Possible role of hydrogen in geometry-driven sp3 formation during MPCVD diamond growth

There is ongoing debate about the exact mechanisms that cause diamond formation in the microwave plasma chemical vapor deposition (MPCVD) process.

While it’s well established that methane (CH4) and hydrogen (H2)are the key gases Hydrogen etches away non-diamond (sp2) carbon, while carbon from CH₄ contributes to diamond (sp3) growth.

Yet the exact carbon-containing species responsible for diamond growth ,whether CH3 radicals, C2 dimers, or other species are the dominant contributors are not known.

It's also not clear what surface reactions and growth mechanisms contribute to growth and how these species attach to diamond surfaces and stabilize sp3 bonds.

While the general scheme is agreed upon, the precise atomic and plasma-chemical pathways that make diamond grow in MPCVD[2] are still a topic of active research and debate.

Here's what I think happens Hydrogenation of carbon structures adds H atoms to carbon.This process promotes sp3 hybridization in formerly sp2 ,sp carbons. As a result, bond angles shift toward the tetrahedral 109.5°, both for C–C–C and H–C–H angles.

This is clear if we study the bond angles of single bonded carbon species like CH4,C2H6 vs graphite and C2H2.

When these molecules decompose on the heated substrate, diamonds start growing by addition of pre sp3 hybridised carbon atoms.

A key insight can be obtained from Diamond like carbon films which are grown at a much lower temperature. These films contain both sp2 and sp3 hybridised carbon. But while films that are grown in hydrogen atmosphere are generally transparent, the films grown without hydrogen are darker in color. Indicating that hydrogen atoms change the bond angles towards sp3 hybridisation. Structurally these films could be simillar to perhydrogenated polycyclic aromatic hydrocarbons.

This is why atomic hydrogen is necessary during film growth that require transparency [1].

The shift is not just about stabilizing dangling bonds it physically changes the geometry of the carbon network.

Hydrogenation does not generally break single C-C bonds; it mainly converts double/triple bonds to single bonds .

REFERENCES

1.Synthesis and Characterization of Hydrogenated Diamond-Like Carbon (HDLC) Nanocomposite Films

https://pmc.ncbi.nlm.nih.gov/articles/PMC7178644/

2.Growth of 2-inch diamond films on 4H–SiC substrate by MPCVD

https://www.sciencedirect.com/science/article/abs/pii/S0042207X23000921

Ref #2 is important because it establishes you don't need a diamond substrate to grow diamonds. A diamond-like substrate eg SiC would work as well.

Some recent breakthroughs that solidify the position of carbon as a material of choice in electronics & structural applications

Comments

Why does collapsing a bubble with a sound wave produce light?

My thoughts on a reddit discussion https://www.reddit.com/r/AskPhysics/comments/1lwxxc3/comment/n2jx8gp/?utm_source=share&utm_medium=mweb3x&utm_name=mweb3xcss&utm_term=1&utm_content=share_button The collapsing of a bubble with sound wave leads to the emission of light in a phenomenon known as sonoluminescnce. The bubble collapse is rapid and the gas inside the core doesn't have time to exchange heat with the surroundings as it's compressed rapidly leading to what is known as adiabatic compression. This compression heats up the gas to very high temp. The exact temperatures are inferred from the spectrum of emission which is thought to be a blackbody. But some sophisticated models have also been developed that put the temp in the range 5000k-20000k some even higher. There's also debate on whether the bubble emission spectrum is truly a blackbody or is it line emission or bremsstrahlung? Personally I think its a mix of all three. The pressures create...

WeWork India Sustainability Summit 2025 Tackling Technical Challenges in Green Building Innovation

I thank we work India for organising sustainability summit 2025 to help drive real change towards decarbonising the commercial real estate sector. I gained valuable insights from the esteemed speakers especially around policy and regulation in this space. My own thoughts kept pulling me towards some of the more technical challenges which are quite significant. The current strategy of making buildings sustainable focuses on reducing the carbon footprint of a building during its operation and construction. In the operational stage the challenge is to ensure that the building can run on green energy. Heating and cooling are the heaviest users of energy and thus obvious targets for decarbonisation. Since buildings these days scale vertically it's impossible to cover the energy requirements from rooftop solar panels. Unless solar panels can be installed vertically along the facade, the surface area would be too limited to generate any significant power. The idea has been tr...

Can you compress water and turn it solid?

A question asked on reddit https://www.reddit.com/r/askscience/comments/1n02vlg/ Yes and this has been experimentally confirmed. Shock compression of water has produced different forms of ice crystals. SOME REFERENCES Experimental evidence for superionic water ice using shock compression https://www.nature.com/articles/s41567-017-0017-4 This particular form of ice melted at 5000K at 200Gpa. https://www.llnl.gov/article/44081/first-experimental-evidence-superionic-ice An interesting tidbit from the research is in this paragraph >Using diamond anvil cells (DAC), the team applied 2.5 GPa of pressure (25 thousand atmospheres) to pre-compress water into the room-temperature ice VII, a cubic crystalline form that is different from "ice-cube" hexagonal ice, in addition to being 60 percent denser than water at ambient pressure and temperature. I'm not really sure at what temp this compression was performed but ice vii is known to exist at room temp at high enough pre...

Is there a future for materials science students in tribology?

