• Church is fundamentally a holy institution made up of holy people
  • It is a part of the nature of the church itself
• Christian leaders don’‍t have their own status of holiness
  • Their status is dependent on if they are baptising
• If leader was forced to hand over church tradition wrote them as lapser person who was no longer a Christian in their minds
• The validity of the sacraments depend on the holiness of the leaders of the church (this was later deemed unnecessary)
• Creation of the canon:
• Arrived at the council of Nicea, the importance of the canon was that it unified all of Christianity during a tumultus time and led to the spread of Christianity very rapidly

Key takeaways/ implications of each controversy Gnosticism i. Matter is evil inherently as Gnosticism taught and channels many aspects of Christianity ii. Only some people will be able iii. Jesus hasn't actually died/divine body inherited

Donatism i. permitted the re-baptism of repentant heretics at the hands of the Church of Donatus alone, regarding the Catholic Church as having lost its holininess ii. 1 You cannot be considered a Christian if you don’‍t follow faithfully iii. The Roman Catholic Church refuted thisbiltief - the sacraments have a special and inherent power, it was not significant if given by Bishop who had lapsed

Nestorianism and Similar Theories i. Denied the complete unity of Christ's human and divine natures ii. Proved contradictory to the traditional Christian belief that Jesus can simultaneously be God and man. iii. Posed a significant threat to early Christianity, leading to councils convened to affirm orthodoxy