My comments on a reddit discussion https://www.reddit.com/r/materials/comments/1nmooy5/comment/nfg6vub/ Tribology is a very important subfield of Mat sci and highly relevant anywhere there are moving parts. Like many other materials science domains its cross disciplinary and overlaps with automotive , aerospace ,manufacturing and even nano systems. I think its definitely worth studying and one should atleast know about core concepts. From a purely research point of view the field is quite deep especially as it is being developed for nano systems and other emerging areas like triboluminescence. It does have a future. Wear is one of the major failure mechanism in materials and lots of resources are allocated to minimise it. Turbines,engine components, tyres ,cutting tools all suffer from wear and constant monitoring and refinement of process parameters is necessary.Many coatings are designed to reduce friction and wear Diamond like carbon films are cutting edge if you can build some...

What IMC 2025 Revealed About the State of Telecom

IMC 2025 lived up to its reputation as India's most anticipated communication event in India attracting big industry players—Intel,Qualcomm,Mediatek,Ericsson,Nokia along with research institutions and startups. All the 7 layers of the networking stack from the PHY to APPLICATION were well represented by various organisations. Mobile operators serve as the face of the network but we often forget that they are powered by a long list of manufacturers and service providers. IMC gave them a platform to showcase their products and directly engage with customers. 5G is already here and very predictably there were talks around whether it has delivered on the promises it made. Speakers shared their thoughts and while the general consensus was that 5G did bring about somewhat faster speeds and a bit of lower latency the massive promises that it made especially around remote healthcare AR,VR and smart cities have all been forgotten. mmwave is no where to be seen or even heard of....

Unlocking the Potential of Carbon for Long-Distance Electrical Transmission

ABSTRACT: We present a technique to manufacture large scale carbon based conductors for transmission of electrical energy over continental scale distances. We start by identifying precursors that could be used for production processes.We review the current manufacturing techniques of producing carbon based fibers and explain why certain precursors have dominated carbon materials industry. We identify methods that can be used to increase the yield through alternative precursors.We put forward a theory of why carbon conductors have less conductivity than metals and what can be done to improve it. Finally we postulate that with cheaper production methods even if carbon based conductors are 10 times less effective than poor metallic conductors like steel, they can still outperform them in High Voltage transmission lines if cheap manufacturing techniques could be developed. INTRODUCTION: Copper and in certain very specific applications aluminium & silicon steels dominate when it co...

Do electrons really flow as a beam in cathode ray tubes?

Abstract: It is generally well accepted that a beam of electrons flow from cathode to anode in a cathode ray tube. Taking pressure data from a variety of sources from CRT manufacturers’ data sheets to engineering documents of large hadron colliders we show through calculations that there is enough residual gas in these devices to form a conducting path from anode to cathode due to plasma formation. When high voltages are applied at the anode the gas is ionized and becomes a plasma forming a ‘wire’ between the two electrodes that causes conduction of energy. The objective of this brief note is to encourage scientists and engineers to re-investigate commonly accepted beliefs about vacuum tubes and develop new knowledge that can revitalize the field especially at a time when nano scaled vacuum channel transistors are being envisioned. Most vacuum tubes have operating pressures in the ultra high vacuum range. This is true for cathode ray tubes, vacuum tu...

Low energy fabrication of a high strength layered ceramic composite for high temperature oxidative environments

High temperature materials are required in various applications: in metallurgy, for making combustion chambers of internal combustion engines ,for the body of Stirling engines, for wall material of nuclear fusion reactors, for the body of Jet engines among a few. For such applications we need materials that can retain their strengths at elevated temperatures and can survive in an oxidative environment It is the second requirement which is more stringent. Although numerous metallic alloys have been synthesized that can sustain both high temperatures and oxygen attack they require complex processing steps On the other hand ceramics are good at resisting both oxygen attacks and high temperatures and are relatively simpler to fabricate but are limited by massive amounts of energy required. For example c/sic composites will perform well in demanding high temperature oxidative environments but require vacuum to be manufactured. The acheson process for the formation of sic is...

Force calculations on electron in vacuum tubes

ABSTRACT A claim was made in the paper titled “Do electrons really flow as a beam in cathode ray tubes? ” where we asserted that electrons remain near the cathode surface during the operation of CRT. Here we do force calculations on electrons by estimating the debye length of electrons emitted after thermionic emission and show that under given applied voltages if electrons are placed at debye length they are sufficiently far away from the cathode surface to be accelerated towards it. Debye length, while typically used to measure charge screening distance in plasmas and electrolytes, can also be used to estimate the distance of emitted electrons from the cathode surface. In the same way debye length is used to calculate the thickness of an electrical double layer in which the surface charge and charge on inner helmholtz plane are immobile & the charges on outer helmholtz plane are mobile we can model emitted electrons as mobile charges & image charges distributed on the cathode...

Manufacturing technique for layered carbon /ceramic composite for use in high temperature oxidative environment

We previously described a layered carbon glass material system that is different from c/sic , c/sio2 matrix composites in that it consists of a distinct C/C phase which is coated by an sio2 layer. https://akshatjiwannotes.blogspot.com/2024/12/low-energy-fabrication-of-high-strength.html This material system presents a distinct advantage in a high temperature oxidative atmosphere as the C/C matrix is protected by the oxidation resistant glass shield. Such a material can supposedly be synthesized in an open oxidative atmosphere. In this short note we will answer some questions such as What manufacturing technique will be used? How can silica particles be sintered on the substrate? How can adhesion between sintered particles and carbon substrate be ensured? What, if any ,sintering aids will be used? What would be the mechanical properties of the composite so formed? What level of heat treatment will be required? To make the composite only the minimum amount of heat ...

Notes by Akshat Jiwan Sharma

Search This Blog